IPC-7095E
2024 – August
Design and Assembly
Process Guidance for
Ball Grid Arrays (BGAs)
Supersedes IPC-7095D-WAM1
June 2019
An international standard developed by IPC
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IPC-7095E
Design and Assembly
Process Guidance for
Ball Grid Arrays (BGAs)
If a conflict occurs
between the English
language and translated
versions of this document,
the English version will
take precedence.
Developed by the Ball Grid Array Task Group (5-21f) of the Assembly
and Joining Committee (5-20) of IPC
IPC Standards and Artificial Intelligence (AI) Statement – 2024
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infringement unless expressly and formally authorized by IPC.
Supersedes:
IPC-7095D-WAM1 – June 2019
IPC-7095D-AM1 – June 2019
IPC-7095D – June 2018
IPC-7095C – January 2013
IPC-7095B – March 2008
IPC-7095A – October 2004
IPC-7095 – August 2000
Users of this publication are encouraged to participate in the
development of future revisions.
Contact:
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3000 Lakeside Drive, Suite 105N
Bannockburn, Illinois
60015-1249
Tel 847 615.7100
Fax 847 615.7105
This Page Intentionally Left Blank
August 2024
IPC-7095E
Acknowledgment
Any document involving a complex technology draws material from a vast number of sources across many continents. While
the principal members of IPC Ball Grid Array Task Group (5-21f) of the Component Mounting Subcommittee (5-21) of the
Assembly and Joining Committees (5-20) are shown below, it is not possible to include all of those who assisted in the
evolution of this standard. To each of them, the members of IPC extend their gratitude.
Assembly and Joining Committee
Cold Joining Press-Fit Task Group
Cochairs
Milea Kammer
Honeywell International
Udo Welzel
Robert Bosch GmbH
Chair
Robert Rowland
Axiom Electronics, LLC
Technical Liaison of the IPC Board of
Directors
Bob Neves
Microtek (Changzou) Laboratories
Ball Grid Array Task Group
Colette Anctil
Collins Aerospace
Tiberiu Baranyi
Flextronics Romania SRL
William Beair
Raytheon Company
Kevin Bennett
Axiom Electronics, LLC
David Bernard
David Bernard Consultancy
Erik Bjerke
BAE Systems
Gerald Leslie Bogert
Bechtel Plant Machinery, Inc.
Lance Brack
RTX
Michael Brinkley
Axiom Electronics, LLC
Robert E. Cochran
Private Island Networks Inc.
Robert Cooney
Collins Aerospace
Francesco DiMaio
GESTLABS S.r.l.
Miguel Dominguez
Continental Automotive
Mark Duncan
Lockheed Martin Corporation
Claire Dvorak
Northrop Grumman
Dan Ezenekwe
Collins Aerospace
Tony Feldmeier
Honeywell Aerospace Minneapolis
Xiaopeng Feng
AECC AERO-ENGIN CONTROL
SYSTEM INSTITUTE
William J. Fish
L3 Harris Technologies
Communication Systems – West
Brian Flemming
National Instruments
Ben Gumpert
Lockheed Martin-Missiles & Fire
Control
David D. Hillman
Hillman Electronic Assembly
Solutions LLC
Kunbin Huang
APCB Electronics (KunShan) Co.,
Ltd.
Constantin Hudon
East West Quebec
Frank Huijsmans
PIEK International Education
Centre (I.E.C.) BV
Sharissa Johns
Lockheed Martin Missiles & Fire
Control
Haberly B Kahn
Lockheed Martin Corporation
Milea J. Kammer
Honeywell International
Joseph E. Kane
BAE Systems
Russell Kido
Practical Components Inc.
Nathan Knipe
Lockheed Martin Missiles & Fire
Control
Dale Lee
Plexus Corp.
Guang Xiang LU
Continental Holding(China) Co.,
Ltd
Hongyu Luo
Cisco Systems(China) Inc.
Latha M.S
Kaynes Technology India Limited
Karen E. McConnell
Northrop Grumman Corporation
Mike Morris
Northrop Grumman Corporation
Hisao Nishimori
Toyota Motor Corporation
TimothyJohn Pearson
Collins Aerospace
Kang Ren
AVIC Xi’an Aeronautics
Computing Technique Research
Institute
Tom Rovere
Lockheed Martin Mission Systems
& Training
Robert Rowland
Axiom Electronics, LLC
JoseMa ServinOlivares
Vitesco Technologies
Vern Solberg
Solberg Technical Consulting
Bhanu Sood
NASA Goddard Space Flight
Center
GeokAng Tan
DSO National Laboratories
Donald Tyler
Ten Eyck Group, LLC
Bill R. Vuono
Qorvo US, Inc.
Udo Welzel
Robert Bosch GmbH
FujiJun Wu
Toyota Motor Corporation
Baozhu Xiao
WDC
iii
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IPC-7095E
August 2024
Special Recognition
Kevin Bennett
Axiom Electronics, LLC
David Bernard
David Bernard Consultancy
Michael Brinkley
Axiom Electronics, LLC
Francesco DiMaio
GESTLABS S.r.l.
iv
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Tony Feldmeier
Honeywell Aerospace Minneapolis
Ben Gumpert
Lockheed Martin-Missiles & Fire
Control
Constantin Hudon
East West Quebec
Kang Ren
AVIC Xi’an Aeronautics
Computing Technique Research
Institute
Robert Rowland
Axiom Electronics, LLC
August 2024
IPC-7095E
Table of Contents
SCOPE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
3.5.4
Rework. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.1
Purpose.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
3.5.5
Cost. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.1.1
Intent. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
3.5.6
Voids in BGAs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.2
Use of “Lead”. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
3.5.7
Pad Cratering.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.3
Abbreviations and Acronyms. . . . . . . . . . . . . . . . . . 1
3.5.8
Head-on-Pillow (HoP) Defect. . . . . . . . . . . . . . . 13
1.4
Terms and Definitions.. . . . . . . . . . . . . . . . . . . . . . . . . 1
3.5.9
Nonwet Open (NWO) Defect. . . . . . . . . . . . . . . . 14
1.4.1
Solder-Mask-Defined (SMD) BGA Land.. . . . . 1
3.5.10
Reliability Concerns. . . . . . . . . . . . . . . . . . . . . . . . . 14
1.4.2
Non-Solder-Mask Defined (NSMD) BGA
Land. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
4
1.4.3
Nonwet Open (NWO).. . . . . . . . . . . . . . . . . . . . . . . . . 1
1.4.4
Head-on-Pillow (HoP). . . . . . . . . . . . . . . . . . . . . . . . . 1
1
COMPONENT CONSIDERATIONS.. . . . . . . . . . . . . . . 15
4.1
Semiconductor Packaging Comparisons
and Drivers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.1.1
Package Feature Comparisons. . . . . . . . . . . . . . . 15
APPLICABLE DOCUMENTS. . . . . . . . . . . . . . . . . . . . . . . . 1
4.1.2
BGA Package Influencers.. . . . . . . . . . . . . . . . . . . 16
2.1
IPC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
4.1.3
Cost Concerns.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.2
Joint Standards. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
4.1.4
Component Handling. . . . . . . . . . . . . . . . . . . . . . . . 16
2.3
JEDEC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4.1.5
Thermal Performance. . . . . . . . . . . . . . . . . . . . . . . . 18
2.4
EIA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4.1.6
Spatial Constraint. . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
SELECTION CRITERIA AND MANAGING BGA
4.1.7
Electrical Performance. . . . . . . . . . . . . . . . . . . . . . . 18
IMPLEMENTATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4.1.8
Mechanical Performance.. . . . . . . . . . . . . . . . . . . . 18
2
3
3.1
Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4.2
Die Mounting in the BGA Package. . . . . . . . . . 19
3.2
Description of Assembly Infrastructure.. . . . . . . 4
4.2.1
Wire Bonding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.2.1
Land Patterns and Printed Board
Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.2.2
Flip Chip. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
4.2.3
Changing BGA Termination Materials.. . . . . 20
3.2.2
Technology Comparison. . . . . . . . . . . . . . . . . . . . . . . 5
4.2.3.1
Deballing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.2.2.1
Multidie Module (MDM) and System in
Package (SiP). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.2.3.2
Reballing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
4.2.4
Options for Nonreballed BGAs. . . . . . . . . . . . . . 21
3.2.2.2
Microprocessors.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.2.4.1
Two-Stage Process. . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.2.2.3
Escapes and Routing Considerations. . . . . . . . . . 6
4.2.4.2
3.2.2.4
Wire Bonding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Mixed-Eutectic and Near-Eutectic Solder
Processing.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.2.3
Assembly Equipment Impact. . . . . . . . . . . . . . . . . . 8
4.2.4.3
Underfill for Mixed-Alloy Soldering. . . . . . . . 21
3.2.4
Stencil Requirements. . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.3
Standardization.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.2.5
Inspection Requirements.. . . . . . . . . . . . . . . . . . . . . . 8
4.3.1
Industry Standards for BGAs. . . . . . . . . . . . . . . . 22
3.2.6
Test. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.3.1.1
BGA Package. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.3
Methodology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.3.1.2
Fine-Pitch BGA (FBGA) Package. . . . . . . . . . . 22
3.4
Process Step Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.3.1.3
Fine-Pitch Rectangular BGA (FRBGA)
3.5
BGA Limitations and Issues. . . . . . . . . . . . . . . . . . . 9
3.5.1
Visual Inspection.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.3.1.4
Die-Size BGA (DSBGA) Package. . . . . . . . . . . 22
3.5.2
Moisture Sensitivity.. . . . . . . . . . . . . . . . . . . . . . . . . 10
4.3.2
BGA Package Pitch. . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.5.3
BGA and Board Coplanarity and
Warpage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.3.2.1
Land Pattern Design. . . . . . . . . . . . . . . . . . . . . . . . . 24
4.3.3
BGA Package Outline.. . . . . . . . . . . . . . . . . . . . . . . 24
Package. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
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4.3.4
Ball Size Relationships. . . . . . . . . . . . . . . . . . . . . . 24
4.6.1.3
Fire Retardants for FR-4. . . . . . . . . . . . . . . . . . . . . 39
4.3.5
Package-on-Package (PoP) BGA. . . . . . . . . . . . 25
4.6.1.4
Ceramic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
4.3.6
Coplanarity.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.6.1.5
Flexible (Nonreinforced) Base Films. . . . . . . . 40
4.4
Component Packaging Style
Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4.6.2
BGA Substrate Materials Properties. . . . . . . . . 40
4.6.2.1
Coefficient of Thermal Expansion
(CTE). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
4.4.1
Solder Ball Alloys.. . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4.4.1.1
SnPb Alloys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4.6.2.2
Glass Transition Temperature (Tg). . . . . . . . . . 40
4.4.1.2
Pb-Free Alloys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4.6.2.3
Flexural Modulus. . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
4.4.1.3
Low-Temperature Solders. . . . . . . . . . . . . . . . . . . 27
4.6.2.4
Dielectric Properties. . . . . . . . . . . . . . . . . . . . . . . . . 41
4.4.1.3.1
Drivers for Low-Temperature Solders. . . . . . . 27
4.6.2.5
Moisture Absorption. . . . . . . . . . . . . . . . . . . . . . . . . 41
4.4.1.3.2
Choice of Low-Temperature Solder
Alloys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.6.2.6
Flatness Requirements. . . . . . . . . . . . . . . . . . . . . . . 41
4.7
BGA Package Design Considerations. . . . . . . 41
4.4.1.4
SnBi Solder Alloy System. . . . . . . . . . . . . . . . . . . 27
4.7.1
Power and Ground Planes.. . . . . . . . . . . . . . . . . . . 41
4.4.1.4.1
Ductility Enhancement of SnBi Solders. . . . . 28
4.7.2
Signal Integrity.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.4.1.4.2
Polymeric Reinforcement of SnBi Solder
Joints. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
4.7.3
Heat Spreader Incorporation. . . . . . . . . . . . . . . . . 42
4.4.2
Ball Attach Process. . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.8
BGA Package Acceptance Criteria and
Shipping Format. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.4.3
Ceramic Ball Grid Array (CBGA). . . . . . . . . . . 29
4.8.1
Missing Balls.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.4.4
Ceramic Column Grid Arrays (CCGAs). . . . . 30
4.8.2
Voids in Solder Balls.. . . . . . . . . . . . . . . . . . . . . . . . 43
4.4.5
Tape-Based Ball Grid Arrays (TBGAs).. . . . . 34
4.8.3
Solder Ball Attach Integrity.. . . . . . . . . . . . . . . . . 43
4.4.6
Multiple-Die Packaging.. . . . . . . . . . . . . . . . . . . . . 34
4.8.4
Package and Ball Coplanarity.. . . . . . . . . . . . . . . 43
4.4.7
System-in-Package (SiP).. . . . . . . . . . . . . . . . . . . . 35
4.8.4.1
4.4.8
Three-Dimensional (3D) Folded Package
Technology.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Example for Fine-Pitch BGA (FBGA)
Coplanarity.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
4.8.5
4.4.9
Ball Stack. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Moisture Sensitivity (Baking, Storage,
Handling and Rebaking). . . . . . . . . . . . . . . . . . . . . 44
4.4.10
Folded and Stacked Packaging
Combination. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
4.8.6
Shipping Medium (Tape and Reel, Trays,
Tubes). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.4.11
Package-on-Package (PoP). . . . . . . . . . . . . . . . . . 36
4.4.12
Benefits of Multiple-Die Packaging. . . . . . . . . 36
4.5
BGA Connectors and Sockets.. . . . . . . . . . . . . . . 37
5.1
Substrates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.5.1
Material Considerations for BGA
Connectors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
5.1.1
Organic Substrates. . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.5.2
Attachment Considerations for BGA
Connectors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
5.1.2
Inorganic Substrates.. . . . . . . . . . . . . . . . . . . . . . . . . 45
5.1.3
4.5.3
BGA Socket Materials and Types. . . . . . . . . . . 38
High-Density Interconnect (HDI)
Build-Up Layers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.5.4
Attachment Considerations for BGA
Sockets. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
5.2
Base Materials Considerations.. . . . . . . . . . . . . . 46
5.2.1
Resin Systems.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4.6
BGA Construction Materials.. . . . . . . . . . . . . . . . 39
5.2.2
Laminate Material Properties. . . . . . . . . . . . . . . . 47
4.6.1
Types of BGA Substrate Materials.. . . . . . . . . . 39
5.2.2.1
Thermal Expansion. . . . . . . . . . . . . . . . . . . . . . . . . . 47
4.6.1.1
Bismaleimide Triazine (BT) Glass. . . . . . . . . . 39
5.2.2.2
Glass Transition Temperature (Tg). . . . . . . . . . 47
4.6.1.2
Epoxy Glass (FR-4). . . . . . . . . . . . . . . . . . . . . . . . . . 39
5.2.2.3
Time to Delamination (T260 , T280 and
T300). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
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PRINTED BOARDS AND OTHER MOUNTING
STRUCTURES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
August 2024
IPC-7095E
5.2.2.4
Moisture Absorption. . . . . . . . . . . . . . . . . . . . . . . . . 48
6.2.3
Conductor Width.. . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
5.2.2.5
Reliability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
6.2.4
Via Size and Location.. . . . . . . . . . . . . . . . . . . . . . . 62
5.3
Printed Board Surface Finishes. . . . . . . . . . . . . . 48
6.2.5
5.3.1
Hot-Air Solder Leveling (HASL).. . . . . . . . . . . 49
Parameters Affecting Solder Mask on
BGAs.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
5.3.1.1
SnPb Hot-Air Solder Leveling (HASL). . . . . 49
6.2.6
5.3.1.2
Pb-Free Hot-Air Solder Leveling
(HASL).. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
Multiple-Grid BGA Land Pattern Array
Designs.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
6.3
5.3.2
Organic Solderability Preservative (OSP)
Coatings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
Escape and Conductor Routing
Strategies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
6.3.1
Escape Strategies.. . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
5.3.3
Noble Platings/Coatings. . . . . . . . . . . . . . . . . . . . . 50
6.3.2
Surface Conductor and Space Width. . . . . . . . 68
5.3.3.1
Electroless Ni/Immersion Au (ENIG). . . . . . . 50
6.3.3
5.3.3.2
Electrolytic Ni / Electroplated Au. . . . . . . . . . . 52
Land-to-Via (Dog Bone) Routing
Patterns.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
5.3.3.3
Electroless Ni / Electroless Pd /
Immersion Au (ENEPIG). . . . . . . . . . . . . . . . . . . . 52
6.3.4
Design for Mechanical Strain Mitigation. . . . 70
6.3.5
5.3.3.4
Direct Immersion Au (DIG). . . . . . . . . . . . . . . . . 53
Uncapped Via-in-Land and Its Impacts
on Reliability.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
5.3.3.5
Immersion Ag. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
6.3.6
5.3.3.6
Immersion Sn. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Fine-Pitch BGA (FBGA)
Microvia-in-Land Strategies. . . . . . . . . . . . . . . . . 72
5.4
Solder Mask.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
6.3.7
Power and Ground Connectivity.. . . . . . . . . . . . 73
5.4.1
Wet- and Dry-Film Solder Masks.. . . . . . . . . . . 54
6.4
5.4.2
Jettable Solder Mask. . . . . . . . . . . . . . . . . . . . . . . . . 54
Impact of Wave Solder on Top-Side
BGAs.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
5.4.3
Registration of Board-to-Panel Image
for Solder Mask. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
6.4.1
Top-Side Reflow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
6.4.2
Impact of Top-Side Reflow. . . . . . . . . . . . . . . . . . 73
5.5
Via Protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
6.4.3
Methods for Avoiding Top-Side Reflow. . . . . 75
5.5.1
Encroached Vias. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
6.4.4
Top-Side Reflow for Pb-Free Boards. . . . . . . . 75
5.5.2
Via Tenting, Plugging and Filling. . . . . . . . . . . 55
6.5
Testability and Test Point Access. . . . . . . . . . . . 75
6.5.1
Component Testing. . . . . . . . . . . . . . . . . . . . . . . . . . 75
6.5.2
Solder Ball Damage During Test and
Burn-In. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
6.5.3
Printed Board Testing.. . . . . . . . . . . . . . . . . . . . . . . 77
6.5.4
Printed Board Assembly Testing.. . . . . . . . . . . . 78
6.5.4.1
Printed Board Assembly Flexure During
Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
6
PRINTED CIRCUIT ASSEMBLY DESIGN
CONSIDERATIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
6.1
Component Placement and Clearances. . . . . . 58
6.1.1
Pick-and-Place Assembly. . . . . . . . . . . . . . . . . . . . 58
6.1.2
Rework Requirements. . . . . . . . . . . . . . . . . . . . . . . 58
6.1.3
Global Placement. . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
6.1.4
Alignment Legends (Silkscreened Ink,
Cu Features, Pin 1 Identifier). . . . . . . . . . . . . . . . 59
6.5.4.2
In-Circuit Test (ICT) Concerns. . . . . . . . . . . . . . 79
6.2
Attachment Sites (Land Patterns and
Vias).. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
6.5.4.3
Functional Test (FT) Concerns. . . . . . . . . . . . . . 79
6.6
6.2.1
Land Diameter Size and Its Impact on
Routing.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
Other Design for Manufacturability
(DfM) Issues. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
6.6.1
Panel/Pallet Design. . . . . . . . . . . . . . . . . . . . . . . . . . 80
6.2.2
Solder-Mask-Defined (SMD) Land and
Metal-Defined Land Designs. . . . . . . . . . . . . . . . 61
6.6.2
In-Process/End-Product Test Coupons. . . . . . 80
6.7
Thermal Management.. . . . . . . . . . . . . . . . . . . . . . . 82
6.2.2.1
Metal-Defined Lands.. . . . . . . . . . . . . . . . . . . . . . . . 62
6.7.1
Conduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
6.2.2.2
Solder-Mask-Defined (SMD) Lands. . . . . . . . . 62
6.7.2
Radiation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
6.7.3
Convection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
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6.7.4
Thermal Interface Materials. . . . . . . . . . . . . . . . . 83
6.7.4.1
Adhesives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
6.7.4.2
Greases. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
6.7.4.3
Phase-Change Materials (PCMs). . . . . . . . . . . . 84
6.7.4.4
August 2024
7.1.6.1
Flux Residues That Require Cleaning
(Clean). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
7.1.6.2
Flux Residues That Do Not Require
Cleaning (No-Clean). . . . . . . . . . . . . . . . . . . . . . . . 102
Gels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
7.1.7
Package Stand-Off. . . . . . . . . . . . . . . . . . . . . . . . . . 102
6.7.4.5
Thermally Conductive Pressure-Sensitive
Tape. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
7.2
Processes After Assembly.. . . . . . . . . . . . . . . . . . 103
7.2.1
Conformal Coatings.. . . . . . . . . . . . . . . . . . . . . . . . 103
6.7.5
Heat Sink Attachment Methods for
BGAs.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
7.2.2
Use of Underfills and Adhesives. . . . . . . . . . . . 104
7.2.2.1
Underfill Coverage. . . . . . . . . . . . . . . . . . . . . . . . . . 106
Interaction between BGA packaging
technologies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
7.2.2.2
Corner-Applied Adhesive. . . . . . . . . . . . . . . . . . . 108
7.2.2.3
Solder Joint Encapsulant Materials
(SJEMs). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
7.2.3
Depaneling of Printed Boards and
Modules. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
7.3
Inspection Techniques. . . . . . . . . . . . . . . . . . . . . . 110
7.3.1
X-Ray Inspection. . . . . . . . . . . . . . . . . . . . . . . . . . . 110
7.3.2
X-Ray Image Acquisition. . . . . . . . . . . . . . . . . . . 112
7.3.3
Definition and Discussion of X-Ray
System Terminology. . . . . . . . . . . . . . . . . . . . . . . . 113
7.3.3.1
2D Transmission X-Ray Technology. . . . . . 115
7.3.3.2
Oblique Viewing Inspection Using
Transmission X-Ray Technology.. . . . . . . . . . 115
7.3.3.3
Cross-Sectional X-Ray Technologies. . . . . . 116
7.3.3.3.1
Transmission X-ray or Computed
Tomography.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
7.3.3.3.2
Automated X-ray Inspection (AXI). . . . . . . . 117
7.3.4
X-Ray Image Analysis. . . . . . . . . . . . . . . . . . . . . . 117
7.3.4.1
Field of View. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
7.3.4.2
Manual X-ray Inspection (MXI) Thermal
Reflow Simulator (Heated Stage). . . . . . . . . . . 119
6.8
7
BGA ASSEMBLY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
7.1
Surface Mount Assembly Processes. . . . . . . . . 86
7.1.1
Solder Paste and Its Application. . . . . . . . . . . . . 86
7.1.1.1
Particle Size and Paste Selection. . . . . . . . . . . . 87
7.1.1.2
Stencil Thickness and Aperture Design. . . . . 87
7.1.1.3
Fine-Pitch Printing Technology. . . . . . . . . . . . . 89
7.1.1.4
Cavity Printing (3D Stencil). . . . . . . . . . . . . . . . . 90
7.1.1.4.1
Cavity Print Keep-Out Zone. . . . . . . . . . . . . . . . . 91
7.1.1.5
Importance of Paste Volume. . . . . . . . . . . . . . . . . 91
7.1.2
Component Placement Impact. . . . . . . . . . . . . . . 92
7.1.3
Vision Systems for BGA Placement. . . . . . . . . 92
7.1.3.1
Pick-and-Place Machine Capability for
Nonstandard-Grid BGA Components.. . . . . . . 93
7.1.3.1.1
Offline Teaching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
7.1.3.1.2
Inline Production.. . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
7.1.4
Reflow Soldering and Profiling. . . . . . . . . . . . . . 94
7.1.4.1
Forced-Gas Convection. . . . . . . . . . . . . . . . . . . . . . 94
7.1.4.2
Reflow Atmosphere. . . . . . . . . . . . . . . . . . . . . . . . . . 94
7.1.4.3
Time/Temperature Profiles. . . . . . . . . . . . . . . . . . . 94
7.3.5
Scanning Acoustic Microscopy (SAM).. . . . 119
7.1.4.4
Thermocouple Attachment. . . . . . . . . . . . . . . . . . . 97
7.3.6
BGA Stand-Off Measurement. . . . . . . . . . . . . . 120
7.1.4.5
Thermal Profiling for BackwardCompatibility with SnPb and Pb-Free
Alloys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
7.3.7
Optical Inspection (Endoscopy). . . . . . . . . . . . 121
7.3.7.1
Cracked Peripheral Interconnect
Determinations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
7.1.4.6
Low-Temperature Soldering of BGA
Components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
7.3.8
Destructive Analysis Methods. . . . . . . . . . . . . . 122
7.1.4.7
Unique Profile for Each Printed Board
Assembly.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
7.3.8.1
Cross-Sectioning. . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
7.3.8.2
Dye Penetrant Methods. . . . . . . . . . . . . . . . . . . . . 123
7.1.5
Effects of Materials on Flux Activation,
Component Damage and Solderability. . . . . 101
7.4
Testing and Product Verification.. . . . . . . . . . . 124
7.4.1
Electrical Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . 124
7.1.6
Clean vs. No-Clean. . . . . . . . . . . . . . . . . . . . . . . . . 102
7.4.2
Functional Test (FT) Coverage. . . . . . . . . . . . . 124
viii
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IPC-7095E
7.4.3
Burn-In Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
7.8.5
Head-on-Pillow (HoP). . . . . . . . . . . . . . . . . . . . . . 137
7.4.4
Product Screening Tests. . . . . . . . . . . . . . . . . . . . 125
7.8.5.1
Dynamic Warpage. . . . . . . . . . . . . . . . . . . . . . . . . . 138
7.5
Void Identification. . . . . . . . . . . . . . . . . . . . . . . . . . 125
7.8.5.2
Reflow Profile. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
7.5.1
Sources of Voids. . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
7.8.5.3
Solder Paste. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
7.5.2
Void Classification. . . . . . . . . . . . . . . . . . . . . . . . . . 126
7.8.5.4
7.5.3
Voids in BGA Solder Joints. . . . . . . . . . . . . . . . . 127
How to Mitigate Head-on-Pillow (HoP)
Defects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
7.5.3.1
Macrovoids.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
7.8.6
Nonwet Open (NWO)/Hanging Ball.. . . . . . . 139
7.5.3.2
Planar Microvoids.. . . . . . . . . . . . . . . . . . . . . . . . . . 127
7.8.7
Component Defects. . . . . . . . . . . . . . . . . . . . . . . . . 140
7.5.3.3
Shrinkage Voids.. . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
7.9
Rework Processes. . . . . . . . . . . . . . . . . . . . . . . . . . . 140
7.5.3.4
Microvia Voids.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
7.9.1
Rework Philosophy. . . . . . . . . . . . . . . . . . . . . . . . . 140
7.5.3.5
Intermetallic Compound (IMC)
Microvoids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
7.9.2
Removal of BGAs. . . . . . . . . . . . . . . . . . . . . . . . . . 140
7.9.3
Replacement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
7.5.3.6
Pinhole Voids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
7.9.3.1
Land Pattern Site Dressing.. . . . . . . . . . . . . . . . . 141
7.6
Void Measurement. . . . . . . . . . . . . . . . . . . . . . . . . . 128
7.9.3.2
Flux Application. . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
7.6.1
X-Ray Detection and Measurement
Cautions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
7.9.3.3
Paste Application.. . . . . . . . . . . . . . . . . . . . . . . . . . . 142
7.9.3.4
Rework Issues.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
7.6.2
Impacts of Voids. . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
7.9.3.5
Hot-Air Systems for BGA Rework. . . . . . . . . 142
7.6.3
Void Protocol Development.. . . . . . . . . . . . . . . . 128
7.9.3.6
Laser Systems for BGA Rework. . . . . . . . . . . . 142
7.6.4
Sampling Plans for Void Evaluation.. . . . . . . 130
7.9.3.7
Infrared Systems for BGA Rework. . . . . . . . . 143
7.7
Process Control for Void Reduction. . . . . . . . 131
7.9.3.8
Profile Requirements.. . . . . . . . . . . . . . . . . . . . . . . 143
7.7.1
Process Parameter Impact on Void
Formation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
8
7.7.1.1
Solder Paste Formulation. . . . . . . . . . . . . . . . . . . 131
7.7.1.2
Solder Paste Volume. . . . . . . . . . . . . . . . . . . . . . . . 131
7.7.1.3
Component, Printed Board and Solder
Paste Contamination and Oxidation. . . . . . . . 131
7.7.1.4
Reflow Profile. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
7.7.1.5
Reflow Atmosphere (Nitrogen or
Oxygen). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
7.7.1.6
RELIABILITY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
8.1
Reliability Factors for BGA Assemblies. . . . 144
8.1.1
Cyclic Strain. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
8.1.2
Fatigue. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
8.1.3
Creep. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
8.1.4
Creep and Fatigue Interaction.. . . . . . . . . . . . . . 146
8.1.5
Reliability Under Mechanical Loads. . . . . . . 146
8.1.5.1
Shock.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
Multiple Reflow Cycles. . . . . . . . . . . . . . . . . . . . . 132
8.1.5.2
Transient Bend. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
7.7.1.7
Land Surface Finish and Voiding. . . . . . . . . . . 132
8.1.5.3
Cyclic Bend. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
7.7.1.8
Vacuum-Assisted Reflow Soldering
for Void Reduction.. . . . . . . . . . . . . . . . . . . . . . . . . 132
8.1.5.4
Vibration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
8.1.5.5
Continuous Acceleration. . . . . . . . . . . . . . . . . . . . 147
7.7.2
Process Control Criteria for Voids
in Solder Balls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
8.2
Damage Mechanisms and Failure
of Solder Attachments. . . . . . . . . . . . . . . . . . . . . . 147
7.7.3
Process Control Criteria.. . . . . . . . . . . . . . . . . . . . 136
8.2.1
7.8
Solder Defects.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
7.8.1
Solder Bridging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
Comparison of Thermal Fatigue Crack
Growth Mechanism in SnAgCu (SAC)
vs. SnPb BGA Solder Joints. . . . . . . . . . . . . . . . 148
7.8.2
Cold Solder. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
8.2.2
Mixed-Alloy Soldering. . . . . . . . . . . . . . . . . . . . . 149
7.8.3
Opens. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
8.2.2.1
Forward and Backward Compatibility. . . . . . 149
7.8.4
Insufficient/Uneven Heating. . . . . . . . . . . . . . . . 137
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August 2024
Backward-Compatibility Options for
BGAs With SAC Solder Balls Used
in SnPb Solder Paste Reflow.. . . . . . . . . . . . . . . 151
8.5.5.4
Appearance of Pb-Free BGA Solder
Joints. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
8.6
Design for Reliability (DfR) Process. . . . . . . 165
8.2.2.2
Reballing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
8.7
Validation and Qualification Tests. . . . . . . . . . 166
8.2.2.3
Reflow Solder. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
8.8
Screening Procedures. . . . . . . . . . . . . . . . . . . . . . . 166
8.2.2.4
Reflow Solder Using a SnPb Profile. . . . . . . . 153
8.8.1
Solder Joint Defects.. . . . . . . . . . . . . . . . . . . . . . . . 166
8.2.2.5
Implementation of BGAs With Low-Ag
SAC and NonSAC BGA Ball Alloys. . . . . . . 153
8.8.2
Screening Recommendations. . . . . . . . . . . . . . . 166
8.9
Accelerated Reliability Testing. . . . . . . . . . . . . 166
8.2.2.6
Assembly Manufacturing Impacts of
Pb-Free BGA Balls.. . . . . . . . . . . . . . . . . . . . . . . . . 154
8.3
Solder Joints and Attachment Types.. . . . . . . 154
8.3.1
Global Expansion Mismatch. . . . . . . . . . . . . . . . 155
8.3.2
Local Expansion Mismatch. . . . . . . . . . . . . . . . . 155
8.3.3
Internal Expansion Mismatch.. . . . . . . . . . . . . . 155
8.4
Solder Attachment Failure. . . . . . . . . . . . . . . . . . 155
8.4.1
Solder Attachment Failure Classification. . . 155
8.4.1.1
Failure Signature 1: Cold Solder Joint. . . . . . 156
8.4.1.2
Failure Signature 2: Nonsolderable Land.. . 156
8.4.1.3
Failure Signature 3: Ball Drop. . . . . . . . . . . . . . 156
8.4.1.4
8.4.1.5
9
PROCESS TROUBLESHOOTING. . . . . . . . . . . . . . . . . 167
9.1
Solder-Mask-Defined (SMD) BGA
Conditions.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
9.1.1
Solder-Mask-Defined (SMD) and NonSolder-Mask-Defined (NSMD) Lands. . . . . . 167
9.1.2
Solder-Mask-Defined (SMD) Land on
Product Printed Board. . . . . . . . . . . . . . . . . . . . . . 167
9.1.3
Solder-Mask-Defined (SMD) BGA
Failures.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168
9.2
Over-Collapse BGA Solder Ball
Conditions.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168
Failure Signature 4: Missing Ball.. . . . . . . . . . 157
9.2.1
Failure Signature 5: Printed Board and
BGA Stack Warpage. . . . . . . . . . . . . . . . . . . . . . . . 157
BGA Ball Shape Without Heat Slug
500 µm Stand-Off Height. . . . . . . . . . . . . . . . . . . 168
9.2.2
BGA Ball Shape with Heat Slug 375 µm
Stand-Off Height.. . . . . . . . . . . . . . . . . . . . . . . . . . . 169
9.2.3
BGA Ball Shape with Heat Slug 300 µm
Stand-Off Height.. . . . . . . . . . . . . . . . . . . . . . . . . . . 169
9.2.4
Critical Solder Paste Conditions. . . . . . . . . . . . 169
9.2.5
Void Determination Through X-Ray
and Cross-Section Transmission.. . . . . . . . . . . 169
9.2.6
Voids and Uneven Solder Balls. . . . . . . . . . . . . 170
9.3
BGA Warpage.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
9.3.1
BGA Warpage.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
8.4.1.6
Failure Signature 6: Mechanical Failure. . . . 159
8.4.1.7
Failure Signature 7: Insufficient Reflow. . . . 160
8.5
Critical Factors Impacting Reliability. . . . . . 160
8.5.1
Package Technology. . . . . . . . . . . . . . . . . . . . . . . . 160
8.5.2
Stand-Off Height.. . . . . . . . . . . . . . . . . . . . . . . . . . . 161
8.5.3
Printed Board Design Considerations.. . . . . . 162
8.5.4
Reliability of Solder Attachments of
Ceramic Grid Arrays (CGAs). . . . . . . . . . . . . . . 162
8.5.5
Pb-Free Soldering of BGAs.. . . . . . . . . . . . . . . . 163
8.5.5.1
Pb-Free Alloy Selection.. . . . . . . . . . . . . . . . . . . . 163
9.3.2
8.5.5.2
Recommendations for Alloys with Ag
Content Near One Percent. . . . . . . . . . . . . . . . . . 164
Solder Joint Opens Due to Interposer
Warpage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
9.4
Solder Joint Conditions. . . . . . . . . . . . . . . . . . . . . 171
8.5.5.2.1
Solder Joint Reliability.. . . . . . . . . . . . . . . . . . . . . 164
9.4.1
Acceptable Solder Condition. . . . . . . . . . . . . . . 171
8.5.5.2.2
Managing the Change to a Low-Ag Ball
Alloy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
9.4.2
Solder Balls with Excessive Oxide. . . . . . . . . 172
9.4.3
Dewetting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
8.5.5.3
Board Design Considerations. . . . . . . . . . . . . . . 164
9.4.4
Nonwetting.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
8.5.5.3.1
BGA Land Pattern Designs. . . . . . . . . . . . . . . . . 164
9.4.5
8.5.5.3.2
Component Placement. . . . . . . . . . . . . . . . . . . . . . 164
Incomplete Joining Due to Land
Contamination. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
9.4.6
Deformed Solder Ball.. . . . . . . . . . . . . . . . . . . . . . 173
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9.4.7
Deformed Solder Ball – Dynamic
Warping. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
9.4.8
Insufficient Solder and Flux for Proper
Joint Formation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
9.4.9
Reduced Termination Contact Area. . . . . . . . 174
9.4.10
Solder Bridging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
9.4.11
Incomplete Solder Reflow. . . . . . . . . . . . . . . . . . 175
9.4.12
Missing Solder. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
9.4.13
Nonwet Open (NWO).. . . . . . . . . . . . . . . . . . . . . . 176
9.4.14
Head-on-Pillow (HoP) Solder Joint.. . . . . . . . 176
APPENDIX A Process Control Characterization to
Reduce the Occurrence of Voids. . . . . . . . . . . . 177
Table 4‑10
IPC-4101 FR-4 Property Summaries –
Illustrations of Specification Sheets of
Materials Projected to Better Withstand
Pb-free Assembly. . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Table 4‑11
Typical Properties of Common Dielectric
Materials for BGA Package Substrates. . . . . 41
Table 4‑12
Controlled Coplanarity Per Ball Size. . . . . . . 44
Table 4‑13
Moisture Classification Level and Floor
Life.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Table 5‑1
Key Attributes for Various Printed Board
Surface Finishes. . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Table 5‑2
Evaluation Via Filling/Encroachment
Based on Surface Finish Process. . . . . . . . . . . 56
A.1
Process Characterization. . . . . . . . . . . . . . . . . . . . 178
Table 5‑3
Via Fill Options. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
A.1.1
Fine-Pitch BGAs (FBGAs). . . . . . . . . . . . . . . . . 180
Table 6‑1
A.1.2
Via-in-Land Design in Fine-Pitch
BGAs (FBGAs). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
Number of Conductors Between Solder
Lands – 1.27 mm Pitch BGA
(0.75 mm Ball Diameter). . . . . . . . . . . . . . . . . . . 60
Table 6‑2
Number of Conductors Between Solder
Lands – 1 mm Pitch BGA
(0.60 mm Ball Diameter). . . . . . . . . . . . . . . . . . . 60
Table 6‑3
Number of Conductors Between Solder
Lands – 0.80 mm Pitch BGA
(0.50 mm Ball Diameter). . . . . . . . . . . . . . . . . . . 60
Table 6‑4
Number of Conductors Between Solder
Lands – 0.65 mm Pitch BGA
(0.40 mm Ball Diameter). . . . . . . . . . . . . . . . . . . 60
Table 6‑5
Number of Conductors Between Solder
Lands – 0.50 mm Pitch BGA
(0.30 mm Ball Diameter). . . . . . . . . . . . . . . . . . . 60
APPENDIX B Abbreviations and Acronyms.. . . . . . . . . . . . . . 183
Tables
Table 3‑1
Multidie Module (MDM) Definitions. . . . . . . . 5
Table 3‑2
Number of Conductors vs. Array Size on
Two Layers of Circuitry. . . . . . . . . . . . . . . . . . . . . . 6
Table 3‑3
List of IPC Standards Related to Pad
Cratering. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Table 4‑1
JEDEC Standard JEP95-1/5 Allowable
Ball Diameter Variations for FBGA. . . . . . . . 22
Table 4‑2
Ball Diameter Sizes for Plastic BGAs
(PBGAs). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Table 6‑6
Table 4‑3
Ball Diameter Sizes for Die-Size BGAs
(DSBGAs). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Maximum Solder Land to Pitch
Relationship (mm). . . . . . . . . . . . . . . . . . . . . . . . . . 61
Table 6‑7
Escape Strategies for Full Arrays. . . . . . . . . . . 68
Table 4‑4
Land Pattern Design. . . . . . . . . . . . . . . . . . . . . . . . 24
Table 6‑8
Table 4‑5
Land-to-Ball Calculations for BGA
Packages (mm).. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Conductor and Space Width for
Different Array Pitches. . . . . . . . . . . . . . . . . . . . . 68
Table 6‑9
Table 4‑6
Examples of JEDEC-Registered BGA
Outlines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Effects of Material Type on
Conduction.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
Table 6‑10
Table 4‑7
Pb-Free Alloy Variations. . . . . . . . . . . . . . . . . . . 26
Emissivity Ratings for Certain
Materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
Table 4‑8
Column Grid Array (CGA) Land Size
Approximation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Table 6‑11
Interaction Between BGA Packaging
Technologies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
Table 4‑9
Column Grid Array (CGA) Alloy and
Construction Styles. . . . . . . . . . . . . . . . . . . . . . . . . 33
Table 7‑1
Recommendations for Solder Powder
Type for Different Pitches to Achieve
Good Solder Paste Release
(S/P Ratio > 4.2). . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
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IPC-7095E
August 2024
Table 7‑2
Stencil Thicknesses Per BGA Pitch. . . . . . . . 87
Figure 3‑5
Flip Chip Bonded Ball Grid Array (BGA).. . . 8
Table 7‑3
Pros and Cons of Common Stencil
Technologies and Options. . . . . . . . . . . . . . . . . . 89
Figure 3‑6
BGA Warpage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Figure 3‑7
Examples of Pad Cratering. . . . . . . . . . . . . . . . . 12
Table 7‑4
Fine-Pitch BGA (FBGA) Printing
Options.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
Figure 3‑8
Various Possible Failure Modes for a
BGA Solder Joint. . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Table 7‑5
Example of Solder Paste Volume
Requirements for Ceramic Array
Packages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Figure 3‑9
Corner View (Left) and Cross-Section
View (Right) of a Head-on-Pillow (HoP)
Solder Joint Defect.. . . . . . . . . . . . . . . . . . . . . . . . . 13
Table 7‑6
Profile Comparison Between SnPb
and SAC Alloys.. . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Figure 3‑10 Cross-Section View of a Head-on-Pillow
(HoP) Open Defect. . . . . . . . . . . . . . . . . . . . . . . . . 13
Table 7‑7
Inspection Usage Application
Recommendations. . . . . . . . . . . . . . . . . . . . . . . . . 110
Table 7‑8
Field of View for Inspection.. . . . . . . . . . . . . . 118
Figure 3‑11 Examples of Nonwet Open (NWO)
Defects in Side View and
Cross-Section View.. . . . . . . . . . . . . . . . . . . . . . . . 14
Table 7‑9
Void Classification. . . . . . . . . . . . . . . . . . . . . . . . . 126
Figure 4‑1
Table 7‑10
Examples of Suggested Void
Protocols. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
Figure 4‑2
Ball-to-Void Size Image – Comparisons
for Various Ball Diameters. . . . . . . . . . . . . . . . 130
Board-on-Die (BOD) BGA
Construction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Figure 4‑3
Rework Process Temperature Profiles
for SnPb Assembly.. . . . . . . . . . . . . . . . . . . . . . . . 143
Top of Molded Board-on-Die (BOD)
BGA.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Figure 4‑4
Rework Process Temperature Profiles
for Pb-Free Assemblies. . . . . . . . . . . . . . . . . . . . 143
Flip Chip (Bumped Die) on a BGA
Substrate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Figure 4‑5
BGA Solder Joints Using SnPb – (A)
and Mixed-Metallurgy (B)
(Pb-Free Alloy in a SnPb Process)
With Partially Mixed SnPb in a
SAC Ball. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Figure 4‑6
JEDEC Standard Format for
Package-on-Package Components.. . . . . . . . . 25
Figure 4‑7
Dynamic Warpage Plot with Temperature
for a Flip Chip BGA Package.. . . . . . . . . . . . . . 27
Figure 4‑8
Low-Temperature Alloys with
Liquidus Temperatures Between
100 °C and 200 °C and
Which Do Not Contain Pb, Cd or Au.. . . . . . 27
Figure 4‑9
SnBi Phase Diagram. . . . . . . . . . . . . . . . . . . . . . . . 28
Table 7‑11
Table 7‑12
Table 7‑13
Table 8‑1
Types of Pb-free Assemblies.. . . . . . . . . . . . . . 149
Table 8‑2
Typical Stand-Off Heights for BGAs. . . . . . 161
Table 8‑3
Melting Points, Advantages and
Disadvantages of Common Solder
Alloys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
Table A-1
Corrective Action Indicator for Lands
Used With 1 mm,
1.27 mm and 1.5 mm Pitch. . . . . . . . . . . . . . . . 179
Table A-2
Corrective Action Indicator for Lands
Used With 0.5 mm,
0.65 mm or 0.8 mm Pitch.. . . . . . . . . . . . . . . . . 180
Table A-3
Corrective Action Indicator for
Microvia-in-Land Lands Used With
0.3 mm, 0.4 mm or 0.5 mm Pitch.. . . . . . . . . 181
Figures
Figure 3‑1
BGA Package Manufacturing Process.. . . . . . . 4
Figure 3‑2
Multidie Module (MDM) Type 2S-L-WB. . . 5
Figure 3‑3
Conductor Width-to-Pitch Relationship. . . . . . 7
Figure 3‑4
Wire-Bonded Ball Grid Array (BGA). . . . . . . . 7
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Termination Types for Area Array
Packages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Figure 4‑10 Typical Microstructure of SnBi Solder
Alloy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Figure 4‑11 Plastic Ball Grid Array (PBGA)
Package. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Figure 4‑12 Cross-Section of a Thermally
Enhanced Ceramic Ball Grid Array
(CBGA) Package. . . . . . . . . . . . . . . . . . . . . . . . . . . 29
August 2024
IPC-7095E
Figure 4‑13 Ceramic Ball Grid Array (CBGA)
Package with Molded Polymer
Encapsulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Figure 4‑36 Land Grid Array (LGA) Socket with and
Without Pick-and-Place Cover. . . . . . . . . . . . . 38
Figure 4‑14 Typical Ceramic Column Grid Array
(CCGA) With Cu Ribbon Wrap. . . . . . . . . . . . 30
Figure 4‑38 Example of Voids in Eutectic Solder Balls
at Incoming Inspection.. . . . . . . . . . . . . . . . . . . . . 43
Figure 4‑15 Plastic BGA (PBGA) with Variety of
Columns. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Figure 4‑39 Examples of Solder Ball and Land Surface
Conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Figure 4‑16 Typical Solder Column with Cu Ribbon
Wrap. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Figure 4‑40 Establishing BGA Coplanarity
Requirement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Figure 4‑17 Section View of Sn10Pb90 Solder
Column with Electroplated Cu Covered
with Sn60Pb40 Outer Layer. . . . . . . . . . . . . . . . 31
Figure 4‑41 Ball Contact Positional Tolerance. . . . . . . . . . 44
Figure 5‑1
Figure 4‑18 SnPb-Plated Microcoil (Left) and
Au-Plated Microcoil (Right).. . . . . . . . . . . . . . . 32
Possible HDI Build-Ups Using
Laser-Via Generation. . . . . . . . . . . . . . . . . . . . . . . 46
Figure 5‑2
Figure 4‑19 Au-Plated Microcoil Spring on Column
Grid Array (CGA1152) Ceramic IC
Package. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Possible HDI Build-Ups Using
Etching and Mechanical Processes. . . . . . . . . 46
Figure 5‑3
Expansion Rate Above Tg. . . . . . . . . . . . . . . . . . 47
Figure 5‑4
Hot Air Solder Level (HASL)
Surface Topology Comparison. . . . . . . . . . . . . 50
Figure 5‑5
Illustration of Electroless Ni/
Immersion Au (ENIG) Structure.. . . . . . . . . . . 51
Figure 5‑6
Black Pad Fracture Showing a Crack
Between Ni and Ni-Sn Intermetallic
Layer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Figure 5‑7
Typical Mud Crack Appearance of
Black Pad Surface. . . . . . . . . . . . . . . . . . . . . . . . . . 51
Figure 5‑8
Large Region of Severe Black Pad with
Corrosion Spikes Protruding into Ni-Rich
Layer Through P-Rich Layer Underneath
Immersion Au Surface. . . . . . . . . . . . . . . . . . . . . . 52
Figure 5‑9
Au Embrittlement. . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Figure 4‑20 Microcoil Spring with SAC305 Fillet
on Column Grid Array (CGA) Package. . . . 32
Figure 4‑21 Microcoil Spring (Electroplated
Sn60Pb40) Column Grid Array
(CGA1152) With Sn63Pb37 Fillet. . . . . . . . . 32
Figure 4‑22 Polyimide Film-Based Lead-Bond
µBGA Package Substrate. . . . . . . . . . . . . . . . . . . 34
Figure 4‑23 Comparison of In-Package Circuit
Routing of Single- and Two-Metal
Layer Tape Substrates. . . . . . . . . . . . . . . . . . . . . . 34
Figure 4‑37 Example of Missing Balls on a BGA. . . . . . . 42
Figure 4‑24 Single-Package Die-Stack BGA. . . . . . . . . . . . 35
Figure 4‑25 Custom Eight Die (Flip Chip and
Wire Bond) SiP Assembly. . . . . . . . . . . . . . . . . . 35
Figure 4‑26 Folded Multiple-Die BGA Package. . . . . . . . 35
Figure 4‑27 Eight-Layer Ball Stack Package. . . . . . . . . . . . 35
Figure 4‑28 Single-Sided Small Outline Dual
In-Line Memory Module (SO-DIMM)
Memory Card Assembly. . . . . . . . . . . . . . . . . . . . 36
Figure 4‑29 Folded and Stacked Multiple-Die BGA. . . . 36
Figure 4‑30 Package-on-Package (PoP) Assembly. . . . . . 36
Figure 4‑31 BGA Connector. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Figure 4‑32 BGA Connector with Vacuum Cap. . . . . . . . . 37
Figure 4‑33 Pin Grid Array (PGA) Socket Pins. . . . . . . . . 38
Figure 4‑34 Pin Grid Array (PGA) Socket with and
Without Pick-and-Place Cover. . . . . . . . . . . . . 38
Figure 4‑35 Land Grid Array (LGA) Contact Pin. . . . . . . 38
Figure 5‑10 Illustration of Electroless Ni/Electroless
Pd/Immersion Au (ENEPIG) Structure. . . . . 52
Figure 5‑11 Graphic Depiction of Directed
Immersion Au (DIG).. . . . . . . . . . . . . . . . . . . . . . . 53
Figure 5‑12 Examples of Microvoids.. . . . . . . . . . . . . . . . . . . 54
Figure 5‑13 Elements That May Affect Paste
Deposition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Figure 5‑14 Via Plugging Methods. . . . . . . . . . . . . . . . . . . . . . 57
Figure 6‑1
BGA Alignment Marks. . . . . . . . . . . . . . . . . . . . . 59
Figure 6‑2
Solder Lands for BGA Components. . . . . . . . 61
Figure 6‑3
Metal-Defined Land Attachment Profile.. . . 62
Figure 6‑4
›Solder Mask Stress Concentration. . . . . . . . . 62
Figure 6‑5
Solder Joint Geometry Contrast. . . . . . . . . . . . 62
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Figure 6‑6
Good and Bad Solder Mask Designs. . . . . . . 63
Figure 6‑7
Examples of Metal-Defined Lands
with Solder Mask Covered Vias. . . . . . . . . . . . 63
Figure 6‑8
Bad Solder Mask Registration. . . . . . . . . . . . . . 64
Figure 6‑9
Good Solder Mask Registration. . . . . . . . . . . . 64
Figure 6‑10 Balls Anywhere Land Pattern Design
for a Balls Anywhere BGA Component. . . . 65
Figure 6‑11 Uniform-Grid BGA Land Pattern.. . . . . . . . . . 65
Figure 6‑12 Quadrant BGA Pattern. . . . . . . . . . . . . . . . . . . . . . 66
Figure 6‑13 Square Array. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
August 2024
Figure 6‑33 Top-Side Mixed-Component Board
Assembly Wave Soldering
Temperature Profile (SnPb Alloy). . . . . . . . . . 74
Figure 6‑34 Heat Pathways to BGA Solder Joint
During Wave Soldering.. . . . . . . . . . . . . . . . . . . . 74
Figure 6‑35 Methods of Avoiding Top-Side
BGA Solder Joint Reflow
During Wave Soldering.. . . . . . . . . . . . . . . . . . . . 75
Figure 6‑36 Example of a Side Contact Made
with Tweezers-Type Contact. . . . . . . . . . . . . . . 76
Figure 6‑15 Depopulated Array.. . . . . . . . . . . . . . . . . . . . . . . . . 66
Figure 6‑37 Pogo-Pin-Type Electrical Contact
Impressions on the Bottom of a
Solder Ball. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Figure 6‑16 Square Array with Missing Balls. . . . . . . . . . . 67
Figure 6‑38 Area Array Land Pattern Testing. . . . . . . . . . . 77
Figure 6‑17 Interspersed Array. . . . . . . . . . . . . . . . . . . . . . . . . . 67
Figure 6‑39 Board Panelization.. . . . . . . . . . . . . . . . . . . . . . . . . 81
Figure 6‑18 Conductor Routing Strategy. . . . . . . . . . . . . . . . 68
Figure 6‑40 Comb Pattern Examples. . . . . . . . . . . . . . . . . . . . 81
Figure 6‑19 Conductor and Space Widths for
Different Array Pitches. . . . . . . . . . . . . . . . . . . . . 69
Figure 6‑41 Heat Sink Attached to a BGA
Using Adhesive. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
Figure 6‑20 One- and Two-Track Conductor
Routing.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Figure 6‑42 Heat Sink Attached to a BGA
Using a Clip.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
Figure 6‑21 Typical Land-to-Via (Dog Bone)
Layout.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Figure 6‑43 Heat Sink Attached to a BGA
Using a Clip That Hooks into
Printed Board Holes. . . . . . . . . . . . . . . . . . . . . . . . 85
Figure 6‑14 Rectangular Array. . . . . . . . . . . . . . . . . . . . . . . . . . 66
Figure 6‑22 Land-to-Via (Dog Bone) Routing
Options.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Figure 6‑23 BGA Land-to-Via (Dog Bone) Land
Pattern Preferred Direction for
Conductor Routing.. . . . . . . . . . . . . . . . . . . . . . . . . 70
Figure 6‑44 Heat Sink Attached to a BGA
Using a Clip That Hooks onto a
Stake Soldered to the Printed Board. . . . . . . . 85
Figure 6‑24 Preferred Screw and Support
Placement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Figure 6‑45 Heat Sink Attached to a BGA
by Wave Soldering Its Pins in
Through-Holes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
Figure 6‑25 Connector Screw Support Placement. . . . . . . 70
Figure 7‑1
Stencil Aperture Labels for Aspect Ratio,
Area Ratio Calculations (Solder Stencil
Feature Dimensions). . . . . . . . . . . . . . . . . . . . . . . . 88
Figure 6‑26 Cross-Section of 0.75 mm Ball
with Via-in-Land Structure. . . . . . . . . . . . . . . . . 71
Figure 6‑27 Cross-Section Illustration of
Via-in-Land Design Showing
Via Cap and Solder Ball. . . . . . . . . . . . . . . . . . . . 71
Figure 7‑2
BGA Balls After Paste Dipping.. . . . . . . . . . . . 90
Figure 7‑3
Cavity Board and 3D Stencil. . . . . . . . . . . . . . . 90
Figure 7‑4
3D Stencil with Two Cavity Pockets. . . . . . . 90
Figure 6‑28 Via-in-Land Process Descriptions
(BGAs on Top). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
Figure 7‑5
Slit-Metal Squeegee. . . . . . . . . . . . . . . . . . . . . . . . 90
Figure 7‑6
Cavity Keep-Out Zone.. . . . . . . . . . . . . . . . . . . . . 91
Figure 7‑7
High-Pb and Eutectic Solder Ball
and Joint Comparison.. . . . . . . . . . . . . . . . . . . . . . 91
Figure 7‑8
BGA Image by a Placement Machine
Camera (Passed Inspection: Found All
484 Balls). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Figure 6‑29 Microvia Example (Cross-Section). . . . . . . . . 72
Figure 6‑30 Void in Microvia. . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
Figure 6‑31 Ground or Power BGA Connection. . . . . . . . 73
Figure 6‑32 Example of Ball Deformation and
Dewetting of Top-Side Reflow Joints. . . . . . 73
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August 2024
Figure 7‑9
IPC-7095E
Balls Anywhere Image Captures
for Offline Teaching. . . . . . . . . . . . . . . . . . . . . . . . 93
Figure 7‑25 BGA Package with Incomplete
Underfill Coverage.. . . . . . . . . . . . . . . . . . . . . . . . 106
Figure 7‑10 Examples of Peak Reflow Temperatures
at Various Locations at or Near a BGA.. . . . 94
Figure 7‑26 Flow of Underfill Between Two
Parallel Surfaces. . . . . . . . . . . . . . . . . . . . . . . . . . . 106
Figure 7‑11 Schematic of Reflow Profile for
SnPb Assemblies.. . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Figure 7‑27 Examples of Air Bubbles in Underfill. . . . . 107
Figure 7‑12 Schematic of Reflow Profile for
Pb-Free Assemblies. . . . . . . . . . . . . . . . . . . . . . . . . 96
Figure 7‑29 Microsection of BGA With
Corner-Applied Adhesive.. . . . . . . . . . . . . . . . . 108
Figure 7‑13 Locations of Thermocouples on a
Printed Board Assembly
with Large and Small Components. . . . . . . . . 97
Figure 7‑30 Top View of BGA With
Corner-Applied Adhesive.. . . . . . . . . . . . . . . . . 108
Figure 7‑14 Recommended Locations of
Thermocouples on a BGA. . . . . . . . . . . . . . . . . . 97
Figure 7‑28 Example of Partial Underfill. . . . . . . . . . . . . . . 107
Figure 7‑31 Critical Dimension for Application of
Corner-Applied Adhesive
Prior to Reflow.. . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
Figure 7‑15 Proper Thermocouple Location on a
BGA Connector. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
Figure 7‑32 Typical Corner-Applied Adhesive
Figure 7‑16 Comparison of Assembly Processes for a
SAC BGA Component Using SAC Solder
Paste (Top), BiSn Baseline or Ductile
Metallurgy Solder Paste (Middle) and
Resin-Containing Joint-Reinforcement
Paste (JRP) (Bottom). . . . . . . . . . . . . . . . . . . . . . . 98
Figure 7‑33 Examples of Four Strategies for
Polymeric Reinforcement of
BGA Solder Joints. . . . . . . . . . . . . . . . . . . . . . . . . 109
Figure 7‑17 Comparison of the Reflow Temperature
Profiles for SAC, BiSnAg and
Low-Temperature JRP Solder Pastes. . . . . . . 99
Figure 7‑18 Mixed-Alloy BGA Solder Joint Formed
with SAC Ball Soldered with Ductile
Metallurgy BiSn Solder Paste. . . . . . . . . . . . . . 99
Figure 7‑19 Mixed-Alloy BGA Solder Joint Formed
with SAC Ball Soldered with BiSn
Joint-Reinforcement Paste (JRP). . . . . . . . . . 100
Figure 7‑20 Effect of Paste Volume on the Area of
Bi-Mixed Regions with Mixed-Alloy
SAC-BiSn BGA Solder Joints. . . . . . . . . . . . . 100
Figure 7‑21 Solder Joint Shapes and Microstructures
for Three Combinations of Solder Balls
and Solder Pastes for a Paddle-Contact
BGA Socket.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Figure 7‑22 Effect of Solder Mask Relief Around
BGA Lands of a Printed Board. . . . . . . . . . . . 103
Figure 7‑23 Impact of Improper Usage of
Conformal Coating. . . . . . . . . . . . . . . . . . . . . . . . 104
Figure 7‑24 Map of Underfill Adhesive Usage for
BGAs and Other Packages.. . . . . . . . . . . . . . . . 105
Failure Mode.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
Figure 7‑34 Solder Joint Encapsulation Material
(SJEM). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
Figure 7‑35 Fundamentals of X-Ray Technology. . . . . . 111
Figure 7‑36 X-Ray Example of Head-on-Pillow
(HoP) Solder Joints. . . . . . . . . . . . . . . . . . . . . . . . 111
Figure 7‑37 Three X-Ray Examples of
Voiding in Solder Ball Contacts. . . . . . . . . . . 112
Figure 7‑38 Two Examples of Manual X-Ray
System Image Quality. . . . . . . . . . . . . . . . . . . . . 113
Figure 7‑39 Example of X-Ray Pin Cushion
Distortion and Voltage Blooming. . . . . . . . . 113
Figure 7‑40 Transmission Image (2D). . . . . . . . . . . . . . . . . . 114
Figure 7‑41 Tomosynthesis Image (3D). . . . . . . . . . . . . . . . 114
Figure 7‑42 Laminography 3D Automated X-Ray
Inspection (AXI) Section Image. . . . . . . . . . . 114
Figure 7‑43 High-Quality 2D Transmission X-Ray
Image Example. . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
Figure 7‑44 Oblique Viewing Printed Board Tilt. . . . . . 115
Figure 7‑45 Oblique Viewing Detector Tilt. . . . . . . . . . . . 115
Figure 7‑46 Top-Down View of FBGA Solder
Joints. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
Figure 7‑47 Oblique View of FBGA Solder Joints. . . . . 116
Figure 7‑48 Large Board Computed Tomography
(CT) / Partial CT Principle.. . . . . . . . . . . . . . . . 116
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Figure 7‑49 Large-Board Computed Tomography (CT)
Scan (Left) and 3D Rendering (Right)
Showing Head-on-Pillow (HoP).. . . . . . . . . . 117
Figure 7‑50 Large-Board Computed Tomography
(CT). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
Figure 7‑51 Tomosynthesis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
Figure 7‑52 Scanned Beam X-Ray Laminography. . . . . 118
Figure 7‑53 Voiding Creation Dynamics
Within a QFN Device Observed
Using Heated Stage. . . . . . . . . . . . . . . . . . . . . . . . 119
August 2024
Figure 7‑69 Vacuum-Assisted Convection
Reflow Oven. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
Figure 7‑70 Vacuum-Assisted Vapor Phase Reflow
Oven. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
Figure 7‑71 Time vs. Pressure Plot Showing the
Difference Between Vacuum-Assisted
and High-Pressure Soldering
Processes.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
Figure 7‑72 Example of Voided Area at Land and
Printed Board Interface. . . . . . . . . . . . . . . . . . . . 135
Figure 7‑54 Typical Acoustic Microscopy
Configuration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
Figure 7‑73 X-Ray Image Showing Uneven
Heating.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
Figure 7‑55 C-Scan Image (left) and T-Scan Image
(right) of the Same BGA.. . . . . . . . . . . . . . . . . . 120
Figure 7‑74 X-Ray Image at 45° Showing
Insufficient Heating in
One Corner of the BGA.. . . . . . . . . . . . . . . . . . . 137
Figure 7‑56 Endoscope Example 1. . . . . . . . . . . . . . . . . . . . . 121
Figure 7‑57 Endoscope Example 2. . . . . . . . . . . . . . . . . . . . . 121
Figure 7‑58 Endoscope Example 3. . . . . . . . . . . . . . . . . . . . . 121
Figure 7‑59 Engineering Crack Evaluation
Technique. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
Figure 7‑60 Solder Balls Cross-Sectioned
Through Voids in the Solder Balls.. . . . . . . . 122
Figure 7‑61 Cross-Section of a Crack Initiation
Near the Ball/Land Interface.. . . . . . . . . . . . . . 122
Figure 7‑62 Dye and Pull (Pry) Showing No Dye
Indications on the BGA Land or
Printed Board Surfaces. . . . . . . . . . . . . . . . . . . . 123
Figure 7‑63 Dye and Pull (Pry) Showing Dye
Indications on Both the
Printed Board and BGA Lands. . . . . . . . . . . . 123
Figure 7‑64 Dye and Pull (Pry) Showing Laminate
Fractures (Pad Cratering) With
Dye Indications on BGA Side and
Printed Board Side. . . . . . . . . . . . . . . . . . . . . . . . . 124
Figure 7‑65 Small Voids Clustered in Mass at the
Ball-to-Land Interface. . . . . . . . . . . . . . . . . . . . . 125
Figure 7‑66 Typical Size and Location of Various
Types of Voids in a BGA Solder Joint.. . . . 127
Figure 7‑75 Example of Head-on-Pillow (HoP)
Showing Ball and Solder Paste That
Have Not Coalesced. . . . . . . . . . . . . . . . . . . . . . . 137
Figure 7‑76 Head-on-Pillow (HoP) Occurrence
Process Sequence. . . . . . . . . . . . . . . . . . . . . . . . . . 138
Figure 7‑77 Head-on-Pillow (HoP) Due to High
Package Warpage. . . . . . . . . . . . . . . . . . . . . . . . . . 138
Figure 7‑78 Example of Liquidus Time Delay
(LTD). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
Figure 7‑79 Solder Particles on a Printed Board
Noncoalesced After Reflow.. . . . . . . . . . . . . . . 139
Figure 7‑80 Examples of Hanging Ball Defects. . . . . . . . 139
Figure 7‑81 X-Ray Image of Popcorning. . . . . . . . . . . . . . . 140
Figure 7‑82 X-Ray Image Showing Warpage in a
BGA.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
Figure 7‑83 BGA/Assembly Shielding Examples. . . . . . 141
Figure 8‑1
Example of Solder Joint Crack Due to
Thermomechanical Fatigue. . . . . . . . . . . . . . . . 148
Figure 8‑2
BGAs Following Thermal Cycling
Showing Coarsening with a Fatigue
Crack (A) and Coarsening (B). . . . . . . . . . . . . 148
Figure 8‑3
Thermal Fatigue Crack Propagation in
Eutectic SnPb Solder Joints in a Ceramic
Ball Grid Array (CBGA) Module.. . . . . . . . . 149
Figure 8‑4
Thermal Fatigue Crack Propagation in
Sn95.5Ag3.8Cu0.7 Joints in a Ceramic
Ball Grid Array (CBGA) Module.. . . . . . . . . 149
Figure 7‑67 X-Ray Image of Solder Balls with
Voids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
Figure 7‑68 Comparison Between Standard Reflow
Soldering (Top) and Vacuum-Assisted
Reflow Soldering (Bottom) for
BGA Solder Joints. . . . . . . . . . . . . . . . . . . . . . . . . 133
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August 2024
Figure 8‑5
Figure 8‑6
Figure 8‑7
IPC-7095E
Comparison of Reflow Soldering Profiles
for SnPb, Backward-Compatibility and
Pb-Free Printed Board Assemblies. . . . . . . . 150
Micrographs of a Cross-Section of a
BGA SAC Solder Ball Assembled onto
a Printed Board with SnPb Solder Paste
Using Standard SnPb Reflow
Soldering Profile. . . . . . . . . . . . . . . . . . . . . . . . . . . 150
Micrograph of a Cross-Section of a
BGA SAC Solder Ball Assembled onto
a Printed Board with SnPb Solder Paste
Using Backward-Compatibility Reflow
Soldering Profile. . . . . . . . . . . . . . . . . . . . . . . . . . . 151
Figure 8‑8
Mixed-Metallurgy (SAC/SnPb)
BGA Solder Joint Alternatives.. . . . . . . . . . . . 152
Figure 8‑9
Incomplete Solder Joint Formation for
1 % Ag Ball Alloy Assembled at
Low End of Typical Process Window.. . . . 154
Figure 8‑10 Solder Joint Failure Due to Silicon and
Printed Board Coefficient of
Thermal Expansion (CTE) Mismatch. . . . . 155
Figure 8‑23 Reliability Test Failure Due to
Very Large Void. . . . . . . . . . . . . . . . . . . . . . . . . . . 162
Figure 8‑24 Endoscope Photo of SnAgCu (SAC)
BGA Solder Ball. . . . . . . . . . . . . . . . . . . . . . . . . . . 165
Figure 9‑1
Cracked Solder Joint.. . . . . . . . . . . . . . . . . . . . . . 167
Figure 9‑2
Solder Mask Encroaching
Too Far on Land. . . . . . . . . . . . . . . . . . . . . . . . . . . 167
Figure 9‑3
Solder-Mask-Defined (SMD)
BGA Solder Joint Failure. . . . . . . . . . . . . . . . . . 168
Figure 9‑4
BGA Ball Shape Without
Heat Slug 500 µm Stand-Off Height. . . . . . 168
Figure 9‑5
BGA Ball Shape with
Heat Slug 375 µm Stand-Off Height. . . . . . 169
Figure 9‑6
BGA Ball Shape with
Heat Slug 300 µm Stand-Off Height. . . . . . 169
Figure 9‑7
Voids and Uneven Solder Balls. . . . . . . . . . . . 170
Figure 9‑8
Convex (Frowning) BGA
With Bridging at Corners. . . . . . . . . . . . . . . . . . 170
Figure 9‑9
Solder Joint Opens Due to
Interposer Warpage. . . . . . . . . . . . . . . . . . . . . . . . 171
Figure 8‑11 Cold Solder Joint with Grainy
Appearance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
Figure 9‑10 Target Solder Condition. . . . . . . . . . . . . . . . . . . 171
Figure 8‑12 Land Contamination (Solder Mask
Residue).. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
Figure 9‑12 Dewetting of Solder at Interface.. . . . . . . . . . 172
Figure 8‑13 Solder Ball Drop. . . . . . . . . . . . . . . . . . . . . . . . . . . 156
Figure 9‑14 Incomplete Joining Due to
Land Contamination. . . . . . . . . . . . . . . . . . . . . . . 173
Figure 8‑14 Missing Solder Ball.. . . . . . . . . . . . . . . . . . . . . . . 157
Figure 9‑11 Solder Balls with Excessive Oxide. . . . . . . . 172
Figure 9‑13 Nonwetting.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
Figure 8‑15 Dynamic Warpage of Flip Chip BGAs
and Printed Boards.. . . . . . . . . . . . . . . . . . . . . . . . 157
Figure 9‑15 Solder Ball Deformation.. . . . . . . . . . . . . . . . . . 173
Figure 8‑16 Solder Joint Defects Caused by Severely
Warped BGA and Printed Board After
Reflow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
Figure 9‑17 Suspended Solder Ball. . . . . . . . . . . . . . . . . . . . . 174
Figure 8‑17 Examples of Acceptable Convex Solder
Joints. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
Figure 9‑19 Solder Bridging. . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
Figure 8‑18 Example of an Acceptable Columnar
Solder Joint. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
Figure 9‑21 Missing Solder Paste Deposit.. . . . . . . . . . . . . 175
Figure 8‑19 Two Examples of Pad Cratering
(Located at Corner of BGA). . . . . . . . . . . . . . . 159
Figure 8‑20 Pad Crater Under 1 mm Pitch Pb-Free
Solder Ball. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
Figure 8‑21 Cross-Sections Illustrating Insufficient
Melting of Solder Joints
During Reflow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
Figure 9‑16 Column-Shaped Ball Deformation. . . . . . . . 173
Figure 9‑18 Extended and Proper Solder
Connections on the Same BGA. . . . . . . . . . . . 174
Figure 9‑20 Incomplete Solder Reflow. . . . . . . . . . . . . . . . . 175
Figure 9‑22 Nonwet Open (NWO). . . . . . . . . . . . . . . . . . . . . 176
Figure 9‑23 Head-on-Pillow (HoP). . . . . . . . . . . . . . . . . . . . . 176
Figure A-1
Typical Flow Diagram for
Void Assessment. . . . . . . . . . . . . . . . . . . . . . . . . . . 177
Figure A-2
Voids in BGAs With Crack Started at
Corner Lead.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
Figure A-3
Void Diameter Related to Land Size.. . . . . . 182
Figure 8‑22 Solder Mask Influence. . . . . . . . . . . . . . . . . . . . . 162
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August 2024
IPC-7095E
Design and Assembly Process Guidance
for Ball Grid Arrays (BGAs)
1 SCOPE
This document describes design and assembly implementation for ball grid array (BGA) and fine-pitch BGA (FBGA)
technology, focusing on inspection, rework and reliability issues associated with design and assembly of printed boards using
these packages.
1.1 Purpose The purpose of this document is to provide useful and practical information to those who use or are considering
using BGAs. The target audiences for this document are managers, designers and process engineers who are responsible for
design, assembly, inspection and rework processes of printed boards and printed board assemblies.
1.1.1 Intent This document describes how to successfully implement robust design and assembly processes for printed board
assemblies using BGAs as well as ways to troubleshoot some common anomalies which can occur during BGA assembly. For
accept/reject criteria and requirements for BGA assemblies, see IPC J-STD-001 and IPC-A-610.
1.2 Use of “Lead” For readability and translation, this document uses the noun “lead” only to describe leads of a component
(sometimes referred to as terminations). The metallic element “lead” is always written as Pb.
1.3 Abbreviations and Acronyms Periodic table elements are abbreviated in this document. See Appendix B for full spellings
of abbreviations (including elements) and acronyms used in this document.
1.4 Terms and Definitions
with IPC-T-50.
Other than those terms listed below, the definitions of terms used in this document are in accordance
1.4.1 Solder-Mask-Defined (SMD) BGA Land
of the land on the BGA.
A printed board land with a solder mask aperture diameter equal to the diameter
1.4.2 Non-Solder-Mask Defined (NSMD) BGA Land A printed board land with a solder mask aperture diameter larger than the
diameter of the land on the BGA. Also known as Cu-defined BGA land.
1.4.3 Nonwet Open (NWO) One metallurgical mass formed from a BGA ball and reflowed solder paste (or flux) which has
incomplete or no wetting to the printed board land.
1.4.4 Head-on-Pillow (HoP) A solder joint comprised of two metallurgically distinct masses formed from a BGA ball and
reflowed solder paste which has incomplete or no coalescence.
2 APPLICABLE DOCUMENTS
2.1 IPC1
IPC-T-50 Terms and Definitions for Printed Boards and Printed Board Assemblies
IPC-D-279 Design Guidelines for Reliable Surface Mount Technology Printed Board Assemblies
IPC-A-610 Acceptability of Electronic Assemblies
IPC-TM-650 Test Methods Manual2
2.4.53 Dye and Pull Test Method (Formerly Known as Dye and Pry)
IPC-SM-785 Guidelines for Accelerated Reliability Testing of Surface Mount Attachments
IPC-SM-817 General Requirements for Dielectric Surface Mounting Adhesives
IPC-CC-830 Qualification and Performance of Electrical Insulating Compound for Printed Wiring Assemblies
IPC-HDBK-830 Guidelines for Design, Selection and Application of Conformal Coatings
IPC-1602 Standard for Printed Board Handling and Storage
IPC-1751 Generic Requirements for Declaration Process Management
1. www.ipc.org
2. Current and revised IPC Test Methods are available on the IPC Web site (www.ipc.org/test-methods)
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3.5.2 Moisture Sensitivity Plastic BGAs are moisture sensitive. This makes them susceptible to warpage, swelling, popcorning
or cracking if they are not properly baked and kept dry prior to assembly. Component storage and handling procedures are critical
for any moisture-sensitive component, including leaded SMT devices, but it is critical for BGAs. Follow the recommendations
in J-STD-033 for handling, packing, shipping and using moisture sensitive devices.
Component moisture sensitivity is tested using J-STD-020 and is determined by the package thickness. The moisture sensitivity
level should be determined for each BGA package type. It is critical to know at which of the applicable temperatures (220 °C,
235 °C, 245 °C, 250 °C or 260 °C) the BGA was classified. The classification of the package type may drop several levels if
the higher temperature is used.
Due to improvements in molding compounds and laminate systems, most laminate-based BGAs can be mounted and qualified
for temperatures above 220 °C. Hermetic ceramic BGAs are not moisture sensitive, so they can be mounted using any of
the higher temperatures. If a manufacturer will use Pb-free solder, it is important to test and verify at a higher temperature
(e.g., 260 °C), because the higher temperatures for Pb-free applications can create major issues with BGAs and all other SMT
devices.
The plastic BGA package is also susceptible to warpage (the package edges
lift up), which can result in no connections on the outer rows. The edges may also bend down, thus such terms as convex or
concave BGAs have been used to identify these conditions. The convex (smiling) BGA puts a stress on the balls at the outer
rows, while the concave (frowning) BGA puts the stress on the connection of the inter-row ball locations. Package warpage is
of real concern in flux-only applications during rework. Large die sizes can cause CTE mismatch between the printed board and
the package laminate material, which can create package warpage (see Figure 3‑6).
3.5.3 BGA and Board Coplanarity and Warpage
Thermally unbalanced package designs, particularly those with heat spreaders on the top, will warp according to the classic
bimetal effect.
A
B
C
C
B
A
Figure 3‑6 BGA Warpage
A – Row
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Figure 6‑43 shows a heat sink attached to the BGA with clips that hook into holes in the printed board. These holes do not have
to be plated. Unlike the previous case, the printed board supports the weight of the heat sink when the clips are actuated, but
some stress can still be transferred to the solder balls during mechanical shock and vibration. In addition, the heat sink may
create a cantilevered load on the solder joint when the assembly is in a vertical orientation. This load may lead to premature
solder joint failure.
A
B
D
C
E
Figure 6‑43 Heat Sink Attached to a BGA Using a Clip That Hooks into Printed Board Holes
A – Clip
B – Heat sink
C – Grease/gel/PCM
D – BGA
E – Printed board
Figure 6‑44 shows a heat sink attached to a BGA package with clips that hook on to stakes that are wave soldered into holes in
the printed board. This method of attachment transfers even less stress to solder balls during mechanical shock and vibration
than the previous cases; however, the solder joints of the stakes will bear most of this stress.
A
B
C
D
E
Figure 6‑44 Heat Sink Attached to a BGA Using a Clip That Hooks onto a Stake Soldered to
the Printed Board
A – Clip
B – Heat sink
C – Grease/gel/PCM
D – BGA
E – Printed board
Figure 6‑45 shows a heat sink attached to a BGA by directly soldering the heat sink into the printed board during wave
soldering. The heat sink design has four or more pins that insert into holes in the printed board prior to wave soldering. As
opposed to the previous cases, this method does not need any processing to attach the heat sink after assembly.
C
B
A
D
Figure 6‑45 Heat Sink Attached to a BGA by Wave Soldering Its Pins in Through-Holes
A – Grease/gel/PCM
B – BGA
C – Heat sink pin
D – Printed board
The methods in Figure 6‑43, Figure 6‑44 and Figure 6‑45 have one drawback not present in the methods in Figure 6‑41 and
Figure 6‑42. They require holes to be designed into the printed board, which may reduce the trace routing real estate on all
printed board layers. For highly-dense printed board designs, this could impact the final layer count.
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8.2.2.6 Assembly Manufacturing Impacts of Pb-Free BGA
Balls
Pb-free BGA ball alloys may have an impact on
A
the reflow process due to their higher melting point. Some
component manufacturers have had unexpected yield losses
due to low-Ag alloys when they were not aware of their
presence. The change to low-Ag ball alloys may require a
change to the reflow temperatures. For example, an increase
of 10 °C in melting point for a specific BGA may cause other
locations on a printed board assembly to exceed the time
duration or temperature limits of other components or the
printed board.
Improperly assembled low-Ag parts processed with too low a
reflow temperature are a significant reliability risk. They may
pass electrical test, but they may produce unacceptable solder
joints (see Figure 8‑9). Some experimental data suggest
drop performance of well-manufactured low-Ag parts are
better than current SAC alloys (e.g., SAC305, SAC405
and SAC387). However, fatigue life of low-Ag alloys is
consistently lower than their Ag counterparts, and additional
factors (e.g., land finish) also are critical for reliability.
Solder joints are
not homogeneous structures. A solder joint consists of several
different materials, many of which are only superficially
characterized. A solder joint consists of:
8.3 Solder Joints and Attachment Types
B
C
A
• Base metal at the printed board
• One or more IMCs
• Bulk solder
• A layer from which the solder constituent forming the
component-side IMC(s) has been depleted
• One or more IMC layers of a solder constituent with the
component base metal
• Base metal at the component
B
D
The grain structure of solder continues to change over time.
Figure 8‑9 Incomplete Solder Joint Formation for 1 % Ag
At room temperature, eutectic SnPb solder is above its
Ball Alloy Assembled at Low End of Typical Process Window
recrystallization temperature; the grains will grow over time.
A – DSP
C – Unmelted solder ball
This grain structure growth reduces the internal energy of a
B – Printed board
D – Unacceptable solder joints
fine-grained structure, and its growth process is enhanced by
elevated temperatures and strain energy input during cyclic loading. The grain growth process, to some degree, is an indication
of the accumulating fatigue damage.
This indication is significantly more pronounced for solder joints subjected to aging (and is less pronounced in cyclic testing)
than for solder joints in operational use. Contaminants (e.g., Sn oxides and flux residues) sometimes migrate to the outer surface
of the solder, but they reside predominantly at the grain boundaries. As the grains grow, the concentration of these contaminants
increases at specific locations due to agglomeration along these grain boundaries and weaken the solder. After consumption of
~ 25 % of the fatigue life of the solder, microvoids will form at the grain boundary intersections. These microvoids will become
microcracks after ~ 40 % of the fatigue life. The microcracks will then grow and coalesce into macrocracks, which result in
total fracture of the solder joint.
Solder joints frequently connect materials of differing properties (e.g., CTE). Solder often has properties significantly different
than the bonding structure materials, which causes local thermal expansion mismatches. The severity of these thermal expansion
mismatches and the severity of the reliability threat depends on the design parameters of the assembly and the operational-use
environment.
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For Pb-free solder joints, there is a higher propensity for differential solid diffusion causing Kirkendall voids (also known as
IMC microvoids). The higher propensity for IMC microvoiding is associated, at least in part, with higher soldering temperatures
required for Pb-free solders. Furthermore, planar microvoiding occurs on Pb-free surface finishes (e.g., immersion Ag), which
entails typically more complex soldering surface treatments than HASL.
Global expansion
mismatches result from differential thermal expansions
of an electronic component or connector and the printed
board to which it is attached by surface-mount solder joints.
These thermal expansion differences result from differences
in CTE and thermal gradients because of thermal energy
being dissipated within active components. Global CTE
mismatches typically range from about 2 ppm/°C for CTEtailored high-reliability assemblies to ≥ 14 ppm/°C for
ceramic components on FR-4 printed boards.
8.3.1 Global Expansion Mismatch
Figure 8‑10 shows a solder joint failure due to CTE mismatch
on a wafer-level DSP. The silicon die on the top expands
much less than the FR-4 printed board on the bottom. This
causes shear stress on the solder joint, which eventually fails
at the die-to-solder interface when subjected to temperature
cycling stresses.
Local expansion mismatch
Figure 8‑10 Solder Joint Failure Due to Silicon and Printed
results from differential thermal expansions of the solder
Board Coefficient of Thermal Expansion (CTE) Mismatch
and the base material of the component or printed board to
which it is soldered. These thermal expansion differences result from differences in the CTE of the solder and those of the
base materials from thermal excursions. Local CTE mismatches typically range from ~ 7 ppm/°C with Cu to ~ 18 ppm/°C
with ceramic and ~ 20 ppm/°C with Alloy 42 and Kovar. Local thermal expansion mismatches typically are smaller than
global expansion mismatches, because the acting distance (maximum wetted area dimension) is much smaller: in the order of
hundreds instead of thousands of micrometers.
8.3.2 Local Expansion Mismatch
In SnPb solders, an internal CTE mismatch results from different CTEs of Sn-rich and Pbrich phases of the solder. Internal thermal expansion mismatches typically are the smallest, because the acting distance (grain
structure size) is much smaller than either the wetted length or the component dimension (< 25 µm).
8.3.3 Internal Expansion Mismatch
Solder attachment failure is commonly defined as the first complete fracture of any solder joint
which consists of the component solder attachment. Because loading of solder joints is typically in shear, rather than in tension,
the mechanical failure of a solder joint is not necessarily the same as the electrical failure. Electrically, the mechanical failure
of a solder joint results, at least initially, in the occasional occurrence of a short-duration (< 1 µs) high-impedance event during
either a mechanical or thermal disturbance.
8.4 Solder Attachment Failure
This definition of solder attachment failure may not be adequate for some applications. For high-speed signals with sharp
rise times, signal deterioration prior to the complete mechanical failure of a solder joint may require a more stringent failure
definition. Similarly, for applications which subject the electronic assemblies to significant mechanical vibration and/or shock
loading, a failure definition that considers the mechanical weakening of the solder joints as the result of the accumulating
fatigue damage may be necessary.
8.4.1 Solder Attachment Failure Classification There are some common BGA failure signatures. These defects can be induced
during the assembly process, or they could be latent solder joint defects or failures. Such defects and/or failures are the result
of an inadequate assembly process, defective material or excessive mechanical stress during assembly. The defects could be a
partial open or very weak interfaces. Latent failures could be hairline cracks, open joints with a full contact and partially lifted
lands. They are a major reliability concern because they can be intermittent.
These defects are difficult to detect using conventional process verification tools (e.g., X-ray and ICT). Subsequently, they are
tracked down following high levels of failure.
See 8.4.1.1 through 8.4.1.7 for explanations of solder joint failure signatures.
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A cold solder
joint is a result of a low peak temperature during the reflow
process (< liquidus +20 °C). The solder paste partially melts
and will form a cold solder joint.
8.4.1.1 Failure Signature 1: Cold Solder Joint
The joint may have a rough surface and sometimes necking
at the interface to the printed boards. The solder will appear
grainy (as shown in Figure 8‑11), and there will be a
difference between the grain structure of the BGA ball and
the solder paste. This indicates the paste did not reach proper
reflow temperature. In some cases, the solder paste may not
have coalesced. It should be noted solder joint surfaces will
appear grainy for most Pb-free solders.
.
Contamination on a printed board land will cause a
nonsolderable interface between the printed board land and
the BGA ball. The solder will wet to the BGA ball but not to
the land, which could result in a partial or complete open with
the electrical contact. A failure with this signature could be
the result of faulty Ni plating on a printed board with ENIG.
It also could be a result of board supplier rework process and
reapplying solder mask to the BGA area.
8.4.1.2 Failure Signature 2: Nonsolderable Land
Figure 8‑11 Cold Solder Joint with Grainy Appearance
Figure 8‑12 shows a solder mask residue failure.
Ball drop describes an
open solder joint which forms between the solder ball and the
BGA substrate. This causes the BGA ball to drop and creates
an elongated solder ball with a round or flat top. Ball drop
failure is caused by a high top-side temperature during wave
solder (> liquidus -20 °C).
8.4.1.3 Failure Signature 3: Ball Drop
During wave soldering, BGA balls soften due to the high
top-side temperature. Thermomechanical stress causes the
balls to pull away from the component substrate and to create
an open joint, as shown in Figure 8‑13. Ball drop can also
be caused by high peak temperature and dwell time during
reflow.
Figure 8‑12 Land Contamination (Solder Mask Residue)
Figure 8‑13 Solder Ball Drop
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Figure 8‑14 shows
a missing solder ball, which can occur during the ball attach
process or due to handling damage. This defect signature is
usually detected with X-ray or ICT.
8.4.1.4 Failure Signature 4: Missing Ball
Note: Some devices may have unpopulated arrays at
specific locations to optimize trace/routing options as well
as to provide relief for thermomechanical stress (e.g., corner
areas). Consult the device ball array specification to ensure
observed lands are not intentionally depopulated.
8.4.1.5 Failure Signature 5: Printed Board and BGA Stack
Warpage As package substrates and printed boards become
thinner, the magnitude of dynamic warpage has increased,
which causes new and various solder joint shapes.
This signature occurs when the printed board and/or BGA
stack warps during reflow, as shown in Figure 8‑15. For
flip chip BGAs, the silicon die expands much less than the
package substrate laminate. This expansion mismatch creates
a generalized bimetallic strip effect when the BGA is heated
and cooled during reflow.
Figure 8‑14 Missing Solder Ball
This effect creates a dynamic warpage of the package. Flip
chip BGAs may become concave in shape, with negative warpage, when heated to > 220 °C but then become less warped when
cooled after exiting the reflow oven. Similarly, the printed board also exhibits dynamic warpage behavior and may go from
being relatively flat to becoming convex or concave (see Figure 8‑15).
A
B
F
H
C
D
C
D
E
E
G
K
(or)
J
C
D
E
L
Figure 8‑15 Dynamic Warpage of Flip Chip BGAs and Printed Boards
A – At room temperature, before reflow
G – Printed board relatively flat
B – When heated to reflow temperature
H – FCBGA package negative (–) warpage / concave shape
C – Silicon die
J – Printed board positive (+) warpage / convex shape
D – Package substrate
K – FCBGA package negative (–) warpage / concave shape
E – Printed board
L – Printed board (–) warpage / concave shape
F – FCBGA package: positive (+) warpage / convex shape
BGA and printed board warpage during reflow can affect solder joint formation, which results in various solder joint defects.
This is especially true with SMT processes which are not optimized. These defects include:
• HoP
• HoP open – similar to HoP but the solder ball does not make contact with the solder on the land
• NWO – no solder on the land
• Solder bridging
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Figure 8‑16 shows a severely warped printed board and BGA stack causing these solder joint defects across the ball array.
See 9.4 for SMT process optimized solutions.
A
B
C
D
E
F
G
Figure 8‑16 Solder Joint Defects Caused by Severely Warped BGA and Printed Board After Reflow
A – Die
C – Printed board
E – HoP
B – Package substrate
D – NWO
F – Solder bridging
G – HoP open
The dynamic warpage of the printed board and/or BGA stack also leads to varying shapes of solder joints that are acceptable
from a quality standpoint (see Figure 8‑17 for examples). Most BGA solder joints are convex solder joints, since the smallest
angle (in blue in the top left photo of Figure 8‑17) of the solder joint surface tangent to either land surface is ≤ 90 ° at all points
along the solder joint surface.
Figure 8‑17 Examples of Acceptable Convex Solder Joints
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Printed board and/or BGA stack dynamic warpage can lead
to some solder joints being stretched into a columnar shape.
For columnar solder joints, the solder joint surface is normal
to either side of the printed board land. Figure 8‑18 shows an
acceptable columnar solder joint.
Mechanical
stress caused by printed board flexing from ICT is not
uncommon. As the size of the BGA increases, the stress
experienced by corner joints becomes more significant. Even
probing lands in areas beneath and surrounding the BGA are
required. Mechanical stress caused by probe pins and vacuum
force is sometimes ignored. It is important to note excessive
monotonic stress induced by mechanical stresses will lead to
solder joint failures.
8.4.1.6 Failure Signature 6: Mechanical Failure
Since the weakest interface is the one that breaks, this failure
signature could be different. The crack could be within
the BGA ball, at the printed board or package interface or
within the printed board as a lifted land. Figure 8‑19 shows
two examples of a lifted corner land caused by excessive
mechanical stress. This defect is also known as pad cratering.
Figure 8‑18 Example of an Acceptable Columnar Solder
Joint
Pad cratering can result in a failure of the joint due to electrical
opens. An initial crack weakens the joint mechanically, and
then as it progresses, the crack may intercept electrical traces,
which will cause an open (see Figure 8‑20). This failure
signature is enhanced by higher temperatures of Pb-free
reflow temperatures, harder laminates and increasing land or
trace densities.
A
Figure 8‑20 Pad Crater Under 1 mm Pitch Pb-Free Solder
Ball
A – Fracture in the etch line to the BGA land
Figure 8‑19 Two Examples of Pad Cratering (Located at
Corner of BGA)
Figure note: T
he crack in the metal trace connected to the land is clear;
however, the pad crater is difficult to see in bright-field microscopy.
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Robustness of BGA joints against mechanical stress is a function of several factors:
• Location of the BGA
• Printed board thickness
• Stack-up
• Land size
• Stiffening mechanism
• Solder volume
• Solder mechanical properties
• Solder creep properties
• Solder joint interface quality
As a remedy, some designers (especially in the cell phone industry) use larger corner lands, elongated lands and/or edge bond,
corner bond and underfill adhesives to enhance robustness. From an assembly perspective, enforcing proper fixturing and
handling are keys to avoiding solder joint damage.
8.4.1.7 Failure Signature 7: Insufficient Reflow Insufficient reflow occurs when a ball does not receive sufficient heat for the
solder to reach a temperature above liquidus of the solder. These solder joints are typically found underneath the center portion
of BGAs, because those areas heat the slowest during soldering process and would be most prone to not reaching adequate
soldering temperatures.
Occasionally, insufficiently reflowed solder joints occur due to the existence of a component feature depriving the heat from
that area during the reflow process. Figure 8‑21 illustrates an example of insufficiently melted solder joints due to this.
Figure 8‑21 Cross-Sections Illustrating Insufficient Melting of Solder Joints During Reflow
Figure note: T
hese solder joints are located below the cam of a socket.
8.5 Critical Factors Impacting Reliability
8.5.1 Package Technology Area array components are available in a variety of styles and materials. Most commercial array
devices utilize plastic encapsulation and a reinforced rigid organic substrate interposer material for packaging. For package-toprinted board interconnect, a metallized land or alloy sphere (ball) is used. LGA ICs are often specified when package height is
an issue, whereas BGAs use small alloy spheres for the interconnect system.
The contact alloys furnished on most plastic-based BGAs is SnPb (eutectic) or SAC (Pb-free) composition. Area array
packages using a ceramic-based substrate interposer may be supplied with high-Pb solder balls or columns (e.g., Sn10Pb90).
An increasing number of area array package variations adapt nonreinforced film dielectric for the substrate and a diverse
combination of encapsulation materials. FBGA and die-size packages are also widely used (especially in portable or hand-held
electronic products), and many higher-power applications incorporate an in-package heat spreader or heat-spreading layer (see
Section 4).
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Long-term reliability of the solder attachment of the area array package, when soldered to a conventional printed board, is of
primary concern. CTE difference in materials can generate undue stress to the solder interface. The solder attachment integrity
for area array packages will vary, depending on the loading conditions to which the solder joints are subjected and the reliability
requirements for the product. CTE mismatch is further aggravated when large silicon die are attached to an organic substrate
with a noncompliant epoxy compound. Silicon CTE is ~ 3 ppm/°C, while the organic substrate is ~ 16 ppm/°C. Package warp
during assembly processing and even the power dissipation within the package can subject the solder joints to significant tensile
stresses. Excessive stress and strain at the solder interface will cause solder joint failure and separation of the metallized lands.
When the die is attached to the package substrate with rigid epoxy, the substrate material directly beneath the die may be
restricted to a CTE nearer that of the die. When solder balls are retained in the same zone and exposed to a wide variable of
operating temperatures, the solder interface will be subjected to excessive strain. For die attached facing away from the package
substrate (also known as cavity-up components), only a thin dielectric layer separates the solder joints from the die. The larger
the die, the more acute the concerns for solder attachment reliability. Furthermore, when the BGA solder joints fracture, they
are typically near the ball-to-package interface. This is a consequence of the local expansion mismatch between the solder and
the die-constrained BGA substrate.
There is industry interest in larger BGA package outlines due to the desire to move the contacts toward the package perimeter, with
the possible exception of some thermal solder balls and vias retained at the central area of the package. Several manufacturers
that cannot move the interconnect outside the die attach area have adapted a more compliant die attach material. This compliant
die-to-package interface is slightly thicker and exhibits a dramatic reduction in stress at the solder-to-printed board interface,
which results in a substantial increase in fatigue life.
8.5.2 Stand-Off Height Stand-off height significantly affects solder joint reliability. BGAs attached with Sn63Pb37 solder
balls result in solder joint heights that are less controlled and lower (height ~ 400 µm to 640 µm), while Sn10Pb90 solder balls
(diameters of 760 µm to 890 µm) result in uniform solder joint heights of the same dimension. This is because Sn10Pb90 solder
has a liquidus temperature significantly above near-eutectic SnPb solders and does not melt during a typical reflow process.
Table 8‑2 provides information on typical stand-off heights for SnPb BGA ball and solder paste metallurgy packages.
Table 8‑2 Typical Stand-Off Heights for BGAs
Ball Pitch (mm)
Stand-Off Height (mm)
Ball Diameter Prior to Reflow (mm)
Printed Board Land Size (mm)
1.27
0.4 to 0.6
0.45 to 0.55
0.35 to 0.45
0.3 to 0.4
0.35 to 0.45
0.3 to 0.4
0.28 to 0.35
0.18 to 0.25
0.18 to 0.26
0.08 to 0.15
0.16 to 0.2
0.11 to 0.15
0.09 to 0.125
0.165 to 0.18
0.75
0.6
0.5
0.45
0.5
0.45
0.4
0.3
0.25
0.17
0.225
0.2
0.11
0.2
0.65
0.45
0.4
0.35
0.4
0.35
0.35
0.25
0.25
0.25
0.25
0.25
0.17
0.18
1
0.8
0.5
0.4
0.3
Package weight also affects solder joint reliability because weight impacts solder joint or stand-off height. Key factors that
control stand-off are land size, available solder volume and component weight. The lower the weight, the smaller the land size;
the larger the solder volume, the higher the stand-off.
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8.5.3 Printed Board Design Considerations Other influences
on reliability are solder joint geometry and solder land
metallization. Solder masks can have a negative influence if
they are used for SMD lands, in which solder mask on the
metallization lands affects solder joint geometries. Stress
concentrations created by SMD solder joint geometries can
be the origin of solder joint failures and reduced reliability.
More than that, solder mask shape and thickness could
influence the reliability of the solder joint. Figure 8‑22 shows
a crack due to stress concentration at the solder mask.
For equal solder joint heights, increasing fatigue life by
factors of about 1.25 to 3 can be anticipated with the use of
NSMD rather than SMD lands, with larger improvements for
solder joints with more severe loading conditions.
Surface finish also plays a critical role in BGA solder joint
reliability. HASL may be too thick or too thin. Insufficient
Figure 8‑22 Solder Mask Influence
solder thickness may be available because most of the surface
finish may be consumed as intermetallic, which is unsolderable. Immersion Au over electroless Ni is prone to black pad, which
is thought to be caused by excessive corrosion of the Ni during the Au plating process.
Black pad is an intermetallic layer which forms during soldering and results in an embrittled solder joint, leaving a smooth black
or dark surface. Black pad is caused by contamination of electroless Ni plating baths. These baths require constant monitoring
to prevent build-ups of contaminants and to ensure proper chemical balance. Cu substrates prepared by pumice grinding that
are insufficiently cleaned may cause Ni plating to be porous. This may be magnified if the Ni plating bath is contaminated.
Porous plating provides a pathway through which the Cu can diffuse, which may embrittle the solder joint as well. See 5.3.3.1
for more information on black pad.
Laminate cracking is also a possible failure mechanism under
BGA solder joint lands. Such failure is thought to be caused
by thermal mechanical stress during reflow and/or subsequent
mechanical stresses on the joints.
Via-in-land or vias next to lands are generally not
recommended because they may cause drainage of solder.
Via-in-land should be considered only by companies with
extensive internal resources to validate reliability of solder
joints with via-in-land technology.
Microvias are common in BGA lands, but most BGAs
will have voids when microvias are used. Studies showed
that most voids are not a reliability risk to initiate a crack;
however, they reduce the joint area and will shorten the time
to failure when a crack is propagated. Figure 8‑23 shows a
failure after reliability testing in which the void was so large
the ball collapsed.
Figure 8‑23 Reliability Test Failure Due to Very Large Void
8.5.4 Reliability of Solder Attachments of Ceramic Grid Arrays (CGAs) Ceramic CTE is about 6 ppm/°C; the CTE of organic-
based printed boards is ~ 16 ppm/°C to 20 ppm/°C. Thus, a global CTE mismatch of ~ 10 ppm/°C to 14 ppm/°C exists between
ceramic components and organic printed boards. To compensate for the large global CTE mismatch, ceramic components
typically require solder columns to function reliably in most applications. Since the corner joints are loaded more than other
solder joints (they are farthest distance from neutral point, or DNP), they fail first.
Solder columns, which are only used for CGAs, are Sn10Pb90 columns with lengths of 1.27 mm to 2.29 mm which are either
cast onto the CGA or are wire soldered to both the CGA and the substrate with near-eutectic SnPb solder. With all other
conditions being equal, the ratio of CBGA solder joint fatigue life of three column heights 0.41 mm, 0.76 mm and 2.29 mm
is 1:4:45. Solder column height is limited by the requirement the column aspect ratio (height-to-diameter) does not produce
slender columns, which changes the loading conditions. Cast columns can accommodate larger aspect ratios.
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APPENDIX B
Abbreviations and Acronyms
AABUS
As agreed upon between user and supplier
Ag
Silver
Al
Aluminum
ASIC
Applications-specific IC
AOI
Automated optical inspection
AR
Acrylic resin (conformal coating)
Au
Gold
ATC
Accelerated temperature cycling
AXI
Automated X-ray Inspection
B
Boron
Be
Beryllium
BGA
Ball grid array
Bi
Bismuth
BOD
Board-on-die
BT
Bismaleimide-triazine
CAF
Conductive anodic filament
CBGA
Ceramic ball grid array
CCGA
Ceramic column grid array
ccc
Controlled coplanarity
CCD
Charged-couple device
CGA
Column grid array
Cd
Cadmium
CT
Computed tomography
CTE
Coefficient of thermal expansion
CTF
Critical to function
Cu
Copper
Df
Dissipation factor
DfM
Design for manufacturability
DfR
Design for reliability
DIG
Direct immersion gold
Dk
Dielectric constant
DMA
Dynamic mechanical analysis
DOB
Die-on-board
DSBGA
Die-size ball grid array
DSP
Die scale package
DRAM
Dynamic random-access memory
DSC
Differential scanning calorimetry
dT
Temperature differential
ECM
Electrochemical migration test
ENEPIG
Electroless nickel electroless palladium immersion gold
ENIG
Electroless nickel immersion gold
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ER
Epoxy resin
ESD
Electrostatic discharge
ESS
Environmental stress screening
FBGA
Fine-pitch ball grid array
FRBGA
Fine-pitch, rectangular ball grid array
FT
Functional test
HASL
Hot-air solder level
HDI
High-density interconnect
HoP
Head-on-pillow
I/O
Input/Output
IC
Integrated circuit
ICT
In-circuit test
ILM
Independent loading mechanism
IMC
Intermetallic compound
In
Indium
JRP
Joint-reinforced paste
LFBGA
Low-profile fine-pitch ball grid array
LGA
Land grid array
LMC
Least material condition
LTD
Liquidus time delay
MDM
Multidie module
MDA
Manufacturing defect analyzer
MMC
Maximum material condition
MXI
Manual X-ray inspection
NCMS
National Center for Manufacturing Sciences
Ni
Nickel
NSMD
Non-solder-mask defined
NWO
Nonwet open
OEM
Original equipment manufacturer
OSP
Organic solderability preservative
P
Phosphorous
Pb
Lead
PBB
Polybrominated biphenyl
PBBO
Polybrominated biphenyl oxide
PBDE
Polybrominated diphenyl ether
PBGA
Plastic ball grid array
PCM
Phase-change material
PCT
Perfusion computed tomography
Pd
Palladium
PGA
Pin grid array
PLCC
Plastic-leaded chip carrier
PoP
Package-on-package
PR
Paraxylene resin (conformal coating)
PSA
Pressure-sensitive adhesive
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Pt
Platinum
PTH
Plated-through hole
QFP
Quad flat pack
RMS
Root mean square
RoHS
Restriction of hazardous substances
ROSE
Resistivity of solvent extract
RSS
Ramp-soak-spike
RTS
Ramp-to-spike
SAC
SnAgCu
Sb
Antimony
SAM
Scanning acoustic microscopy
SDRAM
Synchronous dynamic random-access memory
SEM
Scanning electron microscope
SiP
System-in-package
SIR
Surface insulation resistance
SJEM
Solder joint encapsulant material
SMD
Solder mask defined
SMT
Surface mount technology
Sn
Tin
SO-DIMM
Small outline dual in-line memory module
SOIC
Small outline integrated circuit
SPC
Statistical process control
SR
Silicone resin (conformal coating)
SRAM
Static random-access memory
SSO
Simultaneously switching output
STII
Soldering temperature impact index
TAL
Time above liquidus
TBBPA
Tetrabromobisphenol A
TBGA
Tape ball grid array
Td
Decomposition temperature
TFBGA
Thin-profile fine-pitch ball grid array
Tg
Glass transition temperature
TIM
Thermal interface material
Tm
Melting temperature
TMA
Thermal mechanical analysis
TSV
Through-silicon via
UV
Ultraviolet
VFBGA
Very thin-profile fine-pitch ball grid array
W
Tungsten
ZIF
Zero insertion force
Zn
Zinc
µCT
Microcomputed tomography
3D AXI
Automated cross-section X-ray
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