FCBGA Package Warpage
Definition Stage Project
Raiyo Aspandiar - Intel
HDP User Group Member
Meeting
Host: Oracle
Santa Clara, CA.
Feb. 26. 2013
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Purpose
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Background
 Package/board Warpage increasing trends
•
Driven by thinner package substrates and thinner die
 Package/Board contacts getting smaller and closer
thereby reducing ability to overcome increased Warpage.
 Solder Joint Quality Impact of increasing Package and
Warpage.
 With advent of lead free soldering, the assembly
temperatures have increased and the warpage impact has
been exacerbated.
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Examples of Warpage Induced Defects
for Area Array Solder Joints
Die
Board
Head-on-Pillow
Open
Non –Wet Open
Stretched joint
Head on pillow
 Various Solder Joint Defects can occur during SMT Reflow
Soldering due to Excessive BGA component and/or Board Warpage
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Real Time Videos
of Solder Joint Formation
Real Time Videos will be shown for two cases
– `Bad` Solder Paste causing Non-Wet Open Defects
– `Good` Solder Paste resulting in acceptable solder joints
Video Camera Set up
FCBGA Package
Solder Balls
Solder Paste
Malcolm Tech
Video camera
Camera fixture
Reflow Oven Belt or Rail
5
Real Time Videos
of Solder Joint Formation
1
2
3
4
5
6
7
8
9
10
Cooling
6
Temperature
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Time
6
Two Real Time Videos of Solder Joint Formation
of a FCBGA package with high dynamic warpage
will now be shown
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Project Scope - What is IN the Scope
FCBGA Package just as its entering the SMT Reflow Oven
Die
FCPackage
BGA Package
Substrate
Substrate
Project
Focus Area
Printed Circuit Board
Reflow Process
 Temperature –Time Profile
 Oven Atmosphere
Solder Paste
 Rheology
 Wetting
 Metallurgy
 Activator chemistry
 Volume printed on land
Surface Finish
 OSP/ENIG/ImAg/
ENEPIG/ etc
Package Termination
 Geometry (ball, pillar, column, etc)
 Metallurgy (SAC, low Ag SAC, BiSnAg, other)
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Project Scope - What is OUT
of the Scope
Package Warpage Mitigation
 Laminate Type
 Stack-up
 Die Thickness
 Die Size
Package Warpage Measurement
 Metrologies
 Specifications
Die
FCPackage
BGA Package
Substrate
Substrate
Printed Circuit Board
Board Warpage Mitigation
Board Warpage Measurement
 Laminate Type
 Stack-up
 Metrologies
 Specifications
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Goal
Establish a limit for dynamic package warpage
that can be mitigated during board assembly
without impacting solder joint quality
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Project Objectives
1. Identify mitigation paths for solder joint
yield loss caused during the SMT reflow
soldering process specifically due to the
excessive warpage of package and/or
boards
2. Evaluate these mitigation paths for their
effectiveness in increasing solder joint
yield despite high levels of package
and/or board warpage
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Technical Discussion
Potential Mitigation Paths
•
Alternate solder paste and package solder ball metallurgies,
i.e., low temperature solders
•
Alternate solder temp profiles (steep ramp, soak, spike
reflow profile, for instance)
•
Alternate package termination geometries (instead of balls)
•
Optimized solder paste printing geometries
•
New solder paste formulations
•
Tacky Fluxes, applied by dipping
 Each mitigation path can comprise a separate project
proposal or all can be combined into one project
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What has been Done to Date
Project Scope, Objectives, and Flow defined
Key Variables Identified to Control and Monitor during SMT Reflow
Soldering
19-21
o Gap between Ball and Paste
Selected the Metrologies to vary and monitor the gap between Ball
and paste during the reflow soldering process
22-29
 Modified Plexus’ Method of Adhesive and Solder Pre-form under Package
 Cisco’s Rework Equipment Use Method
 Real Time observation of Solder Joint Formation using Malcom Tech Camera’s
and overs
Drafted Experimental Plans and Resources Needed for initial
Objectives
Defined Test Substrate /Board
Requirements
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34
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at is Planned For the Near Future
Develop Modified Cisco Rework Method Metrology:
o Run the designed experiments to confirm the feasibility of using Hot Air Rework machine
to control the gap between solder ball and solder paste with temperature with a full array
package instead of a single solder ball at a time
Develop Modified Plexus Cisco Rework Method Metrology:
o Confirm proof of concept for using the expansion of a high CTE adhesive to vary ball-topaste gap in the pre-reflow zone of an in-line reflow soldering oven
o Confirm proof of concept of solder preform wetting into multiple PTHs in the board for
sharply decreasing ball-to-molten paste gap in the reflow zone of an in-line reflow
soldering oven
Develop Real Time Monitoring:
o Confirm the capability for real time monitoring of ball-to-paste gap and solder joint
formation mechanisms of high dynamic warpage area array packages during the reflow
process and of
1. the Malcom RCA-1 Observation Monitor Video Camera in an in-line reflow oven
2. the VDS-1 Video Monitoring System in a Reflow Simulator Batch Oven
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hat is Planned Beyond the Near Future
Brainstorm Mitigation paths: for excessive warpage of package
and/or boards induced SMT solder joint yield loss and select potential
candidates for assessment
Select Mitigation Path: Obtain Components and Design and Procure
Boards for Evaluation of Mitigation Paths
Assess Effectiveness of Mitigation Path: Design and Run
Experiments to evaluate present capability of materials and processes
and feasibility of the Warpage-induced Defects’ Mitigation Paths
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Proposed Project Flow
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Team Members –to date
• Akrometrix
• H3C
• Phillips
• Alcatel-Lucent
• Huawei
• Plexus
• Arlon
• Hitachi
• Rockwell
• ASE
• Hitachi-Chemical
• Sytech
• Celestica
• IBM
• TTM Tech
• Ciena
• Indium
• Ventec
• Cisco
• Intel
• Zestron
• Curtiss-Wright
• IST Group
• ZTE
• Emerson
• Juniper
• Ericsson
• Medtronic
• Fiberhome
• Multek
• Flextronics
• Nihon-Superior
• Fujitsu
• Panasonic
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Back-up
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Effect of Typical Dynamic Warpage Characteristics of FCBGA packages
on Solder Joint Formation
Post Solder Ball Collapse
Point
Maximum Ball-Board
Separation Point
Temp
Start of Significant Pull
Way of Ball from Board
reflow
`Flat Package` Point
Post Solidification Point
Room Temperature
Head-on-Pillow


The typical Dynamic Warpage of a FCBGA package entails
 For a corner solder joint…….contact first, then separation between the solder ball and the solder paste
 For a center solder joint……separation first, then contact between the solder ball and the solder paste
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This contact + separation or vice versa sequence creates solder joint defects
Open
Time
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Variation of Gap between Bottom of Solder Ball
and Top of Solder Paste (when solid or molten)
Gap
Temp
Maximum Ball-Board
Separation Point
Start of Significant Pull
Away of Ball from Board
Gap in Center
joint of
Package
Room Temperature
`Flat Package` Point
Gap in Corner
Joint of
Package
Post Solder Ball
Collapse Point
Post Solidification
Point
Sharp Decrease in Gap
due to collapse of
central solder joints
 Besides first contact , then separation for the corner ball, there is a sharp decrease in the gap as
the solder balls melt and collapse in the reflow zone within the reflow soldering oven
 This sharp drop and gap can facilitate coalescence of the molten solder ball and molten solder
paste if paste flux is still active
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Time
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Key Points
Any method of simulating BGA package warpage during reflow
soldering needs to address the following to simulate the conditions
for corner solder joints
Initial Contact of the BGA solder ball with the solder paste and subsequent
separation before or during the soak zone or ramp region
Sharp drop in the gap between the molten solder ball and molten paste
when the solder balls melt and collapse in the reflow zone region
Any method of simulating BGA package warpage during reflow
soldering needs to address the following to simulate the conditions
for central solder joints
No contact between the BGA solder ball and solder paste before or during
the ramp zone or soak zone until the flat package point is reached
Contact developed between the solder ball and solder paste later in the
soak zone
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Simulation for the Corner and Outer Row Solder Joints of the BGA
Requirements
• Initial Contact of the BGA solder ball with the solder paste and subsequent separation before
or during the soak zone or ramp region
• Sharp drop in the gap between the molten solder ball and molten paste when the solder balls
melt and collapse in the reflow zone region
SAC Solder Pre-form
and Solder Paste or Flux
Room Temp ~20C
Package
Adhesive
Gap < 0
Initial set up entails amount (thickness)
of adhesive adjusted to ensure negative
gap between the solder balls and the
paste;
Board
Soak Zone Temp ~160C
Gap > 0
Board
Reflow Zone Temp ~240C
Gap < 0
Board
Expansion of the adhesive in its
thickness direction raised the balls from
the paste and creates a positive gap
Melting of solder preforms in the reflow
zone and the subsequent flow of the
molten solder into PTH will
dramatically drop the stand-off height of
the package and eliminate the gap
 The amount of gap and rate at which it is created in the ramp zone of the profile is
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User
International,
Inc.
controlled by the expansion coefficient
theGroup
adhesive
in its thickness
direction
22
e Proposal to Simulate Gap Variation between the
A Solder Ball and the Solder Paste on the PCB Land
BGA Package
BGA Solder Balls
Adhesive
Solder Paste
Gap > 0
Board
Solder Preform
 Function of Adhesive: To simulate the increase in the gap by
changing its length with increasing temperature due to its coefficient
of thermal expansion
 Function of Solder Preform: To melt at reflow temperature and flow
into the PTH it is placed over and simulate the sudden decrease in
the gap that occurs when the balls collapse after becoming molten
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Simulation for the Central Solder
Joints of the BGA
Requirements
• No contact between the BGA solder ball and solder paste before or during the
ramp zone or soak zone until the flat package point is reached
• Contact developed between the solder ball and solder paste later in the soak zone
Low Temp Solder
Pre-form and Solder
Paste or Flux
Room Temp
~20C
Soak Zone Temp
~160C
Reflow Zone Temp
~240C
Package
Adhesive
Gap at RT >
0
Gap <
0
Gap < 0
Initial set up entails a gap between the
solder balls and the paste; gap amount
controlled by amount (thickness) of
adhesive
When the low temp solder pre-form
melts balls lowered and touch SAC
solder paste
Balls and solder paste melt while in
contact
 The temperature at which the solder ball and paste make contact can be varied by
using different solders with different melting points in the SAC profile soak zone
Requirements for Adhesive Under
Component to Simulate the Gap between
the Ball and the Paste during SMT Reflow
Soldering
Adhesive
Gap > 0
Board
Expansion of the adhesive in its
thickness direction raises the balls from
the paste and creates a positive gap
Minimum Gap to simulate problematic
warpage is 150 microns
1) High Coefficient of Linear Expansion after Cure;
2) Sufficient Hardness/Modulus/Rigidity to push the package up
as the adhesive expands
3) Survive temperatures up to 250C after cure
4) Dispensable or screen printable
Key question: What is the range of Linear Expansion that is needed for the adhesive?
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Cisco’s SRT Rework Equipment Method
for Head-on-Pillow Testing
 BGA rework equipment was also used to reflow the solder ball and the
solder paste, while controlling the movement of the solder ball with
respect to the solder paste on the pad.
 The purpose of controlling the movement is to mimic the movement of
 the corner balls of a BGA as they warp during the reflow process.
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Conditions for Cisco’s Method
C1
C1: Initially there is no initial contact between the
solder ball and the paste. Then at 200 ° C during
the cooling down phase, the solder ball is pulled
down slowly (1 mil/second) so that it makes
contact with the solder paste.
C2
Note: When initial contact is made between ball and
paste, no H-o-P defects were formed
C2: Initially there is no initial contact between the
solder ball and paste. Then at 190 °C during the
cooling down phase, the solder ball is pulled
down slowly so that it makes contact with the
solder paste. This condition is similar to C1 but
there is less contact time
before solidification.
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Photo’s of Cisco’s Method for
Evaluating H-o-P defects
Before Solder Paste Reflow
After Solder Paste Reflow
Aspects of Actual Reflow Soldering of high warpage BGAs NOT
Simulated in this Test
 Lifting up of the solder ball from the solder paste during initial temperature
ramp (though this can be done with the equipment)
 Un-constrained Ball Collapse when the solder melts
 Temperature Profile simulated with hot air rework machine instead of a
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reflow oven
28
Malcom RCA-1 Observation Monitor
Observes and Records the components
on a PCB as it goes through the Reflow Oven
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ummary of Obj # 3 Experimental Plans
riment Name
Phase Description of Experiment
A
High CTE Adhesive
Development
Solder Preform
Development
mbined Adhesive and
er Preform Validation
Feasibility of ME-280+ silicone fillers adhesive Sample
Preparation and its expansion effect on gap variation between
BGA ball and PCB land through the reflow oven
B
effect of adhesive volume on gap variation and package tilting
during reflow soldering
C
Explore other materials with higher CTE than that of ME580+silicone fillers
A
Proof of Concept Validation using off-the-shelf preform
B
Preform Design
C
Plated Through Hole Design
D
Preform Fabrication at Indium Corp
E
Board Fabrication at Member PCB Fabricator
A
Using Developed Adhesive and solder preform with substrate
and boards,
conduct test runs with printed solder paste
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ummary of Obj # 3 Experimental Plans
riment Name
elopment of Modified
sco Hot Air Rework
Machine Method
Phase Description of Experiment
A
Exploratory Experimental Runs to confirm the method works
Comprehensive Factors DOE, using critical process variables
from screening DOE results and including material Variables and
ball pitch/ ball size to determine main effects and 2 factor
interactions
B
Screening DOE using Process Variables to determine main effects
and 2 factor interactions
C
Comprehensive Factors DOE, using critical process variables
from screening DOE results and including material Variables and
ball pitch/ ball size to determine main effects and 2 factor
interactions
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Resources Needed for Initial Objectives
periment
ied Cisco
ir Rework
od
Resources
Potential Source
Test Substrate Laminate
Panasonic
Fabrication of Test Substrate and
Boards
Member PCB Fabricator, to be
identified
Solder Balls
Senju
Solder Paste
Senju/Indium/Alpha/Shenmao
Stencils for solder printing
Non-member Supplier
Running Experiments with Hot Air
Rework Machine
Intel/Celestica/A.P.E
Failure Analysis including Dye and
Pry
Intel / other members to be identified
High CTE material
Lord Corp / Panasonic / Other yet to
be identified
Solder Preforms
Indium Corp
SMT Reflow Oven
Flextronics / Intel
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Designers for Solder Preform
and
Members, to be identified
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Resources Needed for Initial Objectives
Experiment
odified Plexus
Method usign
h CTE Material
and Solder
Preform
Resources
Potential Source
High CTE material
Lord Corp / Panasonic / Other yet to
be identified
Solder Preforms
Indium Corp
SMT Reflow Oven
Flextronics / Intel
Designers for Solder Preform and
Boards
Members, to be identified
SMT Reflow Oven
Flextronics / Intel / Other
Camera for In-line Reflow Oven and
l Time
In-line SMT Oven
nitoring of BallBatch Reflow Oven with Video
aste Gap
Camera
Intel / Other Member(s) to be
identified
Nihon Superior / Other Member(s) to
be identified
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Test Substrates Proposal
Ball Pitch
Ball Size
Body Size
Quantity of
Substrates
Quantity of Balls
per Substrate
(Approx)
(Approx)
0.5 mm
0.3 mm
7 mm
150
600
0.8 mm
0.5 mm
15 mm
150
800
1.0 mm
0.6 mm
35 mm
300
1000
•
•
•
•
Thickness: 400 microns w/two copper layers, on each side of the core
Panasonic labs to build the substrate using low warpage materials
Substrate / Board Fabrication to be done at a PCB supplier member
Ball Attach to be done at Outside sub-contractor
Proposed Schedule