Surface Mount Requirements for
Land Grid Array (LGA) Packages
Applications Engineering
Amkor Technology, Inc
September 2002
.
For additional information please contact marketing@amkor.com
Surface Mount Considerations for LGAs
t LGA Considerations for Surface Mounting
t PCB Design Considerations
– PCB Technology Trend
– Pad Size
– Line/Space
t PCB Assembly Issues
– Solder Paste and Stencil Design Considerations
– Placement & Reflow
t Rework
–
–
–
–
Part Removal
Site Redress
Part Placement
Reflow
© 2002 Amkor Technology, Inc.
Applications Engineering/A. Syed/0902
LGA Considerations for Surface Mounting
t Package Pad Type
– SMD Pads Standard for BGA Type Packages
– NSMD Pad
SMD
NSMD
t Enhance Thermal Cycle Reliability
t May Degrade Bend/Drop performance due to pad ripping off the substrate
– SMD Pad recommended for packages designed for portable electronics
applications.
t Bumped vs Non Bumped
– Non Bumped Packages
Tape
t Surface Mount Integrity strongly dependent on Paste Printing on PCB and
Part
Placement (Speed and Force)
– Package Coplanarity and PCB Warpage Major Issues to Overcome
t Not Recommended for Tape Packages due to deeper cavity
– 50 to 65 microns for Tape
– 15 to 25 microns for Laminate
t Inspection and Final Test Methods Need to be Modified
t May Result in No Standoff between Package and Board
Laminate
– Bumped Packages
t Extra Process in Package Assembly
t More Robust PCB Assembly
© 2002 Amkor Technology, Inc.
Applications Engineering/A. Syed/0902
PCB Design Considerations
© 2002 Amkor Technology, Inc.
Applications Engineering/A. Syed/0902
PCB Design Considerations
t PCB Technology
Feature
Line Width
Spacing Width
Drill Via Diameter
Drill Capture Pad
Microvia Diameter
Microvia Capture pad
PCB Capability
Conventional Advanced Leading Edge State of the Art
0.006
0.004
0.003
0.002
0.007
0.004
0.003
0.002
0.018
0.014
0.009
0.006
0.028
0.022
0.016
0.014
0.004
0.002
0.011
0.008
* All Dimensions in inches
© 2002 Amkor Technology, Inc.
Applications Engineering/A. Syed/0902
PCB Routing Considerations
Calculations
4 Traces Between Pads (Outer Layer)
W = (P-S-2t)
No = (W+L)/2L
Where
P
L = Line Width/Space
W = Solder Mask Web
4 Traces Between Via Pads (Inner Layers)
Ni = (P - V -2t + L)/L
where
V = Via Capture Pad Diameter
S
t
W
D
Assumes 1 Built Up Layer on Each side
for µVia (State of the Art) Technology Boards.
© 2002 Amkor Technology, Inc.
Applications Engineering/A. Syed/0902
PCB Routing Considerations
1.27 & 1.0 mm Pitch
Commodity
Advanced
(mm)
0.150
0.100
Pitch (P)
Pad Dia (D)
SM Opening (S)
Sm to Trace Clearance (t)
SM Web b/w Pads (W)
Pitch (P)
Pad Dia (D)
SM Opening (S)
Sm to Trace Clearance (t)
SM Web b/w Pads (W)
Drill
Capture
Pad Dia
(mm)
0.70
0.55
1.27
0.55
0.67
0.1
0.4
1
0.38
0.5
0.1
0.3
Commodity
4
Advanced
3
2
1
0
2
3
4
5
6
7
8
Number of Peripheral Rows
5
Number of Signal Layers
Required
PCB Technology
Line &
Space
Number of Signal Layers
Required
5
Advanced
4
Commodity
3
2
1
0
2
3
4
5
6
7
8
Number of Peripheral Rows
© 2002 Amkor Technology, Inc.
Applications Engineering/A. Syed/0902
PCB Routing Considerations
0.8 & 0.5 mm Pitch
PCB Technology
Line &
Space
Drill
Capture
Pad Dia
microvia
Capture
Pad
(mm)
0.70
0.55
0.40
(mm)
Commodity
Advanced
Leading Edge (µVia)
(mm)
0.150
0.100
0.075
Pitch (P)
Pad Dia (D)
SM Opening (S)
Sm to Trace Clearance (t)
SM Web b/w Pads (W)
0.8
0.33
0.45
0.1
0.15
0.5
0.28
0.4
0.1
0
leading Edge
4
Advanced
3
2
1
0
2
3
4
5
6
7
8
Number of Peripheral Rows
5
Number of Signal Layers
Required
Pitch (P)
Pad Dia (D)
SM Opening (S)
Sm to Trace Clearance (t)
SM Web b/w Pads (W)
0.280
Number of Signal Layers
Required
5
4
Leading Edge
Advanced
3
2
1
0
2
3
4
5
Number of Peripheral Rows
© 2002 Amkor Technology, Inc.
Applications Engineering/A. Syed/0902
PCB Design Considerations
t Trace Width Should be < 1/2 of Pad Size
– For 12 mil or Smaller Pads, Use 4 mil Line
t Wider Traces Result in
– Bigger and Elongated Pads
– Reduced Reliability (Lower Standoff)
© 2002 Amkor Technology, Inc.
Applications Engineering/A. Syed/0902
Motherboard Recommendations
t Pad Size
t
t
t
t
1.27mm Pitch: 0.55 to 0.63mm
1.0 mm Pitch: 0.38 to 0.45mm
0.75/0.8mm Pitch: 0.33 to 0.38mm
0.5mm Pitch: 0.25 to 0.3mm
– Smaller Pad better for Thermal Fatigue Reliability
– Larger Pad Better for Bend or Drop Performance
t Pads should be Non Solder Mask Defined (NSMD)
t OSP or NiAu Surface Finish
t Thinner board results in better for Reliability
© 2002 Amkor Technology, Inc.
Applications Engineering/A. Syed/0902
PCB Assembly Considerations
© 2002 Amkor Technology, Inc.
Applications Engineering/A. Syed/0902
PCB Assembly Considerations
Stencil
t Stencil Type & Thickness
– Laser cut Stainless Steel, Electropolished
– Thickness
t 0.5/0.65mm Pitch: 100 to 125 microns
t 0.8/1.0mm Pitch: 125 to 150 microns
– Stencil thickness may need to be increased by 25 microns for non bumped
parts
t Aperture Size and Shape
– Aspect Ratio ( W/T, 2R/T) > 1.5
– Area Ratio (W/4T, R/2T) > 0.66
t
t
t
t
t
W
2R
0.5mm Pitch: 0.25 - 0.3mm, Square
0.65mm Pitch: 0.3 - 0.35mm, Square
0.8mm Pitch: 0.35 - 0.4mm, Square
1.0mm Pitch: 0.40 - 0.45mm, Square
1.27mm Pitch: 0.55 - 0.60mm, Round
– Rounded corners to Minimize Clogging
– Positive Taper with Bottom Opening 25 to 50 microns Larger than the Top
© 2002 Amkor Technology, Inc.
Applications Engineering/A. Syed/0902
PCB Assembly Considerations
Paste & Paste Inspection
t Solder Paste
– No Clean, Type 3
t Cleaning is not an option for LGAs
Class
Type I
Type II
Type III
Type IV
Type V
t Squeegee
– Metal
– 45o Angle
– Speed
Mesh Size
-100/+200
-200/+325
-325/+500
-400/+500
-500/+635
100
200
325
400
500
635
150 microns
75 microns
45 Microns
38 Microns
25 Microns
20 microns
t Starting Point 15mm/Sec.
t Increase with Experience
t 0 Snap Off to Minimize Bleeding
t Paste Inspection a Key Process Step
– Solder Paste Volume is The Best Predictor of Finished Board Quality
– Manual Inspection
t Least Expansive and Least Sophisticated, Subjective, 80% Reliable
– 2-D Inspection
Cost of Defect Found
t Single Point Height and Area, Volume Calculations Not Accurate
– 3-D Inspection
t Height, Area, Volume, Automated In-line/off-line
© 2002 Amkor Technology, Inc.
After Paste Printing
After Reflow
At In-Circuit Testing
In Field
$0.50
$5.00
$35.00
$350.00
Applications Engineering/A. Syed/0902
PCB Assembly Considerations
Placement & Reflow
t Placement
– Slower speed and Higher force may be required, especially for non
bumped LGAs
t Reflow Oven
– Forced Convection Reflow is Preferred in N2 environment
t Profile
– Depends on Other Parts and Board Density
– Follow Paste Manufacturer’s Guideline
– Max Temperature: 220 - 240oC (Depending on Package Qualification
MSL)
– Time Above Liquidus: 45 - 60 Seconds
© 2002 Amkor Technology, Inc.
Applications Engineering/A. Syed/0902
Rework of LGAs
© 2002 Amkor Technology, Inc.
Applications Engineering/A. Syed/0902
Rework Guidelines for LGAs
Component Removal
t Prior to Rework, Assembly Should be Free from Moisture
t Board Should be Uniformly Supported
– A tilt may result in Solder Bridging
t Under Board Preheating is Required
– 100 - 110oC for 32 - 62 mil Thick Boards
– 120 - 125oC for 125 mil or Densely Populated Boards
t Reflow Profile
– 3 Stage Ramp-Hold-Ramp If Component will be Reused
t Same Profile for Removal and Replacement
t Otherwise Direct Ramp-up may result in shorter throughput
– Peak Temperature: 200 - 205oC
– Time Above Liquidus: 45 - 60 seconds
© 2002 Amkor Technology, Inc.
Applications Engineering/A. Syed/0902
Rework Guidelines for LGAs
Component Removal (Cont.)
t Delta T Across Solder Joints Should Be Less Than 10oC
t Temperature Around Rework Component: < 150oC
t Die Temperature <225oC
– To Avoid Component Damage (Delamination)
t Flux is not Recommended (Adds Process Step/Cost)
t Air Velocity - As Low As Possible (Avoid Component Skew)
– 500 FCH - Top Heater, 100 FCH - Bottom Heater
t Nitrogen Atmosphere
– Better Heat Distribution and Removal Quality
t Zero Force Vacuum Pick Up During Transition to Cool-down
– Avoids Bridging of Reflowed Balls
– Forced Pick-up OK for Ball Pitch of 1.27mm and Greater
© 2002 Amkor Technology, Inc.
Applications Engineering/A. Syed/0902
Rework Guidelines for LGAs
Site Redressing
t Don’t Redress from Smaller Pitch and Tightly spaced
Components
– Use Hot Air Leveling after Component Removal
t Methods
– Soldering Iron with Solder Wick - Conductive
– Vacuum De-soldering - Conductive
– Hot Air Scavenging - Convective
t Pros/Cons
Method
Solder Wick
Vacuum
Scavenging
Initial
Cost
Low
Moderate
High
Process
Control
Low
Low
High
Operator
Skill
High
Low
Moderate
Quality
Repeatability
High
Low
Low
Moderate
Moderate High
– Solder Wick - Cost Effective & Efficient - Operator Skill
– Vacuum De-Soldering - Board Damage
t Recommendation - Solder Wicking with Flux
– 30 mil wide Wick for Ball Pitch 1.0mm or Less
– 60 mil wide Wick for Pitch > 1.0mm
© 2002 Amkor Technology, Inc.
Applications Engineering/A. Syed/0902
Rework Guidelines for LGAs
Component Replacement
t Clean Site with Solvent if the Site Has Been Redressed
t Solder Paste/Flux
– Print Paste on the Package (non bumped) for Smaller Pitch & Tightly
Space Parts
t Paste Printing may Result in Bridging for 0.5 mm Pitch Devices - Use only Flux
– Use Mini Stencil wherever possible
t Squeegee of same width as Stencil
t Align Aperture with Pads under 50 - 100X Magnification Before Paste Printing
t Placement & Reflow
– Split-Beam Optical System for Component Alignment
– 50 - 100X Magnification
– Placement Machine Should Allow fine Adjustments in X, Y, and Rotational
Axes
– Profiles Developed during Initial Placement or Rework Can be Used
– Maximum Temperature 220 - 240C
© 2002 Amkor Technology, Inc.
Applications Engineering/A. Syed/0902