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an Alent plc Company
Reducing Head in Pillow
Defects
September 2009
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
Introduction
• Potential sources of Head in Pillow Defects
• What is the mechanism of failure
• Evaluation of Package Warpage – Measurement
– Industry Standards
• How Can Solder Paste Reduce HIP Defects? – Print Volume
– Wetting Force/Speed
– Paste Activation Level
• Future Experiments
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
What is Head in Pillow?
Board Side
Component Side
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
Difficult Problem
In circuit testing may not detect the HIP defect
Z Direction X-Ray may not detect the HIP defect
Devices that are exposed to Drop Shock or Thermal Cycling in
field unfortunately Will over time experience this defect
Head in Pillow =
Where the solder joint
and the sphere are
touching but no
intermetallic layer is
formed
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
Head in Pillow Defect C&E
Overview
Warpage of
substrate
Inconsistent
bump size
Insufficient solder
paste volume
Printing misalignment
Inaccurate XY
placement
Insufficient
placement force
inadequate reflow
profile that results in
component & PCB
warpage
Lifting of BGA bumps
due to wetting force
Excessive Peak
Temperature
Too much TAL
Opportunities of defects from the different stages of a SMT process
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
Head in Pillow Defect Mechanism
•BGA Oxidizes
•Flux Activity Being
consumed
•Flux Becomes Liquid
•BGA Oxidizes
•Flux Activity Being
Used
•Oxidized Sphere
rejoins the Paste
deposit with Limited
Activity
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
Jeita Maximum Warpage Standards
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
Measuring BGA Warpage
Schematic of Shadow Moiré Method
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
Shadow Moiré Test Unit
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
Moiré Computer Generated Image
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
How Can Solder Paste be
Engineered to Reduce HIP?
I
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
Alpha Response
Solder Paste that…
produces higher and more consistent volume
deposition
has a greater resistance to longer soak profiles
has faster wetting speed
• Gage R&R testing for determining in-house Head
on Pillow defects to confirm solder paste
effectiveness
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
0.25mm round BGAs, 0.1mm laser cut stencil
OM338 T45
-20
0
20
40
60
80
100
120
140
160
1 7 13
Board #
Vo
lum
e (
cu
mil
)
Average - Boards 1-6 (Initial) Average - Boards 7-12 (wipe)
Average - Boards 13-18 (pause) Minimum vol. - Boards 1-6
Minimum vol. - Boards 7-12 Minimum vol. - Boards 13-18
450-31
-20
0
20
40
60
80
100
120
140
160
1 7 13
Board #
Vo
lum
e (
cu
mil
)
Average - Boards 1-6 (Initial) Average - Boards 7-12 (wipe)
Average - Boards 13-18 (pause) Minimum vol. - Boards 1-6
Minimum vol. - Boards 7-12 Minimum vol. - Boards 13-18
Print Volume
Increased print Volume and Volume Repeatability
Improved Paste Print Provides 40% More Paste Height!
Standard Paste Grizzly Bear
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
Preventing Defect with Paste
Print Height
Probable Defect
Defect
Prevented
70µ Deposit
100µ Deposit
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
Wetting Force
• Test Method
– Malcom Wetting
Balance Test
• Equipment
– Malcom SWB-2
• Test Procedure
– See Malcom SWB-2
Operating Manual
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
Wetting Force
Average
-12.00
-10.00
-8.00
-6.00
-4.00
-2.00
0.00
2.00
4.00
6.00
0 2 4 6 8
Wetting time , SecW
ett
ing
Fo
rce
, m
N
Average
-12.00
-10.00
-8.00
-6.00
-4.00
-2.00
0.00
2.00
4.00
0 2 4 6 8
Wetting time , Sec
We
ttin
g F
orc
e, m
N
Grizzly Bear Standard Paste
Goal: Increased Wetting Force and Speed
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
Head in Pillow
Test Method
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
Creating HIP Defects
The Occurrence of the HIP defects average 200 ppm based on customer
feedback
Issue: How do we create a test method that creates higher DPMO
(Defects per million opportunities) so we can test for it?
Good Joint
HIP Joint
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
Manage Reflow and Warpage
Time, Temperature, Z-Axis Location
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
HIP Test Equipment
• Test Vehicle (TV)
• BGA338 Dummy component
• BGA rework station
• Fabricated TV holder and fixture for holding the
dummy BGA with vacuum.
• Thermocouple data acquisition
• Solenoid Valve
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
HIP Experimental Set-Up
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
HIP Experimental Set-Up
1. The BGA component is held a few mm above
the test vehicle by applying vacuum to the cup.
2. The BGA is then dropped on to the test vehicle
by releasing vacuum.
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
Reflow Profile Indicator
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
Drop Component at Precise Time
During Reflow
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
Experimental Results
• Test Highly Activated Paste vs. Very Low
Activity Paste and Measure HIP DPMO.
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
Head in Pillow Resistant Paste
Good reflow at corner pads
Only one HIP Defect was
Observed after prying the BGA
from Test Vehicle
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
Less Activated Paste
After prying BGA from TV
Obvious HIP joint in the
center of the BGA block!
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
Initial results suggests that flux
chemistry does affect HIP
More Active Paste Less Active Paste
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
Future Work ZhuoMao BGA Rework -- HIP A reflow profile
0
50
100
150
200
250
0 50 100 150 200 250 300 350
Time sec
Te
mp
era
ture
°C
lower left corner
upper right corner
lower BGA row
center BGA block
217°C
TC positions
Under the BGA
Reflow Profile vs. Head in Pillow Defect Rate
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
Summary
Component Size/Warpage Can Affect HIP Defect Rate
Key attributes for Solder Paste to reduce HIP DPMO’s
Taller, More Consistent Paste Deposits
Faster, Stronger Wetting Force
Enhanced paste flux Activity and Activity Duration
High Gage R&R HIP Test to Confirm Paste Properties
HIGHLY CONFIDENTIAL AND PRIVILEGED INFORMATION an Alent plc Company
For more information click the
link below:
Alpha Products
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