Transcript Document 7259147

Surface Mount Technology (SMT)
experiment - problem solving in a
manufacturing environment
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2 types of defects, probably related
- Solder balls
- Solder-on-gold
Statistician invited in for a “quick fix”
experiment
• High volume memory card product
Problem in screening / reflow
operations
Prep
card
Solder paste
screening
Solder paste
reflow
Clean card
insert
Inspect (T1)
Component
placement
Inspect
(T2)
8 potential process factors
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Clean stencil frequency: 1/1, 1/10
Panel washed: no, yes
Misregistration: 0, 10 ml
Paste height: 9ml, 12 ml
Time between screen/ reflow: .5, 4 hr
Reflow card spacing: 18 in, 36 in
Reflow pre-heat: cold, hot
Oven: A, B
Experiment design conditions
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Resources only permit 16 trials
Get efficiency from 2-level factors
Measure both types of defects
Introduce T1 inspection station for counting
defects
• Same inspectors
• Same quantity of cards per trial
Can we measure effects of 8
factors in 16 trials? Yes
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A
5.5
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B
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-62 404 314 -109
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F
G
H factor
5.5 136 -7.3
response
7 more columns contain all
interactions
• Each column contains confounded
interactions
AB AC BC
AD
BD CD
AE
CG DF DE
CF
CE BE
DG
DH BG AG
BH
AH AF
BF
EF
EG
FG GH
CH
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EH FH
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Normal plot for factor effects on
solder ball defects
Normal plot- 15 mean effects
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C
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CD
Z Variate
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Mean Effects
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Which confounded interaction is
significant?
• AF, BE, CD, or GH ?
• The main effects C and D are significant, so
engineering judgement tells us CD is the
true significant interaction.
• C is misregistration
• D is paste height
Conclusions from experiment
• Increased paste height (D+) acts together
with misregistration to increase the area of
paste outside of the pad, leading to solder
balls of dislodged extra paste.
• Solder ball occurrence can be reduced by
minimizing the surface area and mass of
paste outside the pad.
Implemented solutions
• Reduce variability and increase accuracy in
registration.
• Lowered solder ball rate by 77%
• More complete solution:
• Shrink paste stencil opening - pad
accommodates variability in registration.
The Power of Efficient
Experiments
• More information from less resources
• Thought process of experiment design
brings out:
– potential factors
– relevant measurements
– attention to variability
– discipline to experiment trials