impact of microvia-in-pad design on void formation - Sanmina-SCI

Test 2: Effect <strong>of</strong> Surface F<strong>in</strong>ish Test 3: Effect <strong>of</strong> Component Type
There was vary<strong>in</strong>g data for the surface f<strong>in</strong>ish
comparisons. Mean and standard deviations were fairly
close but there was about a 25% <strong>in</strong>crease <strong>in</strong> the number <strong>of</strong>
voids for the bottom slice on the boards with Immersion
Ag plat<strong>in</strong>g.
12000
10000
Dimension <strong>in</strong> mils
8000
6000
4000
2000
Dimension <strong>in</strong> mils
Dimension <strong>in</strong> mils
0
16
14
12
10
8
6
4
2
0
14
12
10
8
6
4
2
0
16
14
12
10
8
6
4
2
0
Total Number <strong>of</strong> Voids
Middle Slice Top Slice Bottom Slice
Slice 1 - Middle (Total Void Count - 18,697)
Mean Std Dev. Range M<strong>in</strong>imum Maximum
Slice 2 - Top (Total Void Count - 6,801)
Mean Std Dev. Range M<strong>in</strong>imum Maximum
Slice 3 - Bottom (Total Void Count - 17,847)
Mean Std Dev. Range M<strong>in</strong>imum Maximum
Gold
Silver
Gold
Silver
Gold
Silver
Gold
Silver
For the component type data a normalization <strong>of</strong> the data
was performed. There are 4 <strong>of</strong> each BGA type on the PCB
but the I/O count drops as the pitch decreases. To
compensate for the decrease <strong>in</strong> the number <strong>of</strong> solder jo<strong>in</strong>ts
it was assumed that the data distribution was fairly normal
and did a straight multiplication for the number <strong>of</strong> voids.
The results when us<strong>in</strong>g this normalization shows that
there is an <strong>in</strong>crease <strong>in</strong> the number <strong>of</strong> voids although they
do decrease <strong>in</strong> size. This is to be expected s<strong>in</strong>ce the viahole
sizes are held constant and become a larger
percentage <strong>of</strong> the <strong>pad</strong> volume as the pitch decreases.
12000
10000
8000
6000
4000
2000
Dimension <strong>in</strong> mils
Dimension <strong>in</strong> mils
Dimension <strong>in</strong> mils
0
16
14
12
10
8
6
4
2
0
14
12
10
8
6
4
2
0
16
14
12
10
8
6
4
2
0
Total Number <strong>of</strong> Voids
1.27 1.0 0.8 0.5
BGA Pitch <strong>in</strong> mm
Slice 1 - Middle (Total Void Count - 18,697)
Mean Std Dev. Range M<strong>in</strong>imum Maximum
Slice 2 - Top (Total Void Count - 6,801)
Mean Std Dev. Range M<strong>in</strong>imum Maximum
Slice 3 - Bottom (Total Void Count - 17,847)
Mean Std Dev. Range M<strong>in</strong>imum Maximum
Middle Slice
Top Slice
Bottom Slice
1.27
1.0
0.8
0.5
1.27
1.0
0.8
0.5
1.27
1.0
0.8
0.5