Probing Lead Free Solder Bumps in Final Wafer Test
Probing Lead Free Solder Bumps in Final Wafer Test
Probing Lead Free Solder Bumps in Final Wafer Test
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<strong>Prob<strong>in</strong>g</strong> <strong>Lead</strong> <strong>Free</strong> <strong>Solder</strong><br />
<strong>Bumps</strong> <strong>in</strong> F<strong>in</strong>al <strong>Wafer</strong> <strong>Test</strong><br />
By<br />
Sam McKnight<br />
Southwest <strong>Test</strong> Workshop<br />
June 2002<br />
Microelectronics
Microelectronics<br />
Outl<strong>in</strong>e<br />
Why lead free ?<br />
Background Info<br />
Focus areas<br />
Setup<br />
<strong>Lead</strong>/T<strong>in</strong> and T<strong>in</strong> “Rich” results<br />
Summary<br />
Acknowledgements<br />
Sam McKnight June 2002 Southwest <strong>Test</strong> Workshop<br />
2
Microelectronics<br />
Why <strong>Lead</strong> <strong>Free</strong>?<br />
Increas<strong>in</strong>g use of <strong>in</strong>tegrated circuits and shortened<br />
product life cycles prompted a world wide<br />
environmental concern regard<strong>in</strong>g the disposal of<br />
electronic components.<br />
<strong>Lead</strong> countries with environmental <strong>in</strong>itiatives are<br />
Japan, Europe and the US<br />
All levels of packag<strong>in</strong>g <strong>in</strong>clud<strong>in</strong>g the <strong>in</strong>terconnect<br />
to the <strong>in</strong>tegrated circuit are be<strong>in</strong>g addressed.<br />
This presentation focuses on wafer level only<br />
Sam McKnight June 2002 Southwest <strong>Test</strong> Workshop<br />
3
Microelectronics<br />
Background Info<br />
Cobra probe (5 mil diameter - flat tipped) is the<br />
primary contact<strong>in</strong>g system for C4 VLSI test<br />
C4 = Controlled Collapse Chip Connection<br />
(<strong>Solder</strong> <strong>Bumps</strong>)<br />
C4's are normally reflowed before and after test<br />
<strong>Test</strong>s temperatures -10, 25, 85 and 100C<br />
Thermal unit range is -10 - 140C probe space<br />
transformer limit 100C (self imposed)<br />
Sam McKnight June 2002 Southwest <strong>Test</strong> Workshop<br />
4
Microelectronics<br />
Focus areas<br />
Basel<strong>in</strong>e comparison measurements to<br />
<strong>Lead</strong> T<strong>in</strong><br />
– Contact Resistance<br />
– Clean<strong>in</strong>g<br />
– Material Transfer (Pickup) To Probe Tip<br />
– Pad Deformation<br />
– Alignment to C4’s (<strong>Solder</strong> <strong>Bumps</strong>)<br />
Sam McKnight June 2002 Southwest <strong>Test</strong> Workshop<br />
5
Microelectronics<br />
Probe layout<br />
76 contacts total<br />
Die size ~ 9.1 mm<br />
square<br />
Probed pads<br />
Sam McKnight June 2002 Southwest <strong>Test</strong> Workshop<br />
6
Microelectronics<br />
<strong>Test</strong> wafer build structure<br />
<strong>Lead</strong>-T<strong>in</strong>/<strong>Lead</strong> <strong>Free</strong><br />
~4.5 mils<br />
4.5 mils<br />
Unreflowed C4's<br />
(photo resist removed)<br />
BLM (Ball Limit<strong>in</strong>g Metallurgy)<br />
Insulator<br />
Si wafer<br />
Scale none<br />
Sam McKnight June 2002 Southwest <strong>Test</strong> Workshop<br />
7
Microelectronics<br />
Setup<br />
TEL P8XL wafer prob<strong>in</strong>g system with <strong>in</strong>tegral -10 to 140C<br />
thermal unit w/ IBM custom tester <strong>in</strong>terface with hand<br />
wired space transformer<br />
Z drive - maximum impact velocity (~40 mm/sec)<br />
SARA (Socket Analog Resistance Analyzer) (DC<br />
switch<strong>in</strong>g matrix with measurement unit)<br />
Cres Measurement method - "p<strong>in</strong> return" with 10 ma<br />
forc<strong>in</strong>g current and 5V clamp w/null<strong>in</strong>g file - to subtract<br />
path resistance<br />
Clean<strong>in</strong>g frequency - 1/wafer (>300 sites) - 5 micron<br />
abrasive material<br />
Environment - m<strong>in</strong>i-clean hood over prober<br />
Sam McKnight June 2002 Southwest <strong>Test</strong> Workshop<br />
8
Microelectronics<br />
Contact Resistance Measurement<br />
VI source<br />
~ 10 ma@ 5V<br />
Contact under<br />
test<br />
Return path<br />
Cobra contact<br />
C4's<br />
Note: actual return path p<strong>in</strong>s ~ 75<br />
<strong>Wafer</strong><br />
Sam McKnight June 2002 Southwest <strong>Test</strong> Workshop<br />
9
Microelectronics<br />
Cobra Probe Measurements<br />
50<br />
Probe force sample measurements<br />
Probe outer row - Ceramic lower guide plate<br />
Amb Temp - after ~ 11K touchdowns, ~10 Temperature cycles<br />
PCB deflection @ temperature vs overdrive<br />
1.1<br />
1<br />
Force (<strong>in</strong> grams)<br />
45<br />
40<br />
35<br />
30<br />
25<br />
20<br />
15<br />
10<br />
5<br />
P<strong>in</strong> 1<br />
P<strong>in</strong> 2<br />
P<strong>in</strong> 3<br />
P<strong>in</strong> 4<br />
P<strong>in</strong> 5<br />
P<strong>in</strong> 6<br />
P<strong>in</strong> 7<br />
P<strong>in</strong> 8<br />
P<strong>in</strong> 9<br />
P<strong>in</strong><br />
10<br />
PCB deflection (<strong>in</strong> mils)<br />
0.9<br />
0.8<br />
0.7<br />
0.6<br />
0.5<br />
0.4<br />
0.3<br />
-10C<br />
25C<br />
85C<br />
100C<br />
0<br />
0.85 2.44 3.69 5.16 6.63 7.98 9.70<br />
1.67 3.05 4.43 5.89 7.33 8.74<br />
Probe deflection (mils)<br />
0.2<br />
6 7 8 9<br />
Overdrive sett<strong>in</strong>g (<strong>in</strong> mils)<br />
Sam McKnight June 2002 Southwest <strong>Test</strong> Workshop<br />
10
Microelectronics<br />
Un Reflowed C4’s<br />
<strong>Lead</strong> free<br />
<strong>Lead</strong> T<strong>in</strong><br />
Sam McKnight June 2002 Southwest <strong>Test</strong> Workshop<br />
11
Microelectronics<br />
Contact Resistance – <strong>Lead</strong> T<strong>in</strong> C4’s<br />
10<br />
Average Contact resistance<br />
PbSn 97/3 UNREFLOWED C4's<br />
Each plot po<strong>in</strong>t = 86K measurements<br />
9<br />
8<br />
7<br />
(OHMS)<br />
6<br />
5<br />
4<br />
-10C<br />
25C<br />
85C<br />
100C<br />
3<br />
2<br />
1<br />
0<br />
6 mils 7 mils 8 mils 9 mils<br />
Contact + Overdrive<br />
Sam McKnight June 2002 Southwest <strong>Test</strong> Workshop<br />
12
Microelectronics<br />
Contact Resistance - <strong>Lead</strong> <strong>Free</strong> C4’s<br />
Note scale<br />
Average Contact resistance<br />
<strong>Lead</strong> <strong>Free</strong><br />
Each plot po<strong>in</strong>t = 86K measurements<br />
1<br />
0.9<br />
0.8<br />
0.7<br />
0.6<br />
-10C<br />
25C<br />
85C<br />
100C<br />
(OHMS)<br />
0.5<br />
0.4<br />
0.3<br />
36 open read<strong>in</strong>gs (500 ohms)<br />
0.2<br />
Sample contam<strong>in</strong>ant<br />
open p<strong>in</strong><br />
0.1<br />
0<br />
6 mils 7 mils 8 mils 9 mils<br />
Contact + Overdrive<br />
Sam McKnight June 2002 Southwest <strong>Test</strong> Workshop<br />
13
Microelectronics<br />
-10°C Cobra/C4 Photos<br />
6 MIL O D<br />
7 MIL O D<br />
8 MIL O D<br />
9 MIL O D<br />
6 MIL O D<br />
7 MIL O D<br />
8 MIL O D<br />
9 MIL O D<br />
Sam McKnight June 2002 Southwest <strong>Test</strong> Workshop<br />
14
Microelectronics<br />
25°C Cobra/C4 Photos<br />
Probe<br />
6 MIL O D<br />
Probe<br />
7 MIL O D<br />
Probe<br />
88 MIL O D<br />
Probe<br />
9 MIL O D<br />
C4 Pad<br />
6 MIL O D<br />
C4 Pad<br />
7 MIL O D<br />
C4 Pad<br />
88 MIL MIL O D<br />
C4 Pad<br />
9 MIL O D<br />
Sam McKnight June 2002 Southwest <strong>Test</strong> Workshop<br />
15
Microelectronics<br />
85º C Cobra/C4 Photo’s<br />
Probe<br />
6 MIL O D<br />
Probe<br />
Probe<br />
Probe<br />
7 MIL O D 8 MIL O D 9 MIL O D<br />
C4 Pad<br />
C4 Pad<br />
C4 Pad<br />
C4 Pad<br />
6 MIL O D 7 MIL O D 8 MIL O D 9 MIL O D<br />
Sam McKnight June 2002 Southwest <strong>Test</strong> Workshop<br />
16
Microelectronics<br />
100°C Cobra/C4 Photo’s<br />
Probe<br />
Probe<br />
Probe<br />
Probe<br />
C4 Pad C4 Pad C4 Pad C4 Pad<br />
Sam McKnight June 2002 Southwest <strong>Test</strong> Workshop<br />
17
Microelectronics<br />
Pad Deformation<br />
C4 AVERAGE deformation comparisons<br />
PbSn to Sn<br />
Deformation<br />
2<br />
Inconclusive!!<br />
1.5<br />
O ffset<br />
probe<br />
Unprobed<br />
Centered<br />
probe<br />
(MILS)<br />
1<br />
0.5<br />
0<br />
PbSn-10C<br />
PbSn25C<br />
PbSn85C<br />
PbSn100C<br />
Sn-10C<br />
Sn25C<br />
Sn85C<br />
Sn100C<br />
<strong>Test</strong> temperature<br />
S. McKnight<br />
B. Budd<strong>in</strong>gton<br />
04/10/01<br />
Sam McKnight June 2002 Southwest <strong>Test</strong> Workshop<br />
18
Microelectronics<br />
Typical <strong>Wafer</strong> level Contact Resistance<br />
plot <strong>Lead</strong> <strong>Free</strong> C4’s<br />
Sn Average Contact Resistance/site<br />
6 mil OD - temperature -10C - 2nd pass<br />
283 sites/wafer<br />
Note scale<br />
Cres (ohms)<br />
1<br />
0.8<br />
0.6<br />
0.4<br />
0.2<br />
0<br />
F<strong>in</strong>ish<br />
h<br />
Notch<br />
Start<br />
1<br />
2<br />
3<br />
4<br />
5<br />
6<br />
7<br />
8<br />
9<br />
10<br />
11<br />
12<br />
13<br />
14<br />
15<br />
16<br />
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20<br />
S. McKnight<br />
B.Budd<strong>in</strong>gton<br />
04/04/01<br />
Sam McKnight June 2002 Southwest <strong>Test</strong> Workshop<br />
19
Microelectronics<br />
Typical <strong>Wafer</strong> level Contact Resistance<br />
plot for <strong>Lead</strong>/T<strong>in</strong> C4’s<br />
PbSn Basel<strong>in</strong>e Average Contact Resistance/site<br />
6 milOD - temperature -<br />
25C 283 sites/wafer<br />
Note scale<br />
F<strong>in</strong>ish<br />
20<br />
15<br />
10<br />
5<br />
0<br />
Notch<br />
Start<br />
1<br />
2<br />
3<br />
4<br />
5<br />
6<br />
7<br />
8<br />
9<br />
10<br />
11<br />
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15<br />
16<br />
17<br />
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19<br />
20<br />
S. McKnight<br />
B.Budd<strong>in</strong>gton<br />
03/29/01<br />
Sam McKnight June 2002 Southwest <strong>Test</strong> Workshop<br />
20
Microelectronics<br />
Summary<br />
Contact resistance for <strong>Lead</strong> <strong>Free</strong>
Microelectronics<br />
Acknowledgements<br />
Barry Budd<strong>in</strong>gton – IBM - software/setup operations<br />
Gob<strong>in</strong>da Das – IBM – PhD<br />
Steve Kilpatrick – IBM – PhD<br />
Amador Cantu Jr. – TEL Field Service<br />
Sam McKnight June 2002 Southwest <strong>Test</strong> Workshop<br />
22
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