Post on 06-Feb-2016
description
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Accelerated Testing of Flip Chip Underfill - Sensitivity to Aging/Moisture
Nikhil Vichare
Graduate Research AssociateDepartment of Systems Science and Industrial Engineering
State University of New York at Binghamton
Binghamton NY 13902
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Experiment
Performance in cycling is relative measure of degradation in preconditioning
Preconditioning Time, Temperature, Humidity • 72 hours - 6 months• Room temperature - 130oC • Dry N2 - 85%R.H.
• No Preconditioning
Subsequent Cycling in Liquid to Liquid Thermal Shock (LLTS)• 5 minutes hold at -55oC and 125oC• 10 seconds transfer time
Measure corner fillet cracking and delamination around bumps v/s number of LLTS cycles
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Experiment• 1056 die 4224 corner fillets
• 3 underfills Dexter FP4549 Namics U8437-3 Honeywell JM8802
• 2 fluxes Kester TSF-6522 Indium NC-SMQ 75
PB08 chips on 62 mil board with Taiyo PSR4000 mask
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Effects of Moisture
• It is well “established” that moisture exposure may weaken the underfill.
• Pressure Cooker Test (PCT) is a common accelerated test of sensitivity to humidity Also called unbiased HAST 85% R.H.,130°C, 2 atm.pressure (JESD22-A118)
• Is PCT meaningful?
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Fillet Cracking in Cycling after PCT
14-16 mil Thick Namics U8437-3 Fillets (Kester TSF-6522 Flux)
• Clear effect on subsequent cycling
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5
10
15
20
25
30
250
500
1000
1500
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2500
250
500
1000
1500
2000
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250
500
1000
1500
2000
2500
Num
ber
of F
illet
s
Crack No Crack Direct LLTS
72 Hours PCT + LLTS 144 Hours PCT + LLTS
LLTS Cycles
No Preconditioning
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PCT?• Characteristics of damage in cycling after PCT different from
that after other humidity/temperature exposure
85°C/85%R.H. 3 Weeks + LLTS PCT 72 Hours + LLTS
• Also discoloration of underfill and solder mask (see poster)
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Time/Temperature and/or Moisture has an Effect !
• Faster Cracking of Namics (TSF-6522) after 85°C/30% R.H.
14-16 mil Thick Namics U8437-3 Fillets (Kester TSF-6522)
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10
20
30
250
500
1000
1500
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2500 25
0
500
1000
1500
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2500 25
0
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1000
1500
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2500 25
0
500
1000
1500
2000
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Num
ber
of
Fill
ets
Crack No Crack2 weeks
3 weeks
No Preconditioning1 week
LLTS Cycles
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More Moisture is Worse
2 Weeks of Preconditioning of 14-16 mil Thick Namics U8437-3 Fillets (Kester TSF-6522)
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10
20
30
250
500
1000
1500
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2500
250
500
1000
1500
2000
2500
Num
ber
of F
ille
ts
Crack No Crack
85°C/85%R.H.
85°C/30%R.H.
LLTS Cycles
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Also Faster Delamination from Solder Bumps after Moisture Exposure
250 1000 2000
1000 2000 3000
• After 3 Weeks of 85°C/85% R.H.
• Without Preconditioning
Namics U8437-3 (Kester TSF-6522)
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Acceleration?
Similar cracking in subsequent cycling for some
encapsulant/ flux/ fillet thickness combinations
Example
• 3 months aging in ambient 85°C/30%R.H. for 3
weeks
• 6 months aging in ambient 85°C/85%R.H. for 3
weeks
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Acceleration?• 3 months ambient 85°C/30%R.H. for 3 weeks• Namics(Kester) 14-16 mil fillets
0
10
20
30
50
0
10
00
15
00
20
00
25
00
50
0
10
00
15
00
20
00
25
00
Num
ber
of F
illet
s
No Crack
Crack
85°C/30% R.H. 3 Weeks
3 Months Ambient
Namics(Kester)
LLTS Cycles
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Acceleration?
• 3 months ambient 85°C/30%R.H. for 3 weeks• Same material thinner fillets (10-12 mils)
0
10
20
30
500
1000
1500
2000
2500 500
1000
1500
2000
2500
Num
ber
of F
illet
s
No Crack
Crack3 Months Ambient
85°C/30% R.H. 3 Weeks
LLTS Cycles
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Acceleration?• 3 months ambient 85°C/30%R.H. for 3 weeks• Dexter(Indium) 10-12 mil fillets
0
10
20
30
500
1000
1500
2000
2500 500
1000
1500
2000
2500
Num
ber
of F
illet
s
No Crack
Crack
3 Months Ambient
85°C/30% R.H. 3 Weeks
Dexter Indium
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14Namics U8437-3 (Kester TSF-6522) 14-16 mils
Acceleration?
• 6 months aging in ambient 85oC/85%R.H. for 3 weeks
0
10
20
30
500
100
0
150
0
200
0
250
0
500
100
0
150
0
200
0
250
0
Num
ber
of F
illet
s
Crack No Crack
6 Months Ambient 85°C/85%R.H. 3 weeks
LLTS Cycles
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Acceleration?
• 6 months ambient 85°C/85%R.H. for 3 weeks
and 3 months ambient 85°C/30%R.H. for 3 weeks
(totally different cracking in subsequent cycling) for
other encapsulant/ flux/ fillet thickness combinations
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Acceleration?• 3 months ambient 85°C/30%R.H. for 3 weeks• Honeywell (Kester) 12-14 mil fillets
0
10
20
30
500
1000
1500
2000
2500
500
1000
1500
2000
2500
Num
ber
of F
ille
ts
No Crack
Crack
3 Months Ambient
85°C-30% R.H. 3 week
LLTS Cycles
Honeywell (Kester) 12-14 mils
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Acceleration?
Dexter FP4549 (Indium NC-SMQ 75) 10-12 mils
• 6 months ambient 85°C/85%R.H. for 3 weeks• Dexter (Indium) 10-12 mil Thick Fillets
0
10
20
30
500
1000
1500
2000
2500
500
1000
1500
2000
2500
Num
ber
of F
illet
s
NoCrack
Crack
6 Months Ambient
85°C-85% R.H. 3 week
LLTS Cycles
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Moisture isn't Everything!
• Underfill also weakens with time (even in dry storage)
• That’s why we didn't have a single acceleration
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Effect of Time As Well• Aging in Nitrogen Cabinet
10-12 mil Thick Namics U8437-3 (Kester TSF-6522)
0
10
20
30
500
1000
1500
2000
2500
3000 500
1000
1500
2000
2500
3000 500
1000
1500
2000
2500
Num
ber
of F
illet
s
No Crack
Crack
No Preconditioning
3 Months N2
6 Months N2
LLTS Cycles
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1000 2000 3000
1000 2000 3000
• After 3 Months Aging in Nitrogen Cabinet
• Without Preconditioning
• Faster Delamination from Solder Bumps
Effect of Time As Well
Namics U8437-3 (Indium NC-SMQ 75)
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Preconditioning Sometimes Decreased Cracking
10-12 mil Thick Honeywell JM88202 (Kester TSF-6522)
• 85°C/30%R.H. reduces subsequent cracking of Honeywell (Kester)
• Effect of time/temperature or moisture?
0
10
20
30
250
500
1000
1500
2000
2500 25
0
500
1000
1500
2000
2500 25
0
500
1000
1500
2000
2500 25
0
500
1000
1500
2000
2500
Num
ber
of F
illet
s
Crack No Crack
3 weeks
No Aging
1 week 2 weeks
LLTS Cycles
No Preconditioning
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More Moisture Increased Cracking
• At same temperature / time more moisture (85°C/85%R.H.) is worse in
this case
10-12 mil Thick Honeywell JM88202 (Kester TSF-6522)
0
10
20
30
250
500
1000
1500
2000
2500 25
0
500
1000
1500
2000
2500 25
0
500
1000
1500
2000
2500 25
0
500
1000
1500
2000
2500
Num
ber
of F
illet
s
Crack No Crack
LLTS Cycles
85°C/30%R.H. 2 Weeks
85°C/85%R.H. 2 Weeks 85°C/30%R.H.
3 Weeks
85°C/85%R.H. 3 Weeks
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Moisture Not Always Bad • A little moisture seems to help (same time /temperature)• Dexter (Indium) 8-10 mil fillets
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10
20
30
500
1000
1500
2000
2500
3000 50
0
1000
1500
2000
2500
3000
Nu
mb
er
of F
illet
s
NoCrack
Crack
3 Months Ambient
3 Months N2 Cabinet
LLTS Cycles
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SUMMARY
• Moisture and time/temperature each affect underfill
properties
• Time/temperature may not always be bad (depends on
encapsulant)
• Sometimes a little moisture reduces subsequent cracking
• Relative contribution of time/temperature Vs moisture
depends on encapsulant/ flux combination
• Design/choice of accelerated test must account for this