related document
quality & reliability
Low Melting Point Phase Study
Effects of the Bi Contamination on Sn/Pb solder (Smt, Sept. 2000, p91-94)
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Possible low Tm Phase(Theoretical)
- 16Sn/32Pb/52Bi: 96°C
- 43Sn/57Bi 139°C
- 43.5Pb/56.5Bi 125°C
- 2% Bi Adding: Increase the strength and plasticity
- 5% Bi Adding: Increase strength, decrease the plasticity
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The reason for high Time-to-Failure(5% Bi Adding):
Fatigue strain range(?=0.2%)for Nf is well below the plastic strain at fracture( p??12%)
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Sample prep.: SnBi lead finish+SnPb paste(48TSOP) detach the joint part with knife(As mounted state)
sample weight: 23.85mg/48 leads Module cond.: 265°C Peak(During IR Reflow) -
Analysis: DSC2910(TA Instrument), 5°C/min(ramp up)
cell constant: 1.1387 - Results: No low Tm Phase(SnPbBi) was detected.
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Conclusion :
Low temperature binary and ternary eutectics will not exist unless Bi content exceeds the primary solid solution. (23.5Bi in Pb, 21Bi in Sn) Bi atoms up to 5% are expected to enter the Sn crystal lattice, Pb crystal lattice or both.
