Tools › Reliability › Physics of Failure › Solder Joint Fatigue › Example
IPC-SM-785 Appendix A: CC1820 chip capacitor solder joints, 25 to 85 °C daily cycles, tested at 0 to 100 °C
| Tool | Solder Joint Fatigue |
| Source | IPC (1992). Guidelines for Accelerated Reliability Testing of Surface Mount Solder Attachments. IPC-SM-785, Institute for Interconnecting and Packaging Electronic Circuits, Northbrook, IL. Section 4.3 (eqs. 3, 5), Section 4.4 (eqs. 12, 15, 16, 17) and Appendix A, Step-by-Step Example. |
| Level | Professional |
Problem
A CC1820 chip capacitor (CTE 6.8 ppm/°C, distance to the neutral point 0.080 in, solder joint height 0.005 in, F = 0.7, Weibull slope 4) is soldered with eutectic SnPb to a low-CTE board (10.5 ppm/°C) in a Navy computer that cycles daily between 25 and 85 °C (715-minute dwells). The design life is 10 years (3,650 cycles) at 0.5 % acceptable cumulative failures. Find the cyclic shear strain range, the fatigue ductility exponent, the mean and 0.5 % cycles to failure, and the acceleration factor to the IPC-SM-785 test of 0 to 100 °C with 15-minute dwells on an FR-4 test board (16.0 ppm/°C); the test gave 6,310 cycles for daisy chains of 8 capacitors.
Inputs to Enter
- Leadless with fillets, SnPb (ε′_f 0.325, c = −0.442 − 6 × 10⁻⁴ T_SJ + 1.74 × 10⁻² ln(1 + 360/t_D)), F 0.7, β 4, L_D 0.080 in, h 0.005 in
- Field: α_C 6.8, α_S 10.5 ppm/°C; board 25 / 85 °C, dwell 715 min, ramp 5 min, 365 cycles/yr, 10 yr, x = 0.5 %
- Test: 0 / 100 °C, 15-min dwells and ramps (24 cycles/day), test board 16.0 ppm/°C, 32 samples; measured 6,310 cycles, chains of 8 (m = 1/8); Norris-Landzberg SnPb constants
Answers
- Δα = 3.7 ppm/°C, ΔT_e = 60 °C, T_SJ = 55 °C; Δγ = 0.7 × 16 × 3.7 × 10⁻⁶ × 60 = 0.2486 %; c = −0.4679 (test: Δγ 1.030 %, c = −0.4160)
- N_f(50 %) = ½ (Δγ/0.65)^(1/c) = 73,331 cycles (book 73,000); N_f(0.5 %) = 73,331 × 0.2916 = 21,384 (book 21,400); margin against 3,650 cycles +4.86
- Model test life 10,611 cycles; the measured 6,310 chain cycles give 10,612 per component by eq. 16 and 73,337 / 21,386 field cycles by the transform (book 73,000 / 21,400)
- Acceleration factor: Engelmaier transform 6.91 field cycles per test cycle; Norris-Landzberg on Δα ΔT_e 6.05 (1.07 on ΔT alone); 1,453 equivalent mean test cycles (60.5 days), 672 failure-free cycles for 32 samples (28 days)
Notes
The tool's default inputs are this case; press Submit. Every printed value of Appendix A (both temperature swings, the leaded 68 I/O chip carrier with K_D = 52 lb/in, the test-result transforms) and twenty cells of the handbook's Table 2 are checked in test_solder_fatigue.php together with the Norris-Landzberg example of JPL Publication 16-3 and the numpy script References/Solder-Fatigue/checks/solder_check.py. The handbook prints the leaded joint area as 6 × 10⁻⁶ in²; its lives follow from 6 × 10⁻⁴ in².