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Physics of Failure

2 tools in the Reliability area.

Solder Joint Fatigue

Thermal-cycling fatigue life of surface-mount solder joints by the Engelmaier-Wild creep-fatigue model in the form of IPC-SM-785: the cyclic shear strain range from the distance to the neutral point, the solder joint height and the CTE mismatch (the leadless form, or the compliant-lead form with the diagonal lead stiffness), the fatigue ductility exponent from the mean cyclic solder-joint temperature and the dwell time, the mean cycles to failure, the cycles at an acceptable failure fraction from the Weibull slope, and the margin against the design life. The field cycle and an accelerated test cycle (IPC-9701 TC1 to TC5 or the IPC-SM-785 0 to 100 °C test as presets) are compared by the Engelmaier acceleration transform and by the Norris-Landzberg equation (SnPb constants, or the SAC constants of Pan et al. or Vasudevan and Fan), giving the test cycles and days that stand for the design life and the failure-free cycles for the sample size; a measured test life is carried to the field. Solder parameters for SnPb and, tentatively, SAC405/305, SAC205, SAC105 and SnAg from Engelmaier (2010). The default case is the step-by-step example of IPC-SM-785 Appendix A (a CC1820 chip capacitor on a low-CTE board, 25 to 85 °C daily cycles, tested at 0 to 100 °C), whose printed strain, exponent, lives and test-to-field transform the page reproduces.

1 worked example reproduced, listed on the tool page.

PCB Vibration and Thermal Cycling Fatigue

Vibration fatigue screening of a printed circuit board assembly by the Steinberg relations as mathematics: the board's fundamental frequency from the plate formula with Warburton's coefficients for any supported, clamped or free edge set (exact for all edges simply supported, stiffening ribs as an entered factor, component mass smeared), the random-vibration response at the fundamental by Miles' equation with Q = √f_n or an entered amplification, the 3σ relative displacement against the 0.00022 B/(c h r √L) limit for 20 million cycles with the position factor r and the component constant c as entered values, the life by the slope-6.4 displacement relation, the three-band (1σ, 2σ, 3σ) Miner sum and the narrow-band Rayleigh sum beside it, the resonant sine dwell, the half-sine shock response by direct integration of the damped oscillator, the component lead as a plane frame loaded by the board curvature and the body's inertia with the lead stiffness, the component frequency and the octave rule, an isolator's transmissibility, sway space and the attenuated spectrum, and the plated-through-hole barrel strain from the z-axis expansion mismatch with a Universal Slopes life. The input PSD is entered as breakpoints (GEVS and MIL-STD-810H profiles fill the box) and integrated exactly on log-log segments. Solder joint thermal fatigue is in the Solder Joint Fatigue tool. Default: a 6 × 8 in, 0.062 in FR-4 board, simply supported, 0.04 g²/Hz from 20 to 2,000 Hz, a 1 in DIP at the centre (illustrative).

1 worked example reproduced, listed on the tool page.

Other Reliability sections

Life Data · System Models · Growth and Testing · Maintainability and Availability · Safety Analysis