Flex Performance • Flex Cracks are created when a physical displacement generates sufficient stress within the ceramic body to fracture the ceramic material. • Pb-Free soldering systems are less ductile resulting in industry concern about the effects on flex performance. Flex Test Procedure • • • • Parts mounted on test boards Flex at a rate of 1 mm/Second, to a maximum of 10 mm. Capacitance continually monitored. Continue to crack detection, defined as a 2% capacitance change. Test Fixture 90 mm Chip Fixed posts holding ends of board KEMET Electronics Corp. Ram moving 20 mm/min Individual Part Results • The calculated failure rate line is generated using the lower end of the Weibull distribution. 0603C224K4RAC SnPb Solder Pb-Free Solder • This line is used to predict the expected failure rate at a given displacement. • The calculated failure rate line is also used to calculate the amount of flex required for 1 PPM, 10 PPM, and 100 PPM failure rates. 0805C224J3RAB SnPb Solder Pb-Free Solder Comparative Flex Test Results • Red arrows point to instances of one solder having a clear advantage over the other. • • Findings don’t support prediction that Pb-Free solders will always result in an increased failure rate at a given displacement. Only in half the trials we see an improvement of one soldering system over another. Pb vs. Pb-Free (Flex) PN 0603C224K5RAC 0805C224J3RAB 1206C822K1RAC 1206C104J4RAB 1812C474K5RAB Solder Pcs SnPb 193 PbFree 194 SnPb 200 PbFree 199 SnPb 198 PbFree 197 SnPb 200 PbFree 200 SnPb 200 PbFree 197 Level 0.5% 1.0% 1.0% 1.0% 1.0% RR (%) Flex @ 1mm FR Flex @ 2mm FR Flex @ 3mm FR 94.05 <1 PPM 0.1% 8.9% 97.11 1 PPM 755 PPM 3.6% 98.33 <1 PPM 61 PPM 2.0% 96.40 <1 PPM 9 PPM 0.3% 96.39 <1 PPM 0.19% 82% 97.13 16 PPM 0.90% 31% 98.56 16 PPM 43.6% 90% 97.89 37 PPM 28.2% 92% 98.00 806 PPM 40.0% 93% 98.28 2 PPM 8.6% 93% Pb-Free Flex Test Conclusion • Pad Size has a direct impact on flex performance. Pb-Free • A smaller pad has better flex capability. • Pb-Free solders do not flow as well as SnPb solders, reducing the effective pad size. • The difference in fillets may have a larger impact on flex performance than the ductility of the solder. SnPb