INVESTIGATION OF IMPACT RESPONSE OF Pb-FREE ASSEMBLIES AND COMPARISON OF DROP TEST WITH CYCLIC 4-POINT BEND

摘要

The popularity and miniaturization of handheld consumer electronic products such as cell phones, notebook computers, and PDAs has enhanced their probability of being subjected to shock loads; hence making impact reliability study an important area of research. The transition from tin-lead (Sn-Pb) to lead-free (Pb-free) solder has pressed the electronics industry to characterize formulate essential design and process changes to counter the no-lead situation Investigation and improvement of the performance and reliability of the electronic packages is being addressed by many researchers. This paper deals with the investigation of the impact response, i.e., acceleration, bending strain, impact reliability, and the failure modes of Pb-free test vehicles subjected to high strain-rate environments. The test vehicles were subjected to impact loading conditions including the JEDEC standard impacts of 1500-g, 2000-g and 2900-g and input shocks at nominal amplitude of 1500-g with varying shock periods. Reliability under each shock loading condition was scaled with the relative kinetic energy and a simple relationship predicting failure for the test vehicle was developed. In addition, drop testing is compared with high-speed cyclic 4-point bend test and a scaling factor between the drop and bend reliability is determined. Failure analysis revealed that the failure mode for the test vehicle used in this study was independent of the shock amplitude, shock period, and component location; pad cratering on the board-side solder joint was seen in all the reliability tests. The proposed strategies that scale impact reliability could lead to the minimization of drop testing for design validation and product development, thereby reducing the overall cost and time to market.