Mechanical Characterization of SAC305 and SnPb36Ag2 BGA Assemblies Under Static Flexural Loading

Abstract

Static bending-induced solder joints damage is a main reliability concern for aerospace and military industries whose Printed Circuit Board Assemblies (PCBAs) are required to remain functional under flexural loading. In order to dissipate heat in an equipment, it is common to install thermal gap pads on electronic packages. When compressing thermal gap pads during the fixture process, the PCBA can bend and solder joints can therefore crack if the deflection is too important. This paper reports the durability of 96.5Sn-3.0Ag-0.5Cu (SAC305) and 62Sn-36Pb-2Ag (SnPb36Ag2) Ball Grid Array (BGA) assemblies under static flexural loading at -55°C, 20°C and 125°C. As electronic equipment can be stored at high temperature for prolonged durations, some SAC305 test vehicles were also aged at 125°C for 192 hours. For each test configuration, the bending tests were conducted at a ramp-rate of 2 mm/min and the central displacement-to-failure was measured. Finite Element Modeling (FEM) analysis was conducted considering a global-local approach and the transfer function between the central displacement-to-failure and the local PCB strain near the critical solder joints was determined for each test configuration. The results give the necessary data for designers to assess whether a specific PCBA design subjected to static bending is at risk or not.