Analytical k-Factor Model for Monotonic Four-Point Bend Test Design

Advanced electronic systems are increasingly integrated into various transportation, communication, and industry applications. The mechanical reliability of these electronic systems, especially their solder interconnects, is vital. The mechanical strength of the package and board interaction with the solder joint is often characterized by monotonic four-point bend testing. The bending strength of the interconnects relates to their ability to handle mechanical loading from assembly, test, handling and field-use operations. Recently, there are efforts to better understand the influence of printed circuit board assembly (PCBA) and monotonic four-point bend test parameters on solder joint interconnect mechanical strength. In addition, a better correlation between the global strain and local critical strain is desired. The purpose of this work is to develop an analytical model capable of quickly and accurately predicting response in monotonic four-point bend test design for ball grid array (BGA) devices. Models were developed for strain intensity factors k1 and k2 based on five key parameters identified by Spearman rank correlation analysis. The models were observed to be highly accurate with 5% and 4% error for k1 and k2, respectively, when compared to randomly excluded test points. The model will be referenced in the next IPC/JEDEC-9702 revision, improving accuracy and repeatability of the test method. Additionally, the model can be used by designers, early in the test board design process to assess flexural bending strength impacts of design changes.