The effect of pcb flexural modes on dynamic reliability of ball grid array packages

To enable richer consumer experiences, more IC chipsets with various functionalities and greater memory density have been deployed in the limited phone board area. A new generation of surface mount devices such as fine pitch BGA, package-on-package (POP), and wafer-level packaging, are being introduced to reduce board area for the given feature set. Board level reliability of new packages is one of the most important aspects to system performance under impact loadings. The dynamic reliability characterization of the components has been used as a basis for predicting a system (phone) level reliability. Package characterization methodologies must be designed to capture the interconnect failure modes of the actual IC packages commonly encountered in phone drop conditions for better prediction of phone-level reliability. Strain gage measurements and finite element analysis (FEA) of drop tests performed on portable electronic devices revealed mixed printed circuit board (PCB) flexural modes during impact. Dynamic planar and spherical bend tests were developed to study the effect of PCB bend mode on solder interconnect reliability. In the present study, a planar flexural mode was generated through utilization of a 4-point bend test fixture, and a spherical bend test was developed to achieve an equi-biaxial strain state at the vicinity of a corner solder joint as opposed to predominantly uni-directional strain state in four-point bend test. A failure prediction model based on connector finite element modeling was developed to understand the significantly different solder joint reliability under the two loading conditions. The ability of the new modeling technique to accurately predict failure of solder joints under different loading conditions was appreciated showing excellent agreement to failure analysis of actual test samples. The new methodology can enable efficient and accurate means of assessing package reliability under various conditions that simulate portable electronic devices being dropped in the field.