BOARD LEVEL FLEXURAL RELIABILITY TESTING AND FAILURE ANALYSIS OF PRINTED CIRCUIT BOARDS WITH WCSP PACKAGES

Abstract

Printed circuit boards, widely known as PCBs; are the skeleton behind every technology today. Electronics have integrated with every other engineering domain to improve the outcomes. It is very important that they remain intact in slightly extreme physical conditions. They are used in wide range applications which may lead to mechanical stress-strain in some conditions.

There are various boards with different kinds of packages on them. A 0.7mm thick board with WCSP; Wafer chip scale package is a prime specimen for my work. The research includes designing exact replica of given PCB into ANSYS and its reliability testing. A 3-point and a 4-point bend test are the perfect methods to test flexural response. All tests are carried out by ASTM standards. The reference of this test is an Instron™ machine, which is widely used for 3 and 4 point flexural test.

I replicated the exact model of given PCB in ANSYS-15. Being 0.7mm thickness it has several layers of different materials to it. In order to get accurate results, layers should be constructed properly. Also, the circuit boards have WCSPs mounted on it. According to standards, different set of loads are used for 3-point and 4-point bend tests.

Test results are then analyzed which predicts the failure points as a part of failure analysis. This gives an idea about mechanical reliability of PCB and its package. Failure modes in solder joints can be cross referenced from previous work to get accurate point of failure.

The results from the analysis are compiled from different tests under different loads. The conclusion from analysis suggests the optimum conditions for the structural stability of given PCBs, in other words performed analysis has successfully proven the reliability of PCB up to a certain limit without failure.