Failure Mechanism and Testing of PCB Pad Cratering

Abstract

Pad cratering of printed circuit board (PCB) is becoming a prevailing issue encountered in the PCB assemblies which is accelerated when switching to leadfree process. These units with pad cratering may not fail during functional test as and raise potential failure in the field. This paper uses both experimental and finite element analysis (FEA) approaches to understand the pad strength and pad stresses. An extensive mechanical test by pin pull tests are performed on PCB materials. Cohesive elements are employed to simulate the bonding at the interfaces of pad, laminate and fibers. The results from FEA show that the laminate cracking can be successfully simulated. The design variables such as traces and solder fillet impact are also critical for pad cratering.