Investigation of the correlation of peel strength and pad adhesion measurements using different printed circuit board base materials

Abstract

The adhesion of pads to the PCB base material has, along with the assembly method, an essential impact on the reparability of components without damaging the PCB. Various test methods have been developed to evaluate Cu adhesion to different base materials. Two of those methods, the pad adhesion test and the peel strength test, have been investigated with the objective of finding the degree of correlation between the results obtained. A correlation of both methods would allow the use of the simpler measurement to obtain data about the more interesting parameter. In the test plan, the main factors influencing peel strength and pad adhesion are discussed, and the test matrix for both the initial and the main test is shown. The pad adhesion and peel strength measurement methods are explained, along with design of the test boards. The influence of the period between sample preparation (conventional print and etch process) and measurement, stripe width and stripe orientation at the base material on the peel strength values and the effect of pad shape, number, size and pattern on the pad adhesion data is shown and discussed. After fixing the test parameters, the main measurements were made using a conventional FR4 material. A correlation of pad adhesion and peel strength values has not been found due to the different fracture interfaces resulting from the different kinds of stress. A second test using Speedboard N/sup TM/ material showed a correlation of peel strength and pad adhesion data, based on the same fracture mode despite different kinds of stress.