Abstract
Conventional reliability tests for the evaluation of pad cratering resistance are mainly classified into two categories: the board level test and the joint level test. The board level test is to imitate the loading conditions during normal operation. However, this type of test is expensive and not flexible. The joint level test is used extensively in the industry because it has the advantages of lower cost, higher throughput, and more quantitative results. It also allows the elimination of confounding factors such as PCB and component stiffness. Therefore, it is always desirable to predict the board level performance by a joint level test. In order to achieve this objective, the correlation between the joint level and the board level tests must be fully understood. Nevertheless, a precise correlation between the two types of tests for pad cratering evaluation is yet to be defined.
This study investigates the pad cratering failure mode for the correlation of critical failure factors between joint and board level tests. An intermediate critical failure factor could be taken as a failure criterion in board level testing for failure detection. For verifying the validity of such a failure criterion, an experimental study should be performed. The 4-point bending test is chosen as the board level test for critical failure factor validation. In addition, an innovative pin shear test method is developed as the joint level test for failure factor detection. Both test methods are assessed by a series of parametric studies with an optimized process to ensure the accuracy of the results. From the results of the experimental study and simulation, the critical failure factor correlation is established between the board level 4-point bending and the joint level pin shear test. Using finite element analysis (FEA), the critical failure strain is identified from the pin shear test model and will be employed as the board level failure criterion. Subsequently the obtained failure criterion is verified by a 4-point bending model. As a result, this indirect correlation method can predict the board level failure with various geometric parameters.