Board level drop test simulation using explicit and implicit solvers

Abstract

Drop test is transient and dynamic in nature. Therefore, explicit solvers such as ANSYS/LS-DYNA and ABQUAS Explicit are employed extensively for the free fall analysis [1-3]. To avoid complexity in modeling contact event, a simplified Input-G method was suggested [4-5]. However, the explicit algorithm suffers from poor numerical stability unless a very fine time increment is used, which means that it is very costly. Implicit solver, on the other hand, is an affordable alternative. Nevertheless, it is not compatible with the direct application of acceleration profile without additional treatment of the boundary conditions [6]. To overcome these numerical obstacles, a dynamic-static modeling approach was introduced where a dynamic analysis is performed to calculate the maximum bending moment of the printed circuit board (PCB), which is used as boundary conditions of the consecutive static analysis of the stress in a detailed local model [7]. This paper investigates the simulation methodologies of board level drop test using both explicit and implicit solvers. It demonstrates that explicit solver could be replaced by implicit solver to model the current industrial specified drop test, which is a moderate transient process, as both solvers gave similar results in terms of peeling stress of solder joints. Moreover, it is possible to model complicate material behavior as well as geometric details, which are extremely difficult for dynamic modeling using explicit solver unless sub-modeling or mass scaling techniques are applied. The results of the numerical analysis are compared and discussed in details.