Impact of Warpage Effects on Quality and Reliability of Solder Joints

Abstract

Printed circuit boards (PCB)and SMD packages are made from different materials which coefficients of thermal expansion can differ much. Hence, under thermal load, e.g. board assembly or at field conditions, PCB and package deformation and deviation from the initial state often occur as warpage. During board assembly this warpage can cause failures such as open solder joints and/or shorts of solder joints. In this paper, the use the of shadow moire technique will be introduced for capturing the warpage under thermal loads. Measurement results of single substrates and a selected BGA package will be shown. Furthermore, a design process for PCBs to be applied for investigation of the influence of assembly process parameter will be described. It is assumed that the applied variations and their influence on the assembly quality are linked by the equilibrium of mechanical forces between PCB, BGA and solder joint. Additionally, it is assumed that mechanical stress - especially in out-of-plane direction-may occur in the solder joints. These thoughts apply for soldering process as well as temperature cycling conditions. A finite element model was implemented to analyze the stress for the selected BGA under defined conditions and to investigate warpage impacts on reliability. Finally, a novel approach to measure the electrical functionality will be introduced addressing BGAs under test which come with a high number of connections.