Effect of Shield-Can on Dynamic Response of Board-Level Assembly

Abstract

In order to protect the electronic components of electronic devices on a printed circuit board (PCB) against electromagnetic radiation, a conductive shield-can or box is normally attached to the PCB covering the electronic components. In particular, handheld electronic devices are prone to be subjected to drop impact. This means that the products would experience a significant amount of out-of-plane deformation along the PCB, which may cause stresses eventually resulting in solder joint failures. The attached shield-can could provide additional mechanical strength and minimize the out-of-plane deformation, especially where the electronic package is located. In this study, both the dynamic responses of the PCB and the characteristic life of solder joints with different shield-can designs were investigated, which are seldom explored by other researchers. In the board-level drop tests, a noncontact full-field optical measurement technique, digital image correlation (DIC) with images taken by stereo-high-speed cameras, was used to obtain full-field displacement data showing the dynamic responses of the PCB during the drop impact. PCBs with a fine ball grid array (FBGA) package were prepared with various types of shield-can attached. From the experimental results the effects of different shield-can types, varying in shape and size on the dynamic responses of the PCB, were analyzed. In addition, the number of drops to failure for each shield-can was also recorded by an event detector. Using ANSYS/LS-DYNA, an accurately validated finite element model has been developed. Then the stress analysis could be performed in order to study the failure mechanism by finding the maximum tensile stress of the solder joints during the drop impact and correlate the stress results with the characteristic life of solder joint.