EFFECTS OF COMPONENT WARPAGE ON BOARD ASSEMBLY DEFECTS AND EFFECTIVE MITIGATION MEASURES
Authors: Peng Su and Guhan Subbarayan Company: Cisco Systems, Inc. Date Published: 10/24/2010
Abstract: Warpage of components during the reflow process is a key contributing factor to some of the common PCB assembly defects. One of these defects is the so-called Head-in-Pillow (HiP) defect, in which the BGA spheres only make partial contact with the solder paste at the end of the reflow process. Such defects can often pass X-ray and electrical test at the end of the assembly process, but they pose a significant risk for infant field failure because of the poor formation of the joints. In this paper, we will first present the data from recent investigations on the detailed forming process of the HiP defects and the effects of solder paste properties on the HiP failure rates. Our results suggest that by optimizing the flux system, the HiP defect rates can be effectively controlled. On the component side, structural design and packaging material both play important roles in determining the level of warpage. For some packages, a re-design of the package construction can significantly reduce the warpage level through the reflow process and thus eliminate the needs for mitigation measures on the assembly lines. The data from such work will also be presented.