The electronics assembly market has experienced a material shift from lead (Pb) based solders to Pb-free solders. This is a result of the widespread adoption of Reduction of Hazardous Substances (RoHS) legislation and practices in commercial industry. As a result, it is becoming increasingly difficult to procure commercial off-the-shelf (COTS) components with tin-lead (SnPb) solder balls or finish.
There are countless challenges in making mobile electronics more reliable, including the thin form factor of cellphones and tablets that is forcing mobile computing packages to get thinner. Using coreless ball grid array (BGA) substrates decreases the overall height of the component, but it presents manufacturing challenges and potential reliability concerns when subjected to thermal cycling. This study presents results from tests performed on a coreless 25 mm by 27 mm BGA package with a relatively large die and stiffener ring that survived over 8,000 temperature cycles without failure. In order to investigate the reason behind this robust performance the coefficient of thermal expansion (CTE) of the part was measured using digital image correlation (DIC). The DIC results indicated that this combination of die size, package size, and stiffener ring reduces the CTE mismatch between the BGA package and printed circuit board (PCB).
Since 2006 RoHS requirements have required lead free solders to take the place of tin-lead solders in electronics. The problem is that in some environments the lead free solders are less reliable than the older tin-lead solders. One of the ways to solve this problem is to corner stake, edge bond or underfill the components. When considering what mitigation technique and material to use, the operating conditions must be characterized. The temperature range is important when selecting a material to use since the glass transition temperature (Tg) and coefficient of thermal expansion (CTE) are important properties. If improperly chosen, the mitigation material can cause more failures than an unmitigated component.