The impact of SMD post baking process on the yield of printed circuit board assemblies

A baking process widely used in integrated circuit (IC) manufacturing prior to printed circuit board assembly reduces the moisture level in the permeable surface mount device (SMD). Baking prevents moisture-induced delamination and popcorn failures. However, baking can degrade component solderability, e.g., the intermetallic compound (IMC) Au/sub 0.5/Ni/sub 0.5/Sn/sub 4/ can grow and cause the solder ball falling off issues at ball grid array (BGA) board assembly. From a risk tradeoff perspective, a longer baking time at relatively high temperature is beneficial to drive out moisture but has the disadvantage of being sensitive to the formation of IMC (Au/sub 0.5/Ni/sub 0.5/Sn/sub 4/). It is difficult to simultaneously achieve an acceptable yield of print circuit board assembly (PCBA) due to the tradeoff between the critical moisture level and formation of IMC unless the baking process is optimally controlled. Moreover, as the "green" electronics are introduced into SMD with characteristically higher moisture resistance, the baking time must be increased. In this article, the moisture-induced failures and IMC induced solder ball falling off will be addressed, and the mechanism of IMC formation and its influence on solder bail strength will be analyzed. Both moisture and IMC removal by the optimization of the baking process and component reflow after baking will be described to achieve high PCBA yield.