Influences of SMD Package and Substrate Warpage on Quality and Reliability –Measurement, Effects and Counteractions

Abstract

The coplanarity difference between a substrate or printed circuit board and a SMD package is a very important characteristic. It depends on the warpage of package and substrate and is caused by their heterogeneous build up. The materials involved – namely polymers, metals, ceramics etc. – come with differing coefficients of thermal expansion. This leads to temperature depending deformations due to thermal loads during assembly or field use. These warpage called deformations appear as twist and bow. A significant coplanarity or warpage mismatch can lead to quality issues during manufacturing. Solder joint shorts, pad cratering and open solder joints like head-inpillow or pin-in-pillow are examples of typical failure types. Also, additional mechanical stress especially in z-direction may occur in the solder joints and cause early failure under use.