Qualitative Model Describing Hot Tear Above VIPPO and Numerous Other Design Elements

Abstract

Over the last couples of years there have been numerous reports of a unique soldering failure resulting in a separation of BGA solder joints from the intermetallic compound at the interposer during reflow. In most cases, the failures were correlated with the use of Via-In-Pad-Plated-Over-Technology. Since the separation could be proven to occur during the phase transition from solid to liquid [1] the term Hot Tear was used. Even though this term is traditionally only used for tears during solidification its scope was extended to tears during any phase transition. Since the Hot Tear results in a very thin separation it is usually not inspectable, neither by means of X-Ray inspection nor by electrical testing, but results in very early field failures.

In this paper, the general mechanism for the formation of Hot Tears will be discussed and applied to numerous other design elements that can be found on Printed Circuit Board Assemblies. We will show that due to several industry trends e.g. VIPPO, heavy copper PCBs, buried vias, non-eutectic alloys, thinner components, thicker boards, via in pad, etc. the probability of Hot Tears is steadily increasing.