Head and Pillow SMT Failure Modes

Dudi Amir, Raiyo Aspandiar, Scott Buttars, Wei Wei Chin, Paramjeet Gill
Intel Corporation, Hillsboro, OR, USA
Kulim, Kedah, Malaysia

With the electronics manufacturing industry moving to lead free soldering and with Ball Grid Array (BGA) packages becoming thinner and having finer ball pitches, there is an increase in the incidences of a SMT non-wet type of defect known as head-and-pillow (HnP). This defect is hard to detect after SMT assembly and most likely will fail at the customer. There are a number of causes for this type of defect. They can be categorized into process issues, material issues, and design related issues.

This paper will examine these different causes for the head-and-pillow non-wet defect after surface mount assembly and the mechanism to create this defect. The paper will also describe the critical factors that are affecting head-and-pillow. It will discuss how to identify the root cause and give potential solutions to prevent the defect and have a robust SMT assembly process.

HnP is not an easy defect to solve since there are many failure modes that can cause this defect. This paper describes all known failure modes that can create and modulate HnP. Understanding these modes can be used to solve an existing HnP problem or avoid it from happening completely. In many cases, the HnP problem is very complex and consists of more than one failure mode at a time.

The best problem solving approach would be to identify which are the primary failure modes that need to be addressed to solve the problem and how to make the assembly process more robust and not as sensitive to these modes. Using a nitrogen atmosphere in the reflow oven is an effective way to mitigate most of these problems and reduce or eliminate HnP on some of the failures modes. But, it will certainly not solve all HnP issues.