Solder Paste Ingredients vs. Performance

Frank Murch, Derrick Moyer, Krupali Patel, John McMaster, Steve Ratner, Martin Lopez
Heraeus Materials Technology, LLC, West Conshohocken, PA, USA

With the majority of the circuit assembly industry focused on Lead-free soldering, Tin-Lead has been overlooked for a long time. So when paste formulators set out to create a brand new Tin-Lead platform, they wanted to use the most modern materials and methods available.

Synthetic or highly purified raw materials have displaced many of their naturally occurring predecessors as primary ingredients due to their superior stability, and the old trial and error experimental strategies that were used to develop past generations of solder pastes have been replaced with sophisticated Design For Six Sigma tools. The result is a better understanding of the relationships between a paste's composition and its behavior in print and reflow processes.

This paper provides a brief overview of the new solder paste development and benchmarking processes, and introduces a new method for assessing a solder paste's robustness against Head-In-Pillow defects.

The Design For Six Sigma process has produced a reliable, data-driven method of characterizing the influence of raw materials on multiple aspects of solder paste performance. The latest test developed under the DFSS program assesses a paste's robustness against Head-In-Pillow defects.

The new test method increases the opportunity for oxidation on the surfaces of both the balls and the paste deposits. In addition to the atmospheric exposure due to package warpage during reflow, the test exposes the surfaces throughout the entire pre-liquidus phase of the the soldering cycle by propping up the device on its own solder balls.

The test has consistently shown clear results, and has proven to be very successful in predicting which raw materials help or hinder HIP prevention. It has become an integral part of solder paste evaluations