Indium - Six Sigma® Techniques for Solder Paste Selection

Our thanks to Indium Corporation for allowing us to reprint the following article.


By Ronald C. Lasky, Ph.D., PE and Wang Ming, Indium Corporation; Professor Daryl Santos, Ph.D. and Aniket A. Bhave, Binghamton University


Numerous studies have shown that greater than 60% i of end of line defects in SMT assembly can be traced to solder paste and the printing process. Reflowing adds another 15% or so. In light of this fact, it is surprising that no simplified procedure for solder paste evaluation has been documented. This paper is about such a procedure.

By using designed experiments and the measurement of critical solder paste-related process metrics, we were able to develop a solder paste evaluation procedure that maximizes information about the solder paste and its processability while minimizing experimentation. While using only 12 stencil printed PWBs, we were able to generate statistically significant results that enabled us to rank solder pastes according to their performance. Response metrics that were investigated were print volume and definition before and after pause, squeegee hang up, slump, tack, release from aperture, and solder joint quality.

In addition, we found such variation in solder paste volume repeatability that this criterion alone can be used as a screening procedure.


The heat of modern Six Sigma® Techniques is DMAIC. DMAIC refers to a data-driven strategy for improving processes, and should be an integral part of any company's Six Sigma Initiative. DMAIC is an acronym for five interconnected phases: Define, Measure, Analyze, Improve, and Control.

Each step in the cyclical DMAIC Process is required to ensure the best possible results. The process steps:

1. Define the Customer, their Critical to Quality (CTQ) issues, and the Core Business Process involved.
a. Define who customers are, what their requirements are for products and services, and what their expectations are.
b. Define project boundaries - the stop and start of the process.
c. Define the process to be improved by mapping the process flow

2. Measure the performance of the Core Business Process involved...

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