SMTA International Conference Proceedings

An Interesting Approach to Yield Improvement

Author: Keith Bryant
Company: Technology and Business Consultant
Date Published: 9/22/2019   Conference: SMTA International

Abstract: The engineers responsible for Product Introduction always try to get the customer design to a standard that allows for high yield in production. However sometimes the design is fixed, the boards purchased already or there is another reason why the board has to be built as is.

In these cases, redesigning key stencil apertures or modifying other process parameters can make the difference between a low quality and expensive result and a high-level first-time pass rate and a cost-effective build.

These engineers noticed that despite making improvements in many areas the production yields were often lower than anticipated. This led to some further investigation of root cause and a design of experiment to look at these issues, with a view to improving the manufacturing process still further. It was discovered that issues related to problems hidden from view were by far the biggest cause of the reduction in yield.

So they started to use their 2D off line x-ray system to check the paste after component placement on the pre-production runs, instead of using it as an AQL tool and for checking production ‘first offs’.

This checking was in depth and required a high-resolution system with the ability to see angled views at maximum magnification.

By checking the solder paste dimensions and shape after component placement and then checking the finished boards for solder balls, solder joint quality and voiding levels were compared to the solder paste. Correlation was found between instances of poor quality and paste shape and volume. So, changes were made so that any problems could be addressed before putting the job into production. Quality was now built into the product at the start rather than bad boards inspected out and reworked to achieve acceptable results.

This has led to significant improvements in yield, reduced rework and scrap, proving that the methodology of this procedure offered significant process improvements.

Key Words: 

X-ray, Yield improvement, NPI, cost saving, Process improvement, fault reduction

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