One Big Cause of Assembly Problems
Up to 75% of assembly problems stem from paste printing. This report reveals variability in aperture size between various stencil manufacturers.
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Authored By:
Ahne Oosterhof
Eastwood Consulting Hillsboro, OR, USA
Stephan Schmidt
LPKF Laser & Electronics Tualatin, OR, USA
Summary
Many articles have been published indicating that 60 to 75% of all board assembly problems stem from solder paste printing. The important outcome from the printing process is to get the correct amount of solder deposited in the right place. A significant part of that solution is the stencil and its correctness depends on how well its manufacturing process is controlled using proper machines, materials, methods and manpower.
The quality of the stencil can be measured a number of ways: smoothness of the cut wall, material quality, thickness and thickness uniformity of the material, proper aperture location, proper aperture size. This report will show that significant variability exists in aperture size precision between various stencil manufacturing sources.
Conclusions
The above measurement results indicate that without knowing the manufacturing method used to produce the stencil the AR may vary between 0.7 and 0.53, possibly resulting in very poor print performance. However based on paste release test results with the best choice of stencil manufacturing method and stencil material it may be possible to get acceptable paste deposits even with lower AR values.
Initially Published in the IPC Proceedings
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