Reflow process handles the (w)hole board

A novel process promises to increase efficiency for process engineers by eliminating the wave soldering process altogether.

Photo Stencil has developed a new process that can increase efficiency for process engineers by eliminating the wave soldering process altogether.

The new process is described in a paper "Intrusive reflow of lead-free solder paste", which is free to download from the Photo Stencil website.

Dr Bill Coleman, Vice President of Technology for Photo Stencil wrote the paper and ran tests to improve the printing process for lead-free materials.

In the intrusive reflow process, solder paste is printed on and around the through-hole area, as well as in the through-hole itself.

Through-hole devices are placed along with the SMT devices and processed together during reflow.

One objective of the study was to maximise the amount of solder paste printed into the through-hole (percentage hole fill).

With proper squeegee speed and squeegee angle, 100% hole fill was achieved for 63mil-thick boards and 85% hole fill for a 93mil-thick boards with a 6mil-thick stencil.

This resulted in good top and bottom fillets and continuous solder fill around the pins with a 6mil-thick stencil for both 63 and 93mil-thick boards for resistors, DIPs and four row header arrays.

"Results of the study are very encouraging since, with proper pin-to-hole ratios and screen printer setup, a 6mil stencil is successful in providing good lead-free through-hole solder joints", explains Dr Coleman.

X-ray pictures of paste hole fill and cross-section pictures of through-hole pins after reflow are shown in the paper, which can be downloaded from the Photo Stencil website.

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