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Intrusive Reflow Challenges Wave Soldering
December 31, 1969 |Estimated reading time: 1 minute
A process referred to as "Intrusive Reflow" for lead-free solder paste reportedly will increase efficiency by eliminating the wave soldering process. Bill Coleman, Ph.D., authored a technical paper detailing the process, which outlines proper pin-to-hole ratios and screen printer settings for successful lead-free thru-hole solder joints.
With Intrusive Reflow, solder paste is printed on and around the thru-hole region as well as in the thru-hole opening. SMT and thru-hole devices are then placed at the same time during assembly then reflowed together in one step. Coleman asserts that the process enables continuous solder fill around pins with a 6-mil-thick stencil for 63- and 93-mil-thick PCBs. It was tested with resistors, DIPs, and four-row header arrays.
The Intrusive Reflow study was conducted to determine methods for maximizing solder paste quantities printed into the thru-hole. Proper squeegee speed and angle resulted in 100% hole fill on 63-mil boards and 85% hole fill on 93-mil boards, both with a 6-mil-thick stencil. The fill percentage and top and bottom fillet formations were encouraging, said Coleman. Printing lead-free solder paste for thru-hole and SMT devices simultaneously could improve process times for mixed assemblies, according to the company.
X-ray images of paste hole-fill and cross-sections of thru-hole pins post-reflow are available in the full study on the company's Website. Photo Stencil, Colorado Springs, Colo., www.photostencil.com.