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The Knowledge and Know-how Connection
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May 21, 2012
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More Ask the Experts »
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Cause of Blow Holes During Wave Soldering
What causes blow holes in tightly clinched radial lead LEDs? Why does loosening the clinch resolve the blow hole issue?
When wave soldering radial lead LED's, we are seeing blow holes. We have found that loosening the clinch applied by the placement machine resolves the blow hole issue.
Any ideas why the tight clinch may be causing blow holes?
M. J.
Expert's Panel Responses
Sounds to me that the tight clinch is acting as a dam preventing the flow of both the flux and the solder thru the vias. When you relax the clinch the materials flow smoothly eliminating the blow holes.
Edward Zamborsky
Regional Sales Manager, OK International Inc.
Mr. Zamborsky serves as one of OK's technology advisers to the Product Development group. Ed has authored articles and papers on topics such as; Low Volume SMT Assembly, Solder Fume Extraction, SMT Rework, BGA Rework, Lead Free Hand Soldering, Lead Free Visual Inspection and Lead Free Array Rework.
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It is possible that if the clinch is too tight then the LED will form/sit over the top of the hole not allowing the hot gasses to escape from the flux and other items during wave soldering. Loosening the clinch a little may help in allowing the gasses to escape from the top of the joint.
Greg York
Technical Sales Manager, BLT Circuit Services Ltd
Greg York has twenty two years of service in Electronics industry. York has installed over 350 Lead Free Lines in Europe with Solder and flux systems as well as Technical Support on SMT lines and trouble shooting.
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Most likely this is being cause by no escape route for the flux gas when the PCB enters the wave. If the clinch is too tight or there is no escape path the flux gas will escape out the bottomside barrel when the unit exits the wave.
A tight clinch will pull the LED tight/flush to the board surface and not allow for the gas to escape leaving what looks like a blow hole.
I hope this helps.
John Norton
Eastern Manager, Vitronics Soltec
John Norton started his soldering career in 1983 for Hollis Engineering. He has also worked with Electrovert as a technical training manager and Vitronics Soltec for the last ten years. He has held various technical development and sales positions.
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Use the form below to submit a comment.
The crystal was providing a seal so the flux couldn't escape. That must've been causing a small gas bubble to form around the pad area and prevented solder from reaching the pad. We use a "dip" type solder machine made by Unit Design. That was really a fun puzzle to solve!
Patrick Muldoon, JPD Controls, Inc