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.
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 over thirty two years of service in Electronics industry. York has installed over 600 Lead Free Lines in Europe with Solder and flux systems as well as Technical Support on SMT lines and trouble shooting.
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.
Ed Zamborsky is a Regional Sales & Technical Support Manager for Thermaltronics, located in New York. His position requires frequent customer visits throughout North America and the Caribbean and his position encompasses not only sales but the role of trainer and master applications engineer for all of Thermaltronics products. His expertise includes such specialties as hand soldering, convection and conduction reflow techniques, array rework, fluid dispensing equipment, and fume extraction. Ed has authored many articles and has presented many papers on topics such as; Low Volume SMT Assembly, Solder Fume Extraction, SMT Rework, BGA Rework, Lead-Free Hand Soldering, High Thermal Demand Hand Soldering, Lead Free Visual Inspection and Lead Free Array Rework.
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