Can we pour left over paste into the solder pot?

What is the effect of pouring left over solder paste from a screen printer into a wave solder machine pot? Is the flux capable of contaminating the pot, or will it be evaporated rapidly with the pot temperature?? Is this a normal practice?

M.S.

Expert Panel Responses

Solder paste scrap should never be placed in a solder pot. The solvents in the solder paste may flash and create a fire hazard. This is not at all a normal practice in industry. Spent solder paste should be placed in buckets and disposed according to local regulations.

Brian Smith
General Manager - Electronic Assembly Americas
DEK International

Mr. Smith has been supporting customers in the electronics assembly industry since 1994. His expertise is focused on solder paste printing and reducing soldering defects. He holds a BS in Chemical Engineering and an MBA in Marketing. He has authored several papers in trade magazines and at industry conferences. He is an SMTA Certified Process Engineer.

Don't really want to do that, your much better off if you just sell it back to your paste vendor. If the alloy is the same it won't cause a problem but will cause more maintenance with the build up of the solder paste flux. But then again if you are talking only small amounts then no problem.

Greg Hueste
Senior Applications Engineer
Speedline Technologies

Greg joined Electrovert in February 1984. Based out of the Electrovert applications laboratory in Camdenton Missouri, Greg has been in the process applications support role since 2000. His primary responsibilities include providing process and machine applications support for the wave soldering lines as well as process, machine and operations training. He also provides applications support for the reflow and cleaner lines. Greg is a PBET certified trainer and holds two patents on wave solder nozzle design.

Adding solder paste to a wave pot can be a messy practice. The flux in paste is approximately 50% by volume, so half of the paste added needs to burn off. Some of the material especially no-cleans in high concentrations can catch on fire. The existing residues can be very gummy. I would not recommend this practice. This could be dangerous and could cause a lot of residue to be trapped in the pot depending on amount of paste added and how it is added. However if it is done properly the wave pot will be nice and clean.

Karl Seelig

Deck Street Consultants

In his 32 years of industry experience, Mr. Seelig has authored over 30 published articles on topics including lead-free assembly, no-clean technology, and process optimization. Karl holds numerous patents, including four for lead-free solder alloys, and was a key developer of no-clean technology.

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