Ask the Experts
September 14, 2017 - Updated
October 15, 2007 - Originally Posted

Cleaning residue after wave solder process

We are currently using "wave solder pallets" for our wave soldering process because there are SMT parts on the solder side. After the boards come out of the wave, we notice white marks (stains) on the board. We are using lead-free solder and no-clean flux. These marks seem excessive, and cosmetically the boards do not look clean. Is there any cleaning process available that will remove these marks?

J. P.

Expert Panel Responses

The presence of white stains is typically the result of partially removed flux residue. This occurs from inadequate post solder cleaning. The occurrence of white residue on SMT parts after the wave soldering process may be caused from the solvent content in the wave solder flux. The solvent content in the wave may partially dissolve the resin content in the surface mount flux residue surrounding the surface mount parts. This will leave a while crystalline residue commensurate with the flux residue surrounding the SMT components. To remove the white residue, a post soldering cleaning step is required. To confirm root cause, you can send a sample board to Kyzen's Application Lab for analysis. We will confirm that the white residue is flux residue. The lab personnel will provide you with the proper cleaning procedure for removing these residues based on your current method of cleaning. Address: Kyzen Application Lab 430 Harding Industrial Drive Nashville, TN 37211 Attention Charlie Pitarys

Mike Bixenman
Kyzen Corp.
Mr. Bixenman is the CTO for Kyzen Corp. Kyzen Corp. is a leading provider of engineered cleaning fluids for high technology manufacturing environments.

Permali, the maker of Durostone pallet material, recommends a method for cleaning solder pallets. See:

Bill Schreiber
Smart Sonic Corporation
Mr. Schreiber developed the original ultrasonic stencil cleaning process in 1989. Obtained the only EPA Verification for specific parameters of Environmental Safety, User Safety and Cleaning Efficiency for a stencil cleaning process.

There was not any mention of the type of no-clean flux used in the process or the amount of flux being deposited on the board. It sounds like there is a lot of flux being applied and it is not all getting removed during the wave soldering process. No-clean flux does not mean no-residue, so the more flux that is applied the more residue will be left. If you are using a foam or wave fluxer you are stuck with what you have because you can not control the amount of flux applied with those fluxers. If you have a spray fluxer then you can reduce the amount of flux applied to the board to a point that you still get good results but leave less residue. I would also contact your flux vendor to look at this issue and determine if what you are seeing is normal or not for the type of flux you are using.

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.

You are correct, white residues on the pallets and the boards are unattractive and unprofessional, so everybody always has to work to minimize or even eliminate these results. While there are many sources of white residues, the most common source of white residues are the halites in the no-clean fluxes which have not been encapsulated by the heat of the wave solder system. As such, those salts are open to the atmosphere and can cause corrosion and premature failures. To clean the pallets, I would recommend a strong, noncorrosive, aqueous based cleaner (you don't want to use flammables around a wave solder machine, and the fast-drying solvents would evaporate too quickly around the heat of the systems). While there are several good ones on the market, MicroCare makes an excellent product which is safe for people and the pallets. The "Reflow Oven Cleaner" is nonflammable, slower-drying, and actually uses the heat of the pallet and the wave soldering system to improve it's cleaning. MCC-ROC is available in refillable pump sprays, gallons, pails and drums. To clean the boards, now this is a trickier issue because we can't leave any residues, you require faster drying so your people aren't wasting too much time on this process, and you can't use a really strong cleaner (like the Reflow Oven Cleaner) because you'll worry about materials compatibility. One excellent option is PowerClean™ from MicroCare. PowerClean is just about as strong a cleaner as you can get in a nonflammable, residue-free defluxer. Importantly, it was engineered specifically to remove the white residues frequently produced by lead-free materials. Not only will it remove those residues, it actually precludes their formation. So most customers will find PowerClean a great choice on lead-free PCBs. MCC-PW2 is available from all authorized MicroCare distributors around the world.

Mike Jones
Vice President
Micro Care
Mr. Jones is an electronics cleaning and stencil printing specialist. Averaging over one hundred days a year on the road, Mike visits SMT production sites and circuit board repair facilities in every corner of the globe, helping engineers and technicians work through the complex trade-offs today's demanding electronics require.
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