Ask the Experts
October 5, 2009 - Updated
October 5, 2009 - Originally Posted

Concerns with High Humidity.

Will higher than normal humidity in our facility affect reflow soldering? What impact might it be? Are there special concerns regarding our solder pastes when they are exposed in a high humidity environment?

S. A.

Expert Panel Responses

High humidity can have an effect on reflow soldering. This is typically the case for Water Soluble Solder pastes. When making a water soluble paste our goal is to leave a residue behind that is water soluble. This makes the paste hydroscopic thus the paste will absorb moisture. Because of this we can have issues with slump, solder balling, etc... To minimize this some companies like ours has developed new water soluble pastes that are less soluble and more water washable. The downside in this is that the flux residue isn't as easily removed but in most cases the positives of being less hydroscopic outweigh the negatives.

Mike Scimeca
FCT Assembly
Mike Scimeca created FCT Assembly after the purchase of Fine Line Stencil, Inc., and consists of two major operations: stencil manufacturing and the manufacturing of electronic assembly products such as solder paste, flux and solder bar.

High Humidity will affect solder finish specifically longtermand paste deposition/solder wetting during production shortterm. You should determine what solder finish/system you have with your assembly, but short and long term answer to this question is, YES. Concerns about solder paste, involve moisture absorption with the fluxes used. There are different organic and synthetic fluxes on the market that are more or less hydroscopic in nature. We have had good performance with synthetics, but we are not a high humidity environment. Our facility in Asia also uses synthetic chemistries for this reason, and have had good results.

Rodney Miller
Capital Equipment Operations Manager
Specialty Coating Systems
Rodney is currently Operations manager at SCS coatings, Global Leader in Parylene and Liquid Coating equipment. Rodney applies his BS in Computer Integrated Manufacturing from Purdue University, along with 20+ years of Electronic manufacturing and Equipment Assembly, to direct the Equipment business at SCS Coatings. "We provide unique, value added coating equipment solutions for our customers". Including conformal, spin and Parylene coating expertise.

Solder pastes can be affected by high humidity in the plant. The traditional upper limit where pastes may start to show signs of being impacted by higher humidity would be around 55-60% RH, but this value may vary from one solder paste product to another. Some pastes have been designed to accommodate a higher humidity - even up to 80-85% - and others will have problems as low as 50%. My recommendation is to speak with your solder paste supplier and review the acceptable range of humidity for the paste that you are using. There area few possible failure modes that you may see with the elevated humidity in your facility. They include micro-solderballs, lower paste viscosity, worsening hot slump (inducing bridging defects) and decreased solder paste coalescence & wetting behavior.

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.
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