Ask the Experts
July 20, 2009
Can Residues Contaminate a Cleaning Solution?
We typically leave masking and Kapton tapes that fall off during cleaning in the bottom of our aqueous cleaning wash tank. Normally we will remove the trapped masking and Kapton tapes once per day.
Can the adhesives on the tapes in our tank contaminate the recycled solution?
Expert Panel Responses
The answer is an unequivocal "maybe." It depends on why the tapes fell off in the first place.
For example, if they fell off because of physical abuse, or they weren't attached too well to begin with (separate issues), then they probably won't affect the recycled solution.
If they fell off because of adhesive failure caused by the wash solution, then absolutely they will contaminate the recycled cleaning solutions. A wash solution (whether aqueous or solvent based) may attack an adhesive bond, in one of several ways.
Typically, aqueous wash solutions contain small amounts of detergents or co-solvents, to lower the surface tension of the cleaning solution. This allows for better "wetting"of the various surfaces on a subassembly, which is necessary to provide intimate contact of the cleaning components with these surfaces.
If the cleaning solution attacks the adhesive bond, it is usually due to either,
a. absorption of the detergent or solvent by the polymer materials in the adhesive, causing them to soften and/or swell (which weakens the adhesive bond); or,
b. it either extracts/dissolves components from the adhesive into the solvent, which not only weakens the adhesive bond, but also results in soluble materials in the cleaning solvent.
In the former case, there may be little, if any contamination of the solvent by leaving the tape in the solution. However, in the second instance, problems will occur. In this instance, repeated use of this same solvent, will increase the concentration of the soluble materials, if the adhesive actually dissolves in the solvent. This will subsequently increase the amount of residue left on the products, from the cleaning solutions!!
Usually adhesive attack occurs only at the edges of the adhesive bond, in contact with the solvents. By leaving the tapes in the solvent, the entire surface of the tape is now available for the solvent effects to occur more thoroughly.
Once something dissolves into a solution, it stays there, unless the solvent in that solution can be purified, say by distillation, or ultra-filtration/reverse osmosis processes. So, if something is dissolving, as each new board comes through, the concentration of the dissolved material increases.
If the tape falls off because of these latter defects..CHANGE TAPE! In any case, I'd suggest removing the pieces from the baths.
Jim Willimas is a PhD Chemist in Polymers and Materials Science. He specialize in printing, cleaning, inks, and coatings used in electronics manufacturng operations. Williams has more than 30 years experience.
Daily removal of such contaminants manually or through particle filtration (filter cartridges, filter bags,etc.) would help extending the bath lifetime of an aqueous chemistry up to some extent. However, we have to remind ourselves that there are two types of contaminants:
A) Suspended Type
B) Molecularly Dissolved Type
Aqueous cleaning agents based on surfactant technology suffer frequent bath loadings the most due to the accumulation of molecularly dissolved contaminants. Unfortunately the manual removal or removal via particle filtration could only target the "suspended" contaminants in the wash tank, and not the "molecularly dissolved" ones. Molecularly dissolved contamination is the reason why the surfactant-based aqueous cleaning agents face freauent bath loadings and require frequent bath changes.
Bath Loading Issues can be resolved :
a) Either through the use of modern aqueous cleaning agents that are non-surfactant in nature and based micro phase active ingredients
b) Or through the use of a proprietary advanced filtration system that's capable remove the molecularly dissolved contaminant from the cleaning agent molecules without removing the cleaning agent itself.
Application Technology Manager
Mr. Tosun has published numerous technical articles. As an active member of the SMTA and IPC organizations, Mr. Tosun has presented a variety of papers and studies on topics such as "Lead-Free Cleaning" and "Climatic Reliability".
Depends on the temperature of the solution. Typical tape adhesives will break down relatively quickly and could cause major problems for other units later.
Applications Project Manager
Quick Turn Flex Circuits LLC
James Mahoney is a Technical Operations Manager with a 20 year track record in managing new product introduction. He is a skilled leader, motivator and problem solver with a strong background in Product Knowledge and Engineering Management.