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Response: How Do You Clean PCB Assemblies?
June 28, 2010 |Estimated reading time: 1 minute
– In response to the editor’s question, “how do you clean PCB assemblies?” that was posed in the May/June issue of SMT, Jade Bridges of Electrolube describes the relationship between no-clean PCBs and coating adhesion. The relationship is not good. Bridges explains why dewetting and poor adhesion can occur.
Although no-clean flux residues have been designed to be left on the board without cleaning, there are other issues aside from possible corrosion that need to be addressed. In the ‘no clean’ process the solids content of the flux is lower than traditional types, however they still contain rosin and activator which are not removed prior to the next process, such as coating or encapsulating of the PCB. Such residues, along with any other unwanted elements collected due to the missing cleaning stage, could cause issues with adhesion and possibly affect the performance of the protecting media applied.
With trends moving away from solvent-based conformal coatings, for example, the application of such materials has changed. Low solvent or solvent-free materials commonly have a higher surface tension than the solvent-based coatings and therefore any flux residues could cause issues with de-wetting or coating appearance/coverage in general. This in turn makes the application of coatings more difficult. Even in the case of solvent based materials, a difference in the amount or type of residues and the solvent base in the coating, could cause de-wetting or lack of adhesion in some areas. Lack of sufficient coverage or adhesion means a lower level of protection offered by the coating or encapsulant and therefore to ensure optimum performance, cleaning is still advised in most applications.
Contact the company at http://www.electrolube.com/.