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SMT007-July2020

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96 SMT007 MAGAZINE I JULY 2020 Conformal coatings provide protection for electronic assemblies against moisture, dust, chemicals, and heat in a variety of end-use operating environments. When the removal and replacement of components due to field failures or manufacturing defects need to occur, this overlying coating layer first must be removed before being able to remove and replace a component. The choice of the correct removal method for a specific coating is neces- sary so as to not damage the PCB or neighbor- ing components. Incomplete coat- ing removal, such as on the underside of components, can result in pads being ripped off of the board when attempt- ing to remove the c o m p o n e n t d u r - ing the rework pro- cess. Incomplete removal of the coat- ing may mean that solder can "squirt out" from encapsu- lated reflowed sol- der during the rework process, thereby caus- ing bridging. These problems, as well as others, can result from improper conformal coating removal. There are numerous methods for the removal of conformal coatings from an electronics assem- bly. The methods and materials used to remove Removing Conformal Coatings for PCB Rework coatings are determined by the coating type, the hardness of the coating, as well as the size of the area requiring removal. The types of removal methods most often employed include chemi- cal stripping, peeling, heating, mechanical abra- sion, and laser ablation. For some coatings, chemical solvents are used to soften up or partially dissolve the coating. The removal agent is either rec- ommended or formu- lated by the coating manufacturer. Fol- lowing the manufac- turer's guidance will limit potential board and component dam- age, though it is always a good idea to test the removal agent on scrap boards. In many cases, the solvent can be selec- tively applied using a swab, with the sur- rounding area being masked off. Once the material is softened, the coating can be gently removed using a brush or wooden stick. In many cases, a neutralizer then needs to be added around the removal area to stop the continuing effects of the solvent. Ionic residues can be left behind on the board if the removal Knocking Down the Bone Pile by Bob Wettermann, BEST INC.

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