Etched circuit board re-entrant coatings for solder repairs

Packaging of military electronic equipment frequently utilizes etched circuit boards. The need for insulating, or protective, coatings on etched boards is recognized, particularly if the circuit boards are to be used in even moderately severe environments. Protective coatings must maintain a high resistance between conductive paths on circuit boards, must maintain cleanliness, prevent corrosion, and occasionally the coating must contribute to the mechanical integrity of the completed circuit. To effect the desired performance, the typical list of coating properties is as follows: 1) High moisture resistance consistent with good recovery 2) Resistance to thermal shock 3) Good adhesion to coated materials 4) Uniform wetting properties 5) High insulation resistance 6) Long pot life 7) Short time and low temperature cure 8) Ease of processing.