MASK APPLICATION TECHNOLOGY.

A primary goal in automated soldering of printed wiring assemblies is to achieve uniform wetting of all solderable metal surfaces. When these surfaces must remain unwetted, such as with gold contact fingers or plated through holes that must be reserved for post wave assembly, an effective and efficient masking procedure must be implemented. This paper discusses the types of masks, compares manual and automated methods of mask application, describes screen printing and the use of a water soluble tape. It is concluded that when aqueous cleaning techniques are employed, water soluble masks can dramatically improve operating efficiency by eliminating the need for manual mask removal. By combining the use of a soluble mask and automatic dispensing, additional savings are accrued by reducing application time and increasing masking accuracy. Criteria for mask selection should include shelf life, ease of application, solubility of the mask deposit after extended storage, and the ability to protect the underlying circuit.