TABLE OF CONTENTS The manufacturing steps involved in coating an electronic part or assembly are numerous; each is essential to the performance and reliability of the end product. Among these steps are:
Masking (if necessary)
Cleaning
Surface preparation
Preparation of the coating
Application of the coating
Drying and curing
Mask removal
Inspection
Rework (if necessary)
Numerous choices are possible for each process step and trade-offs must be made based on the part to be coated, the expected performance of the coated part, yield and cost, and equipment available. The manufacturing engineer must be concerned not only with the traditional process variables such as yield, cost, and equipment, but also with the many local, state, federal, and even global regulations concerning volatile organics, toxicity, and flammability.
Often, not all the components of an assembly require a coating; in fact, some surfaces must be left uncoated, for example, surfaces where electrical connections are subsequently to be made. Masking can be a tedious and labor-intensive operation especially for small areas and non-flat surfaces. Adhesive-backed tape or a temporary coating, one that will not dissolve or be attacked during application of the permanent coating, can be applied manually. The maskant should be easily removable, preferably with water or a solvent that is compatible with the final coating. Maskants, such as solder maskants, are generally left permanently on printed circuit boards. Solder maskants based on epoxy resins are widely used to protect large areas of a printed circuit board from solder bridging between conductor lines.
