What Is PCB Measling?

Measling is the occurrence of discrete white spots in the base laminate material of a PCB. Measling usually occurs when the resin is not properly applied to the board during the lamination process. These defects appear during the PCB production cycle and signify a malfunctioning board.

A small amount of measling can be tolerated on printed circuit boards however when excessive this can degrade electrical and overall performance of the board. A combination of moisture and other contaminants is responsible for measles.

Adopting proper production techniques can help prevent its development. However, sometimes PCB Measling can occur during the life of the board due to mechanical stress. The finish on the glass fabric also contributes to measling. A higher the surface tension finish on the board, results in better wetting and better resistance to measling.

How to prevent PCB Measling?

• By adopting the well-managed manufacturing process
• By ensuring proper temperature and resin control methods
• By ensuring the quality of surface finishes and storing the PCBs in dry space
• Maintaining the board temperature before proceeding for thermal processing

Measling Test Procedure: 

Various test methods are used to validate the measling defect. One is to expose the laminate to moisture prior to its immersion in 500 degrees Fahrenheit solder paste. If the laminate passes this test, then it will normally go through the etching and soldering process without measling and the appearance of white spots.