Controlling Moisture in Printed Circuit Boards

Printed circuit boards have come a long way since the time when they existed mainly as a platform for connecting components. Boards are now part of the design, as features and even components are built into layers. The electrical and thermal properties of printed circuit boards are becoming critical factors in system designs. Many board developers do not realize that moisture in boards can significantly alter board performance. Moisture can negatively affect the integrity and reliability of printed circuit boards. The presence of moisture in a printed circuit board alters its quality, functionality, thermal performance, and thermo-mechanical properties, thereby affecting overall performance. Moisture content can vary widely depending on how boards are handled. Regardless of how much protection is used, some moisture will be absorbed. Parameters will be changed, even if boards are baked to dry them before they are used; this can alter performance from the specification sheet listings. This paper summarizes moisture-related issues and provides guidelines to reduce the impact of moisture on the reliability of printed circuitry boards. The controls and guidelines provided in the paper can be implemented at different stages of PCB production.