Techniques for Reducing Off-gassing Issues in Printed Circuit Boards
In the world of electronics, particularly in space and military applications, the issue of outgassing in printed circuit boards (PCBs) is a critical concern. Outgassing refers to the release of trapped gas or vapor from a PCB when exposed to heat or vacuum, leading to potential issues such as blowholes, lamination voids, and plating voids.
To combat this issue, designers must ensure that the materials used in PCBs have low outgassing rates and can withstand fluctuating pressure and temperature. The four mechanisms contributing to outgassing are vapourisation, desorption, diffusion, and permeation.
A key strategy to prevent or reduce outgassing is the selection of materials with low outgassing properties. Using PCB substrate materials and components that are certified or known for low outgassing in vacuum environments helps minimise the release of volatile compounds.
Conformal coatings play a critical role in this process. These coatings seal PCB components and surfaces, preventing the escape or accumulation of gases during vacuum exposure. They also help mitigate environmental challenges such as moisture, radiation, extreme temperature swings, and mechanical vibrations, all of which can exacerbate outgassing effects.
Thorough cleaning of PCBs is also vital. Controlling the soldering process carefully to avoid excessive heat is another essential step to preserve PCB substrate integrity and reduce potential outgassing sources by preventing thermal damage during assembly.
Outgassing rate measurements may be necessary to verify or validate bakeout techniques or surface treatments, and to compare different circuit board materials. A board material with a collected volatile of less than 0.1% and a total mass loss of less than 1% when placed in a vacuum for 24 hours at a temperature of 125°C is considered as the substrate with a low outgassing rate.
Common units of outgassing rate are Torr-Liters/cm-s and Atm-cm/cm-s. Moisture removal from the PCB is vital, and boards should be baked to eliminate volatile molecules.
In summary, the combined approach of low-outgassing material selection, protective conformal coatings, meticulous cleaning, and controlled assembly processes are established methods to reduce PCB outgassing, especially in demanding applications such as space electronics. By adhering to these practices, designers can ensure the reliability and performance of PCBs in challenging environments.
- Data-and-cloud-computing technology can help designers optimize a printed circuit board's (PCB) materials and assembly processes, minimizing outgassing concerns, especially in challenging environments like space and military applications.
- To further enhance the performance and reliability of PCBs in various industries leveraging data-and-cloud-computing, researchers are exploring advanced modeling and simulation tools to accurately predict and test for outgassing rates under different temperature and pressure conditions.
