Strategies for Reducing Off-gassing in Printed Circuit Boards
Reducing Outgassing in Space PCBs: A Guide for Designers and Manufacturers
Outgassing in printed circuit boards (PCBs) can pose a significant challenge in space applications, where ultra-high vacuum (UHV) environments and extreme temperature fluctuations can cause trapped gases and volatile substances to be released, potentially contaminating sensitive equipment and degrading performance.
Key factors contributing to outgassing in PCB materials for space applications include the choice of adhesives and substrate materials, the presence of trapped volatile compounds, and environmental conditions such as vacuum and temperature extremes.
To prevent or minimize outgassing, several best practices can be employed:
- Material Selection: Use adhesive-less constructions, such as directly bonding polyimide and copper layers, to avoid adhesives that outgas significantly. Select low outgassing materials certified for space applications, such as high-grade polyimides and carefully chosen jacketing materials that resist gas release.
- Thermal-Vacuum and Radiation Testing: Perform thermal-vacuum and radiation testing on materials and assemblies to ensure stability and low outgassing under simulated space conditions.
- Material Selection and Design: Avoid materials with volatile compounds prone to gas release in vacuum environments. Design PCBs with materials that withstand space temperature extremes and radiation to prevent degradation that could lead to outgassing.
- Moisture Removal: Moisture removal from the PCB is vital, and boards should be baked to eliminate volatile molecules.
In terms of testing, the ASTM E595-07 test is a widely used procedure to assess PCB materials, evaluating properties such as total mass loss (TML) and collected volatile condensable material (CVCM). A board material with a CVCM of less than 0.1% and a TML 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.
Designers should also consider using materials specifically developed for the end application, such as Rogers Corporation's RT/duroid series and Nelco's meteorwave series, which are examples of PCB materials with low offgassing rates.
To mitigate outgassing in space applications, designers should verify that the circuit board and its components can resist extreme temperature swings, employ heating devices, and direct vapor away from sensitive surfaces. This will help ensure the reliability and performance of PCBs in spacecraft environments.
References: [1] Design for Manufacturing Handbook, NASA-GB-8719.135B [2] SP-R-0022A, Outgassing Requirements and Test Guidelines for Circuit Board Materials Used in Space Environments [3] NASA-STD-6001, Spacecraft and Launch Vehicle Environmental Test Procedures and Acceptance Criteria for Small Spacecraft [4] ASTM E595-07, Standard Test Method for Total Volatile Condensable Materials (TVCM) of Plastics by Thermal Desorption Analysis (TDA)
In the realm of environmental science, addressing climate change demands the utilization of technology and data-and-cloud computing to monitor and mitigate greenhouse gas emissions.
Moreover, the field of environmental science intersects with the science of space technology, as the principles of material selection, thermal-vacuum testing, and radiation protection employed in reducing outgassing in space PCBs can also be applied to minimize environmental contamination caused by volatile substances in everyday electronic devices.
