Techniques for Reducing Off-Gassing in Printed Circuit Boards
Preventing Outgassing in Printed Circuit Boards
Printed Circuit Boards (PCBs) are essential components in many electronic devices, but they can sometimes be plagued by a defect known as outgassing. This article explores the causes, mechanisms, and solutions for outgassing in PCBs.
Causes and Mechanisms
Outgassing in PCBs primarily results from residual moisture, volatile additives, trapped solvents, and thermal or vacuum stress affecting polymeric materials and laminates during fabrication or operation. Moisture trapped in resin-impregnated prepregs or absorbed during storage can vaporize during lamination or reflow soldering, leading to outgassing. Additives and volatile compounds in polymers, such as plasticizers, stabilizers, and flame retardants, can volatilize under elevated temperatures or harsh environments, causing outgassing. Thermal cycling and extreme environments, especially in vacuum environments like space, cause expansion, contraction, and possible decomposition or volatilization of PCB materials, releasing gases. Fabrication processing conditions like excessive lamination pressure, uneven resin flow, and unbalanced copper distributions can create voids or resin-starvation zones that trap volatiles and structural weaknesses that promote outgassing during subsequent thermal processing.
Prevention Strategies
To eliminate outgassing, boards should be baked at high temperatures, with the temperature not exceeding 125 degrees. Ensuring that materials have passed outgassing evaluation tests based on the standards SP-R-0022A and ASTM E595-07 is important to prevent outgassing. Hole plating should be a minimum of 25μm to prevent outgassing. Creating a path for any released gases and directing them into space can help prevent outgassing. The vacuum pre-bake process should be carried out to get the moisture out of boards as much as possible.
The conductance method is used to measure PCB outgassing rate. Outgassing rate measurements may be necessary to verify or validate bakeout techniques or surface treatments and compare different circuit board materials. Flexible circuit materials, such as Kapton, offer excellent outgassing properties.
Material Choices
Choosing the right material for your board can make a lot of difference in preventing outgassing. Always using thermally stable materials, such as Rogers' RT/duroid series and Nelco's meteorwave series, can help prevent outgassing. NASA has designed stringent procedures to test circuit board laminates for outgassing in space applications.
Testing and Verification
Verifying that the circuit board and its components can resist extreme temperature swings in space is important to prevent outgassing. The test sample is placed in a vacuum environment for 24 hours at a temperature of 125°C, and weighed at 23°C after a 24-hour period to reduce the impact of water vapor on the measurement. Outgassing is a defect that releases trapped gas/vapor, creating blowholes, lamination voids, and plating voids. A board material with collected volatile of less than 0.1% and 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 low outgassing rate.
Conclusion
Outgassing in PCBs can hinder the reliability of circuit boards that operate in high-temperature and high vacuum environments. By understanding the causes and mechanisms of outgassing, implementing prevention strategies, and choosing the right materials, manufacturers can produce high-quality, reliable PCBs that meet the demands of various applications.
- In the medical-conditions and real-estate industries, understanding the causes and mechanisms of outgassing in Printed Circuit Boards (PCBs) can aid in the design of equipment and buildings that operate in high-temperature and high-vacuum environments.
- The finance industry, when investing in the electronics sector, should factor in the research and development costs associated with overcoming outgassing in PCBs, as this can significantly affect the reliability and performance of electronic devices.
- The industry focused on data and cloud computing heavily relies on PCBs that have low outgassing rates to ensure the longevity of equipment and to prevent data loss due to the degradation of electronic components.
- To advance the technology sector and produce innovative devices, industries should consider the role of PCB manufacturers that specialize in low-outgassing materials, like Rogers' RT/duroid series, as these materials help ensure the reliability and functionality of electronic components.
