Outgassing on a Printed Circuit Board

Outgassing, also known as offgassing, results in defects during production and use. While unavoidable in certain applications, outgassing must be prevented or mitigated to ensure a functional final product. Learn more about outgassing and what manufacturers can do to prevent or reduce it.

What Are PCB and Solder Mask Outgassing?

When outgassing occurs, gas trapped in a PCB releases within the board. It most commonly happens in two situations:

  • Wave or hand soldering during production: During wave or hand soldering, any moisture close to a through hole turns into vapor due to heat. When this gas escapes, it creates voids in the solder mask.
  • Use in ultra-high vacuum environments: In applications involving ultra-high vacuum environments such as outer space, laboratories or medical facilities, the vacuum can cause vapors to escape from the PCB, creating condensation on the rest of the equipment.

Issues Caused by Outgassing

Since the two common types of outgassing happen during different parts of the PCB’s lifecycle, they each present their own set of challenges for manufacturers. These issues can result in a defective PCB or a product that doesn’t work properly.

When outgassing occurs during soldering, the voids that form in the solder mask cause significant problems. These voids appear in the electroless copper plating that makes the thru-holes in a PCB conductive. During the deposition process, a manufacturer drills holes between the PCB’s layers and plates them with copper This plating creates a conductive path throughout the board’s layers, making the PCB function in the first place. A void in this copper plating prevents an electrical current from passing through the plating, resulting in a defective PCB. A PCB must have an even layer of electroless copper to serve its purpose, and voids prevent that from happening.

The problems associated with outgassing in a high-vacuum environment depend on the equipment’s application. In space-related applications, the condensation that forms from outgassing can interfere with materials like camera lenses or measurement tools. The vapor fogs lenses and interferes with measurement results. Medical facilities and scientific laboratories alike must have a sterile environment to use their equipment properly. Outgassing can contaminate equipment and the surrounding environment, creating danger for a patient or inaccurate testing results.

Common Reasons and Solutions

The situations where outgassing occurs may differ, but its causes are very similar no matter where it happens. Reasons for outgassing include:

  • Incorrect materials: When choosing the materials that make up a PCB, the manufacturer must consider every step of the board’s lifecycle, including production and application. Plating created from gold, silver or tin can contain salts or organics that create gas when heated during deposition. When a PCB used in high-vacuum environments doesn’t have materials with a lower chance of outgassing, the risk of outgassing increases.
  • Faulty manufacturing: The production process determines the quality of a PCB as much as its materials. Outgassing during soldering often happens when the electroless copper plating is too thin or the pre-heat process is done incorrectly. Neglecting to remove moisture during the production process can create the vapors associated with outgassing in high-vacuum systems.


Reducing PCB Outgassing in Ultra-High Vacuum Systems

Even when a PCB has the right materials and production, it can still experience outgassing in a high-vacuum application. Both manufacturer and customer alike must take precautions to reduce the risk of outgassing as much as possible. Baking PCBs for high-vacuum systems during production works effectively to mitigate outgassing, especially when done in a vacuum. The baking process gets rid of residual moisture before use.

When implementing their PCBs, customers can design equipment to keep vapor away from important components. Developing a path for gas to escape through a vent prevents it from getting trapped. Or, the board can be directed away from sensitive parts so any vapor will get in contact with parts not affected by it. Heating elements can burn off ice layers and films formed from condensation. Spacecraft featuring PCBs can face the side including the board toward the sun to allow its natural heat to reduce moisture.

Reduce Your Chance of Outgassing by Choosing the Right Supplier

MCL’s only supply PCB’s that use the proper techniques for your product’s purposes. Contact us to receive assistance finding a PCB with the lowest risk of outgassing possible