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How to avoid PCBs from Oxidation?

2017-04-26 15:19:17

Oxidation is the result of oxygen and moisture reacting with the alloys on the pads. In other terms, oxidation is Rust. Just like our cars rust after the protective coatings (paint) have been removed, PCB pads oxidize after sitting unprotected or exposed for too long.

 

Contamination could be an issue as well. If the operators touch the pads with bare fingers it is possible to transfer oils and dirt to the pads. Either way, once the pads are oxidized or contaminated a good cleaning is the best was to start.

 

To avoid the oxidation make sure to handle the boards properly as determined by the type of coating on the pads. Some board finishes are more forgiving that others. For example, ENIG may stand up to longer exposure than either OSP or Silver coated pads.

 

Follow the board manufacturer's recommendations for handling and storage. No matter which board finish you are using, there are a few steps that will help extend the life of the board finish.

 

1. Keep the boards packaged in vacuum sealed bags with desiccant until immediately before use.


2. Once the boards are in process, finish the process. I have seen situations where double sided boards are processed through a bottom side operation only to be stacked in racks and left exposed for days and sometimes weeks. Those boards WILL oxidize no matter what board coating was applied.

3. If the boards must be opened and stored, make use of a "dry box" or other controlled environment.

4. Handle the boards as little as possible. If the board must be handled by a person, handle the PCB only by the edges of the board. Do not touch the solderable surfaces with bare fingers. Finger cots or gloves, changed often can help keep contamination from the soldered surfaces.


4. It is better to use boards within 6 months to reduce the chances of Oxidation.

 

 

By Kris Roberson

From IPC

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