What causes oxidation on surface mount pads?

In a nutshell, oxidation is the result of prolonged exposure of printed circuit boards to air. However, it is important to first determine whether you are dealing with oxidation as opposed to contamination. Oxidation of pads can be difficult to determine and often requires the process of elimination. Oxidation is a natural process for metallic surfaces when exposed to the environment and cannot be detected visually until it is in an extremely advanced state. Boards finished in gold have a very limited chance of oxidation unless the boards are extremely old or in an environment that is high in humidity. Boards should be received from your board supplier in a vacuum pack, clean and ready to take solder. Once the seal has been broken, the boards become subject to their environment. High humidity will accelerate the process and the longer the exposure, the greater the oxidation potential. Boards should be loaded within a six month (maximum) window. The other possibility is contamination. If your boards are newly out of their safe packaging, are gold or are in a controlled environment, chances are the problem is not oxidation. Most contamination is created at the board manufacturing level and can usually be discovered when the packaging has been opened. Causes at the manufacturing level are a result of faulty conditions such as incorrect ph levels in the rinse bath, improper handling and poorly washed boards with surface film. The safest way to avoid oxidation is the create a dry, clean environment when storing boards not immediately used and to make sure boards are used within a six month window. Contamination of boards is the problem of the board fabricator and should fall within warranty of their product. In some cases where time does not allow for re-fabrication of oxidized or contaminated boards, it is possible to work with your stencil supplier to modify design of your BGA pads to circumvent poor solder joints.

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