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topic 1327

Chromate coating conductivity on aluminum at high temperature over time


(1998)

I have two concerns with a product which is currently under evaluation. The product is an aluminum enclosure that that is machined from solid block and has a top and bottom half that when assembled serves as a heat sink and EMI shield for an electronic circuit board inside. The product is Iridited prior to paint, and the paint is applied only to the exterior of the enclosure. There are a series of hundreds of conical shaped pins on the inside and outside of the top part that conducts the heat away from the unit. The top and bottom lip make electrical contact once the unit is closed prevents EMI leakage.

The first concern has to do with whisker growth. It is my understanding that zinc chromate exhibits microscopic whisker gowth which can fall, as a result of vibration, onto the leads of electronic components with the potential to cause product failure. In the case of chromate coatings on aluminum, I have yet to obtain a satisfactory response to this possibility. Is there any literature that documents whisker growth phenomena on Iridited aluminum?

The second concern has to do with the degradation of the chromate coating on aluminum at temperatures in the 60 degree C range over time. The lip around the periphery of the unit and the back wall of the enclosure need to maintain electrical conductivity for many years. However, it is not evident that there is any literature on this subject. Does anyone have any knowledge of this phenomena? Is there any literature?

Thanks in advance.

Regards,

Patrick McGirr
Positron Fiber Systems



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