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Electric isolation characteristics of Type II

2004

The problem:
I have a component used in an electronics connector that is used to segregate and isolate electronic signal leads. we have found that hard anodizing (Type III) provides the appropriate isolation characteristics on this component but we are experiencing cracks or voids along sharp edges. Through use of the connector the hard coat chips away along the sharp edges and exposes bare base metal which conducts electricity (bad).

Some background:
The component is quite small. The "fingers" that isolate the signal leads and the space between adjacent fingers is 0.010". This allows me no freedom to radius sharp edges to prevent the condition along sharp edges.

The question:
Will Type II anodizing provide me equal or similar electric isolation to Type III and allow better plating continuity around sharp edges? note: abrasion resistance is important but secondary.

Thank you,

John Ohotto
electronics manufacturer - Eagan, Minnesota, US

The component has been made from 7075 and 6061 and we experienced the same problem on both. The current base material is 7075. We switched to it for added mechanical strength.

John Ohotto
electronics manufacturer - Eagan, Minnesota, US
2004

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First of two simultaneous responses --

Anodizing builds perpendicular to the surface, therefore a sharp edge always has a void or gap. Radius is the only way to minimize the openess of the void. The degree of openess is a function of the radius.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2004

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Second of two simultaneous responses --

Type III Hardcoat anodizing is a thicker, denser, higher dielectric version of Type II commercial anodize. They both form aluminum oxide from the base aluminum. On sharp edges there isn't enough aluminum to support the formation of the oxide. Once all of the available aluminum has been converted to oxide the reaction stops. This area of thin, brittle coating which can be easily chipped or broken off has been termed the "edge defect". The best answer is to radius the edges.

Chris Jurey, Past-President IHAA
Luke Engineering & Mfg. Co. Inc.

Wadsworth, Ohio

2004

Thanks for the responses. You've helped dispel some of our concerns and provided some insite to a probable solution.

John Ohotto
electronics manufacturer - Eagan, MN, US
2004