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Opto-electronics mfgr. needs adhesion of plastic to aluminum

2003

We have an application that requires strong adhesion between a plastic piece (Ultem) and an Aluminum piece. The set-up is fairly small --the Aluminum piece is about 1 cm by 0.5 cm and has a rectangular hole with a shelf at the center; the plastic piece gets set into this hole and epoxied on all four sides. The set-up has to stand moisture (85 C, 85% humidity) and temperature cycling (-40 °C to 100 C). Currently the Al piece is Alodined but we are wondering if this is the best finish for us since we are seeing failure of the adhesion between the epoxy and Al after temp cycling. We aren't yet sure if the Alodine coating is coming off (and sticking to the epoxy) or if the epoxy doesn't stick to the Alodine coating any more.

Any suggestions on a better finish that would be economical and corrosion resistive? Any other thoughts?

Thanks in advance.

Hamdi Demirci
opto-electronics manufacturer - Albuquerque, NM, USA

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Limit the thickness of the chromate conversion coating (trade name Alodine) to a very thin film, just barely yellow tint, probably about 20 mg/sq ft. At 100 °C the moisture in your heavy chromate film is allowing the film the shear and pull loose. Put it on very thin.

Boeing's phosphoric anodizing would probably be better, but I think you need a license to use it.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2003