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topic 5280

Coating of Ceramics/But Non Coating of Metals...The


The task: to (chemically) coat a very small electronic part consisting of a ceramic oxide material (with some electrical conductivity) with additional metal electrodes (silver) in that way, that only the ceramic surface is selectively coated. This coating must be inert to acids, because the electrodes will be electroplated in the next step. If the ceramic material is not coated, metal deposition on the ceramic surface will occur.

Of course there is electroless plating, but how could this be done? Tried hydrophobation of the ceramic by use of silicones, but this did not work well...

Ideas highly appreciated, thanks in advance!

Lois Kleewein
Graz. Univ. of Tech'y - Graz, Austria


You want to coat the ceramic parts, but not the metal. That's just not enough information for anyone to be able to give you any help. What coating do you want to deposit, and how thick does it have to be? What coating do you subsequently apply to the metal parts? How thick does that coating have to be? What is the size of the components to be coated?

jim treglio portrait
Jim Treglio
PVD Consultant - San Diego, California


Sorry Jim, and all You others for not being precise enough!

The coating (or better passivation) of the ceramic (which has a non negligible conductivity) has to be done because when I do electroplating on the parts the ceramic gets electroplated too. That makes the part useless, because it's an electronic device, which is then some kind of short cut between the Ag-electrodes. And the low pH of the electroplating solutions dissolve the surface a little bit (etching), which is also bad.

On bigger parts it's no problem to apply a painting or something else to the ceramic, but THESE parts are about 5x3x2 mm. So the coating should be done by chemically masking the ceramic material, which is zinc oxide.

The coating must be as thick to resist the plating solutions (in the sense of the pH) and insulating enough to avoid metal deposition on the ceramic surface. The material doesn't matter.

The next step will then be the deposition of the final electrode materials (Ni first and Sn afterwards as a finish), but only on the outer part of the device (the original silver electrodes), leaving the ceramic part free.

See the drawing below (a = Ag electrodes, b = ceramic)

| a |    b     | a |

Hope this describes the situation completely!

Lois Kleewein
Graz. Univ. of Tech'y - Graz, Austria


Why not dip the entire assembly in wax, melt or dissolve the wax from the silver leads, electroplate away, & then dissolve the mask with solvents. Beeswax, shellac wax, carnuba or maybe paraffin would do the trick, as would an ethylinic polymer such as carbowax. You will likely need a chlorinated solvent, i.e., dichloromethane, TCE, et al., to dissolve the wax completely; a little warming helps.

There are lots of variations on this theme, including coating the leads with a surface which will resist the wax or can be dissolved in water before applying the wax mask.

Dale Woika
Surface Conversion Sciences - Bellefonte, Pennsylvania


I would like to know whether it is possible to electroplate ceramic surfaces with metals. I am interested in electroplating of ZnO ceramic with Aluminum or other metal. Would you give me the developers of such technique, references or else? Are there any companies that supply equipment for such application.

Best regards,

Nabila Zebouchi
- Västerås, SWEDEN

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