Letter 15090

Cracking along seam weld of Au/Ni plated Kovar [Taiwan] 

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We are trying to seam-weld a Kovar lid onto a ceramic substrate on top of which a Kovar-rim is brazed for hermetic sealing. Both the Kovar lid and the Kovar rim are nickel underplated first, followed by gold plating.

After the resistance seam welding, cracks are observed to propagate along the weldseam, leading to failure in achieving hermeticity. Can anybody provide suggestions of how to eliminate the cracking problem?

While the detailed plating process for the Kovar rim on top of the ceramic substrate is unknown (it is a purchased part), two different electrolytic nickel platings of the Kovar lid have been tried, but both gave the same cracking problem. One of them is semi-bright nickel (~110 micro-inches) followed by sulphamate nickel (~130 micro-inches). The other one is nickel strike (~30 micro-inches) followed by the same sulphamate nickel (~130 micro-inches).

Thanks for the input.

Leo Chen
- Taipei, Taiwan

I recently talked with someone who had a similar problem and the general consensus was that a nickel oxide layer was contaminating this person's plating. Evidently the seam welding process won't work if a nickel oxide layer is present (I am not an expert in this, just a practitioner.)

Try and use a lid and body that have a single nickel layer deposited on them.

Good luck! Van

J. V. Rudd
- Ann Arbor, MI, USA

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