Letter 21037

Can passivated stainless steel cause oxidation using silver epoxy? [California] 

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Hello,

I work For HyTech Associates located in Westlake Village, California. One of my customers has encountered a phenomenon that has my colleagues and I looking for an answer. The problem: I have placed a set of passivated stainless steel microwave connectors in a dish with an amplifier (MMIC-based LNA probably the simplest possible LNA in the world) adhered to a substrate with silver epoxy (Epoxy Technology product number H20E) cured at 135 C° for 20 minutes.

Connector Material:

1. Connector out conductor: passivated stainless steel (CRES alloy UNS-S30300 per ASTM-A582))

2. Captured with two center beads: (Front bead, Kel-F, polychlorotrifluorethyene) (Rear Bead: Ultem 1000 polythermide) 3. Center conductor: Heat-treated beryllium copper, gold plated.

The results: The epoxy has become oxidized (silver epoxy discolored, turns black, that can be scraped off the outer layer).

Hypothesis:

1. Hydrogen is being emitted - due simply to the aggressive nature of the oxidation.
2. Connectors materials are out-gassing.
3. Stainless steel passivation causes a reaction to the silver epoxy.
4. This level of oxidation occurred in 20 minutes!

My Question: Can passivated stainless steel react to silver epoxy to cause some form of oxidation?

Todd Cates
- Westlake Village, CA, USA

30300 is a high sulfur grade of stainless steel and will provide the sulfur easily on the surface to to the Ag to AgS (probably the black coating). You need to immerse the 303 stainless in a product to remove the sulfur from the surface before passivation. Then it should be okay. It needs to be immersed in one of the high pH products that are designed to remove sulfur. Let us know if you need help with this. We get excellent results with this process.

Lee Kremer Stellar Solutions, Inc. Algonquin, IL, USA

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