[SI-LIST] Re: Metal to Metal Question
- From: Chris Padilla <cpad@xxxxxxxxx>
- To: dave_hoover@xxxxxxxxx
- Date: Thu, 11 Oct 2001 09:07:58 -0700
Galvanic Series
Group I Group II Group III Group IV Group V
Magnesium Aluminum 2S Lead-tin Solder Copper-Nickel Graphite
Zinc Cadmium Lead Monel Gold
Galvanic Steel Aluminum 17ST Nickel Silver Solder Platinum
Steel Brass Nickel (passive)
Iron Copper Stainless Steel
Galvanic Action
If dissimilar metals are used, a noise voltage may be induced due to the
galvanic reaction between the two metals. Moisture or water vapor in
conjunction with the two metals produces a chemical wet cell. The voltage
developed depends on the two metals used and is related to their positions
on the Galvanic Series Chart. The farther apart the metals are on the
chart, the larger the induced voltage.
The use of dissimilar metals can also produce a corrosion problem. Galvanic
corrosion causes positive ions from one metal to be transferred to the
other. This gradually causes the deterioration of the anode material. The
farther apart the metals are in the galvanic series, the faster the rate of
corrosion. An undesirable but common combination of metals is aluminum and
copper. The aluminum will eventually be eaten away. Since aluminum and
lead-tin solder are closer in the galvanic series, the reaction time can be
slowed down by coating the copper with lead-tin solder.
When dissimilar metals must be combined, try to use metals from the same group
Hope this helps.
----->Chris
>Hello group.
>I have a customer who has an RF metal can made of
>machined Aluminum that bolts up against a PCB. At
>the mating locations between the PCB and the aluminum
>is selective plated Nickel Rails. That multiple
>surface finish requirement has a premium ($$$$)
>and I was wondering what is normal (or typical) in
>the EMC industry. Do most people bolt up against Tin
>Lead (against aluminum), or do they normally have the
>aluminum plated with Nickel?
>
>I did check the electromotive force charts and quite a
>few finishes appear to be "out of the question".
>
>(This is what I have found si far)
>Aluminum (pure) -0.80
>Nickel -0.24
>(Copper -0.34)
>
>
>Tin -0.14
>Lead -0.13
>
>(Possible issues due to fretting or galvanic reaction)
>Silver +0.80
>Gold (I didn't find gold but I know it's a + value)
>
>Let me know what is typical in the RF Industry.
>
>Thanks for any and all replys,
>
>David Hoover
>Field Application Engineer
>Data Circuit Systems, Inc.
>
>
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