IMD problem (RF filter) Aluminium-(Nickel+silver) plated

[chandregowda]

hi,

our RF CAVITY FILTER (MATERIAL : ALUMINIUM) plated with COPPER followed by SILVER (AG7) PLATING is passing the IMD TEST.

(Filter made of Aluminium coated with Copper followed by Silver (Ag7) plating is passing the IMD

but

RF CAVITY FILTER (MATERIAL : ALUMINIUM) plated with NICKEL followed by SILVER Plating is NOT PASSING the IMD.

how can we solve this?

 

[PeterMartin]

Its the Nickel which is ferromagnetic. Nickel must NOT be used at all even in the connectors.

Specify white bronze plating instead for connectors which is essentially a copper-tin-zinc alloy.

Stainless steel isn't good either.

 

[FuBaoquan]

i suggest u use Electroless Nickel Plating which is nonmagnetic.

 

[chandregowda]

hi,

Is it ok if silver thickness increased to 12 um over Nickel on filter housing.
will it pass IMD?

 

[FvM]

Can you give an explanation, why you expect the ferromagnetic properties to cause IMD? It's not obvious in my opinion.
Any literature references or empirical results? Thanks!

 

[chandregowda]

i suggest u use Electroless Nickel Plating which is nonmagnetic.

Is {Electroless Nickel plating + Silver plating} is as good as {copper + Silver} plating for IMD?

 

[Filip]

https://en.wikipedia.org/wiki/Intermodulation , see references

 

[FvM]

Thanks, I was able to confirm the said statements regarding nickel plating. Several manufacturers are claiming electroless
nickel plating according to MIL C-26074 assures good IMD respectively PIM (passive intermodulation) behaviour. I guess,
that an empirical test has to decide about "as good". Generally, the electroless nickel coating is promising better mechanical properties.

 

[PeterMartin]

Why does the plating process change the magnetic properties of Nickel? Isn't that a fundamental physical property of the metal?

The safest solution is to just NOT use any Nickel at all in any application where PIM is a potential problem. The plating can then be checked easily enough with a spectrometer for traces of Nickel. Silver plating without Nickel is no more expensive.

Don't overlook the connectors either - insist on them being 100% Nickel free for both the inner pins and outer bodies.

 

[chandregowda]

hi,
any further informatin on this is good for us.

 

[Filip]

Some data is necessary. Describe pls testing method (Power, freq). What is pass/fail level, what is IM level with Ni plating an IM level without Ni. Some nice drawings will be appreciated.