electroless nickel for low rf attenuation?

I am interested in coating some aluminum parts for an RF (~100 MHz) application. Is electroless nickel boron the best choice for high electrical conductivity, over electroless nickel phosphorus? I am interested in minimizing the RF attenuation. What level of boron is best? Are there vendors who have expertise in electroless nickel boron? It does not seem to be as common as electroless nickel phosphorus. Why? Any information would be helpful.
Cheers,
Grant
My 11/15/2003 posting to sci.chem.coatings, sci.materials, sci.physics.electromag:
What is the bulk electrical conductivity of a typical electroless nickel deposit as a function of phosphorus content? Specifically:
1. Conductivity over the range 1% to 12.5% phosphorus by weight? For example, is there a significant difference in conductivity between low-, mid- and high-phosphorus deposits? Particularly, for 11-12.5% phosphorus (high-phosphorus), is the conductivity higher or lower than for lower phosphorus content? 2. DC (low frequency) and RF (up to 100 MHz)? Is there a significant component to the resistivity attributed to the magnetic response of low- and mid-phosphorus deposits? What is the best type of electroless nickel for rf/microwave applications? 3. Does low temperature annealing (~135 deg. C) have any effect on the electrical conductivity?
Grant

Grant Kiehne wrote:
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If you want low skin effect loss, you don't want nickel of any sort. Gold, silver, and copper are the best things, with everything else a distant also-ran. Inside a cavity, electroless copper lasts a long time. It also tends to get smoother very rapidly as it gets thicker, which is also important for low RF attenuation at high frequencies.
Cheers,
Phil Hobbs

Phil Hobbs wrote:
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t? Specifically:
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When plating be sure you're using a good process. If you plate too fast you'll get porous films that can have a conductivity less than 1/2 of bulk. This will lead to pure perfomance. Gold is good in an wet atmosphere but if you don't need it use silver or copper. It will give you lower losses.
Depending on what you're plating to you may want to plate ~100 nm of Cr first for better adhesion.
We usually use a plating current per area density that falls in the med-range of recommended plating. It seems to give us the best results. If I was you I experiment and plate films on insulators and then measure the conductivity using a standard 4-point method. You'll need a nano-voltmeter and a constant current sourse for that. I would adjust the plating parameters until I got the highest conductivity.

Grant Kiehne wrote:
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Nickel connectors also can cause intermodulation, so is not prefered in some transcievers,
Scott
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Thanks for suggestions on other platings, but I am interested specifically in electroless nickel. What type of electroless nickel is best for low rf attenuation? --Grant
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Grant Kiehne schrieb:
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You should consider that nickel is ferromagnetic !
Therefore I don't believe that nickel is used in RF work. And maybe nobody knows which one is best :)
Regards
Sven Hegewisch

Sven,
High-phosphorus (>~10.5% by wt.) electroless nickel is non-magnetic. As I've discovered, however, it also reportedly has the lowest electrical conductivity of all types of electroless nickel.
Grant
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Why are you married to eletcoless nickel when bare aluminum is probably a better choice? If corrosion is a serious problem you have a lot of problems and unless this is a very short lived item it will probably be less expensive to go with time proven solutions such a silver plated stainless steel or copper flashed with gold.
The coefficient of terminal expansion of aluminum is going to give you fits with the cavity tuning as well.
Gordon
Gordon Couger Stillwater, OK www.couger.com/gcouger

Gordon,
There are a number of other constraints. Without going into the details, electroless nickel is a strong candidate plating material, based on initial results. Since the electrical and magnetic properties of nickel-phosphorus deposits vary with phosphorus content, I am interested if anyone has detailed information on rf attenuation of this or a similar material. The resistivity of nickel-phosphorus increases linearly with phosphorus content, but as the material approaches the "high-phosphorus" regime of 10% by weight or higher, the material becomes non-ferromagnetic. I note that the skin depth is proportional to 1/sqrt(sigma*mu), where sigma is the electrical conductivity and mu is the magnetic permeability. I suppose one should really consider these material parameters as functions of frequency f, sigma(f) and mu(f).
Perhaps someone has encountered this or a similar problem before and could provide some guidance.
Grant
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