questions about electroplating copper to aluminum

[fshegg3]

i'm trying to construct a highly efficient heat sink to enable heat to be tranfered 3" or so. copper is my fist choice but is cost prohibitive so i'm stuck with aluminum.

 

i'm transfering heat from a thermoelectric module (tem) to atmosphere via natural convection. the 3" distance is a long way in thermodynamics.

the engineer i've been working with suggested a pyramidal shape as the only way to go.

 

the most economical way to make a pyramidal shape is to emulate the pyramids of the INCA'S. in effect a series of graduated plates.

 

the copper solution is best because i could stack the plates with solder between plates and bake the entire assembly to 600f when the

solder flows to end up with a solid thermal mass. copper has almost twice the K value of aluminum and this would be thermally ideal

except for the cost.

 

the "incan" pyramidal heat sink would be constructed as follows: 8 plates from 6" x 6" x .375" reducing down to 1.75" x 1.75" x .375".

 

questions:

 

1) is zincation absolutly necessary if the plates are THOROUGHLY cleaned and then immediatly immersed in the chemical bath?

 

2) will the resultant layer of copper be sufficient to solder them together as described above?

 

3) since the plating process physically moves ionized copper atoms would it possibly "fuse" the aluminum plates together obviating

the baking process?

 

4) how do i make home made chemicals (i've heard about white vinigar and hydrogen peroxide boiled works)?

 

5) how would i calculate the proper voltage, amperage and time?

 

any thoughts would be a big help.

 

thanks,

 

steven

 

 

[Enthalpy]

Not exactly the answers you expected, sorry for that...

 

If I got it right you want to cover aluminium with a metal layer that can be soldered. Electroplated nickel does that; it's very common and affordable, including on aluminium, and is hugely more durable than copper. You'll get less contact corrosion of aluminium than with copper, and an excellent protection of aluminium. Ask your plating contractor if some catalytic nickel (then with low phosphorus?) does it. Over nickel, plating contractors can also deposit tin or similar, and then soldering gets really easy. Don't plate with silver, gold, palladium and the like, as they dissolve in solder. Anyway, this is a complete profession, which cannot be learnt in few months.

 

Soldering is one excellent option; the other is thermal grease, as used for electronics. It needs permanent pressure, which solder doesn't. Screws.

 

Nowadays, when people want to spread heat over distance, they use heat pipes (see Wiki). You'll find them in ready-to-use coolers for CPU and video cards in computers, cheap. Keep the whole cooler: this would be the normal way now that they're mass-produced, instead of making one by yourself. Some are passive, if you dislike the fan. Newegg, eBay...

 

Peltier elements use to be stacked in pyramids because each element provides a small temperature difference, and since their efficiency is very bad, the next-warmer element must be much larger than the previous one. The complete stack can have 0.1% efficiency. If you can, the standard refrigerator method is far better; usable and ready hardware is available to sub-cool CPU's for overclocking - ask at http://www.tomshardware.co.uk for instance.