Thanks Syed and Pat,

Our challenge is making the connection between layers. We have used 
zincating to apply an Immersion White Tin finish to the boards and it 
works well, where there is aluminum. The trouble is with connectivity 
across the FR4/PI material sandwiched between the aluminum outer layers 
on vias and edge plating. Even though the dielectric is usually only 
0.0021" thick (before pressing) the zincating doesn't adhere.

We have a solder flux combo which does work well with the solder wick 
braid via solution we use today but we would dearly love to find a more 
elegant solution.

- Paul

On 2/28/14 8:58 AM, Ahmad, Syed wrote:
> Electroless Ni after zincate over device Al pads is commonly used as under bump metallurgy (UBM) for flip chips for solder ball attach/formation.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Patrick Goodyear
> Sent: Friday, February 28, 2014 10:50 AM
> To: [log in to unmask]
> Subject: Re: [TN] Aluminum fine-line PCB
>
> Paul,
>
> You can plate aluminum with zinc then nickel then copper.   The zinc
> keeps the aluminum from oxidizing the nickel replaces the zinc and the
> copper over plates the nickel.    I worked at a power plant, they use
> various products to decrease the oxide layers on buss work not sure what works on aluminum but they use Cool Amp (dry silver plate solution)
> De-Ox-It a conductive grease and some other products.    I think there
> are some solders that will work with aluminum or low temp brazing rod, I think it is all about the flux, Aluminum overlays an oxide layer almost immediately and that is a dang good insulator.  TIG or MIG welding aluminum is about the cover gas keeping the air out of the molten metal, my step dad could weld aluminum with a Oxy acetylene torch, not a clue
> how he did it.      If you marry it with a dissimilar metal it will
> cause major galvanic corrosion, I deal with it on a daily basis, using
> stainless steel bolting in anodized aluminum mounting brackets.    It
> takes about 2 weeks and the stainless and aluminum become one large
> white ceramic mess faster if the anodizing is disturbed.    Look around
> in the Utility industry since they use aluminum buss work all of the time, and bolt it to copper.
>
> Pat Goodyear
>
>
> On Fri, Feb 28, 2014 at 7:39 AM, Paul Jackson wrote:
>
>> Hi Wayne,
>>
>> Thanks for the ideas. The sputtering is one we really hadn't
>> considered and I am very interested into looking into it more.
>>
>> I'll send you the guide directly and if you are interested in seeing
>> what the boards look like they are on the cover of Time magazine, Feb
>> 17, 2014 edition.
>>
>> - Paul
>>
>> On 2/27/14 2:51 PM, Wayne Thayer wrote:
>>> Hi Paul-
>>>
>>> A fascinating application!
>>>
>>> When plating copper into vias is not possible, or is inconvenient,
>>> "macro-scale" designs use eyelets.  You can't attach to inner layers
>>> reliably with them, and I always found the external contacts to be
>>> unreliable as well, so we made sure they were soldered on both sides.
>>> But they can look a lot more professional than braid, and lend
>>> themselves to automation.  I presume that your application would be
>>> much tinier than any commercial eyelets and tooling sets could
>>> handle, but theoretically you could probably come up with something
>>> like that.
>>>
>>> Another possibility might be an organo-metallic paste like ORMET
>>> sells, or perhaps some kind of sintering nano-metals.  But either of
>>> these options would probably have trouble getting through the
>>> aluminum oxide to make a connection without some kind of assistance
>>> from a suitable flux.  Probably a lot of risky development would be
>>> required for this path, but it has the potential to be scalable down
>>> to your preferred geometry.
>>>
>>> Yet another possibility is that aluminum is commonly sputtered onto
>>> silicon wafers, so why not get it deposited into the holes?
>>> Activation and masking problems, but the prettiest and easily
>>> scalable to tiny geometries.
>>>
>>> I don't understand your process (I'd like to get the little guide
>>> available on your company's website, but for some reason it either
>>> isn't sending out the email or my spam filter is eating it).  But
>>> another way people build interesting boards is to put the vias in
>>> before the outer metal goes on.
>>>
>>> Wayne
>>>
>>> -----Original Message-----
>>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Jackson
>>> Sent: Thursday, February 27, 2014 2:31 PM To:[log in to unmask]
>>> Subject: [TN] Aluminum fine-line PCB
>>>
>>> Hi All,
>>>
>>> I'm new here to Technet so I'll ask you to be gentle, at least at
>>> first.
>>> We are manufacturing fine-line aluminum trace PCBs and our customers
>>> are mainly wirebonding chips directly on the aluminum and attaching
>>> components on selective copper pads. We are trying to find a more
>>> elegant way to achieve through-hole connectivity than our current
>>> method of filling vias with solder wick braid and aluminum solder
>>> paste. It works but it's "fugly". The aluminum is 30µm and the
>>> dielectric is typically 2.1mil. Any ideas would be greatly
>>> appreciated.
>>>
>>> Paul Jackson
>>> Omni Circuit Boards
>>> (855) 798 9717
>>> *w*ww.omnicircuitboards.com
>>>
>>>
>>>
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>>
>> --
>> Omni Circuit Boards Ltd.
>> 3-12760 Bathgate Way
>> Richmond, B.C.
>> Canada V6V 1Z4
>>
>> Tel. 604.276.9717
>> www.omnicircuitboards.com
>>
>>
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