Jeremy Taylor wrote:
> no problem
> I drill first with the cnc machine
> then use the ink activation, then bake the board in a convention toaster
> oven,
> Then I plate the whole board in an alkaline "flash" copper. then dry in the
> toaster oven, than a dip in hot tri sodium phosphate, a good scrub and
> rinse, then I laminate on Negative resist, and expose a positive image and
> develop, This results in everything but the traces and pads etc covered in
> resist. I then plate the tin, This plates everything exposed (including the
> holes), in very fine and solid detail, You can clearly see when everything
> is fully plated, over plating is not a problem >you do need oversized holes
> tho<. The next step is the resist stripper, then into the etch, Sulfuric
> Peroxy (which doesn't etch tin) and everything not plated with tin gets
> removed. ... I'm actually using a 10% Lead content in the tin to keep the
> tin from sprouting roots, and to "set" it, I have to reflow it, which means
> back in the oven. For boards, I plan on selling as kits (i.e.... not
> immediately assembling), I also use a nickel undercoat (between the copper
> and the tin, to prevent the anti-solderable intermetallic alloy forming)
> There are other various pre dips and post dips and rinses between each step.
> I've got it laid out in a nearly effluent free process. I can reclaim copper
> sulfate from the etch to replenish the copper plating tank. The only things
> I dispose of are the resist stripper (sodium carbonate) and the developer
> (sodium bicarbonate) which are both very safe chemicals. www.thinktink.com
> and www.caswellplating.com two US links to more info. The only "odd thing I
> had to source was the low lead tin anodes. I didn't feel 60/40 solder plate
> was very Green considering how evil Lead is. Pure tin grows metallic
> fingers that will short circuit traces, and the intermetallic alloy
> formation begins immediately, completely consuming the tin within 3 years
> (in perfect storage)
>
> JT
>
>
Jeremy,
What bath compositions do you use for all three plating tanks ?
I have done some pure tin electroplating on PTH boards and had no
soldering problems with inter metallic alloys forming at least in
the first month. The tin plating thickness is round 5 to 8 um
(measured by amp hours). I have never heard of problems of
electroplated tin creating whiskers. Do you have any knowledge of
tin whiskers being a concern in PCB production.
here is an interesting articles on tin whiskers.
http://nepp.nasa.gov/whisker/reference/tech_papers/brusse2002-slides-tin-whiskers-attributes-mitigation-CARTS-europe.pdfhttp://www.p-m-services.co.uk/electroless_tin.htmI seems that if plated tin is thin then the migration of copper
in to the tin will stop the win whiskers being formed.
The tin bath is 200/L sulfuric + 15g/L tin as stannous sulfate +
proprietary brightener, and the copper plating bath is 200g/L
sulfuric + 20g/L copper as copper sulfate + proprietary brightener
.
Is a nickel plating bath difficult to setup and maintain ?