On 22/12/10 21:54, A S wrote:
>   ...combined with "Re: [PIC] Making a HP print-head connector"
>
> What if a PCB copper layer to be covered with epoxide "resin" and then
> a picture to be printed with polyamine "hardener" ink? Anyone heard of
> a print-head technology to handle polyamine ink?

It sounds like you're describing the way HP made their head connectors.

Basically, they took a polyimide (Kapton) backing and plated it with=20
copper. Next they etched the track pattern into that backing, and=20
"dimpled" it using a heated mould. This added small bumps in the pads,=20
which acted as springs. Then the whole thing (except the pads) was=20
laminated with a second piece of polyimide film. Finally, the pads were=20
plated with nickel, then gold.

While making something like this is *theoretically* possible, it's sure=20
as hell not going to be easy. I'd probably tweak the process a bit:

   - Dimpling. Drive a bunch of panel pins into a wood, plastic or metal=20
base. Use a Dremel with grinding bit to smooth off the tips of the panel=20
pins. Make an inverse of the mould with a Dremel and a drill bit. Hope=20
you've got steady hands and a measured X-Y table for your drill stand!=20
(or a milling tool)

   - Base laminate. Kapton PCB laminates are available, but hard to=20
find. An alternative might be copper foil and Kapton tape -- this is=20
available in widths up to several inches (!). Stick the foil onto the=20
tape, clean and coat with spray-on photoresist (Electrolube PRP seems to=20
work OK for this). Etch as normal.

   - Over-lamination. You'll need a laser cutter for this... Or=20
alternatively blast the board with photoresist again, expose, develop=20
and either leave it as-is or cook it in an SMD oven at 150C for a couple=20
of minutes. This trick makes Kontakt-Chemie Positiv-20 go brown and hard=20
(and from what I've heard, VERY hard wearing -- it's even mentioned in=20
the datasheet). No idea what, if anything, it does to PRP.

   - Plating. Get some solder paste. Apply paste with a squeegee. Pray=20
that it gets stuck in the holes in the over-lamination. Into the reflow=20
oven it goes! SnPb is likely to work better than SAC (lead-free) for=20
this. Forget gold plating unless you're hell-bent on playing with=20
cyanide compounds and shortening your life markedly.


Another method might be to put enough solder paste on the pads to create=20
a ~1mm tall solder bubble when the pads are reflowed. That would provide=20
a bit of a spring...

I think I might have some small sheets of 0.2mm laminate somewhere=20
(read: paper thin, double sided). Might be interesting to play with...

--=20
Phil.
piclist@philpem.me.uk
http://www.philpem.me.uk/
--=20
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