Homebrew_PCBs

Hi all,

I've been reading the messages and looking at some of the links on
thru hole plating. I've also been to thinktink to read over their
stuff.

As thru hole plating appears to just be electroplating - I was
curious about how to properly connect a board...

ie: Most electroplating is (or at least appears to be from the way
I understand it) utilizing opposite charges, where one charge is on
the supply material (like a copper anode) and another charge on the
receiving material (cathode tied to the circuit board). As I
understand it all materials to receive the plating needs to be
connected in the circuit - so how does one plate a circuit board
where traces are not all connected to each other? By using a sheet
of metal pinned to the circuit board to make sure all traces are
tied to the cathode?

I realize what I have written probably at the very least appears
confusing, but unfortunately, I am confused at this point. Any help
would be most appreciated.

-Tony

On Fri, 03 Jun 2005 20:44:31 +0200, Tony H <kg4wfx@...> wrote:

> Hi all,
> I've been reading the messages and looking at some of the links on
> thru hole plating. I've also been to thinktink to read over their
> stuff.
> As thru hole plating appears to just be electroplating - I was
> curious about how to properly connect a board...
> ie: Most electroplating is (or at least appears to be from the way
> I understand it) utilizing opposite charges, where one charge is on
> the supply material (like a copper anode) and another charge on the
> receiving material (cathode tied to the circuit board). As I
> understand it all materials to receive the plating needs to be
> connected in the circuit - so how does one plate a circuit board
> where traces are not all connected to each other? By using a sheet
> of metal pinned to the circuit board to make sure all traces are
> tied to the cathode?
> I realize what I have written probably at the very least appears
> confusing, but unfortunately, I am confused at this point. Any help
> would be most appreciated.
> -Tony

You plate before you etch the traces, then all is still connected.
for small stuff, for example gold plating edge connectors, you can connect
the fingers at the end and cut the connection away later.

ST

Ok, next stupid question...

Let's say I drill all my holes, and plate.

Now I take it to etching - how do I protect my thruholes from being etched away? Also, if I am doing toner transfer, do I transfer the toner - drill - plate then etch?

-Tony

Stefan Trethan <stefan_trethan@...> wrote:

On Fri, 03 Jun 2005 20:44:31 +0200, Tony H wrote:


You plate before you etch the traces, then all is still connected.
for small stuff, for example gold plating edge connectors, you can connect
the fingers at the end and cut the connection away later.

ST



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On Fri, 03 Jun 2005 21:06:59 +0200, Tony Harris <kg4wfx@...> wrote:

> Ok, next stupid question...
> Let's say I drill all my holes, and plate.
> Now I take it to etching - how do I protect my thruholes from being
> etched away? Also, if I am doing toner transfer, do I
> transfer the toner - drill - plate then etch?
> -Tony

You must laminate dry film resist, it tents the holes.
TT and THP could perhaps be done by plating tin as resist over the copper,
but i dunno if negative TT and plating in the "gaps" works well.

ST

Aside from Thinktink is there anywhere else to get dry film resist? I don't want to get a huge quantity until I've tried it out first....

-Tony

Stefan Trethan <stefan_trethan@...> wrote:

On Fri, 03 Jun 2005 21:06:59 +0200, Tony Harris wrote:

> Ok, next stupid question...
> Let's say I drill all my holes, and plate.
> Now I take it to etching - how do I protect my thruholes from being
> etched away? Also, if I am doing toner transfer, do I
> transfer the toner - drill - plate then etch?
> -Tony


You must laminate dry film resist, it tents the holes.
TT and THP could perhaps be done by plating tin as resist over the copper,
but i dunno if negative TT and plating in the "gaps" works well.

ST



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[Non-text portions of this message have been removed]

In a message dated 6/3/2005 1:46:17 P.M. Central Daylight Time,
kg4wfx@... writes:

so how does one plate a circuit board where traces are not all connected to
each other? By using a sheet
of metal pinned to the circuit board to make sure all traces are tied to the
cathode? <<
No, Tony, you are visualizing the PCB being nearly DONE before the holes are
plated through. In reality, just the opposite takes place: Before ANY
resist or etching is applied, the drille, cleaned, and rinsed board is
"sensitized". Some kind of magical fluid is applied so that the walls of all the holes
become conductive. The copper on both sides is, of course, already so. The
"blanks" for plated-through work are also made with THINNER than usual
copper.

Then, the "whole mess" is plated with copper, hole-walls and copper surfaces
as well. This gives nicely-thick copper.

Next, the copper is photo-sensitized so that when developed only the "wanted
copper" is bare; the rest covered up. Then the boards are "solder-plated".
Yep, a tin/lead concoction is electroplated on that. ALL the bare copper
becomes solder-plated, the traces on both sides, and the walls of the holes.

THEN the resist is washed off and the boards etched in a solution that
"eats" copper but does NOT "eat" solder. Then rinsing again, and some heat is
applied, JUST-enough to melt that rather-raggedy grey-looking "solder", but not
enough to loosen the traces from the epoxy. This "shines up" the traces just
fine.

Next would be any solder-mask (that green transparent stuff), and
silk-screening, if wanted (white markings indicating what is what).

Next would be preparation of an OUTRAGEOUS invoice . . .

Got it? This is how it was explained to me. I never was allowed to "watch
it be done", but I have etched a few "copper-only, no PTH" boards at home.
Nasty! Jan Rowland







[Non-text portions of this message have been removed]

I pulled this off a reply by Don Wilkins of the
rec.crafts.metalworking site:

After the holes are drilled in a douple sided board (before etching),
"Plated through holes are done by first sensitizing the inside of the
hole using stannous chloride which leaves a tad of divalent tin on the
surface. This is followed by a treatment with a palladium solution.
The adsorbed divalent tin reduces some palladium in solution to
palladium metal which sticks to the PCB (in the hole). The PCB then
goes into an electroless copper plating bath where the palladium
catalyzes the reduction of copper in the electroless plating
solutions. The result is a thin conducting layer of electroless copper
through the hole. Too thin to use as is. (Of course this plating
through is done before any of the copper on the circuit board is
exposed. i.e. the mask has not been developed)

Finally the board goes into a conventional plating bath to produce a
thicker coat and make contact with the copper on the circuit. This is
a rough outline without the gory details."

If you can't plate the holes, the next best ways are to either solder
a wire or plug on both sides (see earlier discussions on this site),
or fill the hole with a silver compound that Radio Shack sells as a
PCB repair kit (also repairs rear window defroster tracks).

--- In Homebrew_PCBs@yahoogroups.com, JanRwl@A... wrote:
> In a message dated 6/3/2005 1:46:17 P.M. Central Daylight Time,
> kg4wfx@y... writes:
>
> so how does one plate a circuit board where traces are not all
connected to
> each other? By using a sheet
> of metal pinned to the circuit board to make sure all traces are
tied to the
> cathode? <<
> No, Tony, you are visualizing the PCB being nearly DONE before the
holes are
> plated through. In reality, just the opposite takes place:
Before ANY
> resist or etching is applied, the drille, cleaned, and rinsed
board is
> "sensitized". Some kind of magical fluid is applied so that the
walls of all the holes
> become conductive. The copper on both sides is, of course,
already so. The
> "blanks" for plated-through work are also made with THINNER than
usual
> copper.
>
> Then, the "whole mess" is plated with copper, hole-walls and
copper surfaces
> as well. This gives nicely-thick copper.
>
> Next, the copper is photo-sensitized so that when developed only
the "wanted
> copper" is bare; the rest covered up. Then the boards are "solder-
plated".
> Yep, a tin/lead concoction is electroplated on that. ALL the bare
copper
> becomes solder-plated, the traces on both sides, and the walls of
the holes.
>
> THEN the resist is washed off and the boards etched in a solution
that
> "eats" copper but does NOT "eat" solder. Then rinsing again, and
some heat is
> applied, JUST-enough to melt that rather-raggedy grey-
looking "solder", but not
> enough to loosen the traces from the epoxy. This "shines up" the
traces just
> fine.
>
> Next would be any solder-mask (that green transparent stuff), and
> silk-screening, if wanted (white markings indicating what is
what).
>
> Next would be preparation of an OUTRAGEOUS invoice . . .
>
> Got it? This is how it was explained to me. I never was allowed
to "watch
> it be done", but I have etched a few "copper-only, no PTH" boards
at home.
> Nasty! Jan Rowland
>
>
>
>
>
>
>
> [Non-text portions of this message have been removed]