[sci.electronics] plated thru holes

climber@uvicctr.UVic.CA.UUCP (climber) (05/29/90)

I am designing double sided boards that I am planning to etch myself.
Now, I want to start using pin arrays and realized that I will now need 
plated thru holes (where the copper lines the hole itself making a nice
connection between top and bottom traces).  Is there a way I,
a hobbyist with measly resources, can build a two-sided board
with plated thru holes?  I would like to avoid the following:
  
  tremendous equipment expense
  having to spend more than $10 per prototype board (outside the costs
     of blank PC board)

Has anyone tried this?  How does the big-wigs in the industry do it?

Send any responses to: climber@sol.UVic.ca

Any help would be greatly appreciated.  

Craig

thouse@uvicctr.UVic.CA.UUCP (thouse) (05/29/90)

> I am designing double sided boards that I am planning to etch myself.
> Now, I want to start using pin arrays and realized that I will now need 
> plated thru holes (where the copper lines the hole itself making a nice
> connection between top and bottom traces).  Is there a way I,
	 The plated through hole process is very complicated and time consuming.We used to have a machine to make the boards here but gave up because of
the number of steps required.

irwin@m.cs.uiuc.edu (05/30/90)

/* Written  2:57 pm  May 28, 1990 by climber@uvicctr.UVic.CA.UUCP in m.cs.uiuc.edu:sci.electronics */
/* ---------- "plated thru holes" ---------- */
>I am designing double sided boards that I am planning to etch myself.
>Now, I want to start using pin arrays and realized that I will now need 
>plated thru holes (where the copper lines the hole itself making a nice
>connection between top and bottom traces).  Is there a way I,
>a hobbyist with measly resources, can build a two-sided board
>with plated thru holes?  I would like to avoid the following:
  
>  tremendous equipment expense
>  having to spend more than $10 per prototype board (outside the costs
>     of blank PC board)

>Has anyone tried this?  How does the big-wigs in the industry do it?

>Send any responses to: climber@sol.UVic.ca

>Any help would be greatly appreciated.  

>Craig
/* End of text from m.cs.uiuc.edu:sci.electronics */

Though I responded to Craig with e-mail, I thought I might put
some of what I sent to him here, as it may be of interest to
others.

I am with the Department of Computer Science, at the University
of Illinois. Years ago, about 15 or so, we used to have a complete
printed circuit board lab, complete with cameras, PCB layout group,
etch facilities, plating equipement and a wave soldering machine.

The process which we used for plated through holes may have changed
since then, and again, it may still be done in much the same manner.
I will describe the process for the hungry minds on the net.

We started by first drilling the boards (double sided), with what
I believe was called a Panograph. It was simular to the machines used
to make name plates and badges, or engraving. There was a master
template which one followed with the cursor, and the electric drill
followed your every move in the X/Y direction. We used a brass plate
to make the template, making a center punch in the template for each
hole to be drilled in the boards. The cursor had a sharp pin that 
dropped into the center punch hole, which positioned the drill over the
correct spot in the boards and they were stacked and drilled 4 or 5
at a time. The drill was air operated, so as one placed the cursor
into position, they pushed the air button and the holes were drilled.

After the holes were drilled, the board was placed into a copper bath,
and electrodes (2) were connected from a power supply to the opposite
sides of the board, such that when the board was placed into the bath,
a current flowed from one side of the board to the other, through the
bath. This plated the copper through the hole.

After the copper plate, the board was photo sensitized, dried and
exposed to the image via a negative, or I should say, a positive.
The image was developed, leaving the photo resist on the board where
you did NOT want to have any copper remain.

This stripped the resist from the area that would become the trace
or conductors on the board. It was then again placed in a bath and
plated, this time with tin. The tin was to act as the etch resist
in the final process, so, the trace and plated through holes were
tin plated. The image was then stripped, which removed the photo
resist, and the board was then etched, the tin being the resist.

There was also a seperate process for plating the contacts, if it was to
be a "plug-in type board". The contacts had to be I think first nickel
plated, then gold, over the original copper. This was done prior to
the tin plating.

After it was etched, it was trimmed to size, parts loaded and then
passed over the wave solder machine.

In summary, for one to do this on a small scale, one would need the
chemicals to make up the copper and tin bath, the power supply for
plating, the photo resist to apply to the board, an oven to dry it,
and so on. It takes quite a bit of equipement. We also emersed the
board in dye, which dyed the image of the resist on the board black
in color, and one could check the quality of the image. If flaws were
found, they could be patched up with nail polish (of all things) or,
the board could be stripped of the resist and done again.

The board had to be scrubbed with a fine powder like used at the kitchen
sink to clean copper bottom pans, before any of the above process was
started, to remove the oxide, or one would not obtain good results.

All in all, it was not an easy process. I do not know if the technology
has changed much, but I would suspect that the steps taken today are
much the same. I do think that there is a silkscreen process, that
provides the component identification on the board, plus acting as
a resist to the tin plating, though we did not do this with our boards.

Al Irwin
Univ of IL
Dept of CS
Urbana, IL
irwin@m.cs.uiuc.edu

thouse@uvicctr.UVic.CA.UUCP (thouse) (05/30/90)

> I am designing double sided boards that I am planning to etch myself.
> Now, I want to start using pin arrays and realized that I will now need 
> plated thru holes (where the copper lines the hole itself making a nice
> connection between top and bottom traces).  Is there a way I,
> a hobbyist with measly resources, can build a two-sided board
> with plated thru holes?  I would like to avoid the following:
>   
>   tremendous equipment expense
>   having to spend more than $10 per prototype board (outside the costs
>      of blank PC board)
> 
>
Part of my last message was missing so here is my answer again.
The process of making boards with plated through holes is very time consuming
and requires a lot of different chemicals. We used to have a system
here but got got rid of it for this reason. I doubt very much whether
you would ever make a board for the price you are quoting.

henry@utzoo.uucp (Henry Spencer) (05/30/90)

In article <1109@uvicctr.UVic.CA.UUCP> climber@uvicctr.UVic.CA.UUCP (climber) writes:
>... Is there a way I,
>a hobbyist with measly resources, can build a two-sided board
>with plated thru holes? ...

As far as I know, the basic answer is "no".  The plating process used to
lay down copper within the holes needs precise control of temperature and
solution chemistry if you want dependable results.  After masking off
the no-copper-here areas, the surface of the board is exposed to a
catalyst, a very thin layer of copper is laid down by a chemical
process, and then electroplating is used to build it up to a useful
thickness.  Even the electroplating is a slightly fussy job if you
want a smooth, even, solid, well-bonded layer of copper, and the less
said about the chemical process, the better.  It's not a million-dollar
investment to make it work, but you can't do it on a shoestring either.

If all you want is a demonstration technique that sometimes works and
sometimes doesn't, no problem, but if you're after trustworthy boards,
that's different.
-- 
As a user I'll take speed over|     Henry Spencer at U of Toronto Zoology
features any day. -A.Tanenbaum| uunet!attcan!utzoo!henry henry@zoo.toronto.edu

herman@marlin.NOSC.MIL (John W. Herman) (05/31/90)

--
I vaguely recall seeing an ad for a machine that puts sleeves in
PC board holes the claim being that the sleeves could be put in
for much less than plating through holes.  I only remember seeing
the ad and not much else.
-- 
John Herman    ARPA:  herman@marlin.nosc.mil  Phome: (619)553-1466
Naval Ocean System Center Code 712
271 Catalina Blvd
San Diego, Ca. 92512-5000 

a143@mindlink.UUCP (Ed Meyer) (05/31/90)

Replying to a message by Greg Ebert (Grass Valley Group), I thought I'd mention
something which happened to me.  While diagnosing a computer board fault
(ruggedized board for environmental data acquisition) I came to the conclusion
that one or more plated through holes in one section must not have been plated
through.  Well, careful conductivity checking verified my suspicions.  But then
came the surprise -- I'd heard about this kind of thing before but never
experienced it myself until that time -- the holes were falling out!  One inner
wall cylinder was just in its hole and several of the other tiny cylinders were
at the bottom of the case, no kidding.

So, even though the board shop was making plated through holes, {_a quality
problem existed which didn't show up till much later.  

wbrown@beva.bev.lbl.gov (Bill Brown) (05/31/90)

In article <1422@marlin.NOSC.MIL> herman@marlin.nosc.mil.UUCP (John W. Herman) writes:
>
>--
>I vaguely recall seeing an ad for a machine that puts sleeves in
>PC board holes the claim being that the sleeves could be put in
>for much less than plating through holes.  I only remember seeing
>the ad and not much else.
>-- 

---And round and round it goes....

'Way back in the Jurassic age, BPTH, (Before Plated Through Holes) eyelets,
AKA rivets were used for making connections between the two sides of a
double-sided board.  They were sort of squashed or swedged into place, which
was supposed to make a permanent connection.  Of course they usually became
intermittent over time, perhaps due to working caused by thermal expansion.

The next step was to solder the rivets to the artwork.  Eventually, this also
failed intermittently, probably for the same reason.

Usually, we ended up running wire through the rivets which was then soldered
to the artwork.  Seems like we ued #24 soft copper, as best I can recall.

You've never lived until you've tried to trouble shoot a fair sized system
(in those days a few thousand gates built out of discrete components, six
2-input nands per board) full of rivets which sometimes conducted and sometimes
didn't.

Rivets.  Bah!  Humbug!!  Might as well use wire in the first place.  Be sure to
make gentle bends in the wire on either side of the board, and leave a tad-bit
of slack for expansion/contraction.

							-bill
							wlbrown@lbl.gov

Disclaimer:  These opinions are my own and have nothing to do with the
    official policy or management of L.B.L, who probably couldn't care 
    less about employees who play with trains.

grege@gold.GVG.TEK.COM (Greg Ebert) (05/31/90)

In article <1422@marlin.NOSC.MIL> herman@marlin.nosc.mil.UUCP (John W. Herman) writes:
>
>--
>I vaguely recall seeing an ad for a machine that puts sleeves in
>PC board holes the claim being that the sleeves could be put in
>for much less than plating through holes.  I only remember seeing
>the ad and not much else.
>-- 
 
 I saw such a machine demonstrated at NEPCON in 1984(?). You clamp-in a pre
 drilled board, pour a few thousand sleeves in the tank, and then the board
 vibrates. I was astonished to see that, yes indeed, the holes were filled.
 I don't know how reliable the process was. Many moons ago I was a tech, and
 I distinctly remember a particular CPU board nobody else could fix because
 every time you touched it with a scope probe, it died. Guess what! It was a
 hole that wasn't plated through.

raoul@eplunix.UUCP (Nico Garcia) (06/01/90)

In article <1109@uvicctr.UVic.CA.UUCP>, climber@uvicctr.UVic.CA.UUCP (climber) writes:
> connection between top and bottom traces).  Is there a way I,
> a hobbyist with measly resources, can build a two-sided board
> with plated thru holes?  I would like to avoid the following:

Ummm, after a little bit of experience and lots of reading and asking
questions, my answer is "no". The best you can do with hobbyist level
equipment is to drill a hole, put pads around it on both sides, solder a
piece of wire through it on both sides, and run traces from that. It takes
up a bit more room, but not much if you're careful. 

Remember also, things like resistor leads and IC pins can be soldered on
*both* sides of the board: it makes them tougher to replace, but they can
carry your signal for you. And if you have to replace it, plated through
holes are a pain to desolder anyway.

-- 
			Nico Garcia
			Designs by Geniuses for use by Idiots
			eplunix!cirl!raoul@eddie.mit.edu

otmar@hpcvia.CV.HP.COM (Otmar_Borchard) (06/01/90)

> I am designing double sided boards that I am planning to etch myself.
> Now, I want to start using pin arrays and realized that I will now need 
> plated thru holes (where the copper lines the hole itself making a nice
> connection between top and bottom traces).  Is there a way I,
> a hobbyist with measly resources, can build a two-sided board
> with plated thru holes?  I would like to avoid the following:
>   
>   tremendous equipment expense
>   having to spend more than $10 per prototype board (outside the costs
>      of blank PC board)
> 
> Craig
---------
 
I worked in an electronics repair shop for the USMC a few years ago. We
did a lot of work on double sided boards and used a lot of products from
a company called PACE, Inc. They specialize in printed circuit rework and
repair. They have something called a CIR-KIT that has parts to repair runs
and plated through holes. If your boards will have a small number of plated
through holes you could use some of the eyelets they sell. 

To install an eyelet, you drill a hole through the run and the board, place
the eyelet through the hole, flare the ends of the eyelet, then tap them 
flat with a hammer and punch. After you solder them to the runs they make
a reliable plated through hole. Pace makes a variety of sizes to fit 
different thickness of boards and different diameter component leads.

I'll stick their address on here in case you want to contact them.
Good luck!

--- Otmar Borchard
    Hewlett-Packard
    Corvallis, Oregon


Pace Inc.                        Pace US-West
9893 Brewers Court       <or>    14451 Chambers Road, Suite 100
Laurel Maryland 20707            Tustin, California 92680-6913
(301)490-9860                    (714)838-8100