Homebrew_PCBs

Hi all
Well, after much frustration, I thought I would more or less
abandon my efforts at using the toner transfer method, as my results,
despite using the papers and machinery recommended just weren't
working.
i invested around $100 US in a screenprinting setup. I was told
this should have the detail to do the kinds of things I wanted to do
(little 10 mil tracks). For anyone accumstomed to screenprinting, I
used a "12XX" pitch screen, said to be okay for fine details.
I was also unimpressed. Maybe it was because I chose an oil-based
paint, but the graphic I got on my copper was smudgy and way too
thick. Damn. Another failure.
So, in frustration one night, I read someone's post where they had
suggested that the temperature of the laminator (when used) should be
very hot. It made sense that the people experimenting with fusers
would be having luck, since they are awfully hot. I read that
someone bypassed the thermostat in his laminator, but that it hadn't
yeidled good results. I thought "what the heck...the thing's more or
less useless to me anyway" (because it only heats to 242 degrees F by
itself).
I bypassed it and let the thing heat. It got up to 350 degrees
before I stopped it, but not before running a board through a few
times. And wouldn't you know it...it came out pretty good. (I
changed my paper as well, to a "Sports Illustrated On Campus" issue I
happen to have laying around).
Because of the high heat, the cheap Wal Mart laminator's heating
element had fried. It no longer heated up. So...I opened it up and
found a metal housing around the rubber wheels, supported on set of
high-heat resistant plastic legs. I thought hmmm...what if I placed
my iron right on top of the thing, and just heated it that way?
Okay, it's cheasy in it's own regard, but it appears to work well.
I think I might be noticing a slight deformation of the rollers,
but I'm not positive. In any case, the iron's high temp is around
400 degrees F. When pressed against the flat top of the laminator,
it gets it up around 350. With only 4 passes through, I actually had
a board I was semi impressed with! Finally! I'm trying to submit a
picture in the photos area, should you want to be as cheap as me.
Total cost of equipment: laminator: (Henkel 9" electric, with
cartoon duck wearing a hat on the box) $22, iron: $6. Both purchased
at Wal Mart.
Now I have another question...just as I was about to submit my
circuits to a board house...I need a method to align my top and
bottom sides. Is there anything anyone does that works especially
well? I have looked through the messages from the group and have
heard of people taping both top and bottom on, and running them
through at the same time. That sounds like it would work, but how do
you align them accurately?

Thanks
-Josh
Pullman, WA

--- In Homebrew_PCBs@yahoogroups.com, "joshdewinter"

> Now I have another question...just as I was about to submit my
> circuits to a board house...I need a method to align my top and
> bottom sides. Is there anything anyone does that works especially
> well? I have looked through the messages from the group and have
> heard of people taping both top and bottom on, and running them
> through at the same time. That sounds like it would work, but how

do

> you align them accurately?

I use the TT method and a laminator; although I haven't had the heat
problems you had with my stock laminator. It might have to do with
the type of toner you are using. I know a guy accross town that has
been doing 1 sided boards OK with the same laminator (w/o modifying
the heat element btw). What kind of clad are you using? He does .5 -
1 oz 1/16" stock in his --although the rigid roller transport does
make a bit of noise doing so.

Most of the homebrew boards I do are double sided. I print the top
and bottom, (top mirrored) onto magazine paper making a few alignment
crosses outside of the board boundary lines. Under a bright desk
lamp I align the crosses of the two pages with the toner sides in. I
use a glue stick and bind one of the edges to create an envelope.
Sandwich the board into the envelope and insert the bound edge side
in first into the laminator. Make 2-3 passes in the same direction
until the toner "tacks". After that you can clip off the bound edge
and rotate and flip the board for a few passes until the toner has
fastened to the copper clad.

The sandwich works pretty well on some pretty tight via pitches. The
possiblity of the skew from the bound edge justifying to the top or
bottom turns out to be a non-event. The rollers tend to align the
binding with the center of the board when initially fed --as long as
you insert the bound edge in first and fairly perpendicular to the
board edge.

I have a write up on this in case you missed it in the TT links
section...
http://myweb.cableone.net/wheedal/pcb.htm

-Dal
(Pocatello, ID)

In a message dated 2/16/2004 9:31:08 PM Central Standard Time,
joshdewinter@... writes:
Now I have another question...just as I was about to submit my
circuits to a board house...I need a method to align my top and
bottom sides. Is there anything anyone does that works especially
well? I have looked through the messages from the group and have
heard of people taping both top and bottom on, and running them
through at the same time. That sounds like it would work, but how do
you align them accurately?
Drill the holes FIRST.

Or, if you MANUALLY drill all the holes (and break more $$ worth of bits than
having the PC professionally-etched would cost!), and you MUST have the
"copper pattern" present for drilling, then, using a light-box, place the negatives
for top/bottom together, emulsion "inside", and tape them together along TWO
sides, being careful to keep the "targets" aligned while taping. THEN, just
SLIP the sensitized blank between, clamp in a contact-printing-frame, and
expose. Remove, reverse, and repeat. Now develop and etch.

But, if redundant, if the holes are there FIRST, you could use the negatives
"one at a time", and be CERTAIN of registration. Yes, I realize drilling
first would require either a home-brew CNC drilling rig, or the use of some kind
of, say, self-adhesive pattern showing all the hole-centers. And, sadly, most
photo-copy machines will NOT sufficiently accurately copy a pattern for this
purpose. If you "draw" your pattern with an ink-jet printer, then print a
copy on Avery 5265 (etc.) full-sheet adhesive-backed label-stock, and stick that
to your blank, and drill. The paper helps a tiny bit to "center" the bits as
they enter the work. A slow and kludgy method, but possible when the wallet
is so severely challenged. Jan Rowland


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