Re: Printed Circuit Board Supplies

At 10:38 PM 2/9/00 -0600, you wrote:

>From: hansw <hansw@...>
>
>Ted,
>A question comes to mind. As you have a laminator to look at, how

difficult do you think it would be to make one ?

That nightmare- a board shop in a green community is over and cost me, my
family, and the society these people were trying to protect, dearly, but I
will try to answer your quesstions.

The Laminator was a simple device that you will probably be able to fake
quite adaquately with an ordinary iron and ironing board. It consists of
two thermostatically controlled heated rollers covered with a fairlly high
durometer plastic coating, obviously not a low temperature thermoplastic. A
roller with a piece of vinyl tubing pulled over it would probably work.

Instead of heating the rollers internally, infrared floodlights on the
platen, the (aluminum or steel) flat plate on which you would lay the board
to feed it into the rollers might work. An important tool for printed
circuit makers which would work better than a pair of rollers you would
fabricate yourself is the wringer mechanism from an old manually controlled
washing machine.

>Then there is the question of cost of dry film. What are the minimum these

(whoever you use ) will sell for in $... how much

>film would that be ?
>

I used DuPont Riston and another brand. They both worked, but I felt the
Riston was more repeatable and durable. It comes in identical looking
tubes with rolls of different length. Just get the shorter roll.

To expose the sensitized board you can make or buy a vacuum frame, but
careful use of a foam pillow and a piece of glass works fine. Before I got
a proper Uv Exposer usit with a built in double sided vacuum frame to hold
the board in registration with the film, when I made a double sided board,
I taped both pieces of film along two edges to strips sheared off of pc
board, that way I could force registration in the pocket of the film. Then
I taped the board into place on one of the films and taped the third edge
of the films together to maintain registration.

Another possibility which I didn't try, but which should work, depending on
the chemistry, is silk screening film. Since it uses UV to expose, and (as
I remember, bases (not acids) to develop and strip, you need a similar
development chemistry because your etchants and plating baths are acids.
This stuff is available in much shorter rolls and in most medium sized
towns since every town has artists, sign makers and others who silk screen.


Another Alternative

Any of these people as well as the graphic arts store cah show you how to
silk screen. Graphic arts stores and junior colleges often offer classes
in silk screening and some high schools have someone in the art department
who may help you. It is easy although If you don't have good eyes, fine
lines and spaces can be a challange. One line between pads on a .100
spacing IC is within reach of even a nearly blind person. If you goof up,
it is easy to clean off a board with uncured screening ink. In my first
shop, the brightest and most responsible woman in the electronics loft
insisted on learning to do the silk screening. She did a great job,
although I remember wondering if she was too old to learn such a skill,
since she was already in her forties. I remember that the world seemed a
lot younger then.

If you have never tried silk screening circuit boards, you will be
surprised at how little it costs to set up and how cheap it is. Any
graphic arts store will sell you a wooden frame with silk screen material
fastened to it, the screening paddle, and the hinges necessary to make the
screening table. Cloth mesh is used for legends and solder masks.
Normally the circuits are screened with a stainless steel mesh, but the
cloth mesh will work wuite well if you aren't trying to hold .003 inch
lines and spaces. Ten thousandths lines and spaces will be quite easy to
register with cloth mesh.

To make an inexpensive screening table for printed circuit boards, use a
sheet of frosted plastic and mount the hinges to a bar of wood or metal
behind it. Anchor the bar to the top of a larger sheet of plywood and
anchor the pastic sheet to the bar with a bolt at each end of the bar.
that allows you to displace and rotate the silk screen with respect to the
board. Mount another screw on one edge of the plastic sheet and on the
plywood board to alloiw you to displace the screen sideways with respect to
the board. Cut a hole in the plywood under the plastic sheet to allow the
flourescents you mount under it to shine up through the holes in the board.
Now registering a predrilled board to the screen is fairly easy.

>What's the shelf life of the film ? this would be important for me...

As I remember, a year is typical, but if you keep it dark and cool, three
years is probably safe.

Of course screening ink doesn't have the same shelf life problem, it's
cheaper, and graphics stores usually will even make up your screen image
onto their silk screens for surprisingly little cost. When you need
another screen you can have them reimage your old one or make you a new
one. They are cheap enough that you normally just leave the image on a
screen if you might need to reuse it. You are constantly cleaning out the
screen with a screen wash solution they sell the same place. If you don't
leave it clean when you are done, it's scrap. You don't want screening ink
to cure in the mesh.

The only other piece of capital you need to make the boards is any oven,
kitchen or box with a gentle heater in it. A fan helps, but if you just
set it on shelves in a relatively dust free environment like a cabinet, the
ink will cure by itself in a few days or a week. Screening is really
simpler than photographic process unless you have a good UV light source
for exposing the film. Sunlight works faster than such a light source but
it is less controllable.

>
>One thing I like about positive pre sensitized boards, I simply use Red

Devil Lye as a developer and it's fast. Exposure for 1

>minute under my UV light source and develop in Lye for about 30-45

seconds... I make transparencies on my LaserJet, I'm also

>able to consistently get very fine lines <10 mill is not problem, anything

seems pointless for my kind of work.

>
>Hans Wedemeyer
>
>
>Ted Robbins wrote:
>
>> From: Ted Robbins <rtr@...>
>>
>> I, too, graduated to a dry film laminator. I used two of them, one for
>> resist and one for solder mask and legend. But that is a pretty heavy
>> investment for casual use. I have never tried to iron on the resist film,
>> but would probably try that before I would use the liquid film again. I
>> agree that the dry film sensitized boards are really tough. Solder mask
>> and legend film seem as tough as screened inks.
>>
>> One nice thing about ferric cloride is that it dries to a pile of salty
>> rusty copper fines when you let the spent stuff evaporate. The problem

is that you can't

>> use it for plated through boards which use solder to prevent the etching of
>> the copper you want to keep. It eats solder as well as copper.
>>
>> The thick film approach has a lot going for it, but again, it is probably
>> not a practical process for most of us.
>>
>> Ted
>>
>> >From: Jon Elson <jmelson@...>
>> >
>> >
>> >>The hot roll laminating of the dry film allows it to stick well to
>> >boards that are less than
>> >perfectly clean. I clean them as well as I can, but they still have a
>> >few spots or slight
>> >blemishes on them. The resist still sticks to the entire board, blemish
>> >or not.
>> >I don't ever want to use the KPR type process again, but I have no
>> >qualms about
>> >using dry film. The Fe2Cl3 etchant is pretty hard on skin, but I use
>> >rubbermaid
>>

More from Ted which may be useful in the FAQ

The ferric chloride is made by pouring HCl over rusty iron scrap, usually
car bodies, and collecting the ferric chloride at the bottom.

REALLY IMPORTANT

To get the heavy metals out of your spent etchant of any kind, first put it
in a plastic barrel and adjust it to an acid pH, the more acid the faster
it will work, but the more Dry sodium hydroxide, you will have to use later
to complete the process. Throw in aluminum scrap. Thinner sections such
as pop cans and chips from a machine shop work well. Beer cans are coated
with a plastic so they dissolve much slower. Much of the copper and other
heavy metals precipitate out as insoluable salts. Decant or pump off the
clear liquid (acid containing aluminum ions as well as a n unacceptably
high concentration of heavy metals.)

Now slowly ( to prevent too fast a reaction) add dry sodium hydroxide to a
pH between 9 and 11. I prefer to get it as close to 11 as I can. The
metals we are concerned with (copper and lead) are insoluable in this pH
range. That means they are solids. Let them settle out and decant to
another barrel. Then stick a filter and pump in the new decanted barrel
and filter it with at least one filter change to get the fine solids out
that you decanted even though it looked clear.

Then you can bring it to neutral with HCl or use it to neutralize other non
metal bearing acids. It is sewerable under federal EPA guidlines, but not
under green community laws. Our green uommunit, instead of adhearing to
the then standard of two parts per million of copper down the drain
insisted on 0.2 parts per million. Of course we were not allowed to use
PVC water pipe, and copper pipe will add more than that to water flowing
through it. As I said in a previous post, they were technically illiterate.

If you pour spent etchant down the drain without treating itand you are
caught, you can go to prison. I should be more emphatic. You WILL go to
prison. I avoided it by scrupulous attentian to the problems, but the risks
weren't worth it. Remember, you are guilty until you prove yourself
innocent. Without substantial legal resources and a willingness to waste
them on trying to prove yourself innocent to people who assume any
chemicals exept those which make you high are evil, you are presumed
guilty. If you have employees doing this stuff and you don't completely
automate and record it, they will find a way to speed up the process and
you will end up in jail as the responsible party.


The Ammonium Persulphate etching process

Ammonium persulphate is the best chemical process I know of to etch plated
through boards in a closed cycle. This is the process I used. It requires
only one pump exposed to the echant. I pumped the etchant from the bottom
of the etchant tank to a tank about ten feet off the floor. There I cooled
it with a stainless steel tube I coiled up around the inside of the tank
and ran to a window sized refrigeration compressor.

An agitator ran constantly in that tank to prevent the copper sulfate which
precipitated our from settling to the bottom. This overflowed to the next
plastic barrel (Yes, I used a lot of PVC and Poly propylene barrels.) There
the copper sulphate settled out. Then the etchant flowed down to the
etchant tank slowly so the heater in the bottom of the etchant tank could
maintain the proper etching temperature.

I constantly titrated for sulphuric acid and copper. I can't remember if I
checked for any other concentrations. When sulphuric acid got low, I added
it. When copper got high, I pumped it up to the cooling barrel and let
etchant flow down from the settling barrel. If you don't constantly
titrate, the process goes out of control. Big places use automatic
titrators. Obviously not for short run people like most of us.

I'd like to be more encouraging, but I still have nightmares over the 12
years blown in my circuit shop. (I'm a slow learner) An Electronics
Guru, Butterfield (?), said that you should run immediately from any
community that questions your right to do what you want to do inorder to
make a living. I would add, let your society be poorer because you can't
help it solve the problems you wish to address. I didn't believe Mr.
Butterfield, but he was right. Nathan Hale said it and demonstrated the
result. "Give me Liberty of give me Death." He got Death, of course. Do
you think it's really different today? Buy your PC boards, not because you
can't make them yourself, but because the risks don't come near the rewards.