Brian:
Here's ONE ignernt Yank's experience for you to confuse among other good
info: The first-ever home-brew PCB's I ever did were done by "painting" the
pattern with colored lacquer (discarded ladies' fingernail polish was fine
for this!), and/or the use of good cellophane tape put on the "blank" copper,
then trimmed to shape with an Xacto-knife (the kind of "hobby knoves" with
razor-sharp disposable/replaceable blades of many shapes), and then etching
with (here) readily-available Ferric Chloride solution. Nasty, staining,
yellow stuff.
I once bought some photosensitive spray with which one coats the blank copper
like painting, letting that dry in darkness, and then exposing that using a
1:1 negative film contact-clamped to the sensitized board. I have also tried
some "store bought" sensitized board, but it works no better, and is far more
expensive per sq.cm. This makes for a "photographically correct" pattern,
but it is MY contention that electrons moving through copper on a copper-clad
epoxy board have NO clue of this, and have no perceptible preference, so it
is a "user's choice" kind of thing, isn't it!
Lately, world-wide Radio Shack (no, NOT "RS" which you have over there!) has
been selling "etch-resist felt-tip pens" (similar to a "Sharpie" by Magic
Marker, or is it Sanford?). If you are skilled, you can "draw" a pattern
with that, being sure go "go back over" those spots where SOME copper
glistens through the black pattern a bit (i.e., that is NOT strongly opaque
stuff, no!). You can do this for maybe two or three smallish boards within a
fortnight, provided you do each within a half hour or less, and always
TIGHTLY close the pen when done, each time. After that, evaporation will
FINISH the usefulness of the things! No, NOT an exaggeration! ("Creative
Marketing"??
Recently, a gentleman in a local metalworkers' club of which I am member
showed the group some "Permapressed" or whatever he was calling it, a blue
film-like stuff that can be used in conjunction with a laser-printer. I
wasn't TOO interested after I realized he was saying one MUST do the art on
computer, then PRINT it using a laser printer, and this film he showed,
somehow. BUT, it DID make a "perfect" pattern on the copper, which etched
totally pin-hole free, etc. I do not, therefore, recall the name of the
source of the material.
Here, there is a firm by name of Kepro (where? I never remember. Try a
Google search, etc.?) which sells most of these kinds of materials.
There is also ammonium persulfate, which is white delequescent crystals
which, when dissolved in tap-water, will etch copper, and is not as "nasty"
as the yellow ferric chloride, but I have no clue how it compares in price
per liter of ready solution, speed of etch at whatever temperature, need to
dispose of the waste in a gopher-hole, or a tributary of the Volga, or what.
Another thing in this regard: IF you drill holes with a "drill press", you
must ETCH the board first, and then drill the pads on-center, etc. If you
have an X-Y drill under "PC" control (see mine in "Photos" on the Group's
site), you have to drill the board first, then "do the art", registering
carefully over the holes. With care and practice, I much prefer this latter
technique. It is much faster and more precise, and "repeatable", at least
where the HOLES are located!
Feel free to e-mail me direct, if you wish. Ideally, a non-multilayer board
has plated-through holes and good TIN/LEAD "solder-coat". PTH is virtually
unheard of for "home brew". Would, at least, require quite a setup to
effect! I once had some ivory-colored solute from Kepro which was to do
electroless tin-plating, and that DID "brighten" and "silver-color" the
bright pink copper, once etched, but the thickness of the electroless tin was
so thin that it did nothing much to increase "solderability" (the reason a
thicker tin or "solder-plating" will aid solderability requires too much
space to explain here). I know a firm in Suffolk that uses square metres of
PCB's per month, and at least a decade back, if not still, they found it more
economical to have girls inserting solderable rivets by the tens of thousands
in holes which then got a Through Lead (resistor or diode), and were soldered
on both sides, rather than PTH, soldering with a wave-soldering machine. I
never had opportunity to discuss why with any of them, and the proprietor of
the firm married his new helicopter he had just learned to fly (not terribly
well, it seems) to the earth, on his way home from London, one fine
afternoon. With that, I had little contact with any of them, any longer, so
by now, perhaps they are using PTH boards exclusively. Do not know.
Regards! Jan Rowland, Yank Troll