Jack Carroll wrote:
On Wed, May 17, 2006 at 09:04:09AM -0700, Nick LaForge wrote:
How far can a electronics hobbyist go before he hits manufacturing
limitations? I recently read a few articles describing methods to
etch a blank PCB by pouring acid over a laserjet printed toner layout
that resists acid, creating a finished PCB. One could then add
capacitors, resistors, and ICs... but how far can one go? I
understand that making one's own PCB would yeild less precision and
could thus never achieve the same density as commercial productions,
but is it enough to build one's own computer hardware? For example, a
PCI card? Forgive my ignorance, but doesn't the ability to make one's
own PCBs only put ICs and microcontrollers out of our reach, which can
all be bought individually?
It depends. You can buy pre treated photographic board or buy the film
and attach it on copper boards. For the home guy, you can use a laser or
ink jet to print your circuit on transparency paper - you can easily
achieve 0.4mm gaps and traces, and you can even use a 300W mercury vapor
lamp if you are in a hurry (warm up at least 2min, then at 300mm it is
around 17-20sec each side). For the dark room, a yellow lightbulb of 30W
is usually ok as long as it is not on too long. With transparency paper,
you dont have a complete light barrier for the photographic process, but
by under exposing it a little, with care you can easily do double sided
boards with traces that go a little lower. Process with reasonably fresh
riston developer (forgot the formula sorry mind-is-blank-need coffee)
and wash off/wipe off using acetone. The problem is printers have poor
registration accuracy with larger boards 5 - 6 inches.. which limits
where you place through holes and vias, and they need to be reasonably
big. Drilling with router or high speed drill and carbide bits. You can
use high speed drills if desperate and throw them away every couple of
holes, but carbide is better. With pads, bigger is better - say 2mm dia,
as you cant drill as good as a shop.
Solder mask..You can go to the local art shop and do the epoxy solder
mask with screen printing - it becomes worth it if you are printing a
few boards. BGA are a bit different story, but apparently you can do
them. I have a couple of how-to's somewhere that I have been meaning to
try. Here is one..
http://www.lrr.in.tum.de/~acher/bga/
There is a company which will sell you a stainless mask for solder
paste, if you want to use a little oven but I haven't got the link
handy. Perhaps Google will find it.
Etching can be done with acid or Ferric Chloride, which you may be able
to get from your local steel mill, drinks company and water treatment
plant if you talk real nice. Dont make it too strong a mix - and it will
get warm when you first mix it so be wary of plastic containers and wear
glasses! Keep it covered and in a ventilated area, and before using it
you could warm it with a glass goldfish pond heater. The fumes are not
good for you and will destroy your electrical equipment etc carelessly
left nearby, oh - and dont pour it down the toilet unless you want a
terrible mess and huge bill$. A local waste disposal shop will dispose
of it for you for $20. Talk nice and he will tell you what household
chemicals to mix so you can dispose of it, but it is much safer if they
do it.
For making the graphics, eagle have a limited free version, there is
gEda (Circuit Cellar issue 188 Mar2006 has a bit of a guide) and if you
want to pay, there are a heap of options, say Rimu Schematic & PCB for
the lower prices and you can pay much more at the high end<grin>.
Investing in a fine tipped temperature controlled iron is always good.
Don't use the dirt cheap irons as they can destroy your chips, unless
you turn then power off when about to solder - an trick of desperation
only. And good flux is a really, really good idea.
These methods will let a guy churn out fairly impressive epoxy masked
double sided boards containing multiple fpga and micro controllers, with
0603 components.. But this is not a multi layer board with gold edge
contacts and it *is* a lot of work when you realize that you can get a
company to make it for you.
JB
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