( last
updation: 02-April-07)
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Please
Remember:
3. In case of FreePCB(around 5MB), you can create the Gerber file (Gerber is an universally accepted format for PCB layouts, just like PDF for documents), and open the Gerber file in Pentalogix Viewmate software (this is also free, around 6MB)
See my review
about FreePCB and more..
Artwork:
Draw the traces in any PCB software
(I prefer
FreePCB). Take
the laser printout in a plain paper (ordinary A4) of the mirror image of the bottom layer.
Mirroring the bottom layer is important for obvious reasons, because
all PCB
software show the bottom layer as if you look from the top; we have to
mirror
to combat this.
Check the connections, and once you know all the traces are correct, go
to the
following steps:
Let’s
start:
The Toner
Transfer
1. Buy the so called art paper. This is a glossy paper, sold for Rs. 1.5/A4 sheet, in my area. This is analogous to the paper used in magazines. The crux of this process is, we are going to make a big tattoo of our PCB layout!
2. Take the “Laser print out” of the layout (please remember to mirror).
Some printing tips:
· Use the darkest setting possible in the printer, this makes sure that we have lot of toner in the paper, and the subsequent stages are easy.
· Please make sure that the Art paper is dry. A general tendency of this paper is, it will go wet in humid conditions, so when you take laser printout, the paper will literally be fried, and you won’t get good results.
· Don’t take just one printout, take some two spare copies, so even if the first paper goes off in the ironing process, we can use the rest (this will save time and annoyance!)
3. Take a clean copper clad sheet (a
plain PCB, cut to the required
dimensions
of your circuit as per the layout)
4. Scrub the copper area using scotch-brite
scrubber. This is for cleaning the dirt and the copper
oxide formed due to exposure to atmosphere (for techies, scotch-brite
is a
commercial product of steel-wool)
5. Place the toner side of printout over the copper area (remember, you are mirroring the image at this step. So, while you are taking the printout, you would have mirrored once. Double mirroring will give you the exact bottom layer, as you need in the final PCB)
6. Get a heavy iron box, put it to medium heat, and just press the
paper
against the PCB in a floor.
7. Don’t iron the paper to and fro, since this will squeeze
the toner
particles, just give maximum pressure on all sides of the PCB.
8. Do it for 10 minutes (this is the most critical step, and you need
patience
and practice, so don’t expect this to work out on the first
time).
Correct
pressure and heat are important variables, so you need practice and
experience...
9. after 10 minutes of ironing, soak the PCB + paper in a tray of water
for 15
minutes.
10. after 15 minutes, gently peel off the paper, you should get the
paper out,
just like the tattoo on skin
11. If step 10 is not working or the peel off is not working, gently
rub the
paper against the PCB with your fingers, you will get the paper
disintegrating.
Beware, the toner tracks must not get away.
12. Do a visual inspection of any paper left over shorting the tracks;
Get them
off by simply rubbing by an
used, soft
tooth-brush
13. Etch in hot
20% diluted HCl +80% FeCl2 solution
(HCl is a
good
accelerator of etching process, and use hot water to dilute. The
temperature of
the whole solution should be around 50-70˚C)
14. That’s all. (Now see there are 14 steps, and not 13! Many
people
consider
13 as unlucky number, even IEEE! In 802.xx standards, there is no such
thing
called 802.13).
Other important
points:
Minimum trace width
must be:
Ø 50 mils for signal traces
Ø 35 mils
for inter IC traces
Ø 75 mils for ground and Vcc (use 75 and above)
(1 mil is 1000th of an inch and
39mils = 1mm).
In most PCB packages, you can go down to 8 mils, but in this method, it
will
not work out. Try to maintain a profile of at least 50 mil thickness,
and go to 35-40 mils only if necessary.
You need patience and practice, so try it out before going to any big
design.
Mail me if you have any more doubts.
