My PCB prototyping experiments

[Newz2000]

OK, So, I never got the guts to try the silkscreen technique (you guys talked me out of it), but that's OK, there were some obvious problems.

I've tried Ed's technique twice now. Actually three times if you count the very first attempt which majorly bombed out.

First, I tried using clear contact paper, and it has one benefit, it's adhesiveness, but it has some disdadvantages - it is hard to cut with an exacto knife. It likes to stretch and tear at the corners where your knife has a hard time cutting cleanly through.

I reverted back to using my card stock. I simply print the image on 4x6 note cards. Cutting goes much easier on the card stock because you can just trace the lines with your knife and then flip the card over and see where you didn't get all the way through. This allows the traces to come out with out tearing or distorting the masked part.

In order to get the benefit of the contact paper's adhesiveness, I used some spray adhesive.
<img src="http://img401.imageshack.us/img401/8539 ... 2ul.th.jpg" alt=" - " />

I looked and looked and could not find Krylon spray paint. Neither Home Depot, Menards or Walmart carry it. All carry rustoleum. The rustoleum matte black does not work. When you spray it on, it looks nice, for about 20 seconds. Then you notice that it is pulling away from the edges of the mask and pooling up in the middle so that you see a band of copper around the outside of where the black paint is.

It does resist the etchant very well though. It also resists the solvent that you use to take the lines off after the board is done.

So, I'm about to do another test. Here is what I'll be doing, and it doesn't look like I'll finish it tonight:
</font>

• <font size="2" face="Verdana, Helvetica, sans-serif">I've cut out the template from my 4x6 card.</font></li>
• <font size="2" face="Verdana, Helvetica, sans-serif">I've sprayed the card with spray adhesive</font></li>
• <font size="2" face="Verdana, Helvetica, sans-serif">I'll use the resist pen to draw the lines - I'll probably do it twice.</font></li>

<font size="2" face="Verdana, Helvetica, sans-serif"> I'll send pictures when I'm done. Hopefully tomorrow, I've got three projects on my bread board and two of them are done. I'm eager to clean my work area.

I'll end this post with a haiku:
A clean copper board
is a thing of great beauty
It will not last long

[Newz2000]

Lunch break, I have a minute to tell you how the board turned out.

I went over the board with the resist pen twice, like I said. Here is a picture of the results:

Mask cut out and ready to use:
<img src="http://img328.imageshack.us/img328/9471 ... 1tf.th.jpg" alt=" - " />

OK, the resist pen has been used - twice:
<img src="http://img328.imageshack.us/img328/6017 ... 0nc.th.jpg" alt=" - " />

Ah, etchant has done it's work, it looks good:
<img src="http://img328.imageshack.us/img328/1258 ... 9ld.th.jpg" alt=" - " />

But wait! What's this:
<img src="http://img328.imageshack.us/img328/7584/dsc000163hj.jpg" alt=" - " />
When you hold the board up in front of the light, just to the right of the center you see some of the copper has been removed in the middle of the trace. This occurred all over in several different spots.

I have two ideas which are probably both correct:
a: The resist pen didn't coat thoroughly enough and the etchant worked its way through
b: Because its very cold in my basement at the moment, the process took a while, which probably allowed the acid to work through parts that it otherwise might not have had time to get through.

Oh well, it looks like the board works, and I'm happy that soon one of the projects will be off of my breadboard and into my brother's car.

[Newz2000]

Oh yeah, I forgot to mention... this is my first double sided board!
<img src="http://img145.imageshack.us/img145/7360/dsc000171sc.jpg" alt=" - " />

[Gorgon]

Hi Matt,
Congratulations with your first double sided board. I just read through your posts, and I noted that you said you should go over the traces twice with the pen. It's been many years since I made my own boards, but I seem to remember most of the faults I did. One of them was to draw the lines two times. With a fresh pen you only need one time. when you do it the second time the old ink is partly wet and you scrape it, clogging the pen. This way the ink is not of uniformly thickness, creating weak spots to be etched through. Another source of spots is airbubbles in the ink, so speedy drawing is not good either.

BTW after removing the paint/ink, clean the copper propperly and tin the tracks with soldertin. This way you strengthen the tracks and get rid of most of the possible cracks and open circuits. (if any)

TOK

[Newz2000]

Interesting point. Yes, I did notice that if I went over it the second time like I did the first I just rubbed off the old ink, however I did have success at dabbing ink on in places where the first coat was thin.

Next one I do, probably this weekend, I'll compare the difference between doing it fast (like I did this time) and going slow. That sounds reasonable that slowing down may help get a smoother, thicker coating.

I'll look for the solder tin, but I've not heard of it. Is that why many circuit boards look like they have silver traces instead of copper?

Hmm.... A quick google search actually leaves me clueless... Do I just melt solder onto the traces to tin them like I do when I tin the leads of wires?

[haklesup]

"Do I just melt solder onto the traces to tin them like I do when I tin the leads of wires?"

Thats about right.

HASL or "Hot Air Solder Level" basically silkscreens the board with a solder and paste pattern then use hot air to flow it. This is the standard process that you get on most low cost boards you send out for.

You can simply wipe on flux and tin with solder straight off the roll. The tinned surface prevents corrosion of the copper traces when you do not have a soldermask or conformal coating. It preserves unloaded boards in the same way.

The extra metal allows the traces to handle more current too (not that undersized traces are a common problem in home made boards but overetched and thin copper can be)

You need to be careful because the solder can reduce the diameter of plated thru holes. Not a problem on your board.

[Mike]

Looking pretty good!

What you should try next is making your own board through software such as Eagle Layout Editor.

You already know how to etch the board, and I have a tutorial on my website for printing the board design properly from Eagle http://electronet.dyndns.org/electronet/eagle.htm

After you print it, simply heat the board for approx. 20 seconds with an iron on max heat, then place the design facing down onto the board, iron it for another minute and a half to two minutes, and finally, soak in water for approx. 20 minutes then peel off the paper, gently rubbing stuck pieces off with your finger.

[Newz2000]

Originally posted by Mike:
You already know how to etch the board, and I have a tutorial on my website for printing the board design properly from Eagle http://electronet.dyndns.org/electronet/eagle.htm

After you print it, simply heat the board for approx. 20 seconds with an iron on max heat, then place the design facing down onto the board, iron it for another minute and a half to two minutes, and finally, soak in water for approx. 20 minutes then peel off the paper, gently rubbing stuck pieces off with your finger.

Hi Mike, thanks for the tip. Out of curiosity, does this technique work with an inkjet? I don't have access to a laser printer nor a good copier.

It appears that your article mentions a technique where an inkjet can be used but it's not clear how to do that. I'd be very interested in learning a technique that I could do from home with an inkjet printer.

I need to learn eagle... there's just nothing to it, <rant>but I really wish it were as easy to learn as the software from Exress PCB. They prove that it's possible to make layouts intuitively with little effort, so why can't companies such as cadsoft do it?</rant>

Sorry, guess that's a little off topic.

[Mike]

Using an Inkjet is possible if you use an entirely different method. With the laser printer, you heat transfer the toner over to the copper PCB and it acts just like an etch resist pen.

Using an inkjet, you have to expose the image through a transparency using UV light, then put it into special developer soltion, and finally, etch the board. It takes a little more work, and requires special boards. I've never used it, but I'm considering trying it because it looks like the boards come out better overall.

You should just be able to print at a high resolution on an inkjet and then just take it to a copy store and have them copy it onto thick, glossy paper using a laser copier. The quality should be fine as long as you aren't making very close or thin traces.

Soon I'll be posting a new tutorial on ironing and etching the boards on my site - I'll let you know when it comes.

[philba]

or, you can run the inkjet positive through the copier and use toner transfer, like I do.

toner transfer is a pretty easy way to make a board. there are lots of google hits on it - "toner transfer pcb"

photo transfer boards can do much finer features than toner transfer. However, TT can do 25 mil pitch parts and 10 mil traces so its no slouch.

by the way, the etch-through problem you are seeing can be greatly reduced by using heated etchant. The resist pens work ok but longer exposure to etchant breaks it down. Heating speads up the process and reduces the resist breakdown. I heat my etchant up to about 120F with a hacked aquarium heater.

[hamsterears]

Suggestion for heating etchant.

Put board and etchant in a Ziploc type bag. Run hot water in pan in sink, put bagged board into water.

Hot water heats the etchant, bag is easy to see through to check progress, and you don't get etchant all over your fingers while checking.

Only works with smaller boards, but it is cheap.