Hey all,
I used PnP Blue for the first time the other day (Thanks to Steve Daniels, once again, for his great service). What was left when the blue was peeled off was about 95% correct, but there were small holes here and there, missing parts of a few traces, small imperfections that honestly I just can't live with, and some that the circuit wont live with. Do you think I just need to iron it on for a bit longer? Any other suggestions? I'm cleaning with Acetone and Scotchbrite beforehand, rinsing very well... can't think of anything else.
Still, first time at 95% perfect... I'm not complaining that much! :D
Thanks.
There's a photoessay at //www.tonepad.com that explains the whole process. I myself iron for no more than 4 minutes. I start by pre-heating the board for 30- 40 seconds before placing the pnp on the board. I alternate between letting the iron sit on the board with no pressure for 1 minute and moving the iron with good pressure for 1 minute. doing that twice usually gets me there. Every here and there I get a bad trace but I touch up with a sharpie and have no issues. Again, check the photoessay for more tips.
just touch it up with a sharpie... go on THICK with it..
there's always some tiny spot that doesn't quite look right.. always good to be safe and just touch it up even if you think it's probably fine.. better safe than sorry.
"-)
Keep in mind that a temperature at a particular setting on one iron may not correspond to the same temperature on another iron for that same iron setting, so read all the posts to get a starting point, then experiment. When I started, I printed out several small "test circuits" and tweaked my technique until I got it right. When I figured it out, I washed the PNP off the boards and was ready to start live.
Also, note that the bottom of many irons have holes therein. If you routinely place a part of the board over a hole in the iron, it may not heat enough to transfer the PNP. The issues are further compounded because the heat on the bottom of the iron may be greater near the tip compared to the back of the bottom plate. (All the above assumes that you are using a properly cleaned and prepared board).
Therefore, you need to experiment to find the best ironing technique for your iron and your circuits. When I used to iron on PNP blue, I would first center the iron on the PNP for a few seconds to make sure the PNP was stuck to the copper, then I would use a press, lift, advance technique and work across the circuit top to bottom, then left to right, rotate the board 90 degrees and repeat etc. Then I would do a similar technique in several diagonal directions.
I have since abandoned the iron for a laminator. It takes 1/4 the time and more importantly, it is consistent because it applies uniform heat and pressure across the board.
Good luck
Part of this is the toner itself, not the PNP. Remember that the toner acts as a kind of adhesive for the blue backing and also as a means of "competitive adhesion". What I mean by that is that the blue emulsion sticks to the acetate sheet...unless something stronger comes along with more pull, in which case the emulsion goes there instead. The toner adheres to the emulsion, and luckily for us also adheres strongly to the copper so that it pulls the blue emulsion off the sheet.
If the toner thick/dense enough, it will provide strong adhesion to the copper surface and drag along the blue emulsion for the ride. If what you have printed out or photocopied as "black" is really kind of thin and spotty, then there is really not enough "pull" to dislodge the blue emulsion from the acetate sheet.
So, what to do?
First off, if you are deriving your layout from a scanned article, you may want to use your graphics package to retouch the traces and make them black where they ought to be black.
Second, if you have narrow traces and room to thicken them, make them wider to increase the odds of emulsion being dislodged from the acetate. The way I do it is to turn 1-bit black and white Gifs into 8-bit greyscale images, and "soften" the image with Paint Shop Pro (though you can certainly do this with other packages) to blur the edges. Then I use the shadow/midtone/highlight tool to darken up all those mid-greys added to the edges of the traces during the softening process. You can do this repetitively if you like. Once you have a suitable degree of trace thickness/width, just convert back to B/W and all the fuzziness will be gone but the traces will have larger dimensions.
Third, if you have some means of increasing toner density on the page, use it. For instance, if you can select something like "print photos" as an option to lay down a thicker layer of toner, use it. Alternatively, if you can assure that printing to the same sheet twice will lay a second layer of toner on top of the first, go for it. Finally, if you are printing via a photocopier, consider turning up the darkness/contrast on the copier.
All of these tricks will work with glossy photopaper as well.
Having said all of this, ironing technique does matter. Try to iron the board on a sturdy flat surface so that nothing stands in the way of heat being evenly transferred. A nice smooth piece of MDF might be just the ticket. Make sure the iron has few imperfections on it (you may have to buff the iron's surface with fine steel wool), and until you get REALLY good at it, always make sure you print out a few backup copies of a layout. Worse comes to worse you can share them with friends. They make a nice present and are easy to send in regular postal envelopes at regular postal rates once cut out from the sheet.
Thanks for the tips all, and the link. Will try it this week.
AM I CURSED?!?!?!
I have tried 3 more times since reading the Tonepad photoessay and all of your tips, and I'm still getting really bad results :-( Much of the board still comes out fine, but there's always one area on the board, about 3/4" by 3/4", that is devoid of toner. AM I FOREVER DOOMED TO FAIL AT MAKING MY OWN PCBS????? Oh man this is so discouraging. Fortunately I had the foresight to make more than one PCB design on a single sheet of PnP...
Okay here's what I'm doing:
1 - Take Board Out of Package, sand edges, clean with soap and water, scotchbrite, acetone, isopropyl, RINSE EXTREMELY WELL (overkill? lol)
2 - Dry it off using a lint free cloth
3 - Preheat the board with my iron for PnP adhesion...
4 - place the PnP on the board...
5 - I used the technique mentioned on Tonepad (his pictures looked so pretty!!! ugh...), letting the iron rest on the board for 30 seconds, then moving it around using firm pressure for 30... I did this 4 times (totalled about 4 minutes, maybe a little more)
6 - Quench the board to below room temp under water and peel...
7 - Mope away in dissapoinment.
Okay is there any seriously huge flaw any of you are seeing in this method????
One of the things you need to do is to keep an eye out for what the shiny acetate surface looks like. As the toner adheres to the board, you start to see a sort of very shallow "bas relief" in the acetate, as if it were conforming to traces already on the board. You need to hold it up to the light to see it, but it's there, and the shiny surface helps to make it visible. If you see this across most of the board but not in one sector, then you haven't finished ironing.
I'm wondering if your last step of rinsing the board isn't the problem. If it were me, I'd make my last step in board preparation a dry one. So, isopropyl it, then give it a friendly wipe with some superfine steel wool, and THEN a dry lint-free cloth or papertowel to get the little steel wool bits off. The thing about the copper surface is that it IS "chemically active" when it gets shiny. I have no idea what's in the Bow River, or what they have to do to it to make it drinkable, but shiny exposed copper just itching to trade electron orbits with something probably shouldn't come into contact with it. You may well be introducing fine layers of oxidation that are not readily visible.
If this doesn't work, you can't blame Ottawa for your troubles (that's an inside Canadian joke, folks).
i've never had any trouble with press n peel blue. i don't have a laser printer so i just print out the PCB layout then photocopy onto PNP blue.
issues to consider:
1)perhaps your laser printer isn't laying down enough toner. try a photocopier
2a)make sure your PCB is cut to size and all edges are sanded and filed smooth VERY IMPORTANT! otherwise the iron won't contact the board sufficiently.
2)the PnP instructions says heat up the iron to 275-325 F (this is the cotton setting on my iron). use your thermocouple on your multimeter to check the temperature of the iron surface to get it about 300 F.
3)rarely do i need to iron for more than 1 minute (for a small board the size of say the easy face), i don't preheat the board. i use the iron to tack one corner of the layout to the board then immediately place a sheet of paper between the pcb and the iron and iron for 1-1.5 minutes. use tongs and immediately quench the board in a bowl of water and peel off
i've never had any trouble following this method - hope this helps you out.
-addnoize
Here's what really helped me.
The advice about seeing if the traces have adhered due to their darkening/sinking slightly is great, because it gives you a visual indicator that the process is working.
Also, temperature is pretty critical. Too much heat and the backing will shrink and the traces will smear. Too little and there won't be enough adhesion. You need to find the sweet spot.
If you have any way of really checking the temperature of your iron (I stick the bulb of a candy thermometer on it, but I'm looking hard at the DMM with temp probe from Circuit Specialists), do so.
The instructions I originally saw called for way too high a temperature. One other thing is that the temperature control on most irons is not dependable. And one company's "wool" is another's "cotton."
I get the best results by touching the iron to the backing several seconds at a time. I don't like to move it sideways because I get smeared traces that way.
The stuff is surely not as fool-resistant as I thought when I decided to try it, but I have made many successful runs of boards with it.
Still, I look forward to having enough demand and resources to have the boards made by a fab house.
Sharpie touch-ups frequently fail for me. If I have spots to fill in I use my wife's nail polish - works great and comes off with aetone. You don't even have to let it dry completely to etch. I've also used it for simple circuits that could be quickly 'painted' like fuzz faces without using any transfers at all. Just pick a color she won't miss much (mine's blue metallic):wink:.