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home brewed pcb's

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justDIY

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I'm trying to make some PCBs that I drew up with eagle, and having the darndest time of it.

I've tried 3 methods, from el'cheapo to rather expensive

firstly, i was told all I need to do is print my design on some paper with a laser printer, and iron it onto a well cleaned bare board

ok, so I do this, I use lots of heat, I press real hard, I get a decent lookin transfer to the PCB. so... after rubbing and rubbing and rubbing to get the paper off, i'm left with areas where you can see copper through the toner

so after etching, these areas are all speckled copper and composite... including some of the traces.

so i figure, the elcheapo method must be difficult to perfect

so I try the iron-on pcb transfer paper, the blue stuff. it yeilds a clearer resist image on the pcb and no rubbing, but after etching, I get the same speckeled effect, basicly everywhere

in frustration, I tried the photographic method. I printed my design on some acetate, setup a postive sensitized pcb, turned on the fluorescent light as per the directions, and then develop, the resist pattern looks remarkable! but ... end result; speckeled effect

what is causing this speckeled effect?

I have the etchant in a bath of hot water, otherwise it'd be 60°F (sry, i keep my house cold) ... i stand their the whole time sloshing it around, and peaking at the board now and again, to see if its ready ... as soon as all the exposed copper is gone, i remove the pcb to a cold water bath and rinse it till all the etchant is gone

-----

I will try to get a picture posted tomorrow when the sunlight is back.

any thoughts or suggestions appericated!
 
what kind of etchant are you using? maybe try another.
or maybe your etchant is old. it goes bad after a while depending on the type i think.
 
wax the board and scrape off what must be etched.
 
Maybe the paper you are using is picking off little specs of the toner.

The best way I have found to transfer the image with toner is to use glossy photo paper. The toner stays right on top of the glossy paper and doesn't melt into it. Then just iron it on full heat and soak it in water for about half an hour. The paper will dissolve and be peelable without messing up the toner transfer. Use a toothbrush to get the rest of the paper off, the toner will stay put durring this. Then etch.
Hope this helps.
~Mike
 
Hi,
the toner transfer method is working fine.
For good results i use thermo-fax-paper (the rolls used in older fax machines) and laserprint the layout on the printing side of the fax paper. The paper will turn black completely, but that doesn't matter. The coating on the paper's printing side prevents paper fibers from sticking in the toner, what causes pinholes.
You don't need to press very hard and or very long. I have put a ~10kg piece of metal on my iron, what gives a good result. I use to iron the pcb as long as 1l of water needs to be heated from room temperature to boiling (you see i didn't measure the time yet, but it works fine). Pressing too hard/long causes the toner to jump back from the pcb to the paper again. It's also important to put the pcb into HOT water (with a small amount of soap to reduce the surface-tension of the water).
My etchant is ferric chloride (is that the right name in english?), it's cheap and works fine.

hth
regards
joachim
 
The photo method is the best.

I think that the speckeled effect is caused by you shaking the board too much.
When I do it, I put the etchant (ferric chloride, the brown liquid), in a glass container (or plastic). Put it in a bucket of hot (from the tap, not boiling) water. Wait for ~15-20 minutes, without ever touching the board, or taking it out.
After that time, I take the board out and inspect for quality. Most of the time, if the board is put vertically, the bottom part doesn't get etched as fast as the top, so you might want to put it horizontally.

Make sure the board is clean and that you NEVER EVER touch it with your hands. Also, when you blast it with UV light, the pattern from the acetate should be towards the board (i.e. the side where the pattern is printed should touch the PCB). Put some plexiglass (NOT normal glass, as it doesn't pass UV light) to press the acetate to the board.

If you use a positive acting PCB, then the longer you put under the UV, the more chances you will have that the board is developped where it shouldn't be. Follow the instructions of PCB manufacturer on UV timing, distance and intensity.

A good idea would be to take a strip (not too wide, but long) of that precensitized PCB, then remove the protective plastic (with UV off), hide it with some cardboard (or black plastic). Turn UV on, expose 0.5cm of it, for 5 minutes, then the next 0.5cm for another minute (the first 0.5cm being open). Then slide the plastic by 0.5cm more and expose that part for 1 more minute. Do it until you reach 15 minutes.
The first 0.5cm would then be exposed 15 minutes and the last 0.5cm for 1 minute.
Etch that strip and see how long you should expose your PCBs.


Also, what kind of developer (the liquid that you put the UVd board in, before the etching process) do you use? Do you follow the instructions? Usually, it's 10-15 seconds in the solution, then take it out, put on a clinex tissue (DON"T SCRAB IT). Then again, for 10 more seconds. On clinex again, and try to see the pattern on the board (using light, look on the board at different angles, you should see the pattern at some point). If it's not very clear, put into developper again, for 5 more seconds.

I noticed that when I put the board, after the whole process, in the etchant solution, and take it right out, I can clearly see the traces and I notice that the etchant doesn't stay (stick) on them.

Anyways, Good Luck,
TI|CP
 
Hi,

I use the photo-resist board for my homemade PCBs and get excellent results.

I've been using some photo-resist board which I first bought about 6 to 8 years ago, so my times are all a bit odd, I'm sure, but then I'm surprised it works at all! I have just bought some new photo-resist board, so I'm sure some times, like the developing time, will come right down.

I print my circuit tracks on transparency sheets with my Epson Stylus 740 inkjet printer, with it set to photo paper/glossy paper, highest resolution. This means more ink is put on the transparency, so it's nice, thick, and dark. I print the same circuit three times separately, and then dry them with a hairdryer as the ink stays smudgy for ages otherwise. Then I tape the three together, ensuring by this that no UV will penetrate to a large enough extent to expose tracks.

Then I place the transparency bundle on the board, place a piece of glass from a photo frame on top, place my wife's UV face tanner over it 3 inches from the board, resting either end of the tanner on the can tops from my isopropyl can and freezer spray can, and expose for 12 to 15 minutes.

I then fill a tray with my sodium-metasilicate developer solution (I think they call this carbonate-based) and - maybe only as it's old board - have to leave it in there for 15 minutes. I swirl it about every now and then, ensure that all photo-resist has come off where it should do, and that the tracks are clearly visible, then remove and wash with water.

I stick the board in hot ferric chloride (I warm mine in a jug in the microwave :oops: ) and agitate it the whole time it's etching (until I finish building my bubble etch tank) which speeds it up. Takes from 20 to 30 minutes to etch fully.

Results are spectacular. Most professional looking. I used to use the sun to expose the boards back when I first bought the 6-8 year old boards which I still have. Results were highly variable and never as good as now, since I started using the face tanner.

I only had the speckled finish when using normal copper-clad boards and etch-resist pen. Maybe you're over-exposing the board or, from what it sounds like, your print on the transparency (acetate) is too thin, or speckled itself, in the way ink usually is when on a shiny surface. Do what I do with the layers of transparencies (remember highest resolution for more ink) to make the tracks uniform in texture and very dark.

Hope this helps.

Now, I've got to try and work out why a laser printer I've been given is printing faintly in some areas every now and then, cos I only wanted it for printing my circuits on transparency in the hope that I could print just one and that'd be opaque enough to stop the UV, instead of printing it three times and overlaying them. Sadly, even where it doesn't fail to print properly, it still seems very thin and holding it up to the light shows how transparent it is. More so than one print from the inkjet printer! So much for my belief that a nice thick layer of plastic toner stuff would be placed on the transparency... :(
 
Check your toner levels... I think it they are quite low.

Also, try to remove the toner box and shake it a LITTLE BIT (avoid putting it on your clothes and on the floor). Usually, when you see unprinted spots, the powder (toner) level is low.
 
After you iron on the toner image to the pc board and remove the backing (paper or clear mylar, whichever you use) go over the thicker areas and traces with a permanent marker like a "Sharpie", because the toner doesn't always cover completely opaque on the bigger areas. You can see this by holding it up to a bright light before you iron it on.
 
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