photo paper instead of PNP

[Hungeryhippie]

I was reading this topic

I would like to try it out, I have a few questions though,

1, which of these papers do i need?

2, Which etchent is best to use for making small boards every now and then?

3, What other tools/accessories did I need i.e. polishing block, trays etc.

I haven’t tried etching boards at home before only at college with a light box and etch tank. I have a pcb drill n bit though.

Any help will be very much appreciated

[Mark Hammer]

Though I was fussy about paper type initially, I eventually realized that it doesn't matter what you use, so long as it is glossy, and you print to the paper using a laser process (i.e., you can use inkjet paper on a photocopier or laser printer, but NOT on an inkjet printer).

The key thing here is that you need to print onto a medium that has a backing and a detachable layer.  PnP has a plastic backing, and the blue detachable layer.  Glossy photo paper has the paper backing, and the glossy detachable layer.  The laser toner adheres strongly to the detachable layer.  Normally, this would stick to the paper too, but when heat is properly applied and the coating/toner is placed up against a polished copper surface, the toner adheres strongly enough to the copper that it brings the detachable layer along with it.

IT IS NOT THE TONER THAT SERVES TO RESIST ETCHANT, BUT THE DETACHABLE LAYER.

In principle, the smoother the detachable layer, the stronger a vacuum seal is created between that layer and the polished smooth surface of the copper.  In that sense, because PnP has less surface texture by virtue of the plastic backing and the fine-grained detachable coating, it adheres best of all.  Highly glossy photo paper has a smoother surface than moderately glossy paper, so it comes next in line with respect to transfer and adhering  to copper.  Moderately glossy photo paper will still have some surface texture to it, and while the detachable layer WILL detach under heated conditions, and WILL bond to the copper because of the toner, the quality of transfer will be reduced.and less precise.  

My own rule of thumb is that if the layout has any traces passing between IC pins, or if there are more than 2 traces passing under the chip (i.e., between the 2 rows of pins), then avoid photo paper and use PnP.  What I've taken to doing in some cases, is that when I see a layout that seems like the traces may be a bit too small to hold up well using photo-paper, I fatten them up with paint software.  I've been using the shareware version of Paint Shop Pro from 1995 with completely acceptable results, though I suppoe you could use anything you feel comfortable/familiar with.  Soften the image, then use the shadow/highlight tool/filter to make all those dark greys black and the lightest greys white.  That will thicken up the lines nicely and produce a toner image that will stick to the copper nicely, hence pulling off the paper backing with authority and certainty.  Remember, it's a tug of war between the paper backing and the copper for who "wins" the detachable layer.  If the toner is nicely secured to the copper, the copper wins.

There are plenty of people who are lifelong fans of ammonium persulphate for all the right reasons.  Personally, I use ferric chloride, even though I am familiar with the reasons with persulphate is better.  For intermittent one-offs, ferric chloride is fine, available in small quantities at reasonable prices and easy to work with.

I caution you, however, this stuff STAINS big time.  If you are going to keep a bottle around and use it a couple of times a year, make sure you have somewhere to store it where it won't get jostled and spilled.  That's the trouble with stuff you don't use very often - you tend to forget it's there while searching for stuff you use even less often.

Since smooth shiny copper is an essential aspect of a good efficient etch, no matter what resist method you use, a sheet of #400 - #600 emery paper and a pack of fine steel wool will be very helpful in buffing the copper to a nice shine both pre-etch and post-etch.

[Hungeryhippie]

thank you Mark as ever you are consise and informative, I'm looking forward to it even more now!

So any glossy paper will work, and i use emery paper and/or fine steel wool to buff the copper before and after.

Many thanks again

[Mark Hammer]

Yup, both laser and inkjet glossy paper of both mirror and non-mirror finishes will work since both involve an emulsion layer over top of a paper backing.  But, as noted, the glossier it is, the easier it is to do good transfers of complex layouts with a minimum of error and pen touchups required.

And yes, the abrasives listed are to make sure the toner adheres to the copper nicely.  Think of it as the difference between how hard it is to remove a suction cup from a window vs a painted wall.  The wall may *seem* smooth, but it still has texture and does not form a perfect vacuum like the window does.  If the gloss coating on the paper is lightly textured, and the copper is not completely smooth and mirror-like, the toner is considerably less stubborn about sticking to the copper and pulling the gloss layer away from the paper it is attached to.

ALL of this advice is relevent to PnP too, except that PnP is smooth enough itself that you have to be more concerned about the state of the copper than about the quality of what you're transferring.  I haven't tried using overhead transparencies yet but I have some spare sheets at home and may give it a whirl.  Laser-printer transparency blanks also have an emulsion layer to "grab" the toner, over top of a plastic backing like PnP does.  My hunch is that the blue coating on PnP will do a much better job of breaking away from the plastic backing than the clear emulsion on overheads will, though.  Still, worth a try.

[bioroids]

I always wondered, is it necessary to do the transfer process just right after printing, or is it safe if I wait several minutes.

I mean, I dont own a laser printer, but I can make photocopies down the corner, then come back to my 'lab', prepare the things, etc.

Does the passing of time affect the probability of a good transfer?
And in that case, how much time can pass without affecting the process?

Luck

Miguel

[stm]

Besides glossy paper, I arranged to make a decent PCB using transparent photocopy film.  I had my PCB layout on positive, and went to a copy store and asked them to take a transparency photocopy (like the ones used on retroprojectors).

Then I cleaned the copper thoroughly with toothpaste (a mild abrassive) and a piece of cotton.  After washing the residues of toothpaste you get a very clean and shiny copper surface.

I preheated the copper with an iron and applied the film with the toner facing down (it got stuck immediately, so you must be careful).  After a couple of minutes of ironing, I removed the film and got more than 95% of the toner adhered the copper.  I had fine traces (20 mils) and 50 mils letters with 10 mils thickness which appeared just fine.  I only had to retouch a couple of traces near one of the borders of the copper, so you should leave perhaps half an inch (2.5 cm) free of traces to the edges, and later trim the PCB.

According to this (and several other people I know that have been using this method) I can say for sure it's the toner that actually protects the PCB from ferrich chloride.  There was no sign of attack on the traces, however I have seen it when you just use a permanent marker to draw the traces.

Now, I've been wondering if there is a way of helping the toner to adhere less to the film or glossy paper.  It is well known that if copper is not so clean there will be bad adherence.  Perhaps applying a very small amount of oil, WD-40 or something else to the film or glossy paper first could help.  The idea is that you should clean excess with a paper towel, just leaving an undetectable layer, so you won't have trouble with the laser printer or photocopier.

Has anyone thought or tried something like this?

[Gringo]

I always wondered, is it necessary to do the transfer process just right after printing, or is it safe if I wait several minutes.

I mean, I dont own a laser printer, but I can make photocopies down the corner, then come back to my 'lab', prepare the things, etc.

Does the passing of time affect the probability of a good transfer?
And in that case, how much time can pass without affecting the process?

Luck

Miguel

Che Miguel, no hay apuro, tengo transparencias y algun que otro papel fotografico de hace meses, esperando su oportunidad, y se transfieren lo mas bien. Lo unico importante es la cantidad de toner que haya caido en el papel/transparencia (y que la plancha este bien caliente).

[Mark Hammer]

I make my transfers well ahead of time, laying out sheets so that I can get maybe 10 or 12 patterns (depending on board size) from a single photocopied sheet, which I then cut into pieces and save in an envelope.  Although time, bending, and friction can result in such saved/stockpiled patterns flaking or chipping, "fresh" toner is not a requirement in my experience, and even if the toner does change over time, how you apply heat and how clean the board is is FAR more important in quality of transfer.

[Mark Hammer]

STM

Besides glossy paper, I arranged to make a decent PCB using transparent photocopy film.  I had my PCB layout on positive, and went to a copy store and asked them to take a transparency photocopy (like the ones used on retroprojectors).

Then I cleaned the copper thoroughly with toothpaste (a mild abrassive) and a piece of cotton.  After washing the residues of toothpaste you get a very clean and shiny copper surface.

I preheated the copper with an iron and applied the film with the toner facing down (it got stuck immediately, so you must be careful).  After a couple of minutes of ironing, I removed the film and got more than 95% of the toner adhered the copper.  I had fine traces (20 mils) and 50 mils letters with 10 mils thickness which appeared just fine.  I only had to retouch a couple of traces near one of the borders of the copper, so you should leave perhaps half an inch (2.5 cm) free of traces to the edges, and later trim the PCB.

According to this (and several other people I know that have been using this method) I can say for sure it's the toner that actually protects the PCB from ferrich chloride.  There was no sign of attack on the traces, however I have seen it when you just use a permanent marker to draw the traces.

Now, I've been wondering if there is a way of helping the toner to adhere less to the film or glossy paper.  It is well known that if copper is not so clean there will be bad adherence.  Perhaps applying a very small amount of oil, WD-40 or something else to the film or glossy paper first could help.  The idea is that you should clean excess with a paper towel, just leaving an undetectable layer, so you won't have trouble with the laser printer or photocopier.

Has anyone thought or tried something like this?

My experience would suggest something different than yours in the following ways.
1) It is the coating not JUST the toner.  You may not be able to see the layer of coating from the transparency sheet that pulls off the plastic backing, but it's there.  When a person makes PnP, you can see the bare spots on the PnP sheet where the toner pulled the blue coating off.  Similarly, on glossy photo paper you can see the bare paper where the toner has pulled the glossy coating off the papaer backing.  Same thing happens with transparencies, except that the coating is clear so you can still see the toner as black.  Look at the toner under a microscope and you will see that there are plenty of gaps in it, since it only has to be dark/thick enough to LOOK black on the page.  The backing/emulsion helps fill in those gaps.  Similarly, when using a pen, it is not the pigment that protects  against the etchant, it is the medium the pigment is mixed with.  I've used Staedtler Lumocolor pens where you think "There's no way that's dark enough to resist the etchant!", yet it does, because the vehicle the pigments are suspended in is clear.  The darkness of lines gives an indication of how thick the vehicle is painted on (and how thoroughly), but lighter lines can be just as thick.

2) Anything, and I mean ANYTHING that prevents the copper from being exposed ruins the etch.  If you can figure out a way to provide a coating that goes ONLY between the toner and the board without covering any other part of the board, I will personally nominate you to the Nobel committee.  In the meantime, if a bit of condensation, or "finger juice", or corrosion of any kind ends up on the exposed copper, the etchant will have a harder time fighting through it.  How one can provide an easily wipeable coating while at the same time having a kind of vacuum seal between the toner and the copper is beyond me.  How would one even know that the excess had been successfully wiped off?  Would anything flow out from under the toner after one had wiped it?  Even if you can get the toner to stay on the board, will it stay in place or will such a viscous film cause traces to move around?  Especially while wiping the excess.  No, I think a smooth shiny board, a quick warm etch, some alchohol and a wipe, and a good piece of fine steel wool is good enough, convenient enough, and the best most of us can hope for.

[bioroids]

I always had the impression that once the toner dries is harder to make it transfer to the copper, so I did all my boards (not too much) pretty quick.

I always ended up retouching all the board, so last times I just printed on a regular paper, and using a carbon copy paper I copy the traces to the board, then I redraw it with an etch-resistent pen and voilá. I requieres a lot of concentration, though...

Saludos Gringo desde San Telmo! (que paradoja decirle gringo al unico argentino entre tantos extranjeros, no? ja ja)

Regards

Miguel

[stm]

Mark:

So according to what you mention in your last post, adding some treatment to reduce toner adherence to the film or glossy paper might have a negative impact on the final result, as this fine layer from the film/paper could not adhere to the toner anymore  :!:  :?:  :?

I'm gonna give it a try anyway, to see if it works or makes things worse.

Regards,

STM

[markr04]

Hi. I posted the original post you're referring to. I'll add my $.02.

Paper: I've had the best luck with Staples Picture Paper (sku: 471861). I once had to use Staples *Premium* Picture Paper and was met with really bad results. When ironing, the paper began to melt to the iron instead of the toner to the copper. Not all papers are equal.

Treating the PCB: You shouldn't 'treat' the PCB with anything other than soap and water before ironing it. *Do not* use "steel wool". This is bad for results. It tends to leave behind tiny little fibers which will rust. I think every article I've read warns against this.

Of course, clicking the link I posted in the next post would've answered all of your questions .
http://www.fullnet.com/u/tomg/gooteepc.htm

Mark

[Paul Perry (Frostwave)]

I always had the impression that once the toner dries is harder to make it transfer to the copper,

The toner actually melts in the copier (it is a fine powder that transfers onto a drum, then onto the paper or whatever). So it doesn't 'dry', it freezes! the reason it is good to etch the PCB as soon as you can, is that this leaves less time for the PCB to oxidise, or get crap on it that stops the etchant.

As for the toner alone not being enough to stop a board beign etched, I doubt it! I have seen microphotographs of PCBs that are being made by the "glossy magazine paper" technique, and there are only a few fibres left after an overnight soak & rubbing... the fine layer on PnP makes a much SHARPER image, though.

but the bottom line is, whatever works for you! and, most peopel have a lot of experimenting before they get their local materials, irons, laser printers, paper etc to work :x  :cry:

[Nasse]

Think I´ll try cheap but glosssy paper next time. I have tried HP photo paper but it has some plastic layer in the back so water bath does not much help removing the paper after ironing.

[Mark Hammer]

Mark:

So according to what you mention in your last post, adding some treatment to reduce toner adherence to the film or glossy paper might have a negative impact on the final result, as this fine layer from the film/paper could not adhere to the toner anymore  :!:  :?:  :?

Yes.  The toner is not coming off the emulsion/coating very easily, because, as Paul notes the toner is melted onto the coating.  The big question is whether the toner "wants" to stick to the copper more than the emulsion/coating wants to stick to the plastic/paper backing.  This is why poor heat application of PnP causes so much grief for people: the blue coating is more strongly secured to the plastic sheet than the toner is to the copper.  Anything that interferes with the toner and copper fusing will reduce transfer effectiveness.

I don't doubt that there are chemical changes over time with respect to toner being exposed to air, but I've never encountered them.  On the other hand, it is probably very good practice to keep your PnP or glossy paper sheets with patterns on them properly stored, if only to keep dust off.  I stick mine in envelopes and squish 'em between books.