How to protect silk-screen from scratching (toner-transfer)?

[ChildOfVision]

Hi!
I am interested how can I (easy way) protect montage/silk layout on my PCB (made with toner transfer method) from scratching with nail or (accidentally) with skrewdriver or so? Of course, I don't need protection from bullets or some really hard scrubbing. I found on this forum I can use clear acrylic spray, but I don't have it, and I need to protect my PCB NOW, before I start assembling. I have Plastik-70 spray, but I remembered at the last moment, that it dissolves toner!
Hair spray?

TIA!

 

[3v0]

Clear acrylic spray, or semi transparent acrylic spray, or clear conformal coating.

Polyurethane clear spray stays stick too long and I am not sure if it will burn off like acrylic does. Regardless of what you use go with a very light coat now and a heavier one after soldering.

 

[ChildOfVision]

Thank you! I knew for acrylic spray (as I said), but I don't have it, and I can't find it where I live so easy... Furthermore, I need "something" tommorow, some easy-to-find improvisation.

 

[jpanhalt]

I am not sure what Plastik-70 is exactly, but I am assuming it is a type of lacquer, like Plasticote. I am using the term lacquer to mean a coating that hardens principally by solvent evaporation.

In fact, most lacquers are sprayed, because each subsequent coat dissolves in part the earlier coats. With brush application, as with dopes used on fabric-covered aircraft, you can brush through the earlier coats and end up with a mess unless you have experience.

Anyway, the trick is to spray a fog coat. Let it get tacky to hard, then another coat and so forth. The first coat will dry almost instantly and will not smudge the toner-transfer. Subsequent coats can be heavier. I suspect three, maybe four, coats done as described will give a glossy finish and not noticeably affect the toner.

John

 

[ChildOfVision]

Hi, John!

Thanks for advice, I will try with "fog-coating" as you suggested (at first, on small piece of some waste PCB). Anyway, Plastik-70 is the only thing I have right now.
Here are links that describes that spray; as you can see it is acrylic based "lacquer", but you can see also more (second link) "dangerous" (for toner) ingredients, like ethyl acetate, monopropylene glycol methyl ether and so on (scroll down to Section 8!).
PLASTIK-70

PLASTIK-70 - detailed

I see now that Plasticote 70 = Plastik 70, does it help?

 

[jpanhalt]

That misting technique is pretty typical as is the solvent mixture you describe. In the days of water-applied decals that were printed on a nitrocellulose base, it was common to spray on a lacquer, often including diethy ether as a co-solvent, to melt the clear carrier into the the over coats or substrate such that the printing looked like it was applied directly with silk screen. It made those decals permanent and waterproof. Your process with toner transfer is not much different. Just practice.

If you are located in a humid area, be careful of getting entrained water, which will make the coating appear milky. Remember,as the solvent evaporates, there is significant cooling, which can get below the dew point and cause the milky appearance. Once you get that, it is quite difficult to cure.

John

 

[ChildOfVision]

Thank you, John, I will try this later (it is 3am here) - and tell you the result!

 

[3v0]

There is a good chance that if you go with a light coat prior to soldering (aka fog) that the toner will not run. If you put too much on it will become hard to solder.

 

[ChildOfVision]

3v0, I think you didn't understand me: I want to protect component side of PCB, i.e. toner on it (silkscreen), and then, after soldering components, I will protect copper side, for what Plastik-70 is intended to.

I forgot to ask: that Plastik-70 I have is pretty old: it has (good) layer of rust on the weld-joint of spray-can! Also there is a small "clod" of the content (some yellow/amber "resin" , leaked from, obviously, small rupture (I didn't made it!) on the bottom of the can. Question: how dangerous is to use so "damaged" spray dose (I allready used it as such, nothing happened (yet))?

 

[3v0]

I have been making 1 and 2 sided PCBs for some years. I am sorry if I confused you, I was thinking in more general terms.

On the top side make the first few coats very light and dry well between coats. It may prevent the toner from running. If that does not work you may be out of luck on the stuff you have.

This is an example of a single sided PCB with white Krylon Fusion paint followed by a toner silk screen. I am not suggesting you use paint but it does make the toner stand out.

This is the bottom side of the board prior to soldering. On the bottom side use a very light coat prior to soldering and add more after soldering is done.

I have seen people fail on both top and bottom by using too thick a coat.

 

[ChildOfVision]

Thank you 3v0, I understand now what you mean. Btw. your PCB looks really nice (not a little boring "white on brown", but black on white)! Can you tell me what exactly paint were used (Krylon is name of manufacturer), I assume it is acrylic paint - I can find it here (maybe even Krylon brand) - and, I can use e.g. red color, that would be great. I see many products from Krylon (even some spray that is intended for use on all plastic surface without pre-cleaning), so, can you be more specific?.
And, of course, for copper side, before soldering components, only thin layer is needed (if any), it is a little sticky during soldering (when the layer is too thick).
EDIT:
I see now: Krylon "Fusion for plastic" paint - that must be the paint you were used! It will be hard to find it here...

 

[3v0]

I should add that I used pulsarProFx paper to transfer the toner to the paint. It is coated with starch and is very good at not sticking to anything including paint.

If you want to try the paint thing I suggest you set aside some time to experiment. Be sure to make the paper with the toner on it larger then the PCB so the paint has no chance of getting on the laminator. If you are using one.

 

[ChildOfVision]

I should add that I used pulsarProFx paper to transfer the toner to the paint. It is coated with starch and is very good at not sticking to anything including paint.

I repeated many times in this and other forums: I'm using very cheap "gummed" collage paper, it has that starch coating on the back (like a big postal mark!) - children (and adults, of course) just cut the piece of that paper, lick it a little, or moisten with some sponge and it get sticky (it is absolutely non-toxic). Surprisingly, like nobody else in the whole world never heard about that paper!?
Here are some examples how it works (exactly like Pulsar's, it is just much cheaper (about 2 USD for 12 sheets!), and takes a little longer to soak (because of the glossy finish on colored side). I picked randomly orange paper.
So you just print test print on ordinary paper, cut a piece of collage paper and fix it on the place of the image with a little of capton (high-temp.stabile) tape. Than print again with full resolution and highest toner-density (on glue side, of course, not on the colored side!)! Laminate (I make about 15-20 passes with unmodified laminator, just in case...)! There is no harm to laser printer!
1) after few minutes of soaking:
View attachment 63178
2) some 10 min later:
View attachment 63179
3) after about 20 min. the magic begins :
View attachment 63180
4) after about half an hour, the paper just floats on the water surface (without ANY intervention!), leaving just PURE toner (as Pulsar!) on the board!
View attachment 63181
Now, you just have to soak (a little bit) PCB in fresh water, or rinse it under running water to remove any eventual glue residue (again, just like with Pulsar's proprietary paper)! You can apply TRF-Green or White if you wish.

 

[3v0]

It has been a while since we talked toner transfer here. I do recall thinking about using your paper but to order it I need a brand name and product number that is sold in the US.

 

[ChildOfVision]

There is no some particular brand, or e.g. Staples SKU number. It is (at least here in Europe) like ordinary A4 paper for everyday use. Of course, it is not SO easy to find it, but I found it in my small town in school-equipment department (consisted of two shelves) in small shop. So, you (in USA) should go to the nearest, ordinary paper-shop (my google-translate shows me "stationary store" if this is better translation) and ask for collage-paper. When you find it, see on the package if there is a word "gummed" or "water-activated" - and this is it!

I don't speak specifically to you, 3v0 (!), but to everyone! Why is SOOO hard to go in that book-store or paper or stationary-store, whatever, and search a little? It is the same place where you buy school notebooks (not electronic one), pencils, paperclips, erasers and so on for your children! If it IS so hard to you (I don't mean to you 3v0!) - ask your kid to do it for you!

Here is one link from ebay with ordinary (not collage, although there are collage papers too) A4 gummed paper (it is used for water-activated labels). I didn't try that paper (yet) because it is too expensive to me, but it should work:
Ordinary and collage gummed paper from ebay

 

[kasamiko]

I'll visit my nearest office supplies store and have a look at the "gummed" paper...

 

[ChildOfVision]

I'll visit my nearest office supplies store and have a look at the "gummed" paper...

Please, notify me if you found it!

Anyway, the trick is to spray a fog coat. Let it get tacky to hard, then another coat and so forth. The first coat will dry almost instantly and will not smudge the toner-transfer. Subsequent coats can be heavier. I suspect three, maybe four, coats done as described will give a glossy finish and not noticeably affect the toner.

And, I forgot to mention: I tried "fog-coating" with Plastik-70 and it works really great! It should work also with any acrylic spray! Thank you John!
I must try 3v0's method of pre-painting with some nice color and then make the silkscreen - it looks really nice!

 

[kasamiko]

Currently I'm using sticker paper backing for toner transfer...the result is acceptable (at least for my own standard )

View attachment 64318

View attachment 64319



Same method with the component placement guide..


View attachment 64320

View attachment 64322

 

[ChildOfVision]

Not bad at all! But all depends of toner and printer you are using. If toner is too thin... Can you tell me what printer AND ETCHANT do you use (I found muriatic acid too agressive to the toner!)?

 

[kasamiko]

I'm using Brother HL-2140 series laser printer and etch with muriatic+hydrogen peroxide..1:2 ratio