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Dicky Mint
14-05-2012, 16:56
Hi

For my next PICAXE project I'm looking for a slightly more up market appeal so:-

I wonder if there is a simple method to create the silkscreen layer on home build PCBs.

The equipment I have includes a UV box so a solution somehow utilising that would be a possibility.

I was thinking on the lines of spraying/painting on a photosensitive paint then exposing it through a printed transparency and then developing and dissolving the surplus ink/paint.

I don't know if there's any such thing as photosensitive paint?

Is there a simple method I've missed?

Rick

Technical
14-05-2012, 17:14
Many schools simply laser print onto a clear self adhesive label (or even white label, A4/letter size).
Then stick it onto the PCB before drilling.

SAborn
14-05-2012, 17:34
There is UV cure ink that is used in many large printing places, but i have never worked with it to know anymore details.

Jeremy Harris
14-05-2012, 18:14
You can also use the toner transfer method and white TRF to get pretty good looking "silk screen" printing on a board. I've not used it, but keep meaning to give it a go one day. You can get green TRF too, so can make a sort of poor mans solder resist layer.

KeithRB
14-05-2012, 18:51
There is also something like this:
http://batchpcb.com/index.php/Products

Where you can have small quantities of professional boards made.

Dicky Mint
14-05-2012, 19:34
Thanks for the ideas so far...

With the white TRF method how is the white 'ink' silkscreen printed on the TRF film?

Or have I got it wrong? Does one print in black (or red or Green) on the TRF and then 'laminate'?

I think the main problem with UV cure ink is that the cured ink would be the part that was exposed to UV and I'd want it the other way around!

The method of printing the silkscreen on sticky back labels is pretty straightforward but I was looking something a little more 'up market' in appearance.

I am sure this is a practical solution though.

Any more ideas would be welcome

Jeremy Harris
14-05-2012, 20:05
Thanks for the ideas so far...

With the white TRF method how is the white 'ink' silkscreen printed on the TRF film?

Or have I got it wrong? Does one print in black (or red or Green) on the TRF and then 'laminate'?



I haven't actually tried it yet, so please take this into account!

I believe the technique is to print use the laser toner transfer method (laser printing on photo paper, ironing it to the PCB) and then iron on the white TRF. The TRF bonds to the transferred toner, and leaves white lettering on the surface of the board.

bluejets
15-05-2012, 02:44
Thanks for the ideas so far...

With the white TRF method how is the white 'ink' silkscreen printed on the TRF film?

Or have I got it wrong? Does one print in black (or red or Green) on the TRF and then 'laminate'?

I think the main problem with UV cure ink is that the cured ink would be the part that was exposed to UV and I'd want it the other way around!

The method of printing the silkscreen on sticky back labels is pretty straightforward but I was looking something a little more 'up market' in appearance.

I am sure this is a practical solution though.

Any more ideas would be welcome

Sadly, Ultrakeet have folded as a supplier but their articles still remain on their website.
Perhaps it may be of some help. You will find reference to silkscreening at the bottom of the page. Many photos..........

http://ultrakeet.com.au/index.php?id=article&name=makepcbs

Marcwolf
15-05-2012, 04:39
Ultrakeet products will be sold through a new place. http://dfad.com.au/shop.php
The owner's of Ultrakeet work there so we should still get the excellent service.

Dave

boriz
15-05-2012, 05:16
How about a UV LASER style CNC machine that draws onto your board by vector scanning? Articulate the LASER at the back end and use two high-res servos to swing the business end around. Could be a neat Picaxe project. Could also be used to expose the PCB artwork onto sensitized boards.

Well, you did say "Any more ideas would be welcome "

Dicky Mint
15-05-2012, 09:42
Thinking about ultrakeet they reckon they could etch a PCB in Ferric Chloride in a minute!

It takes me close to an hour even in warmed solution in a Bain Marie!

Am I missing something?

Love the idea of a UV laser on a CNC machine!

Could be a future PICAXE project but I reckon...

One of us will need to recline in a darkened room!

i.e. the laser CNC or me! lol

Svejk
15-05-2012, 11:45
Silk screen using laser printing/ironing:

11257

Svejk
15-05-2012, 11:52
And solder mask using Pebeo Vitrea 160:

11258

bluejets
16-05-2012, 03:56
Thinking about ultrakeet they reckon they could etch a PCB in Ferric Chloride in a minute!

It takes me close to an hour even in warmed solution in a Bain Marie!

Am I missing something?

I think so. Many things could be affecting the time. New or used solution, size of the board, how much copper is to be removed etc.
If you look at the article, they mention they are using a thin-layered copper board (0.032 inch)

If it is taking you an hour, then you must also be experiencing "undercut" when the solution starts to etch it's way under the protective traces.

I use the old Dick Smith board (only because it is what I have left in the cupboard) and although it is fairly thick layered copper, a board the size Ultrakeet were using should take no more than about 4 minutes to etch. This is with a plastic tray with the solution and the tray floating in hot water (about 70 degrees C.)

Jeremy Harris
16-05-2012, 10:09
I find that the biggest variable affecting etching time, apart from temperature, is agitation. When I can be bothered to swill the etchant bath around all the time then boards etch a lot quicker than if they are just left. A proper bubble tank would probably be quicker still, but I can't justify that for the few boards I make.

boriz
16-05-2012, 14:17
Jeremy. How about an auto-swiller. It can use a cam on a geared motor, or a servo, or marine propeller, or paddle, whatever. But It definitely needs a timer function with an end of cycle beep, so it will require a Picaxe. :)

beb101
16-05-2012, 18:31
I use the so-called "Edinburgh Etch",

http://www.nontoxicprint.com/etchcopperandbrass.htm

Dissolve 250ml of citric acid crystals in 1 litre of warm water and mix with 4 litres of saturated ferric chloride solution (strength about 40%, or 42-48 BE). Multiply or reduce amounts while retaining correct ratios.

Put about 1/2" of solution in a plastic sandwich container. Wear latex gloves and help the etching process by rubbing the PCB with a soft sponge or a piece of microfiber cloth. Apparently, the citric acid acts as a catalyst. I find it to be fast with little undercutting.

Baxter

bluejets
17-05-2012, 02:59
I find that the biggest variable affecting etching time, apart from temperature, is agitation. When I can be bothered to swill the etchant bath around all the time then boards etch a lot quicker than if they are just left. A proper bubble tank would probably be quicker still, but I can't justify that for the few boards I make.

Referring back to the article from Ultrakeet once again, you will see they simply use a brush to assist etching.
I usually just agitate the dish for a few minutes.

I tried adding citric acid once for the Edinburgh mix but for some reason it didn't seem to make any difference. Then again I tend to use more etchant than probably necessary.

Jeremy Harris
17-05-2012, 07:29
Referring back to the article from Ultrakeet once again, you will see they simply use a brush to assist etching.
I usually just agitate the dish for a few minutes.

I tried adding citric acid once for the Edinburgh mix but for some reason it didn't seem to make any difference. Then again I tend to use more etchant than probably necessary.


I've used brushes, and bits of foam, but both are messy and I've yet to find a brush or bit of foam that tolerates being in ferric chloride without corroding badly/falling apart/being unusable afterwards. Agitation by swilling the dish around is a lot cleaner, in my experience, it's just that often I can't be bothered to stand there rocking the dish around for five to ten minutes.

Grogster
17-05-2012, 10:39
Many schools simply laser print onto a clear self adhesive label (or even white label, A4/letter size).
Then stick it onto the PCB before drilling.

For what it's worth, this is also what I do for prototypes.
Makes it look much neater, and if you use white A4 sticker paper, then the white paper gives good contrast to all the other pretty colours of the components... ;)

Certainly better then just a bare board anyway, and if you go to production, your chosen PCB house can do the silkscreen for you, naturally. :)

Texasclodhopper
17-05-2012, 12:40
Certainly wouldn't be much of a problem to solve that with a PICAXE and a servo or something! :D



... swilling the dish around is a lot cleaner, in my experience, it's just that often I can't be bothered to stand there...