Using sandwich press for PCB transfer

[composition4]

Hi,

I'm doing a large project which will need about 15 PCBs of various sizes (8 same, rest different)

I usually use press n peel transfer method with fairly good success, but the ironing part is always my biggest hurdle.  Specifically, keeping the whole board heated evenly, and also a few other issues. Does a sandwich press or sandwich toaster with flat plates sound like a good idea?  Like this:



I'm not entirely sure on how hot they get - I have one (for food purposes!) and I can take some temperatures

I'm sure I''m not the first person to think of this... so does anyone think this is a good idea, or can you point out why it may not be?

Thanks
Jonathan

[Ice-9]

Sounds like a great idea, i would think it will be hot enough, and if you can get enough pressure on the pcb i think it will work, good luck.

[bassmannate]

That sounds like a great idea! If you plan on putting a silkscreen on the component side, then you can probably do it at the same time as the traces!

[alanlan]

Looks like an expensive bit of gear though - make sure you don't scratch the non-stick surface with the rough edges of the PCB otherwise the owner might be a little annoyed!

[kupervaser]

Awesome idea, when are you going to try?

Just let us know how it goes.

[composition4]

Thanks for the replies, I'm surprised nobody has shot the idea down... yet  There may be a reason yet

They're not expensive (around $30AUD = $25USD) and I'm sure I will be able to find a second-hand one this weekend so that I don't ruin the one I have!

I'll try it this weekend and let you know how I go.  Any more suggestions/comments are welcome, as I'm sure there must be SOME reason it won't work - it seems to make too much sense to work, if you get me...

Jonathan

[kupervaser]

I have actually never seen the grills you show.

I've only seen these kind of things:

[Mark Hammer]

Ah, the George Foreman toner-transfer system!

More seriously, it is possible to buy teflon in sheet form.  I know because my dad left me some.  A thin sheet above and another below, and you can engage in stick-free ironing.  I would imagine that places that deal in commercial plastics would carry it.

[ppatchmods]

if you mess it up you could always do this:

[davent]

You might be able to use parchment paper to protect the grill surfaces. Usually available with the tin foil and plastic wraps in your local grocery store. Designed to withstand high temperatures in your oven so should stand up to the pcb grilling.

dave

[tiges_ tendres]

What a great idea!

I have two concerns.

1) Isolating cold spots on the grill plates.  There may be sections of the grill that are hotter/colder than others which could lead to a poor transfer.

2) Making sure the unit you buy allows you to put pressure directly on something as skinny as a pcb.  My press is hinged so that the plates cant physically touch, or get with in a certain distance.  The unit in the picture looks like it will get you direct contact with a pcb.  Alas, my press will not allow me the same luxury.

GOOD LUCK! LETS US KNOW YOUR FINDINGS!!!!!

(are we going to have any household appliances we can't bend to our pedal making wills?)

[.Mike]

(are we going to have any household appliances we can't bend to our pedal making wills?)

That makes me wonder if a tortilla press would somehow work for PCB transfers. You could get it ripping hot in the oven, toss your board and the transfer image between a couple of layers of parchment paper, and press. As long as your board is thicker than a tortilla, you would probably get good, even pressure.

Just a thought.



Mike

[hday]

At the university I attend, they use a big, flat pancake griddle. It heats the board evenly from the bottom, then you can press it from the top with an iron. Cold spots shouldn't be a big deal if you're only doing one board at a time. You can't really over heat it. Once the paper becomes brown, it's probably been ready for a while. I bet a sandwich press would work, but I would rotate the board several times in case the lid isn't completely parallel to the bottom.

[ralley]

I usually use press n peel transfer method with fairly good success, but the ironing part is always my biggest hurdle.  Specifically, keeping the whole board heated evenly, and also a few other issues. Does a sandwich press or sandwich toaster with flat plates sound like a good idea? 
...
I'm sure I'm not the first person to think of this... so does anyone think this is a good idea, or can you point out why it may not be?

I've been using one very similar to what you pictured quite successfully with laser print transfers on HP Premium Plus Inkjet photo paper (cheaper HP papers don't work for me).  I normally put a sheet of plain paper either side of the PCB, let the press heat up and then stick the wrapped PCB inside.  I hold the press lid down tightly by hand for a minute then weight it down (plastic bowl with ~2l of water) for a further 3 minutes.

I went to this method to try and get some repeatability - I can time how long it's in and use a repeatable amount of pressure.

At first I got great results but for my Easyvibe transfer I went back to the iron - that PCB seemed cursed, it took something like 20 tries to get a decent transfer and etch.  No matter what method I used I had constant problems with tracks bleeding together or not transferring.

Rob.

[tranceracer]

but the ironing part is always my biggest hurdle.  Specifically, keeping the whole board heated evenly, and also a few other issues.

I hear ya! I gave up on irons long ago. Had a hard time getting the edges of the trace to transfer to the board.  Another suggestion is to use a hotplate.  I bought one for 6 bucks at the Goodwill store.  It has a variable heat adjustment and I set it to low-medium heat.  This gets the pan hot enough to sizzle water, when the water sizzles I carefully drop the Cu board with the laser trace on the hotplate.  Then use a cotton rag about the size of the PC board and a pizza roller and roll over board at 90 degrees.  Unplug the pan and drop the PC board into a waiting container of water.  Cheap, consistent results and I can make larger transfers than I could with an iron!   

[davent]

I gave up on struggling with toner transfer altogether and switched to presensitized photo PCB's. From printing out the laser transparency of the traces to having an etched PCB in hand can be done in half an hour, no special tools required.

dave

[composition4]

My only problem with that is the price of pre-sensitised boards over here... about 4x the price of equivalent blank copper PCB, which in itself isn't cheap in Australia. Unless someone has a good source?

Jonathan

[Mark Hammer]

Davent's suggestion of parchment paper is an excellent one.  It'll do the same job I was recommending teflon for, at a fraction of the cost.  It's also a lot easier to find.

Although photo paper can work great, the chief stumbling block with it seems to be being able to tell when it's "done".  Press-n-peel has the advantage of being thin enough that when the toner has properly adhered to the copper the acetate backing sags enough that you can see a complete detailed outline of the pattern.  Photo paper is too thick to see such a "bas relief", though after a while one gets the hang of it.

As some have noted regularly on this forum, glossy magazine paper can also work quite well, and has the advantage of being much thinner than photo paper (which is intended to produce images you can pick up and hold in your hand).  Like photo paper, glossy magazine paper is a paper fibre backing with an emulsion coating; the difference being that photo paper has no colouring in the emulsion (it awaits your image of choice) while magazines already have an image and accompanying pigments embedded in the emulsion layer.  That pre-colouring has no bearing on its ability to hold and transfer toner, though.

The chief shortcoming of magazine paper is that it has an emulsion layer on both sides (the emulsion can melt and stick to the heat source on the side where heat is applied), and that whatever image is on the back side can make it difficult to see the "bas relief" outline of the toner pattern the way you can with the solid-colour PnP.  The first shortcoming can be addressed by using the parchment paper as davent suggests.  The second shortcoming can, for the most part, be addressed by having suitable lighting and holding up the board to the light at a suitable angle for seeing whether the pattern has been affixed to the board.