The stenciling machine from the learning system

[solexious]

Hello all,

I'm looking for where I can get one of the stenciling machines shown in the smt tutorial http://learn.adafruit.com/smt-manufactu ... g-machines , I'm in the UK (but happy to get it from any place that will ship it too me!

I can find the simple ones easily, but none that have the tooling bits shown here: http://learn.adafruit.com/assets/193

I have managed to get a lot of preorders from my local hackspace for boards that are 100% smt, so I want to tool up well for it, so I would rather pay more for a more advanced machine like adafruit use, than one of the plane ones.

Anyone got any leads?

Sol

[BruceF]

I might shoot a note to Mike's Electric Stuff, if he doesn't pick up on your comment here.

[mikeselectricstuff]

The problem with that one is it needs framed stencils, which are rather more expensive than unframed ones. PCBtrain are the cheapest I've found in the UK for stainless stencils, although PCB-Pool offer free stainless stencils with some of their services.
For small qtys, plastic stencils from Smtstencil are fine - I think they recently improved their laser to get useable stencils for 0.5mm QFPs - not tried the new ones but did use some a while ago which were just about useable.
Of course as London Hackspace's resident laser cutter ninja, Sol you should be able to cut plastic ones yourself!

For 1-off jobs you can improvise a stencil holder pretty easily with a few PCB scraps and sticky tape, but for multiples a proper printer that can tension the stencils is very worthwhile. I use the Eurocircuits EC Stencil-Mate, which is pretty good, and although quite expensive, it's the cheapest one I know of that can do proper tensioning of unframed stencils.
I think there is scope for someone to make a much more sensible-priced printer for unframed stencils - I thought maybe using something like 3.2mm PCB material for the structure as it is readily machinable accurately by PCB fab places.

[lyndon]

Do the plastic stencils really need to be stretched, or is it a matter of holding them flat? I have in mind a system where the stencil is captured between two flat pieces of metal that are then fastened together, holding the stencil in place. After this is done, then the center sections of the flat pieces are removed, so the stencil is now still flat, but only gripped by the edges.

Alternately, I wonder if it would work if you used a screenprinting frame, with its fabric already stretched, and taped the stencil to it. That way it's held flat through multiple uses.

I have a screen print frame, maybe next time I have a board made I'll order a stencil and try out that idea.

[mikeselectricstuff]

Plastic ones don't need stretching, and would probably distort anyway. The key is to keep it flat & parallel to the surface.
This gets increasingly difficult (with both metal and plastic) as the board size increases - stretching (and therefore a metal stencil) is the only way to keep it rigid enough to stay flat across the whole surface.
As soon as you get any seperation between stencil and PCB, the paste can squish sideways into the gap and blur the print.
Print quality is the number one factor for getting good yield with minimum rework.

[mikeselectricstuff]

These also look quite good for unframed stencils: (I've heard it's cheaper to buy from this Danish supplier than their UK distributor Blundell :
http://www.printtec.nl/contents/nl/d361.html

[solexious]

Hi Mike,

Funny you should mention the lasercutter, I had been looking at doing it this way. I tried getting my hands on some sheets of kapton film from the US but it kept getting lost in the post. The only suppliers I could find in the UK were £££. Any tips on where to get it, or a better material to use?

Sol

[mikeselectricstuff]

Use polyester film - cheap and readily available

[vincentp]

I use the eurocircuit "EC-fix" for most of my work now. I have a few of those, the frame is 15€ each, and I found stencils to be very cheap for 130 µm stainless steel, very durable.

[solexious]

What thickness is best?

[vincentp]

it depends on the application and stenciling machine, but I'm not expert. Usually between 125 and 130 µm.
I now decrease by 10% all my apertures, there are other rules using the pitch of the parts, but 130µm + 10% off has worked for me so far

[mikeselectricstuff]

Re. thickness, somewhere in teh range 100-150um. There is a tradeoff between resolution for fine-pitch devices (thin) and robustness (thick)

Probably worth getting a selection and playing with laser powers to find the optimum combination.