Author Topic: Manual Paste Screen recommendations  (Read 1155 times)

trev

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Manual Paste Screen recommendations
« on: January 11, 2018, 12:42:00 AM »
I saw on eBay a couple of manual paste printers. Anyone used one or recommend a cheap paste printer?

Gopher

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Re: Manual Paste Screen recommendations
« Reply #1 on: January 11, 2018, 10:18:39 AM »
Most printers (that one included) require your PCB to be in a frame, typically a frame is quite a bit bigger than your printable area to allow for whatever fixes it to the frame plus somewhere for the paste to go when you print. There are reusable frame systems from Tecan and Dek etc but they cost quite a bit and the stencils for them will cost you £150+, fixed frame stencil from major suppliers like Alpha,Tecan & others can cost ~£250. The most common frame sizes are 23 and 29" square
 If you're buying PCB's from China, PCBWay they often have the option to make you a framed stencil at the same time, they are nowhere near as good as proper ones and if you go large they are also often warped but they are like $40. However they are certainly good enough for low volume production as long as you make sure your stencil layer is everything it needs to be. A UK stencil house will look at your data, perhaps apply some special requests like aperture reduction or "homebase apertures" & give some advice on stencil thickness or other design elements, the Chinese just shove it through the laser cutter without a second look.

Mike I believe has the (fairly expensive) protoype stencil printer that takes frameless foils...

The "printer" in your image is about as basic as it can get, alignment seems to be push-pull between some bolts (tedious?), there's nothing in the way of a pcb fixture and then you have a clamp on a hinge. Its probably a reasonable match to the small cheap chinese framed stencils, but it would also be pretty easy to knock up in the garage too. If you move up to the £500 ones on eBay they look a touch more convincing, PCB support (helps with double sided as well as holding in place), the base plate looks more solid (is the cheap one perhaps hollow?) and it still looks a decent match for chinese framed stencils.

We have one of these https://www.pmtech.co.uk/sam-manual-screen-printer.html and use it with a 430mm self tensioning Tecan reusable frame, you really miss the lack of PCB fixtures at times. With manual printing I would say 0402 and 0.5mm pitch is about as far as you want to go, I do print a few things this way that have 0.4mm pitch QFPs on but that does require frequent stencil cleaning and of checking the alignment for each and every print very carefully followed by a very careful pass with the squeegee.

Beyond this tho' I think the market gets really blurred at ~£2.5k you can get over engineered manual printers, mechanically assisted printers and possibly even things like the TWS SR2700.

Mike

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Re: Manual Paste Screen recommendations
« Reply #2 on: January 11, 2018, 11:25:02 AM »
I use the Eurocircuits one
https://www.eurocircuits.com/ec-equipment-ec-stencil-mate/
It works pretty well ( as long as the Chinese stencil place doesn't decide to split the tooling hole apertures!) but somewhat over-engineered and therefore unncessarily expensive.

It can use small stencils- you just need a border of about 50mm top & bottom.

It relies on 2 tooling holes in the stencil for alignment, so there is no positional adjustment, but I've not found this to be a big issue.

It is just about possible, though rather fiddly,  to use stencils without the tooling holes for 1-offs, and you can use plastic stencils but need to take care with mounting and tensioning to avoid creasing.

trev

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Re: Manual Paste Screen recommendations
« Reply #3 on: January 11, 2018, 12:12:07 PM »
Quote
I would be okay with etching stencils from metal sheet myself if I can source a printer that holds sheet stencils. I have an LPKF milling machine and I can drill down to 0.4mm holes. If I can find the right sheet I could probably create stencils as a series of drilled holes.
Brass would probably be a good bet
I actually have some photresist coated brass sheet I've been meaning to try, but then found my vinyl cutter would do a decent job for 1-offs.
For urgen batches I usually have budget to order stainless 24h stencils from PCBTrain, and for less urgent, jobs I get them for peanuts along with a Chinese PCB order

Gopher

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Re: Manual Paste Screen recommendations
« Reply #4 on: January 11, 2018, 05:07:48 PM »
To my mind with that machine and some cut to size aluminum plate, maybe some extrusion and some fittings you could make a pretty convincing one. Maybe steal the tensioning concept from something like this http://blundell.co.uk/product/sd-360u-screen-printer-with-drape-table-effect/ and the alignment on SAM1515 is not exactly revolutionary

trev

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Re: Manual Paste Screen recommendations
« Reply #5 on: January 12, 2018, 11:14:55 AM »
Thanks for the replies. Maybe something second hand will pop up on eBay or Grove, etc. I dont think I want to try and make something. It will take me too long to source materials and experiment, etc.

Gopher

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Re: Manual Paste Screen recommendations
« Reply #6 on: January 12, 2018, 02:01:00 PM »
I've seen more than one place, when building small batches literally just put the PCB on the table, put the stencil on top and paste it there and then, no fixtures, nothing to stop it slipping bar the weight of the frame (which were big and heavy as they all had proper printer(s) as well. Taking that one step further, put a large sheet (metal / acrylic /card)  on the table put your PCB on that, now fit your stencil either using sticky tape of perhaps a hinges and clamps if you have a frame, now you can tweak the PCB alignment by pushing and pulling the sheet around. the PCB can be held to the sheet with PCB offcuts and tape.

trev

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Re: Manual Paste Screen recommendations
« Reply #7 on: January 12, 2018, 02:37:53 PM »
Got me thinking...might be something in that.