Spark Logic

Anyone used OSHstencils? Any wisdom on SMT to share?

gbulmer Thu Jan 21, 2016 12:26 pm

Have people tried https://oshstencils.com ?

Their prices seem good, so I plan to give them a try.

I want to help kids assemble SMT boards, so I want a technique which they can use reliably to paste and assemble the boards.
This is partly why my mini-orone series of designs (Maple-mini plus some improvements) uses 1206-scale parts.

I use a syringe to apply solder paste, and a toaster-oven, to make a board.
However young teenagers can be quite awkward, even clumsy, physically (when their limbs grow but their brain has difficulty keeping up :-)

It is very easy to put too much solder paste on. Also, unfortunately, the STM32 packages are quite fine which means there is quite a lot of ‘bridging’, which requires rework with solder braid. So I end up removing solder on boards I make. I’d like to minimise that for them.

(I should credit Paul Gardiner, a local teacher, who taught 13yo’s, upwards, the solder-syringe + toaster-oven technique on simpler circuits with huge success. So I am following his lead.)

So I intend to experiment, to learn how well stencils work.

Eventually, I’d like to make a jig for each PCB with registration pins, to align the board and stencil, rather than tape everything down.
I’d also like make the PCBs in a ‘mini-panel’, i.e. with the panel border carrying the pin registration holes for the PCB to fit into the jig.

Has anyone experience and wisdom you can share?

Replies

RogerClark Thu Jan 21, 2016 8:21 pm

Thanks for the link.

I have noticed eBay listings for companies who do the same thing, at similar prices, but I have not tried any of them.

I was actually going to try to cut my own stencils on a cheap 40w ( Chinese made) laser cutter, but Ive not had time to see who well it works.
( and of course not everyone has access to a laser cutter)

When I finally get around to cutting a stencil , I will let you know how I got on.

mrburnette Thu Jan 21, 2016 10:08 pm

@Roger
And a low-cost approach: here

RogerClark Thu Jan 21, 2016 10:30 pm

Ray

Thanks for the link. I think I have seen that video before, but need to watch it again.

I don’t have Mylar sheet, I was hoping to use old Overhead Projector acetate slides, but I should probably order some Mylar sheets from eBay as well, as they would be stronger

e.g.
http://www.ebay.com.au/itm/Stencil-Film … Swu4BVmHQF

I also just found this thread on laser cutting stencils

http://www.sawmillcreek.org/showthread. … ting-Mylar

I just need to find time to try it out ;-)

OSHStencils Fri Jan 22, 2016 3:43 pm

There are many things to consider when creating your own stencils. Mylar solutions, while they do work, solder paste doesn’t flow as smoothly off the material like it does with Polyimide. So that can lead to some rework.

Off the shelf hobby lasers also provide very inconsistent results given that they use tube based lasers which are notorious for power fluctuations which can produces a poor quality stencil.

When we started the company we had three major goals. Produce the best quality product compared to anything on the market, have the lowest possible price point, ship stencils in under 24 hours with the fastest methods of delivery worldwide at the lowest price.

We are makers ourselves and love that people want to find ways to make stencils on their own, but in most cases for less than $10 you can have a professional quality product delivered to your door in a few days, making the decision to use our service vs putting time and energy into making it yourself an easier decision.

If you have questions, we’re happy to assist. We’re confident that if you give our product a try, you’ll get incredible results on your project and see why we’re the most widely used film based stencil company on the market.

Enjoy my fellow makers!

gbulmer Sat Jan 23, 2016 3:08 am

mrburnette wrote:@Roger
And a low-cost approach: here

gbulmer Sat Jan 23, 2016 3:17 am

RogerClark wrote:Ray

Thanks for the link. I think I have seen that video before, but need to watch it again.

I don’t have Mylar sheet, I was hoping to use old Overhead Projector acetate slides, but I should probably order some Mylar sheets from eBay as well, as they would be stronger

e.g.
http://www.ebay.com.au/itm/Stencil-Film … Swu4BVmHQF

I also just found this thread on laser cutting stencils

http://www.sawmillcreek.org/showthread. … ting-Mylar

I just need to find time to try it out ;-)

RogerClark Sat Jan 23, 2016 4:21 am

I just ordered some mylar sheets, which should be here in about a week (as they are from a local supplier)

So.. I’ll let everyone know how I get on, when I get around to trying.

BTW. I do also have acetate sheets that I was going to try, but it looks like Mylar is the better bet.

gbulmer Sat Jan 23, 2016 6:04 am

Yes, I’ve been told Mylar is the right material, and my web research seems to support that.

However, a friend said it is quite hard to get mylar thin enough!
AFAICT, the stuff on ebay is significantly thicker than the ‘right’ thickness. So it may apply a layer of paste thicker than ‘correct’.

I have seen ads for the correct thickness ‘thin’ mylar (I’ll need to dig up my notes) but it was sold by the metre for industrial use, and was IIRC relatively expensive.

I wouldn’t care much about ‘over pasting’ on ordinary components, where I apply too much solder now with a syringe.

However, I am a bit more concerned about 0.5mm pitch STM32 packages.
I use footprints where the pad’s are larger than half the pitch, so the space is quite small (IIRC about 12mil pad vs 8mil space)
However, I think a few tests should demonstrate the performance of easy-to-get mylar. It feels like the mylar would have to be very thick to be as bad as my syringing :-)

So, I’ll be very interested in your results.
Keep up the great work :-)

PS – Happy New Year everybody.

RogerClark Sat Jan 23, 2016 6:21 am

OSHStencils wrote:There are many things to consider when creating your own stencils. Mylar solutions, while they do work, solder paste doesn’t flow as smoothly off the material like it does with Polyimide. So that can lead to some rework.

Off the shelf hobby lasers also provide very inconsistent results given that they use tube based lasers which are notorious for power fluctuations which can produces a poor quality stencil.

gbulmer Sat Jan 23, 2016 1:12 pm

OSHstencils, thank you for posting. I apologise for missing your post, it was late when I posted.

I will likely be ordering some stencils (later in the year). I agree your prices are impressive. I’d like to learn to DIY-them too, however your prices mean that isn’t very important.

Much more important to us is making the rest of the assembly process easier and more robust for school children. So may I ask, is it worth using slightly thicker film (thicker than 5mil) to get a more robust process?

OSHStencils Sat Jan 23, 2016 3:45 pm

The most common reason people select 5 mil is two fold.

1) They need slightly more paste on their pads
2) Durability. 5mil film holds up better for repeated use.

The downside to 5 mil is for extremely fine pitch components it may leave too much paste, so you may have to swell your pads a bit.

If you intend to use this for education and are building the same project potentially hundreds of times. Then it’s really better to go with Stainless Steel as it will last a very long time, but naturally it’s more expensive.

mrmonteith Tue Feb 09, 2016 12:06 am

I’m just sharing this because you mentioned stencils. So don’t shoot the messenger as I don’t know anything beyond that. So I’ll leave it to you to wrestled that.

Solder Stencils With 3D Printers

Michael

RogerClark Tue Feb 09, 2016 12:36 am

Interesting…

I’m not sure my 3D printer would be good enough for some small pads, but I guess it may work for larger components

Edit

I didn’t spend ages on it, but my old 3D printer wasn’t up to the job, and I can’t imagine many 3D printers making a good job of a stencil

IMHO, The layer thickness that you need, is just too small to be practical on most printers. I think the minimum number of slices would need to be 2, in order that the two layers are printed as a crosshatch, as a single layer would rely on the filament bonding well to the horizontally adjacent filament, printed some time ago and a lot cooler (even with a heated bed).

Even then, I’m not sure what the minimum practical layer size, i.e if its 0.1mm, you’d still end up with a 0.2mm depth of solder paste, which is probably too much, as Kapton film which is 0.06mm thick

stevech Wed Feb 10, 2016 6:15 am

several folks on teensy (PJRC) forum use OSH.
Maybe one of them has comments on stencils.

Too hard, but the guy at lowpowerlabs.com made stencils from old soda cans cut and rolled flat.

gbulmer Thu Feb 11, 2016 9:05 am

mrmonteith wrote:I’m just sharing this because you mentioned stencils. So don’t shoot the messenger as I don’t know anything beyond that. So I’ll leave it to you to wrestled that.

Solder Stencils With 3D Printers

Michael

OSHStencils Tue Jul 26, 2016 12:23 am

Just a follow up here stencil fans. We now have Stainless Steel stencils at extremely affordable prices. So if you want a higher quality stencil, with longer durability and lots of precision but don’t want to mess with soda cans, we’ve got you covered :)

We also launched our new website, so feel free to pop by and check it out. Some images of our new Stainless stencils are in the gallery.

Enjoy, and happy making! :)

www.oshstencils.com

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