Cutting a stencil to smaller size - Page 1
Forum section: electronics / general

author: greencardigan
author_rank: Contributor
timestamp: July 30, 2018, 10:41:29 am
content: Hi,I’ve just received my first stencils for solder paste application. They are much bigger than anticipated at approximately 380mm x 280mm. The stencil is for a small 40mm x 20mm board. The cut outs are centred in the stencil.I’m assuming I should cut the stencil down to a more managable size?Typically how much space around the board area should I leave?Or how my space should I leave on the side that I will use to tape down as a hinge when applying paste?I haven’t tried yet, but I assume I can just cut them with standard household scissors?Cheers

author: DTJ
author_rank: Super Contributor
timestamp: July 30, 2018, 11:02:50 am
content: I'd take it to my local sheet metal fabricator or even a place that fabricates aircon ducts and ask them if they would guillotine it for you.Mark it clearly with an indelible marker before you take it there to minimise the effort they need to take.It's literally a 90 second job, they might do it for free or for a $5 donation toward their morning tea fund.An alternative is to sneak it into office works and try doing it on their heavy duty paper guillotine. Just try doing a test cut out near the edge in case it folds rather than cuts.Scissors: unless you use very good very big old dress making scissors you may just end up creating a wonky sharp edge. They will cut it but will it be nice?It can be good to keep it quite a bit larger as it can aid in lining things up and handling it when screeding the paste.

author: NorthGuy
author_rank: Super Contributor
timestamp: July 30, 2018, 03:50:12 pm
content: For your next project, you can order your stencil from OSHStencils. They make the stencil the size of the board with small margins. As I remember, you can go as little as 1/2 inch around your border.

author: SMTech
author_rank: Frequent Contributor
timestamp: July 31, 2018, 09:01:26 am
content: Stop, no why?Solder paste is a sticky insidious not very pleasant goop that given half a chance, gets everywhere.When you paste a PCB you want somewhere for you solder paste to sit before you start your squeegee pass and somewhere for it to be when you stop, neither of these places should be on top of any of the apertures in the stencil. As you make the pass solder will roll into the apertures but also outwards, its nice to have it go somewhere nice and easy to clean like unused area of you stencilOK so yes for your very tiny PCB your floppy stencil foil is unusually generous but if you cut it yourself it will end up razor sharp and probably curly, what harm does being too large really do? If I was going to go and bother a local metal shop I would instead ask them to bend the 2 sides up at right angles making the foil inherently slightly rigid.If you're worried that when you lift the stencil it might warp(can happen without frames) and smudge your print you can always stick something rigid to the topside out of the way.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 31, 2018, 09:07:55 am
content: You do want a decent border, at least an inch on each side, ideally 2"You can cut stainless pretty well with a pair of good quality large (6" or more blade) straight-bladed scissors - a metal shop guillotine may not be sharp/close enough to cut such thin material - a heavy duty paper guillotine might also do it.When cut, the edges will be lethally sharp - you probably want to put tape over them to avoid unintentional bleeding to death.

author: greencardigan
author_rank: Contributor
timestamp: July 31, 2018, 11:43:07 am
content: Thanks all. I have quite a small working area so the large stencils take up a big portion of my bench.I tried cutting a strip off with some kitchen scissors and it cut well. The cut edge doesn't feel much sharper than the uncut edge but I'll tape it anyway. I'm definitely not ready for unintentional death by stencil cuts.

author: DTJ
author_rank: Super Contributor
timestamp: July 31, 2018, 01:00:47 pm
content: Carefully run some wet/dry or carbide sanding paper up and down the cut edges just to blunt them a little.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 31, 2018, 05:51:42 pm
content: Never had any issues just using standard office/kitchen/home/whatever you call them scissors on 120µm stainless steel stencils.Guillotines can be tricky. If designed for heavier sheet stuff (as they usually are in machine shops), they may not be able to cut thin stuff at all - even when well maintained -, or they produce a massive bent edge. Scissors tend to work when guillotines won't. With copper, the transition point from scissors to guillotine seems to be around 0.3mm, but with stainless steel, it's probably less.

author: KL27x
author_rank: Super Contributor
timestamp: August 01, 2018, 12:38:34 am
content: QuoteWhere regular scissors don't work, or aren't long enough, a pair of offset aviation tin snips might save you the occasional trip to the local metal fabricator. They look specialized, hanging next to the familiar scissor-looking standard tin snips at your hardware store. There is a right hand and a left hand version, to add to the confusion. But the important functional distinction is that offset aviation snips are bent to keep your hands above the stock, so they have an infinite cut length.For most purposes you just want the right hand, if you're a righty. These will tend to curl the waste piece to the right side of the cut, leaving a smooth and straight edge on the left.*edit: I think I mixed them up, the right hand and left hand. The ones that are hinged like regular scissors are the ones I'm talking about. Apparently, there are 3 kinds. Straight and left cut are both hinged like regular scissors. The ones that are hinged like left-handed scissors are called right cut. This tool will make anyone dyslexic. In hindsight, I think they (either straight cut or left cut offset aviation) would be the first tin snips I would buy, and I'd maybe even stop there. There's not too much downside in anything, compared to a regular (non offset) tin snip. If the nomenclature were simpler, I foresee a huge loss in sales of regular tin snips.

author: mrpackethead
author_rank: Super Contributor
timestamp: August 11, 2018, 06:44:23 am
content: The best thing you can do with an unframed stencil is get it into a proper stencil frame. It makes such a massive difference.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 11, 2018, 09:22:01 pm
content: Quote from: mrpackethead on August 11, 2018, 06:44:23 amOr a stencil printer that can tension them properly.

author: mrpackethead
author_rank: Super Contributor
timestamp: August 12, 2018, 01:57:23 am
content: Quote from: mikeselectricstuff on August 11, 2018, 09:22:01 pmYes. thats kind of what i meant. using unframed untensioned stencils just makes the job harder. Really hard to get reliable, high quality paste.