pcb shear!

Chat about pick and place machines, reflow ovens, assembly techniques and other SMT tips & trix

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adafruit
 
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pcb shear!

Post by adafruit »

ill probably need one of these, too. right now using tin snips, works surprisingly well! still, a guillotine would be nice. MEGA has some.
theres also the T-Tech
http://www.t-tech.com/order/product.asp ... ductid=580
any recommendations from others?

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oskay
 
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Re: pcb shear!

Post by oskay »

The "real" solution is to start getting your boards made either with v-scoring or tab routing. Using a shear is a fine solution for prototyping, but these really are well-developed solutions for making lots of tiny boards.

One thing to watch in any case is that ceramic caps have a tendency to crack when the board flexes. This is a genuine concern when breaking boards out of a larger form by any of these means.

Getting the break-away tabs or v-scores just right is *tricky* and you might have to do more than one run to get it right. If you make the connections too weak, P&P may be awkward, so it's better to err on the side of too stiff and have the shear on hand just in case.

adafruit
 
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Re: pcb shear!

Post by adafruit »

we vscore, but then we still have to cut it. maybe we're just do tabroute. those snap without too much effort, but we always assumed that people sheared w/a guillotine...

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oskay
 
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Re: pcb shear!

Post by oskay »

If you call out your v-scores are *just right* they'll stay flat all the way through reflow and then snap apart exactly when you bend them. Time to try thinner webs?

adafruit
 
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Re: pcb shear!

Post by adafruit »

hmm! we go with advanced circuits' default. do you know what i should spec for v-score depth?

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oskay
 
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Re: pcb shear!

Post by oskay »

Depends pretty strongly on the individual (small) board size, and to a lesser extent on your larger board size. Flatness can be an issue for P&P, so you can sometimes get away with thinner webs/larger boards/more v-scores if your board is supported well in multiple locations.

There's a chart that gives web thickness suggestions based on board size here: http://www.pcbstandards.com/forums/show ... php?t=2261

PCB vendors are NOT interested in depanelization-- they only care about the yield of good boards, so their thickness suggestions are usually serious overestimates.

EDIT: Should say, try a value between where you've been and the ones on the chart. Don't want to underdo it, either. ;)

adafruit
 
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Re: pcb shear!

Post by adafruit »

OMG useful information!!!

freaklabs
 
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Re: pcb shear!

Post by freaklabs »

I pretty much use V-Score for my PCBs. My PCB shear is just used for making my own PCBs on the CNC. Or when my wife wants to use it as a paper cutter for her fliers.

adafruit
 
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Re: pcb shear!

Post by adafruit »

i gotta figure out why its working for everyone else, it always feels like the board is splintering :/

ralphstirling
 
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Re: pcb shear!

Post by ralphstirling »

We use our LPKF machine for cutting boards out of a panel and for cutting stencils. We
haven't tried setting it up to cut out boards after stuffing though. Definitely overkill, but
I actually use it more for these purposes than for engraving 1-sided pcb's.

-- Ralph

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adshea
 
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Re: pcb shear!

Post by adshea »

If you're doing really tiny boards, I've found it helps to run a rock knife/box cutter/BANNED blade across the V-score before breaking. It helps sever/nick the edges of the fibers and makes the boards break cleaner without that nasty peeling feeling.

adafruit
 
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Re: pcb shear!

Post by adafruit »

nice tip! we'll try it tonight

freaklabs
 
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Re: pcb shear!

Post by freaklabs »

@ralphstirling: How is your LPKF machine? I'm using AccurateCNC for my PCB milling. Are you using the LPKF solution for the vias? That's the one drawback I've found to milling my own PCBs is that connecting the vias to top/bottom layers is a total pain in the ass.

ralphstirling
 
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Re: pcb shear!

Post by ralphstirling »

freaklabs - It is very rare that I make a double sided board with the LPKF machine any more. Soldering little wires through the board for vias is too problematic. If I intend to make the board with the LPKF I lay it out for wire jumpers on the back side, and mill it out as a single sided board. It is easier to solder a wire jumper between two vias than to solder a wire on each side of the board in one via. It also saves a lot of milling time and cutters. If I really need a double sided board I just have Advanced Circuits make it. I'll save up a bunch of small projects and put them on a multiproject panel and use the LPKF to separate the boards. I also make stencils with the LPKF, using .005 unclad laminate. They act a bit thicker than laser cut stainless stencils, so I shrink the openings to reduce the chances of shorts. We also use a "corner notcher" type shear for cutting out boards on occasion, although it isn't terribly accurate, and one has to be careful not to damage traces.

Simple boards without many holes we still etch. We print the gerbers directly on .008 single sided laminate using a Xerox Phaser 8400 solid ink printer and etch in a copper chloride bath. Start to finish is about 15 minutes, and our etching tank allows six different boards to be put in or removed independently, which works well for busy electronics lab sessions.

-- Ralph

freaklabs
 
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Re: pcb shear!

Post by freaklabs »

Wow...you use so many different methods for prototyping.
I use my AccurateCNC mill for prototyping double sided boards. I need a bottom-side ground plane since I do a lot of RF and need to make transmission lines. I'd say that a pcb mill is probably most useful for people doing RF since there's usually a lot of trial and error involved. Its probably debatable, but being able to prototype an RF layout in half a day and make modifications has saved my ass a couple of times. I also use the mill for solder paste stencils and light front panel milling.

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