PCB Fab house - pocketing with laser cut or cnc router? - Page 1
Forum section: electronics / projects

author: Mecanix
author_rank: Frequent Contributor
timestamp: August 03, 2020, 02:48:03 am
content: Hey guysI did asked this question over the PCB house last Saturday and didn't get a response, yet, understandably this is the weekend. In a bit of rush I'd like to ask you guys if you know whether the PCB house cuts with a router endmill (i.e. round bit) or use other means like laser, water jet, water-ever they use I'm not entirely sure and hence why I ask. The real question is; can they do "sharp corners" as seen on the visual below? Let's presume I'm going with JLCPCB for instance...Background: I am trying to fit in a 'low profile' MicroUSB connector with 4(four) TH supports and it requires the board shape to be cut. It really need sharps corner cuts otherwise there will be some interference (as in mechanical interference).Grateful if some of you who had to deal with similar board cuts could confirm, I'd really appreciate.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 03, 2020, 06:09:04 am
content: End mill.How about bulging the corners to 1-2mm circles? If you don't need registration between board edge and component right near the corner (and it doesn't cut into any nearby holes or copper), this works.Tim

author: Mecanix
author_rank: Frequent Contributor
timestamp: August 03, 2020, 07:14:53 am
content: Brilliant idea, that would be the way to go, however... see visuals :/Who engineered that connector if we can't have fab houses that does 90deg corners lol Should have checked that before spending 2.5hrs modeling that connector. So I gather that most/all use cnc routers/endmills to cut pockets in FR-4? Yikes...

author: Mecanix
author_rank: Frequent Contributor
timestamp: August 03, 2020, 07:24:58 am
content: Pardon the over-reacting comments above. I now took a deep breath and gave your idea a try, Tim (1mm holes).I'll shoot them this visual with Dim and see if they are keen doing a small pcb run with that in...

author: Ian.M
author_rank: Super Contributor
timestamp: August 03, 2020, 07:28:24 am
content: No problem. The rear of the pocket can tolerate a pair of semicircular recesses to allow the sides to be straight for their entire length.Laser cutting would leave char that would make isolation cuts in high voltage PCBs unsafe, and its hard to achieve the required accuracy with waterjet cutting.

author: Mecanix
author_rank: Frequent Contributor
timestamp: August 03, 2020, 07:34:22 am
content: Was thinking more like 'waterjet'ing those FR-4... less dust, less wear, less tooling/bits, 1,000x faster too.Anyway... first ever pcb I need custom sliced, didn't know. Thanks for letting me know guys.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 03, 2020, 07:45:35 am
content: Wouldn't think they would waterjet because the dimensional accuracy and finish aren't as good, particularly in a stack of boards (large and tapered kerf) which I think they prefer to do versus milling single boards at a time (or is that drilling that's done by stack, I'm not sure).Tim

author: Mecanix
author_rank: Frequent Contributor
timestamp: August 03, 2020, 07:54:26 am
content: Fair enough. Probably didn't see too many high accuracy WJ myself, but do know they exist; some in the micron accuracy however worth a few small towns and oceans of cash (Made in Germany, /medical). Bet the router is that trade-off between cost vs accuracy. So be it then... fillet your FR-4 accordingly folksGood learning, appreciated guys.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 03, 2020, 08:35:04 am
content: They use an endmill, typically 1.6mm dia but can usually do down to about 0.5mm dia - latter is slower so sometimes adds cost. If you need a sharp corner to fit a square part in, best thing is to use a dogbone cuthttps://wiki.imal.org/howto/dogbone-fusion-360-plugin

author: Mecanix
author_rank: Frequent Contributor
timestamp: August 03, 2020, 08:53:02 am
content: Awesome on the endmill standard size intel, thanks. Following guidance, I've amended the radius to 0.8mm (od1.6mm).Looking good. Let me get this out of here and I'll report if there are any issues (I doubt at this stage, thanks for all your help!). If you don't hear me crying for my 0.1cent connector & cut probably it all went fine

author: tooki
author_rank: Super Contributor
timestamp: August 03, 2020, 09:10:40 am
content: Quote from: Mecanix on August 03, 2020, 07:14:53 amBut from your own images it doesn’t even look like it needs a sharp 90° angle anyway, there’s room for a corner radius.

author: Mecanix
author_rank: Frequent Contributor
timestamp: August 03, 2020, 09:26:35 am
content: You don't understand, Tooki, I'm doing some severe micro-management today lolIn all seriousness, that fillet corner looked a bit stuffed and near 'contact', had me worried when I first tried that. Here it goes with a 0.8 radius. Bet it would work (you're probably right), just trying to understand the mfg/cnc processes of those fab houses and hope to cut that board in a way that increases my chance of success (they do take quite a bit of time to come by those pcb). In all honesty those dogbones/reliefs appears like a safer bet. Who knows what those router's accuracy/tol... guessing +/-0.2mm

author: sokoloff
author_rank: Super Contributor
timestamp: August 03, 2020, 09:33:54 am
content: They’re done on a CNC mill as you have learned. You don’t want your boards going through another setup for water jetting (which itself still leaves an inner radius on the hole, of course). Minimizing setups minimizes registration issues.

author: sokoloff
author_rank: Super Contributor
timestamp: August 03, 2020, 09:37:41 am
content: Thinking about it another way: you’re not the first person to face the issue of how to mill out a spot on your PCB for this USB and the designers of the USB part no doubt designed it to be workable with industry-standard processes.The chance that you need a non-standard process for your USB is -100dB down from 1.

author: Mecanix
author_rank: Frequent Contributor
timestamp: August 03, 2020, 09:55:28 am
content: Quote from: sokoloff on August 03, 2020, 09:37:41 amNo doubt, kudos to them indeed. Nearly an industry marvel that connector given its size and shape... certainly gets the inexperienced slightly more experiencedReally need that badboy to sustain the force, particularly the weight of the cable. Not going to re-use that other SMD type I had in a previous design... the one that failed twice, been re-soldered twice, until it took out two pads on its 3rd failure :/ Gotta work...Thanks for all your kind help guys. Hope you've all enjoyed the noob entertainment too! (I'll be asking more questions in future I'm sure, you guys rocks, ty)edit: for those of you who have no clue ab what they are doing(coughs...), avoid this connector at all cost. "The Designers" were drunk when they did that one... trust me lol

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 03, 2020, 12:47:33 pm
content: Yeah, the tolerance isn't great, maybe not as large as 0.2mm but not much better either. Also, they tend to run them as fast as they can, so the mill deflects quite a bit in the cut. And that deflection changes as the cut changes direction. So you get projections and undercuts around corners. And you don't know which side of that corner will get which feature, because you don't know which direction they're cutting around it.The full depth (semicircle) doesn't seem to be necessary; I'd be happy with 50-70% depth as well. Enough to relieve the inside corner fillet, without cutting into the board as much. Not that it matters, nothing looks to be in danger of getting cut, even with wonky toolpaths.Tim

author: phil from seattle
author_rank: Super Contributor
timestamp: August 03, 2020, 03:45:19 pm
content: A suggestion, do a small trial run if you aren't sure. Hopefully it won't cost much and will give you a lot of insight into their practices. I'd put several variants of your footprint/cutout on it to see which works best. Or if you are only planning a small board run to start with, just make your best guess and try it. It's not a tragedy if you have have to rerun it.I once bought a pile of cheap USB connectors on ebay and was getting all sorts of DRC errors trying to fit them so I made a test board and learned what worked. It's a similar part in the sense the design decisions didn't make a lot of sense to me - alignment holes really close to pads (probably why it was so cheap). And, yes, it totally violates even very liberal design rules but it works. Now I can just toss the footprint on and know it will workout ok.If you are new to the PCB house, I'd toss a few other things on the test board to see how they do them.

author: Mecanix
author_rank: Frequent Contributor
timestamp: August 03, 2020, 11:25:42 pm
content: That idea is not a bad one at all, Phil. Thanks. That'd be a good timing also... I'm just starting to get in the mood of doing those footprints having only recently acquired this new EDA software (literally 1.5 week ago) and migrating all footprints and components to their proprietary libraries. I'll take your advice and slip in a second "test pcb" in that shipment/order with variants incl the other bits & pieces I'm working on the sideline, at least for the ones I've done so far.Like yourself I've also brought in-house the whole family of readily available micro connectors to hopefully find one (or two) that works, that 4P.TH low profile one seems like the best candidate so far. Micro, Mini, 5P/10P, USB2/3/C-type, got way too many than I'll ever need I'm sure but always good to have them handy and ready to drag & drop. They aren't exactly fun to model (validate?) though as most came with rather unreliable dwg :/Did the same with micro switches and other Molex/JST-type connectors. Got myself an electronic hardware store slowly building up, I'm sure...

author: phil from seattle
author_rank: Super Contributor
timestamp: August 03, 2020, 11:50:07 pm
content: Yeah. I've got quite a collection going. But, for SMDs, I've started moving away from stocking a lot because I'm using JLCPCB to assemble as well. It's cheaper to use their components and a lot less hassle. Just got an order today - 6 days from order to assembled boards in hand. I still have to do the TH stuff but this is so easy.

author: Rashed100Islam
author_rank: Newbie
timestamp: October 14, 2020, 06:15:07 pm
content: Is it ok if it is GRBL software for the lightweight cnc machine? I found it's great at a reasonable rate. I was searching for such a router bit and reached here- [https://www.woodworkersolution.com/best-router-lift/] and found some drill here-https://handytoolsidea.com/best-lightweight-drill-for-a-woman/as well. Hope these may help you find the great things you need.

author: Renate
author_rank: Super Contributor
timestamp: October 14, 2020, 07:05:35 pm
content: You know that you usually can't drill overlapping drills, but routing overlapping holes should be 100% ok.You can keep your overdrill to a minimum by first drilling a 70.7% hole first, then route the perimeter with the end mill.This is the usual way things happen anyway, nothing special here.The router end mill will not care in the least that it is cutting through a hole.

author: electrolust
author_rank: Unknown
timestamp: October 16, 2020, 04:22:03 pm
content: Quote from: Mecanix on August 03, 2020, 09:26:35 amIn 2D, perhaps. In 3D it looks very clear.