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PCB Placement Stencils (tinyletter.com)
94 points by jamesbowman 3 months ago | hide | past | web | favorite | 42 comments



Interesting idea. I've always done all of those parts with tweezers and eyeballs, but some of the TSSOP packages can be a bit of a challenge to line up well enough for reflow.

If you used FR4 instead of acrylic or whatever, you might be able to leave the aligner stencil in place for reflow. That might let you do some of the smaller parts.


> line up well enough for reflow.

> If you used FR4 instead of acrylic or whatever, you might be able to leave the aligner stencil in place for reflow. That might let you do some of the smaller parts.

When the solder wets it will 'suck' the part into place, the alignment of the part isn't particularly critical. If you are dealing with extremely small parts like 0402 or under caps, you can run into issues where the wetting of one side just before the other causing the cap to pop up on end, but that isn't an alignment issue and the stencil won't help. In a proper production line these parts would have what is basically glue holding the middle in place enough to avoid this.

EDIT: If you're finding the parts aren't sucking into place, chance are you need to use more flux or check the solder formulation you're using against the PCB finish.


There are still dirt-cheap gadgets [1] that you can make before going for a liteplacer.

[1] http://vpapanik.blogspot.com/2012/11/low-budget-manual-pick-...


Having watched the video, I can place components significantly faster with tweezers and an Optivisor. If you really must populate a batch of SMD boards by hand, the best option is a Hakko 392 and a sensibly laid-out board for your cut tape.

The Liteplacer doesn't seem like great value for money IMO - for a bit more money, you could have a small used industrial machine with a decent set of feeders.


DirtyPCBs has never done me wrong, and they offer a cheap laser acrylic service, hmmm!

http://dirtypcbs.com/store/lasercut


If you're in the market for cheap PCBs, PCB Shopper is a fantastic tool - you can fill out one form and get quotes from 24 companies.

https://pcbshopper.com/

Prices for 4-layer boards and boards larger than 100x100mm have fallen significantly over the last year (driven mostly by JLCPCB), which has hugely expanded the possibilities for hobbyist electronics.


No need to compare. Go to easyeda.com. You can get 10 boards for $2 (!). I have gotten a dozen or so sets of boards and they have gotten here in less than a week. (Not affiliated, yadda yadda yadda).


I've used them too about 10 times, and I've only had positive experiences. So cheap!

Not affiliated either.


Last time I checked that offer wasn't available anymore. Did it come back?


EasyEDA have rebranded their PCB service as JLCPCB. They still offer the $2 service for standard 100x100mm 2-layer boards (plus shipping).

https://jlcpcb.com/


Agrreeeeeed. I just did a run of 300 boards through DirtyPCBs and their quality was actually surprising. I feel like OSH Park is a bit higher, but being able to choose the soldermask and the amount of options available is crucial in some of my projects.


OSH will let you get one board cheaper than you can get a 10 board minimum proto-pack order from DPCBs.

But if you need more than a one-off the savings are clear.


Same here, DirtyPCBs is great! I particularly like that you can update orders right up until they have started in production.

The SLA printing service is a real game changer too.


What's unique about their SLA service?

Been using 3D Print UK and have been thinking of using digits2widgets and eventually getting a Form 2 to SLA print in house.


Maybe it's not unique, but it is a nice combination of low cost, fast turnaround, high accuracy, and with a nice interface.

Most of my 3D print experience before had been with the filament type machines, and the DirtyPCBs SLA service is a huge step up in quality, and lower hassle/cost as long as parts are fairly small like mine tend to be.


A simple improvement. add pins (even temporarily) to the PCB. Add pin holes to the top acrylic template. No need for the lower (outer) acrylic part. Plus the pin holes force very good alignment.


Additionally, the accuracy of the PCB fab when drilling holes is going to be better than when routing the edges of the board. Just need to ensure you pick a hole diameter that matches the fabs drill sizes. (and oversize the hole a little or the fit is going to be very tight)


This is really cool. I wonder if it would make hand assembly worth it for small runs of products? PCBs are already so cheap that assembly is by far the biggest cost of making anything on a circuit board.


Chinese PCBA services are relatively affordable for short runs. Unless you place a very low value on your time (a reasonable choice if you're doing it for fun) or need a one-off prototype in a hurry, you should probably just use a service like Seeed Fusion.


It's a tradeoff. I hand assemble all my boards. I try to keep minimal finished-goods inventory, so that means build to order if I don't estimate quantities right. The latency of a contract manufacturer would be unacceptable in this case.


What sort of prices and run sizes are we talking about?

Let's say I had a board about as complicated as an Arduino Leonardo, and I wanted 10 prototype boards populated. Roughly how much should I expect to spend?

[1] https://store.arduino.cc/arduino-leonardo-with-headers


Here you can calculate it for Elecrow: https://www.elecrow.com/pcb-assembly.html

I ended up doing my last 10 boards by hand because the minimum price is too high now, it starts at $141, no matter how few pads you take.

Two years ago I got 20 boards incl. pcb and parts for $120, each had 46 SMD pads to be soldered! 3 cent per pad, 46 pads per board, 20 boards and $30 minimum fee for soldering. $51.60 in parts (20 atmegas, resistors and caps are free), $20 PCBs, $8.40 shipping. That was fantastic!

Does anybody know a cheaper PCBA service? Seeed and itead were not better than Elecrow...


You can get an instant quote from nine different services at PCB Shopper. For a run of 10, you'd be looking at $12-$17 per board for something like the Leonardo. That falls to about $4 per board for a run of 100 and $1 per board for 1000.

https://pcbshopper.com/#assembly


"While this setup has been working really well for large parts, small components haven't worked out".

Too bad. This is a good idea. I have some boards with lots of small components where this would help, and I have access to laser cutters. Maybe with a thinner plastic layer on top... Also, with small components, getting the placement stencil off without taking the tiny components with it may be tough.

Board edge shearing is less precise than the pad placement, and this thing uses a base frame to align to the board edge. Pick and place machines align to reference marks on the board, using cameras. You might need some kind of fine screw adjustment to move the board very slightly.

I've seen videos of the Liteplacer, which is a slow pick and place machine for prototypes. It's useful for when you are only making a very small number of boards, because it can work from components laid out in wells or on tape that's not on reels. The production oriented machines require that you have enough components on reels to get the feeders started.


It seems like this could work for small components especially if one were using solder paste. Would something like this work better machined in aluminum (instead of acrylic) if the holes were bigger on the bottom instead of on the top to allow for the devices to not get stuck to the acrylic?


A stainless steel solder paste stencil, which now costs about $25[1], would probably work well. Those are thin (3 to 8 mils), so the parts aren't going to get stuck in a deep hole. They're usually used in a hinged frame that puts them under tension and makes them rigid. Use one stencil for solder paste, then change to the placement stencil for part placement.

Stencils used to cost about $200, but at $25, this starts to look like a viable option.

[1] https://www.oshstencils.com/#%20


Unrelated, but on the termdriver page, CSI codes C and D are labeled as both being "cursor down", when they should be "cursor forward" and "cursor back".


(author here) Fixed, thanks!


What a great idea! Might be tricky to make this work with fine-pitch QFPs, but for QFN and wide-pitch ICs (e.g. SOIC) I can see this working really well.


I don't get it. If you need 0.1mm accuracy, all the machining, on plastic, mind you, must be done to say 0.05mm accuracy, both in position and size. And, it appears that one of the parts registers to the edge of the pc board, which is inaccurate. Since you got it to work, what am I missing here?


The routed edges of a PCB are generally +/-0.1mm. Most laser cutters will match or exceed that tolerance, even on acrylic. In the worst case this jig will be 0.2mm out, but it's a lot easier to nudge a package from almost aligned to perfectly aligned than to place it purely by eye.


Ok I get it, it’s a manual aid and it gets you close enough to nudge, plus you can correct the fixture cheaply by remaking it.


For reflow soldering they really don't have to be that precise. Capillary action pulls the part into place and aligns it as long as it's somewhat close when the solder wets, it's really neat. Even QFN packages the author mentions don't really need to be that precise, for those it's more important to get the right amount of solder paste dispensed so that you don't have bridging of pads.


Clever! I'm thinking a similar design with a range of hole sizes and wider borders could be a handy generic tool - might have to design and order one next time I'm making boards with QFNs.

Does anyone here know what the smallest practical hole size is in acrylic?


My gut feeling is 0603 might still work but probably not reliable, 0402 tends to get stuck to everything by static attraction so very doubtful in acrylic.


Not to mention ESD issues from rubbing all your components across acrylic.


for small stuff the real limit may be "how round are the corners"


Nice, after doing a bit of electronics, I realize how much todays pcb work is unfit for hand soldering (unless you want to enjoy frustration). Having geometric help is never a waste.


I guess the thing I don't understand is if you do this for some parts and not others (caps and resistors) how do you not smear their solder paste


One possibility is that you can do the C's and R's by hand with regular wire solder.


Since I don't have a laser cutter (yet?): Would 3D printing the jig be feasible?


Thank you! This will help a lot.




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