
PCB Placement Stencils - jamesbowman
https://tinyletter.com/jamesbowman/letters/placement-stencils
======
jimmyswimmy
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.

~~~
mbell
> 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.

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utopcell
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-...](http://vpapanik.blogspot.com/2012/11/low-budget-manual-pick-
place.html?view=classic)

~~~
jdietrich
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.

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

[http://dirtypcbs.com/store/lasercut](http://dirtypcbs.com/store/lasercut)

~~~
bacon_waffle
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.

~~~
antoniuschan99
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.

~~~
bacon_waffle
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.

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matt_the_bass
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.

~~~
meta_AU
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)

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koverda
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.

~~~
jdietrich
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.

~~~
michaelt
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](https://store.arduino.cc/arduino-leonardo-with-headers)

~~~
atesti
Here you can calculate it for Elecrow: [https://www.elecrow.com/pcb-
assembly.html](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...

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Animats
_" 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.

~~~
bb88
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?

~~~
Animats
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](https://www.oshstencils.com/#%20)

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Vendan
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".

~~~
jamesbowman
(author here) Fixed, thanks!

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philpem
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.

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aj7
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?

~~~
jdietrich
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.

~~~
aj7
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.

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bacon_waffle
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?

~~~
janekm
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.

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

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agumonkey
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.

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Taniwha
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

~~~
analog31
One possibility is that you can do the C's and R's by hand with regular wire
solder.

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archi42
Since I don't have a laser cutter (yet?): Would 3D printing the jig be
feasible?

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slededit
Thank you! This will help a lot.

