Tiny PCBs - score, route, or ?

[budgie]

Good pointer - they have very good pricing ($99 for 200 pcs)! I wasn't
aware they did PCBs. Do you find their routing tolerances are good?

The only routing I get from them is board outline - no slots or anything. But
the results are very good/clean/straight edges and curves. I haven't used them
for SMD, only through-hole.

Actually a job I sent them yesterday has slots - small ones for a DC power inlet
receptacle. The Chinese fabs know what they are, and I guess in a couple of
weeks I'll know how Futurlec handle them.

Yes, this is SMT on both sides, and I expect it'll be much easier to
paste and pre-heat / solder as a larger panel. One-offs could be
managed, but panelizing seemed cleaner.

Have you run into problems de-panelizing, or just not interested since
you have a good one-off technique? How is your holder constructed?

All my *small* boards have been through-hole. We had some ~2" * 2" SMD boards
which we sent to a stuffing house that handles small batches (20). I really
don't want to get into SMD stuffing, when there are firms that do it (even in
Oz) for relative peanuts.

For the T-H boards the holder is a weighted base with adjustable "hands" that
simply have a V-groove that clamps the board edge. Would be an issue if the
board didn't have straight (and pref. parallel) sides ;-)

Depending what you are after, I note that Futurlec also do stuffing for >20
batches. Never had occasion to try it. Depending on the load this may also
help. I try to stick to my "core business" and leave tasks such as board fab,
SMD stuffing etc. to houses that have that as their core business.

 

[Richard H.]

The only routing I get from them is board outline - no slots or anything. But
the results are very good/clean/straight edges and curves. I haven't used them
for SMD, only through-hole.

Well, I have to give kudos to Futurlec - I dropped them a note and
already got a reply. They will do v-scoring instead of separation, at
no additional charge. That looks like a winner - thanks!

I try to stick to my "core business" and leave tasks such as board fab,
SMD stuffing etc. to houses that have that as their core business.

Yep. One of the reasons I'm looking at panelizing - trying to work
through a process that'll be easier to farm out when the volume supports it.

Cheers,
Richard

 

[Robert Baer]

I need to make some small PCBs (about 0.5" x 0.75" ea). I've compiled
some options, but I need some insight on the best way to cut these apart
(ideally, pre-scored / pre-cut and snap apart after assembly).

V-scoring seems good because it might require less PCB space than
routing, the parts are large enough to grip & snap apart, and the edge
would be straight, although rough (which is OK).

Tab routing would leave a clean edge except for the tabs, and it might
put less stress on the board to break apart. Drawback is the "jaggies"
left by the tabs.


Do-it-yourself alternatives...
The "string of holes" method using drill hits, which might prove
cheapest, but also the roughest edge. Any tips on how to space the
holes so they don't fall apart in assembly, but aren't too hard to break
later?

Cutting ourselves with a band saw or a shop router on a table stand w/
guide. This seems a bit hazardous with small parts, and may cost more
in the long run because the cuts may be wider (more waste). (Band saw
isn't a bad idea...)

Using a shear, which I've seen suggested, but not for an assembled
board. Pop! Crunch!

Any thoughts on these other other techniques?


(I've found a few board shops that will do tab routing and/or scoring
for protos, but they're pretty pricey so any references would be welcome
too. This is short-run production, so cost per board is a concern.)

Thanks,
Richard

Express PCB has a board size minimum which i think exceeds what you want.
BUT.
They have this special price on a (roughly) 3x4 board, *and* they now
(in their latest software) allow one to indicate routing...
So...
Layout one board in the upper left of the standard low-cost area, and
then group, step and repeat them using 0.1 inch routing cuts (seems to
be standard) and leave (say) 0.15 from center of cut to an edge, so that
the worm-eaten board is still one board.
A little strip of waste on the right and/or bottom is acceptable,
because you may get a dozen units per board.
Snap apart when you get them, and file the tabs.
This is the least expensive way i know (yet) that small boards can be
made.

 

[Robert Baer]

I need to make some small PCBs (about 0.5" x 0.75" ea). I've compiled some
options, but I need some insight on the best way to cut these apart
(ideally, pre-scored / pre-cut and snap apart after assembly). [...]

Olimex (http://www.olimex.com) will panelize and separate boards at no extra
cost. They start with standard 160mm x 100mm boards (single- or
double-sided) and make as many of your design as will fit, for a single
fixed price. For instance, I recently had them build a 1" x 1.5" design;
that works out to 25 boards, for a total of about $43 including shipping.
(The price varies slightly depending on the presence of nonstandard drill
sizes.) I'm pretty sure I've had them do boards as small as yours, in the
past.

The shipping is a bit slow because they come from Bulgaria, and the quality
is not quite as nice as what I've had done locally, but it's well within
spec, and the price is very hard to beat.

I have not yet found anyone else who will panelize for free.

On the original topic, though: you can use tin snips to cut fiberglas board.
It helps if you warm the board up with a heat gun first.

I do not think the use of tin snips for cutting FR-4 should even be
considered.
Stresses the h*ll out of the board for a large distance, spreading a
large distance from the cut itself.

 

[[email protected]]

I need to make some small PCBs (about 0.5" x 0.75" ea). I've compiled
some options, but I need some insight on the best way to cut these apart
(ideally, pre-scored / pre-cut and snap apart after assembly).

V-scoring seems good because it might require less PCB space than
routing, the parts are large enough to grip & snap apart, and the edge
would be straight, although rough (which is OK).

Tab routing would leave a clean edge except for the tabs, and it might
put less stress on the board to break apart. Drawback is the "jaggies"
left by the tabs.


Do-it-yourself alternatives...
The "string of holes" method using drill hits, which might prove
cheapest, but also the roughest edge. Any tips on how to space the
holes so they don't fall apart in assembly, but aren't too hard to break
later?

Cutting ourselves with a band saw or a shop router on a table stand w/
guide. This seems a bit hazardous with small parts, and may cost more
in the long run because the cuts may be wider (more waste). (Band saw
isn't a bad idea...)

Using a shear, which I've seen suggested, but not for an assembled
board. Pop! Crunch!

Any thoughts on these other other techniques?


(I've found a few board shops that will do tab routing and/or scoring
for protos, but they're pretty pricey so any references would be welcome
too. This is short-run production, so cost per board is a concern.)

Thanks,
Richard

Populating, testing then snapping sounds to me like a way to introduce
failures. I havent done it that way before, but from cutting and
snapping PCBs unpopulated and populated, I'd be a bit surprised if you
got away with it without causing failures. No doubt some here have done
it and will know.


NT

 

[Deefoo]

too. This is short-run production, so cost per board is a concern.)

So is it worth all your time and effort then to find the cheapest way to
make them? Sounds to me like you have spent at least a day allready on it.
What is your hourly rate?

--DF

 

[Richard H.]

So is it worth all your time and effort then to find the cheapest way to
make them? Sounds to me like you have spent at least a day allready on it.
What is your hourly rate?

Ah, the voice of reason.

Yes, this is one of those negative-ROI projects, where personal interest
overrides the soft costs. It's a niche product, so we might have to
saturate that small market before we start to recover the true
development costs.

A "huge" volume of these would require <12 medium-sized boards a year.
At proto-house volume, the difference between shops is as much as 5x,
which hugely affects the cost of goods and viability of the product.

So, out of personal interest, it's worth sinking my time to drive down
the hard cost of goods and see if a viable product can be turned out.

Thanks for the thoughts!

Cheers,
Richard

 

[Richard H.]

Populating, testing then snapping sounds to me like a way to introduce
failures. I havent done it that way before, but from cutting and
snapping PCBs unpopulated and populated, I'd be a bit surprised if you
got away with it without causing failures. No doubt some here have done
it and will know.

Valid concerns, I'm sure. I expect it is also highly subjective to the
rigidity of the joint (material, depth of groove / size of tabs) and the
placement of the components.

It may be easy enough to test after separation instead, at least until
the technique is proven under our specific conditions.

Thanks,
Richard

 

[Rich Grise]

There is basically *no* waste with V-groove, provided you don't intend
on putting parts and traces right out to the edge. 60 mils is usually
enough. I have not tried it with >2 layers, you might need a bit more
for that.


Most moderate/small volume PCB suppliers will do it for a nominal
charge. Not so many prototype companies.

Best regards,
Spehro Pefhany

If a board house is doing it, can't you ask them to just shear them? Or
do you want them together for stuffing?

Thanks,
Rich

 

[qrk]

I'm planning to use standard thickness, which IIRC is 0.062". Good food
for thought.


Yes, I'd very much like a sketch, thanks.

After all these comments and some noodling, it looks like tabbed routing
is a strong option, maybe with the indent technique mentioned by John
Popelish. Instead of a whole strip of throwaway, see if I can make the
tab to snap on both sides, recessed from the edge to hide the jaggies.
Separate the first break by hand, and remove the second stub with
pliers. Like this:

| -ooo- #1 |
|-----/ ||| \-----|
tab
|-----\ ||| /-----|
| -ooo- #2 |

The question then becomes how small to make the tab and how close to
space the holes in the tab (balancing ease of snap vs. sag during
assembly), which I expect will be a matter of experimenting. I imagine
with parts this small you can't go less than one tab per side, unless
I'm missing something.

And of course, where to get these made in small proto quantities...

Thanks!
Richard

I have posted a PDF in alt.binaries.schematics.electronic of a tab
layout I like to use. I make the tab a footprint so the board house
won't make a silly choice. Position the tab away from resistors and
capacitors as they are susceptable to cracking if they are too near
the breakaway point. This tab works on 0.062" thick FR4. A quick brush
on sandpaper will remove the jaggies if needed. You can reposition the
drill holes to suit your needs.

This particular panel was run thru Circuit Express
<http://www.circuitexpress.com/>, a prototyping house, due to customer
request. I normally use US Circuit <http://www.uscircuit.com/> for
small to medium runs.

 

[Spehro Pefhany]

If a board house is doing it, can't you ask them to just shear them? Or
do you want them together for stuffing?

Thanks,
Rich

Yes, that's the deal. It's a hell of a lot faster to assemble one big
board with 200 parts manually than 20 boards with 10 parts each.


Best regards,
Spehro Pefhany

 

[Boris Mohar]

I need to make some small PCBs (about 0.5" x 0.75" ea). I've compiled
some options, but I need some insight on the best way to cut these apart
(ideally, pre-scored / pre-cut and snap apart after assembly).

V-scoring seems good because it might require less PCB space than
routing, the parts are large enough to grip & snap apart, and the edge
would be straight, although rough (which is OK).

I have been using 0.032" thick scored FR4 panels of 100 boards per panel.
Each board is 0.4" x 1.0" All components are surface mount. Top and bottom
scoring must line up accurately for good depanelization. Traces run 0.025"
from the score line. No sanding required.



Regards,

Boris Mohar

Got Knock? - see:
Viatrack Printed Circuit Designs (among other things) http://www.viatrack.ca

void _-void-_ in the obvious place

 

[Richard H.]

I have posted a PDF in alt.binaries.schematics.electronic of a tab
layout I like to use.

Got it - thanks! Real-world examples make great references.

I make the tab a footprint so the board house won't make a silly choice.

I'm not following you on this one - what do you mean by footprint?
Meaning you spec the routing pattern as a layer (which I'd plan to do)?

Position the tab away from resistors and capacitors as they are
susceptable to cracking if they are too near the breakaway point.

Makes sense. I'm planning to have PTH connectors closest to the edge,
but how far back do you recommend keeping SMD from the snap? Is 0.03"
enough?

This particular panel was run thru Circuit Express
<http://www.circuitexpress.com/>, a prototyping house, due to customer
request. I normally use US Circuit <http://www.uscircuit.com/> for
small to medium runs.

Also great info. Neither of these were on my list of ~40 vendors to
check with.

Thanks!
Richard

 

[Richard H.]

I have been using 0.032" thick scored FR4 panels of 100 boards per panel.
Each board is 0.4" x 1.0" All components are surface mount. Top and bottom
scoring must line up accurately for good depanelization. Traces run 0.025"
from the score line. No sanding required.

Nice. Thanks for the specifics, Boris!

I hadn't thought about whether they'd align the scores on both sides (or
for that matter, score both sides...)

Who do you use for your small boards? Do you find 0.032" is cheaper, or
did you go that route for other reasons? We're pretty flexible in that
regard.

So far, futurlec.com is coming in cheapest at $50 job + $0.65/square
inch with full mask & screen, and scoring or depanelizing. At least now
we're into the realm of "affordable" trial & error...

Thanks,
Richard

 

[qrk]

Got it - thanks! Real-world examples make great references.


I'm not following you on this one - what do you mean by footprint?
Meaning you spec the routing pattern as a layer (which I'd plan to do)?

Footprint is a PCB component. Thus, I make the drill pattern for the
tab a PCB component and position it where it makes most sense, like
away from parts. You'll notice that I have the tabs staggered to give
the boards a bit more stability in the panel.

Makes sense. I'm planning to have PTH connectors closest to the edge,
but how far back do you recommend keeping SMD from the snap? Is 0.03"
enough?

On 0.062" FR4, I would keep SMD resistors and capacitors at least
0.100" away from the drilled tabs. You might get by with 0.050". More
is always better. You can also mess up thru hole plating if they are
too close to the snap. I've had the most problems with 0402 SMT
ceramic caps cracking near shear lines on thin (0.032") boards.
Orienting the part parallel to the shear line is helpful as it puts
less stress on the part.

Also great info. Neither of these were on my list of ~40 vendors to
check with.

US Circuit is a joy to work with. I've been using them for 12+ years.

 

[Boris Mohar]

Nice. Thanks for the specifics, Boris!

I hadn't thought about whether they'd align the scores on both sides (or
for that matter, score both sides...)

Who do you use for your small boards? Do you find 0.032" is cheaper, or
did you go that route for other reasons? We're pretty flexible in that
regard.

So far, futurlec.com is coming in cheapest at $50 job + $0.65/square
inch with full mask & screen, and scoring or depanelizing. At least now
we're into the realm of "affordable" trial & error...

I am using local supplier http://www.crimpcircuits.com/HOME.htm who although
twice as expensive provides unquestionable quality. At the quantities I make
them (100s) the material cost is not so significant. 0.032 was a customer
requirement.



Regards,

Boris Mohar

Got Knock? - see:
Viatrack Printed Circuit Designs (among other things) http://www.viatrack.ca

void _-void-_ in the obvious place

 

[Richard H.]

Footprint is a PCB component. Thus, I make the drill pattern for the
tab a PCB component and position it where it makes most sense, like
away from parts. You'll notice that I have the tabs staggered to give
the boards a bit more stability in the panel.

Got it. Creating a component makes a lot of sense for consistency and
ease. I didn't notice the offset tabs at first, but that's a good
technique to get away with fewer tabs.


Have you considered dropping the carrier strips and butting the boards
up against each other? You'd have to add vertical tabs for rigidity,
but it might yield another column per board. Or is board cost not
enough to outweigh potential issues with assembly (flexing)?

(Our boards are about 1/4 your scale, so without carrier strips our
yield would nearly double per board.)

US Circuit is a joy to work with. I've been using them for 12+ years.

Good to know. How was your experience with Circuit Express (cost,
volume, quality)? It turns out they're local to us, which is appealing.

Thanks,
Richard

 

[qrk]

Got it. Creating a component makes a lot of sense for consistency and
ease. I didn't notice the offset tabs at first, but that's a good
technique to get away with fewer tabs.


Have you considered dropping the carrier strips and butting the boards
up against each other? You'd have to add vertical tabs for rigidity,
but it might yield another column per board. Or is board cost not
enough to outweigh potential issues with assembly (flexing)?

(Our boards are about 1/4 your scale, so without carrier strips our
yield would nearly double per board.)



Good to know. How was your experience with Circuit Express (cost,
volume, quality)? It turns out they're local to us, which is appealing.

Thanks,
Richard

I was contemplating getting rid of the vertical carrier strip, but was
unsure how flimsy the panel would be. The panels I make usually go
thru pick & place machines. If your assembling the first lot by hand,
I would try the panel without the carrier strip and see how rigid the
panel is.

I've also contemplated v-scoring the tabs. That would give you a very
clean break. Next time I do a panel, I'll ask the board house what
they think about that.

I've only dealt with Circuit Express at arms length (customer dealt
with them). They only do prototype or small quantities. They don't do
production runs unless your production run is small. I've done cost
comparisons with Circuit Express and US Circuit - US Circuit was
slightly cheaper for a 1 week turn. That might have been due to the
relationship we have with US Circuit (they know what to expect from
us). The quality of Circuit Express is very good. I've seen sample
boards from their roving salesman and a few of my customer's boards.
Circuit Express appears to have very good pre-flight personnel. They
caught a few questionable things on my boards that knowledgable folks
would catch.

 

[Richard H.]

I was contemplating getting rid of the vertical carrier strip, but was
unsure how flimsy the panel would be. The panels I make usually go
thru pick & place machines. If your assembling the first lot by hand,
I would try the panel without the carrier strip and see how rigid the
panel is.

I'll let you know when I've given it a try. For this item, I can't see
volume ever justifying P&P setup, but I'd like to design to that goal
and be ready when the next project needs it.

I've also contemplated v-scoring the tabs. That would give you a very
clean break. Next time I do a panel, I'll ask the board house what
they think about that.

Good thought. I've never noticed it done that way (perhaps to its
credit), but it seems viable - just a bit change in the router.

I've only dealt with Circuit Express at arms length (customer dealt
with them). They only do prototype or small quantities. They don't do
production runs unless your production run is small.

Thanks for the comments on Circuit Express. I've pinged them to see how
creative / flexible we can get this.

Cheers,
Richard

 

[Winfield Hill]

qrk wrote...

I've only dealt with Circuit Express at arms length (customer dealt
with them). They only do prototype or small quantities. They don't do
production runs unless your production run is small. I've done cost
comparisons with Circuit Express and US Circuit - US Circuit was
slightly cheaper for a 1 week turn. That might have been due to the
relationship we have with US Circuit (they know what to expect from
us). The quality of Circuit Express is very good. I've seen sample
boards from their roving salesman and a few of my customer's boards.
Circuit Express appears to have very good pre-flight personnel. They
caught a few questionable things on my boards that knowledgable folks
would catch.

We use Advanced Circuits, and despite our flaunted expertise
and our best efforts, they always seem to find a few issues in
the pre-flight inspection of our submitted files. Generally we
get perfect PCBs as a result, after a few day's delay for fixes.