Homebrew PCBs

On Mon, 6 Jul 2015 11:59:44 +1200, you wrote:

>Interesting ideas everybody, to so summarise everybody's comments
>
>1. it does work
>2. use alignment holes and pins as a jig to align the two sides
>3. use epoxy
>4. drill the actual holes after the glue-up
>5. it might not be any easier in the long run :-)
>
>I might grab some 0.8mm and give it a go.
>
>I use PCB rivets for vias, so my thought was to use these as the alignment
>pins, they are a tight fit in 0.8mm holes.

I used to use pcb rivets, but they took too much space.  For my boards
now, I use #26 wire and lace the vias together, solder both sides, cut
them free, and that works.  not pretty, but it works.
>
>> May I ask exactly how you are lining the layers up?
>
>I use photo exposure (dry film resist) on a single sided UV box, when doing
>double sided, I use the inside corner of a plastic set-square as a stop
>agains the same corner on the bottom and top artwork, and push the
>appropriate PCB corner into the square for each side.  It works oookay for
>the most part, but if you don't have two perfectly perpendicular sides on
>your PCB so there is no "wobble" when you push it into the square's inside
>corner, it's easy to get a slight rotational misalignment.
>

then the thing would be to drill the alignment holes first, and use
those holes to position the board and the master negative/positive.

with a dual sided alignment setup, you actually could do a decent two
layer board in one exposure.  You'd want an alignment jig with
accurately positioned (and decently sized) pins.

>That said, my may well be that I can't drill perpendicular hand-held to
>save my life, doesn't take much of an angle to break out of a 0.2 or 0.3mm
>annular ring on the backside when being perfectly centred on the front
>side.  Perhaps I should just get a mini drill press and rig up some camera
>magnification on it :-)
>

please.... <grin>

I tried a dremel, bad runout, drill bit wobbles because of the collet

I used a proxxon, the 12 volt version works fine, although I have
both.

on the other hand (please check other posts under my name for
details), I've got a linear bearing table, one axis, stepper drive,
and a TV camera for the drilling rig.

It does make a difference.  I was trying to drill holes accurately
with a drill press but viewing from the side at an extreme angle....
Doesn't work well.

I also tried thin pins, but the press in map pins are thick enough
that they generally don't wobble much.   The alignment holes in this
are absolutely critical.

Harvey

>
>On Mon, Jul 6, 2015 at 8:36 AM, Harvey White madyn@...
>[Homebrew_PCBs] <Homebrew_PCBs@yahoogroups.com> wrote:
>
>>
>>
>> On Sun, 05 Jul 2015 13:41:48 +0000, you wrote:
>>
>> >I must say, the idea of gluing together two single-sided PCBs to make a
>> >double-sided PCB seems excessively tedious.
>> >
>> >
>> >Perhaps it's because I don't really agree with you that the most difficult
>> >part of a double-sided PCB is lining the holes / tracks up.
>> >
>>
>> Was for me, but I do 0.019 holes (or so, a #76 or so drill), 144 pin
>> FPGA chips, 0.5mm spacing, 0.010 traces. YMMV on that.
>>
>> >
>> >When I first started, I thought lining up the holes would be the most
>> >difficult part. But I've never had anything but great success in this
>> area.
>> >
>> >
>> >The most difficult part for me has been knowing how long to iron and the
>> >time it takes to peel. To get excellent results (really fine / straight
>> >edges to tracks and toner that adheres amazingly well) I iron for 35-40
>> >minutes... and the longer I iron the harder it is to remove the paper.
>> This
>> >to me seems excessive but anything else results in having to use a lot of
>> >sharpie and boards that don't look as nice.
>>
>> I use Pulsar paper, which is not as transparent as what you may be
>> using. aligning top and bottom is not that easy, since the paper is a
>> good 60# paper, about the consistency of a paperback book cover.
>>
>> >
>> >
>> >May I ask exactly how you are lining the layers up?
>> >
>> >
>> >Here's my process. Here I overexplain it, but it doesn't actually take
>> more
>> >than 3-5 minutes.
>> >
>> >
>> >I cut the two pieces of paper, one piece slightly smaller than the other
>> to
>> >allow for better grip when I tape them together.
>> >
>> >
>> >I hold the two pieces of paper up against a worklight and ensure the
>> >designs line-up perfectly, then fold a tiny piece of masking tape over the
>> >two pieces of paper, in the middle of one of the edges. I then hold them
>> up
>> >to the light to ensure they are still lined up, and add another small
>> piece
>> >of tape onto the middle of another of the edges. If for some reason the
>> >papers became misaligned it's then easy to remove a single tab of tape and
>> >do it again.
>>
>> I had tried this with pin pokes through the paper to create holes.
>> Accuracy of drilling is critical, of course.
>>
>> >
>> >
>> >Finally, repeat the process for the third side, check the alignment by
>> >shining the worklight through the papers, then run tape lenghtways down
>> all
>> >three sides.
>> >
>> >
>> >Drop the board in (which has been prepared obsessively with metal wool and
>> >white spirit / acetone) and check there that the effect of separating the
>> >papers with the 1.6mm FR4 hasn't misaligned the papers. Almost every time
>> >I've dropped the PCB in, it hasn't caused any misalignment. Always check
>> >the papers lie flat.
>> >
>> >
>> >When the PCB is in, seal the final 4th side with a line of masking tape.
>> It
>> >doesn't matter if the PCB rattles around, in fact it's better to make the
>> >paper a fair bit larger than the PCB that drops into the envelope you have
>> >created.
>> >
>> >
>> >You then line up the PCB so it fits to the design just before you iron
>> >(using a worklight again).
>> >
>> >
>> >The above hasn't failed for me ever, and it's pretty quick to do despite
>> my
>> >over-explanation!
>>
>> With the Pulsar paper, I don't need to iron that much. I also had
>> pattern damage when feeding a double-sided board through the laminator
>> *if* I was trying to do one side at a time on double sided board.
>>
>> Harvey
>>
>> >
>> >
>> >Thanks
>> >
>> >
>> >Mat
>> >On Sun, 5 Jul 2015 at 12:14, 'Tony Smith' ajsmith1968@...
>> >[Homebrew_PCBs] <Homebrew_PCBs@yahoogroups.com> wrote:
>> >
>> >
>> >>
>> >>
>> >> The drilled holes will never line up properly, it\ufffds a fundamental
>> property
>> >> of universe.
>> >>
>> >>
>> >>
>> >> When gluing use a bright light underneath so you can see both sets of
>> >> tracks, and use something like the mounting hole outlines to align them.
>> >>
>> >>
>> >>
>> >> Tony
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >> *From:* Homebrew_PCBs@yahoogroups.com [mailto:
>> >> Homebrew_PCBs@yahoogroups.com]
>> >> *Sent:* Sunday, 5 July 2015 3:14 PM
>> >> *To:* Homebrew PCBs
>> >> *Subject:* [Homebrew_PCBs] Gluing 2 single sided boards to make a double
>>
>> >> sided board.
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >> Double sided boards as we all know can be a bit of a pain, the biggest
>> >> problem is getting that precise alignment between sides correct so that
>> >> when you drill in the center of your pad on one side, it comes out in
>> the
>> >> center of the pad on the other (and not, as is not uncommon, breaking
>> out,
>> >> and probably messing up the trace, or a trace nearby...). Especially if
>> >> your only able to expose/imprint artwork one side at a time.
>> >>
>> >>
>> >>
>> >> Even more frustrating when one side comes out perfect in part of the
>> >> process (eg, developing) and the other side is too flawed to be useful,
>> >> meaning you get to start from scratch again.
>> >>
>> >>
>> >
>> >>
>> >> So, the thought randomly occurred to me today, if you could prepare,
>> >> expose, etch, drill the two sides of a double sided board completely
>> >> separately, and join them up at the end of the process, it would make
>> >> getting precise alignment of those sides almost a non-issue, assuming
>> you
>> >> can drill even roughly vertically and hit the center of the holes it's
>> just
>> >> a matter of lining up the holes you drilled on each side. And also means
>> >> that the success or failure of each side is independent of the other.
>> >>
>> >>
>> >>
>> >> Of course, it does double the drilling, but that's the easy bit really.
>> >>
>> >
>> >>
>> >>
>> >> This is also of course more or less how multi layer PCBs are made by
>> >
>> >> fabricators, a stackup of already prepared pcb layers and resin
>> impregnated
>> >> sheets.
>> >>
>> >>
>> >>
>> >> Single sided laminate at 0.8mm thick (and you can get down to 0.5mm) is
>> >> available out of China for cheap.
>> >>
>> >>
>> >>
>> >> Eg:
>> >>
>> >>
>> >>
>> http://item.taobao.com/item.htm?spm=a1z10.5-c.w4002-1192550948.12.TIEXsq&id=35870048695
>> >>
>> >>
>> >>
>> http://item.taobao.com/item.htm?spm=a230r.1.14.4.VdTsRT&id=21105435798&ns=1&abbucket=3#detail
>> >>
>> >>
>> >>
>> >> Has anybody done this... am I reinventing a triangular wheel here, is it
>> >> doomed to failure? Suggestions on suitable adhesive... maybe just spray
>> on
>> >> contact adhesive might work, it's a pretty big flat contact area.
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>>
>>  
>>