Homebrew PCBs

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.
>>
>>
>>
>>
>>
>>
>>
>>
>>  
>>