Using a filler is partway what I'm doing. I put a target at each corner of the two sheets, align them with needles then lift one of the sheet to insert a piece of PCB to get the right space between them. I place the filler outside the printed area but as close as possible from the needles. I tape the two sheet to the filler, remove the needles (the tape is supossed to keep the sheets aligned) and put the PCB to etch between the sheets, tape the sheet to the PCB and remove the filler.This is many manipulations and whatever you do, alignement is like playing with dices . Some times you win, some times you loose... Especially with 32 mils vias.
This is the reason why I wanted to use transparent for inkjet. But there are two problems, the first is that the transparent get deformed, bended with the heat of the fusing unit inside the laser printer and the second, toner density is very light, even with density set at max. (laserjet 6P) And I'm afraid that the pcb will be etched with a lot of pinhole.
So I believe I'll get back to blind alignement with plain paper by first driling 12 or 16 mils holes at the corner of the pcb to etch and holes in the sheets and align them with needles in the PCB.
--- On Fri, 7/4/08, Harvey White <madyn@...> wrote:
From: Harvey White <madyn@...>
Subject: Re: [Homebrew_PCBs] double sided PCB, accuracy
To: Homebrew_PCBs@yahoogroups.com
Date: Friday, July 4, 2008, 1:09 PM
On Fri, 4 Jul 2008 09:47:55 +0100 (BST), you wrote:
I've always had a conceptual problem doing it exactly this way. I can
see that if the joint between the two pieces of paper is exactly in
the middle of the board thickness, every thing aligns. If it's not,
then one layer is offset with respect to the other.
Has anyone considered aligning the masks with a filler made from a
scrap piece of etched board, same thickness, and then perhaps a piece
of plastic to duplicate the board?
Harvey
>On Thu, 3 Jul 2008, Michel Baguet wrote:
>
>> hi guys,
>>
>> I got to the point where I can etch 6 mils traces and 32 mils vias with
>> a 12 mils hole with inkjet paper.
>
>First, I presume you're using glossy inkjet paper for toner transfer from
>a laser printer.
>
>If that's the case you don't need to muck around with transparencies.
>Print both sides of the layout to your normal paper, place them together
>face in - hold them to a bright light and use the vias to align. Suitable
>bright lights are: the sun, a table lamp, or best, a light box where you
>can lay it all flat.
>
>Then tape the ends of the paper together at one end, to form a hinge.
>Re-check that it's still aligned. If it is, slip the copper board between
>the paper and get ironing.
>
>I've done lots of double sided boards this way - never had a failure.
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