Felt works well to provide an air path in the bag. Without a porous material, the bag seals off at the vacuum tube connection preventing an evacuation. Try a layer of felt on the top and bottom of the board.
From: Homebrew_PCBs@yahoogroups.com [mailto:Homebrew_PCBs@yahoogroups.com]
Sent: Wednesday, July 26, 2017 2:39 AM
To: Homebrew_PCBs@yahoogroups.com
Subject: RE: [Homebrew_PCBs] Re: Attaching two PCBs together
You need a spacer between the boards and the bag, like Roy said in his last message.
The PCB needs to go between two flat boards (solid) larger than them, then something air can flow past. Usually you cut thin slots in the back of the flat boards.
Like this: http://www.joewoodworker.com/veneering/images/bag-explanation.gif
The idea is the two flat pieces will squish the PCB between them and any trapped air can get out the edges.
Still need to be careful that the halves don’t slip.
You can use those clothes storage vacuum bag things, they’re a fairly heavy gauge plastic.
Tony
From: Homebrew_PCBs@yahoogroups.com [mailto:Homebrew_PCBs@yahoogroups.com]
Sent: Wednesday, 26 July 2017 3:14 AM
To: Homebrew_PCBs@yahoogroups.com
Subject: RE: [Homebrew_PCBs] Re: Attaching two PCBs together
Tried the vacuum bag method with a thick contractor garbage bag. It did pull the bag taut against the boards but also sucked the bag a good way into the shop vac. Not sure if it was having the effect it should have. After letting it cure up a bit I checked but yeah, still large pockets of air.
I then tried simply putting a ton of epoxy on and spreading it around.. then kneading it out by hand. This actually worked best. I also made the bottom piece larger than the top. Here’s a pic of how it came out, next to an original Mark-8 board:
https://drive.google.com/file/d/0B4pq0-BHd2x6U29JNDlpTE1KNnM/view?usp=sharing
It doesn’t look that different in person.. the camera makes the Mark-8 board look much darker than it is. But there is a difference. Despite advertised as being ‘clear’, the epoxy does add a slight yellow tinge.
And yes, in this case what I did was etch one piece, and then actually for the second piece I took an etched piece that didn’t work out (that happens occasionally) etched the rest of the copper off and attached it. Good way to retrieve value from mistakes.
Brad
From: Homebrew_PCBs@yahoogroups.com [mailto:Homebrew_PCBs@yahoogroups.com]
Sent: Tuesday, July 25, 2017 6:09 AM
To: Homebrew_PCBs@yahoogroups.com
Subject: Re: [Homebrew_PCBs] Re: Attaching two PCBs together
On Tue, 25 Jul 2017 06:46:25 -0400, you wrote:
>Dumb question:Yep.
>
>If the boards you are gluing together are single sided boards don't you end
>up with either a double sided board OR a single sided board with a layer of
>copper in the middle (depending on which way you glue the boards together).
>If you end up with a layer of copper in the middle your leads going throughNope. You create donuts around the feedthrough locations in the inner
>the board are going to short out on the center copper layer.
layer. However, you've got no way of soldering them at all. Inside
layers work with plated through holes, and sometimes with homemade 4
layer boards, but it's awkward.
>If you create ayou will get a board that looks indistinguishable from the thicker
>double sided board then that would not be true to the original - would it?
>Maybe I missed something. Either way gluing two boards together isn't going
>to look like the original. It seems you went to a lot of trouble to find the
>original board material all for not.
material if you do it right. If the original board was single sided,
then you simply etch all the copper off one board and use it only as a
thickness builder.
You don't see the gap between the boards.
Harvey
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