Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

Brad,

As Andrew V. mentioned, vacuum bagging is an effective process for laminating. There are a couple of issues when using epoxy, or any resin that requires mixing. Mixing the resin and hardener introduces air bubbles into the epoxy. It is true that the vacuum will pull the air out, but a better way is to degas the resin before you apply it. Lots of descriptive material on the epoxy manufacturer's sites. The fly in the ointment is that the epoxy is curing while you are doing this. You need to use an epoxy with a relatively long pot life. Once the epoxy is degassed, you can apply it to your board and process in the vacuum bag. In both vacuum operations, it is important to have some kind of "filter" in the vacuum line to keep the volatiles that the vacuum pulls out of the epoxy out of the pump.Otherwise, the pump will eventually get gunked up with this material. A water bath might work, or a large chamber that slows down the flow to where the volatiles condense on the surfaces, rather than entering the pump.

Here is a reference to the degassing process: www.epotek.com/site/files/Techtips/pdfs/tip4.pdf

Another thing you should give a thought to, is how to produce an epoxy layer with a uniform thickness.

Harvey A.

 

Brad –

 

Use a vacuum press.  Vacuum is useful for many things, especially if you are also into woodworking (veneering), molding, etc.  The vacuum will draw the bubbles out.  Vacuum pumps are available from Harbor Freight.  Just need a few fittings and a reinforced hose and a chamber or bag in which to put the boards.  (See http://www.veneersuppliescom/pages/DIY__Vacuum__Press.html).

 

Andrew V.

 

From: Homebrew_PCBs@yahoogroups.com [mailto:Homebrew_PCBs@yahoogroups.com]
Sent: Tuesday, July 18, 2017 6:15 PM
To: Homebrew_PCBs@yahoogroups.com
Subject: RE: [Homebrew_PCBs] Attaching two PCBs together

 

 

The material used to glue layers together in multilayer boards is called prepreg.  I don’t see prepreg sold online anywhere though.  Not even Ebay. 

 

From: Homebrew_PCBs@yahoogroups.com [mailto:Homebrew_PCBs@yahoogroups.com]
Sent: Tuesday, July 18, 2017 7:58 PM
To: Homebrew_PCBs@yahoogroups.com
Subject: Re: [Homebrew_PCBs] Attaching two PCBs together

 

 

Brad,

I think you slipped a decimal point o the thickness of your boards- 0.031 and 0.0625".

There is another (better?) way, but it is problematical. You would get a much more uniform layer of adhesive by going with sheet adhesives. I my prior life, I was involved in some production that used sheet type adhesives to bond fairly big boards to heatsinks. The adhesive we used was an epoxy. I recall being able to buy sheet adhesives with or without a carrier layer, but since they were basically mixed, but uncured epoxy systems, they had to be kept in the freezer until use. The are other types of adhesives that also are available in sheet form. That was the good news. The bad news is that I couldn't find a place to buy these materials in reasonable quantities. I found an acrylic adhesive, recommended for this type of application, but it came on 3" rolls that were 250' long and 24" wide. Price was in the stratosphere. I looked at ebay, Amazon, McMaster-Carr and MSC to see if any of them carried these materials. Nada. A general Google search turned up some manufacturers, but no sellers at the retail level.

If you want to do your own search, look for sheet adhesives, adhesive preforms, bonding adhesive sheets.

If you should find a source, you will still be faced with the need to provide a fairly high, uniform pressure, and an elevated cure temperature. The material we used needed to withstand high temperatures, so we used something that cured over 150°C. Others are lower, but then it will depend on what you can find.

I did find some two sided adhesive mounting sheets at a craft store. No information available about what type of adhesive. They might work, but I am not so sure about how long they will stick, or if they might dry out.

Good luck in your search.

Harvey A.

 

On 7/18/2017 11:14 AM, 'Brad' unclefalter@... [Homebrew_PCBs] wrote:

 

So as I stated in a previous post, I have acquired some vintage 1973 PCB stock, which is perfect for a project I’m doing that replicates the 1973 TV Typewriter.  Except for one thing – the stock is 0.31” thick, rather than 0.625”.  So my thought was to epoxy two pieces together.  And that works, except despite my best efforts, I end up with these ugly voids you can see.  I’ve tried putting the boards under a press with heavy pressure but there’s always a few spots.

 

Is there a better way/adhesive to do this? 

 

I realize it’d be easier to use 0.625” stock from the outset, but stock of the correct vintage just isn’t available, and it means a lot of me to be using actual boards from the time.

 

Thanks!!