Homebrew PCBs

Trevor White wrote:
>  
> 
> Hi all.
> 
> I have been looking into making 4 layer boards. I have most stages
> sorted but the big stumbling block is the bonding of the layers
> together. It seems a special press is required that has enough pressure,
> exhausts the gases away and generates the correct temperatures. I am
> surprised its so difficult. I have been told second hand presses cost
> \ufffd4000 to \ufffd5000. This is totally out of budget for me. Has anyone any
> experience/thoughts /comments on bonding boards together?
> 
> Thanks
> 
> Trev

Hi, I've done a number of 4 layers, its very laborious (about 5 hours 
was my record time to make a 4 layer from printing the artwork to the 
final solder mask bake)
  As for lamination, you can use room temperature curing liquid epoxy 
and a layer of fibre glass cloth for separation of inner layers. My 
method cheats, and uses two DS 0.8mm boards bonded together, so inner 
layers are about 0.2mm apart.

4 layer steps (over simplified)
------------------
* cut two pieces of 0.8mm double sided board
* protect outer layers from etchant with self adhesive book covering.
* drill 4 or more registration holes
* print and etch inner layers (clean, photoresist, expose, develop & etch)
* place one board on aluminium plate
* place sheet of class cloth,
* pour epoxy
* place 2nd PCB, align with pins on holes
* place 2nd aluminium plate
* place some bricks
* place on top of electric hot plate and heat PCB to 90C to 110C, 30 
minutes.
* cool, trim sides, remove self adhesive film.
* process like an ordinary plated through PCB.



To improve copper/epoxy bond you can make it black oxide by wiping it 
with strong bleach solution with 10% NaOH for a few seconds. this 
improves bond a lot.