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
> £4000 to £5000. 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.