Homebrew PCBs

Ok, let me get a bit more specific.

The process obviousely depends on wether a two layer or four layer PCB
is to be made. I use 18um copper plated base material. In case of a
two layer board this is of 1.5 mm thikness, in case of a four layer
one 0.5 mm only. First step is to drill all holes through all layers.
In case of four layers, I screw the layers together using two
diagonaly positioned screws that I place outside of the final PCB
area. Then comes the plaiting trhough process of the inner layer
(obviousely there is only one inner layer with two sided PCB's). After
this I laminate a photoresist film onto the two sides of the PCB (or
inner layer respectively). The result is then exposed and etched, then
the remaining part of the photoresist is removed by exposing the whole
print once more and develop (which will completely remove the
remaining parts of the photoresist). If this is going to be a four
layer PCB, the outer layers are glued onto the two sides of the inner
layer using a thin film of 5 minute epoxy. The previousely two screw
holes are now used to propperly align the layers. After this I drill
all holes once more to remove glue. After this the whole PCB is once
more through plated, the outer surfaces are laminated with photoresist
film, exposed, developped, etched and reexposed developped to remove
the remaining parts of photoresist.

Now to the time it takes:

exposure = 1.5 minutes per run
develop = 1 minute
laminateing = ~1.5 minutes per side
plate trhough run = 30 minutes up to ~1 hour depending on size of pcb
etching = ~4 minutes.
drill the holes = ( I do it manually. The photofilm is manually
alligned so as it matches the alredy present holes) - depending on the
board but rarely more than 30 minutes.
Glueing = ~15 minutes

The times needed of course vary depending on the size and complexity
of the PCB and of course wether its a two layer or four layer one.
Bigger PCB's may take longer than 3 hours, but I think that 4 hours
should be sufficient in mostly all cases. I must add though that I do
not apply a solder stop mask or anything else because the PCB's I
create are exclusively used for prototypes.

The chemicals I use are partially concentrates and partially ready
made mixtures which can be bought from Bungard. The photoresist is
also from Bungard. I will list them in detail later, but they do only
have "brand kind" of names which don't tell much about what they
consist of like C400 and names like this.

The method used was shown to me by a friend I got to know through an
electronic online forum in the internet (in case you read this - thank
you John). I visited him so as he could show everything to me and he
was kind enough to explain everything to me in detail. I personally
asisted a plating through process and the result was simply stunning.
From what I understood the speed of the plating through process and
the quality of the result extremly depends on the chemicals used. He
had much inferior results before he started to use Bungard chemicals.
Let me state that neither he nor I are in any ways related to Bungard.

As mentioned, I will post more information including pictures as soon
as I'm ready.

Markus

>Markus Zingg wrote:
>
>[deleted]
>>The main advantage
>> however is independancy and the possibility to have a four layer PCB
>> completed within say 2 - 3 hours.... 
>
>Multilayer in 2 - 3 hours !  No offense, but that statement 
>made me laugh. Even if you had a fully automated machines 
>that did everything from drill to the final dry, it will 
>take much longer than 3 hours.
>With your experience of the pattern plated through hole, you 
>must of learned to appreciate the complex nature of the 
>process. As you said earlier its not easy, so unless the 
>hobbyist wants convert to PCB making as their primary 
>interest then plated through holes will be best left to 
>professionals or semi-professionals.
>
>I appreciate your enthusiasm in attempting to make plated 
>through hole boards at home. I've always had a interest in 
>chemistry and find the inner workings of the PCB process 
>quite fascinating. I'm interested in the basic method you 
>are using or plan to use. Is it the pattern plating process 
>or the "tent and etch" or the "etch back" process ?
>
>In the "etch back" process you take a thin copper clad board 
>18 um or less (1/2 oz/ft^2), apply photoresist, expose, 
>develop, and copper plate the tracks so an additional 35um+ 
>is added. Remove the photoresists and etch the whole board 
>until the original 18 um copper cladding is completely 
>etched  and so the thicker tracks are not etched. Obviously 
>this requires an etching apparatus capable of uniform etch, 
>something much better than simple bubble tank.
>
>Adam
>
>
>
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