Homebrew PCBs

>Markus Zingg wrote:
>> 
>> As you can see I have 5 bath's. 
>> 
>> 1 - A cleaning solution (7 minutes) followed by static and spray rinse
>> 2 - so called "pre dip" (1 minute)  NO RINSE after this step
>> 3 - activation (7 minutes, this is the most expensive one - it
>> contains paladium) followed by static and spray rinse
>> 4 - intensifier (4 minutes). This bath should transport the paladium
>> that happen to stay on the copper sides into the holes also thereby
>> avoiding an other wise needed cleaning step of the pcb. Still, static
>> and spray rinse is requiered
>> 5 - the electrolytic bath (24 minutes) followed by static and spray
>> rinse.
>
>You do not mention an electroless copper bath ! If this is 
>so then your process uses palladium activation , not 
>electroless. Electroless copper involves one additional bath 
>containing copper sulfate, formaldehyde plus other 
>chemicals. This final bath deposits copper onto all surfaces 
>without electricity. After the board is covered with a thin 
>layer of copper (usually less than one micrometer) it can 
>then be plated at high speed in the electroplating tank. I 
>remember Tom (twb8899@...) talking on this group about 
>using the palladium process in his PCB shop. Out of interest 
>what's the price of the palladium solution ?

You are right, I am using palladium activation. The palladium is 200
EUR per 0.5 liter. That's expensive, but my 2.5 liter tank only needs
125ml per load. The remaining part is filled up with the pre-dip
solution which is a lot cheaper. That said, the 200 EUR palladium is
sufficient for four loads which last quite a while.

I made a fairly simple calculation. The through plating station along
with the chemistry AND base material to create 55 four layer and 55
double sided PCB's costs me around 1500 EURO. With 55 boards I asume
boards that are sized 10x10 cm. I use this size because it makes price
calculation with external board suppliers easier.

On the other hand, the external costs for making such PCB's are here
where I lilve:

~ 50 EUR for a double sided PCB
~ 96 EUR for a four layer PCB

Multiplied wiht the 55 pieces that are included with what I payedthis
makes:

- 2750 EUR for the double sided PCB's
- 5280 EUR for the four layer PCB's

Hence a total of EUR 8030 for the same thing! Let me point out that
this is about the cheapest offers I could get! But wait, to be fair!
It's NOT the same thing. Add to this the fact that if the boards are
made externally I have to wait 8 to 10 working days plus another week
probably for the shipement (the faster and cheaper service houses are
located in Germany hence I would need to import them adding this time
lag because of customs). If it should be faster, the firms charge
usually 50% to 100% more for say 5 says and 100% to 300% more for a 3
day delivery. HOWEVER, unless I can have them produced in Switzerland,
the shiping / customs delay is constant over all variants. 

After I made a double sided PCB yesterday I can say that I will need
probably 2 hours for such a 10x10 cm sized print including drilling
through plating, etching etc. Then, to be fair the external ones have
a solder stop mask and are thin plated. The former is no problem. The
solder stop mask film is already on the way to me. My fried John I
mentioned already some times just did his first solder stop mask last
night. He is all exited about how simple it was. It's about the same
as applying the dry film photoresist (laminate, expose, develop) and
the costs are also not so extremly high. Thin film is not applied with
the homebrew method as of now, but I will surely address this also.

So, to me my solution really looks cheap! But let me point out that to
me the prices are just half of the story. I HATE waiting for PCB's
that's probably the main reason why I started this project.


>> This will produce plates that have 35 u of copper if you start with
>> copper plates that have 18u alreay. After this a photoresist is
>> laminated on the board. The negative mask is made in a way so as the
>> holes are not there, that said, the hole areas do get light during the
>> exposion and hence they will not be etched. The developement of the
>> photoresist is made with soda. After the etching of the board the
>> remaining parts of the photoresist is once more "developped" with
>> natriumhydroxid solution.
>> 
>
>
>What type of photoresist are you using, liquid or dry film ?,

dry film.

>Is the photoresist soluble in developer solution BEFORE 
>light exposure ? (this is called "negative resist")

I have to laminate it, then do the light exposure then developp it. I
used the term "negative" becuase the exposed parts of the film are
thereafter resisting to the developper and those which are not exposed
to light will be taken away from the developper.

>How are you applying the resist to the board ?

I laminate the film with a regular office laminator - well, I took
care to choose a model that "eats" 1.5mm thick PCB's.

> From what you mentioned above I suspect your using dry film 
>negative photoresist. Developer of this resist is 10g/L of 
>Na2CO3 at 25~30°C and the stripper (remove all resist) is 
>usually 10 to 30g/L of NaOH.

I use  20g/L of Na2CO3
and later on to strip 15g/L of NaOH

Markus