Homebrew PCBs

Ed Okerson wrote:

>>There is nothing wrong with wet chemistry if handled properly. I've been
>>plating holes at home and nothing compares to real copper inside the
>>holes.
> 
> 
> So how exactly do you do this?  What chemicals, equipment are needed?
> 
> Ed



I happen to find chemistry fascinating, which I guess started since I 
was introduced to the subject back in high school. Because it this I was 
able to spent a *lot* of my time experimenting and learning about doing 
PTH for the end goal of being able to fabrication PCBs at home. Having 
spend the last 4 years or so fiddling with this I conclude PTH a time 
consuming and tedious task, even with all the equipment laid out in 
front of you. It is *not* possible to make a quick and simple PTH board 
but rather requires lots of patients combined with enthusiasm to make it 
work.

I've made probably a dozen PTH PCBs so far using my latest tank 
equipment. About the quickest time I've made a PTH board is 4.5 hours, 
counting from the time I begin drilling to the time I'm ready to solder 
parts on, and no board yet has come out perfect. I prefer to make single 
sided PCB whenever possible. When I've finally finished my setup I'm 
hoping to get it down to 3 hours or less, otherwise PTH is just too 
monotonous.

There are lots of steps, all of which have potential problems.
The processing tanks and the maintenance of the chemicals is important, 
as well as a good understanding of how the process behaves.

These are most of steps and chemicals I use to make a PTH PCB. I'm still 
refining the "Make holes conductive" step, as my current method needs 
much improvement.

**********************************************
1) Drill board

2) Cleaning

  dishwashing detergent
  60~80\ufffdC
  5 minutes immersion

3) immersion rinse

4) Make holes conductive

  high purity conductive carbon black aqueous dispersion
  using a cationic type dispersion agent.
  pH controlled to 9.0 with sodium bi-carbonate
  room temp
  5 minutes immersion


5) Absorb excess liquid with sponge.

6) Hot air dry

... repeat steps 4 to 6 ...

... repeat steps 4 to 6 again ...


7) Microstrip

  Ammonium persulfate
  room temp
  5~10 minutes immersion

8) Spray Rinse

9) electroplate the holes

  200g/L H2SO4
  75g/L CuS04.5H20
  Macdermid Macuspec copper plating additive
  30~60ppm chloride
  15~35 \ufffdC
  120 minutes, bubble agitation

10) immersion rinse

11) laminate dry film photoresist

12) Expose

13) Develop

  9g/L sodium carbonate
  25~35 \ufffdC
  2 minutes, paint brush agitation

14) immersion rinse

15) Etch

  CuCl2+O2
  room temp
  5 minutes spray

16) immersion rinse

17) strip resist

  50g/L NaOH
  20~55 \ufffdC
  10 minutes immersion


18) immersion rinse