Homebrew PCBs

I've started fiddeling around with photoresist spray and developing it 
using caustic soda, and have a few questions as the board is still not 
coming out 100%


1) How thick should the photo resist be sprayed on. After I've sprayed 
it on and its dried you can clearly see the purple film - there's no 
gaps. 

2) After you put the board in CS - how do you know when to take it 
out? I can see the tracks clearly but the pcb is still have a layer of 
the purple stuff on it. Should the purple film vanish completly 
(except for on the tracks) 

3) Which is a better etchent to use - Ferric Chloride (mine works 
really slowly even when heated up - like 30-40mins) or Hydrochloric 
Acid+Hydrogen Peroxide 

I've done another board (etched) and the top half of it is perfect - 
nice clear tracks. But on the bottom half none of it is etched. If I 
leave it in too long it starts to eat away the tracks, but still 
doesnt touch the bottom section? Does this sound like too thick spray?

>From: "gmc_za" <gmc_za@...>
>Reply-To: Homebrew_PCBs@yahoogroups.com
>To: Homebrew_PCBs@yahoogroups.com
>Subject: [Homebrew_PCBs] Using Photoresist Spray
>Date: Mon, 04 Oct 2004 18:26:37 -0000
>
>
>
>
>I've started fiddeling around with photoresist spray and developing it
>using caustic soda, and have a few questions as the board is still not
>coming out 100%
>
>
>1) How thick should the photo resist be sprayed on. After I've sprayed
>it on and its dried you can clearly see the purple film - there's no
>gaps.
>
>2) After you put the board in CS - how do you know when to take it
>out? I can see the tracks clearly but the pcb is still have a layer of
>the purple stuff on it. Should the purple film vanish completly
>(except for on the tracks)

All the resist should have disappeared where it was exposed to the UV.

>
>3) Which is a better etchent to use - Ferric Chloride (mine works
>really slowly even when heated up - like 30-40mins) or Hydrochloric
>Acid+Hydrogen Peroxide

Warm ferric chloride etches in less than 10 minutes for me with continuous 
agitation.

>
>I've done another board (etched) and the top half of it is perfect -
>nice clear tracks. But on the bottom half none of it is etched. If I
>leave it in too long it starts to eat away the tracks, but still
>doesnt touch the bottom section? Does this sound like too thick spray?

Make single-sided boards until you get the process right, then try 
double-sided ones.

Leon

1.Clean board
2.Shake can before each use.(What I did not do the first few times)

(in the dark with safe light)
3.Tilt board upright on 45 degree angle
4.Spray from right to left working your way to the bottom
5.Blot off excess that runs to the bottom of board
6.Lay board flat to dry. (I used an old hair drier to
dry the board.)

I found I need more exposure time than the instructions in order
to get a good trace.



--- In Homebrew_PCBs@yahoogroups.com, "gmc_za" <gmc_za@y...> wrote:

> 
> 
> I've started fiddeling around with photoresist spray and developing it 
> using caustic soda, and have a few questions as the board is still not 
> coming out 100%
> 
> 
> 1) How thick should the photo resist be sprayed on. After I've sprayed 
> it on and its dried you can clearly see the purple film - there's no 
> gaps. 
> 
> 2) After you put the board in CS - how do you know when to take it 
> out? I can see the tracks clearly but the pcb is still have a layer of 
> the purple stuff on it. Should the purple film vanish completly 
> (except for on the tracks) 
> 
> 3) Which is a better etchent to use - Ferric Chloride (mine works 
> really slowly even when heated up - like 30-40mins) or Hydrochloric 
> Acid+Hydrogen Peroxide 
> 
> I've done another board (etched) and the top half of it is perfect - 
> nice clear tracks. But on the bottom half none of it is etched. If I 
> leave it in too long it starts to eat away the tracks, but still 
> doesnt touch the bottom section? Does this sound like too thick spray?

Although I have not tried it myself, It was suggested to me that for 
best results a layer of uniform thickness is essential. 
So to accomplish this place the PCB flat and with two strips strips 
of brass shim place them on the board along two opposite edges and 
then spray the board. Now with a glass tube or suitable rod gently 
roll this along the board with its ends bearing on the shim. This 
should roll an even thickness of resist equal to the thickness of the 
shim. 
Note - I have not tried this, so there may be unforseen problems, I 
realise the glass would pick up some of the resist behind it, so 
maybe more than one rollover is necessary. Anyway it may be worth a 
try, unless someone warns against it from experience.

What are you spraying the board with, the Electrolube product or is 
there another product available?
Electrolube also sell a developer for their product, a bit expensive 
but it may be something special. 
Does anyone know if their developer is necessary or will anything 
else do?

Leon.

--- In Homebrew_PCBs@yahoogroups.com, "crankorgan" <john@k...> wrote:

> 
> 1.Clean board
> 2.Shake can before each use.(What I did not do the first few times)
> 
> (in the dark with safe light)
> 3.Tilt board upright on 45 degree angle
> 4.Spray from right to left working your way to the bottom
> 5.Blot off excess that runs to the bottom of board
> 6.Lay board flat to dry. (I used an old hair drier to
> dry the board.)
> 
> I found I need more exposure time than the instructions in order
> to get a good trace.

Leon Crowther wrote:
> 
> Although I have not tried it myself, It was suggested to me that for 
> best results a layer of uniform thickness is essential. 
> So to accomplish this place the PCB flat and with two strips strips 
> of brass shim place them on the board along two opposite edges and 
> then spray the board. Now with a glass tube or suitable rod gently 
> roll this along the board with its ends bearing on the shim. This 
> should roll an even thickness of resist equal to the thickness of the 
> shim. 
> Note - I have not tried this, so there may be unforseen problems, I 
> realise the glass would pick up some of the resist behind it, so 
> maybe more than one rollover is necessary. Anyway it may be worth a 
> try, unless someone warns against it from experience.
> 
> What are you spraying the board with, the Electrolube product or is 
> there another product available?
> Electrolube also sell a developer for their product, a bit expensive 
> but it may be something special. 
> Does anyone know if their developer is necessary or will anything 
> else do?

11g/Lt of sodium hydroxide is ideal for developing prp. It is important
that the pcb is free of oil before coating with prp.

> --- In Homebrew_PCBs@yahoogroups.com, "crankorgan" <john@k...> wrote:
> 
>>1.Clean board
>>2.Shake can before each use.(What I did not do the first few times)
>>
>>(in the dark with safe light)
>>3.Tilt board upright on 45 degree angle
>>4.Spray from right to left working your way to the bottom
>>5.Blot off excess that runs to the bottom of board
>>6.Lay board flat to dry. (I used an old hair drier to
>>dry the board.)
>>
>>I found I need more exposure time than the instructions in order
>>to get a good trace.

This is similar to the doctor knife method to make small samples of experimental dry film resists.  Works fine.  I suggest a beveled stainless steel straight edge would be preferable to a glass rod as it will not pick up as much resist

  ----- Original Message ----- 
  From: Russell Shaw 
  To: Homebrew_PCBs@yahoogroups.com 
  Sent: Wednesday, October 06, 2004 3:31 AM
  Subject: Re: [Homebrew_PCBs] Re: Using Photoresist Spray


  Leon Crowther wrote:
  > 
  > Although I have not tried it myself, It was suggested to me that for 
  > best results a layer of uniform thickness is essential. 
  > So to accomplish this place the PCB flat and with two strips strips 
  > of brass shim place them on the board along two opposite edges and 
  > then spray the board. Now with a glass tube or suitable rod gently 
  > roll this along the board with its ends bearing on the shim. 

[Non-text portions of this message have been removed]