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Forums
4hv.org :: Forums :: General Science and Electronics
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Chemical for PCB fabrication

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dexter
Tue Sept 16 2014, 05:48PM
dexter Registered Member #42796 Joined: Mon Jan 13 2014, 06:34PM
Location:
Posts: 195
Steve Conner wrote ...

I always used sodium hydroxide to develop the photoresist and ferric chloride for the etching.

i use the same and it works perfect
for the concentration of the sodium hydroxide i use 4-5 flakes (~1cm^2) and 250 ml water (empiric testing). It takes ~20 sec to develop
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Daedronus
Wed Sept 17 2014, 09:00AM
Daedronus Registered Member #2329 Joined: Tue Sept 01 2009, 08:25AM
Location:
Posts: 370
 		Sodium hydroxide is the worst choice for developing etch masks.
Normally sodium carbonate is used, unless the product specifically calls for sodium hydroxide.
Easily made from baking powder by thermal decomposition.

For most film masks this should be true.
Only product that I know of that uses sodium hydroxide is the Positive 20 aerosol.
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Hazmatt_(The Underdog)
Thu Sept 18 2014, 04:14AM
Hazmatt_(The Underdog) Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
 		MG Chemicals Positive Etch:
Sodium Hydroxide, approx. 0.9M (last time I titrated it years ago)
and Ferric Chloride Etch.

All of it takes some practice, but it works.

The Hydroxide, sold as a Concentrate, tells you to dilute it on the bottle. If you pour it straight onto the board, it will remove your mask.

All you have to do is Follow the directions.
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Daedronus
Thu Sept 18 2014, 08:31AM
Daedronus Registered Member #2329 Joined: Tue Sept 01 2009, 08:25AM
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Posts: 370
 		Most negative etch masks films I have seen on eBay and such specificity use sodium carbonate for developing and sodium hydroxide for stripping.

In the end check the manufacturer's data, both chemicals are easily accessible.
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IamSmooth
Thu Sept 18 2014, 09:32PM
IamSmooth Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
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Posts: 1567
 		I'm etching now with ammonium persulfate.

I use the sodium silicate to remove positive resist and it works quite well. I'm going to try NaOH and compare them.
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Hazmatt_(The Underdog)
Fri Sept 19 2014, 12:27AM
Hazmatt_(The Underdog) Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
 		When developing, make sure you agitate the board.
Don't just drop it in and stare at it, and hope it develops, it doesn't work that way.

Agitate the solution and it will develop fairly fast, and rinse with water.

I ususally use a large pan and rock it back and forth.
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IamSmooth
Fri Sept 19 2014, 01:50AM
IamSmooth Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
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Posts: 1567
 		I have a bubbler. I submerge the system in near-boiling water to passively heat the solution. I get it developed in minutes.
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Daedronus
Fri Sept 19 2014, 08:32AM
Daedronus Registered Member #2329 Joined: Tue Sept 01 2009, 08:25AM
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Posts: 370
 		what etch mask do you you IamSmooth?
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IamSmooth
Fri Sept 19 2014, 09:59PM
IamSmooth Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
 		I wonder if I should make a video on all of this. Here is my process:

I design the tracings using PCB Wizard, which I believe is from the UK. I print the tracings out on transparency film and expose my PCB with it in an exposure unit. I currently develop the positive resist in sodium silicate to leave the tracings on the copper. I develop in ammonium persulfate.

I then use a drill press (but now I am using a micro mill, which allows me to control the movement by 0.001") to make the holes.

Would anyone want me to make a video for this? There are videos out there already; I don't know if I'd contribute much more.
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IamSmooth
Sun Sept 21 2014, 12:13AM
IamSmooth Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
 		What are the rest of you doing for vias when you have a double-sided board? I've seen conductive gel/epoxy and videos for copper electroplating.

Right now I'm just soldering small leads through the hole on both sides to make the connection, but I'm looking for a cleaner method.
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