Project: Photographic methods of making PCBs

cmartinez

Joined Jan 17, 2007
7,060
I etch my boards in Sodium Persulfate using an economy etcher. Using this etcher has greatly reduced my consumption of sodium persulfate. I can etch three times the number of boards for the same amount of sodium persulfate as compared to using an unheated tray. It is a lot faster also.

That's a very nice looking tank. And quite economical too!, after doing some searching, I found it here.
Question, how many PCBs can you process with 1 Kg of sodium persulfate? In other words, how many litters of sodium persulfate solution do you get out of one std bottle of crystals?
 

Thread Starter

Lestraveled

Joined May 19, 2014
1,946
C
For a full tank, I mix 2 liters of water with 2 kg of sodium persulfate. My normal board size is 4 X 6 inches single sided. The first four boards will normally complete is 5 to 6 minutes each. I can etch a lot of boards before the etch time goes over ten minutes each. I can't recall an exact number but it is a lot. I highly prefer sodium persulfate over ferric chloride. Look for sources of sodium persulfate other than MCG. It is a standard industrial chemical and can be obtained from many sources.
 

cmartinez

Joined Jan 17, 2007
7,060
C
For a full tank, I mix 2 liters of water with 2 kg of sodium persulfate. My normal board size is 4 X 6 inches single sided. The first four boards will normally complete is 5 to 6 minutes each. I can etch a lot of boards before the etch time goes over ten minutes each. I can't recall an exact number but it is a lot. I highly prefer sodium persulfate over ferric chloride. Look for sources of sodium persulfate other than MCG. It is a standard industrial chemical and can be obtained from many sources.
Will do, thanks! I've just had it with the stupid FeCl₃... the darn thing is worse than red wine for staining things and making a mess...
Question, is it better to use bottled water instead of chlorinated water from the faucet? Or it won't make any difference?
 
Don't use transparency film. Print on Translucent Polyester paper. I don't have a current source for the paper right now.

A drop of water can actually hold the paper to the board without a frame when exposing.
 

Robin Mitchell

Joined Oct 25, 2009
819
This is a really interesting post but how do you overcome the dimensional inaccuracies in the laser print? A simple scale will not solve the issue because the page warps causing a slight rotational inaccuracy (one corner curves in one direction and the other corner curves in the opposite direction).
 

Thread Starter

Lestraveled

Joined May 19, 2014
1,946
............... how do you overcome the dimensional inaccuracies in the laser print? A simple scale will not solve the issue because the page warps................
Very good point! The larger the board, the worse the dimensional inaccuracies become. This is a real problem on double sided boards. Sometimes I have had to reprint images to get the "warpage" to line up. Single sided boards generally are not a problem, especially if I manually drill them. There have been cases, such as long connectors with lots of pins, where I have had to use the accuracy of my mill to drill.

How do you generate your artwork?
 

atferrari

Joined Jan 6, 2004
4,069
@cmartinez

Tonight I had to do a single 4 X 6 inch board, so I only mixed 1 kg of sodium persulfate in 2 liters of tap water. It took 7 minutes at 50 Deg C to complete. Just a data point.
Hola Les,

Once the mix prepared, what is the shelf life? In a dark container?

What are the precautions for disposal? Is it as much contaminant as the ferric chloride?
 

Robin Mitchell

Joined Oct 25, 2009
819
Just made around 20 prints onto laser transparency all with different settings and can confirm that scaling is not the issue. There is enough page warp that if you take an accurate square to a large printout of a square the angle between the lines is less than 90 degrees.
 

Thread Starter

Lestraveled

Joined May 19, 2014
1,946
Hola Les,

Once the mix prepared, what is the shelf life? In a dark container?

What are the precautions for disposal? Is it as much contaminant as the ferric chloride?
I can't remember the last time I stored sodium persulfate. I pretty much wear it out when I make boards.

Here is an article on how to make worn out sodium persulfate safe to pour down the drain.

http://frgmnt.org/tag/sodium-persulfate/
 

Thread Starter

Lestraveled

Joined May 19, 2014
1,946
Yea, I have looked at those and at several other home built rigs. Not promising. I also looked the laser tables. There are a few You-tube videos of people using them to expose PCB. Again, not promising. They all share a common bad feature, the image is pixelated. None of them come close to resolution of a true photoplotter.
 
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