Circuit Board Photo Resist Etching - Fail.. What went wrong?

jpanhalt

Joined Jan 18, 2008
10,095
I just looked up one of the common Riston films:
upload_2016-5-10_18-12-40.png

I tend to use potassium salts, as they dissolve easier. However, once dissolved the difference between potassium and sodium salts is insignificant. According to this, make a 1% solution by weight (1 g per 100 mL of solution ≈ water), and see how it works. Warming to 50 to 60°C will probably help. Don't forget the sponge.

John
 

Lestraveled

Joined May 19, 2014
1,946
Tonight I made two PCBs with dry film resist but, this time I used a quarter of the developer (sodium carbonate) I normally use, in 1 liter of water. HUGE SURPRISE!! The fine line detail improved dramatically!!
This is a simple board with large traces, but the I used 12 mil traces to indicate cut lines and mounting holes. These sized traces were normally not reliable with the over dose of developer I unknowingly used before. Now, the 12 mil traces on both boards came out perfect. Here are some photos:







To repeat, the correct developer to water mix ratio is: 10 grams (heaping 1/2 tablespoon) of sodium carbonate into 1 liter of tap water (hot).

The art work was generated with Express PCB, transferred to Copper Connection and printed with a Brother inkjet printer on to "Apollo Ink Jet transparency film" (two copies, aligned on a home built light table.)
 

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Thread Starter

Qsilverrdc

Joined Aug 3, 2014
34
So I have figured out that the problem is with developing the resist.
This is possibly my exposure box..it's possible that the film is possibly not good.
Also got better when 4 layers of laser print were used.
I almost have gotten a successful board.
2016-05-13 22.03.35.jpg
 

GopherT

Joined Nov 23, 2012
8,012
So I have figured out that the problem is with developing the resist.
This is possibly my exposure box..it's possible that the film is possibly not good.
Also got better when 4 layers of laser print were used.
I almost have gotten a successful board.
View attachment 106045
Your board looks good. You just need to etch a bit more. If you can see copper-colored copper, that material will dissolve in the etch bath. Don't over think it. Just get a pair of rubber gloves and steal some of your wife's or mothers make-up removal sponges (or buy a pack for about a buck). They are not abrasive but last forever in etch bath. They are very fine grained and will not wipe off the resist if done gently. Make sure you wear rubber or nitrile gloves and safety glasses. Very gentle rubbing across the board for 5 minutes and it will all be clean. You can dip the board you have posted back I to the bath. It will be fine.
 

Thread Starter

Qsilverrdc

Joined Aug 3, 2014
34
There is something wrong in his film or the developing. He is trying to figure out what is wrong. He should have no problem producing a perfect board with dry film resist. He is trying to fix his problem, not band-aid it.
Yes, I could repair and use this last board.
Most of the copper etched in about 5 minutes. 2 parts 3% Hydrogen Peroxide and 1 part 20% HCL
(Klean Strip Green Muriatic Acid - You know the low fuming kind.. lol. It's low fuming because it is 20% not 37%)
It works fine, so I know the etch is not at fault.
All the traces had a haze about them that mostly faded.
I left the board in the etch for 35 minutes, to get to that point.
----------------------
So what is new. I made an extension to my exposure box.
UV Box A.jpg UV Box Extended.jpg
The developing plane is now 18" from the bulbs, so the intensity will be significantly less.
The other benefit is less angular leak. Down side is longer exposure time. This is now 36W @ 18 inches.
Resist Apply H20.jpg
So here I am trying to apply the resist with water. I have seen this done in several videos.
Resist Fail.jpg
Fail...
Here is after a couple passes thru the laminator. With this film seems that the water doesn't squeegee out.
So what to do... Develop this fail and see what happens.
After 2 minutes in the developer, the film started dissolving. Cool, like expected.
After 15 minutes in the developer, I put the board into new developer solution... Finally after another 10 minutes I went to the sink.
Here is what the board looked like after running hot water on it.
Result pre scrub Fail.jpg
I grabbed my scotch bite pad and cleaned 1/2...
Result Fail.jpg
So my conclusion is that the film I bough on E-Bay is bad, or the developer they provided is not good.
It really seems to be near the adhesive layer of the resist that this problem shows.
Resist Scrap Roll.jpg
This is the resist as it appears on the roll.. (yellow light dark room)
 

jpanhalt

Joined Jan 18, 2008
10,095
Not so sure I agree with the conclusion. But the experiment was a nice idea.

One comment about your exposure box. You want collimated light for maximum resolution, not scattered light. The aluminum lining increases sideways illumination (scatter). Of course, that is not the major problem right now, but I would get rid of the lining on the sidewalls. I have not found a reflector behind the lamps to be a problem, and it probably reduces exposure time a little. Mine is made from a sheet of aluminum, not wrinkled aluminum foil. Even wrinkled foil in that location shouldn't be such a problem as foil on the sides.

John
 

Lestraveled

Joined May 19, 2014
1,946
@Qsilverrdc
After you expose the board can you see the image like in this photo?



Is the color of your film really purple(ish), or is it blue like in this photo (taken in white light)?


Perhaps your film is a different kind than the Dupont Riston I am using.
 

jpanhalt

Joined Jan 18, 2008
10,095
BTW, I have been using positive photoresist for many years. My comments are related to that and to a general knowledge of the photochemistry involved. Just bought some some negative resist. It may make a difference as to which of the Riston photoresists you are using.

Did your eBay supplier give that information?

John
 

Lestraveled

Joined May 19, 2014
1,946
@Qsilverrdc
I read where you kept the board in the developer for 2 minutes and then 15 minutes. The Riston dry film I use takes seconds to develop. I leave it in the developer for one minute total while I scrub it. (The spec sheet says 13 to 18 seconds.)
Then I rinse it in hot tap water.

I am starting to be convinced that either your film is bad or it is a completely different film then what I am using.
 

jpanhalt

Joined Jan 18, 2008
10,095
Now that looks promising!

I used ferric chloride or cupric chloride exclusively for etching. I found the peroxide-based solutions attacked my resist. When I was worried about whether the resist had been removed, a quick dip in the etch solution removed any doubt. Bare copper will almost instantly turn a salmon red and be wetted. Those areas with remaining resist remained the original copper color and the etch solution beaded on them.

The neat thing about the acid/base (alkaline) systems is that if the resist is not removed by testing in the acid etch, I could re-treat it with the alkaline developer again. Of course, you cannot do that under bright fluorescent or other high UV lights. I worked in a dimly lit kitchen with incandescent lamps.

John
 

Thread Starter

Qsilverrdc

Joined Aug 3, 2014
34
Another...
Try expose 2.jpg here is the exposed before film peel and developing.
This went into developer. Washing soda in water.
Went quickly to a point, abut 2 minutes, then kind of stops.
Just in.jpg just put into etch.
I can already see fail.
Etch.jpg after a very long time.
Backlght.jpg back light..
Another fail...

Can the laminating temperature be a cause?
Is this not getting hot enough at the lamination step?
It seems like the problem is right at the interface of the copper and resist.
I can feel all the traces, but there is still that stubborn layer that does not want to come off..
 

Thread Starter

Qsilverrdc

Joined Aug 3, 2014
34
BTW, I have been using positive photoresist for many years. My comments are related to that and to a general knowledge of the photochemistry involved. Just bought some some negative resist. It may make a difference as to which of the Riston photoresists you are using.

Did your eBay supplier give that information?

John
No. No information. I have ordered more from 2 other sources. I really feel there is something wrong with the resist that I have. Or the developing process. Makes me want to try thermal toner process. I also could not get that to work.
 
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