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

Lestraveled

Joined May 19, 2014
1,946
@Qsilverrdc
I have been using dry film exclusively for a year and a half. My failures are better than your best board (to date). You have done diagnostics that has changed everything except the film with no change in the result. You have ordered new film from two different sources, which is excellent!! Dupont developed Riston over 25 years ago. It has been a mainstay of the PCB industry all that time. Your PCB should look like the pictures in post #26 and they will. I hear your frustration, hang in there. I think you got some bad film.
 

jpanhalt

Joined Jan 18, 2008
8,778
It is probably too late now, but I would not order Riston unless the seller said with it was. On eBay I have seen FX515 and MM540. The photos I have seen appear slightly different in color and perhaps thickness. Once you get your material, I suggest trying to match what you have with the DuPont site.

Re: post #39
The first picture looks good. Second looks good too. Notice the salmon color of ALL of the coper areas to be etched. Based on those observations, your third and forth look under etched to me.

Are you using ferric chloride or the peroxide/HCl etch solution? Both have been mentioned in this thread. I recommend ferric chloride as your best bet until you get a system working. In every video I have seen of commercial board houses ferric chloride (or maybe cupric chloride -- they are quite similar).

Are you using a sponge when developing? YOu can also use a sponge with ferric chloride when etching. It can help get in the small areas. However, I do not usually find that to be necessary.

Finally, when you remove during etching, are the areas of copper to be removed wetted and is the etch solution beaded on the areas of resist? If so, the wetting is a clear sign that the resist has been removed.

John

Edit: Just checked the DuPont site. It produces 7 different Riston dry-film photoresist series. Unfortunately, the site is down right now, so none of the links work. Moreover, within each series, there may be multiple products.

Capture.PNG
 
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jpanhalt

Joined Jan 18, 2008
8,778
UPDATE: Got the TDS's for various Riston types through Google. In brief, the various formulations appear to differ primarily in thickness and compatibility with alkaline etching solutions. Probably, no one here is using an alkaline etching bath, so I won't describe those differences.

1) Recommended lamination temperature: 105-120°C (115°C preferred). Some of the products have a more lengthy discussion of preferred lamination conditions.
2) Exposure: 350 to 380 nm (not much discussion or variation in that recommendation).
3) Development: 0.7 to 1 wt. % Na2CO3 (and other carbonates) w/ 0.85 wt% preferred. Again, not much discussion or variation in that.
*4) Rinse: Use hard water that contains at least 150 to 250 ppm CaCO3. If your water is not hard, add MgSO4 or CaCl2 to make it hard.
*5) Etch: Ferric chloride, cupric chloride (≤3.0 M free HCl), or H2O2 with the same limitation on acid concentration. (see edit below)
6) Stripping: 1.5 to 3.0 wt% NaOH or KOH (3 wt% preferred),

Items #4 and 5 may be causing some problems here. Insufficient rinsing after developing might leave enough residue in the board to affect good etching. Second, the acid concentration being used by the TS may be too high. A 20% ("non-fumng") HCl solution is approximately 6.6 molar. In order to be 3M or less, it will need to be diluted 45 mL to a final volume of 100 mL or more. The usual recommendation to add the acid to water applies, but be particularly careful with H2O2.

EDIT: The DuPont recommendation for H2O2 etching is to use sulfuric acid. I had that in my notes, but forgot to mention it. The DuPont TDS does not mention using HCl with H2O2. Whether that is an oversight or whether an HCl/H2O2 bath works poorly is not discussed. If H2O2/HCl works fine for you, then I wouldn't change. But since the TS is having problems in this process, I would recommend going to H2SO4/H2O2 or ferric chloride until his system is working well. BTW, the dry-resist used by @Lestraveled also mentions the need to rinse with hard water.

Regards, John
 
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Lestraveled

Joined May 19, 2014
1,946
- I run my laminator at 230 deg F. I accidentally ran it 330 deg F and still got good results. I measured the exit temperature with an infrared thermometer at 120 deg F.
- I live in Tucson so I have plenty of hard water.
- I etch using Sodium Persulfate at 45 deg C.

There is a Chinese company called Kolon that produces dry film photo resist products identical to Dupont Riston. They look the same and use identical processing. It is called Kolon PK2100, KP2140 and KP2150.

20101226224849_s.jpg

I am pretty sure that this is what you get from China and Hong Kong. Which means I am probably using it right now. Here is the TDS on it.
 

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Thread Starter

Qsilverrdc

Joined Aug 3, 2014
34
... Insufficient rinsing after developing might leave enough residue in the board to affect good etching.
Regards, John
The problem is defiantly with the "CloneRiston".
I made another attempt today, and had some success.
Expose Box Shorter.jpg Before Etch Peeled.jpg
I lowered the box height, and increased the effective exposure time. (square of the ratio of the distances)
I also dropped back to 3 layers transparency. You can see a little leaking / misalignment, but not bad.
The big part was a very aggressive brushing of the resist during development.
Temperature of Na2CO3 was at 86 degrees F. 1 rounded teaspoon per liter.
I used a small hobby paint brush to constantly work the surface of the resist.
As before at about 2 minutes a lot had come off, but not that sticky layer next to the copper.
I kept going another 4 minutes. Changed to new tank of developer.
I rinsed to see if the film was coming off.
I ended up brushing this resist vigorously for another 6 minutes. That's when some letters came up.
You could see that it had finally given up pre etch.jpg after 12 minutes.
So into the etch, and in a few seconds it looked like this. Begin Etch.jpg
I knew that it should work now.
After about 3 to 5 minutes (wasn't timing) it looked like this. little Left.jpg and a half minute later the etching was done. result.jpg
So I thought I would finish (practice) drilling the holes.
Final Traces.jpg back light final.jpg As you can see not perfect, but I am confident that with some good resist, I will be able to get a good board. I can tell that I will re-design the layout of the board to increase pad sizes. My eyes are old.
Thanks to all so far for the help. I will update when I get better resist to try.
Richard
 
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jpanhalt

Joined Jan 18, 2008
8,778
Hi Richard,

Those results look great compared to what you started with. The second picture you post is perfect, except for a little raggedness around the traces. I wonder whether you may have the FX version of the counterfeit resist? That is the thin, 15 mil (0.4 mm) version of the thicker resist?

Have you tried a sponge for the development? If I get into town, I will try to get the brand and picture of the sponge I use, but I live quite far from Cleveland (42 miles). The local town is only about 10 miles away. Also, as mentioned before, I use the same type sponge to get the little crevices during etching. Commercial labs use vigorous bubbling and spray tanks, but I have not found they are necessary when I use a sponge.

Are you still using the peroxide-based etching solution? Can you get ferric chloride? (Its most common use is for sewage treatment.) The most common commercial form of ferric chloride is either as a concentrated solution are as the hexahydrate solid. Don't be afraid of it in either form. It does attack stainless steel (because of the high chloride concentration), but plastic and glass are unaffected.

John
 

GopherT

Joined Nov 23, 2012
8,012
I am guessing that you do not have enough contrast between your image and clear film.

UV light is too intense

Are you clamping between glass plates to make sure the clear film is in intimate contact with the board?

Also, don't let hard rinse water dry on your board from developing, the etch may not eat dry carbonate deposited away.
 

Thread Starter

Qsilverrdc

Joined Aug 3, 2014
34
Hi Richard,
Those results look great compared to what you started with. The second picture you post is perfect, except for a little raggedness around the traces. .....
Have you tried a sponge for the development? If I get into town, I will try to get the brand and picture of the sponge I use, but I live quite far from Cleveland (42 miles). The local town is only about 10 miles away.

Are you still using the peroxide-based etching solution? Can you get ferric chloride?
John
Hi John,
I think because I have 3 layers I am getting some edge distortion on the image.
Trapped tight in glass.
I am about 20 miles west of Cleveland.
Yes I used peroxide to etch as show in photos.
I do have a jug of ferric. Started with that but is very prone to stain everything.
Will try again once I get a resist that develops reasonably.
 

Thread Starter

Qsilverrdc

Joined Aug 3, 2014
34
Update.
Thanks to Lestraveled for the film.
Definitely far better then what I got with my film.
20160523_225124.jpg 20160523_233930.jpg 20160523_235356.jpg
I developed only for 3 minutes.
I did not work the resist very hard, juse a gentle brushing. This is far better film.
Will try another board soon.
You can see where resist was left.
 

GopherT

Joined Nov 23, 2012
8,012
Must the photoresist be removed? The commercial presensitized boards suggest leaving it in place -solder right through it and the rest serves to protect the traces. Just a light coat of clear acryllic over it.
 

Thread Starter

Qsilverrdc

Joined Aug 3, 2014
34
OK, I say reduce your exposure to 1/4 of the time.
I have no doubt that the film I have bought is bad.
I can see a little misalignment in my stack of art. (Possible future experimentation here)
http://forum.allaboutcircuits.com/attachments/20160523_225124-jpg.106658

Will clean up a couple of variables and proceed again.
I first tried to apply the resist with water but it did not look good.
I started over, applying dry, it works fine. Laminated then exposed.
Looking forward to improving my process.
 

Thread Starter

Qsilverrdc

Joined Aug 3, 2014
34
Ok. Next update. I took a close look at my transparency image, and found it was not clean on n the edges.
I reprinted and applied 2 layers.20160524_213339.jpgshown on resist just before exposure.
20160524_214507.jpg after exposure.20160524_220201.jpg and now developed.
20160524_222325.jpg 20160524_222342.jpg etched and back lit.
All of the problems I was having were related to poor resist.
 

Lestraveled

Joined May 19, 2014
1,946
@Qsilverrdc
I made a PCB tonight. I used the same film you did, just a few inched down the roll. I had an imperfection on the board. Take a look...

Here is what it looked like after exposure
DSCF1760.JPG

Here is what it looked like after developing, about 1 minute. Notice the top right edge.
DSCF1761.JPG

Here is after etching. Notice top right edge.
DSCF1765.JPG

Close up of bad area
DSCF1766.JPG

Resist removed
DSCF1767.JPG

I can't explain it. Maybe some goop that was left on the board after cleaning. I think I am going to start using alcohol as a final board clean.

The thin traces between the groups (cut lines) are 10 mil traces.

@Qsilverrdc I hope this encourages you to keep on it. You are very close to nailing it.
 
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Thread Starter

Qsilverrdc

Joined Aug 3, 2014
34
This is the best so far.20160525_221620.jpg
My skills with the drill need work..lol.
Next update will hopefully be with UV led.
Still working on the transparency image.
 

Lestraveled

Joined May 19, 2014
1,946
Yes. The edges of the traces look pretty sharp and clean.

I still think you can take your exposure time down.

I have gotten much better results using an ink jet printer making the art work, then using a laser printer.
 
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Thread Starter

Qsilverrdc

Joined Aug 3, 2014
34
Hi to all following this thread.
I have been working on several things to improve my boards.
As you saw from above my drilling needs work. My solution was to make an accessory for my 3d reprap printer, and write some software. 20160529_122256.jpg In blue is the dremel hand tool adapter I printed. I wrote software to find centers of holes from the graphics and create gcode for the printer. This version of reprap is not super ridged, but good enough for drilling.
I 3d printed a pcb board holder that clips the the build plate.20160529_122321.jpg
So I thought I would try pre-drilling and post drilling.
And post..
.
So pre-drilling 20160603_172657.jpg there are burrs, so I filed then cleaned the board to get this. 20160603_180041.jpg
20160603_180619.jpg Here is a quick overlay check. I laminated with the photoresist as usuall and alighned and exposed.20160603_190112.jpg Then developed.20160603_191503.jpgYou can see where holes were on and a little off.20160603_193318.jpg After etching, and cleaned.2016-06-05 10.07.05.jpg
Kind of neat not having to hand drill after etching. This board has 108 holes.
 

Thread Starter

Qsilverrdc

Joined Aug 3, 2014
34
So for post drilling. I created and etched the board. Then into the holder. Alignment was done by hand drilling the first hole. The drill introduced allows the x-y to be zeroed. The biggest problem is squaring the fixture to x-y. 20160604_205837.jpg 20160604_210031.jpg
After 20160604_214719.jpg on back light. 20160604_214850.jpg 20160604_214900.jpg Cleaned up, burrs on.
 

Thread Starter

Qsilverrdc

Joined Aug 3, 2014
34
So as far as the drilling goes, I think my preference would be to pre-drill.
Drill walk is noticed, so while this is better then my hand drilling, there can be cosiderable (relatively) error.
I noticed about 1/2 drill diameter, or in this case about 0.015 inch, is the max. Most holes are less then .004 error.
I also like this way because the burr can be filed down before anything.
It's very satisfying that the board is effectively done after etching.

I still have to work on the LED UV exposure unit, as I still have a little edge bleeding.
A few experiments remain.

Richard.
 

Lestraveled

Joined May 19, 2014
1,946
@Qsilverrdc
Richard, EXCELLENT! Very cool.

Your boards are looking good. Drilling a zillion holes has always been a pain. Very nice solution.

Have you thought about milling the PCBs with your Reprap?

Also have you thought about mounting a pin point UV light source in the Reprap and use it to expose your boards? This is something I have been working on for a while using a pin plotter.
 
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