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Bad PCBs

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Hi there

I have made a couple of PC boards like I normally do, but this time they were awful. The etch solution etched the already etched traces and made large holes in it. I think it's because I normally just do smaller board under 10x10cm, but now it's a 16x10cm. What can I do to avoid this? More UV, more developing, hotter etch solution...?
 
It has been a few years since I did the photo process but.

It is more apt to be in the exposure or developing. They are more difficult to scale up then the etching itself.

Is there a pattern to where the problems are on the board or is it spread evenly? Is it undercutting from the edge?
Maybe post an image of the board.
 
If you are getting under-cutting and etching where there should be resist, I would not increase the temperature of the etch tank as my first step.

Are you using a positive or negative resist? If you are using a positive resist and get good resist removal, then increasing the UV exposure would probably make the problems worse.

Here are some suggestions and guesses based on using positive-resist, pre-sentized boards (Injectoral):

1) Sensitized boards have a limited shelf life. I store mine in a cool place, but after a year, there are very definite changes in terms of decreased exposure
sensitivity. Resist removal is more difficult probably as a result of that. Water will tend to bead up on the resist and wet the copper. So, after development, I look at the board carefully under running water to see if all of the resist that should have been removed was removed. If not, I will try more dips in the developer or even increase the amount of NaOH or KOH very carefully. If you cannot get the resist off, you probably have a lost board at that point. Increasing UV exposure time for another board might help. I do not think you can effectively re-expose a board that has been put into developer, although I have never tried it.

2) After it looks like the resist has been removed properly, I heat the board with an air blower or in the oven until the remaining resist becomes glossy. This step may seal very small pin holes. I think it gives a smoother edge to the traces.

3) I then place the board in ferric chloride etchant, and after a short time, check it to be sure the copper is etching. It will have a distinct appearance. If it is not etching, I rinse and try re-developiong it in a stronger developer. It is probably ruined anyway, so I am pretty liberal in adding additional NaOH. Then repeat step 2.

4) I aggitate the boards constantly in the etch tank and keep it at about 60 to 70 degrees C.

I have not had problems with boards up to the size you mention. The edges tend to etch faster than the center, but the constant aggitation helps a lot.

John
 
Electronics4you said:
Hi there

I have made a couple of PC boards like I normally do, but this time they were awful. The etch solution etched the already etched traces and made large holes in it. I think it's because I normally just do smaller board under 10x10cm, but now it's a 16x10cm. What can I do to avoid this? More UV, more developing, hotter etch solution...?

The Size of the board shouldn't matter at all. I do all dfifferent board sizes.

It sounds like either the board wasn't Properly coated, OR you used too Long of an Exposure Time.
 
I just tried something cause it could be anything. I raised the temperatur, lowered the exposure time and developed for a bit longer than usual. Then I also aggitated more in the etch solution than normally. The result were absolutely perfect PCB with fine edged traces.

Thanks for the help
 
So rough edges are caused by the etching taking a long time due to the solution not being warm enough? I am using Ferric and that happened to me as well.
 
Avoid Too Long of a Developing, as it will eventually Weaken the resist on the Traces.

After Developing the Board, I usually take a little Deluted Hydrochloric acid and wipe the Board with it.

The Unprotected copper will come up BRIGHT AND SHINY, showing how well the resist coating is.
It will also show Bad Spots in the resist.

If the Developing Wasn't Completed Enough, this will also show up. If you Rinse it off in water, you can just develope it a bit more, than check it again with a little more HCL.

When your satisfied its OK, just rinse it in cold water to remove most of the acid and proceed with the etching.

COLD Ferric Chlorde will take a Long time to etch and Results in Under-Cutting at the edges of the traces.

Ideally keep the Ferric Chloride at 120 to 150 Degrees Fahrenheit. (Quite Hot to touching it.)
 
The simplest way to heat it is using a 'double boiler' method. Like submersing the chemical tank in a second tank of heated water. Some people say fish tank heater work well too as they're enclosed in glass.
 
I have a flat tray and point one of those 300W halogen floodlights onto it. Works great with horizontal trays but if it's a plastic tray you must be quite careful not to melt it. Clear plastic is much better than dark plastics. You wanna monitor the etchant temp too, it's possible to get it too hot and it will fume.
 
I had a problen with my develpoing solution.
As it's developing the board, the solution gets dirtier and weaker.
Your board make look like it is developed but may still have a very thin film of resist still on it.
Thats why some spots seem to etch quiker than other spots.

I usually finish developing with another fresh batch of developing solution.
 
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