PCB Fabrication Problems

[remz]

positiv 20 uneven bubbles

Hi all,

First post, so please bear with me if I don't follow your general board guidelines.

I have a modest PCB setup at home using photosensitive boards. These are the symptoms of the boards problems.

1. Not all the copper which is to be removed actually gets etched away (see figure attached).

For the board shown in the figure, it was evident that the copper around the edges was not coming away in a timely fashion, so the board was then placed back in the developer solution for a short while and re-etched. This greatly helped remove the unwanted copper however, by this time, the etchant was also havign a go at the tracks.

Currently, I use 5min for the UV which I have found works well. Around 2 minutes for the developer and the etchant time varies from around 30min - 1h30 and his highly dependant on ambient conditions.

A later board was left in the developer solution for 3min and whilst the effects were greatly reduced, a small patch of copper still remained, again, positioned slightly off the edge.

I will be making some more boards today. What should I do, increase the exposure time or increase/decrease the development time. Currently, the board is kept in the development solution until the tracks are clearly visible...and then a bit.

Regards,

Rem

 

[pakitos]

Hi first you have to be sure that the traces on the transparent paper is black 100%.
put the paper against light there should not be any blank spaces or dust particles.
the time to expose under the uv light is important.

second when you put in the base solution (the % of base and water is critical) leave it there until you see the traces clearly . try to put in a tray and shake the tray so that the solution evenly is distributed do not leave it there. Remove quickly when you see the traces.

clean it with water and put in the acid. Remember your container must have a heater and bubbler. Try to check it once a while so that the traces will not be etched.

Since you are using a simple way, you need to do trials to find your suitable timings.
Good Luck

 

[dindeds]

Probably u can try my method in this thread. Made it in less than an hour.

 

[picnoobie]

I used fluorescent screw on lamp a regular one the household type,
it's longer exposure time 'bout 10-15min, but I get good result, I print
my positive on a clear overhead projector film. A couple times I even tried
printing on a coupon band, but I had to wipe it with oil to make it more translucent.
it also gives good result. it needs good contact on the glass. I'm using scrap flatbed
scanner glass and cover and I put heavy stuff on top of it while exposing.

warm etching solution makes it faster to develop, I use a 100watt bulb under my
etching bath to preheat the solution, I don't have a fancy etching tank just an empty
biscuit container, and still using nasty ferric chloride.
and Oh yeah, I have to shake it once in a while.

 

[the_risk_master]

hi dude, yer board's been soaked too much of UV rays that might have prolonged the exposure. When using the UV for photosensitive PCBs, it ususally just take 60-200 sec. for UV exposure. The photo-developer solution is another factor. I have calculated the best mixture for these, usually a bag (100g) of developer granules are dissolved in 5 cups or about 500mL of water for best results. picnoobie's right, warm solution makes the whole thing a lot better and faster to etch. As I can see, your etchant solution might be weak, leaving unwanted copper. Another thing, you must till the etchant solution while etching (dont leave alone the etchant to etch the board itself) that might eat up the traces on your board!

 

[farhadtehrani]

warm etching solution makes it faster to develop, I use a 100watt bulb under my
etching bath to preheat the solution, I don't have a fancy etching tank just an empty
biscuit container, and still using nasty ferric chloride.

 

[Azaruk]

Exposure time is dependant on several factors. The most important is the wavelength of the light, second is the thickness of the coating, and, of course, what spray you use.

I use Positiv 20, but when my supplier was out of stock, I purchased a spray from Cramolin. The results were terrible, until I read the instructions and discovered that the processes are completely different.

The example you showed, looks to me like uneven spray. The flaw is most likely where the sprayed coating was a bit too thick.

I find that as long as your track density is good (REALLY black!), increasing the exposure will more than likely give a good board.

The previous post suggested a VERY strong developer. I use 5ml (one teaspoon) of caustic soda to one litre of water. (Positiv 20). Cramolin uses 7ml/litre.

As suggested by the other posts, warming the etchant will make the process much quicker, as will bubbles or regular agitation.

 

[Meridian]

Hi all,

I have a modest PCB setup at home using photosensitive boards. These are the symptoms of the boards problems.

1. Not all the copper which is to be removed actually gets etched away (see figure attached).

Currently, I use 5min for the UV which I have found works well. Around 2 minutes for the developer and the etchant time varies from around 30min - 1h30 and his highly dependant on ambient conditions.

Rem

Hi Rem:

Reading thru your post and all the good answers by others given, I have a couple good tips. Some already partly answered.

I use the same method like yours for a good 20 years. However, I invested in a good SunLamp, which is a special lamp (deuteronium I think) of high intensity. I always follow manufacturer's specifications and guidelines at first and then tweek it for my own purpose.

1 - The exposure with the SunLamp is 90 seconds. Overexposure will result in pitted tracks after etching.

2 - Use fresh developer and more importantly, just the correct water/developer mix, 10 parts water to 1 part developer is common I think.
If the solution is too strong *OR* warm, it will weaken the photosensitive coating (film), so make sure your developer solution is COLD! Rinse excessively with cold water when you're done developing which should be at the most 2 minutes or so. Any longer will indicate your solution is 'over-used' or too old.

3- Purchase an aquarium-heater(thermostat) and a aquarium airpump with a bubbler to circulate the etchant. Preheat your etchant to no more than about 35°C. Any hotter and it will take off the film and etch through the copper.
I recommend swithing to Ammonium Persulphate as an etchant. Works much better (heated to 35°C) and is clear so you can see what's going on. Rinse excessively with cold water after you're done. Very important to stop the etching process.

That's basically it. I use a laserprinter and transparancies to make my boards.
I put the transparancy a couple times through the printer to get a real black image. Can be a bit tricky sometimes to position the sheet at exactly the same location, so make a mark somewhere on the transparency and the printer tray to get as close as possible. This will avoid being 'off' by a pixel or so...
And last, don't touch any part of the pcb with your fingers. It results in being unable to etch that part of the board.

If you have more questions, fire away and I will answer them as good as i can.