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PCB UV Method Help

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Matthew21

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Hi
I am using a UV SYLVANIA F8W T5 BLB BLACK-LIGHT TUBE I am putting the PCB underneath it with the artwork on top and the glass. I am putting the UV light tube around 5cms away from the PCB and first tried to leave it for 12 minutes, then for around 30 minutes and finally for 1 hour. The picture hereunder is showing the 1 hour result. What am I doing wrong?

I would appreciate your help. Thanks.


https://i55.tinypic.com/14kguwg.jpg
 
hi,
The PCB looks as though the UV exposure is OK, it difficult to be 100% without seeing the pcb artwork itself. I would say 12 mins should be enough.

After you have exposed the PCB film, you are supposed to use a 'developer' solution to remove the exposed sections of the light sensitive film, then use an etchant solution to remove the exposed copper.

Can you explain the steps in the process that you are expecting to happen.??
 
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It does look like the edges of the pcb weren't deburred and this stopped the art image from being 100% on the pcb, another cause is the laser print isn't dark enough so what I do is print 2 images then put one over then stick them with sticky tape ensuring they are purfectly aligned. If I find the UV exposure fails after developing now I thoroughly clean the board and go find some glossy paper and print the image onto that. Iron it on until the image is seen thru the paper then soak it water for about 10 minutes. Gently peel off the paper and rub off all the remaining paper gently under water will leave a good image for etching. If any tracks are missing etc a fine sharpie pen is a good fix as it is also resistant to the ecthant.

Regards Bryan
 
Hi Matthew21,

it looks like you did two or three things wrong.

First: Check the contrast on the film. Pads and traces should be deep black not allowing light to penetrate. If that is the case go with bryan1's suggestion.

Caution: Printers never do two 100% matching prints, prescribed by law (to prevent false money to be printed). If the board size doesn't exceed 160X100mm (6.3X3.9") the prints should match pretty well. If they aren't the same scale start from the center an juggle prints to fit for optimum sharpness before taping them together.

Second: Exposure time should not exceed 240 seconds!

Third: To develop the exposed board use caustic soda (NaOH). Do not use more than 7g for one liter of lukewarm water. When dissolving in water caustic soda develops more heat.

Observe the process closely and remove the board as soon as all contours are clearly visible and the photo resistant layer of the board has dissolved into the caustic soda.
Rinse with water thoroughly to stop further developing.

Forth: Etching test: dunk the board into the etchant for 5 to 10 seconds - remove and rinse. Check for glossy areas on the board. These are under developed areas which won't get etched as quickly as the dull areas. Keeping the board to long in the etchant will most likely result in under etched traces. Use an etch proof permanent marker to correct possible gaps in traces (mostly at bends) and touch them up properly.

Edding 800 and Edding 400 markers are etchant proof. The 800 marker has a coarse tip (0.6 - 0.8mm) and the 400 marker has a fine tip (0.3mm).

Finally, if your budget allows use three CFLs for exposure.

Good luck and regards

Boncuk
 
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