UV light and Developer Problem

[joebanks]

Hello, I’m new here and I am having a problem in making a PCB board.

I use my home made UV light box to expose my circuit design to the PCB board. After warming the bulbs up for 2 minutes I place the acetate design on the glass then place then place the light sensitive copper down then exposed for different times (between 1 to 2 minutes).

The UV Lamp Light is 1 x 36W, with 4 x 9W lamp tubes.

how long should I be exposing for with this wattage?

I take the copper out in a darkroom and put it into the developing solution for a minute, then put it into water. The first time I did this it worked, leaving copper tracks ready for etching.

However, in other attempts when looked at it, it was complete copper.

What am I doing wrong? Any advice would be appreciated. Thanks.

Here’s a picture of the developer:
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.....and two pictures of my lightbox:

**broken link removed**

**broken link removed**

 

[ericgibbs]

hi Joe,
I think your UV exposure time of 1 to 2 mins is too short.

Depending on the the type of photoresist lacquer, it could take 5 to 10 minutes.

If you can, cut some 1 inch squares of lacquered pcb, say about 4 pieces, half cover the surface of the pcb. Piece of tape would do.

Expose each piece for a longer period, starting at 2mins in 2 minute intervals.
This will give you an idea of the correct exposure time.

Then do the same timings with these pieces in the developer solution.

You dont need to work in a dark room, just keep the boards covered before you expose them.

 

[Hero999]

Please do not make duplicate posts or threads, they do not increase your chance of a helpful response but only reduce it, as people get confused and can't always see what others have suggested in the other thread(s).

 

[jpanhalt]

From the looks of your UV box, the lamps may be too close to the board, assuming the glass is right over the lamps. Although the PCBs I use (Injectorall) are not terribly sensitive and require about 15 min with a single 15W bulb, you want to be far enough away so you do not have hot spots of over-exposure and cold spots of under exposed board. My bulb is about 5 inches away, and there is a small difference from edge to edge on a 4" wide board.

My boards do not need to be worked with in a dark room. If yours do, they may be much more sensitive to light and these comments might not apply. My developer is simply 0.5 M KOH or NaOH, which can be done in a lighted room. The exposed immulsion just truns bluish/purple and comes right off. I then rinse in water. You can put it back in the developer, if needed. John

 

[Hero999]

It's been awhile since I did it but I don't remember it taking that long using two 8W tubes.

I don't like the way you've arranged the tubes, the tubes on either side should be more interlocked so there aren't any dark patches.

 

[joebanks]

Well ive done some tests and 5 mins works so the bulbs are in perfect space apart and evenly light the board thanks for the help. the tests really paid off because it seems that i wasnt keeping the pcb in for long enough

 

[picbits]

I normally expose at 6-8 minutes on a twin tube lightbox. If I'm using older photoresist PCB then a bit longer.

 

[jbeng]

I use two #F15T-BL lamps at 4 inches with 1/4" plate glass as the contact frame. My exposure time is 90 seconds when using transparency film and positive pre-sensitized stock from Circuit Specialists. The results are just what I need every time.
Just my $0.02 worth.
Jeff