PCB expousre

[Chris]

Is it possible to use any other types of light sources than a UV lamp for exposing fotoresist PCBs?
If so, what is the recomended expousure time?

Thanx

[Possum]

I've used a 150W or so halogen desk lamp on full brightness a few inches from the PCB with great results. The boards were the presensitized ones sold at PartsExpress.com. Exposure time was about 10-15 minutes, but I think even 8, as written on the board packaging, would've been fine.

[audioPT]

My post is only to remember you that a good source of UV light can be obtained by direct sunlight

There are a lot of people making PCB's by this way in the world

Regards

Pedro Martins

[AuroraB]

The photo material used on PCBs is designed to accept what is known as "actinious " light, with a wavelength of appx 370-380 nM. Although other light sources as e.g. sun light will or may work, you are best off with buying specialy deisgned lamp sources. A tip- light bulbs sold as disco black lights will also work...

[audioPT]

Ok!

Check my UV page (you may need altavista to translate)

The 4 lamps cost me 35€.

I think it's cheap making PCB's with UV lamps...

[Devil_H@ck]

Originally posted by AuroraB
A tip- light bulbs sold as disco black lights will also work...

These lamps will NOT, I repeat, NOT work! Save yourself the trouble of going back to the store to ask your money back.
Black lights emit UV-B light if I remember correctly, the UV light needed for PCB boards is UV-A.

Lamps that can be used for this are lamps from a tanning device.
This is probably the cheapest way to get good lamps. Just go to a recycling store and buy yourself a tanner (correct word?).

I bought myself a tanner with 6 UV lamps in it for only 5€! It works great and it's so big that if I wanted to I could make PCB's of 1.5m * 50 cm .

[jackinnj]

8 minutes

about 5 years ago I took a photographic densitometric step tablet and used it to measure the optimal exposure -- for my light box (which also serves as a light table for examining negatives) it turned out to be 8 minutes

developing is a little trickier -- if you are using NaOH you should play around with various time and temperature combinations -- if you are using a less polar developing agent it becomes less critical. in the U.S. I have used drain cleaner when (Drano) when I ran out of NaOH.

you can do the developing using a red safelight -- then examine the board under white light turned on for a few seconds. if you are using NaOH wear rubber gloves.

[sam9]

The presensitized posative process PCB sold by PartsExpress will form a nice image with just an ordinard 100W bulb hung in cheap relector about 12 inches above the board. Exposure time 7- imutes. With boards larger than 5in x 5in it works better to hang the lamp a bit higher and expose a bit longer. Use an inverse square calculation to estimate the time when hanging higher.

I've done enough boards this way that i've lost count.

[Christer]

Has anybody tried daylight tempered fluoroscent tubes
(5500 K)? I have both a light box with them for sorting slide
fillm and two larger ones in the ceiling over my painting easel.
Actually, I also have a light therapy panel, which is probably
even somewhere around 6500 K.

[cm961]

I just recently got a flourescent daylight bulb. It fits in a normal light bulb socket and is rated at 23W. It is very bright, like you can face it towards the opposite wall and still read a book no problem. The last board I made I mounted the light 7 inches above the board and exposed for 6 minutes, but I overexposed it. I'm not sure if it was due to too much exposure time or the fact that my crappy ink jet printer didn't get the transparency mask dark enough. I think its the latter. I've tried to run the transparency through the printer a few times, but often it doesn't line up correctly and totally ruins it. Unfortunately as far as making boards goes, I've never had much luck although I've done a few correctly. I've wasted so much money, but I see no other option. Hopefully I'll develop a technique that works, because my next board will be a double sided one too.

Pete