Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

In "Re: das-labor.org UV scanner direct exposure of photoresist", Duane
C. Johnson wrote:

> Where do you get UV SMD LEDs.
> They seem very expensive?
> What wavelength should I look for?

There are multiple types of DuPont Riston, and I guess many other
non-DuPont negative photoresist films with the same or similar
characteristics.

I recently bought some Riston from Martin Dusek in the Czech Republic:

∗ http://myworld.ebay.com/gaminn/
∗ http://www.tech-place.com/content/4-about-us

I bought this item, but via his eBay store:

∗ http://www.tech-place.com/pyralux/23-photosensitive-film.html

It is sold as 20 A5 sheets, but it is actually a single roll 318 x 2000
mm. I wrote about modifying a cheap laminator to laminate it successfully:

∗ http://tech.groups.yahoo.com/group/Homebrew_PCBs/message/30148

The datasheet is:

∗
http://www2.dupont.com/Imaging_Materials/en_US/assets/downloads/datasheets/mm500series.pdf

This states that the "peak response" of the material is 350nm
(nanometre) to 380nm. This is the same as in the other Riston
datasheets I looked at, but I did not look at them all. The shorter the
wavelength of light, the more energy per electron is coupled, so 350nm
light is more energetic than 380nm.

According to:

∗ http://en.wikipedia.org/wiki/Ultraviolet

this is in the "Near UV" (NUV) range. A quick look at:

∗ http://en.wikipedia.org/wiki/Black_light

indicates that fluorescent "black light" tubes emit energy in or near
the 350 to 380nm range. A quick look at:

∗ http://en.wikipedia.org/wiki/Light-emitting_diode

indicates that there are NUV "black light" LEDs which emit in the 375 to
395nm range. "365nm" is mentioned as one such wavelength.

Googling:

∗ LED "365nm"

finds many LEDs. SMT may be harder to get, such as:

∗ http://www.osa-opto.com/uv_light.html

There are more hits searching for:

∗ LED NUV SMT
∗ LED NUV SMD


- Robin


(Asterisks added to thwart Yahoo Groups web archive's gobbling of
leading spaces.)