Homebrew PCBs

None of the Chinese suppliers I've used ever publish details like 
wavelengths or even instructions. I guess with the language barrier they 
figure if you don't already know what you're doing they can't help you.

I use a mercury-vapor UV bulb for PCB exposure work (both photoresist and 
solder mask)

http://www.elightbulbs.com/catalog_product.cfm?source=NexTagCSE&prod=SL69444

My exposure box has the bulb about 10" from the board with some 
first-surface mirrors to reduce wasted energy. This kind of bulb has a 
borosilicate glass envelope to filter out the harmful UV spectra. A mercury 
vapor lamp transmits in several bands, including 184.45nm, 253.7nm and 
365.4nm in the UV band. The glass envelope blocks most of the radiation in 
the shorter wavelengths, leaving the 365.4 band to do the work. 404.7 is 
visible violet light. The shorter wavelengths are the ones that will damage 
your retinas if exposed.

I suspect the UV sensitivity of the PCB materials is not an extremely narrow 
band, and so most UV from visible violet down to the harmful range will 
work. My exposure time for both resist and solder mask is about 3 and a half 
minutes. I use the blue dry film negative photoresist and the liquid solder 
mask mentioned earlier in this thread. I've tried the green and the white, 
and have some blue now but have not yet tried it. The key to success with 
the solder resist seems to be getting as thin a coat as you can use. The UV 
does NOT penetrate very deep at all. I've taken finished boards and placed 
them in the Arizona sun for half an hour and was still unable to cure the 
ink where it was too thick.

I've seen exposure boxes made from UV LEDs, UV fluorescent tubes and regular 
fluorescent tubes. And there's always the sun. I used that for quite a while 
but got tired of trying to figure out the effects of clouds.
--
Phil M.

----- Original Message ----- 
From: "Kirk McLoren" <kirkmcloren@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Saturday, June 29, 2013 3:55 PM
Subject: Re: [Homebrew_PCBs] Re: shelving vinyl toner transfer


http://www.ebay.com/itm/High-Power-5w-uv-led-chip-395nm-Factory-price-ROHS-/221247492077?pt=LH_DefaultDomain_0&hash=item338360cfed


will 395nm uv do it? What is the specd wavelength for the resist?







________________________________
 From: Gustavo Villada <villada@...>
To: Homebrew_PCBs@yahoogroups.com
Sent: Saturday, June 29, 2013 8:40 AM
Subject: Re: [Homebrew_PCBs] Re: shelving vinyl toner transfer




On Sat, Jun 29, 2013 at 12:45 AM, James <bitsyboffin@...> wrote:

> **
>
>
> On 29/06/13 14:47, Terry wrote:
> >
> > So, to clarify, are you saying to spread the ink on the board, then
> > cover with cellophane? Then while still wet, place the mask and expose?
> > .
> >
> >
> >
>
> Yes that's correct.
>
> Thin layer of the ink (paint, whatever you want to call it), cover it
> (still wet) with your cellophane (or other suitable plastic which
> works), put your artwork against the cellophane, expose for XX minutes,
> remove artwork, peel off cellophane. The unexposed areas (black in your
> artwork) will be wet and simply wipe clean, the exposed areas will be
> cured hard like epoxy.
>
> The ink is cured (dried and hardened) by UV, drying it any other way is
> virtually impossible, and just makes it really hard to remove the
> unexposed areas afterwards.
>
> The cellophane (whatever) covering serves two purposes, one it keeps the
> ink off your artwork, and two it seals the ink against air while you are
> exposing it - air inhibits curing.
>
>
I test today and work fine, but I'll need to buy a couple of UV tubes since
this winter is raining a lot :(

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[Non-text portions of this message have been removed]



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