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

----- Original Message -----
From: "twb8899" <twb8899@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Friday, September 15, 2006 3:27 PM
Subject: [Homebrew_PCBs] UV Exposure system ideas


>
> Here are some additional ideas for UV exposure systems. The UV system
> I use is a Colight DMVL-930 which has two lamps operating at 1500
> watts. The lamps are standard 1000 watt mercury vapor. These lamps are
> mounted vertically with one on top and the other on the bottom. During
> the exposure cycle a capacitor is switched in to over drive each lamp
> to 1500 watts.
>
> Sheet aluminum with a mirror finish is in place on four sides forming
> a rectangular enclosure for each bulb. The aluminum is angled at 45
> degrees to the bulb to reflect the light to the exposure surface.
>
> The exposure frame is 1/4" thick window glass held in a frame that has
> a hinged top. The top section of this frame uses a 10 mil mylar sheet.
> There is a rubber gasket around the edge and a vacuum line is attached
> to one corner. This is the standard exposure frame for double sided
> systems. Sandwich your board between top and bottom artwork films,
> place it on the glass close the mylar top and pull a vacuum. The mylar
> will conform to the board and hold everything in tight contact for a
> perfect exposure.
>
> After the vacuum is pulled this entire frame rolls into the machine
> and is centered between the top and bottom lamps and reflectors. It
> triggers the timer and when the preset time has elapsed the frame is
> released and it rolls out of the machine.
>
> It's really a simple system and a home made system like it could be
> constructed from easily obtained materials. The easiest way would be
> to mount a mercury vapor lamp assembly in a box about 18" to 24" tall.
> At the bottom of this box and at the front edge cut a slot tall enough
> and wide enough to slide in a contact frame for exposure. The lamp has
> to warm up for a few minutes and then runs continuously with the
> exposure time determined by how long the contact frame is slid into
> this light box. It's just that simple. No automation is needed unless
> you want a fancy system. A kitchen timer could be used to time the
> exposure cycle.
>
> Mercury vapor bulbs use quartz glass and emit ozone but this is not a
> problem since the quartz tube is enclosed in a second glass bulb.
> Regular window glass works fine in a system like this. I have never
> had a problem when using regular window glass (untinted) in eposure
> systems.
>
> A friend of mine bought a used mercury vapor lamp assembly with
> reflector for $20.00 and made his exposure unit from that. I laminate
> his boards with dry film photoresist and he gets the same results as
> my commercial exposure unit which is 17 seconds with a 1000 watt bulb.
> We use DuPont 1.5 mil dry film and can easily do 5 mil lines and
> spaces with almost zero defects when using photoplotted films.
>
> Smaller wattage lamp and reflector assemblies are available such as
> the 400 watt types. These would also work but the exposure time would
> be slightly longer.
>
> Another type of lamp to consider is the quartz bulb 500 watt portable
> lamps. These bulbs will expose dry film photoresist but it will take
> about a minute at a 12" distance. With this lamp there would be no
> sliding exposure frame needed as the lamp could be switched on and off
> while the mercury vapor type can not.
>
> Maybe these ideas will help some of you planning to set up a UV system.

I've got some sodium vapour lamps I was intending to use, by removing the
outer envelope. The cat removed one of them for me by knocking the lamp off
the bench and breaking it. I've got some suitable ceramic holders, but need
to get some ballasts.

Leon