Homebrew PCBs

>> John Craddock wrote:
>>
>>   I read somewhere on the web that a
>> mercury vapour lamp with the outer uv
>> blocking envelope removed gives a very
>> good source of uv light for photo-pcb
>> resist curing. Obviously removing the
>> outer envelope would require that the
>> uv exposure box be totally enclosed when
>> the system is operating. Can any one
>> confirm that this is comparable or
>> better than the black-light fluorescent
>> approach?

> WilliamK wrote:
>   Well mercury vapor bulbs are a popular
> choice for lighting amongst reptile owners 
> because they offer a decent amount of UVB
> that is needed by a number of reptile
> species for proper vitamin D3 production
> but I don't know that it would be enough
> for curing the photo resist.  For that you
> might want to look at the UV bulbs used in
> aquarium and pond UV sterilizers.  They put
> out considerably more UV to the point that
> they can be hazardous if not totally
> enclosed.

Yes the mecury vapour lamps work fine for
PCB resist.  Most expensive comercial
machines use them I think.

They also (as others have pointed out) need
to be run for a while to be up to temprature.

This means you either need to have some kind
of shutter to expose the PCB or as someone
else said (can't remeber who or when) you can
pre-heat them at a lower voltage and then up
the power for the exposure.

The light from them is also more like a point
source.  This has good and bad points.

I good point is that you can more easily
collimate the rays.  Bad point (as Leon-H
pointed out) you need to have the bulb at a
long distance from the PCB.


Fish tank STERILISING tubes are NOT suitable.
They are shorter wave length UV that is both
useless for the photoresist and dangerous.

AFAIK The arc lamps with covers removed also
produce dangerous UV rays as well as the
usefull (for PCBs) rays.

All up - I think that black light tubes are
probably the most convenient and easiest to
setup and use option.

They don't produce appreciable amounts of
dangerous UV.  Several of them in parallel
will put out plenty of UV.  They are easy
to get.  I think the biggest problem with
them is they don't seem to age gracefully
(at least im my experience they didn't)


If you can't get or have surplus arc lamps
then they should be great for PCBs though.