Homebrew PCBs

Just something else that occured to me in regards to MV bulbs put to use for photoresist.
If you want to find them cheap/free make friends with some local reptile owners.  Many of us
use them for the UVB that they emitt for a number of reptiles that require UVB for Vit D3 
systhesis.  The kicker is that UVB levels drop off to a point of being of no use for us
and as a result have to be replaced.  However, they should still emitt plenty of UVA which would
longer wavelength UV.

  Also beware of the self ballasting MV bulbs.  I know of several people
that have had issues with them since the filaments tend to be quite fragile, especially when hot.
I have yet to hear of someone experiencing a failure with an externally ballasted bulb though.


  ----- Original Message ----- 
  From: Leon Heller 
  To: Homebrew_PCBs@yahoogroups.com 
  Sent: Monday, September 25, 2006 2:26 AM
  Subject: Re: [Homebrew_PCBs] UV Light Sources


  ----- Original Message ----- 
  From: "John Craddock" <John.Craddock@...>
  To: <Homebrew_PCBs@yahoogroups.com>
  Sent: Monday, September 25, 2006 3:35 AM
  Subject: RE: [Homebrew_PCBs] UV Light Sources

  >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?

  It's a lot better (much shorter expoosure), but needs to be a long way from 
  the PCB/artwork for good collimation (something like 1 m, IIRC). I've got 
  some similar sodium lamps that can have the outer envelope removed. The 
  ballasts can be difficult to find. For accurate exposure I think you need 
  some sort of shutter arrangement as they take some time to warm up.

  Leon 



   


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