Perspex or Glass for UV Cover?

J

John Dough

Guest
Hi all,

I'm busy building a UV box for photosensative PCB's

I've read various posts about how you shouldnt use glass to cover the
artwork as it stop UV rays. I've also read a few post where they say don't
use perspex - use glass!

Which is it :)

Is anyone using glass successfully? Or is perspex better? Or nethier - is
there something else I should look at?

Thanks
 
real question; What are you using for a light source ? A Blacklight bulb
with a UV max at ~ 360 or a Germicidal bulb with a UV max ~ 254 nMeter
wavelength. Without a spectrophotometer, to verify bandpass, easiest trick
is to use some of your UV sensitive material and run some test strips with
and without glass and or perspex and see if it changes the exposure time.

After you gather that data, it doesn't really matter what the wavelength or
cover material is . It either works or it sort of doesn't.
BTW Perspex is a ARCHAIC trade name for a Polymethacrylate plastic now
usually called Acrylic and often replaced with Polycarbonate or Lexan and
sometimes with polyethylene terapthalate.or even Polystyrene. So just
because it clear and it is made of a rigid plastic and not glass does not
mean it will behave like Perspex.

Same story with "Glass!!, After all , both types of UV Lamps are made of
"GLASS". Most comercial glass is a Soda Lime Silica glass and will block
Short-Wave 254 nMeter UV. light. Germicidal UV lamps are constructed
with a High Silica or Quartz glass envelope. This is why an ordinary light
bulb is "Safe" from a UV hazard point of view, (soda-lime glass envelope)
but Quartz Halide bulbs must be operated with an appropriate UV Shield in
place. The high operating temperature makes the Quartz glass envelope
necessary but a soda-lime glass filter must now be ftted to block the
excessive amounts of UV being generated. Ordinary incadescent lamps are
cheaply manufactured using a soda-lime based glass which fortuitously blocks
any shortwave UV that is generated..

In summary you are going to have to run test strips anyway no matter what
you are told. So take everything with a grain of salt . NB. Some UV
Photo-sensitve materials materials react better to Longer Wavelength UV than
Short (254)nmetersUV.

Yukio YANO
VE5YS


"John Dough" <1@2.3> wrote in message
news:59idnUxxlt0jNcjcRVn-ig@is.co.za...
Hi all,

I'm busy building a UV box for photosensative PCB's

I've read various posts about how you shouldnt use glass to cover the
artwork as it stop UV rays. I've also read a few post where they say don't
use perspex - use glass!

Which is it :)

Is anyone using glass successfully? Or is perspex better? Or nethier - is
there something else I should look at?

Thanks
Click to expand...
 
Thanks for the detailed reply. I'll try one and see how it works :)

"Yukio" <yano@shaw.ca> wrote in message
news:2Ur5d.107968$%S.46247@pd7tw2no...
real question; What are you using for a light source ? A Blacklight bulb
with a UV max at ~ 360 or a Germicidal bulb with a UV max ~ 254 nMeter
wavelength. Without a spectrophotometer, to verify bandpass, easiest
trick
is to use some of your UV sensitive material and run some test strips with
and without glass and or perspex and see if it changes the exposure time.

After you gather that data, it doesn't really matter what the wavelength
or
cover material is . It either works or it sort of doesn't.
BTW Perspex is a ARCHAIC trade name for a Polymethacrylate plastic now
usually called Acrylic and often replaced with Polycarbonate or Lexan and
sometimes with polyethylene terapthalate.or even Polystyrene. So just
because it clear and it is made of a rigid plastic and not glass does not
mean it will behave like Perspex.

Same story with "Glass!!, After all , both types of UV Lamps are made
of
"GLASS". Most comercial glass is a Soda Lime Silica glass and will block
Short-Wave 254 nMeter UV. light. Germicidal UV lamps are constructed
with a High Silica or Quartz glass envelope. This is why an ordinary
light
bulb is "Safe" from a UV hazard point of view, (soda-lime glass envelope)
but Quartz Halide bulbs must be operated with an appropriate UV Shield
in
place. The high operating temperature makes the Quartz glass envelope
necessary but a soda-lime glass filter must now be ftted to block the
excessive amounts of UV being generated. Ordinary incadescent lamps are
cheaply manufactured using a soda-lime based glass which fortuitously
blocks
any shortwave UV that is generated..

In summary you are going to have to run test strips anyway no matter what
you are told. So take everything with a grain of salt . NB. Some UV
Photo-sensitve materials materials react better to Longer Wavelength UV
than
Short (254)nmetersUV.

Yukio YANO
VE5YS


"John Dough" <1@2.3> wrote in message
news:59idnUxxlt0jNcjcRVn-ig@is.co.za...
Hi all,

I'm busy building a UV box for photosensative PCB's

I've read various posts about how you shouldnt use glass to cover the
artwork as it stop UV rays. I've also read a few post where they say
don't
use perspex - use glass!

Which is it :)

Is anyone using glass successfully? Or is perspex better? Or nethier - is
there something else I should look at?

Thanks
Click to expand...
 
I use standard window pane glass to keep the artwork flush with the
PCB and have not had any problems.

Eric N7DLV


"John Dough" <1@2.3> wrote in message news:<59idnUxxlt0jNcjcRVn-ig@is.co.za>...
Hi all,

I'm busy building a UV box for photosensative PCB's

I've read various posts about how you shouldnt use glass to cover the
artwork as it stop UV rays. I've also read a few post where they say don't
use perspex - use glass!

Which is it :)

Is anyone using glass successfully? Or is perspex better? Or nethier - is
there something else I should look at?

Thanks
Click to expand...
 
With UV rays, glass will subdue their intensity, or filter them out.
Plexy-glass, or acrylic will let them pass with not too great a loss,
but will degrade over time from exposure. Some types of plexy-glass
and acrylic, may become opique or less transparent after a while. The
stronger the intensity, and the more exposure, then the greater the
rate of these materials being damaged.

In UV systems where there is a transparent plate between the UV lamp
or UV light source and the subject, they use transparent quartz.

The quartz material is not effected, and has very little loss to the
UV rays.

Jerry G.
========


"John Dough" <1@2.3> wrote in message news:<59idnUxxlt0jNcjcRVn-ig@is.co.za>...
Hi all,

I'm busy building a UV box for photosensative PCB's

I've read various posts about how you shouldnt use glass to cover the
artwork as it stop UV rays. I've also read a few post where they say don't
use perspex - use glass!

Which is it :)

Is anyone using glass successfully? Or is perspex better? Or nethier - is
there something else I should look at?

Thanks
Click to expand...
 
"John Dough" <1@2.3> wrote in message news:<59idnUxxlt0jNcjcRVn-ig@is.co.za>...
Hi all,

I'm busy building a UV box for photosensative PCB's

I've read various posts about how you shouldnt use glass to cover the
artwork as it stop UV rays. I've also read a few post where they say don't
use perspex - use glass!

Which is it :)

Is anyone using glass successfully? Or is perspex better? Or nethier - is
there something else I should look at?

Thanks
Click to expand...
Glass on my UV box works just fine.
I also get sunburned from the UV though my car windscreen just fine as well.

Dave :)
 
It depends on the type of glass and the frequency of the UV.
However, as a guide, 1/8th inch normal window type glass will attenuate
the UV used for photographic work by about one third. So it will work
quite well with circuit boards. You would get the same sort of loss
with an aged UV tube.

Note also that the cheaper UV tubes used for this type of work are
simply fluoro tubes without the phosphor - and they use glass not quartz
for their tube.

David L. Jones wrote:
"John Dough" <1@2.3> wrote in message news:<59idnUxxlt0jNcjcRVn-ig@is.co.za>...

Hi all,

I'm busy building a UV box for photosensative PCB's

I've read various posts about how you shouldnt use glass to cover the
artwork as it stop UV rays. I've also read a few post where they say don't
use perspex - use glass!

Which is it :)

Is anyone using glass successfully? Or is perspex better? Or nethier - is
there something else I should look at?

Thanks


Glass on my UV box works just fine.
I also get sunburned from the UV though my car windscreen just fine as well.

Dave :)
Click to expand...
 
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