Homebrew PCBs

Ok, shame on me, I broke the glass in my UV box.  Too much vacuum.
We've checked a few local places, the glass they have has UV blockers
on it.  I've got more places to try, but I thought I'd ask...

What else can be used besides glass, which will still pass UV without
bending or blocking it?  Something less brittle, more flexible, but
still stiff enough to mostly hold it's shape (my UV box has a foam
gasket along the outside edge of a piece of plywood, the glass rests
on it and is sucked down onto the board).

Even rubber-like flexibility is OK, I suppose - I can make a wooden
frame to hold the edges and use an even thinner gasket, but that's
more work, and it means I have to cut up my films into individual
sections so I don't bend or crease them from the shrink-wrap effect.

DJ

The stress concentration in the glass at the corners of the PCB causes breakage when you attemp to suck it down against a rigid backing. Better to suck a flexible membrain against the glass, rubber or polythene. Greenhouse glass works fine.
Polycarbonate block UV so don't use that. 

Malcolm

I don't suffer from insanity I enjoy it!

--- On Mon, 8/16/10, DJ Delorie <dj@delorie.com> wrote:

From: DJ Delorie <dj@...>
Subject: [Homebrew_PCBs] UV: alternatives to glass?
To: Homebrew_PCBs@yahoogroups.com
Date: Monday, August 16, 2010, 9:54 PM







 



  


    
      
      
      

Ok, shame on me, I broke the glass in my UV box.  Too much vacuum.

We've checked a few local places, the glass they have has UV blockers

on it.  I've got more places to try, but I thought I'd ask...



What else can be used besides glass, which will still pass UV without

bending or blocking it?  Something less brittle, more flexible, but

still stiff enough to mostly hold it's shape (my UV box has a foam

gasket along the outside edge of a piece of plywood, the glass rests

on it and is sucked down onto the board).



Even rubber-like flexibility is OK, I suppose - I can make a wooden

frame to hold the edges and use an even thinner gasket, but that's

more work, and it means I have to cut up my films into individual

sections so I don't bend or crease them from the shrink-wrap effect.



DJ



    
     

    
    


 



  






      

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

DJ Delorie wrote:
> Ok, shame on me, I broke the glass in my UV box.  Too much vacuum.
> We've checked a few local places, the glass they have has UV blockers
> on it.  I've got more places to try, but I thought I'd ask...
>
> What else can be used besides glass, which will still pass UV without
> bending or blocking it?  Something less brittle, more flexible, but
> still stiff enough to mostly hold it's shape (my UV box has a foam
> gasket along the outside edge of a piece of plywood, the glass rests
> on it and is sucked down onto the board).
>
> Even rubber-like flexibility is OK, I suppose - I can make a wooden
> frame to hold the edges and use an even thinner gasket, but that's
> more work, and it means I have to cut up my films into individual
> sections so I don't bend or crease them from the shrink-wrap effect.
>
> DJ
>
>   
There used to be (and I assume still is) a clear plastic - acrylic or 
polycarbonate? - that was labeled  UVT for UV transmission or UV 
transparent.  I believe it was made by Rohm and Haas.  TAP Plastic may 
stock it.  A quick Google for UVT Plastic yielded:
www.polymer*plastic*s.com/transparents_*uvt*a.shtml,
plus a bunch more.

Norm
W6NIM

> There used to be (and I assume still is) a clear plastic - acrylic or 
> polycarbonate? - that was labeled  UVT for UV transmission or UV 
> transparent.  I believe it was made by Rohm and Haas.  TAP Plastic may 
> stock it.  A quick Google for UVT Plastic yielded:
> www.polymer*plastic*s.com/transparents_*uvt*a.shtml,
> plus a bunch more.
>
> Norm
> W6NIM
>
>   
Yahoo or someone put **** into the URL. :-(  
Delete all four of them and the link works. :-)

www.polymerplastics.com/transparents_uvta.shtml

Norm
W6NIM

On 08/16/2010 02:17 PM, Norm wrote:

> stock it.  A quick Google for UVT Plastic yielded:
> www.polymer*plastic*s.com/transparents_*uvt*a.shtml,
> plus a bunch more.

Why did you put random asterisks in the URL? The correct one is:

http://www.polymerplastics.com/transparents_uvta.shtml

bye
as

Hmm... my UV box is single-sided at the moment, are you suggesting 
putting the PCB on a rubber membrane, then the film, then glass - and 
letting the vacuum pull the rubber UP to the glass?  That might be 
tricky to get air-tight...

UVT plastics still have considrable absorption at the actinic wavelengths (50% absorption at 275nm), which are the wavelengths of peak emulsion sensitivity. They are used in sunbeds where you don't want the customer exposed to the carcinogenic actinic wavelengths.

Malcolm

I don't suffer from insanity I enjoy it!

--- On Mon, 8/16/10, Alessio Sangalli <alesan@...> wrote:

From: Alessio Sangalli <alesan@...>
Subject: Re: [Homebrew_PCBs] UV: alternatives to glass?
To: Homebrew_PCBs@yahoogroups.com
Date: Monday, August 16, 2010, 10:28 PM







 



  


    
      
      
      On 08/16/2010 02:17 PM, Norm wrote:



> stock it.  A quick Google for UVT Plastic yielded:

> www.polymer*plastic*s.com/transparents_*uvt*a.shtml,

> plus a bunch more.



Why did you put random asterisks in the URL? The correct one is:



http://www.polymerplastics.com/transparents_uvta.shtml



bye

as





    
     

    
    


 



  






      

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

Yes, glue your vacuum connection to the rubber, like an inflatable boat, near the edge seal so that it does not seal like a shut off valve when under vacuum.

I don't suffer from insanity I enjoy it!

--- On Mon, 8/16/10, DJ Delorie <dj@...> wrote:

From: DJ Delorie <dj@...>
Subject: Re: [Homebrew_PCBs] UV: alternatives to glass?
To: Homebrew_PCBs@yahoogroups.com
Date: Monday, August 16, 2010, 10:40 PM







 



  


    
      
      
      Hmm... my UV box is single-sided at the moment, are you suggesting 

putting the PCB on a rubber membrane, then the film, then glass - and 

letting the vacuum pull the rubber UP to the glass?  That might be 

tricky to get air-tight...



    
     

    
    


 



  






      

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

CYTOP has excellent transmission (>95% for a 200um coat) all the way out to 200nm wavelengths.  I'd suggest using it as a coating over your glass to prevent stress concentration of PCB on the glass.  Here's a link to the data sheet which includes the transmission curve as well as all the relevant optical, mechanical, and thermal properties:
 
http://www.bellexinternational.com/products/cytop/pdf/cytop-catalog.pdf
 
 
-Marc

________________________________

> To: Homebrew_PCBs@yahoogroups.com
> From: dj@...
> Date: Mon, 16 Aug 2010 17:40:55 -0400
> Subject: Re: [Homebrew_PCBs] UV: alternatives to glass?
>
>
>
> Hmm... my UV box is single-sided at the moment, are you suggesting
> putting the PCB on a rubber membrane, then the film, then glass - and
> letting the vacuum pull the rubber UP to the glass? That might be
> tricky to get air-tight...
>
>

I think any of these exotic solutions would ruin the "homebrew" aspect 
of my lab.  I was hoping for something from the local store, like lexan 
or plexiglass :-)

Have you considered Saran Original?  (I think it's now called Premium.)  Polyvinylidene Chloride is quite transparent to UV, but I don't know over what wavelengths.  Would you care to report how much your exposure changes from glass to Saran?

Donald.
--
"Plain Text" email -- it's an accessibility issue
()  no proprietary attachments; no html mail
/\  ascii ribbon campaign - <www.asciiribbon.org>

----- Original Message -----

> From: "DJ Delorie" <dj@...>
> To: "Homebrew PCBs" <Homebrew_PCBs@yahoogroups.com>
> Sent: Monday, August 16, 2010 8:50:58 PM
> Subject: Re: [Homebrew_PCBs] UV: alternatives to glass?
> 
> I think any of these exotic solutions would ruin the "homebrew" aspect 
> of my lab.  I was hoping for something from the local store, like lexan 
> or plexiglass :-)
>

Hi,

Have you considered clear acrylic sheets? 
I've been using them for a while on the same UV box that came with normal
glass on it.
The difference is considerable in the UV behaviour. Much better for acrylic.
Flexibility vs. rigidity was solved using a slighter ticker acrylic.

Nuno T.

> -----Original Message-----
> From: Homebrew_PCBs@yahoogroups.com 
> [mailto:Homebrew_PCBs@yahoogroups.com] On Behalf Of DJ Delorie
> Sent: segunda-feira, 16 de Agosto de 2010 21:55
> To: Homebrew_PCBs@yahoogroups.com
> Subject: [Homebrew_PCBs] UV: alternatives to glass?
> 
> 
> Ok, shame on me, I broke the glass in my UV box.  Too much vacuum.
> We've checked a few local places, the glass they have has UV 
> blockers on it.  I've got more places to try, but I thought I'd ask...
> 
> What else can be used besides glass, which will still pass UV 
> without bending or blocking it?  Something less brittle, more 
> flexible, but still stiff enough to mostly hold it's shape 
> (my UV box has a foam gasket along the outside edge of a 
> piece of plywood, the glass rests on it and is sucked down 
> onto the board).
> 
> Even rubber-like flexibility is OK, I suppose - I can make a 
> wooden frame to hold the edges and use an even thinner 
> gasket, but that's more work, and it means I have to cut up 
> my films into individual sections so I don't bend or crease 
> them from the shrink-wrap effect.
> 
> DJ
> 
> 
> ------------------------------------
> 
> Be sure to visit the group home and check for new Links, 
> Files, and Photos:
> http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links
> 
> 
>

Most varieties of acrylic (Plexiglas) have very poor transmission of UV wavelengths below 370nm (i.e. they tend to block the Hg I-line).  If the photoresist that you are using is Hg G-line or H-line sensitive, then most varieties of acrylic will be fine at least initially (they will yellow over time), but if your resist is only I-line sensitive, then the only variety of Plexiglass that would work for you is Plexiglas G UVT.  Here are a couple of data sheets that back this up:

See figure 5 in this sheet:
http://www.plexiglas.com/literature/pdf/81.pdf
 
 
And here is the data sheet for Plexiglas G UVT:
http://www.plexiglas.com/literature/pdf/227.pdf


-Marc

________________________________

> To: Homebrew_PCBs@yahoogroups.com
> From: nuno-t@...
> Date: Tue, 17 Aug 2010 11:44:13 +0100
> Subject: RE: [Homebrew_PCBs] UV: alternatives to glass?
>
>
>
> Hi,
>
> Have you considered clear acrylic sheets?
> I've been using them for a while on the same UV box that came with normal
> glass on it.
> The difference is considerable in the UV behaviour. Much better for acrylic.
> Flexibility vs. rigidity was solved using a slighter ticker acrylic.
>
> Nuno T.
>
> > -----Original Message-----
> > From: Homebrew_PCBs@yahoogroups.com
> >
> [mailto:Homebrew_PCBs@yahoogroups.com]
> On Behalf Of DJ Delorie
> > Sent: segunda-feira, 16 de Agosto de 2010 21:55
> > To: Homebrew_PCBs@yahoogroups.com
> > Subject: [Homebrew_PCBs] UV: alternatives to glass?
> >
> >
> > Ok, shame on me, I broke the glass in my UV box. Too much vacuum.
> > We've checked a few local places, the glass they have has UV
> > blockers on it. I've got more places to try, but I thought I'd ask...
> >
> > What else can be used besides glass, which will still pass UV
> > without bending or blocking it? Something less brittle, more
> > flexible, but still stiff enough to mostly hold it's shape
> > (my UV box has a foam gasket along the outside edge of a
> > piece of plywood, the glass rests on it and is sucked down
> > onto the board).
> >
> > Even rubber-like flexibility is OK, I suppose - I can make a
> > wooden frame to hold the edges and use an even thinner
> > gasket, but that's more work, and it means I have to cut up
> > my films into individual sections so I don't bend or crease
> > them from the shrink-wrap effect.
> >
> > DJ
> >
> >
> > ------------------------------------
> >
> > Be sure to visit the group home and check for new Links,
> > Files, and Photos:
> > http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links
> >
> >
> >
>
>
>

The saran wrap web site says their films are Polyethylene - they removed 
all the chlorine-based variants.

I might try it anyway...