Those are interesting thoughts on LED light boxes. I had the idea some
time ago ,but my preliminary calculations showed that my 400W mercury
vapour light box would give lower undercut than 20 degree LEDs. I'd love
to chuck that old heavy thing away and replace it with an
environmentally friendly shoe box size exposure unit.
Now you mention +-8 degree LEDs are available, then I might re-consider
the project.
Off ebay you can get bulk +-10 degree UV LEDs really really cheap
http://cgi.ebay.com.au/SUPER-BRIGHT-UV-3000MCD-VIOLET-5MM-LED-X-100pcs_W0QQitemZ190193336488QQihZ009QQcategoryZ105796QQssPageNameZWDVWQQrdZ1QQcmdZViewItemDoing precise calculations will only give an estimate. The only way to
check undercutting is the test with various exposure times. You run
minimum exposure, and then at increasing times. If the features in the
developed photoresist don't change much between exposure times then you
have a pretty good setup. A microscope helps a lot in diagnosing any flaws.
Adam
javaguy11111 wrote:
>
>
> While searching around I saw the 8 degree LEDs from LEDTronics as
> well. I decided to stick with the 20 degree leds.
>
> I had done a quick calculation for the amount of undercut of 10 degree
> half angle versus 8 degree half angle. This is not taking into account
> the affects that index of refraction would have.
>
> For .0015 resist with 10 degrees gives an under cut of .26 thousands
> of an inch. A 4 degree half angle gives .1 thousands of an inch undercut.
>
> If I could find an index of refraction for the photoresist, then I
> could take that into account as well. The undercut would be a little
> less since the index of refraction(IOR) of resist is greater than the
> IOR of air. If we were taking glass, the angle for 10 degrees would
> reduce to about 7 degrees. Since I expect that the IOR for resist is
> less than glass, the angle would be somewhere between 7 and 10.
>
> After going through all this, my conclusion is that unless I
> eliminate other things that cause scattering such as glass that is not
> optically flat and better masking materials, I would not reach the .26
> thousands undercut of the 10 degree, much less the .1 thousands of the
> 4 degree.
>
> So when I do build my UV LED box, I personally will stick with 20
> degree viewing angle LEDs.