My results are different. I have built two exposure systems and use boards that are laminated with photo resist by a PC shop in Jamestown,NC. With the 24 inch bulbs from Japan made with optimized dopants for UV, my exposure time at about 4 inches is about 50 seconds. This system required 4 lamps and 4 ballasts which were expensive but work very well. Total cost was around $90. The UV lamps off e-bay cost around $18 for 150 pieces. I made up a board 6X6 and made an array of 10X10 and current regulated each 10 piece row for an additional $2 with SMT devices. I get similar exposures at 6 inches and use much less power, get instant and RELIABLE turn-ons and prefer it for sure. I will provide boards and schematic for $12 if interested.Will include regulator components also.
Ed Smith W4EDS
Spencer, VA
w4eds@... ===============================================================
--- On Sat, 9/5/09, Adam Seychell <a_seychell@...> wrote:
From: Adam Seychell <a_seychell@...>
Subject: [Homebrew_PCBs] exposure sources (was: Solder Mask)
To: Homebrew_PCBs@yahoogroups.com
Date: Saturday, September 5, 2009, 3:35 AM
jcarlosmor wrote:
>
> And by the way, as someone stated, UV Leds are not used for UV curing or
> imaging of PCB processes. If you want to build a real-use UV
> photoimaging box, do not waste money on UV leds. Use blacklight
> fluorescent tubes. They are cheaper, and provide real results. In fact,
> they are used widely in PCB making (However, for fast batch use, there
> is no substitute for high power mercury arc lamps).
>
After experience with both 395nm UV LED and BL tube (spectral peak
365nm) light sources, I would totally agree. The major problem with LEDs
is light non-uniformity and inadequate intensity for solder mask and
positive resists. Only the negative dry film photoresists seem to be
sensitive enough. For some reason, extending the exposure time with LEDs
does not work on these materials.
One would expect excessive light undercut from the relatively wide angle
radiation pattern emitted by an array of BL tubes. In my experience,
0.2mm (0.008") line/spaces are easily achievable. It is critical the ink
side of transparency makes contact with the photoresist. I found the
ratio of maximum/minimum exposure time can be high as 1.5 while still
maintaining an acceptable deviation in line & space widths.
The limit to minimum line & space is not the exposure source, but that
of inkjet printer resolution.
Adam
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