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Hello....
After long time I got time and stuff to check thing about this topic.
I had some liquid photoresist (similar to positiv 20) produced localy. I smear it to test board and dry it.
After that I put 50mW/405nm laser on stand to get same height all the time and focused to have spot under 0.1mm. The shape of laser is not round as if I move in one direction the width is 0.06 and perpendicticular is 0.98mm. So I just moved by hand test sample under the beam with aprox 2cm/s and 5cm/s. After developing I got clear trace. So system works and speed can be higher too.
If I got laser out of focus to have 0.5mm spot the photoresist is not developed.
In same sample I do 3W UV led test too. I just put LED few mm over the board (had some plastic with 8mm hole under) and does "flash test" with 0.5, 1,2,3,4,5,10,20,30 second turned led on. Only 0.5s sample is not developed! the 1s has blury edge all other are perfect!!! So with little focusing should be nice too.
So both things works.
for laser the width is under 0.1mm (need litle better lenses that my module have) and to correct astigmatism. At my opinion this system is best suited for raster scanning of pcb.
Led can develop 8mm thick line with no problem but need lower speed. With vector scanning this method should work faster. As only "gaps betwen traces" should be developed it should be quite fast. (at least my boards have all unused space connected to ground polygon).
Need to got some lenses with wery short focal point to try to "colimate" LED.
And I do yet another test. I buy UV solder resist (green) to and do same test. Both Laser and UV led does polimerize the photoresist!! So same system can do both. (and same timing seem to be needed!)
Does someone know how to colimate led?
---In homebrew_pcbs@yahoogroups.com, <eslavko@...> wrote:I had ordered
http://www.ebay.com/itm/221248115201?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649
and this should match my photoresist. They are marked as peak
sensitivity at 400nm. So this led should bje just right (and blueray
laser at 405 too)
Will check...On 09/18/2013 01:06 PM, Robin Whittle wrote:
> A further correction . . . The LED I bought was advertised
>
> http://www.ebay.com/itm/120896174810
>
> as:
>
> 380 to 385nm
> 1000mA
> 9 to 11V
> 900 to 1100mW output
>
> actually has a peak output at 394nm. I measured it with a monochromator
> from an old spectrometer. The monochromator reads correctly within 1nm
> for both a 532nm green laser and for the 404.7nm mercury emission line,
> so I think my reading is reasonably accurate. Half power was +/- 6nm.
>
> When I wrote my first message I thought this was probably the same as an
> identical-looking device for which there is a little more data:
>
>
> http://www.leds-global.com/ultra-violet-380nm-high-power-led-modules-p-7.html
>
> 375 to 385nm
> 1050mA
> 10 to 12V
> 400 to 500mW output
>
> However, there is a serious mismatch in the specified output.
>
> This LED runs at almost 10 volts with 1 amp, which matches the eBay
> specification exactly, but would be at the low end of the range for the
> p-7 device above. The shorter the wavelength the higher the voltage, so
> this is consistent with the eBay specification being for a LED with a
> longer wavelength than "380 to 385nm".
>
> I think the eBay LED is a closer match for this one:
>
> http://www.leds-global.com/uv-10w-390395nm-high-power-led-p-146.html
>
> 390 +/- 5nm
> 1050mA
> 9 to 10V
> 800 to 1000mW
>
> I don't have a chart for the wavelength sensitivity of Riston - I was
> referring to:
>
>
> http://www2.dupont.com/Imaging_Materials/en_US/assets/downloads/datasheets/mm500series.pdf
>
> which states that the "peak response" of the material is 350nm
> (nanometre) to 380nm.
>
> I was keen to get a high powered LED with as short a wavelength as possible.
>
> While I may have paid more than I needed to for a 395nm LED, the good
> news is that Riston seems to respond just fine to 394nm.
>
> Searching eBay for UV LED 10W 395nm I find various cheaper LEDs, but
> 395nm is not their center wavelength - they are typically 395 to 405.
>
> There are likely to be uncertainties regarding the actual wavelength of
> LEDs vs. how eBay seller advertise them. However, if a 3 minute
> exposure is OK at 30cm, which is fine for small PCBs, then I think a 3W
> 390 to 395nm LED would be a good, inexpensive, choice.
>
> For instance, this supposedly 3W 390 to 395nm LED:
>
>
> http://www.ledfedy.com/products/1-500w-led/3w-led/3w-uv-led-390-395nm-double-chips-with-star-pcb-1492.html
>
> costs USD$4.69 - not counting postage.
>
> A LED like this would be easy to run - just get a 12 regulated power
> supply and choose a resistor which drops (12 - 3.3) volts at 0.7A = 12
> ohms. The LED would need a heatsink and the resistor would dissipate
> about 6 watts.
>
> - Robin
>
>
>
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>
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