Homebrew PCBs

warrenbrayshaw - Thanks ! indeed the article is very close to what I
was searching.
It seems that the peak sensitivity is around 370 nm and some resists
are better at 405nm. I have found on a forum about using laser diodes
from BlueRay players that they have achieved 60mW and more (depending
a lot on optics used).
In order to see how much time is needed to LDI an pcb we must see how
much time should be exposed. Also on net I have seen that various
photoresists  and soldermasks needs about 100 mJ/cm2 exposure (I have
seen some with 10mj and some with 200mj).

Considering such a laser diode focused on a 0.1 mm diameter spot
(that's other issue because a laser diode doesn't generate a circle
spot)  means = 3.14*(0.05)^2 = 0.00785 mm2 =~
0.008mm2=0.000008cm2=8*10-5 cm2

100mJ/cm2 means equivalent 0.008mj/0.008mm2

0.008mj means 0.008mW-Second. the blueray diode has 60mW this would
mean that it could "expose" 7500 spot's per second.
a pcb of 320mm wide would be exposed with a speed of 0.2mm per second
if the pcb is 320mm long it would take 1600 seconds ~ 27 minutes.
A higher sensitivity resist would reduce the time.

If someone could tell me if I am wrong or what could go wrong in this
calculation please don't hesitate to contribute.
Until now I don't know if it is possible to focus that diode to
0.1mm2. In disc readers the track width it's more narrower.

Regards,
Daniel



--- In Homebrew_PCBs@yahoogroups.com, "warrenbrayshaw"
<warrenbrayshaw@...> wrote:
>
> The following article may be of interest
>
http://www.circuitree.com/Articles/Column/18623649067d7010VgnVCM100000f932a8c0____
>