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In industry, it's common to cut steel using 50-200 W $\mathrm{CO}_2$ laser.

Meanwhile, for making holes in PCB (35 $\mu$m of Cu), DPSS 355 nm laser is usually used and secondary $\mathrm{CO}_2$ to drill through glass.

Why $CO_2$ cuts steel easily, but cannot be used to make holes in Copper?

UPDATE: Will it help to add thin layer of black paint + pre-heat to 200 °C to get through damn 0.035 mm of Cu?

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More to the point: Why does copper reflect CO2 laser light (8-10 µm) significantly better than steel? –  Nick T Jan 11 '11 at 17:34
    
Yes, this is what puzzled me too. Probably that's because DPSS works in pulsed mode, while CO2 is usually constant emission => worse hole quality probably. –  BarsMonster Jan 11 '11 at 17:53

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can You read German? here http://de.wikipedia.org/wiki/Laserschneiden all Your questions are answered. The English pendant is much shorter and does not deal Your problems. In case You can't read that, some short excerpt: Main problem with copper and Aluminium are high reflectivity at 10 µm, the high thermal conductivity and and no "assistance" from oxidation possible. One special problem is "Einstechen" (initial penetration?). I don't know an English expression for that. It is the making of a hole when starting a cut. This is a time consuming step in laser cutting anyhow. Now, making holes in a PCB is more or less "Einstechen" all the time. Georg

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I see... What about silver and gold? Can they be cut by CO2? From what I already see is that there is no oxidation too... –  BarsMonster Jan 17 '11 at 16:28
    
Also, can preheating/painting help? –  BarsMonster Jan 17 '11 at 16:37
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Silver's thermal conduction in even higher than copper's by about 20 %, Gold is about the same as copper. Preheating is limited with a PCB, one could ruin the epoxi resin. Painting? Hmmm, one needed some paint which is "black" at 10 µm! I don't know one. Georg –  Georg Jan 17 '11 at 19:00
    
200C is ok for PCB for long-sessions, and 250C for short ones. As this is 1/5 of the melting temperature, this should help I believe. –  BarsMonster Jan 18 '11 at 4:04
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The temperatures You name are somwhat optimistic. At 200°C even PTFE decays slowly. Look at the figures for wire enamel, even the best are limited to 150°C, epoxi is below that. Of course all that depends on what You define as "long term". –  Georg Jan 18 '11 at 12:57

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