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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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up vote 7 down vote accepted

can You read German? here 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
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
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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