That's quite a difference from what I knew, thanks! On Mon, 17 Apr 2017 05:17 Andy Bardagjy, <[email protected]> wrote:
> Synthetic sapphire has come down in price quite a bit, a 25mm dia 5mm thick > sapphire window can be had for just $71 > > https://www.thorlabs.com/thorproduct.cfm?partnumber=WG31050 > > Andy ◉ Bardagjy.com <http://bardagjy.com/> ◉ +1-404-964-1641 > > On Sun, Apr 16, 2017 at 12:03 PM, Scott Stobbe <[email protected]> > wrote: > > > As a practical aside regarding surface resistance, ignoring guard > > amplifiers and guard traces, the historic solution is to point to point > > wire in air. With some designs using Teflon standoffs for a more rigid > > approach. Some of this can still be seen today, your smoke-detector > likely > > has a one-layer phenonlic PCB with the sense pin of a DIP package IC bent > > up off board and point-point wired in air to the Ion chamber. > > > > On Sun, Apr 16, 2017 at 1:25 PM, [email protected] <[email protected]> wrote: > > > > > Possibly Macor (machinable ceramic) from Corning, or the comparable > > > Vitronit, which are both glass ceramics. > > > > > > Comparable to borosilicate glass. > > > Extremely machinable (HSS or carbide tools, use proper speeds and > > > coolant), continously stable until 800°C. > > > No safety concerns or toxic effects. The dust created when machining > can > > > be an irritant. > > > > > > Available from Corning as standard size maxi slab of 36*36*6 cm. > > > Price = ? > > > > > > Quoting Wikipedia for technical data for Macor: > > > --- > > > Density: 2.52 g/cm³ > > > Young's modulus [GPa @ 25°C]: 66.9 (FR4 = 21 - 24, Aluminium = 69, > Steel > > > = 200) > > > Specific stiffness [E6 m²/s²]: 26.55 (Al = 26, Steel = 25 +/- 0.5) > > > Poisson's Ratio []: 0.29 (FR4 = 0.118 - 0.136, Al = 0.32, Steel = > > > 0.27-0.31) > > > Thermal conductivity [W/(m*K)]: 1.46 (FR4 ~ 0.3 - 1, Al ~ 300, Steel ~ > > > 15-50) > > > compressive strenght [MPa]: ~350 > > > Electrical resistivity [Ohm*cm]: 1 E17 (FR4 = 1 E14, PTFE = 1 E23 to 1 > > E25) > > > Coefficient of thermal expansion [E-6 m/(m*K)]: 9.3 (FR4 ~ 13 , Copper > = > > > 16.6) > > > > > > Firat > > > > > > > > > Am 16.04.2017 um 13:08 schrieb John Devereux: > > > > > >> > > >> Hi Chuck > > >> > > >> But the context is "PCBs with ceramic substrates". Are any of *those* > > >> tough? They may well be, perhaps you know of some? It does not help us > > >> with the subject much if there are ceramics with these amazing > > >> properties if they are not available as PCBs. > > >> > > >> There is also the question of exactly what properties of FR4 are > > >> limiting for "metrology" use. > > >> > > >> John > > >> > > > > > > _______________________________________________ > > > volt-nuts mailing list -- [email protected] > > > To unsubscribe, go to https://www.febo.com/cgi-bin/m > > > ailman/listinfo/volt-nuts > > > and follow the instructions there. > > > > > _______________________________________________ > > volt-nuts mailing list -- [email protected] > > To unsubscribe, go to https://www.febo.com/cgi-bin/ > > mailman/listinfo/volt-nuts > > and follow the instructions there. > > > _______________________________________________ > volt-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. > _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
