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.
