[volt-nuts] PCBs with ceramic substrates
andy at bardagjy.com
Sun Apr 16 20:16:43 EDT 2017
Synthetic sapphire has come down in price quite a bit, a 25mm dia 5mm thick
sapphire window can be had for just $71
Andy ◉ Bardagjy.com <http://bardagjy.com/> ◉ +1-404-964-1641
On Sun, Apr 16, 2017 at 12:03 PM, Scott Stobbe <scott.j.stobbe at gmail.com>
> 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, fala at gmx.net <fala at gmx.net> 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
> > 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
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