Alumina Substrate

Why alumina?

No.

John

Because of it's dielectric properties. What else would you suggest that would give me Er = 10?

Andrey

Does it have to be a solid?

Er=10 at a quarter inch thick must be some interesting application.

John

Rogers RT/Duroid 3210.

There are several other boards the have a dielectric constant of 10. Some of the substrates are ceramic substrates, copper conductors, and aluminium bonded to the ceramic for heat conduction. No need for

The matt stuff is easily machineable.

If you absolutely must use alumina ceramic, the usual method is laser drilling is CO2 laser. Ceramic is opaque to IR light:

However, drilling through 0.25" thick is going to cost plenty.

What do thay use to sharpen drills? :)

I have a pair of those sharpening sticks with a V.

greg

We built a precision electromechanical measurement system (a magnetic field mapper, actually) on a big slab of granite. It was a nightmare to drill. Next one, we used Corian.

John

I used some 1-inch square x 12 inch long alumina rods for optical waveguide modelling a few years back. Worked great.

Cheers,

Phil Hobbs

It is quite easy, actually, provided you've got enough diamond drills and the bank account to match.

Jim

-- "It is the mark of an educated mind to be able to entertain a thought without accepting it." --Aristotle

Probably still much cheaper than Rogers?

It ain't easy. OTOH I was involved in the design of lots of hybrids (not the cars...) in the late 80's and early 90's. Cost was remarkably low, and we did have numerous vias on each. One factory was particularly spooky. Only emergency lighting, everything was dim, all the machines humming, barely any personnel. It was almost frankensteinisch.

Somehow hybrids fell from grace in the industry shortly thereafter. I still miss active laser trimming. You could do RF stuff that's nearly impossible today. The good old days.

When I was making hybrids (back in the dark ages :-) we _punched_ holes in the "green" alumina, _before_ firing. Drilling/lasering is a royal pain-in-the-ass.

Holes were primarily to attach lead frames, since components were "chip-and-wire".

...Jim Thompson

Hmm, ok, mine were in Europe. All were double-sided and the back side was usually ground. RF stuff so I needed lots of vias. Every time I asked about the extra cost if I did two more here and another via there the answer was that it doesn't matter much.

The active laser trim was a whole 'nother matter.

You don't need location accuracy for via's like you would for a multi-pin thru-hole device.

For trimming I used mostly thick-film resistors with automated sand blasters. I had a scheme where I trimmed active filters to precision center frequencies by probing them with an extra circuit that turned them into AGC'd oscillators... output fed into a counter... voila!

...Jim Thompson

Yeah, those were the tricks. But we always used laser trimming. Optimizing the cut pattern was paramount because every seconds on the laser station cost a lot.

And used less power than a supercomputer!

Ever looked at microwave ceramic resonators? They're slick. The lower-frequency ones are tiny shorted coaxial transmission lines, with amazingly low prop velocities... a 600 MHz resonator is about an inch long. The hf ones are little aspirin-looking things you put on a pc board and run traces past. They have huge Er's, in the thousands, very high Q, and tc's not a lot worse than quartz crystals.

PLZTs have interesting optical properties, too. I have a friend who has a bunch of interesting patents for using them as attenuators, modulators, and beam deflectors... but no commercial luck so far.

John

Surface mount has pretty much killed hybrids.

You can buy surfmount laser-trimmable resistors and caps.

John

Presumably:

Hope This Helps! Rich

Sure, except that many of those active laser trim stations are now gone. Plus you can't get trimmable inductors/resonators/stubs/baluns. The degrees of freedom one could enjoy on a hybrid was tremendous. A totally different design philosophy.

Of course now they'd probably argue that laser trimming fumes contribute to gloabal warming.