measuring low-value device capacitances

Win, yes, one end of whatever FDC1004 measures is grounded. But its such a lovely little chip when I need measurements for the grad students. The dr iven shield scheme is well executed. The included software in the EVM is fa r better then some expensive commercial data loggers we use...

Again, just an idea...

Steve

Nice probe. I have two of them.

Yeah. There's a power adapter box that lets them work with any 50 ohm scope.

Fet probes are amazing. Capacitance is so low that there's no giant current spikes into the ground clip to cause ringing. They often work with fast signals with no ground clip. Or even without touching the signal to be probed; just get close.

Some Tex scopes have the connector built in, as an option.

I used one at Microdyne to check clock circuits, to prevent stopping the crystal from oscillating on frequency. We had a batch of 32.768 KHz crystals running at the wrong frequencies, or at multiple frequencies that caused the MC68340 MPUs to run at the wrong clock rate.

Update: I've updated the PCB to 89 flip chips, covering all kinds of footprints and measurements. A floating- measurement capability, one of the HP instruments, is required. I thought of adding a bottom-section that includes a capacitance readout, but I'm out of room on total board size (6.5x8.7 inches) for Advanced Circuit's limit for their $33 special.

The same dropbox link should still work.

I'll enterta>

I'd like one. I'll share any electrical (or thermal) measurements that I do.

Thanks

John

OK, John, excellent.

I've made updates, additional test-chips for more transistors, including Phil's RF types, enlarged motherboards, added mounting holes for stability. Lacking more suggestions, Gerbers will go out tomorrow.

Now has 89 flip chips.

The PC boards have arrived. Please see the photo I added to the dropbox folder: RIS-663_chopped-up.jpg

Each 8.7 x 6.5-inch board has 89 test "flip chips" to solder your D.U.T. parts, plus three test boards to connect your capacitance-measuring instrument.

The prototype house charges me an extra $50 because they detect multiple sections, but they don't add scoring or other means to separate them, nor will they let me pay extra for that. Hence you see in the photo our hand-operated shear that I used to divide up 92 pieces for myself.

My question: Do y'all board recipients also have a simple way to make shear 92 pieces, please note: a tin snip won't work? If not, I'm happy to spend 20 minutes to do this before mailing your board(s).

Also, any other takers, last chance!

Also, I don't recommend using a bandsaw. That might be OK for one small cut, but certainly not for 92 pieces. Using our shear instead is a much better way.

Tin snips (the proper scissors kind, not the wonky "aviation snips"

If you have a sander, knocking down the edges by a modest depth exposes clean, solid material, as well as taking off the burrs (which are, in part, loose glass fibers ready to pierce you). You can also take the opportunity to round over the edges.

A bandsaw with a toothed blade, no. Will eat it up in minutes.

OTOH, at a PPoE, they cut a lot of G10 (aka mechanical FR4) for fixtures and electrical insulators. An abrasive cutoff wheel in a table saw makes quick work of rip cuts (just be careful not to let it bind -- the smell of burnt epoxy was a frequent experience..), while an abrasive bandsaw blade makes quick work of curved cuts, or for general rough shaping.

And of course, carbide is fine for machining the stuff, but you want to keep it sharp, and run fast. Your uncle's Bridgeport won't do a pleasant job of it. PCB mills run at >>10k RPM using tiny drills and mills.

Tim

We have a really nice foot shear, but I'm not allowed to use it to cut FR4. We also have a klutzy old rusty hand-operated brake/shear thing that chops up FR4 fairly well (so far.)

My throatless shear tends to bend just like a tin snip. My Dremels run fast enough, but nothing beats my hand held 5" circular saw.

Just clamp down a small piece of angle aluminum to use as a cutting guide and let it rip. It cuts through sheet metal like butter. Metal carpentry at its finest. It's easy precision almost makes me feel guilty about not using the proper metal shop tools for the job. A table saw would make it even easier, but there's no room for it.

Thank you,

I cut FR-4 using some snub-nosed aviation shears with slightly serrated blades, and they work great

Looking forward to trying out the gizmos!

Thanks

Phil Hobbs

I bought a low cost paper shear for cutting 0.8mm FR4 prototypes. works great and does not bend the board much, but I would not cut populated boards.

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something like this would be perfect for fr4

Diamond blade for FR4? A fine-tooth carbide blade should be fine and make a lot less mess (not need water cooling).

That looks good. But not quite as quick as our shear punch.