We'd like to test 0805 and 0603 surface-mount resistors, at receiving inspection. What would be nice is a really good fixture that we could drop individual resistors into. Some sort of gold-plated (?) spring-loaded or screw-operated blocks would contact the resistor ends and give us a good 4-wire connection, to run to a good DVM.
Any recommendations? My production people are using some dinky thing they got somewhere, 2-wire aluminum connections, fairly useless for low-value precision resistors.
The Farnell catalogue has a couple of pages of "spring contact pins" and "spring loaded contact probes and receptacles" both intended for test fixtures, where you drop a printed circuit board into the fixture and the sprung contacts make electrical contact with copper pads on the printed circuit board.
Presumably the force available is high enough to pierce any crud on the ends of the resistors.The thinnest receptacles might just be narrow enough to mounted close enough together to vertically probe an
0603 chip - to get a four-wire connection you'd either have to angle the probes in or clamp the resistor between two pairs of two-pin probes,
Would that work with 0805 and 0603 parts? Seems like that would be hard to handle. I was thinking it would be easier to pick up a part with tweezers, place it on a flat surface, and close in with the spring-loaded contact blocks.
There are lots of things like this around
where they press the part down onto planar contacts, looks like a PCB maybe. They are not explicitely 4-wire though, intended mostly for microwave measurements. We need something like a few milliohms of contact resistance to test, say, 49.9 ohm 0.05% resistors. Doesn't look speedy, either, not too well suited to receiving inspection.
Most shops, and I assume yours included usually have means of doing small machining and fabing of special tools and jigs. Or at least you can get your hands on some one that does. Why don't you simply make an automation set up?
Not to long ago I did do such a thing using standard industrial PLC controls for an in-house testing unit as one of my consulting side jobs.
Of course the software maybe a little challenging which I wrote in Delphi to operate the visual camera so that I can move the chip caps around into place via a small X,Y axes arm with a miniature vacuums suction finger. All they had to do was dump a pile spread out on the table and it was seek out a piece, pick up and shuffle it into position for testing. It did this very fast.
I mean, you don't need to go all the way like that but you could instead use a conical spiral funnel that turns where it positions the pieces to move into a testing jig slot, from there the simple PLC program can operate a miniature pinch finger to clamp and apply a test.
If you're serious about doing things right for production then get serious about the tools you're going to use otherwise, don't be lazy and pick up the damn Kelvin tweezers and get to work! :)
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You can't have a sense of humor, if you have no sense.
If they were purchased from a reputable source and you didn't get what you ordered, why not ship the entire lot back and let them sort it out? I certainly wouldn't sign up to solve someone else's problem.