Connectors for high-vibration environments with extremely low humidity

Glenair connectors are often specified for high vibration/temperature downhole use, a bit like the old saw "nobody ever got sacked for buying IBM".

MWDM2L-9SCBRP-.110-513 for example, that may be over the top but they do several other types.

Check your bank balance first, and lead-free solder is tougher.

A client has the same application but in rugged automotive conditions (mining equipment, etc.). They use a thermopile sensor. (They're detecting direct flame; sounds like your case needs more sensitivity, so that probably wouldn't go, and explains the TIA, with, I guess, a long wave photodiode or pyroelectric sensor.)

I forget what the minimum temperature is (maybe it was more or less than your requirement?), but they use M-series Turck connectors throughout. Pigtail type, leads soldered directly to the board. Don't remember what plastics they're made of or if they say, but they're rated for the service in any case. And as much potting as possible, no direct route for moisture to get in.

They do have problems with vibration of connectors causing dropouts of power or signal. A recent change has been to put an MCU inside the boxes, so instead of a DC signal, a serial keepalive message is sent, and the system can be more aware of its integrity as well as more forgiving of momentary dropout.

Not sure what you're showing with the rectangular header -- internal board-to-board wiring? External connections??

Tim

-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website:

Sn63 is distinctly Europe non-RoHS!

Hence my comment about nobody in the EU growing cotton. For this one I don't have to care about Ro so-called HS.

Cheers

Phil Hobbs

Thanks. I was perhaps unclear--the connector I'm concerned about is inside the case, connecting the short wiring harness from the M12 connector to the board. We're expecting to put some heat shrink tubing on the wires to damp out vibration.

The issue we're concerned with at the moment is preventing the connectors from crumbling into dust, which is the likely fate of nylon connector shells in this environment.

Thanks

Phil Hobbs

We have a visible channel, a SWIR channel (0.9-1.7 um), and a MWIR channel (3-5 um). The SWIR detector is 0.3 mm in diameter, so it needs a very high-Z TIA. (It uses two 100M resistors in series, shunted by a series pair of very low leakage diodes so that it doesn't rail in bright light.)

I don't have any experience using potting, so I'd be reluctant to use it for this one. We do have to use goop between the board and box to keep it from vibrating much.

Mining is a very dirty business indeed. I've been down a few working mines--underground, a mercury mine in BC (Pinchi Lake) and a gold mine in the Northwest Territories (the Con) as well as an open pit lead/zinc mine also in the NWT (Pine Point). My Dad used to work for the old Cominco [not the company currently trading under that name], and he took me with him on a tour of their operations in the North. It was pretty cool--I was 12 at the time, and got to hold an 80-pound gold bar. (It was 75% gold and 25% silver iirc.)

Yeah, ours have an LPC845 Cortex M0+ in them. Nice part--32 MHz, with a gigantic pin mux so you can have almost any function on (almost) any pin.

It's to go from the pigtailed M12 to the board.

We've been going back and forth about soldering the wires directly to the board, but have heard stories about vibration causing fatigue failure at the stress concentration point where the tinned region ends, as well as anecdotal wisdom about the goodness of crimped connections in environments like that.

Cheers

Phil Hobbs

Glenair do that sort of thing. 'Latching Microstrips' they call them. Good quality stuff.

Standard way is to loop the wire through holes adjacent to the solder pads, so through the board with insulated wire, then double back through a pad to solder. That is reliable.

If you have heavy parts - eg large through hole MOSFETs, then don't solder them to the PCB, use looped wires soldered to their pins. /Extreme/ vibration calls for potting, but a conformal silicone coating is fine otherwise. And lead-free solder makes a stronger joint.

Place small parts along the least flexy direction, use Flexicap capacitors, expect microphony. No BGAs, and be more generous with the solder than normal.

Yeah, automotive does that a lot. Not uncommon to see modules with electrolytics sticking up from the muck.

Might do, then, to have just a little more, enough to cover where the wires come out -- or put some extra goop around them?

And yeah, NASA doesn't like tinned wire either, indeed they have a whole methodology for doing that correctly (which must be pretty inevitable for the popularity of solder-cup MIL terminals?). If they can do it, it's definitely possible; whether it's worth following that procedure, or maybe a watered-down version of it, is a potentially costly question though. Alas, I don't have that experience to offer...

Also a possibility, solder-in crimp termals. Seen 'em on ATX PSUs plenty of times. Probably more of an assembly expedient than for reliability though? (The crimp is basically just the barrel, no socket/pin. The barrel and wire is what goes into the board to get soldered. There's usually a retention tab, I assume to hold it in place for wave soldering.)

I think in my example, the connections are all hand soldered. Which has to be a big adder to their assembly cost. It's not mass production quantities, and they don't seem to have much competition (and for an end product that doesn't have much competition in turn), so I guess they don't mind. YMMV.

Oh also, I forget what they do with the IR sensors, if they're fully potted, or partial, and if they have a seal around the optics. Might be the latter. Yet another thing to think about...

Very cool. Unless you were in one of those super deep mines that's over

They also like to wash down the trucks, and I mean using whatever is handy: steam, seawater... Electrolysis in connectors (even if they're IP67) is sometimes a problem too. At least you wouldn't have that problem I guess. :)

Ah, yep, cheap too. Though I've heard they're Microchip levels of buggy. (Haven't looked at them in enough detail to know that myself.)

We use a ton of STM32s: affordable enough, easy to use (even supported by Arduino, should you happen upon that route), not too many bugs.

Personally, I like AVR XMEGA, charming 8-bit machines, pricey though they are. Fortunately, as a hardware guy, I just play with them; I'm in no danger of putting one into production. :^)

Tim

Potting is very effective. But I'd go talk to your local Master Bond rep, and their application engineers.

There are some kinds of metal-pin connector that are *very* vibration-resistant, ones having a cage of hyperbolic contact wires pinching a solid male pin. The patents have long since expired, so there are mnay makers. Here is one:

There was another family where the male pin was a birdcage of smaller wires that were pushed into a slightly undersize cylindrical tube female pin, but I can't find these any more. Probably harder to make than the hyperbolic design.

The US Military and NASA did extensive reliability studies of crimped versus soldered connection between connector pins or sockets and stranded wire under heavy vibration. Crimped won hands down.

The solder-cup connectors were usually backfilled with polysulfide rubber (which looks and smells like s**t, and sticks to everything except teflon) to provide moisture sealing and strain relief. Non-teflon wire would make a firm bond with polysulfide rubber.

Joe Gwinn

Speaking of NASA, how did they do OPs task aboard spacecraft? High vibration, check, low humidity, check, smoldering fire extremely serious situation, check, so I'm assuming they must have built a similar device...

• Have seen that many times over a 50 year period.

• YES! MIL testing has shown that crimped connections are far more reliable than soldered connections, due to fact of compression alloying of wires.

Hi Phil, I have good results using the JST XA series which is the 2.5 mm version of what you propose. I use the latching clips and side entry pcb header as then a locating peg takes some stress off the through hole pins.

The non replaceable alternative is a solder pin or turret and then hand solder the wires to that and shrink sleeve the joint to absorb strain on the fragile portion where solder has wicked along the strands, but it ends up more work than using a connector.

piglet (Using google groups on a phone while travelling in Africa)

Thanks. Have a good trip!

Cheers

Phil Hobbs