board to board interconnect suggestions wanted 2

[MagicSmoker]

For interconnecting multiple pc boards (both signal and power), I have typically used flat flex cable/connectors or ribbon cable/IDC connectors. I admit I have always been skeptical of the long term reliability of both interconnect systems and a new project I am starting on has placed reliability above all other concerns so I am rethinking my default choices on just about everything (even the type of termination used on SMT components).

Before I go through the exceptionally painful process of calling up Molex or Tyco, I thought I'd solicit the eng-tips denizens for other board to board interconnect systems. My primary requirements are:

* high reliability, natch.
* cable/connector terminations able to be performed by us in house without requiring extraordinary care or skill
* availability from low-volume distributors like Mouser/DigiKey - we make things in quantities of 100s per year and so we rarely use high volume distributors and/or purchase directly from the manufacturer.
* good shielding capability through the use of making every other conductor a "return" (like with ribbon cables).

Notice how price isn't listed? That's because it's most definitely a secondary requirement. If an interconnect system meets all four primary requirements but costs 5x more than the equivalent number of signals with a plain old ribbon cable + header + IDC connector system then so be it.

 

[VEBill]

You need to define and specify the signalling speed as well. An on/off discrete or low speed serial signal will pass though any connection probably without problem. A high speed digital signal needs to be coddled like RF.

 

[IRstuff]

The other thing that's missing is reliability under WHAT CONDITIONS? Vibration? Salt fog? Temperature?

TTFN
faq731-376

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[MikeHalloran]

The only problem I've had with IDC connectors is accidental separation when some hero didn't bother to specify a latch.

... but if you don't need the connection to be separable, I'd go with ribbons soldered directly to each board, and strain relieved if there's vibration or motion.





Mike Halloran
Pembroke Pines, FL, USA

 

[LiteYear]

Could take a leaf out of a mobile device manufacturer book - all the interconnects in mobile phones and laptops tend to be FFC, but the sockets have a clamp. Depending on the particular hazards of your environment, I'd be leaning towards FFC with latched sockets for low current, and IDC connectors bathed in hot-melt glue for higher current. Remember that spring/friction connections like IDC can be susceptible to tarnish at the contact point if currents are very low.

 

[MagicSmoker]

Thanks, MikeHalloran, for your input. I haven't really had any problems with ribbon cables + IDC connectors, either, but I was curious to see if that was just because I have been lucky...

Otherwise, this is more of a general question/survey. Which is to say that this isn't for an exotic signal or especially hostile environment. Indeed, having an unusual signal or environmental requirement can make the interconnect selection process much easier by the virtue of eliminating so many choices from consideration!

That said, the signals will be a mix of low speed digital (up to, say, 100kHz max) and power supply (multiple pins/lines dedicated to ground and semi-regulated supply voltages.). I do not attempt to distribute regulated supply voltages like 3.3V for logic via interconnects, preferring instead to derive such voltages via a local linear regulator operating off, e.g., a 6.5VDC rail, so that takes a bit of the stress off the ohmic loss requirements of the interconnect system. The usual environments I design for are industrial and automotive, and because of that the enclosures tend to exhibit a minimum ingress protection rating of IP55. No salt spray, no unusual chemical vapors, etc.

 

[mcgyvr]

And one more tip.. Try Samtec instead of TE/Molex.
That "exceptionally painful" process turns into a "beautiful walk along the beach"

 

[MagicSmoker]

mcgyvr - I see you know what I'm talking about when it comes to asking TE or Molex for technical assistance...

Thanks for the tip on Samtec. Just loaded up their website and it looks like they have all kinds of good stuff.