Hi Inge,
O.k., cannot be the contact fingers—high contact pressures do not allow impact of "knock, knock."
SJs are 'famous' for being impacted by "knock, knock," because fractured SJs do NOT have high contact pressures, just very moderate ones—so that is where I would look first. Of course, knowing nothing about your wire bonds, I could not exclude them either.
Needle in the haystack‚ Sysiphus, here I come.
Werner
-----Original Message-----
From: Inge <[log in to unmask]>
To: [log in to unmask]
Sent: Tue, Sep 22, 2009 3:33 pm
Subject: [TN] Knock, knock, knock on the heaven's door
Well, not exactly that, but knock, knock, knock on a earthly board. One
customer needs fix a intermittent problem asap. 19 inch racks with hundreds
of PTH double sided boards, old technology, no BGAs, no QFMs etc, but lots,
lots of DIPs. The edge contact fingers have a very thick and good gold over
nickel, and the backplane connectors have really stiff double tongues. The
contact pressure/sq is extremly high and I think the contact spots are
really gastight once the board is plugged in. Now, they have electrical
issues, and they've found, that the signals are interrupted or coming back
when they knock on the boards. Someone is going to take a flight the other
day to fix the problem. The electricians believe, stubborn as mules, that
the only think needed, is to take out the boards and clean the edge contact
fingers with a solvent and that will f
ix it. Myself, with quite many year's
experience from connectors, I don't think that is the problem, because when
such robust contact springs wipe along the contact fingers, they slide
pretty deep into the gold and makes good connection. Each spring has double
contact ridges, so the risk that some dirt should cause interrupts is
minimal. There is more that talks against their theory, namely, that the
problem is still there after plugging, deplugging more than once. I'm sure
there is a solder joint issue, or maybe a bond wire problem in the packages.
Logically, this later is more likely because you have thousands of
solder/bond joints vs, just some one hundred edge connector ditto. A ratio
like 10,000/100 per board. Without knowing all details, what is your general
experience between the index finger and the big toe?
/Inge
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