PLCC socket problems

Hi

Has anyone experienced problems with PLCC sockets where the IC contact seems intermittent and possibly affected by variations in temperature. We have a problem with a Z80 micro and PLCC socket where the micro seems to behave erratically and a socket problem is suspected. Changing socket manufacturers didn't solve the problem.

Reply to
nospam
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I have had to 're-form' both socket contacts (cantilever, and bifurcated haispring) as well as flip chips over and carefully re-form their legs with a scribe.

More problems with the chips I think. Particularly if they are handled roughly/frequently in partial tubes. They band into each other and the pins suffer. Mostly the corner pins.

Try upgrading to bifurcated contacts and inspect the chips.

You don't think a thermal spec is being violated do you?

good luck

Reply to
1 Lucky Texan

What led you to believe/suspect this? Do mechanical tweaks to the assembly *while* it is misbehaving cause noticeable changes? I.e., power down, reseat the device and power back up again, etc.

And you're *sure* it's not software, right? :>

Does "erratically" mean "totally crazy" or just "not as we expect it to behave"? I.e., if you were to write a piece of code that just ran a simple scope loop, would you expect it to *also* "behave erratically"? (i.e., this would be something easy to prove!)

Are you sure the contacts on the Z80 aren't oxidized or otherwise contaminated with something that is preventing good contact?

With a high quality ohmmeter, have you measured the resistance between the pin *at* the PCB foil and the device itself? This requires some careful positioning of "probes". You can also "gut" a package (one part is a small price to pay for an answer) and probe from the bond wires "out".

Have you tried *soldering* the device to the board (make or buy a little adapter that lets you solder the PLCC to the adapter and the adapter to the circuit board)? This allows you to remove the socket from the equation entirely (at least while you attempt to identify the real problem)

HTH

Reply to
D Yuniskis

You make this sound so easy! Decapsulating plastic parts to the leadframe - even without trying to preserve the silicon - is pretty darn difficult.

I'd pick an EPROM or ceramic part in a compatible LCC footprint and crack the lid off - much easier.

Reply to
larwe

For sockets that were used a lot, I've sometimes had to use a fine bent pin to pull out all the connection springs to stretch them a little - that has often helped.

But most of the problems I've seen with PLCC sockets where when customers changed the chips themselves. I've seen what happens when people can't work the chip extractors, and use a large pair of pliers instead. And it doesn't matter how well you label the board and the chips, and tell people they only fit one way - with the help of a hammer, customers can always get the chip to fit the way they want it to.

Reply to
David Brown

We once found the a similar problem that was caused because the sockets were gold plated and the ICs were tin/lead. The lead and gold form a non-conductive amalgam. It turned out that it was possible to buy tin plated sockets which solved the problem.

Reply to
Rocky

That doesn't tell you anything about the Z80 that is believed to be (at least part of) the problem!

Reply to
D Yuniskis

Your posting that I have requoted above appears to be asking the OP to do a continuity check from the leadframe to the PCB foil, nothing to do with the die.

Reply to
larwe

Correct. His concern is that there *appears*/suggests that there is a problem in which "the IC contact seems intermittent". This involves two components -- an IC and a socket. *That* IC and

*that* socket.

Note that I never made any claims about the *die*. Rather, I was commenting on the PHYSICAL PART that the OP was having problems with. In particular, how it mates with the other physical component that the OP was having problems with -- the socket.

Are you advocating he check continuity from ANY similarly sized PLCC package from ANY (possibly different) manufacturer and, from that, come to a conclusion about *this* PLCC package from *this* manufacturer??

Why not test some *other* PLCC part in some other *vendor's* PLCC socket and come to conclusions that you hope apply to *this* part in *this* socket??

If you think you can come to conclusions using a *different* PLCC component than the one in question, then just buy a PLCC test harness and plug *that* into the socket in question.

Google (images) for "plcc plug". You'll find lots of off the shelf solutions for this problem (I have a PLCC68 in my cable bin). Buy one. Probably $100 (less than an hour of your time).

And, from that, you will know whether *that* PLCC harness/plug works in *that* socket -- and very little more about why the Z80 PLCC appears *not* to.

Reply to
D Yuniskis

This is usually a longer term problem caused by the corrosion ("galvanic corrosion") resulting from the dissimilar metals being in electrical contact with each other.

Reply to
D Yuniskis

Poor debugging logic. If he tests a shape-compatible LCC part and it does have a problem, then the case is more or less proven. You are asking him to jump straight to a process that ideally requires fuming nitric acid and a fair amount of skill. Note: Not that I necessarily believe the problem has been correctly diagnosed. A quick squirt of freeze spray and/or a puff from a heat gun would probably help him learn a lot. At the speed of a Z80, I wouldn't expect serious issues with an in-spec socket and in-spec chip body.

Reply to
larwe

As has been stated before in this thread...your idea to change the part in evaluation is nonsense. It really does need to be his part in his socket.

To bare the lead frame of a PLCC chip does _not_ require working with hazardous chemicals. A piece of fine grit carborundum abrasive cloth or paper laid on a nice flat surface can be used to sand off the top of the PLCC chip in short order.

--
Michael Karas
Carousel Design Solutions
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Reply to
Michael Karas

We may have seen that - google fretting corrosion. IIRC.

There are some vendors of pre lubricated PLCC sockets, but not easy to source. eg

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We changed process to include a contact lubricant on the PLCC devices, and have since had no reports.

Reply to
malcolm

He's already tried a different manufacturer's socket. So, either two manufacturers have produced defective parts *or* the problem lies with his Z80's (or, the problem is "otherwise").

No, you only need fuming nitric acid if you want to decap the device with the intent of salvaging the die. I had stated that the component could be *sacrificed*. His assertion is that the problem is not something internal to the package -- so, assume the die, bond wires, etc. are working perfectly... he assumes the problem is with the connection between "chip" and socket.

He has stated that he has already tried another socket vendor. And the results are unchanged. So, if the problem *does* lie with the chip+socket, then it has to be THE *chip* that is tested, not some other that could be manufactured differently, etc.

(e.g., what if the contacts are oxidized, enameled, etc. Or, the dimensions of the leads and/or chip body are not "to spec")

Testing some other device's "connectivity" with the socket tells him nothing about the device that he is actually *using*.

Reply to
D Yuniskis

Exactly. An end mill -- or a surface grinder if you are *really* skillful -- will make quick work of shaving the top off the device. The trick will be ensuring that you don't significantly impact the position and retention of the lead frame within the

*remaining* bits of epoxy. As such, you might have to mill off different parts of different "samples" so that what remains is still "testable" (*not* the electronics but just the lead frame).

Recall the Z80 is a rather small die -- compared to the size of the PLCC. So, you have a fair bit of "mass" of lead frame that can remain embedded in non-abraded epoxy while still exposing "enough" for a test probe.

My money is still on something *other* than a bad *mechanical* fit -- which is what the "connection" hypothesis seems predicated upon (unless the sockets are deforming in the board preheat cycle -- is this SMT or thru-hole assembly?)

Reply to
D Yuniskis

Do not use sockets. Socket usually sucks over about 10MHz ;-)

Instead use in-circuit upgrade?

PS: Could it be a faulty PCB/via hole?

Reply to
Glenn

Z80 has nothing internally to upgrade. I'd guess the socket is there to:

- allow SMT component (the Z80) to be used on a thru-hole PCB

- allow ICE connection for development

- allow easy access to all the I/O's for cheap ICT, etc.

- allow optional daughterboard connection "on the cheap" etc.

OP hasn't given enough information about his implementation, the actual symptoms observed, or the actual conditions under which it works/fails. The focus on "bad socket" (despite the fact that two different vendors' parts exhibit the same symptom?) seems either premature or there is a lot we haven't been told...

(e.g., did the design *ever* work? Is the oscillator running properly? etc.)

Reply to
D Yuniskis

We had this problems with SMD sockets, different socket manufacturers didn't fix the problem. Changed to a through hole socket fixed the problem. an extreme fix but it seemed to work for us.

Reply to
Dennis

How did you determine that the sockets were at fault? As you said, a bit "extreme" to alter the layout (so, presumably, you had convinced yourselves that this

*was* the problem before undertaking such a big step).

Were you ever able to determine what *aspect* of the sockets was the problem? E.g., deformation during assembly, bad wash, "made out of spec", too flimsy, contaminants, etc.? Or, perhaps some subtlety of the *layout* that changed when you moved to the thru-hole layout? Did you ever get any feedback from socket vendor(s) regarding the problem?

As with the OP, did the fault appear to be temperature correlated?

I.e., do you now have a "policy" of *never* using SMD sockets in designs? Or, have you been able to qualify

*when* they can be used and when they shouldn't? (device size, types of signals involved, etc.)

Out of curiosity, what size socket and what sort of device (technology) was *in* the socket?

Reply to
D Yuniskis

The problem could be "fixed" by tweaking the contacts or squeezing the sides of the socket in by hand. ie Squeeze it works, let go it fails.......

Poor cleaning was something we suspected but ruled out. We also looked at oxidation of the contacts on the package. The socket frames deformed slightly when the ic was inserted.

Our volume was so small we didn't worry about conversing with the socket manuf.

Probably not.

I prefer to not use sockets anywhere if possible.

IIRC 128 way Lattice pld or similar, it was about 10 years ago.

Reply to
Dennis

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