[SI-LIST] Re: question concerning socket for SDRAM module - mechanical problem?
- From: "John Thomas" <jthomas@xxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Tue, 8 Apr 2003 13:46:07 -0500
Jan,
I've seen this due to the PCB being too thin. You're measuring in the right
place on the edge connector. It did appear as if some manufacturers' SDRAM
could overcome the marginal contact better than other; I believe this is
probably due to drive strength. Since the board manufacturer didn't adhere
to the specifications we supplied, they took care of the problem. I have,
however, noticed that boards on the lower side of the spec range can
occasionally give problems that are 'fixed' by rocking the DIMM in the
socket. This is with one of the 'better' sockets. This is something I'd
consider intolerable in a manufacturing test setup. For this case, I'd go
with a zero-insertion-force socket designed for test.
Best Regards,
John Thomas
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Jan Vercammen
Sent: Tuesday, April 08, 2003 9:52 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] question concerning socket for SDRAM module -
mechanical problem?
Hello si-list,
we assume we have a mechanical problem with SDRAM modules and the socket on
the motherboard.
At least this is the understanding of the situation, that is, it could be a
dimensional or mechanical problem.
We changed the socket on the motherboard because the old connector has
become obsolete. The
connector is from a respectable connector company, the replacement of the
old connector is on
recommendation of that same company. The 133MHz memory modules are also
from a respectable SDRAM
manufacturer. Both the connector and memory modules are from THE big
companies.
With the new connector we have memory failures, but only with one kind of
memory module
type. This memory module is from a batch, of which we tested about 20 ones.
But the new connector is
only recently being used in our design, so ...
The errors are repeatable: if we exersize a small sideway pressure on the
SDRAM module then things
go wrong. This can be recovered (sometimes) by a small pressure in the
opposite direction. Once
OK, the module remains OK (we did run some modules overnight on a RAM
test).
We also noticed that memory modules with a thinner thickess are more prone
to memory failures whereas
thick modules are not (not even under some sideway pressure).
Old connectors never have memory failures - even with sideway pressure -
with the memory module type
we currently experience problems.
So we think that the problem has to do with the new SDRAM socket connector.
Maybe the memory modules
are also out of spec on the thickness, anyway with the old socket we did
not experience any problem.
So for now we can - very likely - exclude signal integrity.
So my questions for the si-list:
-1- has anyone experienced similar problems as we do and was this a
mechanical problem?
-2- can we expect dimensional problems with SDRAM sockets and memory
modules?
-3- how can we pratically solve this kind of problems, that is, is it
possible to do lot inspections (measure thickness
of SDRAM memory module PCB, test memory modules, .... on a sample
basis?)
-4- how do you measure the PCB thicness and where? We measured it at the
connector edge - gold to gold plating. We
found - currently at least one module (of a total of 5) - out of spec
with 1.12mm (the spec says 1.27+/-0.1mm).
-5- any other tips???
Your help is appreciated.
Kind regards,
Jan Vercammen
Kind regards,
Jan Vercammen
Agfa-Gevaert NV
Mortsel, Belgium
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