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August 2012

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Subject:
From:
Victor Hernandez <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Wed, 15 Aug 2012 09:27:59 -0500
Content-Type:
text/plain
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text/plain (130 lines)
You can also cut one side of the trace leading to the component in question and conducting measurements.   Avoid heat/soldering suspected failing components.

Victor,

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bruce Tostevin
Sent: Wednesday, August 15, 2012 9:08 AM
To: [log in to unmask]
Subject: Re: [TN] Intermittent single part failure

Hello Michael,

You mentioned "aside from some slight discoloration." Something has to have caused that if it's unique to the failed parts. The component's thermal, chemical, airflow pattern,  and environmental exposures all need to be investigated. 

In summary notes 4 and 5, the failure was "cleared" by reheating R37
which properly measured 49.9Kohm after it was removed.   I suggest that
next time you have a confirmed failure, DO NOT reheat the part or use soldering irons/talons to remove it.  Instead, remove it by slowly and carefully digging away the solder joints with a sharpened pick or graver. Practice first on a scrap card until you get the technique down.
With this method  you can measure its value "as is" on the card without the influence of reflowing the joints.  If the resistor is defective then you can pursue that avenue of analysis.  At the same time you'll be able to inspect the component underside and the pcb location for signs of contamination, residues, etc. You're sure that nobody's doing any "hand" touch-up at this location?

Bruce Tostevin
Benchmark Electronics
Nashua, NH
 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kuczynski, Michael (H USA)
Sent: August 14, 2012 2:24 PM
To: [log in to unmask]
Subject: [TN] Intermittent single part failure

We're experiencing a consistent intermittent (if such a thing?), contact failure for a single resistor (about 5% of 3K pcbs) . There are 2 of the same resistor on the PCB, yet just the one always has failure. Poor solder joints or voiding don't seem to be the issue, as I'd expect other failures elsewhere on the board. Aside from some slight discoloration, we're kinda puzzled. Even the measurements of the signals on the boards don't point to a path to look at.

Anyone have an opinion on a different angle we can try to look at?
Thanks in Advance.

SIEMENS
Michael Kuczynski      Healthcare Diagnostics Inc.
Product Eng. II CID      511 Benedict Ave.
914-524-3118 (Ph)       Tarrytown, NY 10591
914-524-3322 (Fax)      Mail Stop P25-1-C
[log in to unmask]<mailto:[log in to unmask]>


Here's a summary of our findings to date,


1.       We re-test the assembly on receipt and confirmed the failure.
The assembly originally recorded a pass when first manufactured.

2.       R37 and the adjacent components were X rayed and viewed under
high magnification and showed no signs of heat damage or physical damage. The solder fillet conforms to IPC standards. See pictures below
(removed) ,


3.       The SMT profile was re-ran and confirmed to be within
specification.

4.       We have re-created the effect described in your email -  by
touching up the solder joint at R37 the fault cleared.

5.       R37 was removed and resistance measured at 49.9K ohms, the
component was re-examined and showed in signs of physical damage.

6.       R37 was refitted and the board passed test.

7.       The range of serial number suggest the problem isn't batch
related having date codes from Week 25 Year 09 to Week 09 Year 12.

We will look at the other board when it arrives but at the moment we cannot draw any conclusions to the cause of these failures.



 
WET/DRY
                     S1_SIG        S2_SIG:         S1_REF:
S2_REF.:
S/N:             TP25:             TP24:              TP23:
TP26:             FINDINGS:
COMMENTS:
57901011     4.53 / 2.18     4.64 / 2.05          3.5
3.5                 WORKS                                           *
88011123     4.53 / 2.18     4.65 / 2.06          3.5
3.5                 WORKS
11800925     4.50 / 2.15     (3.40 / 1.33)        3.5
3.5                 S2 SHOWED DRY WHEN WET         DOWN SHIFT OF S2
92661209     4.52 / 2.15     4.63 / 2.30         (2.4)
3.5
REFERENCE VOLTAGE S1 FELL
14270925     4.51 / 2.14     (2.31 / 0.90)        3.5
3.5                 S2 SHOWED DRY WHEN WET         DOWN SHIFT OF S2**
91021147     4.50 / 2.14     4.60 / 2.02          3.5
(3.5 / 4.1)***
REF. VOLTAGE S2 ROSE EVEN ISOLATED FROM COMPARATOR
93511209     4.50 / 2.20     (1.57 / 0.63)        3.5
(1.8)
SENT FOR ANALYSIS
15510925     4.45 / 2.05     4.62 / 2.04         (4.6)
3.49
RXD 8/8/12

* GOT QUESTIONABLE COMPARATOR
** LOST QUESTIONABLE COMPARATOR
*** INTERMITTENT


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