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August 2012

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Subject:
From:
Paul Reid <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Paul Reid <[log in to unmask]>
Date:
Wed, 15 Aug 2012 08:12:01 -0400
Content-Type:
text/plain
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text/plain (136 lines)
I would look at intermittent board defects. 

Microvias and butt joint failures produce intermittent board level
failures. See if the failure is brought on by heating and flexing the
board.


Paul Reid 

Program Coordinator  

PWB Interconnect Solutions Inc. 
235 Stafford Rd., West, Unit 103 
Nepean, Ontario Canada, K2H 9C1 

613 596 4244 ext. 229  

Skype paul_reid_pwb 
[log in to unmask] 

 

-----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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