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August 2012

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Subject:
From:
"Wenger, George M." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Wenger, George M.
Date:
Tue, 14 Aug 2012 13:41:40 -0500
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Michael,

One thing I forgot to mention was that you should send the photo that was stripped off to Steve to post on his site.

Regards,
George
George M. Wenger
Senior Principal Reliability / FMA Engineer
Andrew Corporation - Wireless Network Solutions
40 Technology Drive, Warren, NJ 07059
(908) 546-4531 Office (732) 309-8964 Mobile
E-mail: [log in to unmask]


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wenger, George M.
Sent: Tuesday, August 14, 2012 2:36 PM
To: [log in to unmask]
Subject: Re: [TN] Intermittent single part failure

Michael,

I have several questions:
1. Is the resistor a ceramic chip resistor?
2. What is the physical size of the resistor?
3. What is the surface finish on your PCB?
4. Is it ENIG?
5. Where is the resistor that you are having problems with located?
6. Is the resistor soldered during the first side reflow and would then see a second side reflow? 

Regards,
George
George M. Wenger
Senior Principal Reliability / FMA Engineer Andrew Corporation - Wireless Network Solutions
40 Technology Drive, Warren, NJ 07059
(908) 546-4531 Office (732) 309-8964 Mobile
E-mail: [log in to unmask]


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kuczynski, Michael (H USA)
Sent: Tuesday, 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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