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Subject:
From:
Chris Mahanna <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Chris Mahanna <[log in to unmask]>
Date:
Wed, 16 Mar 2011 23:39:20 -0400
Content-Type:
text/plain
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text/plain (1 lines)
Joyce,
Agree 100%.  I assumed from the story that both PBA tests were the same.
If one root cause, and reflow fix and flexure fix then very likely hop.
But he may well have more than one root cause.
Chris

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo
Sent: Wednesday, March 16, 2011 11:20 PM
To: [log in to unmask]
Subject: Re: [TN] Query on failure of assembled PCB

One major difference: the exit test is possibly connectivity test: open or short, not function.  The BGA intermittent is a functional test.  You could pass open or short, but still got intermittent fault.  HOP may pass open short test if it got some contact, sounds like either bga cracked, or hOP,or microvia cracked.  All of them will exhibit intermittent but partially show connectivity when apply pressure. Are those parts underfilled? 
--------------------------
Sent using BlackBerry


----- Original Message -----
From: Wenger, George M. [mailto:[log in to unmask]]
Sent: Wednesday, March 16, 2011 10:42 PM
To: [log in to unmask] <[log in to unmask]>
Subject: Re: [TN] Query on failure of assembled PCB

U.Nagaraj

What was the PCB surface finish?

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 Uppina Nagaraj
Sent: Wednesday, March 16, 2011 10:28 PM
To: [log in to unmask]
Subject: [TN] Query on failure of assembled PCB

Dear All,

1. We are manufacturers of PCBs. One of our customer has reported
   failure in assembled boards. The main observation is that after
   assembly, the assembled units were functioning normally
   and had passed all the stipulated electrical tests. These parts
   were kept at the assembly house for around over 3-4 months. Later
   when the assembled units were scheduled to be integrated into
   the system, the assembled units were tested again, but now they
   see failure.

    These are the inputs given to us..........
    a) Failures are intermittent in nature.
    b) Failures are concentrated in and around the area where
       BGA is mounted.
    c) Some failures are recovered by applying mechanical stress on
       the PCB.
    d) Some are recovered by subjecting to reflow.
    e) There are no component failures.

2. Our customer's assembly process flow is…
    a) 100Deg C, 16 hours baking
    b) Assembly done within 24 hours after baking
    c) Pb-free reflow conducted with a peak temperature of 262Deg C
    d) Reflow is done 2 times (once for each side of components)
    e) Visual and physical inspection done
    f) Cycling done at -20~+70Deg C for 10 cycles. First 9 cycles
       are 30minutes per cycle and the last cycle is 1 hour cycle
   g) Electrical testing

3. We had retrieved a blank PCB from the same batch and conducted
   the following trial......

   a) A standard step of baking prior to assembly (100Deg C,
      16 hours baking) was skipped due to time constraint.
   b) 2x reflow done at customer's place using standard profile
      used for assembly of this part.

     Electrical Testing (BBT) on bare PCB passed .

   c) 10 cycles of temp. cycling done at customer's place using the
      standard cycling profile used for assembled unit.

      Electrical Testing (BBT) on bare PCB passed .

   d) Repeated 2x reflow (2nd time) at customer's place using
      standard profile used for assembly of this part.

      Electrical Testing (BBT) on bare PCB passed .

     Based on the above trial, we feel that the failure seen is
     not due to PCB failure.


4. This particular PCB is a 8 layer PCB, built using ISOLA FR370HR
   material.
-----------------------------------------------------------------


Please share your inputs and thoughts on the failure phenomenon and how to ascertain if the failure is due to PCB or assembly.

Thanks in advance!

Best Regards,
U.Nagaraj




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