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March 2011

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Subject:
From:
Vladimir Igoshev <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Sat, 19 Mar 2011 20:16:49 -0400
Content-Type:
text/plain
Parts/Attachments:
text/plain (171 lines)
Here we go again!
If you want to get down to the root cause, have the assembly analyzed! 
One of the last times we had a similar discussion here the root cause 
turned out to be very interesting and as far as I remember no one 
"guessed" it correctly. 
Regards,

Vladimir Igoshev
SENTEC Testing Laboratory Inc. 

Quoting Uppina Nagaraj <[log in to unmask]>:
> Hi George,
>
> Surface finish is ENIG. 
>
> Regards,
> U.Nagaraj
>
>
> > 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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