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March 2011

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Subject:
From:
vladimir Igoshev <[log in to unmask]>
Reply To:
Date:
Sun, 20 Mar 2011 02:20:17 +0000
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Hi George,

I did it on purpose, as that e-mail had "brought in" possibility of Black pad. 

The responses were great, as always but they represented a set of typical suspects for the situation and only analysis can show what really caused the problem.

Regards,

Vladimir

SENTEC Testing Laboratory Inc.
11 Canadian Road, Unit 7.
Scarborough, ON M1R 5G1
Tel: (416) 899-1882
Fax: (905) 882-8812
www.sentec.ca

-----Original Message-----
From: "Wenger, George M." <[log in to unmask]>
Date: Sat, 19 Mar 2011 20:55:05 
To: TechNet E-Mail Forum<[log in to unmask]>; [log in to unmask]<[log in to unmask]>
Subject: RE: [TN] Query on failure of assembled PCB

Vladimir,

I'm not sure your "Here we go again!" comment is correct.  In the email you responded to all I see is a simple question about what the surface finish was and a simple answer that it was ENIG.  The many responses since then gave lots of possibilities including micro cracks, brittle solder joint fractures, Head-on-Pillow, etc.  All of which are possibilities.  I don't think anyone was pointing a finger in one direction but they were suggesting possibilities.

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 Vladimir Igoshev
Sent: Saturday, March 19, 2011 8:17 PM
To: [log in to unmask]
Subject: Re: [TN] Query on failure of assembled PCB

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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