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January 2004

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Subject:
From:
JaMi Smith <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 13 Jan 2004 23:26:32 -0800
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Mike,

A second thought is that you need to look into the temperature characteristics of
the resistor substrate material verses the temperature characteristics of your BGA
substrate material, and the rates of expansion of each as opposed to the overall
heating and cooling profiles that you are using in your seperate processes for
initial resistor attachment, and reflow for the underfill, and then again for the
attachment of the completed BGA assembly to the final board. Don't forget to take
the thermal characteristics of the specific type of solder that you are using into
account also.

This reminds me of the early days of SMT where high rel ceramic packages were
popping off of boards and failing at points of attachment due primarily to differing
thermal expansion characteristics with the boards to which they were attached.

JaMi


----- Original Message -----
From: "Michael Forrester" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, January 13, 2004 3:30 PM
Subject: [TN] 0603 Resistors failing after Reflow


>       We use a thick film 50 ohm 0603 .2 W resistor on a ceramic substrate
> BGA device.  The BGAs are pretested before
> PCA assembly.  After placing the BGA on a PCA assembly and reflowing the
> PCA a number of the resistors either increase
> in resistance or open.  The resistors on the BGA substrate have already
> seen a reflow cycle to mount the resistors on the
> substrate.  They are on the substrate during underfill cure.
>
>       During BGA removal from the PCA we have discovered that more of the
> resistors ( 6 per part) either open or high
> resistance.  The BGA in question is used on two completely different
> assemblies built by two different PCA houses.  The
> BGAs have different date codes.  The only thread we currently have is that
> most of the suspect BGA lots (all but one) used
> resistors from the same lot.  We are pointing toward some defect with the
> resistors.  I have both "good" and bad resistors
> from the same lot of parts.Does anyone know where I would send some of the
> defect resistors for an independent analysis?
>
> Thank you in advance.
>
> Best Regards,
>
> Mike Forrester
>
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