Mike,

200 milliwatts sounds a bit much for an 0603 resistor, which are usually rated at
100 milliwatts in that size, even in thick film. Typically to get that kind of power
rating you need to go to a 1206, or at least an 0805.

You do not say whether these are failing after power is applied, and just how they
are configured in the circuit, and just how much current you are actually pumping
thru them.

The first question I would ask, is whether or not you are just simply "smoking" them
by applying too much current.

I would address these issues before I would look for other reasons for resistor
failure.

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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