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January 2002

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Subject:
From:
"Mcmaster, Michael" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 23 Jan 2002 17:03:24 -0800
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There could possibly be an interaction with the via pattern under the BGA.
The dense drilled hole grid perforates the glass reinforcement matrix and
reduces the mechanical integrity of that section of the board.  You can
actually see a localized increase in the CTE of the material because of the
loss of reinforcement.

> ----------
> From:         Guy Ramsey[SMTP:[log in to unmask]]
> Reply To:     TechNet E-Mail Forum.;Guy Ramsey
> Sent:         Wednesday, January 16, 2002 1:42 PM
> To:   [log in to unmask]
> Subject:      Re: [TN] BGA/Vias
>
> No, I understood you. Some boards will do this. Sometimes they crown
> instead
> of sag. I have not studied why. But increasing the size of the area
> subject
> to preheat may help. In a worst case scenario you may have to reflow the
> entire board in an oven.
>
> Sometimes, as the MoonMan mentions, the BGAs like to curl up on the
> corners
> or down on the corners as well. This is do to CTE mismatches in the
> package
> itself. Then you just have to slow the process down and use as low a
> topside
> heat as you can.
>
> An old axiom worth remembering, when in doubt go low and slow. I give
> credit
> to an old mentor, Ken Lindsey, for this rule. Hope he is doing well.
>
> Guy Ramsey
>
>
>
> > -----Original Message-----
> > From: TechNet [mailto:[log in to unmask]]On Behalf Of Rick Howieson
> > Sent: Wednesday, January 16, 2002 2:41 PM
> > To: [log in to unmask]
> > Subject: Re: [TN] BGA/Vias
> >
> >
> > I probably didn't make myself clear. The problem is the board itself
> > collapses/sinks/"potato chips"...in the area being heated, i.e. BGA
> > location.
> > Rick
> >
> >
>
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