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
>
>

---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------