Let me try answer some of question ;

  The better thing is use a real board with all components, in this way the
thermal mass will be same.

  Some vendors ask to use one termocouple at top in order to monitor peak
temperature at body of the component just to protect their package, and
you'll feel really confortable when you use the termocouple under the BGA (
you can drill the board or use a fine termocouple wire to route between the
balls )

  Be aware about holes under the BGA because they can cause problems at
solder wave machine, we cover our BGAs with adesive tape before solder wave
operation to avoid solder transfer from the solder pot to the bottom of the
BGA.If you intend to make a hole in a design keep this in mind.

Thanks

Jorge Dourado de Santana
Maintenance / Process Engr
Microtec - Brazil

> -----Original Message-----
> From: Bob Walker [SMTP:[log in to unmask]]
> Sent: 25 de Agosto de 1999 23:09
> To:   [log in to unmask]
> Subject:      [TN] temperature profiling for BGAs
>
> Hi all,
>
> I'm interested in finding out how a temperature profile is developed for a
> new PCB design that contains BGA components   Are bare boards along with
        dummy BGAs required for developing the profile prior to the actual
build or
        do you jump right into building an actual board and then test it to
prove
        out the profile that was used?  Are the thermocouples used for
monitoring the
> temperature placed above the components or are they placed between the
> board
> and BGA by drilling a hole through the board to get under the BGA with the
> thermocouple? I'm thinking of adding an unplated hole under each BGA that
> may be in a design, so that a thermocouple could be used to monitor the
> temperature for developing a temperature profile. Does this sound like a
> good idea or is this already a common practice for designs that use BGAs?
>
> Regards,
>
> Bob Walker
> [log in to unmask]
>
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