Good point, Guy, and these heat sinking components often are not available
as dummy parts, so one is them faced with using a genuine part if it's felt
to be critical in terms of thermal mass on the board. There may well be a
case of dwell time being insufficient or inadequate peak temp spike.

Peter Duncan



                    Guy Ramsey
                    <gramsey@ACIU        To:     [log in to unmask]
                    SA.ORG>              cc:     (bcc: DUNCAN Peter/Asst Prin Engr/ST
                    Sent by:             Aero/ST Group)
                    TechNet              Subject:     Re: [TN] Reflow profiling
                    <[log in to unmask]
                    ORG>


                    10/26/01
                    08:33 PM
                    Please
                    respond to
                    "TechNet
                    E-Mail
                    Forum."






Good plan. I would add a reminder. Some packages have internal structures
to
conduct heat away from active device(s) in the package. These may not be
represented in the dummy component, and can result in an oven profile that
is too cool.

> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of <Peter George Duncan>
> Sent: Thursday, October 25, 2001 10:00 PM
> To: [log in to unmask]
> Subject: Re: [TN] Reflow profiling
>
>

>
> I also am involved with high mix, low volume builds, and I try to get one
> board of each type from the fab house that has failed electrical with
> internal shorts or whatever (cheaper than sacrificing a good
> board). I then
> buy in a stack of dummy components from Practical Components or
> Topline and
> populate the profile board with those. I don't bother with discrete
> passives, as they contribute precious little to the thermal mass. The
> thermal profile board is them reflowed using the standard profile
supplied
> by the solder manufacturer.
>
> For BGA's and so forth, I then drill a hole up through the board into one
> of the central contacts to take a thermocouple wire, which is bonded in
> place, and add other thermocouples around the board.  plug them all into
a
> high-temp data logger
>
>

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