Carrie,

Yes, the best method for placing chip ceramic capacitors is reflow.  You
can reliably hand solder if you apply the heat to the pad instead of the
part, but with some risk.  Your customer is looking for a no/low risk
option accross the board.  Usually only the largest capacitance values for
a particular size package have issues with hand soldering.  This is due to
the density of those packages and the very thin dielectric which can be
cracked by the hand soldering process rapid temp changes.  This causes an
increase in leakage current or even a shorted condition in time.

Jim Carlson
Rockwell Collins Reliability Engineer




"Morse, Carrie" <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
11/17/2003 03:26 PM
Please respond to "TechNet E-Mail Forum."; Please respond to "Morse,
Carrie"


        To:     [log in to unmask]
        cc:
        Subject:        [TN] Not that our process is out of control or anything, but --


Just wondering what would be considered the "Industry Standard" on rework
method (remove and replace, or touch-up) for ceramic chip caps?  We are
currently using Metcal Irons or Tweezers and periodically a hot air tool
(hand held wand)

We have a customer asking us to use ONLY the Hot Air Tool.  He feels that
the thermal shock of bringing the cap from room temp to liquidous causes
stresses within the cap which may cause a failure in time.  To minimize
the rapid temp changes the irons introduce, we have been asked to use the
Hot Air Tool only.

I was surprised at this request as we build some boards for this customer
that have ceramic chip caps that get wave soldered.  I can only imagine
the rapid temp changes those caps see.

Any input or feedback concerning this customer's request would be
appreciated.

Thanks,
Carrie

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