Many manufacturers of multi-layer ceramic chip caps have recommended procedures for rework on their web sites. We have had a couple of problems with cracking in the past, and
we solved them by reviewing the vendor recommendations and developing a procedure that says, whenever we have to hand solder these caps, we preheat them to 300-350 Deg. F
place them on a preheated board, and then solder them using only a 500 DEg. F iron or hot air tool. If an iron is used the operator is not supposed to touch the cap itself
with the iron, only the pad. This seems to have worked quite well for us.
[log in to unmask] wrote:
> 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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