Lou,
Thanks for the info. It seems consistent with what happened. The
perplexing part is I found on the data sheet
a statement that allows use to 125c if you derate the cap, which seems fine
for the capacitance but not for
the material. Go figure!! I think I have a little more digging to do on
this one.
Thanks again for your response........DT
At 12:02 PM 10/13/00 -0400, you wrote:
>Darrel, in case you are interested, regarding electrolytic capacitors, the
>85 C rating means they can be baked at that temperature for 1000 hours and
>the increase in equivalent series resistance (due to loss of electrolyte)
>will not be more than 10%. I'm not sure what the boiling point of
>electrolyte used in 85 C caps is, my recollection is that it is in the
>range of 100-105 C. It has been a while since I looked, but there used to
>be electrolytics rated at 105 and 125 C.
>Lou Hart
>----------
>From: Darrel Therriault[SMTP:[log in to unmask]]
>Sent: Friday, October 13, 2000 10:58 AM
>To: [log in to unmask]
>Subject: Re: [TN] Baking PWA before BGA rework
>
>Charles,
>
>Good question. I just recently had some boards baked at 125c for 24 hours
>to do BGA replacement
>only to find when they came out of the oven that the shrink wrap on several
>electrolytic caps had
>cracked and peeled. I found the upper operating environment for the caps
>was stated at 85c, although I
>don't believe that means it is the max temp they can stand. The spec sheet
>did not indicate a max
>temp for prolonged periods (e.g. bake time) other then to provide an
>assembly thermal profile, which had
>ramp/dwell time at around 150 seconds and max temp around 260c for 30
>seconds.
>
>I hope I missed something in the data sheet that will shed some light on
>this spec, as we rework BGAs
>often and I don't want to be destroying or degrading anything on the board.
>
>Regards....DT
>
>
>
>At 09:34 AM 10/13/00 -0400, you wrote:
> >Hello TechNetters!
> >
> >I am interested in the baking parameters being used for assembled PCBs
> >prior to BGA rework in order to reduce risk of moisture-related damage.
> >
> >Component vendors often suggest 125'C for 24 hours, but this is based on
> >component level requirements for drying out unmounted components. I
> >have heard of baking assembled PCBs at 90'C for 48 hours.
> >
> >Your input is most appreciated.
> >Charles.
> >
> >--
> >Charles Elliott, P.Eng.
> >Physical Technology Engineer, Alcatel CID
> >[log in to unmask]
> >
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