Let me throw back the question of cap shorting with the emphasis that these
caps are quite a few places on the bottom side of the board but only the
caps at low voltage high impedance circuit give us trouble.

Did anybody seen the problem circuit related where epoxy might be playing a
roll to help short across the pads. I can not visually see the short but low
resistance reading makes to believe it. To me this is strange as epoxy is
nonconductive and we are seeing problem with the caps at particular circuit.

Any suggestion from process /design / rework will be greatly appreciated.

re,
ken patel


At 05:41 PM 11/19/97 -0800, Ken Patel wrote:
>Cap shorting Problem????
>
>Failure Analysis Expert,
>
>In a low voltage high impedance circuit we are finding ~700ohm short
>across a .1uF capacitor in a low voltage, high impedance DC circuit.  We
>find that over time the short develops, but a thermal cycle (touch-up) of
>the location causes the problem to disappear.
>
>We tried using X-ray of the cap's but proven inconclusive due to the density
>of the ceramic cap body and the suspected low mass of the short.  Our initial
>impression is that dendritic growth is occurring, and over time the two pads
>short through this growth but we were not able to find any dendritic growth
>(?) using microscope (30X). Is dendritic growth possible through epoxy which
>porous in nature? This cap is glued on the bottom side using epoxy and goes
>through wave soldering operation.
>
>We are looking for any answer cum suggestion from anyone who has seen this
>kind of problem were able to resolve.
>
>Thanking you in advance.
>
>Re,
>Ken Patel
>
>______________________________________________________
>Ken Patel                      Phone:  (408) 490-6804
>575 Cottonwood Dr.             Fax:    (408) 490-6859
>Milpitas, CA 95035             Beeper: (888) 769-1808
>
>
>
______________________________________________________
Ken Patel                       Phone:  (408) 490-6804
575 Cottonwood Dr.              Fax:    (408) 490-6859
Milpitas, CA 95035              Beeper: (888) 769-1808

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