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Conformal coating breakdown.

Discussion in 'Electronic Repair' started by N_Cook, May 29, 2010.

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  1. N_Cook

    N_Cook Guest

    Supposed to be there to keep damp/condensation out but over 20 years or so
    does the opposite. The waxy/jelly type coating (not the epoxy potting stuff)
    breaks down to an oily film that is probably hygroscopic - plenty of green
    copper carbonate and rotted IC pins. Gets inside chips capilliary-wise and
    rots them internally as well. Anyone happen to know what this oily breakdown
    product is chemically?
     
  2. N_Cook

    N_Cook Guest

    This is a previous encounter
    Digisonic 502 ultrasonic metal thickness meter
    The conformal coating may have been breaking down and causing an
    oil film on the board which could have seeped into the IC,
    74C00 on the display board had
    one NAND gate o/p stuck high
    Only ever used indoors

    Yesterday I broke into a new old stock , stored indoors (UK that is)
    Racal PIR unit to rob the RPY93 6.5 to 14 micron long-IR pyro to play around
    with, for remote temp monitoring
    and the pcb was covered in this waxy stuff now oily and green on some pins.
    Not powered up yet
     
  3. N_Cook

    N_Cook Guest

    Translucent appearance, so can make out form but not detail of components
    under it, same when new. There is also iron rust brown colour as well as the
    green.
    If it was a mixture of paraffin wax or petroleum jelly and silica gel I
    could see the silica taking in water and the other breaking down to an oil.
     
  4. N_Cook

    N_Cook Guest

    Didn't work , I'd not noticed one of the pyro TO5 size leads was corroded
    through.
    So much for Racal RLC1/2 , opened up a used working Racal IR771 with a RPY96
    (same spectral response) and LM324 to play with, no conformal around that
    one
     
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