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Black Convex 8mm Dot on Circuit Boards??

Discussion in 'General Electronics Discussion' started by Tinkerat, Jan 18, 2010.

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  1. Tinkerat

    Tinkerat

    2
    0
    Jan 18, 2010
    Hi, Just joined this forum and am no electronics pro, just a hobby but I try. I have notices on 2 boards lately a black covex about 8mm dia. black what looks like resin of some sort, that traces lead into. Anyone know if there is an IC or something underneath? Also on the back of LCDs there is a larger convex black dot about the same. I have no clue what gives. Please share some of your knowledge with me. Sincerely John
     
  2. davenn

    davenn Moderator

    13,620
    1,882
    Sep 5, 2009
    John,
    Yup there is an IC under each of those black blobs .... generally what they call
    LSI ... large scale intergration IC's specially designed to perform a number of tasks

    you find them in all sorts of electronic equip .... alarm clocks, calculators, Home
    weather stations etc etc the list is endless :D I have some microwave transmitter
    and receiver gear that uses a similar idea but doesnt cover the area with sealer because
    that would destroy the RF properties of the circuit. see the attached pic ... although the
    part isnt a LSI chip the principle of connection the chip to the PCB is the same using fine
    gold bonding wires between the chip area track pads and the PCB area track pads

    cheers
    Dave
    VK2TDN
     

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  3. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Yes, as davenn says there is a chip under the epoxy blob.
    In my experience that kind of "packaging" method does not vouch for a reliable product.
    I guess the different expansion coefficients can shear off the bonding wires.
     
  4. Tinkerat

    Tinkerat

    2
    0
    Jan 18, 2010
    Thanks for the info Dave and Super Moderator. It is nice to finally know what it is. Very good explanation and pic.
    Appreciatively John
     
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