Black Convex 8mm Dot on Circuit Boards??

[Tinkerat]

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

 

[davenn]

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

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 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

 

[Resqueline]

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.

 

[Tinkerat]

Thanks for the info Dave and Super Moderator. It is nice to finally know what it is. Very good explanation and pic.
Appreciatively John