Chip On Board - Skip the Package and Join the Fun
Substrates are used as a carrier for the silicon. The two main reasons are to avoid a CTE mismatch and to protect the integrated circuit from the environment. Another benefit is that the connections can be spread out so that a lower technology PCB can be used. Some types of packaging will have a lead time measured in months. They also cost a lot of money in non-recurring engineering (NRE) and a bit more per piece. There are cases where it makes more sense to lose the transposer and put the device right on the PCB. Let’s take a look at that idea.
Chip-On-Board (COB) is just what it says on the tin. There are basically two ways to perform die-attach. One way involves bumps on the bottom of the die; just like a normal BGA except smaller. These “Flip Chips” will test your PCB vendors ability to create tiny footprints. Then they will test your assembly partner’s ability to place, reflow and underfill the Flip Chip On Board (FCOB).
The underfill is necessary because of the different coefficient of thermal expansion of the materials. Without the underfill, the CTE mismatch will stress the flip chip to the point where the connections will not be reliable.
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4 年Good job John. Did you know that due to the asymmetric pin patterns sometime the underflow is not evenly spread. Also did we take care of the sacrificial balls concept in the wafer level packaging.