One of the biggest factors that is always considered in the semiconductor industry is heat and its movement. As we all know, semiconductor chips (or dice) produce heat during operation and when the heat stays on the chips, it would cause a lot of problems. This is the reason why an efficient heat transfer is of absolute importance.
One factor to consider in the efficient heat transfer is the flatness of the interfaces from the die to the heatsink. The image below shows us the optimal set-up of the die, interface (baseplate) and the heatsink.
We can see in this image that the heat from the die is being transferred to the baseplate, which is then transferred to the heatsink. This optimal set-up unfetters the heat generated by the die, providing the die a longer life.
However, if the interface is concave (see image below), the heat stays on the interface and in the die. This is because of the presence of a hollow space in between the interface and the heatsink. As we all know, air has a low molecular density, making it a poor conductor of heat. This is also the reason why solder voids at die attach are not acceptable.
This phenomenon makes the life of the die shorter and will make the product fail in a short span of time. As much as possible, manufacturers would want to have 0 flatness reading or a convex reading in cases where bolts are being used to connect the package to the heatsink (see figure below).
A certain convexity is preferred for packages like this which needs bolts. One good example is the SOT-227 where the baseplate is being locked at the heatsink using bolts.
Here at TEAM PACIFIC CORPORATION, we have developed a robust process to avoid this flatness phenomenon. This process ensures that the interfaces are connected evenly on the heatsink when mounted. TEAM PACIFIC CORPORATION had also developed a fast and accurate process of measuring the flatness of the baseplate to ensure that all the products being sent to our customers are passing the flatness criteria.