chip scale package cooling solutions
CSP (chip scale package) packaging refers to a packaging technology in which the size of the package itself does not exceed 20% of the size of the chip itself. In order to achieve this goal, LED manufacturers reduce unnecessary structures as much as possible, such as using standard high-power LEDs, removing ceramic heat dissipation substrates and connecting wires, metallizing P and N poles and directly covering fluorescent layers above LEDs.
Thermal challenge：
CSP package is designed to be directly welded to printed circuit board (PCB) through metallized P and N poles. In one way, it is indeed a good thing. This design reduces the thermal resistance between the LED substrate and the PCB.
However, since the CSP package removes the ceramic substrate as a heat sink, the heat is transferred directly from the LED substrate to the PCB, which becomes a strong point heat source. At this time, the heat dissipation challenge for CSP has changed from "level I (LED substrate level)" to "level II (whole module level)".
From the thermal radiation simulation experiments in Figures 1 and 2, it can be seen that due to the structure of CSP packaging, the heat flux is only transmitted through the solder joint with a small area, and most of the heat is concentrated in the center, which will reduce the service life, reduce the light quality, and even lead to LED failure.
Ideal cooling model of MCPCB：
The structure of most MCPCB: the metal surface is plated with a layer of copper coating of about 30 microns. At the same time, the metal surface is also covered with a resin medium layer containing heat conducting ceramic particles. However, too many thermal conductive ceramic particles will affect the performance and reliability of the whole MCPCB.
Researchers found that an electrochemical oxidation process (ECO) can produce a layer of alumina ceramics (Al2O3) with tens of microns on the aluminum surface. At the same time, this alumina ceramic has good strength and relatively low thermal conductivity (about 7.3 w / MK). However, because the oxide film is automatically bonded with aluminum atoms in the process of electrochemical oxidation, the thermal resistance between the two materials is reduced, and it also has a certain structural strength.
At the same time, the researchers combined nano ceramics with copper coating to make the overall thickness of the composite structure have high total thermal conductivity (about 115W / MK) at a very low level. Therefore, this material is very suitable for CSP packaging.
The thermal problem of CSP packaging leads to the birth of nano ceramic technology. This nano material dielectric layer can fill the gap between traditional MCPCB and AlN Ceramics. So as to promote designers to launch more miniaturized, clean and efficient light sources.
