PCB Blog - PCB Cooling Technology and IC Packaging Strategy

It is difficult for semiconductor manufacturing companies to control the systems that use their devices. However, the system with  IC devices is critical to the overall device performance. For customized  IC devices, system designers usually work closely with manufacturers to ensure that the system meets many cooling requirements of high power consumption devices.

This early mutual cooperation can ensure that the IC devices meets the electrical standards and performance standards, while ensuring normal operation in the customer's cooling system. Many large semiconductor companies sell devices with standard parts, and there is no contact between manufacturers and terminal applications. In this case, we can only use some general guidelines to help achieve a better passive cooling solution for IC and system.

Figure 1 PowerPad Design
The first aspect of PCB design that can improve thermal performance is  PCB design layout. Whenever possible, the high power consumption components on the PCB should be separated from each other. This physical spacing between high power consumption components maximizes the area of the PCB around each high power consumption component, thereby contributing to better heat conduction. Care should be taken to isolate the temperature sensitive components on the PCB from the high power consumption components. Whenever possible, high power consumption components should be installed away from PCB corners.

The more central PCB position can maximize the board area around the high power consumption components to help heat dissipation. Figure 2 shows two identical semiconductor devices: components A and B. Component A is located at the corner of  PCB design, and there is a chip junction temperature 5% higher than that of component B, because the position of component B is closer to the middle. As the area around the component for heat dissipation is smaller, the heat dissipation at the corner of component A is limited.

Fig. 2 Effect of component layout on thermal performance. The chip temperature of PCB corner assembly is higher than that of intermediate assembly.
The second aspect is the structure of the PCB, which has the most decisive influence on the thermal performance of PCB design. The general principle is that the more copper in PCB, the higher the thermal performance of system components.

The ideal heat dissipation condition of semiconductor devices is that the chip is mounted on a large piece of liquid cooled copper. For most applications, this mounting method is not practical, so we can only make some other changes to PCB to improve the heat dissipation performance. For most applications today, the total volume of the system continues to shrink, which has a negative impact on the thermal performance. A larger PCB has a larger area that can be used for heat conduction, and also has greater flexibility, leaving enough space between high power consumption components.
Whenever possible, maximize the number and thickness of PCB copper grounding layers. The weight of ground plane copper is generally large, and it is an excellent heat path for the whole PCB to dissipate heat.

For improving heat dissipation performance, the top and bottom layers of PCB are "golden locations". Using wider wires and wiring away from high power consumption devices can provide a heating path for heat dissipation. The special heat conduction plate is an excellent method for PCB heat dissipation. The heat conduction plate is generally located on the top or back of the PCB and is thermally connected to the device through direct copper connection or thermal through-hole.

In the case of inline packaging (only the packaging with leads on both sides), this heat conduction plate can be located on the top of the PCB, and its shape is like a "dog bone" (the middle is as small as the package, the copper area connected far from the package is large, and the middle is small and the two ends are large). In the case of four side packaging (there are leads on all four sides), the heat transfer plate must be located at the back of the PCB or enter the PCB.

Figure 3 Example of "dog bone" method for dual in-line package
Increasing the size of the heat conducting plate is an excellent way to improve the thermal performance of PowerPad packaging. Different sizes of heat conducting plates have great influence on thermal performance. The product data sheet provided in tabular form generally lists these dimensions. However, it is difficult to quantify the impact of copper added to customized PCBs. With some online calculators, users can select a device, and then change the size of the copper pad to estimate its impact on the thermal performance of non JEDEC PCB. These calculation tools highlight the influence of PCB design on heat dissipation performance. For the four side package, the area of the top pad is just smaller than the bare pad area of the device. In this case, the first way to achieve better cooling is to bury or back layer. For dual in-line package, we can use the "dog bone" pad style to dissipate heat.

Finally, systems with larger PCBs can also be used for cooling. When the screw heat dissipation is connected to the heat conduction plate and the ground plane, some screws used to install PCB can also become effective heat paths to the system base. Considering the heat conduction effect and cost, the number of screws should be the maximum value to reach the point of diminishing returns. After connecting to the heat conduction plate, the metal PCB reinforcement plate has more cooling area. For some applications where the PCB cover has a housing, the type controlled welding repair material has higher thermal performance than the air-cooled housing. Cooling solutions, such as fans and heat sinks, are also common methods of system cooling, but they usually require more space, or need to modify the design to optimize the cooling effect.

In order to design a system with high thermal performance, it is far from enough to choose a good IC devices and closed solution. The thermal performance scheduling of IC devices depends on the capacity of PCB and the thermal system that allows IC devices to cool rapidly. The passive cooling method can greatly improve the heat dissipation performance of the system.