Materials Selection for Mechanical Design
CONCEPTS AND EMBODIMENTS FOR COOLING POWER ELECTRONICS

Student Programme: MSc in Mechanical and Manufacturing Engineering

Concepts and Embodiments for Cooling Power Electronics
1.Problem
The failure rate of electronic equipment are dramatically increased with high temperature. Also, the high thermal stresses in the solder joints of electronic components which are mounted on circuit boards resulting from temperature variations are major causes of failure. Therefore, thermal control has become increasingly. In addition, the important heat cause is the current flow through resistance which result heating in the integrated circuits (IC) where several components such as diodes, transistors, resistors, and capacitors are placed in a single chip. Design and operation of electronic equipment are required heat flux which flow out from the circuit board from 1 Watt/cm2 to 100 Watt/cm2.

2.Concept

a) Heat flux conduction b) Heat flux convection c) Cooling immersion
Figure 1. Three possible concept which can exhaust heat flow out the electronic device There are three concepts design to get rid of heat generation which is the diffusion of heat from electronic equipment through a solid, liquid or gas. The first concept is heat conduction method which heat flux transfer to thermal medium such as copper, aluminum or silver. The cost of this method is expensive depending on the material medium property. The second choice is convection method which have cool air or any coolant flow pass electronic equipment . The convection heat transfer between a solid surface and a fluid is proportional to the velocity of the fluid. High fluid flow rate is forced by fan or pump and low fluid flow rate is use natural air to flow heat out. However, this method is fitness of the low heat generator. The third method is immersion method to eliminate heat which is heat exchanger between the electronic equipment surface and completely surrounded by a much larger volume. The advantage of this method is very high heat transfer flow out to surrounding. Therefore, the selection of a cooling mechanism for electronic equipment depends on the magnitude of the heat generated, reliability requirements, environmental conditions and cost 3.Embodiment 3.1 Heat conduction concept

Figure 2. Lead frame which is the medium of heat conduction
3.1.1 Lead frame
From figure 2, this method have heat occurring which is transported outside the electronic device through the leads. The chip is attached to the lead frame which have a highly conductive bonding material that provides a low-resistance path for heat flow from the chip to the lead frame. There is no metal connection between the lead frame and the leads, since this would short-circuit the entire chip. Therefore, heat flow from the lead frame to the leads is through the dielectric case material such as plastic or ceramic. However, the benefit of this method is large surface where the air flow pass.
3.1.2 Heat frame

Figure 3. Conduction cooling of a printed circuit board (PCB) with a heat frame, and the typical temperature distribution along the frame. From figure 3. a thick heat frame is used instead of a thin layer of copper cladding.
This is especially the case for multilayer printed circuit board (PCB) that are packed with high power output chips. Therefore, the generated heat from electronic equipment flow pass through high thermal conductivity coefficient material which is large area. The large heat flux are exhausted out to cold plate which is numerous different temperature.
3.1.3 Thermal conduction module

Figure 4. Cut away view of the thermal conduction module (TCM), and the thermal resistance network between a single chip and the cooling fluid.

From figure 4. In the TCM, one side of the chip is