The Design And Optimization Of PCB-Level Electrical-Thermal Coupling

Due to the high power density and low supply voltage of electronic system, large amounts of current need to be supplied through the power distribution network (PDN). Joule heat, generated by the current flowing through the conductors, e.g. traces, vias and planes, will affect the thermal conductivity of material, thus affecting the heat distribution of system. Besides, heat distribution will also affect the electrical conductivity of conductor, thereby affecting the voltage and current distributions of system.The coupling between electrical and thermal fields is getting more and more serious, which leads to temperature rise and reliability problem of interconnect. For PDN, since the lower and lower noise margin and threshold voltage, the impact on the system caused by the voltage fluctuation is getting growing serious, which makes the analysis of power supply system become increasingly important. There are some shortcomings existing in traditional electronic design that engineers always design electrical and thermal fields separately. For the purpose of designing power supply system accurately, in addition to know the operating current and voltage of system, we should consider some factors that affect the power supply system as well, such as joule heating, air convection. Based on the theory of electrical-thermal, This paper proposes a new method, taking the electrical-thermal design into account simultaneously. The content includes the following four aspects:1. Based on the theory of heat transfer, analyze the mutual influence between electrical and thermal fields by the use of equivalent thermal field; solve the equations of voltage distribution in electric circuit and heat distribution equation in thermal circuit by means of finite volume method, and lay the groundwork of iterative analysis on the electrical-thermal coupling.2. Electrical-thermal coupling analysis, study the relationship between electrical and thermal fields, including two aspects:one is the impact on the voltage and current density distributions caused by the heat from thermal field; the other is the impact on the heat distribution caused by the traces, vias and joule heat from electrical field.3. Electrical-thermal coupling optimization, put forward a concept of heat flow control, use a new strategy to optimize the design of anisotropic thermal conductivity in the multilayer PCB, and verify its effectiveness.4. Doing well in both of electrical and thermal fields simultaneously has significant effect on the overall methodology for electronic system design. In view of the proposed conceptual framework, summary a new system development process which takes electrical function and thermal effect into account.