Brochures

2 Electrothermal Mechanical Stress Reference Design Flow for Printed Circuit Boards and Electronic Packages // components, mainly the ICs. Power losses in conductors within the board and heat generated by ICs increase their temperatures, leading to thermal problems. Moreover, modern microprocessors can demand peak currents of 100 amperes or more. These high currents cause significant heat dissipation in the ICs and significant Joule or Ohmic heating in the connected power planes and traces. Even a small change in temperature can affect a device's performance due to the inverse relationship between electrical and thermal conductivities. Temperature gradients across the board and components can produce mechanical reliability problems owing to the cyclic nature of thermal transients. This follows f rom the principle of the bimetallic strip, which can convert temperature differences into mechanical displacement. Per this principle, when two metals with dissimilar CTEs are bonded together, they will bend if they are heated. Because a PCB is made up of many layers of different materials laminated together, it can bend when heated. This bending can cause solder joints to crack or even result in delamination of the board or traces on the PCB. / Electrothermal Mechanical Stress Solutions from ANSYS These electrical, thermal and mechanical challenges become significantly worse as the board complexity increases. Therefore, it is critical to use simulation tools to identify potential failure points prior to fabrication and perform "what-if" tests to mitigate these problems early in the design cycle. ANSYS provides time-tested simulation tools for solving any physics f rom electromagnetics, computational fluid dynamics or mechanical engineering. Specific challenges impacting performance and PCB reliability are power integrity, signal integrity, electromagnetic interference, vibration, thermal transients and stress. ANSYS has developed a unique Chip-Package-System (CPS) electrothermal mechanical stress reference design flow to detect these problems early in the design cycle. The solution is comprehensive, carefully examining the interaction between the chip, package and system f rom standpoints of electrical issues and thermal stress in an integrated environment. Products used to analyze electrothermal and structural problems are as follows: • ANSYS SIwave • ANSYS Icepak • ANSYS Mechanical Enterprise (which includes ANSYS SpaceClaim Direct Modeler) / Simulation Tools from ANSYS This section gives a brief description of ANSYS products and the role each of them plays in the flow. ANSYS SIwave SIwave is a specialized tool that allows users to import electrical CAD (ECAD) data to predict electrical behavior and performance. In SIwave you can predict signal integrity, power integrity and DC voltage drop performance along with EMI/EMC and various other analyses. In the electrothermal stress problem, SIwave is used for running a DCIR analysis to calculate the DC power losses across the ICs and PCB. ANSYS Icepak Icepak performs computational fluid dynamics analyses for IC packages, PCBs and electronic assemblies f rom chip level to data centers. Icepak predicts steady-state and thermal transient temperatures for heat transfer mechanisms such as conduction, radiation, forced air and natural convection. For our problem, Icepak calculates temperatures across the board and ICs while predicting whether components are within safe operating temperature limits. Icepak has forced convection and natural convection thermal analyses options for the board and its components. In forced convection, you can model air flow analysis with fans and specify the speed and direction of the air flow. In natural convection, the distribution of heat across the board is used to determine the air flow. Figure 2. Pictorial depiction of reference design flow

• Cover