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4 Electrothermal Mechanical Stress Reference Design Flow for Printed Circuit Boards and Electronic Packages // / Stage 2: Schematic Review Reviewing a schematic and understanding how it works involve recognizing the key components, ICs and electrical connections. This will help you comprehend how to set up the power sources and sinks within SIwave. Divide the schematic into functional blocks and identify components such as microprocessors, voltage regulators and sensors that generally do the most work on a circuit. Also, follow the nets, and find the corresponding pins and electrical connections. To illustrate, see a portion of the schematic shown in Figure 5. On our board, there are six power nets and two ground nets. These six power nets are P1.0V, P1.2V, P1.8V, P1.8VA, P3.3V and P5.0V. The two ground nets are EMI_GND and GND. Voltage sources should be attached to these power nets to model voltage regulators. To do this, you must identify the corresponding pins on the voltage regulator module (VRM). For example, in the schematic, Pin5 on U503 connects through an inductor L503 to power net NetL503_1 P1.8V. For Pin14, the net NetL304_1 connects through inductor L304 to power net P1.0V. Later in SIwave you can easily add voltage sources to represent the outputs of the VRM along with the associated series resistance. Ground and the 5-volt power net are supplied off-board through a B-style micro-USB connector with the reference designator P703. Therefore, voltage sources must be added to P703 too. Similarly, you must identify the power consumers on the board. Typically, RAM, FPGA and microprocessors are the main power consumers. To these ICs, assign current sinks in SIwave. After reviewing the schematic and "cracking the code" so to speak, list all the nets and components for assigning current sinks and voltage sources in a table: Figure 5. Schematic

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