PCB Tech - PCB production process and improve thermal reliability?

1. Design the schematic diagram according to the function of the circuit. The design of the schematic diagram is mainly based on the electrical performance of each component and the reasonable construction according to the needs. Through the diagram, the important functions of the PCB circuit board and the relationship between the various components can be accurately reflected. The design of the schematic diagram is the first step in the PCB production process, and it is also a very important step. Usually the software used for designing circuit schematics is PROTEl.

2. After the schematic design is completed, each component needs to be packaged through PROTEL to generate and realize the grid with the same appearance and size. After the component package is modified, execute Edit/Set Preference/pin 1 to set the package reference point at the first pin. Then execute Report/Component Rule check to set all the rules to be checked, and OK. At this point, the package is established.

3. Formally generate PCB. After the network is generated, the position of each component needs to be placed according to the size of the PCB panel. When placing it, it is necessary to ensure that the leads of each component do not cross. After the placement of the components is completed, a DRC check is finally performed to eliminate the pin or lead crossing errors during the wiring of each component. After all the errors are eliminated, a complete PCB design process is completed.

4. Use special carbon paper to print out the designed PCB diagram through an inkjet printer, and then press the side of the printed circuit diagram against the copper plate, and finally put it on the heat exchanger for hot printing. The carbon paper is printed at high temperature. The ink on the circuit diagram is glued to the copper plate.

5. Board making. Prepare the solution, mix sulfuric acid and hydrogen peroxide in a ratio of 3:1, then put the copper plate containing ink stains into it, wait for about three to four minutes, wait until all the copper plate except the ink stains are corroded, then remove the copper plate, And then rinse off the solution with clean water.

6. Punch holes. Use a hole drill to punch holes on the copper plate where holes are needed. After completion, introduce each matched component into two or more pins from the back of the copper plate, and then use a welding tool to weld the components to the copper plate. 7. After the soldering work is completed, conduct a comprehensive test of the entire circuit board. If there is a problem during the test, you need to determine the location of the problem through the schematic diagram designed in the first step, and then re-sold or replace the components. When the test passes successfully, the entire circuit board is completed.

How to improve the thermal reliability of PCB circuit boards?

Under normal circumstances, the distribution of copper foil on a PCB circuit board is very complicated and difficult to model accurately. Therefore, the shape of the wiring needs to be simplified when modeling, and the electronic components on the ANSYS model circuit board that are close to the actual circuit board can also be simulated by simplified modeling, such as MOS tubes, integrated circuit blocks, etc.

Thermal analysis

Thermal analysis in SMD processing can assist designers in determining the electrical performance of components on PCB circuit boards, and help designers determine whether components or circuit boards will burn out due to high temperatures. The simple thermal analysis only calculates the average temperature of the circuit board, and the complicated one needs to establish a transient model of the electronic device with multiple circuit boards. The accuracy of thermal analysis ultimately depends on the accuracy of component power consumption provided by the circuit board designer.

In many applications, weight and physical size are very important. If the actual power consumption of the component is small, the safety factor of the design may be too high, so that the circuit board design uses the power consumption value of the component that does not match the reality or is too conservative. Perform thermal analysis. The opposite (and more serious) is that the thermal safety factor is designed to be too low, that is, the temperature of the component during actual operation is higher than that predicted by the analyst. Such problems generally require the installation of heat sinks or fans to the circuit board. Cool down to solve it. These external accessories increase the cost and prolong the ** time. The addition of a fan in the design will also bring unstable factors to the reliability. Therefore, the circuit board mainly adopts active rather than passive cooling methods (such as natural convection, conduction and Radiation heat).

Simplified modeling of circuit boards

Before modeling, analyze the main heating components in the PCB circuit board, such as MOS tubes and integrated circuit blocks, etc. These components convert most of the power loss into heat during operation. Therefore, these devices need to be considered when modeling.

In addition, consider the copper foil coated on the circuit board substrate as a wire. They not only play a role in conducting electricity in the design, but also play a role in conducting heat. Their thermal conductivity and heat transfer area are relatively large. The circuit board is an indispensable part of the electronic circuit. Its structure is made of epoxy resin substrate. It is composed of copper foil coated as a wire. The thickness of the epoxy resin substrate is 4 mm, and the thickness of the copper foil is 0.1 mm. The thermal conductivity of copper is 400W/(m°C), while the thermal conductivity of epoxy is only 0.276W/(m°C). Although the added copper foil is very thin and thin, it has a strong guiding effect on heat, so it cannot be ignored in modeling.