In view of the working environment characteristics of the engine electric pump controller, in order to solve the heat dissipation problem and improve the heat dissipation efficiency of the controller in the working process, the FR-4 and LTCC substrates are compared from the aspects of technology, size, material and performance, and the temperature rise simulation experiment is carried out; the technology of the electric pump controller is introduced. According to the process characteristics, the quality control scheme and quality control elements in the trial-manufacture process of parts are introduced. Finally, the heat dissipation test of the electric pump controller based on LTCC substrate is carried out. The results show that the heat dissipation effect of the controller based on LTCC substrate is improved to some extent compared with that of the controller based on common FR4 material. At present, with the continuous development of integration and intellectualization of automotive electrical devices, more and more functions and more controllers on automobiles, some control circuit boards are required to be installed in the engine compartment together with the controlled system, while the working environment near the engine is at a higher temperature, so the circuit boards are required to have high temperature resistance and resistance. High humidity performance and high reliability. LTCC (Low Temperature Co-fired Ceramics) has been widely used in the automotive field, such as various sensor modules, engine management system (EMS) and so on, because of its excellent characteristics. The engine electric pump is installed on the cylinder block of the engine and controlled by the controller. The controller is integrated into the inner part of the electronic pump assembly, as shown in Figure 1.
Because the engine block is near the worst environment in the engine room and the temperature field is high, if the heat dissipation design is not good, the stability of the controller will be poor, the life of electronic components will be reduced, the reliability and efficiency of the controller will be reduced, and the working efficiency of the electric pump will also be greatly reduced, not only can it not play the role of energy saving and emission reduction. Even the engine can not be effectively cooled, so the heat dissipation requirement of the electric pump controller is higher.
At present, FR-4 is one of the most commonly used sheets in our products. The electric water pump controller was manufactured on FR-4 substrate in the early stage. In the high temperature endurance experiment, the temperature of the controller was 130-140 degrees due to the poor heat dissipation of the substrate. The controller had many faults such as overtemperature protection and electrolytic capacitor bursting. In order to solve this problem, LTCC and FR-4 substrates with high thermal conductivity and good heat dissipation performance were selected for temperature modeling and simulation experiments. Firstly, the heating power of the electric pump controller is calculated, P=I2R, the internal resistance of the MOSFET on the controller is 10.5m_, and the maximum working current of the electric pump is 20A. Therefore, the heating power is P=20*20*10.
5/1000=4.2 W. Then, the same size LTCC and FR4 PCB are placed on the heater of 4.2W. The temperature rise of two PCB boards at the same position is simulated in real time.
The real results are shown in Fig. 2. It can be seen from Fig. 2 that the temperature rise can be reduced by 8-10 degrees with LTCC substrate. From Table 1, we can see that FR-4 sheet has the advantages of mature technology and low cost, but it has the disadvantages of low thermal conductivity and poor heat dissipation. LTCC sheet has higher cost, but its thermal conductivity is obviously better than FR-4 sheet. According to the design requirements of a scientific research project in Dongfeng, LTCC substrate is selected as the board of the controller for process, quality control process and performance verification.
The performance parameters of LTCC substrates used in this paper are detailed in Table 2 below.
Brief introduction of process flow The trial production process of engine electric pump controller mainly includes two parts: LTCC bare plate production and SMT (Surface Mount Technology) patch process. The following paper introduces the process flow and quality control scheme of these two parts separately. The technological process of LTCC bare plate is shown in Fig. 3. The sensitivity of technological parameters, the non-visualization of processing results and the non-reproducibility of burnt-out substrate are important factors affecting the quality of LTCC bare plate.
For specific product substrates, due to the difference of material, size, number of layers, structure, graphic distribution and post-burning state, it is often necessary to pass multiple rounds.
Only by adjusting and gradually optimizing the processing parameters of the actual products, can we get a satisfactory LTCC substrate [2]. After sintering, key indicators such as shrinkage, density, strength, smoothness and on-off state of the substrate are monitored. As can be seen from Table 3, on the premise of correct PCB design and guaranteed quality of components and solder paste, solder paste printing and reflow soldering are two key processes to ensure product quality.
At present, stencil printing is commonly used in solder paste printing. Stencil formwork is the steel mesh tooling in our trial production process. There are three main ways to improve the quality of solder paste printing: processing qualified stencils; selecting solder paste suitable for process requirements and using solder paste correctly; and controlling printing process.
For the control of solder paste printing process, the first step is to ensure that the leak pattern of PCB plate and steel mesh completely coincide. D: The reflux zone is above 183 C, maintained at 60S-90S and above 200 C at 20S-60S. E: The cooling zone temperature is set to be between 100 20 C, and the cooling rate is kept below – 5 C/S. The real-time temperature curve should be basically consistent with the above temperature curve in the welding process. LTCC has good thermal conductivity. Therefore, when reflow welding is carried out, the setting of equipment parameters should be reduced by about 5 degrees. At the same time, the welding quality of the first printed circuit board should be checked, such as whether the welding is sufficient, whether the surface of the solder joint is smooth, whether the shape of the solder joint is half a month or not. The temperature curves are adjusted according to the inspection results to meet the requirements of the above temperature curves. After the sample production is completed, it needs to be inspected to determine whether it has quality defects and meet the design requirements. In this paper, the quality of the sample is mainly inspected and evaluated from the following elements, as detailed in Table 4. In this paper, the heat dissipation test of the prototype is carried out. The verification condition is that the LTCC controller and assembly are put into the high temperature box for testing.
The high temperature box is heated to 120 degrees and runs at the highest load for 1 hour.
The results are shown in Figure 5 below. The red line is the temperature curve in the high temperature box, the green line is the temperature curve of LTCC controller, and the yellow line is the temperature curve of FR-4 controller. From the temperature test results of Fig. 5, the temperature of the controller of LTCC substrate is improved by 4 to 5 degrees compared with that of the controller of FR-4 substrate. This shows that LTCC can improve the heat dissipation effect to a certain extent. This paper mainly introduces the technological process, quality control scheme and elements of LTCC control board of engine electric pump, and tests its heat dissipation performance. The results show that the heat dissipation effect of the electric pump controller based on LTCC substrate has been improved to a certain extent. If the expected improvement effect is to be achieved further, thermostatic element the following will be from increasing the dispersion of LTCC controller.
Starting with the hot area, combined with the effective trial and verification method, the heat dissipation efficiency of the controller in the working process is improved.