PCB layout follows many conventional methods, such as: hot spot dispersion; placement of the most heat-generating devices in the best heat dissipation position; high heat dissipation devices should minimize heat resistance between them when connected to the substrate; each layer of the PCB To put a lot of copper and more through holes. Prior to PCB layout, thermal design of the PCB is critical. The thermal distances that define the long side and the wide side of the device are equal, all x (mm), taking the thermal distance into consideration, the PCB area occupied by the device is: PCB layout, the above calculated data is often not feasible, because the PCB area is limited, if the layout according to the above data, the PCB area is not enough, so you need to compress the above data in a certain proportion, you can put The upper thermal distance divides by 2 as the compressed thermal distance, from which the PCB area occupied by the heat source device is calculated as follows: Annealing Machine,Pv Copper Strip Annealing Machine,Pv Copper Strip Annealing Equipment,Annealing Heat Treatment Machine Jiangsu Lanhui Intelligent Equipment Technology Co., Ltd , https://www.lanhuisolar.com
Current status and challenges of card-based terminals in the market
With the deployment of LTE wireless networks, the downlink data rate has reached and exceeded 1 Gbps. To handle such a high data rate, data terminals must have high data processing capabilities, which inevitably leads to increased power consumption. Several of the products we are developing have experienced thermal problems. Several prototypes have experienced system crashes even in a matter of minutes during high-rate data transmission. The root cause of these problems is heat generation. Thermal design has become a A challenge for card terminals. An example of Apple's iPAD product, a large number of users feedback their products in a higher environment problems, which reflects the importance of thermal design for the end product. Heat dissipation has become a key issue that engineers need to seriously consider in the early stages of product design.
The heat source devices of the terminal platform mainly include baseband chips, radio frequency chips, power amplifiers, and power management chips. Some of the power consumption of these devices can be found in the datasheets provided by manufacturers, and cannot be found in some data sheets. Heat source devices for power consumption data need to be estimated based on experience or similar project test data, and can also directly request relevant data from the platform provider. Table 1 shows the power consumption evaluation results of the main thermal power devices of a project. 
From the data in Table 1, we can see that the power consumption of a data card has approached 4W. To dissipate such a large amount of heat in a U disk-sized structure, the thermal design of PCB can be said to have become a product energy. A crucial design consideration for reliable work.
A thermal layout algorithm for card terminal products
The empirical heat flow density of natural convection cooling is 0.8mW/mm2, which means that when the power distributed per square millimeter of area is 0.8mW, it can produce good natural convection cooling effect. The thermal distance of the heat source device is calculated based on this empirical value. The calculation method is as follows:
The length of a certain chip is L (mm), and the width is W (mm). The power consumption of the device is Pd (mW).
The above calculation only considers the heat dissipation of the PCB on one side. Both sides of the actual PCB can dissipate heat. If the back of the heat source device is not placed on other devices, the copper on the back can also play the role of heat dissipation. The thermal distance at this time will be calculated as above. Half of the data, the PCB area occupied by the heat source device is calculated below. 
Table 2 calculates the layout thermal distance and layout area of ​​the heat source device in this project. 
Thermal operation reliability analysis of the device
The maximum junction temperature that any heat source device can withstand is limited, and this maximum junction temperature can be found in the data sheet given by the manufacturer. If the actual operating junction temperature of the heat source device is higher than the maximum junction temperature that can be tolerated, then the heat source The work of the device will enter an unreliable state. In this case, it is necessary to consider the placement of these devices away from other heat-generating devices in the PCB layout. Copper is surrounded by a large area and the inner layer and the bottom layer located directly below are also widely spread. Copper, in order to solve this kind of device junction temperature is too high, so calculating the actual operation of the heat source device junction temperature is also very important in the PCB thermal design. In addition, the temperature rise of the heat source device with respect to the environment needs to be calculated. Knowing the temperature rise of the heat source device with respect to the environment, it is known which of the heat source device has the highest temperature, so that the heat distribution process will be well aware.
Application of Thermal Design Algorithm and Reliability of Terminal Products in Projects 
The power consumption analysis of the heat source device, the calculation of the thermal distance layout area of ​​the heat source device, and the ambient temperature analysis of the heat source device are all completed and the layout of the PCB can be started. The layout of the PCB needs to follow the most basic thermal design principles, such as: hot spot dispersion; Place the device with the highest power dissipation and heat generation in the best position for heat dissipation; do not place devices with higher heat on the corners and the edges of the printed circuit board; heat-dissipating devices should be minimized when connecting to the substrate. The thermal resistance, etc., in addition to the above calculation of the compression thermal distance to place the heat source device, the heat source device within the compression thermal distance as little as possible cloth devices, but can not be deployed heating device, the back of the heat source device also try to cloth device It is even more difficult to deploy heating devices. Figure 1 shows the final PCB layout of this project, and Figure 2 shows its temperature measurement. As can be seen from the figure, this design method is practical.