Temperature. What do we understand about its nature and influence? We can easily estimate the temperature of the surrounding air, water or even kettle without using auxiliary devices. The result of this evaluation is simple and rough: cool, comfortable, warm and hot. In most cases, we don’t even think about exact values because we don’t really care about accuracy. However, the temperature in the world of electronics means a lot on each stage of the device’s life, from creation (while soldering for example) till end usage.
The temperature may influence the resistance of resistors, the capacitance of capacitors, the electrical conductivity of copper, the dielectric constant of materials, etc., which affects the product’s reliability and performance in general. Manufacturers guarantee the fulfilment of the stated parameters of each integrated circuit or discrete component only in the temperature range specified in datasheets. But is it so important to follow these requirements, or you can decide to use components with extended temperature performance and forget about this problem at all? It’s very important! Because nowadays electronics has entered almost every sphere of our life, the market imposes strict requirements for performance, design and size of products. At the same time competition is forcing manufacturers to use cheap components and reduce the time gap between the start of design and date of release of the finished product. That is why thermal management cannot be ignored in the design process.
One of the most fast-growing areas of electronics is the development of so-called Embedded Systems and Systems on Module (SOM). All the latest trends of the electronics are submitted in this segment: each manufacturer of SOM-modules tries to make tiny printed circuit board with top configuration and lot of interfaces. It increases placement density and power consumption per unit area of the PCB. Thermal analysis and optimization is a paramount and inalienable part of the design process for such a technological solution.
Even at the stages of selecting and placing components engineer is able to make a primary thermal analysis of the future product and, if it’s necessary, to correct BOM (Bill of Materials) before PCB layout. Proper location of major energy-consuming units and equal distribution across the surface of the board can significantly decrease the probability of thermal issues in future. Obviously, it is much easier and cheaper to take care of the problems related to power dissipation at the design stage than to solve them after product assembly. Furthermore, in most cases, it is totally impossible to fix completed product because of design constraints and a significant increase in cost. That fact forces vendors to launch new product revision and significantly shifts release date of product on the market.
Right after optimization of BOM and placement goes PCB layout design. On this stage, it is necessary to optimize the path for heated air to remove it from critical places on board if it has not been solved on the placement stage. In systems with natural cooling, about 70% of the heat goes from chip down through the copper to the board, and only 30% can be dissolved with the environment. Therefore foil of power and ground layers should thicker than 1oz. Using wide copper areas, the maximum exposed pad connection to the ground plane through vias can significantly improve the heat dissipation of the circuit board. Free space on the board has to be filled by copper and connected to the main ground plane. For the most powerful integrated circuits, like processors, memory chips, power converters, it is strongly recommended to put mounting holes for fastening the local heatsinks, if space permits on the board.
Thermal analysis is a complex procedure, which starts with the selection of components and goes through the whole product development cycle. Not every design is able to dissolve the heat without auxiliary cooling devices. But this important goal may provide a better hand in tough competition between manufacturers and to increase the reliability of the final product. But it is necessary to try just to get the slightest advantage in a tough manufacturer competition and increase the reliability of the final product.