Thermal management in high speed device development

25/05/2015

Temperature… What do we know about it? We can easily estimate the temperature of environment, 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, temperature in the world of electronics means a lot on each stage of device’s life, from creation (in soldering, for example) till implementation and domestic use.

It is known that temperature may influence on resistance of resistors, capacitance of capacitors, electrical conductivity of copper, dielectric constant of materials, etc. It affects product’s reliability and performance in general. For these reasons manufacturers guarantee that stated output and input parameters' values for the each integrated circuit or discrete component only within specified temperature range. But do we really need to follow only these requirements? Can we just take components with extended temperature range and forget about problems with heating? No! Nowadays electronics has entered almost every single 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 time gap between start of design and date of release of finished product. That is why thermal management can’t be ignored during design process.

Thermal analysis of SMARC module

One of the most fast growing area of electronics is 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 performance and lots of interfaces to communicate with outer world. It increases placement density and power consumption per unit area of ​​the PCB. Thermal analysis and optimization is paramount and inalienable part of design process for such a technological solutions.

Even at the stages of components selection and placing engineer is capable to make primary thermal analysis of 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 probability of thermal issues in future. Obviously, it is much easier and cheaper to take care of the problems related to power dissipation at 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. This forces vendors to launch new product revision again and again, 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 this issue has not been solved on the placement stage. In systems with natural cooling about 70% of heat goes from chip down through copper to the board, and only 30% can be dissolved with the environment. Therefore foil of power and ground layers should be thicker than 1oz. Using wide copper areas and proper connection between exposed pad and 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 from 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 the better hand in tough competition between manufacturers and to increase reliability of final product.