june 2005

pace micro technology, united kingdom, used thermal and electromagnetic compatibility (emc) software to reduce temperature of a new set-top box by 5%, substantially increasing disk drive reliability and life. alan bate, senior design engineer for pace micro, used flotherm software from flomerics to simulate the thermal performance of the case. he used the simulation results to trade off the thermal performance of different heat sink geometries and materials and venting arrangements against their cost. meanwhile, bate used generic emc design guidelines developed by araf suhail, consultant emc engineer for pace micro, using flomerics flo/emc software to ensure that the mechanical design kept emissions below the level required to maintain electromagnetic compatibility (emc). “flotherm enables us to evaluate many cooling strategies at a fraction of the time and cost required for physical prototyping,” bate said.

pace micro technology is the world's largest dedicated developer of digital tv set-top box technology and the only company to design digital tv set-top boxes for all broadcast platforms ― cable, satellite, terrestrial and digital broadband media. in the highly competitive set-top box market, a difference of a month or two in how quickly a product can be brought to market can make the difference between success and failure. the company has long faced the challenge that physical testing of just one design iteration for important mechanical design considerations such as thermal performance and emc requires a long process for the construction of a physical prototype.

before beginning the use of simulation, bate validated flotherm results against physical testing and demonstrated its ability to predict internal enclosure temperatures within one half degree centigrade. because temperature is critical to the life of the hard drive, the fan is positioned to blast the hard drive directly while exhaust air is used to cool other electronic components. bate developed a special cowling for this model designed to reduce hard drive temperature by augmenting the air flow around the hard drive and extracting heat from the sides of the drive.

in order to validate and optimize his design, he created a flotherm model that allowed him to visualize airflow and temperature profiles inside the enclosure and predict the temperature of the hard drive body and air. in particular the cowling provides a thermal path from the sides of the drive to remove heat generated by the motor and air friction produced by the magnetic disk spinning at 7200 rpm. the heat is then transferred into the fan air stream using a specialised fin arrangement, which was developed using the thermal simulation software. the relative performance of aluminum plate versus mild steel as the cowling material was also carried out.

in evaluating the thermal impact of venting arrangements, bate paid close attention to the guidelines developed by suhail in order to assure that the resulting design also met emc requirements. suhail had previously evaluated generic metallic enclosures of the type used in nearly all of pace micro’s products using flo/emc to predict the electromagnetic interference (emi) generated by the design and diagnose its causes. these simulations provided him with an understanding of how electromagnetic resonances are generated within the set-top box enclosures. he then developed design methods to reduce the magnitude of these resonances. “flo/emc helped us identify and avoid enclosure resonances and develop generic emc guidelines that help meet emissions requirements the first time around,” suhail said. these design methods were used by bate during the optimization process to be sure the resulting product met emc as well as thermal requirements.