Power in small packages

Packaging improvements let dc-to-dc converters and power modules pack in the juice. Modular dc-to-dc converters once came in half-inch-high packages that measured about 2 X 5 in. When first introduced, there was nothing like it in terms of concept, form factor, or topology. Although the basic elements of concept, form factor, and topology have remained essentially unchanged through a number of generations, the packaging has changed significantly. Continued tweaking together with electrical enhancements have produced families of modules with different electrical performance characteristics and operating ranges, sizes, baseplate and mounting options, pin styles, standoffs, and termination options. More importantly, today's modules boast three times the power and power density and one-third the parts count of the originals. Plus, the price per watt has been dramatically reduced. Most packaging changes are made in the interest of higher power density. The main objective is to get the maximum volume in those elements that transfer power or magnetic flux. From a packaging standpoint, the challenge translates to physically minimizing the size of elements not in the power train while maintaining structural integrity and dielectric capability. For instance, package wall-section thicknesses that were once 50 thousandths of an inch are now 6 or 7 thousandths. Packaging improvements show up on baseplates and termination systems, customized transformers and chokes, and interconnect systems. Improvements focus on maximizing performance and minimizing converter volume. The challenges designers face include increasingly higher power demands, greater electromagnetic disturbance, and more heat. Recent converters have a higher power density which meant finding creative ways to remove heat from the module. Foremost of these was the plated-cavity design. Also significant is the effectiveness of the thermal interface between the module baseplate and the user's heat-conducting material. Its effectiveness depends on minimizing thermal resistance across the interface which minimizes air in the interface. One