Requirement for robust capacitors in high density power converters

Power supply designers are faced with complex component size and part shape issues in order to minimize circuit board land area and maximize cubic space efficiency. Packing density and logical layout of the topology is often made difficult because of the mechanical and electrical shortcomings of the components. Chip capacitors are perhaps the most fragile components in the power system, being easily damaged by external physical events. Capacitor damage often occurs from process events such as pick and place, part soldering, temperature shock, and circuit board flexing during circuit board assembly. Less obvious reasons for damaged capacitors are location of chip capacitors near board edges, proximity to large heat sinks, pad size and solder fillet mass. Large chip capacitors are very fragile to mechanical shock of any kind, so it is often necessary to use multiple small units or employ special lead frame chip carriers to avoid cracking. Field problems related to chip component fragility cause converter designers to add cost in terms of component safety margin allowance and special handling and housing for the chip components on the board. This paper discusses tantalum capacitors, multilayer ceramic capacitors, and metallized film capacitors with respect to their robustness in power supply applications.