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108 The PCB Magazine • December 2015 The use of structural metal in the manu- facture of electronic circuits has been a part of the electronics' industry technology toolkit for many decades. For example, metal chassis structures were required and used in the early days of the electronics industry to both sup- port the weight and handle the heat generated by the vacuum tube components that were the transistors of their day. Vacuum tubes are still used to this day in many applications, but most notably in large-scale sound amplifiers such as those seen at outdoor events and rock concerts (Figure 1). Such assemblies typically employed sock- ets to receive the pins of the vacuum tube and discrete wires were soldered to the pins of the socket to make interconnections between vari- ous components and distribute power and ground. Many early printed circuits also had to deal with significant heat flux and ceramic re- fractory materials were commonly called upon to address the challenge. Well, ceramic materi- als are quite capable of dealing with the heat one of the problems they have is that they are brittle. As a result, they require more attention than traditional resin glass composites, which by Joe Fjelstad Verdant electrOnIcS e.i. files Insulated Metal Base Circuits— an Enabling Technology for Power Electronics ColuMn Figure 1: present day audio amplifier employing vacuum tube technology.