TO-3 at Motorola around 1955. The lead spacing was originally intended to allow plugging the device into a then-common tube socket. The metal package can be attached to a heat sink, making it suitable for devices dissipating several watts of heat. Thermal compound is used to improve heat transfer between the device case and the heat sink. Since the device case is one of the electrical connections, an insulator may be required to electrically isolate the component from the heatsink. Insulating washers may be made of mica or other materials with good thermal conductivity. The case is used with high-power and
Distributed element circuit led to wider applications. Distributed element circuits are those circuits designed using the distributed element model. This model is an alternative to the lumped element model in which the passive electrical elements of electrical resistance, capacitance and inductance are assumed to be "lumped" at one point in space in, respectively, a resistor, capacitor or inductor lumped component. The distributed element model is used when this assumption no longer holds and those quantities are considered to be distributed in space. The assumption breaks down when there is a significant time taken for electromagnetic waves to travel from one terminal of the