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
Mechanical–electrical analogies using a topological network diagram even when components needing a distributed element analysis are present. In the electrical domain, a transmission line, a basic distributed element component, can be included in the model with the introduction of the additional element of electrical length. The transmission line is a special case because it is invariant along its length and hence the full geometry need not be modelled. Another way of dealing with distributed elements is to use a finite element analysis whereaby the distributed element is approximated by a large number of small lumped elements. Just such an approach was used