The TO-66 package consists of a diamond-shaped base plate with diagonals of 31.4mm (1.24in) and 19.0mm (0.75in). The plate has two mounting holes on the long diagonal, with the centers spaced 23mm (0.91in) apart. A cap attached to one side of the plate and under which the semiconductor chip is located, brings the total height to up to 8.63mm (0.340in). Two pins on the other side of the plate are isolated from the package by individual glass-metal seals. The metal case forms the third connection (in the case of a bipolar junction transistor this is typically the collector).
Variants
TO-66 is often used as a synonym for any of the variants that have the same footprint (i.e. position of mounting holes and pins) as TO-66.
TO-123
TO-123 reduces the maximum thickness of the base plate from 1.90mm (0.075in) to 1.02mm (0.040in).[4]
TO-124
TO-124 increases the maximum thickness of the base plate from 1.90mm (0.075in) to 2.59mm (0.102in) and the maximum total height from 8.63mm (0.340in) to 9.02mm (0.355in).[5]
TO-213
TO-213 is intended to replace previous definitions of flange-mounted packages with a 5.08mm (0.200in) pin spacing.[6] The different outlines are now defined as variants of TO-213: TO-66 is renamed to TO-213-AA, TO-123 to TO-213-AB, TO-124 to TO-213-AC.
It is relatively common to find packages that contain other components than their designated ones, such as diodes or voltage regulators in transistor packages, etc.
