Transistor Ruggedness

Author: Leonard Krugman

Insofar as ruggedness is concerned, the superiority of the junction transistor compared to the point-contact type can be anticipated from a comparison of the basic construction details (Chapter 2). The emitter and collector electrodes of the point-contact type depend on a force contact with the germanium surface. These cat-whiskers, it will be remembered, are fastened to the main electrode conductors which are embedded in, and held by, the plastic stem. It is possible, then, to vary the contact pressure of the cat-whiskers by a twisting force applied to the plastic stem. This distortion can be introduced by direct mechanical force, humidity or temperature variations.

Most of the present transistors are hermetically sealed. Sealing is important because of the ease with which an unprotected junction surface may be contaminated by water vapor. The contaminating effects are particularly noticeable so far as the value of the saturation current in an unsealed unit is concerned. In a typical case, the saturation current of a junction transistor will increase one hundred times its dry air value when the relative humidity is increased by 50%.

The transistor can withstand shock, vibration, and drop tests far beyond those of the vacuum tube. However, it is a good plan to treat the transistor with reasonable care to avoid unnecessary damage. The effect of distortion of the stem on electrode contact pressure was noted in earlier paragraphs. Any damage to the hermetic seal is, of course, serious. Transistor electrode leads are generally as flexible as those of regular carbon resistors. These leads should not be subjected to continual bending or flexing, or to pulls greater than a half-pound.