The term Transistor Outline package (more commonly referred to as TO packages) has been used for several decades. It is an industrial standard that governs the design and size of current-conducting microelectronic packaging and housings. A TO package always consists of two components: a TO header and a TO cap. While the TO header makes sure that the encapsulated components are provided with power, the cap ensures the smooth transmission of optical signals. This includes the transmitters (e.g. laser diodes) as well as the receivers of the optical signals (e.g. photodiodes).
The TO header provides a mechanical basis for the installation of electronic and optical components such as semiconductors, laser diodes or simple electronic circuits, while at the same time providing power to the encapsulated components with the aid of pins. Optical components in TO packages such as photodiodes and laser diodes are particularly susceptible to damage from their environment. Humidity, in particular, can cause semiconductor elements to corrode rapidly, leading to failure of the entire component. This is why these TO header components require reliable and permanent protection.
In general, there are three different types of TO headers which are distinguished based on the production technology used in their manufacture:
- Shelled TO headers consist of a metal foil that was shaped using thermoforming and in which the pins are fixed using glass.
- Stamped TO headers come with raised heads (Stamp A) or flat heads (Stamp B):