Transistor outline cans

Silicon micromachined semiconductor gas sensors are mainly packaged using standard metallic transistor outline (TO) headers as support, and wire bonding is used for their electrical connection. Typically, a metallic cap with a grid is fixed to the TO header with a hydrophobic gas permeable membrane on top of it. A filtering agent can be also included in the package. 

Post-reflow AOI systems cannot inspect hidden solder joints, such as those for ball grid arrays, pin grid arrays, and in some cases J-leaded devices, and can have high false accept or reject rates for some component types, such as fine-pitch components at or below 0.5 mm pitch or small outline transistor (SOT) devices. If tall components are placed on the board very close to smaller components, post-reflow AOI systems can also have difficulty inspecting these smaller components. 

Transistors are the subject of whole books by themselves. This section presents only the bare outline of transistor types and modes of operation, focusing primarily on materials-related issues. Later chapters make reference to these devices and so it is useful to know the general aspects of their structure and operation. However, virtually all important aspects of the science and engineering of electronic materials can be illustrated through discussion of diodes and capacitors. Consequently, the following description is very brief. 

---