IAN LANG ELECTRONICS
There are three main packages in which an IC is supplied. These are the TO92, which is rather like a transistor, the small outline or flat package, and the dual inline package more commonly known as DIP. The latter is the most common you will come across. The shape is shown below:
How to Count Pins on an Integrated Circuit.
On an IC there is either a dimple or a notch or both. If there is a dimple, hold it away from you so that it is in the top left hand corner, if there is a notch , hold it facing away from you. In either case you should be looking down at the top of the IC. Now start counting from the top left hand corner downwards, and the top left hand corner is pin 1. If the IC has 8 pins, the one in the bottom left hand corner is pin 4, if 12 it is pin 6 and so on. Up the right hand side you count upwards, so the bottom right hand corner in an 8 pin IC is pin 5, on 12 pin 7 and so on. On an 8 pin then, the top right is pin 8.
The encapsulation is made of moulded plastic or ceramic, the former being the most common and the latter used for high-reliability (and high cost) devices. It is marked with a type, this one shows itself to be a small power amplifier as it is an LM386. The manufacturing company usually is named, and there will be a batch number. This may be a proprietary code unfathomable to the end user, or it may have a date marking. The two halves of the enclosure in a plastic casing are compacted and heat sealed, this provides a reasonable degree of hermeticity but is not perfect.
To the right is a simple model of the inside of a DIP packaged IC. The die sits on a gold plated mounting area which, if heated, when the die is pressed on forms a good mechanical bond. The terminal pads on the die are brought out to the leads out by means of extraordinarily thin gold wire, some 0.002 mm in diameter. This is welded at each end by forming a ball on the wire with a hydrogen flame and then compressing and allowing to solidify. The wire is then cut with the flame and the process repeated. The wire is held in a capillary tube to ease the process.