The IC – The Heart of Electronics
Modern computer processors and other microcontrollers rely on compact, low-cost ICs to function. These small, affordable circuits have made computers and mobile phones essential parts of contemporary life.
ICs contain electrical components such as transistors, resistors and capacitors on a piece of silicon semiconductor substrate and are sealed in packages with multiple terminals. The physical stresses on IC signals as they leave the die, travel through the package and lead to conductive traces on a printed circuit board require special design considerations.
Basics
A single IC contains many components, such as transistors, resistors and capacitors, all on a small semiconductor wafer. ICs also include internal “wiring” connecting various components. ICs are very small — their critical dimensions are typically on the order of 10 nanometers (nm: 10-9) meter.
Integrated circuits are constructed using two main techniques: monolithic and thin film. The monolithic IC consists of a single block of semiconductor material with various small areas processed to afford diode, transistor, resistor and/or capacitor action. This construction allows high reliability and uniformity.
Monolithic ICs are generally operated from a single op amp reference voltage DC supply voltage, V, which is supplied to the device through metal pins at its edges. Some devices require dual supplies, e.g., Vrc and V **, with Vrc connected to the device’s “collector end” and V ** to its “emitter end.” The maximum and typical supply-voltage values for an IC are specified in the manufacturer’s literature.
ICs can be classified according to their construction, operating mode and packaging. A basic logic IC combines logic gates to create timers, counters, latches and shift registers, etc. Logic ICs are commonly packaged in DIP, SOIC and SSOP packages. ICs can also be used to store data and perform calculations. Some ICs are digital while others are linear. A digital IC, such as an EEPROM or a microprocessor, is designed by following the steps of a logic design method.
Applications
The IC is the heart of most electronic devices. It can contain a collection of miniature versions of basic components such as transistors, resistors and capacitors or more complex circuits like logic gates, timers, counters and shift registers. It can also include memory chips that store data permanently or temporarily. ICs are so powerful that they can perform billions of operations per second. They have revolutionized electronics, making possible the handheld calculators, personal computers and cell phones that most people now carry around.
ICs are made from multiple layers of semiconductor material that are defined by photolithography. Some of these layers mark where various dopants are diffused (diffusion layers), some define where additional ions are implanted (implant layers) and others define the conducting paths that connect different parts of the chip (contact or via layers).
An IC’s functionality depends on how the various circuit elements are connected inside it. ICs that use digital circuitry process signals as discrete values such as on and off, using the logic of Boolean algebra. Analog ICs, on the other hand, produce signals that change continuously over a range of values. ICs that combine both types of processing are known as mixed-signal, and they’re commonly found in screen and sensor systems for portable electronics. An example is the microcontroller (microprocessor) used in a computer.
Fabrication
The IC fabrication process begins with the creation of a circuit diagram. This is converted into a physical layout using custom-designed software tools. The layout defines the shapes and relative locations of the various IC elements on the chip. It should match the schematic and obey design rules to minimize manufacturing defects.
The next step is to produce the silicon wafer that serves as the base for the IC. Electronic-grade silicon is purified from sand and heated to produce a molten liquid. A single piece of solid silicon is dipped into the liquid and pulled out, leaving behind a thin round slice of semiconductor material called a wafer. This forms the base or substrate for the IC.
Layers are then built up on the wafer. Each layer is etched, creating the desired patterns for different electrical components. Areas of the wafer are treated differently by adding or removing impurities, known as doping. Finally, a layer of metal is deposited and patterned by photolithography and etching to create wires and contact pads.
The individual ICs are then encapsulated into plastic or ceramic packages to protect them and provide a means of external connections. These packages may vary in shape and size depending on the application, but the ac motor controller most common form is the DIP (double in-line) package, with two parallel rows of pins extending perpendicularly from a square or rectangular shaped black plastic housing.
Packaging
The encasement called an IC package protects the semiconductor block from damaging environmental elements and corrosive ageing. The package also promotes the electrical contacts that deliver signals to the circuit board of an electronic device.
Choosing the right IC package type for an application is crucial. Various factors come into play such as power, connectivity and cost. The type of package you select should fit your design ideally and not be over engineered – which will raise the cost – nor under engineered, causing a sub par performance.
For example, if you have a microcontroller that requires a large number of pins then opt for a QFP (Quad Flat Pack) or TQFP (Tiny Quad Flat Package). These are smaller than BGAs and can accommodate more pins in the same footprint. Similarly, sensors like accelerometers and gyroscopes are typically offered in a tiny QFN form factor while more advanced microprocessors such as the ATmega328 that you’d find on a pcDuino or Raspberry Pi will be in a BGA package.
There are also surface mount packages, known as SMDs, which consist of a row or matrix of pins that extend perpendicularly from a rectangular black plastic housing. These are usually not hand-assembly friendly and require special tools to handle. Other small packages include DIPs, which have two parallel rows of pins that plug into socket-type connectors on a PCB.
