What is Circuit Design

Circuit Designers try to make connections.

4. What is in a microcontroller package?

Most engineers who design circuit boards today have to include at least one integrated circuit in their design.  Decades ago, engineers had to make everything from base components -- transistors, relays, resistors, capacitors, etc...  In the 1960s, manufacturers began perfecting the techniques required to miniaturize those base components into some of the first prefabricated and ready to use packages they called Integrated Circuits (IC).  You likely have experience working with some of these devices in a digital logic class: the 555 timer IC, the 7400 series of integrated circuits, etc...  Nowadays, many of those purpose-built devices have been replaced by programmable microcontrollers such as the ATMega328P we will use in this design.

These integrated circuits are made by carefully exposing incredibly pure silicon to a variety of impurities in a very controlled environment.  Through the application of light, chemicals, vacuum, and heat, these engineers create microscopic transistors, diodes, and other rudimentary elements that make up a microchip or IC.  

This image of a silicon die shows a microcontroller complete with a microprocessor, and areas of RAM and ROM. (Wikipedia)

These silicon dies are often very small, very fragile, and usually difficult to work with directly so they are usually attached to stronger metal lead frames with tiny gold bonding wires.  Then the die and the lead frame are hermetically sealed into an epoxy package and stored in a warehouse at a distribution center until they are needed.  The packaging helps to protect the IC die during storage and use, and it allows for quick testing and installation.

This transparent picture shows a SOIC-14 package interior

There are other packaging options, including BGA and flip-chip packages.  And indeed, the silicon dies can be attached directly to a PCB in a Chip-on-Board configuration.

BGA Package

This artistic impression is an exploded image of a fictional BGA device.

Hard Way Hughes"Why would an electrical engineer ever need to know what's inside a package, just throw them on the board and go, right?  Not really, no.  There is a phenomenon known as 'ground bounce' that is caused by changing logic-levels and the inductive loop formed by the bond wires connecting the leadframe to the die.  'Bypass', also known as 'decoupling' capacitors are used to provide a short burst of electrical energy to the die to prevent the reference potential from changing as well as to localize the phenomena to the chip.  They have to be placed as close as possible to an IC."