In this series, I will be going in depth on the topic of Electronics Packaging Assembly. As engineers and product designers, this is important to understand as it informs our design decisions in products which contain electronic components and helps us forecast the future of the electronics industry.
Before I can introduce Electronics Packaging Assembly, we must briefly discuss what an electronic system is. This may seem trivial, since we are surrounded by electronic systems every day, but can you formally define an electronic system? You may know that your smartphone is electronic and your desk lamp is not, but what is the intrinsic difference?
At it’s heart, an electronic system uses electricity to bring together or manipulate information. Electronic systems are designed for specific applications and therefore each collects and handles different information in different ways. However, all electronic systems use electrical currents to communicate and manipulate information, and are therefore made of components with special electrical properties. As these systems have evolved, the basic elements of these systems have become standardized and can be described as follows.
At the heart of most electronic systems is the integrated circuit, or IC. ICs are highly complex electrical circuits made up of a large number of transistors. Transistors act as gates for electrical current, and can be either “open” or “closed”. This open-or-closed behavior is the basis of binary signals (0s and 1s) in electronics, which makes up all digital information. ICs are built on a special class of materials called semiconductors with unique properties that allow for easy creation of tiny transistors. The most commonly used semiconductor material in ICs is silicon. Many ICs can be built on a single silicon wafer using chemical processes, and the processed wafers are broken up into “chips” or “dies”.
All electronic systems also contain some combination of the basic electrical circuit elements – including resistors, capacitors, inductors, op-amps, diodes, and more. Since electronic systems manipulate energy and information using electricity, engineers use these circuit elements to further control the behavior of their electronic systems. It should be noted, that these elements have associated losses. Resistors, capacitors, and inductors all contribute to the impedance of the electrical signal, which is mostly converted into heat and must be managed carefully for the system to be operational.
ICs and circuit elements come together when they are mounted on a substrate – a flat or planar component designed specifically for this purpose. A substrate’s function is often electrical, mechanical, and thermal. The electrical function of the substrate is to provide the pathways for the IC to receive and send signals to other components in the system. The mechanical function of the substrate is to support the IC and the “interconnects” which connect it to the system (more on this later). The thermal function of the substrate is to conduct heat away from the IC and, ideally, out of the system. Substrates are generally made from a combination of electrically conductive materials, like metals, and electrically insulated materials, such as organic polymers or ceramics.
The electrical connections between the IC and the substrate are known as the “first level interconnects”. These are crucial, as they are what allow the IC to send electrical signals to other parts of the system. Like the substrate, interconnects often serve a mechanical and thermal purpose in addition to their electrical purpose. Interconnects must provide mechanical connection between the IC and the substrate and a thermal pathway for heat to move out of the chip and into the substrate – without generating to much heat themselves. In modern electronics, interconnects can be broadly classified into two types: Wire Bond and Flip Chip. The process by which interconnects are formed is generally referred to as “assembly”.
Next time, we will discuss Assembly and the differences between a Wire Bond and a Flip Chip.
