What Makes Up a Circuit Chip?
A circuit chip contains a multitude of microscopic components, like transistors, resistors, and capacitors, that are interconnected to form complex digital or linear devices. These ICs (Integrated Circuit) make up most modern electronics and are used to power everything from computer processors to washing machines.
ICs are far smaller and cheaper than the discrete components they replace, while offering much higher performance. The process of constructing an IC involves many steps.
The Wafer
A wafer is the base unit of chip making. It’s a circular plate of a core raw material (typically silicon) that goes through many microfabrication steps, including thin-film deposition of various materials, photolithography patterning, etching, doping and ion implantation. Wafers are often divided by a process called wafer dicing into individual microcircuits. They then undergo further specialized processes to form transistors, integrated circuits and other complex electronics.
In the beginning, the wafer has a rough surface. It’s then polished, using a chemical-mechanical process in which a polishing slurry (a mix of chemicals and abrasive particles) is used. This makes the wafer smooth, and it also allows light to pass through it more easily. This step is important because it reduces the amount of impurities that can affect the performance of a finished IC.
Once the wafer is polished, it’s sliced into individual “die” that will become a chip. These dies appear glued to one another, but there’s actually a gap between them, which is known as a scribe line. This gap is left so a diamond saw can safely cut the dies apart during the final step of wafer processing.
The wafer is then positioned in front of a mask that contains a pattern that will be transferred to the chip. A special light is then used to expose the portion of the mask that’s over the wafer, transferring the pattern onto it. Some of the wafer’s surface then gets etched, or sculpted, to make it fit the pattern. Other areas get a dose of added materials, which is known as doping.
The Die
A die is a pre-shaped tool that’s used with a press to manipulate the size and circuit chip shape of raw materials like sheet metal. It’s like a mold, except it stamps the material rather than casting it. It can also be used in other ways such as etching patterns on coins or medals, or cutting sheet metal into pieces.
A circuit chip contains thousands of individual “die”, each containing a different part of the integrated circuit. Each die is the unbonded form of a finished IC, so it’s important that they are properly floor-planned, verified and debugged together to make sure they work as intended. This is a significant challenge as designs become increasingly complex and disaggregated.
The dies in an IC are tiny, with millions or billions of transistors and other components on a small area the size of your thumbnail. They’re too fragile to solder directly or connect to, so they are packaged.
The IC package encapsulates the delicate integrated circuit die and turns it into the black chip you see in electronic devices. The insulating layer of the die can include a seal structure with contact windows opened by etching in dielectric layers. The etched dielectric layers can contain plugs in various shapes and patterns. The block-shaped plugs in the example shown above (which are referred to as a “die seal structure”) help the integrated circuit resist sawing stress, thereby protecting the underlying integrated circuit.
The Substrate
The IC substrate is an essential component in the design of a circuit chip. It serves to help support the bare integrated circuit (IC) and route connections between the IC and PCB. It also provides a means of dissipating heat and providing the necessary stability to the IC during operation.
The type of IC substrate used will depend on the needs of the circuit being designed, with different materials available for a variety of applications. Resin-based materials are often used for smaller components, while organic materials are typically more suited to larger ones. The choice of material will also depend on the desired characteristics of the resulting product, such as thickness, CTE, and mechanical properties.
IC substrates are also available in a range of different shapes and sizes to suit the specific needs of each project. For example, flex substrates can be manufactured using polyamide or polyimide resin, while ceramic substrates are primarily made of aluminum nitride or silicon carbide.
Another recent trend in IC substrates has been towards smaller linewidths. This has been driven by the growing market for mobile devices like smartphones and tablets, which require smaller traces to accommodate more components in a smaller space. As such, a number of device manufacturers are now using IC substrates with linewidths much closer to those found on HDI PCBs.
The Package
A circuit chip’s components — transistors, resistors, capacitors, and inductors — are interconnected on a single piece of silicon or another semiconductor material. This unification is what allows an IC to perform all of the functions required by modern electronic devices.
Integrated circuits have three main advantages over circuits constructed with discrete components: size, cost and performance. Their small size makes them more affordable and efficient to produce, whereas their high performance is due to the fact that all components are Electromechanical component suppliers printed together on a single substrate by photolithography, allowing them to switch rapidly and use less power.
The final step in circuit chip design is preparing the IC for manufacturing by creating a physical layout based on GDS II files, a format that the fabrication plant can understand. Once the IC is ready for production, it is sent to be packaged and soldered to a circuit board.
Packages for ICs vary widely, from the DIP (dual in-line) flat pack that is the most common through-hole IC you’ll encounter, to surface-mount packages such as SOIC and SSOP. Some are designed to sit side-by-side on a circuit board, while others require special tools for hand assembly. Most ICs are also tested before shipping to the customer, a process known as ATE testing. This is usually done in a cleanroom with specialized equipment that can handle the high temperatures generated during a chip’s operation.