When I was studying MCUs in college, I realized that the MCU might look something like the image below. These two are known as 51-series MCUs, but they seem to have different chip structures. So what does an MCU actually look like? The answer lies in a concept called "package."
It might look like this:
Or it could also be like this:
So, what exactly is a package? In simple terms, a package refers to the physical form of an electronic component. It’s how the chip is structured and connected to the circuit board. Encapsulation is the process of enclosing the internal components of a chip into a protective housing with specific pin arrangements. This allows the chip to be mounted on a PCB and function properly.
Encapsulation combines data and functions into a single unit—commonly known as a "class" in object-oriented programming. The main goal of encapsulation is to protect the internal details and provide controlled access through well-defined interfaces. This makes the system more secure and easier to manage.
In hardware design, the package determines how the component will be placed on the board. There are two main types of packages: DIP (Dual In-line Package) and SMD (Surface Mount Device). For example, the STC89C51 microcontroller comes in both DIP40 and LQFP48 formats. The DIP version has pins arranged in two rows, while the LQFP version is a flat package with pins on all four sides.
Component packages follow international standards, and even the same device can come in multiple package types. That’s why it's important to specify the package when ordering parts. Let’s take a closer look at some common package types.
Patch Transistor: SOT23-2
A transistor usually has three legs: emitter, base, and collector. The SOT23-2 package is a small surface-mount version of a transistor. When placed on a PCB, the pads align with the three leads of the transistor. Here’s what the package looks like:
Chip Resistor: 0805
Chip resistors come in various sizes, such as 1210, 0805, 0603, and 0402. The 0805 package is one of the most commonly used. It’s named after its dimensions—0.08 inches by 0.05 inches. Here’s an example of the 0805 package:
MCU Package: LQFP48
You might have seen the DIP40 version of the STC89C51 microcontroller. But there's also the LQFP48 package, which has 48 pins spread across four sides. Each side has 12 pins, making it ideal for compact designs. Here’s what the LQFP48 package looks like:
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