Many companies only participate in one stage of chip manufacturing. For example, Huawei, Qualcomm, Apple, and MediaTek only design chips; TSMC, SMIC, and Hua Hong Semiconductor only manufacture chips; and companies like ASE and JCET only package and test chips. China's share of global chip packaging and testing is expected to jump from 22% in 2018 to 32% in 2025. Chip design and manufacturing receive much attention, so today we'll introduce the final stage of chip production—chip packaging technology within chip packaging and testing.
Packaging refers to the enclosure used to mount semiconductor integrated circuit chips. It involves using a series of technologies to lay out, attach, and connect the chips on a frame, bring out terminals, and encapsulate them with a plastic insulating medium to form a unified three-dimensional structure. This is the narrow definition of packaging. In simpler terms, it's adding a casing to the chip and fixing it onto a circuit board.
In a broader sense, packaging refers to packaging engineering, which involves connecting and fixing the package to the substrate to assemble it into a complete system or electronic device, and ensuring the overall performance of the entire system. Combining the two definitions above constitutes the broad concept of packaging.
Why is encapsulation necessary?
Packaging is of great significance. Obtaining an IC chip involves a lengthy process from design to manufacturing. However, a chip is quite small and thin, and without external protection, it can be easily scratched and damaged. Furthermore, due to its tiny size, it is difficult to manually mount it onto a circuit board without a relatively large casing. This is where packaging technology comes in handy.
Packaging serves to house, secure, seal, and protect the chip, enhance its electrical and thermal performance, and act as a bridge between the chip's internal world and external circuits—the contacts on the chip are connected to the pins of the package via wires, and these pins, in turn, connect to other devices via wires on the printed circuit board. Therefore, packaging plays a crucial role in integrated circuits.
I. The role of chip packaging
1. Protection
Semiconductor chip manufacturing facilities operate under extremely strict conditions, including constant temperature, constant humidity, rigorous control of airborne particulate matter, and stringent electrostatic discharge (ESD) protection. Exposed chips will only fail under these controlled environments. However, our living environment is far from meeting these conditions. Temperatures can range from -40°C to 60°C, and humidity can reach 100%. In the automotive industry, operating temperatures can exceed 120°C. Furthermore, various external impurities and static electricity can damage the delicate chips. Therefore, encapsulation is necessary to better protect the chips and create a suitable working environment.
2. Support
The support serves two purposes: first, to support the chip and fix it in place for easy circuit connection; second, after packaging, it forms a certain shape to support the entire device and make it less prone to damage.
3. Connection
The purpose of the connector is to connect the chip's electrodes to external circuitry. Pins are used to connect to external circuitry, while gold wires connect the pins to the chip's circuitry. The die carrier holds the chip, epoxy adhesive is used to attach the chip to the die carrier, the pins support the entire device, and the molding compound provides fixation and protection.
4. Heat dissipation
Enhancing heat dissipation is necessary because all semiconductor products generate heat during operation, and when this heat reaches a certain level, it can affect the normal operation of the chip. In fact, the various materials in the package itself can dissipate some heat. Of course, for most chips that generate a lot of heat, in addition to cooling through the packaging material, it is also necessary to consider installing an additional metal heat sink or fan on the chip to achieve better heat dissipation.
5. Reliability
Any package needs to achieve a certain level of reliability, which is the most important metric in the entire packaging process. Raw chips will deteriorate once removed from their specific operating environment, necessitating packaging. The lifespan of a chip depends primarily on the choice of packaging materials and packaging processes.
II. Types and processes of encapsulation
There are currently thousands of distinct package types, and there is no unified system to identify them. Some are named after their design (DIP, flat, etc.), some after their structural technology (molded, CERDIP, etc.), some after their size, and others after their application.
Chip packaging technology has undergone several generations of evolution, with each generation boasting more advanced technical specifications. These include increasingly closer chip-to-package area ratios, higher usage frequencies, better temperature resistance, increased pin counts, smaller pin pitch, reduced weight, improved reliability, and greater ease of use – all of which are visible changes. This article will not delve into these details; those interested can research and learn about packaging types on their own.
The main encapsulation process will be explained below:
The packaging process can generally be divided into two parts: the processes before plastic encapsulation are called the front-end operations, and the processes after molding are called the back-end operations. The basic process flow includes: silicon wafer thinning, silicon wafer dicing, chip mounting, molding technology, burr removal, lead trimming, soldering, and marking. Each step will be detailed below:
1. Front section:
Backgrinding: The newly manufactured wafer undergoes backgrinding to achieve the thickness required for encapsulation. During backgrinding, adhesive tape is applied to the front side to protect the circuit area. After grinding, the tape is removed.
Circular mirror cutting (waferSaw): The circular mirror is pasted onto the blue film, then the circular mirror is cut into individual dices, and then the dices are cleaned.
Light inspection: Check for defective products.
Die Attach: Die attaching the chip, curing the silver paste (to prevent oxidation), and soldering the leads.
2. The latter part:
Injection molding: To prevent external impact, the product is encapsulated with EMC (emulsifying compound) and then heated to harden.
Laser marking: Engraving relevant information onto products. For example, production date, batch number, etc.
High-temperature curing: protects the internal structure of the IC and eliminates internal stress.
Remove overflow: Trim the edges and corners.
Electroplating: Improves electrical conductivity and enhances solderability.
Slice and shape the product to inspect for defects.
This is a complete chip packaging process. my country is already at the forefront of chip packaging technology globally, providing a solid foundation for our vigorous development of the chip industry. In the next few years, the overall growth rate of the chip industry will remain above 30%. This is a very considerable growth rate, meaning the industry size will double in less than three years. Such rapid growth will benefit all three major sub-sectors of the chip industry—design, manufacturing, and packaging and testing (collectively known as "packaging and testing"). We believe that with the efforts of the Chinese people, our design and manufacturing capabilities will one day reach the world stage and lead the era.
