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IC Substrate

IC Substrate

The development history of IC packaging technology
2021-08-22
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Author:Belle

1. Introduction to IC Packaging
Encapsulation is necessary for integrated circuit chips, because the chip must be isolated from the outside world to prevent dust and impurities in the air from corroding the chip circuit and causing electrical performance degradation or even electrical function failure. Packaging can also be said to refer to the housing used to install semiconductor integrated circuit chips. It not only plays the role of placing, fixing, sealing, protecting the chip and enhancing thermal conductivity," it is also a bridge between the internal world of the chip and the external circuit-the on-chip The bonding points are connected to the pins of the package shell through wires, and these pins are connected to other devices through wires on the printed circuit board. In addition, there are standard specifications for the size, shape, number of pins, spacing, and length of the package. It is not only convenient for integrated circuit packaging and processing, but also for the integration of integrated circuits and printed circuit boards, and the related production lines and production equipment are universal. This is very convenient for packaging users, circuit board manufacturers, and semiconductor manufacturers, and it is easy to standardize.
In general, there are three main functions of integrated circuit packaging: 1. Physical protection; 2. Electrical connection; 3. Standardization. Therefore, the package should have strong mechanical properties, heat dissipation properties and chemical stability; good electrical properties; standard size and form. Integrated circuit packaging is advancing with the development of integrated circuits. With the continuous development of various industries such as military, aerospace, aviation, and machinery, the whole machine is also developing in the direction of multi-function and miniaturization, which requires the integration of integrated circuits. Higher and higher, more and more complex functions, correspondingly require greater and greater density of integrated circuit packaging, higher and higher applicable frequency, better and better temperature resistance, more and more leads, and more and more volume The smaller the weight, the lighter the weight.

IC packaging

2. History of IC packaging
2.1 From the 1960s to the 1970s: Dual in-line (DIP) packaging
With the emergence of IC, the production of the whole machine is mainly based on discrete devices, and IC is supplemented. At this time, the technical demand is only to seek more stable work. Because on the one hand, the manufacture of IC chips is still in the initial stage, and the integration level is very low; on the other hand, from the electron tube to the transistor, the volume of the whole machine itself has been greatly reduced, so there is no more requirement for IC packaging. Therefore, at this stage, the most easily realized package represented by dual in-line (DIP) is used, supplemented by single in-line (SIP) and pin grid array (PGA) packages, which meets the needs of circuit board (PCB) wave soldering Assembly requirements. At this time, the lead pitch is about 2.54mm.
2.2 In the 1980s: plastic package with leaded chip carrier (PLCC), quad flat package (QFP) compact package
With the introduction of surface mount technology (SMT) in 1978, the size of the whole machine was reduced, and the area of the circuit board was also reduced. SMT technology is in line with the development trend, and reflow soldering has replaced wave soldering, which has further improved the yield of PCBs, and has also put forward new requirements for IC packaging. The development of IC chip manufacturing technology conforms to its requirements. IC packaging has developed a plastic-encapsulated leaded chip carrier (PLCC) with a lead pitch of 1.27mm and a quad flat package (QFP) with a lead pitch of 0.8-1.0mm. The compact package form, supplemented by small dual in-line (S-DIP), pin pitch 1.778mm, small package (SOP), pin pitch 1.778mm, tape carrier automatic soldering package (TAP), etc., package The form is becoming diversified. However, there is only one goal-to reduce the area, to comply with the trend of miniaturization, thinning and assembly automation of electronic products.
2.3 Early and mid-1990s: narrow-pitch small-outline package (SSOP), narrow-pitch quad flat package (SQFP), ball grid array (BGA) package
With the rapid development of computer technology, the computer industry represented by the personal computer (PC) has experienced rapid development from 386 to 486 to 586. With each generation, IC integration and speed supporting its development have leaped a step. . On the one hand, computers are extended to high-end workstations and supercomputers; on the other hand, Microsoft, in particular, has launched an epoch-making Windows operating system, which has made computers from experts to civilians, and from enterprises to families, thus bringing about the computer industry Significant changes in quality and quantity. At this time, the original PLCC, QFP, and SOP can no longer meet its development requirements. In the PCB SMT, a smaller and thinner package is introduced. The narrow-pitch small-outline package (SSOP) is used with a pin pitch. 0.65mm, narrow-pitch four-side lead flat package (SQFP), the pin pitch is 0.65mm as the representative package form; in particular, the package form of the ball grid array (BGA) with inner leads is proposed, and the typical BGA is organically lined The bottom replaces the lead frame in the traditional package, which greatly increases the IC lead-out pins, and makes it easy to implement the original 400-pin QFP form of the difficult SMT in the BGA, so that the high integration function of the IC chip can be applied in practice.
2.4 Mid to late 1990s
With the rise of the IT industry, the prosperity of wireless communications, and the emergence of multimedia, the amount of information on a global scale has increased sharply. The exchange and transmission of information and data have achieved large-capacity, high-speed and digitalization, which has promoted the development of high-performance and high-performance electronic information equipment. The rapid development of integration and high reliability has enabled the electronic information industry to grow rapidly; supporting its development and the key technology is IC assembly technology, which includes IC packaging and PCB SMT technology. IC packaging is the cell of electronic information equipment. In recent years, it has entered a period of rapid development, and new packaging forms continue to emerge and obtain applications. IC packaging is not only used as the functional manifestation of the IC chip, but also protects the chip; at the same time, it also meets the ever-increasing performance, reliability, heat dissipation, and power distribution at a certain cost, including the following requirements: 1) Chip speed and The increase in processing power requires more pins, faster clock frequencies and better power distribution. 2) More functions, lower power consumption and smaller size are required. 3) Make the assembled electronic products thinner, lighter and smaller. 4) More in line with environmental protection requirements. 5) Cheaper in price.

3. IC packaging development trends
3.1 Development of packaging materials
Packaging technology has a huge driving effect on the development of packaging materials. In turn, the development of packaging materials will further promote the development of packaging technology. The two promote and restrict each other. In recent years, packaging materials have been showing a trend of rapid growth. In 2003, the total global sales of packaging materials reached 7.9 billion U.S. dollars, including 2 billion U.S. dollars for rigid packaging substrates, 320 million U.S. dollars for ductile polyimide (PI) substrates and tape automated bonding (TAB) substrates, and 2.62 billion U.S. dollars for lead frames. USD, 1.28 billion USD for metal leads, 1.25 billion USD for molding compound, 240 million USD for patch adhesive, and 90 million USD for polyimide resin.
Liquid epoxy encapsulant material is 70 million US dollars, liquid underfill is 40 million US dollars, and micro solder balls are 60 million US dollars. In 2008, the global sales of packaging materials reached 12 billion U.S. dollars, with an annual growth rate of 20%.
The current situation and development trend of several integrated circuit packaging materials that are most closely related to integrated circuit packaging, and are the most critical at the same time, are expounded one by one.
3.1.1 Epoxy molding compound (EMC)
EMC takes the lead in integrated circuit packaging materials due to its low cost, simple process and suitable for large-scale production. At present, 97% of integrated circuit packaging worldwide use EMC. With the rapid development of integrated circuit and packaging technology, EMC has increasingly demonstrated its fundamental and supporting role.
The technological development of epoxy plastic encapsulants presents the following trends: ①In order to meet the needs of the development of VLSIs in the direction of high density and high I/O number, it is moving towards a packaging form that adapts to high density and high I/O number (such as BGA). ) Direction development; ② In order to adapt to the rapidly growing demand for portable electronic products represented by mobile phones, notebook computers, flat panel displays, etc., to adapt to miniaturization, thinness, asymmetrical, and low-cost packaging (CSP/ QFN) direction development; ③In order to meet the requirements of lead-free solder and green environmental protection, the rapid development towards high heat resistance, bromine-free flame retardant direction.
3.1.2 High-density multilayer packaging substrate
The high-density multilayer packaging substrate mainly serves as an electrical transition between the semiconductor chip and the conventional printed circuit board (PCB), and at the same time provides protection, support, and heat dissipation for the chip. Packaging substrates account for a high proportion of the manufacturing cost of advanced packaging devices based on BGA and CSP, which can reach 40%-50% and 70%-80%, respectively.
3.1.3 Liquid epoxy packaging material
Liquid epoxy packaging material is the representative packaging material of the third revolutionary change in microelectronic packaging technology. It is one of the key packaging materials required for BGA and CSP, mainly including liquid epoxy underfill for FC-BGA/CSP ( Underfill) and liquid epoxy chip encapsulating material (Encapsulants) 2 categories.
3.1.4 Polymer photosensitive resin
Polymer photosensitive resin mainly includes three types: polyimide photosensitive resin (PSPI), BCB photosensitive resin and epoxy photosensitive resin. They are mainly used in the ball making process and multilayer build-up (BUM) of BGA and CSP chip surface solder ball arrays. Package-based
The interlayer insulation of the epitaxial signal line is the key packaging material of BGA/CSP.
3.1.5 Electrically conductive/thermally conductive adhesives
High-performance conductive/thermal conductive adhesives mainly include conductive adhesives, thermally conductive adhesives, etc., and are mainly used to paste IC chips on lead frames or substrates. At present, the most common conductive adhesives and thermally conductive adhesives on the market are mainly epoxy resin or polyurethane
Ester, silicone resin, etc. are matrix resins, filled with flake conductive silver powder (or alumina, silicon nitride, etc.), and then curing agent, accelerator, surfactant, coupling agent, etc. are added to achieve the required comprehensive performance . At the same time, in order to meet the high heat resistance requirements of electronic products, polyimide can also be used as the matrix resin. Epoxy conductive adhesives can be divided into two categories: isotropic conductive adhesives and anisotropic conductive adhesives. According to the composition, epoxy conductive adhesives are divided into two forms: single-component and two-component. Currently, single-component is the main form.
3.2 Electrostatic treatment of packaging system
With the development of micron, sub-micron, deep sub-micron and nano-level IC technology, the inner insulating layer of integrated circuits is getting thinner and thinner, and its antistatic performance is getting weaker and weaker, and materials that generate and accumulate charge (such as plastics, rubber, etc.) The large-scale use of high-molecular organic matter) and the insufficient electrostatic protection during the use process have led to more and more serious damage from electrostatic discharge to integrated circuits. Therefore, it is imperative to formulate relevant electrostatic protection measures. Integrated circuit electrostatic protection needs to be considered in combination with many factors such as chip design, wafer processing, and packaging. Electrostatic discharge has an inseparable relationship with integrated circuit performance, yield and reliability. The chip is generally designed by power clamp ESD protection circuit structure, power bus ESD protection circuit structure and current shunt, etc., using semi-floating gate, ballast, substrate coupling and other technologies to improve the circuit, so as to perform the circuit during electrostatic discharge. Effective protection. The electrostatic protection measures for wafer processing and integrated circuit packaging process lines are similar. Electrostatic discharge can damage integrated circuits with destructive, potential and slow failure. Circuits that are completely broken down and damaged by static electricity during the packaging process can be rejected during production or testing; but if they are not completely damaged by electrostatic discharge Circuits will have potential reliability hazards. It is difficult to detect changes in performance even with sophisticated instruments. However, with the use of circuits, the cumulative damage caused by electrostatic discharge deepens and becomes serious.
Causes the circuit to fail. Therefore, effective system electrostatic protection is of great significance to ensure the quality and reliability of the production and manufacturing of integrated circuit packaging lines.
3.3 The crater problem of the packaging system
The early failure of integrated circuits is the main factor affecting the internal quality of electronic products and complete machines. There are various forms of early failure, and the chip surface crater is a key factor. As we all know, integrated circuit packaging is to connect the chip and lead frame with wires through pressure welding, and then encapsulate it with plastic encapsulant to provide output and protection for the integrated circuit chip, avoid damage by man-made or environmental factors, so as to ensure the stability of the integrated circuit , Work reliably. Crater is a phenomenon in which the aluminum pad aluminum layer and the underlying silicon compound of the chip are destroyed due to various factors in the process of collecting circuit packaging. With the rapid development of integrated circuit design technology, the miniaturization and multi-functionalization of chips have caused the appearance of multi-layer wiring in the design of the chip, and the number of products with devices and circuits under the aluminum pad is increasing. At the same time, copper wire technology and ball planting have appeared. In order to improve the reliability of products, the prevention of IC craters and early failures becomes more and more important under the requirements of customers for high-quality and low-cost products such as packaging technologies.

Four. IC packaging outlook
From a technical perspective, IC packaging has developed from DIP to WLPCSP and SOC so far, which has realized the function conversion from the surface to the inner layer, and the progress from simple to complex. Future packaging technology will be integrated with SMT and IC chip manufacturing, which will have two extremes for IC packaging. ① For complex and multi-functional electronic devices, the packaging will become more complex due to the need to achieve multi-functional integration, and the integration of technologies will be further intensified. ②As a result of the SOC, the integration of the system will make its external manifestations simpler for electronic devices with common functions. IC packaging will still return to a certain extent.
From the perspective of social needs, from simple radios to PCs to today's complex supercomputers, the IT industry is in the ascendant, and the needs of society will also be polarized: ①Transmit electronic equipment with more powerful and complex public IT, Build a bridge for the high-speed transmission of information. ②Personal electronic consumer products that target the ultimate public demand, such as PCs, mobile phones, electronic office supplies, etc., are developing in the direction of miniaturization and individualization: the needs of society will also extend in the direction of diversification and greening.
From the above rules, it can be seen that IC packaging extends to a higher level on the one hand: high density, high speed, high reliability, diversification and environmental protection are its development trends and the mainstream in the future. On the other hand, some packaging forms that have existed in the development process will still exist for a certain period of time: because with the increase in integration and the enhancement of functions, the original whole machine can be turned into a single chip, such as the semiconductor at the beginning. The radio has developed into a monolithic radio, so small that it can fit into the ear.