Study on semiconductor die bonding process, including adhesive bonding process, eutectic bonding process, soft solder bonding process, silver sintering bonding process, hot pressing bonding process, flip chip bonding process. The types and important technical indicators of semiconductor die bonding equipment are introduced, the development status is analyzed, and the development trend is prospected.
1 Overview of semiconductor industry and packaging
The semiconductor industry specifically includes upstream semiconductor materials and equipment, midstream semiconductor manufacturing, and downstream applications. my country's semiconductor industry started late, but after nearly ten years of rapid development, my country has become the world's largest semiconductor product consumer market and the world's largest semiconductor equipment market. The semiconductor industry has been developing rapidly in the mode of one generation of equipment, one generation of process, and one generation of products. The research on semiconductor process and equipment is the core driving force for the continuous progress of the industry and the guarantee for the industrialization and mass production of semiconductor products.
The development history of semiconductor packaging technology is the history of continuous improvement of chip performance and continuous miniaturization of systems. The internal driving force of packaging technology has evolved from the field of high-end smartphones to fields such as high-performance computing and artificial intelligence. The four stages of the development of semiconductor packaging technology are shown in Table 1.
As the semiconductor lithography process nodes move towards 10 nm, 7 nm, 5 nm, 3 nm, and 2 nm, the R&D and production costs continue to rise, the yield rate decreases, and Moore's Law slows down. From the perspective of industrial development trends, currently constrained by the physical limits of transistor density and the huge increase in manufacturing costs, packaging is developing in the direction of miniaturization, high density, high performance, high speed, high frequency, and high integration. The semiconductor industry has entered the post-Moore era, and advanced processes are no longer just focused on the advancement of wafer manufacturing technology nodes, but gradually turning to advanced packaging technology. Advanced packaging technology can not only improve functions and increase product value, but also effectively reduce manufacturing costs, becoming an important path to continue Moore's Law. On the one hand, the core particle technology is used to split complex systems into several packaging technologies that can be packaged in heterogeneous and heterogeneous packaging. On the other hand, the integrated system technology is used to integrate devices of different materials and structures, which has unique functional advantages. The integration of multiple functions and devices of different materials is realized by using microelectronics technology, and the development from integrated circuits to integrated systems is realized.
Semiconductor packaging is the starting point for chip productization and a bridge between the internal world of the chip and the external system. At present, in addition to the traditional semiconductor packaging and testing companies, semiconductor wafer foundries, semiconductor design companies, and integrated component companies are actively developing advanced packaging or related key packaging technologies.
The main processes of traditional packaging technology are wafer thinning, cutting, die bonding, wire bonding, plastic sealing, electroplating, rib cutting and molding, etc. Among them, the die bonding process is one of the most complex and critical packaging processes, and the die bonding process equipment is also one of the most critical core equipment in semiconductor packaging, and is one of the packaging equipment with the highest market value. Although advanced packaging technology uses front-end processes such as lithography, etching, metallization, and planarization, the most important packaging process is still the die bonding process.
2 Semiconductor die bonding process
2.1 Overview
The die bonding process is also called chip loading, core loading, die bonding, chip bonding process, etc. The die bonding process is shown in Figure 1. Generally speaking, die bonding is to pick up the chip from the wafer using a welding head suction nozzle using vacuum, and place it on the designated pad area of the lead frame or packaging substrate under visual guidance, so that the chip and the pad are bonded and fixed. The quality and efficiency of the die bonding process will directly affect the quality and efficiency of subsequent wire bonding, so die bonding is one of the key technologies in the semiconductor back-end process.
For different semiconductor product packaging processes, there are currently six main die bonding process technologies, namely adhesive bonding, eutectic bonding, soft solder bonding, silver sintering bonding, hot pressing bonding, and flip-chip bonding. To achieve good chip bonding, it is necessary to make the key process elements in the die bonding process cooperate with each other, mainly including die bonding materials, temperature, time, pressure and other elements.
2. 2 Adhesive bonding process
During adhesive bonding, a certain amount of adhesive needs to be applied to the lead frame or package substrate before placing the chip, and then the die bonding head picks up the chip, and through machine vision guidance, the chip is accurately placed on the bonding position of the lead frame or package substrate coated with adhesive, and a certain die bonding force is applied to the chip through the die bonding machine head, forming an adhesive layer between the chip and the lead frame or package substrate, so as to achieve the purpose of bonding, installing and fixing the chip. This die bonding process is also called glue bonding process because adhesive needs to be applied in front of the die bonding machine.
Commonly used adhesives include semiconductor materials such as epoxy resin and conductive silver paste. Adhesive bonding is the most widely used semiconductor chip die bonding process because the process is relatively simple, the cost is low, and a variety of materials can be used.
2.3 Eutectic bonding process
During eutectic bonding, eutectic bonding material is generally pre-applied on the bottom of the chip or the lead frame. The eutectic bonding equipment picks up the chip and is guided by the machine vision system to accurately place the chip at the corresponding bonding position of the lead frame. The chip and the lead frame form a eutectic bonding interface between the chip and the package substrate under the combined action of heating and pressure. The eutectic bonding process is often used in lead frame and ceramic substrate packaging.
Eutectic bonding materials are generally mixed by two materials at a certain temperature. Commonly used materials include gold and tin, gold and silicon, etc. When using the eutectic bonding process, the track transmission module where the lead frame is located will pre-heat the frame. The key to the realization of the eutectic bonding process is that the eutectic bonding material can melt at a temperature far below the melting point of the two constituent materials to form a bond. In order to prevent the frame from being oxidized during the eutectic bonding process, the eutectic bonding process also often uses protective gases such as hydrogen and nitrogen mixed gas to be input into the track to protect the lead frame.
2. 4 Soft solder bonding process
When soft solder bonding, before placing the chip, the bonding position on the lead frame is tinned and pressed, or double tinned, and the lead frame needs to be heated in the track. The advantage of the soft solder bonding process is good thermal conductivity, and the disadvantage is that it is easy to oxidize and the process is relatively complicated. It is suitable for lead frame packaging of power devices, such as transistor outline packaging.
2. 5 Silver sintering bonding process
The most promising bonding process for the current third-generation power semiconductor chip is the use of metal particle sintering technology, which mixes polymers such as epoxy resin responsible for connection in the conductive glue. It has excellent electrical conductivity, thermal conductivity, and high-temperature service characteristics. It is also a key technology for further breakthroughs in the third-generation semiconductor packaging in recent years.
2.6 Thermocompression bonding process
In the packaging application of high-performance three-dimensional integrated circuits, due to the continuous reduction of chip interconnect input/output pitch, bump size and pitch, semiconductor company Intel has launched a thermocompression bonding process for advanced small pitch bonding applications, bonding tiny bump chips with a pitch of 40 to 50 μm or even 10 μm. Thermocompression bonding process is suitable for chip-to-wafer and chip-to-substrate applications. As a fast multi-step process, the thermocompression bonding process faces challenges in process control issues, such as uneven temperature and uncontrollable melting of small volume solder. During thermocompression bonding, temperature, pressure, position, etc. must meet precise control requirements.
2.7 Flip chip bonding process
The principle of flip chip bonding process is shown in Figure 2. The flip mechanism picks up the chip from the wafer and flips it 180° to transfer the chip. The soldering head nozzle picks up the chip from the flip mechanism, and the bump direction of the chip is downward. After the welding head nozzle moves to the top of the packaging substrate, it moves downward to bond and fix the chip on the packaging substrate.
Flip chip packaging is an advanced chip interconnection technology and has become the main development direction of advanced packaging technology. It has the characteristics of high density, high performance, thin and short, and can meet the development requirements of consumer electronic products such as smartphones and tablets. The flip chip bonding process makes the packaging cost lower and can realize stacked chips and three-dimensional packaging. It is widely used in packaging technology fields such as 2.5D/3D integrated packaging, wafer-level packaging, and system-level packaging. The flip chip bonding process is the most widely used and most widely used solid die bonding process in advanced packaging technology.
Post time: Nov-18-2024