Analysis of silicon carbide semiconductor packaging core technology -- Silver sintering technology

With the development of electronic industry, electronic products are developing in the direction of light weight, thin thickness, small volume, low power consumption, complex functions and high reliability. This requires the power module to have good thermal conductivity and reliability in both transient and steady-state conditions. The volume reduction of power module will cause the increase of module and chip current, terminal voltage and input power, which will increase the loss of heat energy, and bring some problems, such as temperature drift, which will seriously affect the reliability of power devices and the aging of accelerator devices. In order to solve the problems faced by high temperature and high power devices, nano silver sintering technology has attracted more and more attention in recent years.


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Low temperature sintering interconnection technology

In the early 1990s, researchers realized the interconnection of silicon chip and substrate by sintering micron sized silver powder particles, which is called low-temperature sintering technology. In the process of making silver powder, organic additives are usually added to avoid agglomeration and polymerization of micron sized silver particles. When the sintering temperature is above 210 ℃, the organic additives in silver powder will volatilize due to high temperature decomposition in oxygen environment, and finally become pure silver bonding layer, and no impurity phase will be produced. The whole sintering process is a densification process of silver powder particles, and a good mechanical bonding layer can be formed after sintering. The melting temperature of silver itself is as high as 961 ℃, and the sintering process is much lower than this temperature, and no liquid phase will be produced. In addition, when the sintering temperature reaches 230-250 ℃, an auxiliary pressure of about 40MPa is needed to accelerate the sintering of silver solder paste.

This sintering method can obtain better thermoelectric and mechanical properties, lower joint porosity and thermal fatigue life more than 10 times of standard solder. However, with the deepening of the research, it is found that the large auxiliary pressure will cause certain damage to the chip, and require a large economic investment, which seriously limits the application of this technology in the field of chip packaging. The results show that the melting point and sintering temperature of nano silver materials are lower than micron silver due to nano size effect. The bonding temperature is lower than 200 ℃ and the auxiliary pressure can be lower than 1-5mpa. Moreover, the bonding layer can still maintain high heat resistance temperature and good thermal conductivity. The driving force of sintering process mainly comes from the surface energy and the defect energy of the system. The smaller the particle size is, the larger the specific surface area is. Therefore, the higher the surface energy is, the greater the driving force is. The external pressure on the system, the chemical potential difference in the system and the stress between the two contacting particles are also the driving forces for the diffusion and migration of silver atoms. The results show that the bonding layer is porous structure, and the hole size is in micron and nanometer level. When the porosity of the joint layer is 10%, its thermal conductivity and conductivity can reach 90% of that of pure silver, which is much higher than that of ordinary solder.


Interconnection diagram of silver sintering

Application of silver sintering technology in power module packaging

The SiC chip can work stably above 300 ℃, and the module temperature is expected to reach 175-200 ℃. In the traditional power module, the chip is soldered to the substrate by soldering, and the interface is usually two-phase or three-phase alloy system. In the process of temperature change, the interface forms metal compound layer to interconnect the chip, solder alloy and substrate. At present, lead-containing solder or lead-free solder are commonly used in electronic packaging, and its melting point is below 300 ℃. The junction temperature of power module using soldering process is generally lower than 150 ℃. When applied to the temperature of 175-200 ℃ or even above 200 ℃, the performance of the bonding layer will deteriorate rapidly, which will affect the reliability of the module.

In order to obtain the power module with good reliability, Infineon launched the package form of easypack1 in 2006, using single-sided silver sintering technology and double-sided silver sintering technology respectively. Through the corresponding high temperature cycle test, it is found that compared with the traditional soldering process, the service life of the module with single silver sintering technology is increased by 5-10 times, and that of the module with double-sided silver sintering technology is increased by more than 10 times.


Double side silver sintering technology

Then in 2007, semicon introduced skinter technology. Fine silver powder was used to connect the chip and substrate by silver sintering process, and low porosity silver layer was obtained under the condition of 250 ℃ and pressure assistance. Compared with the brazing layer, the power cycle ability is increased by 2-3 times, the thickness of sintered layer is reduced by about 70%, and the thermal conductivity is increased by 3 times. In 2012, Infineon has launched XT interconnection technology, which uses silver sintering technology to connect chips and substrates. The cycle test shows that the life of power module without base plate is increased by two orders of magnitude, and the life of module with base plate is also increased by more than 10 times. In 2015, Mitsubishi Motor used silver sintering technology to produce power modules, with a cycle life of about 5 times that of soft solder.

The sintering equipment developed and produced by our company can provide appropriate auxiliary pressure, atmosphere environment and appropriate heating temperature to meet the technical indicators required by silver sintering technology, and provide corresponding sintering equipment and technical support for power device manufacturers in the industry.


Atmosphere sintering furnace (left) SPS plasma discharge sintering system (right)

According to the market demand, Haoyue technology continuously develops and improves the technology, and introduces sintering equipment with excellent performance to assist the domestic semiconductor packaging market. It provides various atmosphere sintering furnaces, hot pressing sintering furnaces and spark plasma sintering furnaces, providing perfect heat treatment solutions for the sintering process of semiconductor packaging enterprises.

Haoyue technology is a high-tech enterprise integrating R & D, production and sales of electric furnace. The company has been focusing on advanced ceramics and composite materials, semiconductor materials, carbon materials, lithium batteries and new energy materials equipment four major fields, has rich industry experience and professional technology, wholeheartedly serves customers and provides perfect integrated industrial solutions.

Updated date: 2020-11-23
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