2021, 10(1):3-13. DOI: 10.12146/j.issn.2095-3135.20200916001
Abstract:The rapid development of third-generation semiconductors and power devices has put forward new requirements for packaging interconnection technology. Nano-copper and silver sintering interconnections have become the key technology to further breakthroughs in third-generation semiconductor packaging due to their excellent electrical conductivity, thermal conductivity, and hightemperature service characteristics. Compared to nano-silver, the nano-copper sintering technology has obvious advantages such as low-cost and better resistance to electromigration. However, the preparation, collection and oxidation resistance of small-sized copper nanoparticles are difficult to guarantee, which will affect the low-temperature sintering performance, and the reliability of use and storage. This paper reviews the latest research results of nano-copper sintering technology for third-generation semiconductor and power device packaging in recent years, analyzes the scale effect, the influence of copper oxide on sintering temperature and diffusion, and summarizes the advantages and characteristics of multiple technologies such as nano-modification of bonding surface, preparation and sintering of copper nano-solder, and self-reduction of copper nano-solder, prospects the research direction of nano-copper sintering technology for further industrial application.
2021, 10(1):14-22. DOI: 10.12146/j.issn.2095-3135.20201223001
Abstract:Al2O3-AlN/silicone rubber composites with high thermal conductivity were prepared by using Al2O3 and AlN as thermally conductive fillers. By using theory of granulartity, we obtained the densest packing of fillers in the polymer composites. The results showed that the thermal conductivity of the composites reached up to 9.6 W/(m?K) at the loading of 96 wt%, which was 60% higher than that filled with Al2O3. The significant increase of the thermal conductivity of the composites resulted from the increase of the internal thermal conductivity of the sample. Although the composites have undergone extreme cold and hot cycle application conditions, the thermal conductivity of the composites was maintained well, showing excellent reliability.
2021, 10(1):23-34. DOI: 10.12146/j.issn.2095-3135.20200925001
Abstract:As a key technology to solve advanced manufacturing and packaging, temporary bonding technology, as a high reliability solution for the processing of thin wafer devices, has attracted more and more attention. According to the different ways of de-bonding, thermal slip de-bonding material system and ultraviolet laser de-bonding material system are introduced in this paper. Thermal slip de-bonding materials (WLP TB130 and WLP TB140) were manufactured. Both of materials showed higher heat resistance and chemical resistance properties than foreign products. And the 5% weightlessness of materials were over 400 ℃. WLP TB140 even could be separated from the supporting waferat 160 ℃ by thermal-slipde-bonding technique. Ultraviolet laser de-bonding material system with release layer (WLP LB210) and adhesive layer (WLP TB4130) was manufactured, ultra-thin device bonded were separated from the supporting wafer using ultraviolet laser at room temperature and stress free.
2021, 10(1):35-46. DOI: 10.12146/j.issn.2095-3135.20201119001
Abstract:The use of Tantalum (Ta) electrolytic capacitors as embedded components constitutes a promising strategy to extend the application of embedded capacitors, because Ta electrolytic capacitor can provide both high capacitance and excellent stability. However, the huge thickness of conventional Ta electrolytic capacitor makes it hard to be embedded in a printed circuit board or substrate. In this work, we propose to employ the electrochemical etching of thin Ta foils to fabricate the anode of Ta electrolytic capacitors for embedded application.The specific capacitance of electrochemically etched Ta anode reaches as high as 74 nF/mm2 when measured in 0.1 mol/L H2SO4.The etched Ta anode is then fabricated into electrolytic capacitors, and a stable capacitance of ＞30 nF/mm2 is demonstrated in the frequency range from 100 Hz to 1 MHz and a low leakage current of 2.7×10－6 A for a duration of 1 200 seconds at a direct voltage (DC) of 10 V. The whole thickness of the capacitor is decreased to~75 μm.
2021, 10(1):47-54. DOI: 10.12146/j.issn.2095-3135.20200927001
Abstract:The reliability of solder joints is one of the key concerns in electronic packaging. Underfill was employed to match the thermal expansion coefficient between the substrate and the IC chip in electronic packaging, thereby protecting the solder joints and improving the reliability of the solder joints. However, the reliability of solder bumped flip chip will be affected by the changes in performance of underfill during the aging process. Therefore, the effects of several aging treatments on the thermo-mechanical properties and adhesion of underfill were studied in this paper. The thermo-mechanical properties of the underfill have the most obvious changes after hydrothermal aging treatment and high-temperature storage life treatment. There is no obvious similarity on organic interface and the inorganic interface for adhesion of underfill. High temperature storage has the most obvious effect on the adhesion of inorganic interfaces, while hydrothermal aging has the most obvious effect on the organic interfaces.
2021, 10(1):55-62. DOI: 10.12146/j.issn.2095-3135.20200924001
Abstract:Nanotwinned copper has excellent properties of high strength, high conductivity and high toughness, which makes it a research hotspot in the field of electronic packaging in recent years. During the electrodeposit procedure, the additives play a vital role in the quality and property of nanotwinned copper. Among these additive, methylene blue is commonly used in the direct-current (DC) electroplating regular copper industry. In this study, the effect of methylene blue on the microstructure and mechanical property of nanotwinned copper was investigated. It was found that the microscopic morphology and mechanical properties of nanotwinned copper are closely related to the concentration of methylene blue. As the concentration increases, the growth rate of electrodeposits shows a decreasing tendency, demonstrating a strong grain refinement effect. When the methylene blue concentration is 2 mg/L, columnar grains start growing from the bottom substrate to upper surface, and there exists a high-density twin structure within the columnar grains. What’s more, the tensile strength of the film at this concentration is 194 MPa, which is almost twice as that of regular coarse-grain copper (about 110 MPa) as measured by the dynamic thermomechanical analyzer (DMA). The surface hardness of the film can reach 1.6 GPa, which is also higher than the hardness of coarse-grained copper.
2021, 10(1):63-73. DOI: 10.12146/j.issn.2095-3135.20201119002
Abstract:With the rapid development of the electronic packaging industry, the industry’s requirements for the reliability of packaging structures are becoming more and more stringent. At present, most people regard Poisson’s ratio as a fixed value, which will affect reliability prediction to a certain extent. In order to further improve the reliability, it is of important engineering practical significance to properly consider the influence of the material Poisson’s ratio on the package structure. This paper uses finite element method (FEM), through design chip simulation and board-level packaging simulation, to explore the effects of Poisson’s ratio of epoxy molding compound on the chip warpage, chip interface stress, and the impact of board-level packaging solder joint life. Through analysis, it can be known that the variable EMC Poisson’s ratio has a greater impact on the warpage of the package structure, and it may cause the chip interface to be delamination and the chip to reach the stress limit and damage. In addition, it is necessary to properly consider the influence of Poisson’s ratio on the fatigue life of solder joints. Especially with the continuous development of chips in the direction of large size, the study of material Poisson’s ratio will have more important significance.
2021, 10(1):74-83. DOI: 10.12146/j.issn.2095-3135.20200703001
Abstract:In the aerospace power module, the voltage value of the line is as high as 300 V, which requires good insulation between the lines. The insulation resistance between lines is not likely to be an ideal state due to various factors influenced in the manufacturing process of flexible circuits. In particular, the seed layer between the lines would strengthen the conduction capacity between the flexible lines, thus the resin insulation between the lines is weakened. In this paper, the high-voltage conductive anode filament (CAF) high-current transmission requirements are established, and the corresponding high-voltage breakdown model is established to compare the CAF resistance of flexible circuits at different distances between lines by COMSOL. In addition, a model with or without polyimide as the medium is established to compare the line loss at a high current of 10 A. At the same time, we varied the thickness of polyimide in the model to study the temperature change around the circuit. The simulation results show that the spacing between the lines is 2 mm under high current, regardless of whether there is a seed layer between the lines, the lines have good breakdown resistance, which provides an overall solution for the design of flexible circuits.