| Integrated circuits have undergone more than 70 years of miniaturization,gradually slowed down by physical limitations.Due to the front-end-of-line process of the chip tends to the limit of 3-5 nm,the performance of the chip reaches the bottleneck.Three-dimensional packaging technology of stack chips was proposed by the industry for the purpose of breaking through the limits of chips.The core technology of three-dimensional packaging is mainly utilized the electroplating copper filling.Microvia filling by copper electroplating exhibits excellent electrical conductivity.However,the disadvantages of the copper electroplating,such as longer time,higher cost,and more pollution cannot be ignored.In this thesis,a new method for filling microvias in electronic manufacturing based on metal nanoparticles was proposed.By investigating on filling material,filling method and sintering process,the improvement of filling conductivity and reliability can be achieved.In terms of filling materials,Cu-Ag core-shell nano-microparticles(Cu@Ag NMPs)were synthesized by chemical replacement method,which exhibited the characteristics of dense and uniform silver-coated layer,high sphericity,and excellent oxidation resistance.The assynthesized Cu@Ag NMPs showed the superior microvia filling properties to Cu nanoparticles(NPs),Ag NPs,and Cu NMPs.In terms of filling method,a densified filling method with multi-step filling was developed.Compared with the traditional screen-printing method,the cross-sectional porosity of the sintered microstructure by using this method was significantly reduced from ?20% to ?8%,and the electrical conductivity was improved 20 times.Under the sintering parameters of 260 °C,30 min,and 2 MPa,the resistivity of the filled microvias can be as low as 6.3 ??·cm.Compared with the microvia filling by copper electroplating,the resistivity of the filled microvias is only 5% higher under the same depthdiameter ratio.The results showed that the filling technique can meet the interconnection requirements.In this thesis,the effects of sintering accelerator,sintering process,and the depth-diameter ratio of microvias on the sintering properties were studied.The results showed that the effect of ethylene glycol as a sintering accelerator is obviously better than that of 1,2-propanediol,terpineol and polyethylene glycol-200.With the increase of sintering pressure,the porosity of the filled microvias decreases gradually,and the cross-sectional porosity is as low as 7.2% at2 MPa.Increasing the sintering temperature and time can promote the formation of sintering necks and improve the electrical conductivity after sintering.After holding at 220 °C for 50 min,the resistivity of the filled microvias can be as low as 7.0 ??·cm,which means that the technique can be realized at low temperature.Combined with the filling material,filling method and sintering process,high-density filling of microvias with a depth-diameter ratio of2:3 and a diameter of 75 ?m can be achieved.The greater the depth-diameter ratio increase,the lower the density of the filled microvias decrease.Finite element simulation showed that the stress inhomogeneity of the microvia filling is higher with a larger depth-diameter ratio,and the low stress region formed at the bottom of the microvia makes the particles insufficiently sintered,resulting in a decrease in the density of the filled microvia.This thesis also tested the mechanical-thermal reliability of the filled microvias using the multi-step filling method through various experiments.The results showed that the filled microvias still maintains stable electrical conductivity after 500 times of bending strain tests with a bending diameter of 5 mm,and no obvious delamination occurs after 3 times of Solder dip test at 288 °C.Moreover,the electrical conductivity did not change significantly after 168 hours in the Damp heat test at 85 °C/85 %RH.Therefore,the novel method for filling microvias in electronic fabrication based on Cu@Ag NMPs has great potential. |
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