| Miniaturization of electronic equipment and high-power devices will make the operating temperature of the chip higher and higher,and the corresponding packaging materials have become an urgent problem to be solved.Sintering nano-silver has excellent mechanical properties and long-term reliability,which is the most promising material for large-size chip insertion.However,the current literature on the high-temperature reliability of sintered silver solder joints does not have uniform experimental parameters and aging environment.It has little reference to industry evolution,so we need to focus on the high-temperature reliability of solder joints on different substitutions.In this paper,the sintered nano-silver joints prepared by pressure assisted sintering and pressureless sintering were studied.The effects of silver plating and gold-plated pads commonly used in industrial practice on the mechanical properties and microstructure of solder joints were studied systematically.The effects of sintering temperature and pressure on the shear strength of pressure assisted sintering nano-silver joints were studied experimentally.Increasing the sintering pressure and temperature will increase the solder joint strength.The experimental results show that the joint shear strength reaches to maximum in 225 °C and 5 MPa.By studying the microstructure of nano-silver joints obtained under saturated conditions(225 °C,5 MPa),we found that the nano-silver particles sintered well and formed a continuous sintered vein.It was found by TKD that there are a large number of grains with average diameters of 112 nm.The grain has no obvious preferred orientation.In addition,there are many circular or elliptical holes in the sintered silver structure,and the morphology of these holes avoids the microcracks from being preferentially initiated from the interior of the tissue.In this paper,the reliability of pressed sintered joints after aging is studied.In addition to aging at 200 °C,the solder joint strength of the copper-plated silver substrate will increase abnormally at the initial stage of aging,and finally stabilize at about 175 MPa.The solder joints of other substrates will decrease in strength after prolonged aging,while copper plating is performed.The copper-plated silver substrate solder joints completely failed after aging for 200 h at 300 °C.The microstructure and cross-section of the solder joints were found.The copper oxides grown in the center of the copper-plated silver substrate were found to be a mixture of Cu O and Cu2 O by EDS and phase diagram.Nickel oxides were found at the nickel interface of the nickel-plated gold and copper-nickel-silver substrate solder joints.This topic studies the aging reliability of pressureless sintered joints.The solder joints of the silver substrate did not change much after aging,while the shear strength of copper substrate solder joints increased at the initial stage of aging at 200 °C,and the strength decreased to 30.3 MPa in the later aging period,and completely failed after aging at 300 °C.Oxidation at the substrate interface adversely affects solder joint strength.The interface oxidation of the copper substrate without pressure sintered joint at 300 °C aging causes the solder joint to fail,and no obvious interface oxidation phenomenon is observed on the silver substrate. |
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