Anisotropy Properties of Ni Doped Cu₆Sn₅ Intermetallic Alloys AITranslate

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Basic Information:

DOI：10.13373/j.cnki.cjrm.XY23100007

Chinese Library Classification Number:TG425.1

Citation Information:

With the lead-free and miniaturization of solder joints in microelectronic packaging，intermetallic compounds （IMCs）usually form at the Pb-free solder joints/interconnects，which are the basic premise to realize the metal interconnection. The structures and properties of IMCs have a vital influence for the integrity and reliability of lead-free solder joints. To further analyze and understand the microscopic nature of the physical properties of IMCs，and to explore the influence of IMCs on the interconnection interface in lead-free solder joints，the research mainly focuses on the properties of Cu₆Sn₅ IMCs and the influence of the third element on the properties of Cu₆Sn₅. Cu₆Sn₅ is not only the IMC formed during the reaction between Sn-based lead-free solders and Cu substrates but also serves as the primary constituent of anode materials in lithium-ion batteries. For the study of Cu₆Sn₅，the current study mainly focuses on the growth morphology and its distribution at the interface of solder joints，as well as the study of the thickness and rate of Cu₆Sn₅ growth at the interface. As for Cu₆Sn₅ IMC itself，its mechanical properties also have a very important impact on the reliability of the electronic device interconnection structure. The transformation of the high-temperature phase hexagonal structure to the low-temperature phase monoclinic structure is also a major factor causing the fracture of the electronic interconnection structure. In recent years，it has been found that the addition of some trace elements can inhibit the transition of Cu₆Sn₅ crystal structure，thus improving the stability and reliability of the solder joint interface. The essential reason for how the doping elements inhibits the transformation of Cu₆Sn₅ crystal structure is still unclear，as is the study of the effects of the added elements on the mechanical properties and other properties of Cu₆Sn₅ IMCs. In the application and research of new Sn-based composite lead-free solder，Ni element is usually used as the third element phase added to the lead-free solder or as the main component of the substrate plating layer，Ni as one of the most common elements added to Sn-based lead-free solder，can reduce the prominence of Sn crystal，effectively inhibit the solubility of Cu to the solder internal and reduce the generation of IMCs at the interface，thus playing the role of organization and improve the wettability，solder reliability. Wettability，welding reliability of the role of the appropriate amount of Ni elements can also be at the interface with Sn，Cu reaction to form the corresponding compounds，and increase the connection strength of the welded joints. The addition of Ni elements increases the resistance of the high temperature phase η-Cu₆Sn₅ to deformation. In practical applications，especially in the field of electronic packaging，an important factor affecting its reliability is the ease with which the material can undergo fracture. Bulk modulus （B），Young's modulus （E），and hardness （H）are all important parameters that simply describe the ease with which a material will fracture. From a microelectronic soldering application point of view，the addition of Ni atoms keeps Cu₆Sn₅ in a high-temperature phase structure，which is better for the realization of interconnections and thus improves the reliability and integrity of lead-free solder joints. Cu₆Sn₅ has at least two crystal structures，denoting as the high-temperatureη-Cu₆Sn₅ phase and the low-temperatureη'-Cu₆Sn₅ phase，with an allotropic transformation occurring at 186 ℃. This phase transformation has 2.15% expansion in volume which will create significant internal stress in solder joints and promote the propagation of cracks within the Cu₆Sn₅. Ni is an important alloying element in Sn-based lead-free solders. The addition of Ni has been associated with such benefits as superior solidification micro structures and lower propensity for interfacial IMCs to crack during service. With a remarkable influence on the formation and property of Cu₆Sn₅，it can also increase Young's modulus and hardness of Cu₆Sn₅. Cu₆Sn₅-xNi alloys （x=0，3% and 6%，mass fraction）were prepared by using Ni powder as doping component using high temperature melting technique. The microstructure of the alloy was characterized using X-ray diffraction （XRD），scanning electron microscopy （SEM）and other equipment，and the hardness of the alloy was tested. The effects of different contents of Ni element addition on the properties of high-temperature phase Cu₆Sn₅ IMCs were investigated，and the mechanical properties and density of states of η-Cu₆Sn₅ and （Cu，Ni）₆Sn₅ were calculated by using the first nature principle. The results showed that Cu₆Sn₅-xNi alloys were mainly present in three different forms，all of which were large masses and no other impurities or precipitates were generated. The addition of Ni inhibited the anisotropy of bulk modulus （B），Young's modulus （E），and hardness （H）of η-Cu₆Sn₅，with a more significant decrease in the elastic anisotropy on the （001）plane and a slight increase on the （100）plane. The density of states analysis yields that the orbital hybridization of Ni elements led to an enhanced bonding effect ofη-Cu₆Sn₅，which was conducive to the formation of a stable （Cu，Ni）₆Sn₅ structure.