Preparation Of Copper Foil And Soldering Of Copper Foil And Copper Substrate

With the development of science and technology and people’s pursuit of smaller,lighter,and more functional intelligent devices,modern electronic products are designed as thinly as possible.This has led to smaller electronic device sizes,requiring printed circuit boards(PCB)to become smaller and thinner.This requires the Cu foil acting as a solder pad to become thinner and perform better and also requires further improvement in the performance of lead-free solder joints on it.In order to improve the mechanical properties of the solder joints,the nickel-plated copper substrate was subjected to a heat treatment at 400 °C for 2 h.Then,Sn-3.0Ag-0.5Cu(SAC305)soldering material was used to solder the copper substrate,the nickel-plated copper substrate,and the nickel-plated copper substrate after heat treatment.The microstructure evolution,the growth mechanism of the intermetallic compound(IMC)layer,and the shear strength of the three soldering joints after reflow and isothermal aging were compared,and the effect of substrate heat treatment before reflow soldering on lead-free solder joints was studied.The results showed that with the isothermal aging time,the intermetallic compound layer at the interface became thicker,and the mechanical properties of the solder joints decreased.The growth rate of the intermetallic compound layer at the interface of Cu/SAC305/Cu soldered joints was the fastest and thickest,followed by nickel-plated copper/SAC305/nickel-plated copper soldered joints.The growth rate of the intermetallic compound layer at the interface of nickel-plated copper after heat treatment/SAC305/nickel-plated copper after heat treatment soldered joints was the slowest and thinnest.After reflow soldering,the shear strength of the Cu/SAC305/Cu soldered joint is the highest,but its shear strength decreases the fastest during aging.After isothermal aging at 150 °C for 240 h,the shear strength is lower than that of the other two soldered joints,which indicates that the addition of Ni coating can indeed improve the performance of lead-free solder joints.After reflow soldering and isothermal aging,the shear strength of nickel-plated copper after heat treatment/SAC305/nickel-plated copper after heat treatment soldered joint is always greater than that of nickel-plated copper/SAC305/nickel-plated copper soldered joint,which indicates that heat treatment of nickel-plated copper substrate before reflow soldering can indeed inhibit the growth of interfacial intermetallics and improve the performance of lead-free solder joints.In order to prepare suitable Cu foils,ultrasonic vibration of chitosan sacrificial layer solution was used at different times,and then chemical deposition Cu foils were prepared on glass substrates using a chemical plating process.Then,SAC305 solder was used for wetting and spreading tests on the chemical deposition Cu foils and commercial electrolytic Cu foils,as well as soldering the chemical deposition Cu foils with three different substrates,Study the effect of ultrasonic vibration of chitosan acetic acid solution time on the preparation of independent Cu foil and the solderability of chemically deposited Cu foil.The results show that when the ultrasonic oscillation time of chitosan acetic acid solution is 30 minutes,the chitosan sacrificial layer attached to the glass substrate can be completely degraded during the chemical plating process,resulting in the automatic detachment of chemically deposited ultra-thin Cu foil.The thickness of the chemically deposited Cu foil is uniform,the surface is continuous without pores,the preferred orientation is(111)plane,and the surface roughness Ra is 0.0942 μm.The wetting and spreading process of SAC305 solder on two types of Cu foils is similar,which can be divided into three stages: 1)the initial stage;2)the rapid deployment phase;3)the progressive equilibrium stage.The wetting and spreading process is mainly controlled by chemical reactions.However,the wettability of SAC305 solder on chemically deposited Cu foil is better than that on commercial electrolytic Cu foil,with a larger equilibrium equivalent radius,smaller equilibrium contact angle,and thinner intermetallic compound layer at the interface.Cu foil can form good soldering joints with all three substrates.The chemical-deposited Cu foil produced under this process has excellent solderability.