Corrosion And Electrochemical Migration Behavior Of Sn And Ag Electronic Bonding Materials

Social division of labor and cooperation has greatly improved,but also brought some problems,compared with parts,electronic materials,parts connection materials lack of outer packaging protection,exposure to the atmospheric environment,easy to form liquid film,under the influence of atmospheric pollutants,easy to corrosion;In the case of working power,electrochemical migration(ECM)will occur,resulting in a short circuit.It brings hidden trouble in the service process of electronic equipment.Tin-based solder alloy due to its low melting point and high conductivity is currently the most widely used electrical connections,but the material as the miniaturization of electronic devices and the development of miniaturization,encapsulating connection of electronic equipment put forward higher request,the traditional tin solder alloy is more and more can't meet the demand of traditional electronic devices connected to the material,Conductive silver paste has low surface tension,good electrical conductivity,and is considered as the most likely alternative to traditional tin-lead alloy electronic bonding material due to its silkscreen printing method.Electrochemical corrosion and migration are the main failure factors of tin-based solder alloy and conductive silver paste in service.This paper studies the corrosion and migration behavior of tin-based solder alloy and low-temperature solidified silver paste,and the specific conclusions are as follows:(1)The effect of chloride on the corrosion behavior of tin alloy was investigated by electrochemical impedance and polarization methods.The results show that the corrosion rate of tin alloy decreases with the increase of chloride ion concentration at low temperature,but at high temperature,the corrosion rate of tin alloy increases with the chloride ion concentration.XRD and SEM studies revealed chloride ions form complex with tin base alloy at high temperature,tin forms basic tin chloride with chloride ions at low temperatures,which could suppress the corrosion effectively.(2)The inhibition effect of Precipitation type corrosion inhibitor on the electrochemical migration(ECM)of pure tin was investigated by means of water drop testing and surface characterizations.The effects of concentration of Na₂HPO₄ and applied direct current(DC)bias voltage on the ECM were also studied.Results showed that the mean time to failure caused by ECM decreased with the increasing bias voltage.Upon addition of relative high concentrations of Na₂HPO₄,Na₂HPO₄can react with metallic tin or tin ions to form a protective film on the surface of anode and increase the pitting potential.The rate of anodic dissolution can be slowed down and thus ECM of tin was retarded.Fractal-like dendrites formed after ECM tests in the absence and presence of low concentrations of Na₂HPO₄ mainly consisted of tin elements.Relevant reactions were proposed to explain the inhibitory effect of Na₂HPO₄ on the ECM of tin.(3)Corrosion behavior of low-temperature sintered silver nanoparticle(Ag NP)paste in NH₄Cl solution was investigated using electrochemical measurements(electrochemical impedance,potentiodynamic polarization,and localized electrochemical impedance spectroscopy)as well as surface characterizations(scanning electron microscope and X-ray photoelectron spectroscopy).The thiazolyl derivative was first applied as the corrosion inhibitor for the sintered Ag NP paste.Results showed that the corrosion rate increased with the rising NH₄Cl concentration while it decreased with the increase of solution alkaline.Due to the formation of a protective film through the coordination of N and S with Ag atoms,2-mercaptobenzothiazole and sodium 2-mercaptobenzothiazole both showed excellent corrosion inhibition efficiencies(more than 97%)for the sintered Ag NP paste in NH₄Cl solutions.Relevant mechanisms have been proposed.The electrochemical migration(ECM)behavior of low-temperature-sintered Ag nanoparticle paste electrode was investigated using water-drop method.The effects of applied direct current bias voltage and Na Cl concentration on ECM behavior were discussed.Results show that:hexadecyltrimethylammonium chloride(CTAC)was proved to act as an effective inhibitor to migrate dendrite growth by selected adsorption.And the ECM inhibition efficiency increased with the concentration of CTAC.Relevant mechanisms of ECM behavior and ECM inhibition effect of CTAC for low-temperature-sintered Ag nanoparticle paste were proposed.The protective self-assembled monolayers(SAMs)were fabricated on the surface of low-temperature sintered nano-Ag paste electrode in the sodium mercaptobenzothiazole(MBT-Na)solution at room temperature.The SAMs-coated electrode can reduce the rate of anodic dissolution and thus retard the growth of dendrite.The ECM inhibition efficiency increased with the concentration of MBT-Na rising.And the optimum self-assembled time was 60 min.A higher applied bias resulted in a shorter failure time for ECM.And relevant mechanisms have been proposed.