Mechanism And Control Of Electrochemical Migration For Sintered Nanosilver In Salt Fog Environment

Nanosilver paste as a new type of lead-free chip interconnect materials, has good mechanical property, electrical conductivity and thermal conductivity, can meet the requirements of high temperature, high density packaging for high-power electronic semiconductor devices. With the rapid development of wide band-gap semiconductor devices of high frequency, high temperature application characteristics for the third generation, the power electronics industry is promoting the new type of lead-free interconnect materials. Because its simplification of the traditional connection technology and equipment, and its excellent performance, it is gradually replacing traditional solder alloys and become one of the key interconnect materials of the third generation semiconductor devices for electronic package with high density, high temperature.This paper mainly studies electrochemical migration(ECM) failure behavior and mechanism of sintered nanosilver in salt fog environment, which is of important significance and can provide the key theoretical basis for the reliable packaging design of the application of power electronic devices in the coastal or marine environment.In this paper, the thick electrolyte layer(TEL) method was mainly adopted for the research on electrochemical migration behavior of sintered nanosilver in the impurity "chlorine" environment. This method can make a constant connection area between electrolyte layer and electrodes, so that the experiment result has a good repeatability. During in-situ observation of electrochemical migration process, the TEL method can make relatively smaller reflection than water droplet experiment. At the same time to obtain the micro-image information of high quality on pH distribution, formed precipitate and growth process of dendrite.The ECM behavior of sintered nanosilver strongly depends on the Clconcentration. It was found that both of the cloud-like layer of silver and silver dendrites exit in the electrolyte between the electrodes with the low Cl- concentration,i.e., 0 ppm and 10 ppm. The growth of the cloud-like silver layer is attributed to reduction of Ag2 O, but the silver dendrites growth is attributed to the reduction of silver ions. Only silver dendrites can be found in the TEL with the immediate Cl-concentration, i.e., 100 ppm, 200 ppm or 300 ppm. The reason is that silver ions are not enough to produce both Ag+and Ag2 O resulting from the suppression of the silver ions dissolution caused by the coverage of AgCl and Ag2 O precipitates on the anode surface. With high Cl- concentration, i.e., 400 ppm, only precipitates but no dendrites were presented because of the accumulation of precipitates layers on anode which could act as a barrier to prevent the dissolution of metallic Ag and migration of Ag+.For carrying on predecessor's research of electrochemical migration phenomenon at high temperature in dry air and improvement of reliability of sintered nanosilver paste, the ECM test of sintered nanosliver was also conducted in the inert gas environment. The result was that silver migration phenomenon in high temperature does not appear under the condition of pure nitrogen, which further explain that oxygen is an important component involved in silver migration. It provides important basis on improving the reliability of sintered nanosilver with exclusion of ambient oxygen.