Test methods for electrochemical migration: a review

There are three main test methods used in the study of electrochemical migration, i.e., thermal humidity bias (THB) test, water drop (WD) test and thin electrolyte layer (TEL) test. However, each method has their own characteristics and application scope. In this context, the state-of-the-art in the test methods for electrochemical migration is reviewed. This review covers the definitions, set-ups and operational approaches of set-ups, applicability and in situ inspection availability of each method. To offer a reference for people to select the appropriate electrochemical migration test method, the advantages and disadvantages of each method are also compared in detail. The THB test cannot only simulate the operating conditions of electronics but can also be performed in accelerating conditions in laboratory as well as industry assessment. However, it shows a poor availability in quantitative analysis because the parameters including the locations and the thickness of electrolyte layer are uncertain. The WD test which has been widely used in the laboratory study is more quantitative than THB test. The first limitation is that the WD test cannot simulate the electrolyte layer formation process, and secondly, the spherical electrolyte drop and the changes in its shape during the test decrease the in situ inspection availability and the reproducibility in electrochemical test results, respectively. The TEL test shows a good performance in in situ inspection and a good reproducibility in electrochemical test results under a horizontal and continuous electrolyte layer. However, like the WD test, it cannot simulate the electrolyte layer formation process. Simultaneously, it is also very difficult to perform an electrochemical migration test under an ultra-thin and continuous electrolyte layer.