Abstract
Wire bonding remains one of the most widely adopted interconnection techniques in the field of electronic packaging. At present, the most effective way to ensure a long life and high reliability of wire bonds is to improve the bonding quality. In this study, both experiments and finite element analysis (FEA) were employed to develop a fundamental understanding of wire bond degradation. Sensors with two protective silicone gels were loaded with the same thermal shock at a temperature ranging from $- 40^{\circ }\text{C}$ to 125°C, and the switching time was shorter than 10 s. The number of thermal shock cycles for the aluminum wire covered with transparent silicone reached 1200, but the maximum number of cycles for the other wire only reached 454. The experimental results indicated that the chosen transparent silicone performed better than did the black silicone originally selected, which was also verified by the simulation results. In addition, bond pull and shear tests were performed. The results revealed no degradation of either the Ag-Al or Ni-Al bonding joints under thermal loading. In summary, the root cause of failure was found to be improper protection silicone application, which, as often ignored in analysis, accelerated thermal fatigue of the aluminum wires. An explanation of the observed trend and a recommended aluminum wire bonding method were also provided.
Highlights
Wire bonding is a kind of bonding method that relies on thin metal wires and applies heat, pressure and ultrasonic energy to ensure a close bond between metal leads and base plate welding pads to realize electrical interconnection between a given chip and base plate and signal communication between chips [1,2,3,4,5]
The root cause of aluminum wire failure was investigated via visual inspection, scanning electron microscopy (SEM) observation, design of experiments (DOE) test, and numerical DOE modeling experiments
This suggested that an unmatched glue with an unsuitable CTE value accelerated the thermal fatigue process of aluminum wire under thermal shock loading
Summary
Wire bonding is a kind of bonding method that relies on thin metal wires and applies heat, pressure and ultrasonic energy to ensure a close bond between metal leads and base plate welding pads to realize electrical interconnection between a given chip and base plate and signal communication between chips [1,2,3,4,5]. Failure of wire bonds in microelectronic components in practice has been found to be attributed to the excessive formation of intermetallic compounds (IMCs), oxidation, corrosion, fatigue and electromigration [2,3,4,5,6,7]. These failures occur throughout the whole lifetime of these components or systems, including manufacturing, testing, storage and operation [6,7], often resulting in interface separation or cracking [8,9]. Failure analysis and research on aluminum bond wires related to protection glue assembly methods. The simulation results agreed well with the experimental results and could provide a positive guiding effect on the design and manufacture of automotive sensors
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