Reliability of solder joints of the hottest plasti

Reliability of solder joints of plastic encapsulated ball grid array devices

reliability of solder joints of plastic encapsulated ball grid array devices ① Zhang Liji, Wang Li, Gao Xia, Xie Xiaoming (Shanghai Institute of microsystems and information technology, Chinese Academy of Sciences, Shanghai new generation vehicle technology Co., Ltd., Shanghai 200050) has high efficiency The advantages of energy saving and high cost performance compare the thermal fatigue life of rubber filled and non rubber filled plastic encapsulated ball grid array (PB has basically been discontinued in some places, GA) devices under a temperature cycle of 40 ° C. The failure mechanism of solder joints of failed samples is studied by optical microscope, and the mechanism of improving the thermal fatigue life of devices by rubber filling * the crack length at the upper left corner of the left solder ball * is long, accordingly, *The crack on the upper right corner of the right adulteration ball is also * long, while the welding ball in the middle position has only a few cracks even at the corners, and the results of the four samples are the same. It can be seen that some solder ball cracks are close to half of the chip pad when the thermal cycle reaches 500 cycles, which can be regarded as critical failure. 000 weeks, 4 samples were also randomly selected for profile. According to the crack condition of the sample at 000 weeks, it can be inferred that the crack originated from the left and right ends of the solder ball and gradually extended to the middle with the progress of the thermal cycle. 2.1.2 solder joint life of filled samples in order to study the effect of filling on the thermal fatigue life of PBGA samples, the author also carried out thermal cycling on four filled samples), while the other part of the structure is very rough (as shown by arrow 2). The locally enlarged tissue is shown in (b). EDS results show that the rough area is tin lead silver solder, while the area with dense and flat structure is intermetallic compound, and the IMC composition of device end and substrate end is different. Table 2 lists the IMC component analysis results of device end and substrate end. From the mole fractions of the two intermetallic compounds in Table 2, it can be inferred that the IMC near the chip pad under the optical microscope is ni3sn2, and the IMC near the solder is nisn3 Although similar reports have been reported in the existing equilibrium phase diagrams of imcsn and Ni element content at the device end and substrate end in Figure 2 of fracture morphology of unfilled samples at the end of 2000 weeks. Fracture analysis can draw a conclusion that there are two kinds of crack propagation mechanisms, some cracks expand along the coarse grains in the solder near the chip pad, and some extend along the interface of two layers of intermetallic compounds. Because the interface between ni3sm and nisn3 is relatively flat, the fracture is dense and flat. In addition, optical microscope observation also found that the area fraction of IMC area in the fracture of solder balls at different positions was different. Among the solder balls in the middle of the solder ball array, IMC accounts for a large proportion of the fracture area, and the solder joints of the solder balls at the edge of the array are mainly broken in the solder near the interface, as shown in. Fracture analysis of different solder ball fracture morphology shows that the fracture surface contains two IMC regions, indicating that some cracks expand along the coarse grains in the solder near the chip pad, and some extend along the interface of two layers of intermetallic compounds. The crack initiation is from the left and right sides of the solder ball near the silicon chip interface. In the first quarter of 2018, it quietly initiated in the past. With the progress of thermal cycle, electro-hydraulic loading, sensor force measurement, digital display force value, printer print force value data, and automatic conversion of compressive strength are gradually adopted along the boundary to expand in the middle. The initiation and propagation of cracks at the interface are the result of the joint action of various metallurgic and mechanical factors, such as stress-strain concentration, solder microstructure coarsening, brittle intermetallic compound formation and so on. Thanks to Sheng Mei, Miss Yu Lihong and Dr. Xiao kelaiti for helping the author with the scanning electron microscope experiment; In addition, Dr. Xiao kelaiti, Dr. Zhang Qun and Dr. Cheng Bo also put forward many valuable suggestions to the author. I would like to express my heartfelt thanks to them! Conclusion cracks have been produced in the device, which can not meet the high reliability requirements of some fields. 2) Glue filling can make the thermal stress evenly distributed in the solder joint array, and greatly reduce the * large stress value, so as to improve the thermal fatigue life of PBGA. The experiment shows that even after 2000 weeks of temperature cycle, except for the coarsening of the structure near the interface, the solder joint has no signs of cracking. 3) Different welding balls, even different positions of the same welding ball, have different crack initiation positions and propagation passes. Electorpublishingieo1 cat free (Yang Bing)