Guozheng Yuan

Effects of solder joint shape on joint reliability under drop impact loadings

The purpose of this paper is to compare the ability of solder joint with different shape (hourglass-shaped, barrel-shaped and cylinder-shaped) to resist destruction under drop impact loadings. Three 3D finite element models of VFBGA (very-thin-profile fine-pitch BGA) packages, including different shape of solder joints, are established respectively. According to the condition B in the drop test standard of JEDEC, the stress-strain responses of the whole packages under drop impact loadings are calculated by ANAYA/LS-DYNA. The results showed that the stress on the solder joint reaches its peak at about 1ms and the maximum peeling stress on the critical solder joint which is located at the most outer corner of the BGA package. The hourglass-shaped solder joints which show the minimum peeling stress at the critical moment, have the strongest ability to resist destruction among three shaped solder joints under drop impact loadings.

Effects of strain rate and temperature on mechanical behavior of SACB solder alloy

With the deep research of the reliability of electronic package, more and more investigator realizes that the study on the high strain rate behavior of materials is necessary. Drop impact reliability has become an important criterion when assessing the reliability of portable electronics. The quality of solder joints directly determines the drop-impact reliability of the product. Therefore, to study the dynamic stress-strain constitutive relationship and the fracture/failure behavior of the solder material due to an external impact rate loading become important. Solder balls, as a structural member of the electronic product, are used to connect the microchip and the associated printed circuit board by a proper joining technique such as the surface mount technology (SMT). The static compressive properties of Sn3.0Ag0.7Cu3.0Bi lead-free solder are studied through quasi-static compression testing. In addition, The mechanical behavior of the two lead-free alloy, at strain rates ranging from 3×102 to 1.2×103s−1 and temperatures between 25°C and 140°C, was investigated with the compressive split-Hopkinson pressure bar (SHPB). The dynamic property of Sn-3.0Ag-0.7Cu-3.0Bi alloy was assessed by means of split Hopkinson pressure bar test technique. The strain rate sensitivity of the lead-free solder is characterized using a modified split Hopkinson pressure bar system. The experimental results indicate that, the strain rate sensitivity parameter increases along with increasing strain and strain rate, but decreases with increasing temperature. The addition of Bi delays the sensitivity of strain rate of the lead-free solder. The influence of the addition of Bi on the dynamic stress — strain constitutive relationship and the fracture/failure behavior of the solder material is investigated. The activation energy varies inversely with the flow stress, and has a low value at high deformation strain rates or low temperatures. In this paper, Quasi-static and high strain rate properties of the lead-free solder with temperature are given. Basing on these experimental data, the constitutive relation of Johnson-cook model for this kind of material was built up.

STUDY ON DYNAMIC FAILURE MODEL OF LEAD-FREE SOLDERS USING SHPB TECHNIQUES

The dynamic compressive properties of 96.3Sn3Ag0.7Cu and 99.3Sn0.7Cu solders were studied by means of a split Hopkinson pressure bar at strain rates ranging from 500 to 2000 s−1. Tests were conducted at room temperature and under uniaxial compressive conditions. Eutectic SnPb solders were used as the reference. From the data of tests, it was found that yield strength and flow stress increased remarkably with the increase of strain rate. On logarithmic scales, the yield strength increased linearly with strain rate. These lead-free solders revealed certain visco-plastic behavior and strain rate sensitivity, which predicted using Johnson-Cook material model. Related parameters in the model were determined from the experiment. Compared with the typical Pb-containing solder Sn63Pb37, these lead-free solders showed some fine properties and could substitute some Pb-containing solder alloys in microelectronic components packaging and interconnects.

CHARACTERISTICS OF TiNi THIN FILMS DEPOSITED BY MAGNETRON SPUTTERING SYSTEM WITH OPTICAL EMISSION SPECTROSCOPY MONITOR

TiNi composite thin films were fabricated using a closed-field unbalanced magnetron sputtering system equipped with optical emission spectroscopy monitor (OEM). The thin films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and nanoindentation. Results show that the TiNi films are amorphous, and their composition varies approximately linearly with the OEM value. Thus, the film composition could be controlled by in situ real-time OEM. The structure of the single B2 parent phase was observed in the annealed TiNi film. The hardness and elastic modulus of the films increased because of the precipitation of the Ti3Ni4 phase in the single B2 parent phase.

Failure analyse of the welding point in flip-chip BGA packages in the drop-free

The failure of plastic ball grid array in vibration and shock under intense dynamic loading will be studied in the project. This paper presents the drop test reliability results for SnPb flip-chip on a standard JEDEC drop reliability test board, the failure mode and mechanism of planar array package in the drop test will be integrated analyzed. High acceleration dropping test method was used to research the reliability of BGA (ball grid array) packages during the drop-free impact process. The model RS-DP-03A drop device was used to simulate the falling behavior of BGA chip packages under the real conditions, dropping from the 650mm high, the drop condition meets the JEDEC22-B111 standards (pulse peak 1500g, pulse duration 0.5 ms). In the testing, based on the real-time changes of dynamic voltage, the relationship between dropping times and different phases of chip failure was analyzed. Solder crack and pad lift failure locations are characterized with the dye-penetrated method and optical microscopy. Stain tests were carried on the expired chip packages, the failure position of solder joints and the internal appearance of cracks were observed; the growth mechanism of solder ball crack under the condition of drop-free was analyzed and discussed.