Surface Of Solder Joints Research Articles

Effect of electron irradiation on microstructural evolution and mechanical properties of Sn3Ag0.5Cu solder joints

Power electronic devices face harsh radiation environments in deep space exploration. It is significant to study the reliability of solder joints of electronic devices in radiation environments. The effect of electron irradiation on the microstructure and mechanical properties of Sn3Ag0.5Cu (SAC305) Ball Grid Array (BGA) solder joints was investigated in this work. The results show that the central position of the SAC305 solder joint surface was damaged after electron irradiation. Then the surface of the solder joints was remelted. The shear strength of solder joints increases as the electron irradiation dose rises. When the electron irradiation dose reaches 80 Mrad, the shear strength of the solder joint is enhanced by 8.62% compared with that of the unirradiated sample. After irradiation, the number of dimples on the fracture surface of solder joints increases and the depth of dimples decreases. Geant4 simulation results show that the surface of solder joint is subject to more severe electron impact than the inside of solder joint is. The interaction between electrons and solder joints is the primary reason for the surface remelting of solder joints.

Effect of gamma irradiation on microstructural evolution and mechanical properties of Sn3Ag0.5Cu solder joints

Sn3Ag0.5Cu (SAC305) Ball Grid Array (BGA) solder joints were exposed to 60Co source gamma irradiation at a dose rate of 1 Gy(Si)/s from 0 to 200 h in air. The effects of gamma irradiation on the microstructure evolution and mechanical properties of the solder joints were investigated. β-Sn interacted with O2 in the air and was oxidized to SnO2 on the solder joint surface after gamma irradiation. The oxidation initiated at the corners of the solder joint/pad interface, extended to the entire solder joint/pad interface, and finally occurred at the solder joint matrix. Microcracks usually grow around SnO2/β-Sn interfaces. The interaction of gamma rays with β-Sn and SnO2 is the primary reason for solder joint oxidation. Gamma irradiation generated atomic vacancies, breaking bonds, and dangling bonds in β-Sn and SnO2 crystals through the Compton Effect, which promoted the physisorption and chemisorption of O2 on their surfaces, as well as the oxidation of β-Sn and growth of SnO2. The interaction between the gamma irradiation and solder joints can be divided into two stages. SnO2 was nucleated at lattice defects induced by the interaction between gamma rays and β-Sn crystals in the first stage. The growth of the SnO2 nuclei resulting from a large number of crystal defects in SnO2 and the potential difference between SnO2 and the β-Sn surface induced by the Compton Effect occurred in the second stage. According to the differential scanning calorimetry (DSC) analysis, the melting temperature of the SAC305 solder alloy decreased with increasing irradiation time. According to the nanoindentation test results, with an increase in irradiation time, the microhardness of the solder joints first increased, then decreased, and finally increased again.

Effect of CNTs and Ni coated CNTs on the mechanical performance of Sn57.6Bi0.4Ag BGA solder joints

In this study, Sn57.6Bi0.4Ag solder joints with different content of CNTs and Ni–CNTs were investigated. Aims were to make a clear description on the effect of Ni coat and to find the best doping amount to improve the mechanical properties of solder joints. Melting point measuring, micromorphology analyzing, ball shear testing, as well as fracture surface detecting were carried out. To make a fair comparison, only the weight of CNTs was counted in the doping amount, excluding the weight of Ni. According to experimental results, the melting point of Sn57.6Bi0.4Ag solder alloy was hardly influenced by small doping amount of CNTs and Ni–CNTs. Besides, the mechanical properties of Sn57.6Bi0.4Ag solder joints could be improved by the addition of CNTs and Ni–CNTs. Solder joints with 0.05wt% CNTs or 0.07wt% Ni–CNTs showed the best performance respectively. With the addition of CNT and Ni–CNTs, the fractured surface of solder joints became rougher, showing better bonding structure. Though both CNTs and Ni–CNTs have the capability to improve the mechanical performance of solder joints, Ni–CNTs worked much better. Ni coat was prove to have significant effect on inhibiting the aggregation of CNTs that could induce cracks and wetting problems and even deteriorate the strength of solder joints.

The Modeling and Prediction Study of BLP Device Solder Joint Three-Dimensional Shape

Solder joint shape refers to geometry that molten solder can be achieved with spreading and wetting along the metal surface in the junction between components solder pins and printed circuit board (PCB) pad, to the metal surface contact angle and solder fillet shape[1]. BLP (Bottom Leaded Plastic) [2] which is not a type of thin out-line surface mount device(SMD) without the side lead is widely used in manufacturing of new generation memory such as SDRAM \ RDRAM \ DDR. For this non-lead SMD, the shape and reliability of solder joint is the focus of the study. In this paper, we select the C-BLP of 28-pin device as the research object, complete the forming model of solder joint shape based on minimum energy principle and the solder joint shape theory by using Surface Evolver software, and analyze two critical process parameters (solder volume and solder pad width ) impacting on the solder joint shape. The study results show that the solder volume and pad width have a significant impact on the three-dimensional shape of BLP solder joint. The law of which is that: in the case of the other fixed parameters, as the increase of the solder volume, solder joint surface gradually changes from the relatively flat to the convex, solder joint gradually changes from the completely soldered to the partly soldered in the pad connections, and solder joint heights are gradually decreased; in the case of the other fixed parameters, as the increase of the pad in width, the solder joint surface gradually changes from the convex to the flat, solder joint gradually changes from the completely soldered to the partly soldered in the pad connections, and solder joint heights are gradually decreased. The actual solder joint shape designs of BLP devices can be instructed based on predicted results.

Ｓｎ‐Ａｇ‐Ｃｕ系鉛フリーはんだを用いた接合部の信頼性に及ぼす引け巣の影響

Now, the development of lead-free solder alloys and soldering technology using them is pushed forward by global scale. Among them, the examination for the Sn-Ag-Cu solder is pushed forward mainly for the reason of being superior in joint reliability although the melting point is higher. And products using this solder are already on the market partly. However, in flow soldering with Sn-Ag-Cu solder, peculiar defects called shrinkage cavity, fillet-lifting and land-lifting occur at solder joints. And these defects become one of a problem toward full-scale practical use. In this study, we investigated the influence that shrinkage cavities occurred on the solder joint surface in flow soldering with Sn-3.5 mass%Ag-0.75 mass%Cu lead-free solder on reliability. Furthermore, we added examination about prevention of shrinkage cavity. As a result, the shrinkage cavity understood not to become a fatal defect and not to largely decrease reliability of solder joints. We understood also, that shrinkage cavities are prevented by water cooling just after soldering or increasing the silver content.

Support vector machine-based inspection of solderjoints using circular illumination

A method for inspecting solder joints using support vector machines (SVMs) and a tiered circular illumination technique is proposed. The illumination technique provides visual information that allows the 3D shape of the solder joint surface to be determined. The extracted features are used to classify the solder joint using an SVM classifier. Experimental results show the effectiveness of the proposed method.

Neural network-based inspection of solder joints using a circular illumination

In this paper, we describe an approach to inspection of solder joints on printed circuit boards by using a circular illumination technique and a neural network classifier. The illumination technique, consisting of three tiered circular colour lamps and one colour camera, gives good visual cues to infer 3D shape of the solder joint surface. A general aspect of this inspection is that the shape of the solder joint tends to greatly vary according to soldering conditions. Due to this, a neural network classifier based on a supervised version of Kohonen learning vector quantization (LVQ) is proposed to automatically and efficiently make classification criteria of the solder joint shapes according to their quality. The practical feasibility of the proposed approach is demonstrated by building a prototype inspection machine and testing its performance.