Thesis (M.S.)--State University of New York at Binghamton, Department of Systems Science and Industrial Engineering, 2006. / Includes bibliographical references.

This paper presents the results of an ongoing effort to develop a direct solder bumping process for electronics packaging. The proposed process entails delivering molten droplets onto specific locations on electronic devices to form solder bumps. This study is focused on investigating droplet deposition behaviors that affect solder bump characteristics such as final bump volume, shape, and adhesion strength. The occurrence of droplet bouncing has a strong influence on these characteristics. The potential for a droplet to bounce in the absence of solidification was modeled in discrete stages based on energy conservation. Wetting and target surface roughness were identified as the critical parameters affecting bouncing. The experimental results showed that improvements in wetting and decreases in surface roughness retard bouncing. These observations agreed well with the trends predicted by the energy conservation based model. The knowledge acquired in this study is expected to contribute to the development of an efficient solder bumping process. / Singapore-MIT Alliance (SMA)

Thesis (Ph.D.)--State University of New York at Binghamton, 2002. / Adviser: Eric J. Cotts. Includes bibliographical references.

Conductive anodic filament (CAF) is a failure mode in printed wiring boards (PWBs) which occurs under high humidity and high voltage gradient conditions. The filament, a copper salt, grows from anode to cathode along the epoxy-glass interface. Ready and Turbini (2000) identified this copper salt as the Cu2(OH)3Cl, atacamite compound. This work has investigated the influence of polyethylene glycol (PEG) and polyethylene propylene glycol (PEPG) fluxing agents on the chemical nature of CAF. For coupons processed with PEPG flux, with and without chloride, a copper-chloride containing compound was formed in the polymer matrix. This compound was characterized using x-ray photoelectron spectroscopy (XPS) as CuCl and an electrochemical mechanism for the formation of the chloride-containing CAF has been proposed. For PEG flux, with and without chloride, it has been shown that CAF only formed, but no copper containing compound formed in the matrix. It appears for PEG fluxed coupons, a PEG-Cu-Cl complex forms, binds the available Cu and acts as a barrier to the formation of CuCl in the polymer matrix. Meeker and Lu Valle (1995) have previously proposed that CAF failure is best represented by two competing reactions – the formation of a copper chloride corrosion compound (now identified as Cu2(OH)3Cl) and the formation of innocuous trapped chlorine compounds. Since no evidence of any trapped chloride compounds has been found, we propose that the formation of CAF is best represented by a single non-reversible reaction. For coupons processed with a high bromide-containing flux, bromide containing CAF was created and characterized using transmission electron microscopy (TEM) to be Cu2(OH)3Br. In addition, a copper-containing compound was formed in the polymer matrix and characterized using XPS as CuBr. An electrochemical mechanism for the formation of bromide-containing CAF has been proposed based on the XPS data. .

Conductive anodic filament (CAF) is a failure mode in printed wiring boards (PWBs) which occurs under high humidity and high voltage gradient conditions. The filament, a copper salt, grows from anode to cathode along the epoxy-glass interface. Ready and Turbini (2000) identified this copper salt as the Cu2(OH)3Cl, atacamite compound. This work has investigated the influence of polyethylene glycol (PEG) and polyethylene propylene glycol (PEPG) fluxing agents on the chemical nature of CAF. For coupons processed with PEPG flux, with and without chloride, a copper-chloride containing compound was formed in the polymer matrix. This compound was characterized using x-ray photoelectron spectroscopy (XPS) as CuCl and an electrochemical mechanism for the formation of the chloride-containing CAF has been proposed. For PEG flux, with and without chloride, it has been shown that CAF only formed, but no copper containing compound formed in the matrix. It appears for PEG fluxed coupons, a PEG-Cu-Cl complex forms, binds the available Cu and acts as a barrier to the formation of CuCl in the polymer matrix. Meeker and Lu Valle (1995) have previously proposed that CAF failure is best represented by two competing reactions – the formation of a copper chloride corrosion compound (now identified as Cu2(OH)3Cl) and the formation of innocuous trapped chlorine compounds. Since no evidence of any trapped chloride compounds has been found, we propose that the formation of CAF is best represented by a single non-reversible reaction. For coupons processed with a high bromide-containing flux, bromide containing CAF was created and characterized using transmission electron microscopy (TEM) to be Cu2(OH)3Br. In addition, a copper-containing compound was formed in the polymer matrix and characterized using XPS as CuBr. An electrochemical mechanism for the formation of bromide-containing CAF has been proposed based on the XPS data. .

In July 2006, the legislation of RoHS(The Restriction of the use of the Hazardous Substances in Electrical and Electronic Equipment) is fully implemented in EU. Although the major industries have response and preparedness for lead-free products, but they have no complete solution for using lead-free solder paste to replacing tin-lead solder paste. Therefore, two major issues arose in the surface mount process which are the cost increasing and the reliability decreasing of electronic products caused by higher reflow temperature. In addition to these two issue, surface mount of LED is also faced with the problem of attenuating of light intensity of LED due to the increasing of reflow temperature. After years, the companies of solder paste product and surface mount technology accumulate a lot of processing experience and they have certain yield on reflow process of LED. In order to keep competitiveness and market share, the know-how is treated as confidential. By working with about 10 professional surface mount manufacturers, it is interesting to note that solder paste and oven temperature curve used by each manufacturer are not actually the same. By adopting the experiences of cooperation with several professional surface mount manufacturers through experiments, the purpose of this thesis is to find the optimal reflow process parameters such that the light intensity loss of the LED caused by lead-free reflow process can be reduced as much as possible. By using Taguchi method and the executed experiments , the optimal parameter-combination have found efficiently from the four parameters: the peak of reflow temperature, the peak temperature of residence time, the brand of solder and the pre-baking time of LED. The results showed that the peak reflow temperature has the greatest influence among the selected four parameters and the following is the peak temperature residence time. The light intensity loss can be reduced up to 4-9% by adopting the obtained optimal parameters.

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The interfacial reactions of Sn-Zn and Sn-Zn-Al solder balls with Au/Ni surface finish under aging at 150¢J were investigated. With microstructure evolution, quantitative analysis, elemental distribution by X-ray color mapping from an electron probe microanalyzer (EPMA), the reaction procedure of phase transformation was proposed. During the reflow, Au dissolved into the solder balls and reacted with Zn to form £^-Au3Zn7. As aging time increased, £^-Au3Zn7 transformed to £^3-AuZn4. Finally, Zn precipitated near the Au-Zn intermetallic compound. On the other hand, Zn reacted with the Ni layer and formed Ni5Zn21. But the Al-Au-Zn IMC formed at the interface of Sn-Zn-Al solder balls, the reaction of Ni with Zn was inhibited. Even though the aging time increased to 50 days, no Ni5Zn21 was observed. The Joule effect was more apparent than the electromigration in the biased solder balls. First of all, the new phase (Au, Ni)Zn4 was proposed in the biased condition and in 175¢Jaging. Secondly, the thickness of the Ni5Zn21 IMC were the same between the anode and the cathode. Finally, We directly measure the temperature of the biased solder balls which was up to 173¢J.

Solder joints are the most fragile parts in electronic package. The properties of joints made of lead-free material are harder and crisper than those of lead-contained material. They tend to break due to dynamic loading by absorbing the impact energy and result in malfunction. Thus, how to improve the reliability of contact joints made of lead-free material in dynamic loading has become an important topic for research. This work is based on JEDEC Standard JESD22 - B111 ¡§Board Level Drop Test Method of Components for Handheld Electronic Products,¡¨ and JESD22 ¡V B110 ¡§Subassembly Mechanical Shock¡¨. The setup of drop test apparatuses was used to conduct dropping tests with the impact of acceleration 1500 G, in order to acquire the reliability of SnAgCu, SnCu, and SnAg alloy, which would be compared with 63Sn37Pb. The specimens would be red-dyed for an analysis under SEM to examine the distribution of the breakage. The results were analyzed by Weibull distribution to predict Mean Time to Failure (MTTF), it is revealed that MTTF of solder joints made of Sn0.7Cu, Sn2.6Ag0.5Cu, and Sn3.0Ag0.5Cu (MTTF=355.32, 295.82, 289.54 cycles respectively) are longer than that made of 63Sn37Pb (MTTF=152.52 cycles). Notably, MTTF of alloy Sn0.7Cu is 2.3 times of solder joints of SnPb. Alloy Sn3.0Ag0.5Cu has the shortest MTTF among the three, which is also 1.89 times of alloy SnPb. That is to say, under impact of 1500G, solder joints made of Sn0.7Cu, Sn2.6Ag0.5Cu, and Sn3.0Ag0.5Cu possess greater resistance to shock than alloy 63Sn37Pb, which is in common by used at present. In addition, the breakage of solder joints mainly generated on Intermetallic Compound (IMC) and around the four corners, distributed from the periphery to the central area. Especially, those on the corners receive greater stresses due to edge effect.

With electronic packaging towards the development of lead free process, the research on the portable electronic devices subject to impact load is emphasized gradually. At present, for drop test and cyclic bending test, most of the failure modes lie on the modes of "fracturing in IMC layer" or "fracturing on IMC/solder boundary". The purpose of this work is to use 3D numerical analysis software ANSYS/LS_DYNA, that were found out a proper numerical model, to further analyze the impact fracture of lead-free solder. From the numerical results, the strain rate of solder joint ranges from 103 s-1 to 104 s-1 under an impact velocity of 2 m/s. At this strain rate, the mechanical properties of solder joint could be effectively investigated. When IMC strength is smaller than 300MPa, the main failure mode is fracturing of IMC; whilst, IMC strength is greater than 300MPa, the failure mode becomes fracturing of bulk solder, but the failure mode of fracturing of IMC and a partial solder requires a model with more fine meshes to simulate. Different velocities did not affect the numerical results significantly, because the material parameters of a solder ball is strongly dependent on strain rate. Also, we found that the impact test in reality does not present a shear-dominant mode alone even when the impact angle is 0¢X. While using simulation to carry out the dynamic experiment, it can be observed that the course of solder joint suffering the damage provides a good reference and contrast for the experimental work in the future.