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Mycronic is a company that manufactures a solder paste printer used to manufacturecircuit boards. Inside the printer solder paste is fed with the help of a screw pump.The solder paste, consisting of relatively soft metals has a tendency to stick to thescrew surface and form particles. These are then detached and passed on in thesystem and can clog the nozzle of the printer. This project investigated the possibilityof creating a model test where different parameters can be varied to evaluate itsinfluence on the amount of solder paste sticking to the surface of the screw. Testingthese parameters directly in the solder paste printer would be time consuming andexpensive.A pin-on-disk set up with some modified parts was used to emulate the solder pastemotion in the screw pump. The results were then analyzed in light optical microscope(LOM) and scanning electron microscope (SEM) equipped with energy dispersivex-ray spectroscopy (EDS).The parameters that were varied were pressure, temperature, rotation speed,substrate, content of the paste and the shape of the profile, which is supposed toemulate the ridge of the screw. It was shown that the profile shape, the substrate andthe pressure was of great importance in the deformation of the solder balls while therotation speed and the paste content had a small or no effect.The goal of the project is to recreate the agglomerates that have led to malfunctionsin the printing and evaluate which parameters that have the greatest significance.

Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, June 2002. / Thesis advisor(s): Indranath Dutta. Includes bibliographical references (p. 37-38). Also available online.

Includes bibliographical references (p. 80-84).

Thesis (M.S.)--State University of New York at Binghamton, Mechanical Engineering Dept., 2005. / Includes bibliographical references.

Thesis (M.S.)--State University of New York at Binghamton, Materials Science and Engineering Program, 2008. / Includes bibliographical references.

<p> Low-temperature, lead-free solders mitigate heating-induced warpage caused by the  differences in coefficient of thermal expansion between printed circuit boards (PCBs), substrates,  and dies during package assembly. Eutectic and near-eutectic Sn-Bi solders are promising low  temperature candidates because they show high reliability at low strain rates during thermal  cycling. However, Sn-Bi low temperature solder (LTS) has poor performance at high strain rates  during drop-shock testing. Alloying additions such as Ag, Cu, and Sb have been shown to increase  the ductility and strength of eutectic Sn-Bi and therefore improve the overall reliability during both  thermal cycling and drop-shock. Small Sb additions to Sn-Bi LTS are of particular interest because  these additions significantly increase ductility while maintaining the tensile strength. This increase  in ductility was previously attributed to small SnSb intermetallic particles that form within the Sn  phase on the interface of Sn and Bi in 1.0wt% Sb containing samples. Despite the fact the no SnSb  intermetallic compound (IMC) particles have been found in 0.5Sb-42Sn-Bi samples in any  previous studies or in our own studies, it was thought that the SnSb IMC particles were responsible  for the improved reliability and ductility of Sn-Bi.  This work encloses our efforts to understand how small Sb additions to eutectic Sn-Bi  impact the solder microstructure and the resulting mechanical properties of the solder alloy. We  began by studying possible solidification pathways through phase diagram analysis in Thermo?Calc to understand how the microstructure is predicted to develop and compared these models to  the literature data. Next, we analyzed the microstructures of our custom Sb-containing alloys  through a combination of scanning electron microscopy (SEM), energy dispersive spectroscopy  (EDS), and electron probe microanalyzer-wavelength dispersive spectroscopy (EPMA-WDS) and  determined that no SnSb IMC particles were found in the 0.5Sb-42Sn-Bi alloy and at 0.5 wt% the  Sb remained in solid solution with Sn. Nanoindentation was then used to evaluate the strain rate  sensitivity of Sn-Bi LTS with Sb additions and we found that, while the alloy hardness remains  sensitive to different strain rates, the Sb in solid solution with Sn altered the deformation behavior  of the alloy and decreased the amount of planar slip during indentation. To study the stability of  the microstructure and the alloy behavior in use, shear testing was performed before and after  isothermal aging. Our results suggest that Sb in solid solution with the Sn-rich phase contributes  significantly to the changes in the eutectic microstructure and the mechanical properties. </p>

Ball Grid Array (BGA) solder joints are an array of solder alloy spheres sandwiched between package substrate and printed circuit board (PCB). These solder joints provide electrical connections and mechanical integrity to the assembly of package and PCB. Upcoming advanced packaging applications will involve heavier components, higher service temperatures and higher current densities, which will result in additional stresses on BGA joints accelerating their failure. Additionally, mismatch in the coefficient of thermal expansion (CTE) between the substrate, solder balls and PCB results in fracture near the solder-substrate interface posing a reliability risk. Moreover, higher current densities at elevated temperatures, also aggravate electromigration (EM) failure. It is important to mitigate these reliability risks associated with accelerated thermal cycling (ATC) and high current density EM. In this dissertation, various approaches to improve the ATC and EM reliability of packages have been investigated. First, BGA solder alloy composition was modified by doping Bi in the conventionally used Sn-3.0Ag-0.5Cu (SAC305) and Sn-4.0Ag-0.5Cu (SAC405) alloys to improve the mechanical strength of the solder joints. The effect of 1-3% Bi doping on aging induced changes in hardness, creep strength, tensile strength, viscoplasticity and microstructure was studied. Second, a reliability improvement measure (RIM) to mitigate fatigue failure of BGA solder joints was investigated. The microstructures of solder joints subjected to ATC were investigated for fatigue fractures and recrystallization of grains. Third, RIM measures to prevent EM failure of packages caused by high current density were investigated. The ability of novel substrate designs in prolonging time to failure of solder joints in packages along with EM failure mechanisms have been discussed. This dissertation thus provides insights on the efficacy and mechanisms of various reliability improvement measures to mitigate the ATC and EM reliability risks in BGA solder joints to guide future packaging design.

During their production and normal use, electronic packages experience large temperature excursions, leading to high thermo-mechanical stress gradients that cause fatigue failure of the solder joints. In order to prevent premature failure and prolong the fatigue life of solder joints, there is a pressing need for the characterization of the solder, especially lead-free solder, at the micro-level (joint size). The characterization and modeling of solder behavior at the appropriate scale is a major issue. However, direct measurement techniques are not applicable to characterize the deformation response of solder joints because of their micro scale dimensions. Therefore, a non-contact measurement technique utilizing a Scanning Electron Microscope (SEM) in conjunction with Digital Image Correlation (DIC) has been developed. Validation was achieved by performing a four-point bending test in both an in-house optical system with DIC and inside the SEM. This non-contact measurement technique was then used to extract the stress-strain response of the solder. Mechanical tests were performed on solder joints that were created using the same type of solder balls used in the electronic industry and were representative of normal joint scales. The SEM-DIC technique has been proven to be applicable for the determining the stress-strain response of solder material at the micro-scale.This study resulted in a validated material characterization technique specifically designed for micro-scale material response. One of the main contributions of this study is that the method is a lot simpler and cheaper, yet highly effective, compared to the previous methods. This technique is also readily applicable to the measurement of the stress-strain response of any micro-scale specimen, such as other metals, polymers, etc. Also, the measured displacement field by obtained by DIC can be used as the base for calculating the strain field on the surface of a specimen.

With the progress of the semiconductor technology, the devices scaling down to submicron range leads to increase I/Os number and very fine pitch IC package type; such as BGA, Flip Chip and CSP type packages. For Flip chip packaging, the solder bumping process act as the role of I/O interconnection instead of conventational wirebonding process. The ball mounted process is defined as the solder ball mounted on the Flip Chip Ball Grad Array (FC-BGA) substrate for solder bumping. In this study, how to improve the strength of ball-shear; residual tin capability and capability of process kit are the main issues to be investigated for the ball mounted process. To analyze the root cause and to implement the corrective action are the important purpose for solving the failures occurred on the ball mounted process. The following technologies included as (1) engineering ststictic methodology; JMP (statistical software) (2) Problem solving methodology (PSM) (3) Optimizing the process window (4) Set up the main parameters to analyse in machinery (5) how to monitor the CPK capability & material properties analysis, are used for these issues. Finally, the ball mounted process has been successfully investigated and results in solving the failure of Flip Chip ball mounted process and surface mounted technology (SMT) process for assembly packaging manufacture completely.