Thesis (Ph.D.)--University of North Texas, 1993. / Major Professor: James L. Marshall. Includes bibliographical references.

Thesis (Ph.D.)--University of North Texas, 1994. / Includes bibliographical references.

Due to the introduction of Restriction of Hazardous Substances (RoHS) directive Pb containing solders have been banned from the electronics industry and a reliable replacement for the Sn-Pb solder is being sought for by industry around the globe. Medical and Defense industries are currently exempt from the directive and use Sn-Pb solder in their manufacturing process. The switch to lead-free has led component manufacturers to use different lead-free solders, thus causing mixed solder joints of lead-free components with Sn-Pb paste. In this study, mixed assembly microstructures and mechanical properties were examined. Furthermore, six novel lead-free solders were prepared using SAC105 solder doped with elements: Ti, Ni, Mn, La, Ce and Y. The solidification microstructures, fracture behavior and wetting properties of these solders were evaluated to find a suitable replacement for SAC105 solder.

Due to the introduction of Restriction of Hazardous Substances (RoHS) directive Pb containing solders have been banned from the electronics industry and a reliable replacement for the Sn-Pb solder is being sought for by industry around the globe. Medical and Defense industries are currently exempt from the directive and use Sn-Pb solder in their manufacturing process. The switch to lead-free has led component manufacturers to use different lead-free solders, thus causing mixed solder joints of lead-free components with Sn-Pb paste. In this study, mixed assembly microstructures and mechanical properties were examined. Furthermore, six novel lead-free solders were prepared using SAC105 solder doped with elements: Ti, Ni, Mn, La, Ce and Y. The solidification microstructures, fracture behavior and wetting properties of these solders were evaluated to find a suitable replacement for SAC105 solder.

Georgia Techs Packaging Research Centers vision of System on Package (SOP) requires that the ball grid array (BGA) package be eliminated and the integrated circuit (IC) directly assembled on the printed wiring board (PWB). Flip-Chip on board (FCOB) emerges as a viable solution which meets the industry requirements of (i) increased I/O, (ii) increased functionality and (iii) improved performance at lower costs. Nevertheless flip-chip on board (FCOB) reliability continues to be an important concern in electronic packaging industry. Moreover transition to Pb-free solder for interconnects and continuously shrinking geometries result in new modeling challenges. In addition, the integrity of the intermetallics (IMCs) at the interfaces of the solder/PWB and solder/die is one of the determinant factors in the reliability and continuity of electrical signals in flip-chip interconnects. Pb-free solder studies for the flip-chip assembly studies are limited and simplified so far, not fully incorporating the effect of intermetallics in the reliability. New modeling challenges involve many details, from geometry to material properties. A brittle IMC will lead to a fracture at the interface. Also IMC thickness can cause the variation in stresses in the underlying layers, causing delamination. Moreover IMC morphology can also depend on the metal finishes on the PWB. In this work, a combined numerical and experimental program has been developed to address the challenges mentioned above. The flip-chip on board assembly is modeled in 3-D for reliability studies, taking into consideration material non linearities and a 104 order of geometric variation to capture the die size in mm to sub-micron intermetallic thickness. The study intends to determine the stresses induced at the critical interfaces under thermo-mechanical loading incorporating the intermetallic material properties. Various failure modes of these assemblies were studied. Experiments were carried out for comparative reliability studies of Pb-free solder with eutectic Pb-based solder. Intermetallic formation and growth are characterized during thermal aging and its effect on reliability is determined. Parameters affecting intermetallic like under-bump Metallurgy (UBM) thicknesses are varied and its effect evaluated. Moreover experiments with three new substrate pad finishes on PWB are carried out to evaluate them as an alternative to Electroless nickel immersion gold (ENIG) for new Pb-free solder. The final aim of this study is to reach a better understanding of the reliability issues in FCOB.

Optical communication dominates the wire-communication since the requirement of the high speed data transfer in the Internet. Fiber Solder Ferrule (FSF) plays an important role in transceiver modules of the optical communication. For the reason to keep the coupling efficiency between the laser diode and fiber after time using and a various temperature operation, fiber has to be carefully fixed in the metal ferrule. The fixing of the fiber now is finished to let the melting solder flow into a 400£gm diameter ferrule by the capillary action manually. The stability and accuracy of this method can not match the required performance. And the human operation makes this process more unstable to cut down the yield below 30% even by an experienced operator. So, this study analyzes the FSF process and proposes an active strategy to replace the original passive method by capillary action. An active soldering mechanism is implemented to precisely and stable filling the solder into the ferrule. The yield can be significantly raised from 25% to 75%.

As the trend of miniaturization of complex integrated circuit(IC) devices, the current density of flip-chip solder bumps have increased significantly and each solder joint is supporting a current density close to or even over 104 A/cm2 .Therefore, in SnPb eutectic solder, which has a high diffusivity at the operating temperature due to its low melting point, the electromigration becomes a major reliability threat. Thus, the thesis is aimed to investigate the effects of electromigration behavior on flip-chip package eutectic Sn-Pb solder bumps reliability under high current density. The current densities are 2x104 A/cm2 and 1.5x104 A/cm2,the surface of die temperatures are 115¢Jand 95¢J.The bump temperature, the histories of the bump resistance, and mean time to failure (MTTF) testings were conducted. The failure mechanism was observed through SEM and EDS. From the results of the experiment, the dominant failure mode of the bump is due to electromigration behavior that causes voids at UBM/bump interface (cathode) when the sample¡¦s failure time is shorter. As the failure time is longer, the failure is also resulted from heat effect in addition to electromigration behavior.

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The thesis is mainly focused on the investigation of optimal process operation, which is appropriate for new-type stacking package product to achieve the assembly products of two or more packages. By melting solder balls to form the stacking package products, the eventual goals of lightness, thinness and smallness will be accomplished. To increase and stabilize the production yield of stacking package products, different flux, different temperature setting with reflow oven, and different flux dipping method were used. With Taguchi design of experiment, the solder balls combined situations under varied conditions were observed. The best process character of new-type integration assembly products was achieved. The experimental results and mass production data prove that different flux type and temperature setting with reflow oven won¡¦t influence the solder balls connection between two package products. Only the flux dipping method will directly affect solder balls connection between two package products. The abnormal phenomenon is the so-called cold joint in assembly plants. With innovation, silicon gel head is used as a flux adhesive way to achieve the goal of flux transferred. This method can be used in integration process of new-type stacking package products. That will certainly assure that every solder ball on each package product can be helpful for adhesion of flux. The experiments proved that the yield rate of solder balls connection of two package products is 100% after the stacking package products through reflow oven. This proves that using flux with silicon gel head on new-type stacking package products is the best way of process operation. The innovation of this new process has been granted a patent by the Patent office, ROC. Although this is a simple invention, it will bring profit to ASE Co. as well and ensure the leadership of new-type stacking package products in related industries. Keywords: Stack¡BSolder Ball¡BCold Joint¡BSilicon Pad

The purpose of thesis is to study the transient analysis of structural responses of solder joints under high-Speed impact. By using the experimental and simulation analysis. The experimental work can be divided into six parts, such as different impact speeds, different solder¡¦s components, different pad finishing, different UBM and Runner, and different thickness of PBO. From experiments, the variations of solder joint strength and mechanical properties were received and discussed and the failure mode. The empirical results show that maximum impact force on solder joints decreases as the impact speed increasing. The solder joint strength becomes stronger with the solder adopting elements of Ni and Co. The strength of solder ball was reduced significantly after a reflow. The intermetallic compound strength reduces with solder ball adopting high content of Ag. In impact test, the resistance of UBM of TiAl is better than that of TiAlTi. The runner adopted with the element Pd can improve the IMC reliablility to reduce Mode I failure. However, the PBO thickness has little influence on IMC strength. From the numerical results, in the consideration of strain rate on solder joint the mechanical properties of solder joint could be effectively investigated. According to the different IMC strength there will produce three failure modes of solder ball and the impact force becomes higher as the IMC strength setting higher. If the lower yield stress is considered in lower IMC strength, the impact force is not the highest of all, but the time duration is the highest of all.