William T. Chen

Solder ball connect (SBC) assemblies under thermal loading: I. deformation measurement via moiré interferometry, and its interpretation

Thermal deformations that result from mismatches of coefficients of thermal expansion (CTE) in Solder Ball Connect (SBC) assemblies were investigated. The CTE mismatches of the materials and the components in the package have both macro and micro effects on the strain distributions in the SBC interconnections. The geometry of the SBC joint also has a strong influence on the solder strains in the SBC package. An experimental technique with high sensitivity and resolution, moire interferometry, was used to obtain whole-field displacements. Thermal strains in SBC packages, especially the strain concentrations in the SBC joints, were then determined from the displacement fields. The experimental results played an important role in failure analysis, structural design optimization, and finite element model verification in the IBM SBC program. The results also show that moire interferometry is a very powerful and effective tool in experimental studies of electronic packaging.

Thermal-mechanical strain characterization for printed wiring boards

Multilayer printed wiring boards are widely used in electronic packaging assemblies. One critical reliability concern is the thermal-mechanical strains induced by temperature change. For example, the in-plane strain affects the thermal fatigue life of surface mount solder interconnections, while the out-of-plane strain affects the mechanical integrity of the plated-through holes of the printed wiring boards. For this paper, a systematic study of the thermal-mechanical strain of epoxy-glass printed wiring boards, below and above the glass transition temperatures of the epoxies, has been carried out. The study includes measurements of properties of basic constituent materials (epoxy, glass fabric, copper), of intermediate building blocks in the fabrication process, and of final products. The study has led to a quantitative engineering model that predicts the average in-plane thermal-mechanical strain for use in modeling surface mount components on a printed wiring board, as well as the average out-of-plane thermal-mechanical strain for determining plated-through-hole reliability in thermal shock processes. The model was verified by two experimental techniques (measurement by thermomechanical analyzer, and moire interferometry) applied to two epoxy resins and three glass fabrics, with and without copper planes. For thermal shock below the glass transition temperatures of the epoxy resins, the in-plane and out-of-plane strains are described by a modified rule-of-mixtures theory and a biaxial plane stress model, respectively. For temperatures above the glass transition temperatures, the in-plane strains are governed by the copper and glass fabric, whereas the out-of-plane strains are dominated by the incompressible fluid behavior of the epoxy resins. The nonuniform pattern of thermal expansion in regions populated with plated-through holes was examined. The reliability of surface mount solder interconnections and plated-through holes is discussed.

Stresses in a transversely isotropic elastic cone under an asymmetric force at its vertex

ZusammenfassungBehandelt wird das Problem eines transversal isotropischen Körpers, der durch zwei konzentrische Kegelflächen begrenzt ist und durch eine asymmetrische Kraft an der Spitze belastet wird. Geschlossene Ausdrücke werden gegeben für den Spannungszustand und die Verformung. Ein interessanter Spezialfall ist das Cerruti-Problem, wo eine konzentrierte Kraft tangential an der Oberfläche eines elastischen Halbraumes wirkt. Die Lösung ist exakt im Rahmen der linearen Elastizitätstheorie.

Displacement discontinuity over a transversely isotropic elastic half-space

The paper presents a solution to the elasticity problem where the discontinuity is in the displacement component parallel to the plane area inside the transversely isotropic medium. The work previously performed on discontinuity problems is also discussed.

An overview of electrical and mechanical aspects of electronic packaging

An overview of electrical and mechanical aspects of electronic packaging as they pertain to midrange and high-end computer systems is presented. Continued advances in semiconductor technology and manufacturing tools have fueled the expectation for continued greater function, higher performance, and lower costs in electronic systems. To meet this expectation, parallel progress in electronic packaging technology is necessary to realize the benefits of the VLSI technology advancements. Electrical and mechanical aspects of the electronic packaging structure-from the increased circuits per chip to the physical design of the electronic packaging-and future directions in packaging evolution are discussed. Innovations in single-chip and multichip modules, as well as the driving forces from the electrical requirements to the need of the physical design to meet wiring and performance demands are considered.<<ETX>>