The formation and growth of Cu6Sn5 and Cu3Sn at the interface of Sn-Pb solder/copper substrate are factors which affect the solderability and reliability of electronic solder joints. The addition of particles such as Ni to eutectic Sn-Pb solder drastically affects the activation energies of formation for both intermetallics. This study was performed to understand the mechanisms of intermetallic formation and the effects of Ni on intermetallic growth. Cu/Sn and Cu/Sn/Ni thin films were deposited by evaporation and observed in the TEM in real time using a hot stage. The diffusion of Sn through Cu6Sn5 and Cu3Sn followed by reaction with Cu must occur for intermetallic formation and growth to take place. Ni is an effective diffusion barrier which prevents Sn from diffusing into Cu.

Aluminum nitride (AlN) sintered ceramics are a critical new material for electronic packaging applications, principally because of AlN's high thermal conductivity and close thermal expansion match to silicon. AlN is expected to play a key role in the next generation of high powder electronic packages, in applications ranging from high power discrete component substrates to co-fired, multilayer packages for integrated circuits. In the following paper, a detailed picture of the oxygen-related defect in AlN ceramics is presented. This impurity is of critical technological importance, because vacancies associated with oxygen severely limit thermal conduction when present in high concentrations. The results of thermal conductivity measurements, luminescence studies, optical absorption experiments, photo-induced absorption studies and electrical measurements on both ceramic and single crystal samples will be presented in order to understand the detailed nature of this defect and to model its control over a number of important technological properties.

In order to lower the firing temperature of W cofired AlN multilayer substrates, sinterabilities of AlN substrate material and W conductor were investigated at low sintering temperatures around 1650 •C.

In case of AIN substrate material, the effect of AIN powder properties on sinterability and thermal conductivity was evaluated. The powders, with specific surface area between 2.3 and 8.2m2• g−1 and oxygen content between 0.7 and 3.2 wt%, were sintered with CaO and Y2O3 as sintering additives. The finer powder promoted the densification below 1600°C and each powder was fully densified at 1650°C. However thermal conductivity sintered at 1650°C decreased with decreasing particle size due to increasing oxygen content inside AlN grains. The thermal conductivity of optimized AlN substrate sintered at 1650°C had over 100W • m−1 K−1.

W conductor is required dense microstructure for high adhesion strength to AlN substrate. Shrinkage mismatch between AlN and W during sintering caused porous microstructure for coarse W powders or detaching for fine W powders. The optimized W paste was developed for low temperature sintering.

Powder metallurgical fabrication of Cu/Mo composites containing 33–73 wt.% Mo was carried out by using either Cu coated Mo powder or a mixture of Cu and Mo powders. The former yielded Cu/Mo composites of greater density, hardness, compressive yield strength and abrasive wear resistance, and lower electrical resistivity and coefficient of thermal expansion than the latter. This is attributed partly to the lower porosity of the former composites and partly to the separation of the adjacent Mo particles in the former composites and the partial linkage of the adjacent Mo particles in the latter composites.

Multichip Modules (MCMs) have recently received widespread attention in the electronics industry. Owing to its high thermal conductivity, CVD diamond holds great promise for solving thermal management problems in MCMs. Also, large diameter free standing diamond substrates have recently become available. It is thus necessary to develop a reliable metallization for diamond substrates. As Au does not adhere to diamond, refractory metals, viz., Ti, W and Mo have been used as glue layers, as they form carbides above 800 °C. Since CVD diamond looses its properties at these temperatures, there is a need to obtain adherent metallizations at much lower temperatures. In the work reported here, tenaciously adherent Au/Ti and Au/Ni80-Cr20 metallization systems were sputter deposited on CVD diamond substrates for potential use as interconnects in MCMs. The adhesion values obtained by Sebastian V stud pull tester were in the range of 12 Kpsi, with post-deposition anneal temperature as low as 150 °C. The key to good adhesion was preconditioning of the diamond surface using in-situ sputter-etch technique. The effect of post-deposition annealing (up to 450 °C) on the interdiffusion of Au with the underlying metals was studied using AES, EDX, Optical Microscopy and sheet resistance measurements. Results indicate mixing of C from diamond with refractory metals at low temperatures which may be contributing to strong adhesion.

We report here on the Mbssbauer parameters of two intermetallic phases expected to be present in composite solders: the Cu9Sn3Ni phase present in some forms of eutectic Sn-Pb solders and the Ag-Sn (ζ) phase which may be present in lead-free solders containing appreciable amounts of silver. Both samples were prepared by mechanical alloying techniques.

Our results show that the isomer shift of the Ag-Sn ζ phase is + 2.13 mm/sec relative to SnO2 and the phase has a room-temperature recoilless fraction that is 36% of that of SnO2. The results for Cu9 Sn3Ni are an isomer shift of + 1.78 mm/sec and a recoilless fraction 58 % of that of SnO2.

Aluminum-matrix composites containing AIN or SiC particles were fabricated by vacuum infiltration of liquid aluminum into a porous particulate preform under an argon pressure of up to 41 MPa. Al/AIN was superior to Al/SiC in thermal conductivity. At 59 vol.% AIN, Al/AlN had a thermal conductivity of 157 W/m. °C and a thermal expansion coefficient of 9.8 × 10−-6°C−1 (35–100 °C). Al/AlN had similar tensile strength and higher ductility compared to Al/SiC of a similar reinforcement volume fraction at room temperature, but exhibited higher tensile strength and higher ductility at 300–400°C. The ductility of Al/AlN increased with increasing temperature from 22 to 400°C, while that of Al/SiC did not change with temperature. The superior high temperature resistance of Al/AlN is attributed to the lack of a reaction between Al and AIN, in contrast to the reaction between Al and SiC in AI/SiC.

Aluminum nitride has been ablated with a KrF excimer laser (248 nm) at fluences from 1 to 60 J/cm2. Ablation depth, emission spectra and photothermal beam deflection were detected as a function of fluence. An ablation rate of 0.2 μm/pulse was achieved above 30 J/cm2 in vacuum. Ablation rate decreased with decreasing, fluence. Irradiated surfaces have a conductive metallic layer of reduced aluminum nitride. At low fluences, the metallic surface layer was spotty within the area of the laser beam. Below the fluence threshold for producing the metallized surface, emission spectra and photothermal beam deflection were still detected. Emission lines from Al, Al+ and Al-N were observed. Photothermal deflection data was used to calculate supersonic velocities for shock waves propagating from the sample surface. Shock waves resulted from rapid heating near the surface and expansion of ablated material from the laser spot.

Total joint replacements such as the hip and knee result in composite structures. Proper design of these devices and selection of particular devices requires understanding of the structural response of the resulting composite structure of plastic, metal, interface, and human bone. The problem is challenging because of complex geometry, non-homogeneous material properties (dense cortical bone and spongy cancellous bone), and time varying material properties (bone remodeling). Bone is a active material which responds over time to applied load, changing the density and Young's modulus.

This paper addresses several computational issues. Remote sensed data such as computerized tomography scans are used to create finite element models. Nonhomogeneous material properties are represented in finite element models using shape functions. This results in a unique material property for each Gauss point. Finally, stochastic finite elements methods are used to model material variation and uncertainty. Both Monte Carlo and First Order Second Moment methods are used. These problems are particularly well suited for high-level parallelization schemes on multiple instruction multiple data machines.

Density functional theory provides a first-principles approach for computing the geometric and electronic structures, and a wealth of corresponding properties, of a wide range of materials types and compositions, including bulk solids, surfaces, defects and clusters of molecules. Parallel advances in hardware performance, implementation strategies and algorithms have all contributed to a rapid growth in the number of important applications. Recent developments under each of these themes are outlined and the breadth of current applications is illustrated by typical examples. Issues associated with the implementation and performance of density functional methods on parallel computer architectures are discussed.

Microelectronic packages undergo substantial thermal excursions during processing and often in service. Differences in the thermal expansion of the various components may therefore lead to fatigue of the interconnects. A computer simulation has been developed which is based on a damage integral approach for the modeling of damage and failure in the various bonding layers found throughout such a package. This code should apply equally well to solder die bonds and polymeric or epoxy adhesive layers, assuming that the corresponding crack growth parameters and constitutive relations are known. Using literature values for these properties, predictions have been compared to experimental thermal cycling data for solder die bonds. Consequences for the extrapolation of accelerated test results to service conditions are discussed.

Electrical components place high demands on the properties and performance of materials. Potential service environments have both broad temperature ranges and widely varying stress states. Polyimides are a class of polymers that possess the necessary performance characteristics for electronic applications. LARC-CPI, a novel semicrystalline thermoplastic polyimide developed by the NASA Langley Research Center [1], combines the excellent properties of polyimides with an ability to crystallize. This enhances mechanical performance and chemical resistance and imparts the processing benefits associated with thermoplastic materials. The high Modulus of Elasticity (2.5 to 3.6±0.2 GPa [2]), glass transition temperature (Tg = 222 °C [3]) and melting temperature (Tm = 350 °C [3]) combined with a relatively low dielectric constant (ε = 3.2 [4]) of LARC-CPI appear to meet the criteria for a wide range of electronic materials applications. Since many of the properties are attributed to the crystalline region and its orientation, thorough characterization of any ordered structures present in LARC-CPI is essential. The chemical repeat unit for LARC-CPI and a model repeat unit can be seen in Figure 1.

A novel series of BPDA/PDA/6FDAm polyimide copolymers have been developed. These materials are more flexible, soluble, and more optically transparent than the homopolymer BPDA/PDA. A negative acting PSPI has been developed based on one of these copolymers. This PSPI exhibits high resolution. 6 μm lines can be delineated in a 19 μm thick film. In addition, the PSPI exhibits high performance mechanical/physical properties such as a low CTE, low stress, and high elongation at break.

Negative working photodefinable benzocyclobutene formulations capable of obtaining patterned dielectric films from 1 to 20 microns thick are being developed using bisaryl azides as photocrosslinkers. Three different formulations are used to cover this range of film thicknesses. The formulations are very sensitive to the 365 nm and 405 nm wavelengths of light (i-line and h-line) of the high pressure mercury spectrum and require low exposure doses to produce resolved patterns. Twenty five micron round and square vias with sloping sidewalls (geometry good for metallization) have been successfully patterned in 10 micron thick films. The photodefined patterns can be obtained with good film retention using several developing solvents including: Stoddard solvent, ProglydeTM DMM, and n-butyl butyrate.

A means of generating high temperature polymer foams which leads to pore size in the nanometer regime has been developed. Nanofoams were prepared by casting block copolymers comprised of a thermally stable block and a thermally labile material, where the thermally stable material forms the matrix in which thermally labile material is dispersed. Triblock copolymers comprised of high Tg, amorphous polyimide matrices with poly(propylene oxide), as the thermally decomposable coblock, were prepared. The copolymer synthesis was carried out through either the poly(amic alkyl ester) or poly(amic acid) precursor and subsequent cyclodehydration to the polyimide by either thermal or chemical means, respectively. Microphase separated morphologies were observed for all copolymers, irrespective of the block lengths surveyed, by dynamic mechanical analysis. Upon heating, the poly(propylene oxide) underwent thermolysis leaving pores where the size and shape of the pores were dictated by the initial copolymer morphology. A 5 to 15% reduction in density was observed consistent with the generation of a foam.

The effect of the heating rate during curing on the thermal expansivity and mechanical properties of poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA) polyimide thin films has been investigated in the range from 3 to 40 μm, which is commonly used for packaging application. Structural characterization was carried out using birefringence and wide-angle x-ray diffraction (WAXD) techniques. The morphology and packing order are found to be strongly influenced by the heating rate and, to a lesser extent, by the film thickness. The themomechanical properties of the polyimide films show an overall variation consistent with the changes in the molecular packing, thus demonstrating a close structure-property correlation. For slow-cure films, the variation of the molecular order is almost independent of film thickness. In contrast, the molecular order for the fast-cured films strongly depends on the thickness. The in-plane chain orientation decreases, but crystallinity increases with increasing film thickness. The heating rate gives rise to an opposite effect on the morphology for thin (∼ 5 μm) and thick films (∼ 38 μm). For thin films, high heating rate yields a high degree of crystallinity and in-plane chain orientation of the polymeric chains, leading to low thermal expansion coefficient (TEC) and high mechanical strength. In contrast, high heating rate for the thicker film gives a low in-plane chain orientation, leading to high TEC and low mechanical strength. The close correlation between morphology and the thermomechanical properties such as Young's modulus, stress-strain relationship, and lateral TEC is demonstrated.

A variety of low dielectric constant composites have been made into films and characterized. These composites were blends of liquid crystalline polymers (LCPs), hollow glass spheres (HGS) and polytetrafluoroethylene (PTFE). By adjusting the percentage compositions of the various components of the composites, the dielectric constant could be adjusted in the range 2.4 to 3.4. Measurement of the dielectric constant by Time Domain Reflectometry (TDR) and Frequency Domain Reflectometry (FDR) are discussed. Dielectric anisotropy is also discussed. The experimentally observed results are compared with those derived theoretically.

To lower the cost of multichip module packaging, hybridized substrate technologies have recently been reported which blend the desirable aspects of D and L fabrication (MCM-D/L). High performance dielectrics such as Cyclotene™3022 and photosensitive BCB have been shown to be compatible with laminate substrates used in MCM-DIL, however the cure levels of the dielectric on the laminates must be known for optimum processing.

In this paper, the capability of attenuated reflection IR microscopy (micro-ATR-IR) to probe thin films of BCB polymers is demonstrated. This technique enables the polymer layer to be probed regardless of the characteristics of the substrate. Cure levels of both Cyclotene™ 3022 and photodefinable BCB polymer films are obtained with micro-ATR-IR on both silicon and laminate substrate. Micro-ATR-IR is also used to probe a rapid thermal cure of Cyclotene Tm 3022 and photodefinable BCB layers on copper-clad polyimide laminate; these measurements cannot be made with transmission IR due to the high reflectivity of the substrate.

Control of the refractive index in low dielectric constant polyimides through modification of chemistry and structure was investigated. The optical refractive indices of several low dielectric constant polyimides were measured, and the effects of orientation on optical anisotropy were determined. Refractive index in these polyimides was found to decrease with increasing fluorine content due primarily to the low electronic polarizability of the fluorine-carbon bonds. In zone drawn polyimides, refractive index was found to increase substantially in the direction of the draw, but decrease substantially normal to the draw direction. This was explained in terms of the preferential alignment of the polymer chains.

Polymers have found wide usage in microelectronics industry. Their moisture absorption properties cause the concern of reliability without hermeticity (RwoH). For printed circuit packages, the lamination process, the components assembly, and the field performance of final product are strongly influenced by the presence of high level moisture content. For instance, moisture is an important factor in the development of internal shorts through metal migration when printed circuit package is in service. Moisture can also cause dimensional changes in printed circuit cores and delamination during the soldering processes in components assembly, resulting in manufacturing yield loss and defects. Understanding moisture properties of resins and the resin glass composites are therefore important in developing a strategy to control the moisture content of final products. This paper will discuss the moisture fundamental properties of two resins and their resin glass systems. These properties will be related to their assembly and reliability performance.