An analysis of bulk and interfacial damage of film/substrate systems consisting of copper or chromium films deposited on a single polymer substrate, is presented here. For these systems (metal/single polymer substrate) the failure analysis is based on the experimental results obtained from deformation experiments performed in a scanning electron microscope. Critical parameters deduced from the experiments, and microstructural observations allow us to discuss the mechanical behaviour of these systems, and their interfacial adhesion properties.

Low TCE polyimides, typically BPDA-PDA and related materials are well known for their special properties which include low in-plane TCE, up to 3X higher elastic modulus and ultimate tensile strength, and lower moisture uptake relative to the commonly known flexible chain polyimides [1]. These differences are due to the rod-like orientation and highly organized molecular structure of the polyimides that are derived from linear-planar precursors resulting in more anisotropic properties such as the X-Y vs Z-direction TCE [2], and optical as well as dielectric properties.

In the present study, we have measured the WAXD patterns of polyimide films formed from BPDA-PDA and BTDA-PDA polyamic acid mixtures and BPDA-BTDA-PDA random copolyamic acids. In order to examine the effect of a highly flexible chain segment on the molecular anisotropy of rod-like polyimides, preliminary WAXD patterns were recorded for films of BPDA-BDAF and a BPDA-PDA-BDAF copolyimide.

An in-plane and an out-of-plane crystallinity index, measures of molecular order within the polyimide films studied were estimated from the WAXD patterns. The data are correlated with the various blends and copolymer compositions and discussed in terms of structural implications.

High speed, high density packaging requirements have made multichip modules (MCM) one of the most active areas of research in the electronic industry.

High density printed wiring board (PWB) have low production cost and good electrical performance. However, the most questioned issue in application is the reliability. As a result, a thermal and mechanical analysis on a MCM has been conducted to understand its feasibility. The results indicate that with proper design, the components can operate under satisfactory conditions on PWB laminates.

The chemistry that occurs at buried interfaces often determines the performance and reliability of multi-chip modules (MCM's). For example, chemical reactions between sputter deposited metals and polymers may ultimately determine the interlayer adhesion of multilevel metallizations for MCM's. Both destructive and non-destructive probes can used to study these interfaces, and the interfaces may be studied as they are formed or as they age. Complicating the interpretation of any of the results of these techniques is the inherent complexity of the chemistry and, often, the non-planarity of the interface. Several examples of complex interfaces will be described along with strategies for elucidating the chemistry and their reliability.

Durability of metal/polyimide (PI) interfaces is essential for the long term reliability of advanced microelectronics packages. In earlier work, we showed that water absorbed by the PI can affect durability because, at high temperatures, it migrates to the interface and oxidizes the metal. In this study, we have investigated water transport through PMDA-ODA and BPDA-PDA polyimides as a function of ion beam treatment. Thermal desorption mass spectrometry (TDS) and gravimetric water uptake measurements were correlated with XPS spectra obtained from modified films. Transport through films with unmodified surfaces is rapid as shown by water uptake, however uptake is slowed considerably by surface modification. Additionally, only modified films exhibit peaks in TDS spectra–the peak temperature and intensity scale with dose. High resolution XPS spectra taken after modification suggest a graphitic-like surface region independent of dose. However, the extent of this “damaged” region scales with the dose. From the TDS spectra, we determine that the activation energy for water diffusion through this layer is 12–15 kcal/mol.

Differences in thermal expansion coefficients between the dielectric layers, the substrate, the metallizations, and the circuit chips generate complex residual stress fields within multichip module (MCM) packages. For example, encapsulated interconnect lines in a typical MCM are under triaxial stress. Quantifying the triaxial stress is needed to understand critical issues such as stress relaxation, stress-induced voiding, as well as providing benchmarks for finite element calculations. Employing a novel sample design, triaxial residual stresses have been determined in thin aluminum lines encapsulated in benzocyclobutene dielectric layers by x-ray diffraction techniques. Significant differences are observed in the stresses if the lines are deposited on the Si substrate or on intervening polymer layers. The stress level is constant with intervening polymer layer thickness. The results suggest a fundamental difference between the strain transfer across the silicon oxide-aluminum interface relative to the silicon oxide-polymer interface.

The difference in coefficient of thermal expansion (CTE) between substrate, polymer, and metal leads to complicated stress fields in multilevel interconnect structures that can potentially compromise reliability. This study uses a materials set representative of the General Electric High Density Interconnect (HDI) multichip module technology to monitor the stress level in the thin film layers of metal and polymer. A Kapton HN® film is bonded to a substrate with heat and pressure using a thin layer of Ultem 1000® thermoplastic as an adhesive. Mechanical test structures consist of single or multilayer thin films fabricated on oxidized silicon or alumina substrates. Layers consist of Ultem, Ultem/Kapton, metal (Ti/Cu/Ti), and Ultem/Kapton/metal. The composite stress due to fabrication and thermal cycling between ambient and 275°C is determined by substrate deflection. The initial stress in the polymer materials is due to the thermal excursion during fabrication. Initial metal stress is intrinsic but becomes extrinsic upon thermal cycling. The composite stress in multilayer structures shows a contribution from each individual layer. The relatively low processing temperature minimizes the magnitude of the stress.

The effects of accelerated fatigue tests on the crack formation in 95.5%Pb-2%Sn-2.5%Ag and 95%Pb-5%Sn solder joints have been investigated. The fracture surfaces which form upon mechanical stress have been studied by SIMS and XRD techniques. They are always located in the solder layer and show grain growth of the Pb-rich α phase present in the phase diagram of the Pb-Sn and the Pb-Sn-Ag systems. Grain growth is accompanied by tin depletion. XRD patterns of samples after 1, 40, 80 fatigue cycles show no variations of lattice parameters of the phases present in the alloy thus ruling-out the formation of new phases under mechanical stress.

X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) have been used to characterize the polyimide film based on 4,4′ hexafluoro-isopropylidene -bis pthalic anhydride (HFDA) and 4,4′ -bis (4-aminophenoxy) biphenyl (APBP). Films of varying thicknesses made from diluted precursors were studied by IR and XPS. An elemental analysis and a tentative peak assignment for C 1s in XPS is presented. The HFDA-APBP thick films are stoichiometric in composition and binding energies are in good agreement with data on hexafluorodianhydride-oxydianiline (HFDA-ODA). For thinner films, certain chemical modifications were observed at high cure temperatures.

With the advent of new in-line assembly techniques and equipment such as high temperature wirebonders, equipped with rapid cure stations, came the need to develop a suitable, adhesive with high performance characteristics. Typical traditional die attach adhesives were found to be inadequate.

The higher performance characteristics were determined by assembly characterization studies. A new type of rapid cure thermoset dieattach adhesive was then developed to fill the need of these more rigorous assembly requirements.

Early testing showed the new material to possess the desired attributes, such as < 1% wt loss during cure, thermal stability well above 300°C, low ionic species and excellent adhesion strength after cure. In addition, the material is suitable for syringe dispensing at high speeds.

In this paper, we will review the process performance goals, the material evaluation strategy, the various types of screening tests performed on all samples, and some of the findings from the assembly characterization studys. We will conclude with the reliability test results, comparing this new material with four other die attach adhesive samples. Emphasis is given to the overall success of using this evaluation strategy and to the reliable results of this new adhesive used in plastic Dual-in-line packages.

Polysiloxanes are routinely used in the semiconductor industry as die encapsulants. Thermal analysis, NMR, ion chromatography, and dielectric spectroscopy was used to characterize these polymers. The dielectric loss spectrum was found to be directly related to the long term electrical stability of the encapsulated die, and was also found to be a more sensitive technique for determining the concentration of electronically active impurities than GC/MS, and ion chromatography. Dielectric spectroscopy was also used to study the diffusion of acids, and water, through these polymers. While the solubility of acids and water in these materials is low, their diffusion constants are high, on the order of 10−4 cm2/s. In addition, the interaction of the encapsulant with the silicon nitride passivation used on the die surface was found to have an effect on the long term stability of the device. This is believed to be due to the formation of a conductive layer at the silicon nitride/polymer interface which ultimately forms a leakage path between the bond pads, or into the silicon nitride passivation layer.

The performance and reliability of personal computers, workstations and other electronic products depend on the effective soldering of electronic components to printed wiring oards (PWBs). The copper surfaces of PWBs are frequently treated with benzotriazole (or similar organic complexes) to preserve solderability by preventing copper oxide formation. However, new assembly process techniques and more complex processes may degrade protective organo-copper surface complexes and allow copper oxidation to occur, thus inhibiting subsequent solder operations. This study uses Auger electron spectroscopy (AES) in conjunction with meniscograph wettability results to determine the effects of processing conditions on the solderability of PWB surfaces. Effects are characterized for aging up to 19 months; Infrared (IR) reflow in air and nitrogen; cleaning; and temperature cycles associated with adhesive or encapsulant cure. Surface compositions, oxide thicknesses, and solderability measurements are correlated to the above process steps. For example, IR reflow in air increases oxide thickness from ∼10 Å to ∼150Å (relative to sputtering rates in Ta2O5 with an attendant increase in the meniscograph time-to-neutral-buoyancy from <2 seconds to >10 seconds, relative to unprocessed PWBs. Such fundamental information serves as an invaluable complement to standard phenomenological observations of defective solder joints, and can aid in guiding processing decisions for improved yield and reliability.

This is an introduction to Sony's pocket-sized computer “The palmtop”, an example of surface mounting technology applied to a consumer product.

Au-In eutectic bonding method which needs only a low process temperature (˜200°C) but produces high temperature (450°C) bonds is reported. In this study, multiple layers of Au and In are deposited directly on semiconductor wafers in one vacuum cycle to prevent indium oxidation and then bonded to substrates coated with Au. At 200°C the indium layer melts and dissolves the gold layers to form a mixture of liquid and solid. The diffusion process continues until the bond solidifies. Upon solidification, the bond has a melting temperature of 456.5°C. Scanning Acoustic Microscope was used to determine the excellent bonding quality before and after thermal shock tests and SEM with EDX capability is employed to determine the composition of the resulting bonds.

Thin film reactions and its influence on mechanical stress have been investigated in Cr/Cu/Sn and Cr/Ni/Sn multilayer structures. Thin film stresses of different intermetallic compounds in each material system were evaluated using substrate bending technique. Stress state in the thin film structures was round directly related to formation kinetics and thermal properties of intermetallics. In Cu-Sn system, a large internal stress increase in tension was generally observed after being heat treated at high temperatures. In Ni-Sn systems, formation of intermetallics is a relatively slow reaction at elevated temperatures as compared to that of Cu-Sn samples. Contrary to that of Cu-Sn system, formation of Ni-Sn intermetallics causes a decrease in stress in the thin film structure. The correlation of thin film stress state and the structure evolution at the interface is studied and discussed in details.

The potential, feasibility, and time scale of optical interconnect and interfaces are examined for electronic computer applications. Link, bus and random interconnect topologies are included. Recent developments in optical source and detector devices, optical waveguides and optical fiber characteristics are reviewed. Then optical coupling, alignment, interfacing and overall compatibility issues are explored. From this understanding the requirements for the packaging of optical interconnect are derived. Finally key research and development needs are defined.

The need for higher bandwidth interconnect schemes to relieve the communications bottleneck caused by the ever increasing speeds of discreet electronic devices has led to a renewed interest in thin film optical waveguides as interconnect media. This paper reviews some of the polymeric materials that have been investigated for use as thin film passive optical waveguides over the past ten years. Several proposed applications for these waveguides are presented and the specific material requirements of these applications are discussed. The strengths and weaknesses of specific polymeric materials are considered in view of these requirements. While reference is made to a variety of polymers that have been considered for these applications, emphasis is placed on the relative merits of polyimide and acrylate polymer based systems.

We have evaluated the use of either poly(phenylene) prepared via spin-coatable polymeric precursors or fluorinated polysilynes for optical waveguides. Poly(phenylene) precursors were converted into poly(phenylene) by either curing at 300 °C or by deep-UV exposure in the presence of a photoacid generator. The poly(phenylene)s have a number of desirable properties for optical waveguide applications including good near IR transmission, low dielectric constant, thermal and environmental stability and ease of pattern fabrication using microlithographic techniques. Copolysilynes were spin-coated onto various types of substrates and then exposed by deep-UV radiation. Upon exposure of deep UV irradiation in the presence of air, they undergo photooxidative crosslinking to give insoluble glass-like materials. This photo-oxidation process is accompanied by a large decrease in refractive index from n=1.61 to n= 1.485. The photooxidation results suggest that their potential applications are as photoresists and optical waveguides.

New inorganic-organic copolymers (ORMOCERs – ORganically MOdified CERamics) were developed as protective coatings for electronic and optical devices, as patternable insulation and passivation layers for electronics, e. g. MCM's, and as possible interconnects and waveguides for micro optics.

Depending on the chemical composition and the processing parameters, their important features are low permittivity constants (eR ≤ 3.2), high bulk resistance (RD > 1016 Ωcm), high dielectric strength (ED ≤ 400 V/μm), refractive index around 1.48, optical transparency in the range of 400 – 1300 nm, and good adhesion to numerous substrates, such as Al2O3, glass, silicon, copper, aluminum, steel, polyimides, polyesters and epoxides.

The materials can be applied using standard technology. They are patterned by laser direct writing, photolithographic, screen printing or embossing technologies.

Electro-optic (EO)polymers, processed into thin multilayer films, exhibit large nonresonant EO coefficients and low dielectric constants from DC to multi-GHz frequencies. Orientation of the constituent nonlinear optical chromophores, usually accomplished by electricfield poling, provides an EO coefficient suitable for modulation of light beams propagating in the plane of the polymer film. Thus, EO polymers are ideally suited for applications in integrated optics.

The field EO polymer integrated optics has been developing rapidly during the past several years. Recent advances include the formulation of poled crosslinked epoxies and guest-host polyimides exhibiting thermal stability at temperatures significantly higher than those previously achieved with thermoplastic acrylate chemistry. These developments are an essential first step toward achieving practical materials exhibiting stability to manufacture, assembly, and end-use in modem electronic systems applications. This paper provides an introduction to EO polymer waveguide devices for applications to electronic packaging and interconnection.