The rapidly advancing technology which has brought us higher integration and higher speed LSIs has also necessitated the continuous improvement of ceramic packages.

New monolithic multicomponents ceramic (MMC) substrates were made using a glass-ceramic material, low firing high dielectric constant ceramic material, metal oxide resistance materials, piezoelectric ceramic material and metal conductors. In the MMC substrate, many passive components, such as capacitors, resistors and wiring conductors can be included. In addition, designed-space can be formed in the substrate with new designed-space forming technology.

The new MMC substrates have the following excellent characteristics.

1. 1) A wide range of capacitors can be formed in the substrate.(10pF˜3μF).

2. 2) A wide range of resistors can be formed in the substrate.(10Ω/π∼1MΩ/π).

3. 3) A plurality of resistor and capacitor elements can be three-dimensionally constructed in the substrate.

4. 4) Designed-space can be formed in the substrate.

5. 5) Miniaturization and cost reduction can be accomplished in the substrate.

The MMC substrates were applied to voltage controlled crystal oscillators (VCXO), CR active filters, memory cards for personal computers, AC thin film electroluminescent (AC TFEL) devices and drop-on demand ink jet heads.

These devices using MMC substrate showed good electrical propeties and achieved miniaturization, multifunction and cost reduction. The new monolithic multicomponent ceramic substrate can be applied to many kinds of hybrid microcircuits and electronic components and devices.

A novel approach for preparing porous SiO2 thin films by sputter deposi-tion is being developed. The porosity is introduced to reduce the dielectric permittivity of the film to less than 3 for potential use in packaging high speed VLSIs. In the first approach, amorphous silicon is initially deposited to produce a columnar structure with a thickness of 25μm, followed by etching and thermal oxidation to result in closely spaced SiO2 pillars. Capping the structure by a thin film (0.1μm), silica gel layer provides the support for strip line traces. In the second approach, porous SiO2 films are prepared by reactive sputtering. The dielectric properties of the sputter deposited SiO2 films are presented.

Fugitive ink and tape technology permit the inclusion of flat voids at predetermined locations in ceramic microcircuit substrates. Calculations show that critical stray capacitances can be reduced by as much as 65% and the propagation delay of microstrip transmission lines by 30% and more. The selectivity of the void location permits the retention of the full thermal conductance of the substrate under heat dissipating elements.

Use of dielectric films is integral to most microelectronic packaging, as passive components for device insulation (interlayer dielectric, passivation, diffusion layer), as thin layer capacitive structures or as insulating coatings for thin film and thick film hybrid circuits. Depending on deposition technique, film composition may include SiO2, Al2O3, Si3N4, modified silicate or phosphate glasses as insulators. Compositions as well as methodologies for film preparation on Si, glass or metal substrate by spin coating (or spraying) are discussed, including film/substrate interface characteristics and properties related to dielectric film coatings.

A metallo-organic decomposition (MOD) film is one formed by thermal decomposition of a solution containing one or more metallo-organic compounds that were deposited onto a substrate. This process yields metal, glasses, or polycrystalline ceramic films directly without passing through the powder stage. Conductor films studied include a screen printable gold and a screen printable and ink jet printable silver. Dielectric films studied include a low K lead borosilicate glass and a variety of ferroelectric compositions.

To accomplish the interconnect systems which will be required in the next generation of very high speed Ga:As digital ICs, it will be necessary to use strip line techniques for signal traces which must be deposited over very low permittivity dielectric substration. Materials with relative dielectric permittivities k 〈 3.0 and very low loss tangent up to microwave frequencies will be required. For ceramic systems such values are impossible to achieve in single phase monoliths, and composite approaches are required. Techniques for processing ceramic insulators which permit the introduction of controlled pore structures are discussed. The introduction of pores degrades some other desirable properties of the ceramic such as mechanical strength and thermal conductivity so that control of both scale and location of pores is desirable.

Materials investigated include sol-gel processed silica films and monoliths, reactively sputtered silica, etched glass compositions and Macro-Defect-Free (MDF) cements.

For multilayers capacitors, submicron BaTiO3 powders are synthetised by chemical routes including gels. Three routes are described, oxalate precipitation, alkoxide gels and carboxyalkoxide polymerisations. Powders characteristics, relations between grain sizes, agglomerates, sintering capabilities and dielectric properties are discussed

Multilayer capacitors were made from Pb(Mg1/3Nb2/3)O3 compositon by an usual technique: ceramic green sheets formed by slip casting method, printed with an 70% wt Ag- 30% wt Pd internal electrode and sintered at temperature ranging from 950 to 11OO°C. Chip capacitors exhibit large capacitance and temperature characteristics meet Z5U specification. Electrical properties of MLC based on PMN depend on specific parameters such as the average concentration of pyrochlore phase and perovskite phase, and the homogeneity degree of dielectric layers. Load humidity life tests show a degradation of some chips which can be connected with the formation of a surface layer rich in pyrochlore phase.

This study involved the determination of the effects of composition and microstructure on the fracture toughness and susceptibility to environmentally enhanced crack growth of several ceramic materials used in multilayer capacitors. Indentation-fracture procedures were used to measure KIC as well as to assess the possible effects of internal stresses on the fracture behavior of these materials and to correlate dielectric aging phenomena with strength. The environmentally enhanced crack growth behavior of these materials was determined by conducting dynamic fatigue tests in water.

Multilayer ceramic/metal modules are subject to stresses that develop both upon co-sintering and upon cooling. The sources and magnitudes of these stresses are described and discussed. The co-sintering induced stresses derive from densification-rate mismatch and can be analyzed in terms of constitutive laws that describe the densification and creep of partially dense ceramic and metal bodies. Cooling induced stresses are associated with thermal contraction mismatch and are strongly influenced by the plastic flow laws for porous metals. Typical stresses produced during co-sintering and cooling are calculated and techniques for minimizing such stresses are discussed and analyzed. Mechanical damage, manifest as brittle cracks and creep cracks, are also described and analyzed. Critical values of material parameters that exclude extensive crack damage are then emphasized, based on models of crack propagation.

Dynamic fatigue experiments were performed on Z5U multilayer capacitors in an attempt to correlate microflaw fracture behavior due to intrinsic processing defects within the material with predictions of fracture behavior based on macrocrack fracture mechanics determinations. A direct correlation between microflaw fracture behavior and predictions based upon macrocrack fracture mechanics techniques was not observable due to the wide size range of processing defects. A systematic post-mortem examination of fracture surfaces was used to identify fracture origins and sort individual test specimens into groups with equivalent flaw sizes. The correlation between microflaw and macrocrack fracture behavior became more “sorting” the dynamic fatigue data into groups withm oereq uoibvvailoeunst aflfatwer sizes.

Failure of ceramic-metal interfaces induced by residual or applied stress is often brittle in nature although plastic strain in one or more bonding layers may add to the fracture energy for decohesion. Thus, the fracture toughness depends on chemical bonding across the interface, the plasticity and flow stress of the metal as well as other factors, arising from local internal stresses and the microstructure of the ceramic-metal couple, that cause crack tip branching, deflection, bridging, blunting or shielding. Electron microscopy and DCB testing of metal-glass systems provide insights into the relative importance of factors that determine the decohesion resistance.

Results from indentation load relaxation (ILR) tests on thin film-substrate systems are reported. In the case of a 1 pum aluminum film on silicon, the data can be interpreted as reflecting both the properties of the film and the interface between film and substrate. Data from a 37μm TiN film on 304 SS are believed to reflect the combined behavior of the film and substrate.

The magnitude and the distribution of stresses in elongated adhesively bonded bi-material assemblies subjected to uniform heating or cooling are determined and discussed. The suggested approach enables one to evaluate the stresses in the assembly components themselves, as well as the shearing and normal (peeling) stresses in the interface, with consideration of the attachment compliance. The case of an epoxy bonded assembly is used to illustrate the developed theory.

The present paper reports the results of an investigation of the adhesion characteristics of PIQ13, an isoindaloquin-azolinedione-modified polyimide, to silicon wafers. The wafers were used both untreated and pretreated with a layer of CVD SiO2. Also investigated was the adhesion behavior of a condensation-type polyimide, P15878. A comparison is made between the behavior of the PIQ with two different coupling agents, an aluminum chelate (Coupler 3) and γ-aminopropyltriethoxy silane (A-1100). Superior adhesion performance of the A-1100 is indicated; and with A-1100, the adhesion of the two resins is similar.

As the popularity of copper metallizations grows in ceramic-based electronic applications, an understanding of copper-ceramic interactions during firing assumes greater technological importance. Copper metallizations often interact with thick film microcircuit dielectrics during the firing of multilayer interconnects to yield rosy discoloration, or so-called blushing or staining of this insulating ceramic. In the conventional filled-glass dielectrics studied here, blushing is concentrated at special interfaces over Cu conductors where submicron Cu precipitates are localized. Several firing strategies which improve binder burnout can be employed using standard belt furnaces to depress, if not prevent, this precipitation. A multistage blushing mechanism is proposed that is dominated by the reduction of Cu ions in the ceramic by carbonaceous products formed when firing dielectric compositions under non-oxidizing conditions. Dielectric glass composition also plays an important role with respect to solid state Cu ion interdiffusion. Theoretical and experimental analyses show that materials interactions responsible for blushing in conventionally-processed CMS (copper multilayer system) microcircuits degrade neither dielectric performance nor reliability. Microcircuit dielectrics metallized by Cu compare favorably to noble metal systems including gold, an accepted military standard. CMS dielectrics exhibit high activation barriers for ionic conductivity, and an absence of shorting due to solid state diffusion during high temperature/ high bias testing.

Woven fabric composites have been used extensively as substrate materials for multilayer printed circuit boards. This paper presents a brief overview of the recent accomplishments in the modeling and characterization of woven fabric composites. Three analytical models have been developed to predict the thermo-mechanical properties of fabric composites with various weaving geometries. A three-dimensional finite element analysis has also been adopted to determine the properties of plain-weave fabric composites.

Parametric studies are performed for both hybrid and non-hybrid woven fabric composites to generate data for materials selection and design. These data are presented in the form of “structure-performance maps” where the unique characteristics and relative effectiveness of various woven fabric composites can be easily assessed. The potential of tailoring a low thermal expansion coefficient substrate material through suitable materials selection, geometrical design, and fiber hybridization is also discussed.

Consecutive load relaxation tests are performed on a 95 Pb-5 Sn specimen near room temperature, then at 69 ° C and 1°C. The initial relaxation runs at room temperature show evidence of static recovery, which diminishes after a number of load relaxations have been performed. Evidence of grain boundary sliding is also found. The specimen hardens slowly at 69°C, as manifested by successive load relaxation data falling at lower strain rates. At 1°C, the material slowly softens. These temperature effects are believed to result from a dislocation-solute interaction involving tin atoms in the lead matrix.

The microstructure and mechanical properties of Pb-Sn solder joining Cu plates were studied. Yticrostructural observations were made on both the bulk Pb-Sn solder and on the interface between the solder and Cu plates. Pb-Sn solder has a two-phase microstructure in which the Pb-rich phase is the weaker. β-Sn precipitates in the Pb-rich phase were characterized in TEM. Intermetallic phases (Cu6 Sn5 and Cu3Sn) that form during the reaction of molten Pb-Sn solder with Cu were investigated. Solder joints were tested to fracture in both shear and tensile configurations. The mechanical properties and fracture surface characteristics are reported.