Search

Low-temperature (170°C) Cu/In wafer-level and chip-level bonding for good thermal budget has been successfully developed for 3-D integration applications. For the well-bonded interconnect, Cu2In and Cu7In3 phases with high melting temperature of 388.3°C and 632.2°C can be formed, indicating high thermal stability. In addition, stable low specific contact resistance of bonded interfaces can be achieved with the values of approximately 0.3×10-8 Ω-cm2. In addition to exceptional electrical characteristics, the results of electrical reliability assessments including current stressing, temperature cycling, and unbiased HAST show excellent stability of Cu/In bonds without obvious deterioration. The low-temperature Cu/In bonding technology presents good bond quality and electrical performance, and possesses a great potential for future applications of 3-D interconnects.

Three types of bonding, including Cu-In, Sn/In-Cu, and Cu/Ti-Ti/Cu, are investigated for the application of 3D interconnects. Cu-In bonding and Sn/In-Cu bonding can form intermetallic compounds at the bonding temperature lower than 180 °C. In addition, for Cu/Ti-Ti/Cu bonding, Cu can be protected from oxidation by capping Ti on Cu surface before bonding. This method can further decrease bonding temperature. All bonded structures have shown excellent electrical performance and reliability characteristics. Based on bond results, these structures can be applied for low temperature bonding in 3D interconnects.

A low temperature bonding technology of Sn/In composite solder bonded to Cu interconnect is proposed and investigated. The intermetallic compounds formed in the bonded interconnects can survive well in the following process. The Sn/In-Cu interconnects bonded at low temperature all exhibit excellent electrical performance and high resistance to multiple current stressing, showing a great potential in 3D applications.

In this paper, mechanical bonding behaviors of micro-bumps in 2.5D/3D ICs assembly are studied theoretically. Solder force and spring constant of micro-bumps with different bond pad structures are estimated by using Surface Evolver. Deformations of dies with corresponding flattening distances are evaluated based on flexural theory and three-dimensional contact theories. Allowable coplanarity of bond surface or die warpage during both mass reflow and thermal compression bond is developed. Guidelines to ensure successful bond and corresponding structural designs are earned.

Two bonded structures, Cu/In bonding and Cu-Cu bonding with Ti passivation, were investigated for the application of 3D interconnects. For Cu/In bonding, the bonds were achieved at 170°C due to the isothermal solidification. The intermetallic compounds formed in the joint was Cu2In phase. For another case, Cu-Cu bonding with Ti passivation was successfully achieved at 180°C Application of Ti passivation can protect inner Cu from oxidation; therefore, the required bonding temperature can be decreased. Compared to direct Cu-Cu bonding, Cu/In bonding and Cu-Cu bonding with Ti passivation can be performed at low temperature, which can meet low thermal budget requirement for most devices. Besides, with the good electrical performance and reliability, these two bonded interconnects can be applied for 3D IC interconnects.

A method of pressure sintering multilayer glass ceramic packages (MLC) that results in a hermetic product is described. Use of this process results in a reduced process time, and is achieved without the use of a die, which is commonly employed during pressure sintering. Complex glass ceramic multichip substrates have been sintered this way to produce products with a flat edge contour and minimal distortion of the internal vias. In this article, we present a model that provides the fundamental basis for the pressure sintering approach to processing MLC. In this semi-quantitative model, the mechanism of pressure sintering, i.e., the process of dimensional changes, is controlled by viscous flow induced by sintering, and lamination flow created by an applied pressure. The pressure sintering model is capable of predicting the flow, density, and dimensional changes of a glass ceramic carrier during pressure sintering in the absence of a die. Both the temperature and pressure schedules are time dependent, and the pressure can vary over a range from zero, corresponding to free sintering, to large pressures (up to at least 800 psi) that closely simulate experimental data.

Solvent transport in multilayer thin film structures can induce damaging stresses. It is important to understand these quantitatively for the design of processing methods for microelectronics manufacture. As a model for such systems, this article focuses on the connection between solvent transport in a thin, supported film and the induced bending curvature of the film/substrate combination. We develop a simple mechanical model to calculate the bending curvature based on the transport-induced stresses. A phenomenological moving boundary description of non-Fickian solvent transport often found in glassy polymers has been used. The evaluation of dimensionless bending curvature for a number of generic cases is presented. As an application of the model, experimental data for a polymide (PI)/quartz-n-methyl-2-pyrrolidinone (NMP) system involving significant swelling (15–20%) of the PI film is analyzed. The analysis shows that the measured bending during the transport of NMP in the PI film compares well with that predicted based on an “intermediate,” non-Fickian diffusion mechanism of NMP, consistent with the finding obtained from a laser interferometric study. Estimation of the swelling-induced stress shows that it is large and as significant as that due to thermal “curing.”

WLCSP with Ni/Cu UBM and SnAgCu solder interconnect comply completely with European ROHS regulation. SnAgCu solder exhibits best solder joint thermal fatigue life in organic laminate BGA type package to organic PCB during gentle TCT condition, but whether means it can also work well in silicone die level package to organic PCB due to larger CTE mismatch during temperature cycling, is still necessary to be explored. In this report, the interfacial metallurgical reactions of solder joint of the combination of 0.3 mm SnAgCu solder ball and different melting point solder pastes such as Sn37Pb and Sn3.0Ag0.5Cu will be investigated in the wafer level CSP package with 0.5mm ball pitch. After appropriate SMT process at low, medium and high reflow temperature respectively on NSMD FR4 PCB with Cu-OSP surface finish, the sample is subject to TCT (-40-125/spl deg/C) 500 and 1000 cycle, then are followed by solder joint cross-section observation with SEM/EDX. The diverse failure mode on the metallurgical evolution in the interface and solder bulk itself is recorded to illustrate the solder joint integrity. The relationship among the fracture morphology and solder paste type is concluded as well. Furthermore, one new technology with polymer collar structure around the solder ball is integrated to discuss the whole SnAgCu solder joint integrity enhancement during the TCT test. A mature wafer level CSP with Sn37Pb solder ball will be used for comparison as well.

A study was undertaken to select a suitable coating for a high-pin-count flexible edge connector (Flex) that interconnected a multichip thin-film silicon carrier to a printed circuit board. The Flex with cantilevered inner leads were joined to the contact pads at the perimeter of the carrier. 15 polymeric coatings were evaluated by subjecting coated Flexes to tests consisting of inner lead bending, temperature/humidity/bias (85°C/80%/15 V/350 hours), corrosion, line peel, and/or pressure cooker (126°C/20 psig/120 hours). Inner lead bending measurements were performed to assess the potential of lead shorting at the inner lead bonding sites during thermal cycling. From this study, a low-stress silicone evolved as the best candidate. The results leading to this conclusion will be shown and discussed.

A thermomechanical analyzer (TMA) in the parallel-plate configuration was employed to study the viscosity behavior of an unfilled, FR-4 type epoxy resin by monitoring its thickness change with time under a constant compressive force at various temperatures. With a dual-Arrhenius reheology model, we were able to predict viscosities under nonisothermal conditions of high heating rate from more easily obtained isothermal viscosity data. Due to its simplicity and speed, this technique is well suited for investigating resin viscosity behavior during composite lamination in a manufacturing environment.

A simple interferometric technique is described for monitoring thickness changes in solution-cast polymer films as they are dried and cured. This paper follows a freshly spun solution of polyamic acid in NMP as it is converted into a cured polyimide film of 6 μm in thickness. The technique is shown to be nearly quantitative despite the effects of thermal expansion and cure-related refractive index changes.

Aqueous agar gels were directionally frozen in a temperature gradient of 10 °C/ cm at rates between 8.8×10−5 cm/sec and 8.8×10−4 cm/sec to form highly anisotropic ice-agar composites. Observations of the vitrified agar domains which were localized at the ice grain boundaries were made and the ice domain size was measured as a function of the solidifying conditions. The segregation of the noncrystalline agar was dominated by the vitrification character of the agar gel. Thermal analysis indicated that ice crystallization rate decreased to a negligible level as the water content of the gel decreased to approximately 50 percent by weight agar.

A bending-beam technique has been employed to study the effects of film thickness (7–55 μm) and rate of cooling during film preparation (∼ 6°C/h to a dry ice quench) on sorption characteristics of water by poly(methyl methacrylate) films coated on thin fused quartz beams (˜ 84 μm thick). In each experiment, the curvature of a polymer coated beam exposed to liquid water was monitored as a function of time by a low power laser pointer. With the use of a transport model which considers the sorption process as the linear superposition of contributions from Fickian diffusion and a first-order polymer molecular relaxation process, the beam curvature data were analyzed to determine the governing transport kinetics and associated transport parameters such as water diffusion coefficient and relaxation rate constant. From curvature analysis for thin films (7–13 μm in thickness), it was found that water diffusion proceeds at early times in a Fickian-like manner with a diffusion constant of 2–4 × 10−9 cm2/s. At later times, significant relaxation contributions lead to non-Fickian diffusion behavior, an effect that is more pronounced as the film thickness or sample cooling rate decreases. In addition, sorption of water was found to reduce the film stress (initially tensile at ˜ 108 dyn/cm2) at a rate that increases with sample cooling rate. The high initial film stress not present in free-standing films may account for the relatively higher diffusion coefficient (∼ 2 × 10−8 cm2/s) found here for very thick (55 μm) PMMA coatings. Because the bending-beam technique uses coated samples, it is especially well suited for studying penetrant transport into polymer coatings.

A Cu/polyimide thin film couple prepared on a thin quartz reed has been used to study interfacial stress relaxation during thermal cycling between room temperature and 400 °C. The polyimide thickness varies from 0 (no polyimide at all) to 10.5μm while the Cu thickness was fixed at 0.53μm. The average copper film stress has been calculated from the curvature of the quartz reed. The information clarifies the relation between the polyimide thickness and the average Cu film stress. The Cu/polyimide interfacial morphology after thermal cycling has also been examined using the cross sectional TEM technique. The results suggest that the interfacial stress is partially released through the deformation of polyimide near the Cu/polyimide interface.

A double-bending-beam technique has been developed to determine the mechanical properties (e.g., the elastic stiffness parameter and the in-plane coefficient of thermal expansion) of thin polymer films during thermal cycling. The mechanical properties of poly(methyl methacrylate) and a polyimide have been determined from the combined stress-temperature relationships of identical polymer films coated on two rigid beams (each with a distinctly different Young's modulus and coefficient of thermal expansion). The measured mechanical properties were found to agree with data obtained using conventional techniques. The double-bending-beam technique can be applied to a wide variety of dry and wet processing situations involving thin polymer films.