Cone-shaped Bump Research Articles

Hardness Characteristics of Au Cone-Shaped Bumps Targeted for 3-D Packaging Applications

Three-dimensional large scale integration (3D-LSI) packaging is crucial toward obtaining increased circuit density within a small footprint. In a 3D-LSI package, chip-to-chip interconnection is typically obtained using through-silicon vias and microbumps. In particular, microbumps realized by nanoparticle deposition (NPD) are promising to obtain high-density interconnections. However, the effect of temperature on the mechanical properties (i.e., hardness) of NPD bumps is little understood. This paper seeks to investigate the influence of temperature on the hardness of NPD bumps, with reference to NPD films. The results obtained suggest a significant reduction in the NPD bump hardness from room temperature to 200 °C. In particular, the hardness was observed to be mainly dependent on temperature rather than grain size, as the grain microstructures obtained at room temperature and 200 °C are similar. Overall, these results suggest a simple approach to control the NPD bump compression during flip-chip bonding, where the hardness-temperature data for the NPD bumps suffices to estimate for the bump compression during flip-chip bonding.

Fine Cone-shaped Bumps for Three-dimensional LSI Package—An Optimization of Thermocompression Bonding Process

Fine Cone-shaped Bumps for Three-dimensional LSI Package—An Optimization of Thermocompression Bonding Process

Room-Temperature Cu Microjoining with Ultrasonic Bonding of Cone-Shaped Bump

Room-temperature Cu–Cu bonding was realized by applying ultrasonic vibration together with compression force to the bonding of a cone-shaped bump. The size of the bump was about 10 µm. The connection pitch was 20 µm. Mechanical characterization showed that the bonding strength increases with vibration amplitude and depends on the thickness of the counter electrode made of Cu. The thickness dependence of the bonding strength was found to be caused by an increase in the surface roughness of the counter electrode. It was shown that the bonding strength meets the requirement from application to products. Electrical characterization using a daisy-chain connection test demonstrated that more than 10,000 pins on a chip can be connected with a sufficiently low resistance.

Room-Temperature Microjoining of LSI Chips on Poly(ethylene naphthalate) Film Using Mechanical Caulking of Au Cone Bump

We show that room-temperature bonding of LSI chips on a resin film made of poly(ethylene naphthalate) (PEN) can be realized by using mechanical caulking of a cone-shaped bump electrode made of Au. A 20-µm-pitch area array of cone-shaped Au bumps was fabricated on a Si wafer by photolithography and electroplating. The counter electrode with cross-shaped slits on the PEN film was composed of a Au (top)/Ni/Al (bottom) layered structure, where Ni and Au layers were deposited by electroless plating on patterned Al. Bonding of about 10,000 bump connections with 184 mΩ/bump has been achieved at room temperature.

Characteristics of a Novel Compliant Bump for 3-D Stacking With High-Density Inter-Chip Connections

This paper reports on the detailed characteristics of a novel compliant bump for 3-D stacking with high-density inter-chip connections. The novel compliant bump is a cone-shaped bump made of Au. It is fabricated using electroplating of the Au into undercut holes formed in a photoresist. Because the cone bump is easily deformed under a pressing load, it possesses superior properties for inter-chip connection. First, it suppresses a bonding failure by compensating for the bump-height deviation and the nonuniform bonding pressure, and consequently, offers high-density inter-chip connections of which number is at least 30 600 with 20 μm pitch. Second, it reduces the change in the transconductance g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> of the metal-oxide-semiconductor field effect transistor (MOSFET) after chip stacking. In other words, it reduces the strain generation at the Si device level. Third, room-temperature bonding is achieved by mechanical caulking between the cone bumps and the doughnut-shaped electrodes.

Anti-reflective effect of transparent polymer by plasma treatment with end-hall ion source and optical coating

The surface of poly(methyl methacrylate) (PMMA) was treated by plasma with an end-Hall ion source in vacuum in order to enhance its anti-reflectivity. The cone-shaped bumps induced by the plasma etching have shown an antireflective effect. Moreover, PMMA has poor thermal durability due to its low melting point; therefore, the etched PMMA was further coated by a 5 nm thick SiO2 film after 900 and 1300 s plasma etching. Samples after SiO2 coating were thermally annealed at temperature of 70°C for 1 h. Experiments show that transmittance was increased after 5 nm thick SiO2 coating. The of transmittance of PMMA after both sides treated by 900 s plasma etching and 5 nm SiO2 coating was not changed after thermal annealing. However, without SiO2 coating the transmission was reduced 1% after annealing. Atomic force microscope (AFM) demonstrated that the nano-structures of cone-shaped bumps were formed on the PMMA after plasma etching and a smoother nano-structured pattern preserved the transmittance of the PMMA after both sides treated by 900 s plasma etching and 5 nm SiO2 coating. Three dimensional photonic crystal formed by uniformly distributed cone-shaped bumps was assumed to result in the reduction of the anti-reflectivity of treated PMMA.

Room-Temperature Bonding Using Mechanical Caulking Effect of Compliant Bumps for Chip-Stack Interconnection

We propose room-temperature three-dimensional (3D) chip-stacking using the mechanical caulking effect of compliant bumps. The compliant bumps were cone-shaped bump made of Au. By caulking Au cone bumps with doughnut-shaped electrodes also made of Au, high-density large-number inter-chip connections were realized even at room temperature in ambient air. The number of inter-chip connections realized was 30,600 with 20 µm pitch. Material analysis revealed that Au cone bumps bonded to Au doughnut-shaped electrodes at the atomic level.

Fabrication of Back-Side Illuminated Complementary Metal Oxide Semiconductor Image Sensor Using Compliant Bump

We fabricated a back-side illuminated (BSI) complementary metal oxide semiconductor (CMOS) image sensor in which a very-thin BSI photodiode array chip was stacked on a CMOS read-out circuit chip by compliant bumps. Cone-shaped bumps made of Au were prepared as the compliant bumps. The base diameter was 10–12 µm and the height was 9–10 µm. To fabricate the BSI CMOS image sensor, we developed a novel thin-chip assembly process. The key features of the process are as follows: preparation of a photodiode array wafer and a CMOS read-out circuit wafer, Au cone bump formation, bonding to support glass, thinning of the photodiode array wafer to 21 µm, through silicon via (TSV) formation using Cu electroplating, formation of back-side electrodes, transfer of the photodiode array wafer to a polymer support tape, dicing of the photodiode array wafer, separation of support tape, formation of Ni–Au bumps, dicing of CMOS read-out circuit wafer, and three-dimensional (3D) chip-stacking. The BSI CMOS image sensor thus fabricated has the following specifications: number of active pixels is 16,384 (128 ×128), photodiode size is approximately 18 µm square, photodiode pitch is 24 µm, and fill factor is approximately 55%. No defects were observed in the obtained image frames.

A Method for Laser Zone Texturing of Glass Based Magnetic Media Using Nd:Yag Lasers

AbstractLaser zone texturing of nickel-plated, aluminum based magnetic media has become a preferred method of providing a precisely controlled head landing zone. The Nd:YAG lasers used for this process are not suitable for directly texturing glass substrates. A novel method has been developed which allows the use of the existing Nd:YAG laser systems to zone texture glass based magnetic media.An amorphous sputtered film of a non-magnetic Ni alloy provides a texturing layer which absorbs the laser pulse and controllably forms regular, small protrusions. Optimization of the alloy composition results in small cone-shaped bumps. Laser power sensitivity exhibits a region of invariance for a range of film thickness. This behavior provides a wide margin for manufacture by reducing the effect of thickness variation on laser bump height.Disks fabricated using this form of laser zone texture exhibit excellent tribology performance. TEM images show the Ni alloy to be amorphous and featureless. The sputtered film does not influence the properties of the subsequently sputter deposited isotropic magnetic films.