By reflowing Cu/Sn/Ni ultrafine interconnects under a temperature gradient, a new transient liquid phase (TLP) bonding process was proposed for three-dimensional packaging applications. The evolution of the dominant (Cu,Ni)6Sn5 intermetallic compounds depends strongly on the temperature gradient. The essential cause of such dependence is attributed to the different amounts of Cu and Ni atomic fluxes being introduced into the liquid solder. Under the coupling effect of thermomigration and Cu–Ni cross-interaction, the total atomic flux of Cu and Ni is promoted. As a result, the growth of dense (Cu,Ni)6Sn5 is significantly accelerated and the formation of Cu3Sn is eliminated. The new TLP bonding process consumes only a limited amount of the Ni substrate, but much more from the Cu substrate. The mechanism for the new TLP bonding process is discussed and experimentally verified in this study.

Vertically aligned carbon nanotubes (VACNTs) grown on bulk copper substrate are of great importance for CNT real-life applications as thermal interface materials in microelectronic packaging. However, their reproducible synthesis has been a great challenge so far. In this study, by introducing a well-controlled conformal Al2O3 support layer on the bulk copper substrate by atomic layer deposition (ALD) prior to the deposition of the iron catalyst layer, we reproducibly synthesize VACNTs of good alignment and high quality on the copper substrate, using a conventional thermal chemical vapor deposition process. The alignment and the quality are characterized by scanning electronic microscopy and Raman spectroscopy, respectively. The roles of the conformal Al2O3 support layer are discussed. A kinetics-controlled growth mechanism is shown. This progress provides a viable VACNT commercial application for thermal management, on the basis of which, we show a recent progress on a state-of-art Si/VACNT/Cu assembling process, named “chemical anchoring”. The high quality of the VACNTs on the copper growth substrate and the covalent bonding formed between the VACNTs and the silicon mating substrate greatly reduces the thermal resistance of the VACNT-mediated thermal interface.

Creation of superhydrophobic self-cleaning surfaces is an important objective for a variety of applications. Indeed, numerous routes to generate superhydrophobic surfaces have been proposed. In this paper, a facile way of forming superhydrophobic surfaces is reported that uses Au assisted HF/H2O2 etching of silicon wafers. The Au layer was deposited onto a silicon wafer via e-beam evaporation. By controlling the evaporation and etching times, the surface roughness can be manipulated and superhydrophobic surfaces with reduced light reflection can be generated. Contact angles were measured with a CCD camera equipped goniometer; these values determined the water repellency. Light reflection on the as prepared black surfaces was measured to assess the efficiency for low cost solar cell applications. This approach offers a new way both to theoretically study the surface roughness effect and to investigate engineering applications of self-cleaning surfaces in solar cells, MEMS, anti-bacteria coating, and microfluidic devices.

Based on the theory of superhydrophobicity for low surface energy coatings, we describe a superhydrophobic antistiction silica coating for MEMS devices. The process uses a novel sol-gel process sequence with a eutectic liquid as a templating agent. The eutectic liquid displays negligible vapor pressure and very low melting point (12°C at ambient conditions) to reduce solvent loss during the high speed spincoating process. After a fluoroalkyl silane treatment, superhydrophobicity is achieved on the as-prepared silica thin film. The solvent can be extracted after the gelation and aging processes. Spin speed effect, eutectic liquid:TEOS ratio in the solution were studied in order to optimize the surface roughness to ensure excellent super-hydrophobicity. Comparison of the silica thin films with silicon pillar surfaces showed that superhydrophobicity for the traditional sol-gel derived silica films demonstrated significant improvement, especially under humid conditions. The AFM force curve obtained with a tipless probe showed that the interaction force is greatly reduced on a rough silica superhydrophobic surface. This result offers great potential to reduce stiction failures in MEMS devices.

Carbon nanotubes (CNTs) have been proposed as electrical interconnects, due to their excellent properties. However, the current nanotube growth techniques suffer from several drawbacks. One of the main challenges for applying CNTs to the circuitry is the high growth temperature (>600°C). Such temperatures are incompatible with microelectronic processes. The other issue is the poor adhesion between CNTs and the substrates, which will result in long term reliability issues and high contact resistance. To overcome these disadvantages, we have successfully demonstrated a methodology that we term “CNT transfer technology”. The distinctive CNT-transfer-technology features are separation of CNT growth and CNT device assembly at solder reflow temperature. In this paper, we combined our expertise in growth of well-aligned open-ended CNT bundles with the CNT transfer process to assemble CNT bundles for fine-pitch interconnects applications. To demonstrate the feasibility of transfer process to assemble the fine-pitch CNT bundles, the CNT bundles with diameter, aspect-ratio and pitch of 25 μm, 4, and 80 μm, respectively, were assembled on the copper substrates. The measured resistivity of the long CNTs is ∼2.3×10−4 Ω-cm. The CNT-solder alloy interfaces were observed by the SEM. The results indicated that molten SnPb solder form strong mechanical bonding with open-ended CNTs, suggesting the superior CNT/solder interfacial properties by solder reflow process.

In this paper, a novel nano-scale conductive film which combines the advantages of both traditional anisotropic conductive adhesives/films (ACAs/ACFs) and nonconductive adhesives/films (NCAs/NCFs) is introduced and developed for next generation high performance ultra-fine pitch packaging applications. This novel interconnect film possesses the properties of electrical conduction along the z-direction with relatively low bonding pressure (ACF-like) and the ultra-fine pitch (< 100 nm) capability (NCF-like). Unlike typical ACF which requires 1–5 vol% of conductive fillers, the novel nano-scale conductive film only needs less than 0.1 vol% conductive fillers to achieve good electrical conductance in the z direction. The nano-scale conductive film also allows a lower bonding pressure than NCF to achieve a much lower joint resistance (over two orders of magnitude lower than typical ACF joints) and higher current carrying capability. With low temperature sintering of nano-silver fillers, the joint resistance of the nano-scale conductive film could be as low as 10−5 Ohm, even lower than the NCF and lead-free solder joints. The reliability of the nano-scale conductive film after high temperature and humidity test (85°C/85%RH) was also improved compared to the NCF joints. As such, a high performance, fine pitch conductive film was developed.

Tin-lead solder alloys are widely used in the electronic industry. With the recognition of toxicity of lead, however, electrically conductive adhesives (ECAs) have been considered as one of the most promising alternatives of tin-lead solder. While silver is the most widely used conductive fillers for ECA, silver migration has been the major concern for the high power and fine pitch applications. In this paper, a novel approach of using self-assembled monolayers (SAMs) passivation has been introduced to control the silver migration in nano-Ag ECAs. The protection of silver nano particles with SAMs reduced the silver migration dramatically and no migration was observed upon application of high voltages (up to 500 V) due to the formation of surface chelating compounds between the SAM and nano silver fillers. Unlike other migration control approaches which sacrifice electrical performance, the SAM passivated nano Ag fillers also enhanced the electrical conductivity and current carrying capability of adhesive joints significantly due to the improved interfacial properties and high current density of those molecular monolayers. The joint resistance of the SAM incorporated nano-Ag conductive adhesive could be achieved as low as 10−5 Ohm (the contact area is 100 ×100 μm2) and the maximum allowable current was higher than 3500 mA. As such, a fine pitch, high performance, non-migration and high reliability adhesives are developed for potential solder replacement in high voltage, high power device applications.

Carbon nanotubes (CNTs) have been proposed for applications in microelectronic applications, especially for electrical interconnects, thermal management, and nanodevices, due to their excellent electrical, thermal, and mechanical properties. In this paper, we reported a simple process to achieve simultaneous CNT growth and opening of the CNT ends, while keeping alignment of the original CNT films/arrays. The addition of relatively low reactivity oxidizing agents (water) into the reaction furnace enables the feasibility. We proposed using novel CNT transfer technology, enabled by open-ended CNTs, to circumvent the high carbon nanotube (CNT) growth temperature and poor adhesion with the substrates that currently plague CNT implementation. The process is featured with separation of high-temperature CNT growth and low-temperature CNT device assembly. Field emission testing of the as-assembled CNT devices is in a good agreement with the Fowler-Nordheim (FN) equation, with a field enhancement factor of 4540.