Slawomir Rubinsztajn

Synthesis and characterization of new poly(siloxysilanes)

The efficient synthesis of two new monomers, vinyltris(dimethylsiloxy)silane (2) and tris(dimethylvinylsiloxy)silane (3), was developed. Hydrosilation of these new A–B3 monomers affords highly branched starburst poly(siloxysilane) polymers. Polymerization of2 yields a polymer structure that has siliconhydride functional groups on the outer sphere. Polymerization of3 yields a polymer that has the same hyperbranched poly(siloxysilane) core as the polymer produced from2, but the outer sphere contains vinyl moieties. The presence of silicon-hydride or vinyl groups on the surface of both polymers allows functionalization of these materials with a wide variety of reagents.

Utilization of carbon fibers in thermal management of microelectronics

Power dissipation is expected to increase exponentially to 150-250 W per chip over the next decade. To manage this large heat output, it is necessary to minimize the thermal resistance between the chip and a heat dissipation unit that the device is attached to. It is therefore important to further improve the thermal performance of thermal interface materials (TIMs), which can be achieved through 1) improvement of the bulk thermal conductivity of TIMs; and/or 2) reduction of interfacial thermal resistances between the TIM and the device and/or TIM and the heat dissipation unit. The latter improvement may be obtained by enhanced physical properties of TIMs (e.g., viscosity or wetting ability) and/or surface modification of the heat dissipation unit or the inactive side of the device. Researchers have tried to take advantage of the high 1D thermal conductivities of graphite fibers, and more recently of carbon nanotubes (CNT), to reduce the thermal resistance between the chip and the heat dissipation unit. The efforts can be classified into three categories: 1) Forming pre-aligned graphite fiber or CNT films that have high bulk thermal conductivities in the heat transport direction, and applying such films as TIMs; 2) incorporating randomly oriented graphite fibers or CNT into silicone or epoxy matrices in the presence or absence of a second filler to improve bulk thermal conductivities, and applying the thus-formed blend as thermal greases, or adhesives or gels; and 3) growing CNT or graphite fibers from the heat sink/spreader surface and/or silicon backside and assembling them together with a TIM a to increase the bulk heat transport property and reduce the interfacial resistances, In this paper, we will present results for each of the three approaches, and discuss the challenges facing each one.

A novel organometallic route to phenylethenyl-modified polysiloxanes

We have synthesized a series of cyclic and linear siloxane materials with phenylethenyl substituents via transition metal complex-catalyzed coupling of the respective vinylsiloxane systems with styrene and α-methylstyrene. It has been shown that the non-carbene metal catalysts [RuCl(H)(CO)(PPh3)3] and [RuCl(SiMe3)(CO)(PPh3)2] are the most effective ones, pointing to a silylative coupling pathway as the most plausible mechanistic route. The process was studied in the presence of a series of catalysts and styrene polymerization inhibitors under different reaction conditions, leading to useful silicone materials characterized by high refractive index values ranging from 1.51 to 1.59 due to strong π-conjugation in side chain substituents.

Assembly and reliability of flip chips with a nano-filled wafer level underfill

The assembly and packaging of electronic devices today is becoming increasingly challenging and demanding because of requirements for smaller, faster and lighter products that provide increasing functionality at low cost. These requirements continue to place greater demands on the electronics industry and mandate improved packaging technology. In part, flip chip packaging technology is the response to these demands and provides a solution to these challenges. While flip chip packaging provides a solution to evolving device requirements, underfill materials are required to improve flip chip device reliability. These resins overcome poor device reliability issues resulting from the mismatch of coefficient of thermal expansion (CTE) between the silicon die and the organic substrate. However, offsetting the gains in device reliability are additional processing steps that adversely affect manufacturing productivity. To compensate for this adverse effect on manufacturing productivity, several new processes, such as wafer level underfill, have been developed. In this paper, we describe the assembly and reliability of flip chips with a nanofilled wafer level underfill (WLU). This approach allows application of the underfill material on the entire wafer, such that many chips can be underfilled simultaneously. Assembly is then carried out with a compatible epoxy flux material. Air-to-air thermal shock (AATS) results and failure mechanisms are described for this novel approach

Development of no-flow underfill materials and processes for Pb-free flip chip applications

Due to pending legislation worldwide, the semiconductor packaging industry is switching over to Pb-free electronics assembly. Flip chip packaging, which is one of the fastest growing segments of packaging technology, is also affected by this trend. It is a common practice to underfill flip chip devices to compensate for the coefficient of thermal expansion (CTE) mismatch between the die and the chip carrier. However, compatible underfill materials and processes are necessary for the effective migration of flip chip packaging towards Pb-free. Among the various underfilling techniques used in the industry, the no-flow underfill (NFU) process has the potential to increase throughput and reduce manufacturing costs as stated in D. Gamota and C. Melton (1998). There has been a significant research effort within the industry to develop NFU materials and processes for eutectic applications, but Pb-free reflow temperatures pose a significant challenge to the development of a NFU that is compatible with the Pb-free assembly process. Recently, we have developed a Pb-free compatible NFU material with a combination of self fluxing capability and cure kinetics that allows for successful assembly of 95.5Sn/3.8Ag/0.7Cu bumped flip chip devices. In this paper, the effect of various process variables that affect voiding in the underfill interface is investigated. In addition to these studies, the assembly yields for a Pb-free compatible underfill used to assemble different flip chip components with 95.5Sn/3.8Ag/0.7Cu alloy are discussed

Development of a novel filled no-flow underfill material for flip chip applications

Flip chip package design has a significant drawback related to the mismatch of coefficient of thermal expansion (CTE) between the silicon die and the organic substrate. This CTE mismatch creates stress on the solder joints during thermal excursions, which reduces the fatigue lifetime of the solder joints. This leads to premature failures of the package. However, package reliability can be improved by the application of an underfill material. In this communication, we report the development of a novel filled no-flow underfill material utilizing proprietary filler technology, which provides a previously unobtainable balance of low CTE, high glass transition temperature (Tg), and good solder joint formation. The fluxing parameters and effect of catalyst level on assembly yield are presented. Assembly results (yield, void area) are presented and compared with commercially available no-flow underfill materials.

Optical fiber reliability in subsea monitoring

Fiber optic cables have been successfully deployed in ocean floors for decades to enable trans-oceanic telecommunication. The impact of strain and moisture on optical fibers has been thoroughly studied in the past 30 years. Cable designs have been developed to minimize strain on the fibers and prevent water uptake. As a result, the failure rates of optical fibers in subsea telecommunication cables due to moisture and strain are negligible. However, the relatively recent use of fiber optic cables to monitor temperature, acoustics, and especially strain on subsea equipment adds new reliability challenges that need to be mitigated. This paper provides a brief overview of the design for reliability considerations of fiber optic cables for subsea asset condition monitoring (SACM). In particular, experimental results on fibers immersed in water under varying accelerated conditions of static stress and temperature are discussed. Based on the data, an assessment of the survivability of optical fibers in the subsea monitoring environment is presented.

Unusual competition of intermolecular vs. interamolecular reactions. Kinetics of the condensation of decamethylpentasiloxane-1,9-diol

The assistance of a third functional group in the condensation of a bifunctional species may lead to the situation in which the competition of intramolecular vs. intermolecular reactions is not affected by the dilution of the system.