IMPROVEMENT OF JOINT SEALANT CONFIGURATION AND PERFORMANCE

The jointing of concrete pavement is intended to provide free movement within the concrete slab. Joint sealing material, called a joint sealant, has evolved in recent decades to prevent or reduce the amount of water from rainfall events infiltrating a pavement structure. As this evolution has progressed, joint sealant practices have changed. However, current practices and their respective performances have yet to be fully documented. Therefore, it is necessary to establish a standardized approach to joint sealant evaluation, as well as investigate and assess joint sealant practices in Portland cement concrete design. Current joint sealants are designed without consideration of the strength and shape of the bond between the concrete and sealant and its effect on stress concentration. This often results in adhesive failure within 1.5 years, much earlier than the expected service life of the joint sealant (20 years). Bond strength and stress on the interface between the sealant and joint reservoir face play important roles in adhesive failure. Therefore, in the present research, experimental bond tests and a finite element method (FEM) analysis are conducted to examine the nature of the bond at the sealant/joint reservoir interface. In addition, the stress distribution along the interface is also investigated by analyzing the geometric shape factor (SF), degree of curvature (DoC), and joint preparation conditions. For this study, data is gathered through a literature review, the survey of Departments of Transportation (DOTs), and subsequent discussions with selected agencies to determine case documentation practices. In addition, re-evaluation of the SF was conducted, and a new design factor, DoC, is introduced and explored through the FEM and experimental analysis. With these factors, the reduction of bond strength and increase in stress at the interface may be limited, reducing the potential for early adhesive failure. This study examines the effects of moisture content on bond strength, the main cause of joint sealant failure. Sealant use in various climatic regions throughout the United States is examined, and DOTs are surveyed with regards to how they handled moisture. As a result of this investigation, it becomes clear that some advances in the composition, design, and preparation of sealants, especially in terms of the design of and inspection methods for narrow joints, appear to conflict with established recommendations. It also appears that institutions lack the necessary tools and control protocols to facilitate the proper inspection of cleaning and joint preparation work. The effects of poor joint preparation (i.e., dirt and moisture) on joint strength and the shape of the joint sealant (i.e., SF and DoC) should be considered when designing and installing sealants. This research evaluates the effects of surface moisture on the tensile bond strength between a joint sealant and reservoir. The causes of degradation in adhesion strength are evaluated by measuring the sealant wetting angle. Finally, it is determined that the best choice of sealant may depend on climate. Those not currently preferred in wet-freeze regions may be used if accompanied by proper pretreatment and moisture control, contributing to the stable lifespan of joint sealants and concrete pavement alike

Glass multilayer bonding for high density interconnect substrates

The aim of this research was the investigation of bonding borosilicate glass sheets, its trade mark CMZ, 100μm thickness, to create multilayer substrates capable of supporting high-density electrical interconnections. CMZ glass was chosen as it has a coefficient of thermal expansion that is close to that of silicon, thereby minimising thermal stresses in assemblies generated by manufacturing processes or service conditions. Two different methods of bonding the glass were used in this study; pressure assisted low temperature bonding (PALTB), and water glass bonding, using Sodium Trisilicate (Na2Si3O7) solution. These two bonding methods have already been applied in electronics manufacturing applications, such as silicon wafer bonding and multichip modules (MCMs). However, glass-to-glass bonding is a relatively new subject and this study is an attempt to standardise bonding processes. Additionally, the concept of using glass as a multilayer substrate provides a foundation for further exploration by other investigators. Initial tests that were carried out before standardising the procedures for these two methods showed that a two-stage bonding process provided optimum results. A preliminary stage commenced by placing the cleaned (using Decon 90 solution) samples in a vacuum oven for 15 minutes, then heating at 100oC for 1hr. The permanent stage was then achieved by heating the samples in a conventional oven at temperatures from 200 to 400oC, for different periods. At this stage, the main difference between the two methods was the application of pressure (1-2MPa) during heating of the PALTB samples. To evaluate the quality of the bonds, qualitative tests such as visual, optical microscope and dye penetrant were used. In addition, to estimate the strength and the rigidity of the interlayer bonds, two quantitative tests, comprising of deflection under cyclic stresses and crack opening were used. Thermal cycling and humidity tests were also used to assess resistance of the bonds to environmental effects. The results showed that heating to 100oC was insufficient to enhance the bonds, as occasionally a sudden increase of deflection was observed indicating slippage/delamination. These bonds were enhanced during the permanent bonding stage by heating to 300oC in PALTB, under a pressure of 1-2MPa. The crack-opening test showed that the delamination distances of the bonds in the permanent stage were lower than that for preliminary bonding in both bonding methods. The delamination distances from the crack opening tests were used to calculate the strain energy release rate (GIC) and fracture toughness (KIC) values of the interlayers. The results showed that the KIC values of the permanent PALTB and water glass interlayers were higher than 1MPa.m0.5, while the KIC value of the CMZ glass, determined by linear elastic fracture mechanics, was around 0.8MPa.m0.5. The optical observations revealed that the prepared bonded sheets did not delaminate or break after thermal cycling and humidity tests

Developing Metrology for Nondestructive Characterization of Buried Polymer Interfaces in Situ.

Polymers are widely used in modern microelectronics as adhesives, organic substrates, chip passivation layers, insulating dielectric materials, and photoresists in microlithography. The interfacial structures of polymer materials determine the interfacial properties of the materials. Weak adhesion or delamination at interfaces involving polymer materials can lead to failure of microelectronic devices. Therefore, it is important to investigate the molecular structures of such interfaces. However, it is difficult to study molecular structures of buried interfaces due to a lack of appropriate analytical techniques. This dissertation presents the development of the nonlinear optical technique sum frequency generation (SFG) vibrational spectroscopy into a metrology tool for nondestructive characterization of molecular structures at buried polymer interfaces in microelectronic packages in situ and the elucidation of relationships between buried molecular structures and interfacial properties such as adhesion strength. Buried polymer/epoxy, copper/epoxy, and silicon/organosilicate dielectric interfaces were investigated. SFG was used to directly probe molecular structures at buried adhesive interface in situ. Plasma treatment of polymer surfaces was found to alter the molecular structure at corresponding buried interfaces prepared using the plasma treated surfaces. Hygrothermal aging treatment was found to influence hydrophobic polymer/polymer interfaces less than hydrophilic interfaces, showing that hydrophobic materials can better resist delamination during qualification testing in high humidity environments. Copper/epoxy interfaces were found to delaminate near, but not exactly at, the metal/polymer interface and silane adhesion promoters were found to modify the interfacial region near the copper surface which suggests that the interfacial layer near copper needs to be modified to improve adhesion. Quantitative data analysis methodology was developed to simultaneously characterize the surface and buried interface of silicon-supported thin low-k polymer films nondestructively before and after microelectronic processing steps which provided a molecular level understanding of the effects of the processing. The general nature of the methodology enables it to be directly utilized to elucidate structure-property relationships at buried interfaces by correlating interfacial structures to interfacial properties. Structure-property relationships elucidated using this methodology can be used to guide the rational engineering of buried polymer interfaces with optimized properties in many practical applications such as polymer composites, optical fibers, paints, and anticorrosion coatings.PhDChemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/133179/1/myersjn_1.pd