Stock material or miscellaneous articles – All metal or with adjacent metals – Shaped configuration for melting
Reexamination Certificate
2000-02-07
2003-01-28
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Shaped configuration for melting
C428S594000, C428S603000, C428S616000, C428S620000, C428S635000, C228S137000, C228S186000
Reexamination Certificate
active
06511759
ABSTRACT:
FIELD OF THE INVENTION
This invention is directed to the field of materials fabrication and specifically, to the field of materials fabrication involving the joining of materials through the use of controlled atmosphere bonding.
BACKGROUND OF THE INVENTION
One of the most significant inventions of the twentieth century is that of the microprocessor. The ability to provide intelligence on a chip has fostered countless products ranging from cellular telephones to portable life support systems to hand held video games. While the processing ability of these computers on a chip has increased dramatically since their introduction, perhaps even more significant is the fact that as the power of these chips has continued to increase, the cost of these devices has decreased. Indeed, the processing power which once would have cost hundreds of thousands of dollars can now be purchased for just a few dollars. Because of their favorable cost to performance ratio, microprocessors are now nearly ubiquitous in most developed countries. As in most areas of technology, the companion technologies which must be employed to produce these devices such as the microprocessor have advanced as well.
Because of the complexity and high density of electronic components in these devices, coupled with the fine geometries at which they must be fabricated, it is not surprising that their production processes must be carefully controlled. By carefully controlling each step of the complex manufacturing processes, engineers have been able to continuously improve the state of the art, thereby providing dramatic improvements not only in the function of the devices being produced but also in the yield of the processes used to produce these devices. The processes of Chemical Vapor Deposition (CVD) and Physical Vapor Deposition (PVD) are frequently employed to produce exotic or difficult to create materials on substrates. Many semiconductor fabrication processes such as chemical vapor deposition require that the substrate on which materials are to be deposited be first thoroughly cleaned and subsequently heated prior to and during the actual deposition process. The heating process must be controlled precisely since variations in temperature of the substrate can result in variations of the properties of the thin films to be deposited or, indeed whether deposition occurs in the first place. Additionally, if the substrate is not heated and ultimately, cooled evenly and in a precise manner, warping may occur which can result in permanent deformation of the substrate, rendering it unsuitable for the intended purpose.
A variety of means may be employed in the heating of materials such as substrates. Firstly, if the substrate is electrically conductive, it may be directly heated. An electric current may be passed through the substrate thereby causing it to be heated proportionately to the voltage presented to and current passing through the substrate. Many of the materials used for fabrication of micro sensors and integrated circuits for example, are glasses, ceramics or, in the case of semiconductors, silicones. These materials are at best, poor electrical conductors so this heating means is seldom employed when processing these materials.
A heated plasma or an energy beam such as a laser or electron beam may be used to heat the object. These processes are unfortunately, rather complicated and quite costly. Additionally it is difficult to control these energy sources in a manner which will promote even heating of the entire object to be heated. Further, the energy fields induced in the substrate by these methods may damage the substrate or coatings or circuit elements (if any) thereon.
A conductive heating process may be employed which involves placing the item to be heated directly on a heated plate whereby heat is transferred from the heated plate to the object to be heated. Traditional hot plate systems are however, notorious for being anisothermal, thereby creating hot spots in the object being heated which can lead to mechanical deformation or to other process failure.
Conductive heating may also be accomplished by using a suitable gas to transfer heat from a heat source to the object to be heated. Ovens using this process are often referred to as atmospheric ovens and may employ inert, oxidizing or reducing atmospheres as may be beneficial to the process. Mechanically stirring the heated gas serves to make this type of heating process more or less isothermal and minimizes temperature variations which may be induced by thermal convection or through the use of more or less point source heaters. This process is of course not possible in the event that the object to be heated must be processed in a vacuum. Since chemical vapor deposition often takes place at reduced pressures of for example, in the range of 0.1 torr 1 atmosphere, the process of conductive heating employing gasses may not be practical in some of these applications.
Radiative heating may be used to heat the object whereby infrared energy is transferred by radiation from a heated source to the object, whether the object is in vacuum or in an atmosphere. Radiative heating offers an advantage over direct conductive heating in that the object to be heated need not be in contact with the heat source. Eliminating this contact also eliminates surface defects on the object to be heated which can be created when contaminants on the heat source are transferred to the object to be heated. Additionally, if temperatures and contact forces between the heat source and the object to be heated are sufficiently high, diffusion bonding or welding may occur, thereby bonding the object which is to be heated to the heat source and potentially ruining the process part. Ideally, a highly emissive, heated, isothermal plate is used as a radiation source to transfer heat to the object to be heated. Desirable qualities of this plate include flatness and the ability to accurately control thermal radiation from the surface of the plate. The task of producing the desired radiation source which is capable of providing a nearly constant thermal emission over the entire surface is formidable. This task is further complicated when the object and hence, the required radiating plate are of significant size. Additionally, some means for precisely heating and preferably also, cooling the plate must be accomplished. These same critical issues also apply to the previously described process of conductive heating. Copper for example, exhibits a high degree of thermal conductivity but relatively low resistance to bending moments, particularly at elevated temperatures. Additionally, copper is a relatively active metal which may interact negatively with other materials in the process and/or contaminate the operating environment. Stainless steels offer mechanical strength and are relatively inert, but exhibit poor thermal conductivity. Both copper and stainless steel have relatively low emissivity in their natural state, making them inefficient radiators of thermal energy. It can be seen then, that using either of these materials alone fails to provide for an effective heat source for either radiative or conductive heating of planar materials.
U.S. Pat. No. 5,192,623 discloses laminated structural panels and a method of producing them. This patent teaches to the production of structural panels in which at least one of the panel members is perforated so that when laminated between two imperforate panels and brazed in a high vacuum environment, that a substantial vacuum will be formed and maintained between the imperforate panels in the void space created between the panels and the perforations in said perforated plate. Such a panel containing these vacuum pockets is useful as an insulator of temperature and sound. As such, the panel described in U.S. Pat. No. 5,192,623 would not be suitable as a source of isothermal radiation, nor cooling, nor fluid transport.
U.S. Pat. No. 4,359,181 provides for a dip brazed, laminated heat transfer surface. This patent discloses a process to produce an improved fluid
Jones Deborah
McHale & Slavin P.A.
Savage Jason
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