Currently on the market ESD products are dominantly those made of ESD plastic materials. These are basically polymer based composite materials with conductive fillers such as carbon and/or metal powders or fibres at various amounts, generally around 20-30 wt %, depending on the required conductivity and density of the fillers. Polymer based composites are generally injection moulded to form specific parts or products. U.S. Pat. No. 5,409,968 illustrates such a material used as an ESD material. This group of plastic composite materials has limited applications owing to its limited intrinsic mechanical performance, heat resistance and chemical resistance.
Efforts have been reported over the past twenty years with regards to the development of functional ceramic materials and ESD ceramic materials. It is known that by adding conductive materials it is possible to make a ceramic based ESD composite. U.S. Pat. No. 4,866,016 depicts aluminium oxide, titanium oxide and tin oxide composite based ceramics with additives of tantalum oxide, forming a useful dielectric material. U.S. Pat. No. 5,830,819 reports an alumina based ceramic sintered product, with additions of multiple oxides including manganese oxide, iron oxide and niobium oxide, having ESD and antistatic properties, with volume resistivity varying from 1×107 to 1×1013 ohm-cm and an absolute value of the temperature coefficient of volume resistivity of not larger than 1.8%/degree C. at 25 to 75° C. More recently, U.S. Pat. No. 6,136,232 describes an ESD ceramic material comprising stabilised zirconia with additions of lanthanum chromate. These inventions provide materials with limited performance particularly at lower temperatures, and complicated compositions. They are difficult to make and process, with certain additives being cost prohibitive and toxic in practical commercial applications. The prior art also presents U.S. Pat. No. 4,110,260. That patent teaches electroconductive composite ceramics composed of an independent phase of conglomerates having a specific particle diameter of at lease 20μ and also 2-50% by weight of a continuous phase of an electroconductive substance. The present invention does not rely on the addition of any electroconductive substance or electroconductive phase. U.S. Pat. No. 4,931,214 shows ceramic bodies with electronic conductivity for use in oxygen concentration cells, oxygen probes, fuel cells and electrolysis cells. Unlike the present invention, that patent teaches nothing about ESD bonding capillaries, tweezers or anti-static tools and the like and also relies on relatively exotic dopant oxides of metals from Groups Va and VIa of the Periodic System of Elements. U.S. Pat. No. 6,354,479 teaches the fabrication of capillary bonding tips in broad terms but fails to teach either the specific compositions or the specific heat treatment steps or fabrication steps which are disclosed in this specification. In addition, that patent teaches elaborate machining and manufacturing processes which are obviated by the techniques taught in this disclosure.
In the prior art, the electro-conductivity or electro-static dissipativeness of the composite is obtained through the connectivity of the second phase within the base matrix, where the base material is insulative and the second phase is usually a conductive material. By adjusting the appropriate volume percentage of the second phase fillers, the composite can be made electro-conductive or ESD or antistatic. Because the material is a composite, non-uniform dispersions and/or agglomerations of the second phases render so-called hot-spots in the material, which are undesirable for ESD applications.
USPTO Backgrounds
USPTO Backgrounds