required. The dielectric material may be curtain coated or screen applied, or it may be supplied as a dry film or in other sheet form. Typical examples of such circuitized substrates include PCBs and LCCs.

By the term ``circuitized substrate assembly'' as used herein is meant to include at least one and possibly more of such circuitized substrates having at least one and possibly more power cores as defined herein which form integral parts thereof, and at least one electrical component (defined below) mounted on and electrically coupled to the assembly.

By the term ``electrical component'' as used herein is meant components such as semiconductor chips, resistors, capacitors and the like, which are adapted for being positioned on the external conductive surfaces of such substrates as PCBs and chip carriers, and possibly electrically coupled to other components, as well as to each other, using, for example the PCBs or chip carrier's internal and/or external circuitry. The circuitized substrate assemblies formed in accordance with the teachings herein are readily adaptable for having one or more such electrical components positioned thereon and electrically coupled to the internal circuitry thereof, as mentioned, and also having these components coupled to each other if so desired.

By the term ``high speed'' as used herein to define the substrate signal speed capabilities is understood to mean signals within a frequency range of from about 3.0 to about 10.0 Gigabits Per Second (GPS) and possibly even faster. The circuitized substrate assemblies formed herein are capable of operating at such high frequencies if desired.

By the term ``high expansion dielectric material'' as used herein to define the dielectric materials used as part of the invention's power core is meant a material having a coefficient of thermal expansion (CTE) of greater than about 25 parts per million (ppm)/deg. C in the X--Y (in plane) direction and greater than about 70 ppm/deg. C in the Z (out of plane) direction, said directions taken from a cross-section of said material.

By the term ``information handling system'' as used herein is meant to define any instrumentality or aggregate of instrumentalities primarily designed to compute, classify, process, transmit, receive, retrieve, originate, switch, store, display, manifest, measure, detect, record, reproduce, handle or utilize any form of information, intelligence or data for business, scientific, control or other purposes. Examples include personal computers and larger processors such as computer servers and mainframes. Such products are well known in the art and are also known to include PCBs and other forms of circuitized substrates as part thereof, some including several such components depending on the operational requirements thereof.

By the term ``low expansion dielectric material'' as used herein to define the dielectric materials used as part of the invention's power core is meant a material having a CTE within the range of from about 7 to about 20 ppm/deg. C in the X--Y direction and less than about 50 ppm/deg. C in the Z direction, said directions taken from a cross-section of said material.

By the term ``power core'' as used herein is meant a multi-layered structure comprising at least one dielectric layer and at least two conductive layers positioned on opposite sides of the dielectric layer. The materials used to form the power core of the invention are defined herein. One of the conductive layers will function as a power plane while the other conductive layer may function as a ground layer, but may also function in another manner, including as a signal layer. Alternatively, both conductive layers may function as power planes for the substrate. It is understood from the teachings herein that the primary function of the power cores taught herein is to become an integral part of circuitized substrates, particularly an LCC or PCB.

By the term ``thru hole'' as used herein is meant to include three different types of electrically conductive holes formed within a circuitized substrate. As mentioned, it is known in circuitized substrate constructions to provide conductive interconnections between various conductive layers (including power, ground and signal) of the substrate. For some applications, it is desired that electrical connection be made with almost if not all of the conductive layers. In such a case, a thru-hole (which includes a layer or layers of conductive material located on walls of openings of the dielectric material which support same) is typically provided through the entire thickness of the substrate is referred to as a PTH. For other applications, it is often desired to also provide electrical connection between the circuitry on one face of the board to a depth of only one or more of the inner circuit layers. These are referred to as ``blind vias,'' which pass only part way through (into) the substrate. In still another case, such multi-layered substrates often require internal ``vias'' which are located entirely within the structure and covered by external layering, including both dielectric and conductive layers. Such internal ``vias,'' also referred to as ``buried vias,'' are typically formed within a first formed sub-composite, e.g., a power core, which is then bonded to other sub-composites and/or dielectric and/or conductive layers to form the final, thicker multilayered circuitized substrate. Therefore, for purposes of this application, the term ``thru hole'' is meant to include all three types of such electrically conductive openings, each of which includes one or more layers of conductive material located on internal walls of the openings formed within the chosen dielectric material.

As understood from the description herein, a primary object of the present invention is to provide a power core structure readily adapted for use as part of a circuitized substrate such as a LCC or PCB wherein the power core possesses key attributes such as a low CTE, high stiffness and good cracking resistance. The circuitized substrate utilizing such a power core will in turn possess the key attributes of being of relatively lower cost than many known substrates and yet able to meet the high performance obligations demanded in today's environment.

In Figure~\ref{figure_1}, there is shown the initial elements of a structure destined to be a power core in accordance with one embodiment of this invention. This structure includes a first dielectric layer 21 of low expansion material. The preferred material for layer 21 is a low moisture-absorbing thermosetting resin such as epoxy, polyphenylene-ether, bismaleimide triazine or polyimide and, in a preferred embodiment, has an initial thickness of from about 2.95 mils to about 9.84 mils (a mil is understood to represent 1/1000 of an inch). Other low expansion thermosetting resins are possible. This material further includes woven fiberglass cloth as part thereof (the cloth being impregnated with the resin), for added reinforcement, in addition to amorphous spherical silica. Other inorganic particulates than silica may be utilized, including, for example, aluminum oxide, boron nitride, and aluminum nitride, to name a few. The silica (or other inorganic particulate) particles each have a size within the range of about 0.003 mils to about 1.377 mils and, in one embodiment, the silica comprises from about 3 to about 49 percent by weight of the resin material. In this particular embodiment, the fiberglass cloth occupies from about 35 percent to about 55 percent by weight of the resin. Any conventional PCB fiberglass cloth should suffice for use here, with one particular example being sold under the product designation (number) 2116, and available from JPS