Patent Publication Number: US-6221694-B1

Title: Method of making a circuitized substrate with an aperture

Description:
TECHNICAL FIELD 
     The invention pertains generally to circuitized substrates and particularly to chip carriers for integrated circuits. 
     BACKGROUND OF THE INVENTION 
     Integrated circuit devices (hereinafter referred to as chips) having high performance are typically electronically packaged by mounting one or more chips onto a ceramic, e.g., alumina, circuitized substrate (referred to as a chip carrier) and using wire bonds to electrically connect I/O (input/output) contact pads on each chip to corresponding contact pads (and therefore to corresponding fan-out circuitry) on the circuitized chip carrier substrate. Wire bonding is a well known process in the art and further description is not believed necessary. The resulting chip carrier is then typically mounted on a printed circuit board (PCB) and, using circuitry on the PCB, electrically coupled to other such chip carriers and/or other electronic components mounted on the PCB. 
     While ceramic chip carrier structures have proven extremely useful in the electronic packaging field, the use of ceramic as the dielectric material of the substrate does present certain limitations and drawbacks. For example, the speed of propagation of an electrical signal through a conductive wire located on a dielectric layer (or between two dielectric layers for that matter) is proportional to the inverse of the square root of the dielectric constant of the dielectric material layer or layers. As is known, the dielectric constants of most ceramics are relatively large, e.g., the dielectric constant of alumina (the primary constituent of ceramic materials used in these substrates) is relatively high, which results in ceramic chip carriers exhibiting relatively low signal propagation speeds in comparison to substrates of other (e.g., organic) materials, such as fiberglass-reinforced epoxy resin, polytetrafluoroethylene, etc. 
     Utilization of ceramic chip carrier substrates also presents certain I/O constraints. For example, a single-layer ceramic chip carrier substrate includes but a single layer of fan-out circuitry on the upper surface of the ceramic substrate, extending to contact pads around the outer periphery of the substrate. A lead frame having inner leads connected to these peripheral contact pads, is typically used to electrically connect such a ceramic chip carrier to a PCB. As the number of chip I/Os has increased (in response to more recent enhanced design requirements), it has been necessary to increase the wiring density, sometimes to the point where undesirable cross-talk between adjacent wires may occur. Further, it has become increasingly difficult, if not impossible, to form a correspondingly large number of contact pads around the outer periphery of the ceramic substrate. Accordingly, it is understood that single-layer ceramic chip carrier substrates are limited in the ability thereof to accommodate semiconductor chips with significantly increased I/O counts as demanded in many of today&#39;s designs. 
     Various efforts to accommodate chips having relatively large numbers of I/O pads have led to the use of multilayer ceramic chip carrier substrates utilizing what are referred to as “ball grid arrays” (BGAs) in lieu of lead frames. Such multilayer types of ceramic chip carrier substrates differ from single-layer ceramic chip carrier substrates in that these include two or more layers of fan-out circuitry on two or more ceramic layers. Significantly, these layers of fan-out circuitry are electrically interconnected by mechanically drilled holes (called “vias”), which are plated and/or filled with electrically conductive material (e.g., copper). In addition, a certain number of such holes extend from the layers of fan-out circuitry to respective lands on the chip carrier substrates, on which are mounted solder balls (formed in grid arrays, hence the term “ball grid array”). These solder balls are intended to be mechanically and electrically connected to corresponding solderable contact pads on a receiving substrate, e.g., PCB. Unfortunately, the mechanically drilled holes electrically interconnecting the layers of fan-out circuitry have relatively large diameters, requiring the spacing between the fan-out wires to be relatively large. This relatively large spacing between fan-out wires understandably limits the number of chip I/O pads which can be accommodated by such multilayered substrates. 
     Other attempts to package chips having a relatively large number of chip I/O pads have led to the use of multi-tiered cavities in multi-layered ceramic substrates. (As used herein, the term “cavity” denotes a depression in a substrate, not a hole or opening extending entirely through the substrate&#39;s thickness.) When using such a packaging configuration, a chip is mounted face-up (its I/O pads facing upwardly) at the bottom of a multi-tiered cavity. Wire bonds (e.g., using fine gold wire) are extended from the I/O contact pads on the exposed upper surface of the chip to respective contact pads on the exposed upper surfaces of the different layers of the multi-layered ceramic substrate. While this configuration does make it possible to accommodate a relatively large number of chip I/O pads, it unfortunately typically mandates usage of multiple manufacturing set-up operations to accommodate the different tier height for the relatively long wire bonds extending from the chip to the tiers of the multi-tiered cavity. 
     Ceramic chip carrier substrates are also limited in heat dissipation capabilities. For example, in the case of a multilayer ceramic chip carrier having a chip positioned at the bottom of a multi-tiered cavity, heat dissipation is typically achieved by providing a heat sink directly beneath the cavity. This implies, however, that the heat generated by the chip must necessarily be conducted through the ceramic layer at the bottom of the cavity before reaching the heat sink. As a consequence, the rate of heat dissipation is limited. 
     As defined herein, the present invention teaches a method for making a circuitized substrate capable of overcoming the aforementioned drawbacks of other such products. This method is uniquely adaptable for use with many existing manufacturing apparatus (e.g., wire bond and photoimaging equipment) without extensive alteration thereof and can thus be used on a mass production basis to enjoy the benefits thereof. 
     Various methods for making circuitized substrates are described in U.S. Pat. No. 5,022,960 (Takeyama et al), U.S. Pat. No. 5,142,448 (Kober et al), U.S. Pat. No. 5,144,534 (Kober) and U.S. Pat. No. 5,288,542 (Cibulsky et al). In U.S. Pat. No. 5,022,960, a laser beam is used to remove a selected portion of a substrate ( 12 ) which eventually accommodates a semiconductor chip ( 20 ) positioned on a metal layer ( 11 ) also attached to the substrate. In U.S. Pat. No. 5,142,448, there is described the step of compression molding several dielectric layers to form a laminate. Flexibility of certain parts of the board is attained by provision of slots, and a “plug” is located for occupying the defined flexible region. In U.S. Pat. No. 5,144,534, a method of making rigid-flexible circuit boards is described in which a removable plug is used in the PCB during processing and then removed. Finally, in U.S. Pat. No. 5,288,542 (assigned to the same assignees as the present Application), another method is described for making a rigid-flexible circuit board in which a release layer ( 6 ) is used during processing and subsequently removed. 
     In addition to the above, attention is directed to the following patents assigned to the same assignee as the present invention. 
     In U.S. Pat. No. 5,542,175, entitled “Method Of Laminating And Circuitizing Substrates Having Openings Therein”, filed Dec. 20, 1994, there is defined a method of laminating two substrates and circuitizing at least one of these. A plug is provided and shaped to fit within an opening defined in the structure, and then removed following lamination and circuitization. 
     In U.S. Pat. No. 5,798,909, entitled “Organic Chip Carriers For Wire Bond-Type Chips”, filed Feb. 15, 1995, there is defined a chip carrier having a single-tiered cavity within a dual layered (of organic material) substrate and a semiconductor chip located in the cavity. The chip is wire bonded to circuitry on the substrate. The method claimed in the present Application may be used to make a chip carrier of the type defined in U.S. Pat. No. 5,798,909. 
     In U.S. Pat. No. 5,566,448, entitled “Method Of Construction Of Multi-Tiered Cavities Used In Laminate Carriers”, filed Jun. 26, 1995, there is defined a method of forming a chip module wherein a rigid cap and substrate are used, the cap and substrate laminated together with bond pads connected to circuitry disposed in a bottomed cavity of the cap. Following cap circuitization, part of the cap (that over the cavity) is removed and a semiconductor chip coupled to the circuitry. 
     In U.S. Pat. No. 5,599,747, entitled “Method Of Making A Circuitized Substrate With An Aperture”, filed Jun. 27, 1995, there is defined a method of providing a dielectric member and partially routing this member to define a temporary support portion therein. Metallization and circuitization then occur, following which the temporary support portion is removed. This temporary support thus assures effective support for the photoresist used a part of the circuitization process. Thus, the photoresist is capable of being applied in sheetlike form for spanning the relatively small openings of the dielectric without sagging, bowing, etc., which may adversely impact subsequent processing steps. 
     The teachings of U.S. Pat. Nos. 5,542,175, 5,798,909, 5,566,448 and 5,599,747 are hereby incorporated herein by reference. 
     As defined herein, the present invention defines a method that results in a circuitized substrate capable of: (1) exhibiting relatively high electrical signal propagation speeds; (2) accommodating relatively high I/O chips; (3) exhibiting relatively short “time of flight” electrical signal speeds; and (4) exhibiting a relatively high rate of heat dissipation. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is, therefore, an object of this invention to provide a method of making a circuitized substrate capable of being used as a chip carrier assembly which can be performed in a facile and relatively inexpensive manner in comparison to existing carrier manufacturing processes. 
     It is a more particular object of the invention to provide such a process which is readily adaptable to existing manufacturing equipment without extensive modification thereof. 
     In accordance with one aspect of this invention, there is defined a method of making a circuitized substrate, the method comprising the steps of providing an electrically insulative base member having first and second surfaces and removing a preselected portion of the base member to form at least one aperture having at least one sidewall and extending entirely through the base member. This aperture may serve to accommodate a chip. The method, as defined, further includes applying a first electrically conductive layer onto the first and second surfaces of the base member, including on at least one sidewall of the aperture, and then applying a second electrically conductive layer onto the first electrically conductive layer to substantially cover the first conductive layer. The method still further includes applying a photoimaging material onto the second conductive layer, then exposing and developing selected portions of the photoimaging material to define a pattern within the photoimaging material on the second conductive layer. The method even further includes circuitizing the second conductive layer and then removing the photoimaging material from the second conductive layer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1-14 represent the various steps of making a circuitized substrate in accordance with a preferred embodiment of the invention; and 
     FIGS. 15 and 16 represent additional steps to provide a chip carrier assembly in accordance with a preferred embodiment of the invention. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the above-described drawings. 
     The invention defines a method of making a circuitized substrate (and the resulting chip carrier) in which the chip carrier is particularly designed to accommodate wire bond-type chips. In addition to other advantageous features, the carrier produced in accordance with the teachings herein is capable of: (1) exhibiting relatively high electrical signal propagation speeds; (2) accommodating relatively high I/O chips; (3) avoiding the need for multiple manufacturing set-up operations heretofore associated with multi-tiered wire bond packages (as well as achieving a relatively short “time of flight” for electrical signals propagating through the wire bonds); and (4) assuring a relatively high rate of heat dissipation. In particular, the chip carrier produced in accordance with the preferred method taught herein achieves relatively high electrical propagation speeds because it employs organic materials, such as fiberglass-reinforced epoxy resins (in the trade also referred to as “FR4”), polytetrafluoroethylene (e.g., Teflon), etc. in lieu of ceramic materials. (Teflon is a trademark of E. I. Dupont deNemours &amp; Company.) The resulting chip carrier also accommodates relatively high I/O count chips because it uses at least one organic photoimageable dielectric layer in which photo-vias may be formed to electrically interconnect two (or more) layers of fan-out circuitry. The resulting chip carrier achieves a relatively short “time of flight” for electrical signals propagating through the wire bonds. The invention may further provide enhanced heat sinking for such a structure through the attachment of a solid heat conductor (e.g., copper sheet) to one side of the substrate and placement of the chip (or chips) in thermal contact therewith. 
     In FIG. 1, there is shown an electrically insulative base member  13  which may be used in the present invention to produce a chip carrier product (shown in FIG.  16  and described below). It is understood that the invention is not limited to the particular configuration shown in FIG. 1, as others are readily possible. Base member  13  includes first and second conductive layers  1  and  3 , which sandwich therebetween, first and second dielectric layers  15  and  17  and conductive plane  19 . In a preferred embodiment, each of the two conductive layers is comprised of copper or a well known conductive material having a thickness from about 0.25 mils (0.0025 inches) to about 1.5 mils with the thickness of each preferably being about 0.75 mils. Each of the two dielectric layers is comprised of fiberglass reinforced epoxy resin (FR4) and each possess a thickness of from about 2 mils to about 20 mils. Thicknesses less than about 2 mils for this particular material may be undesirable because the resulting structure may be flimsy and difficult to handle during subsequent manufacturing processes. Thicknesses greater than about 20 mils may be undesirable because such thick dielectric layers, in addition to requiring relatively large conductor line widths and thicknesses, also may prevent optimum package electrical performance. 
     Sandwiched between dielectric layers  15  and  17  is the conductive plane  19 , preferably of copper or other well-known conductive material and possessing a thickness of preferably within the range of about 0.125 mils to about 2.5 mils. The thicknesses for plane  19  of less than about 0.125 mils may prove undesirable should the resulting structure by subjected to relatively high temperatures. Additionally, thicknesses greater than about 2.5 mils may prove undesirable because of the additional time necessary to form such layers using conventional plating techniques and associated difficulties with line width control. The resulting structure shown in FIG. 1 thus preferably possesses a thickness within the range of about 4.7 mils to about 44 mils. More preferably, a thickness of about 24.8 mils is used. 
     Conductive layers  1  and  3  and dielectric layers  15  and  17  are bonded to the conductive plane  19  using a lamination process, such a process known in the art and further description is not believed necessary. Base member  13  is thus shown to include at least two surfaces, a first surface  21 , and a second surface  23 . 
     Although two external conductive layers and two dielectric layers are shown for base member  13 , it is understood that the invention is not limited thereto. Specifically, it is only necessary to provide one such conductive layer and one such dielectric layer while still attaining the advantageous results taught herein. At least two layers of each are used when it is desired to incorporate an internal conductive plane (e.g., power, ground or signal) as part of the final structure. Understandably, several conductive dielectric layers and corresponding internal conductive planes may be utilized, depending on operational requirements for the finished product. 
     In FIG. 2, opening  5  having an internal wall  9  is formed substantially through base member  13 . Although only one opening is shown, it is understood that multiple openings may be formed, depending on the ultimate electrical requirements of the circuitized substrate. Opening  5 , preferably a hole, may be formed by mechanical drilling, although other hole forming techniques such as punching and laser drilling can be used. Opening  5  is formed with a diameter of about 6 mils to about 14 mils, preferably about 8 mils. 
     In FIG. 3 ( a plan view of the base member  13  of FIG.  2 ), a substantially rectangular shaped slot  25  is formed within member  13 . As understood, this slot serves to substantially define the ultimate boundaries of an opening (described below) to be provided in member  13  such that the member can accommodate a chip positioned within this opening and electrically coupled to circuitry (described below) of member  13 . As seen in FIG. 3, this slot  25  defines a substantially rectangular portion  27  within base member  13  which will subsequently be removed. 
     Although a substantially rectangular shape is shown for portion  27  in the plan view of FIG. 3, other shapes are readily possible, depending on the ultimate chip configuration and the method of coupling this chip to base member  13 . In one example, the resulting aperture ( 51 , FIGS. 8 and 9) left after removal of portion  27  possessed width and length dimensions each within the range of about 500 to about 700 mils, with slot  25  possessing an average width (“W” in FIG. 3) of about 60 mils. 
     The preferred means for providing slot  25  is to use a routing process using equipment known in the art, further description thus not believed necessary. In one embodiment, the portion  27  to be removed possessed a width (“W 2 ” in FIG. 3) of only about 40 mils. 
     In FIG. 4, a cross-sectional view along plane  4 — 4  of the base member  13  of FIG. 3 is shown. Slot  25 , formed by routing portion  27 , in base member  13  is also shown. 
     In FIG. 5, base member  13  is illustrated with portion  27  removed, leaving an aperture  51  having sidewalls  7  defined by previously routed slots  25 . FIG. 6 is a cross-sectional view along plane  6 — 6  of the base member  13  of FIG. 5, also illustrating aperture  51  with sidewalls  7 . 
     In the next step (FIG.  7 ), it is preferred to provide a first electrically conductive layer  29  on the surfaces  21  and  23  of base member  13 , on the sidewalls  7  of opening  51  and on internal wall  9  of opening  5 . As seen in FIG. 7, this conductive layer  29  substantially covers the entire thickness of base member  13  in aperture  51  and in hole  5 . The preferred material for the conductive layer  29  is a palladium-tin seed. Understandably, the described seed layer serves to enhance subsequent positioning of the invention&#39;s conductive circuitry (described below). The seed layer is comprised of particles of palladium-tin and is substantially continuous; however, space between particles comprising this layer may exist. 
     In FIG. 8, a second electrically conductive layer  30  is applied onto substantially the entire first electrically conductive layer  29  of base member  13 . The second electrically conductive layer  30  covers the first electrically conductive layer on the sidewalls  7  of aperture  51  and the internal wall  9  of opening  5 . The second electrically conductive layer of FIG. 8 may be applied by plating or by any other suitable known technique, preferably by electroless plating. The second electrically conductive layer  30  may be comprised of nickel, aluminum, or copper, but is preferably copper. The thickness of the second electrically conductive layer may be from about 0.3 mils to about 1.5 mils, preferably from about 0.9 mils to about 1.2 mils. 
     An important aspect of this invention includes the forming of at least one filled electrically conductive opening  5  adjacent the opening formed by routing. This allows the circuitized substrate with many multiple layers to easily communicate through the electrically conductive opening. As previously described, opening  5  can have a diameter, before application of the first electrically conductive layer on the internal wall, of about 6 mils to about 14 mils. After application of the second electrically conductive layer the diameter is reduced to about 5 mils from about 13 mils, and can be as small as about 4 mils to about 12 mils. Since the subsequently described circuitization technique involves etching, there is a need to protect the second conductive layer on the internal wall of the opening. This cannot be done in such a small hole using conventional photolithographic techniques. It is therefore necessary to substantially fill the openings with a permanent material to protect the internal wall of the opening. FIG. 9 illustrates the resultant structure after substantially filling opening  5  with a permanent material  11 . The opening is filled such that the external surfaces of the filled opening are substantially planar with the second conductive layer  30  on the base member  13 , yielding a planar surface for subsequent photolithographic processing (described below). Filling opening  5  with material  11  is performed using a material which has a coefficient of thermal expansion, after curing, closely matched to the coefficient of thermal expansion of the printed circuit board substrate. The fill material can be either conductive or non-conductive, and is compatible with all wet processes (metal plating, etching, photo-processing, etc.). Preferred fill materials are those containing particulates or fillers in a resin binder. The binder can be any of the epoxy/resin systems used in printed circuit board manufacture. The particulate fill can be carbon, silica or metal powders. In one example of the invention, a fill material of approximately 75% to about 90% weight percent of copper particulates in an epoxy resin binder was used. 
     As mentioned above, a key attribute of the present invention is its adaptability to many existing technologies, e.g., those used in mass production, by allowing the invention as defined herein to benefit from the several advantages thereof. One particular process involves what is referred to as a liquid resist operation in which the photoresists used are applied in liquid form. Such an operation may be used in the present invention, as defined immediately below. 
     In FIG. 10, a layer of such a photoimaging (photoresist) material  31  is shown as being applied on the respective surfaces of member  13 . In one example, the layer of photoresist possessed a thickness of from about 0.6 mils to about 2.0 mils. A preferred material is a negative-acting photoresist, various examples being known in the art, including Photoresist 3120 available from the E. I. duPont deNemours &amp; Company under this product name. Negative-acting photoresists, when applied and exposed through a suitable photomask, undergo a physical and chemical change in the exposed areas that render these areas insoluble to the subsequent developing solution which is to be applied thereto. Following exposure, the resist-coated base member  13  is immersed in developing solution (e.g., sodium carbonate or propylene carbonate), which allows the unexposed areas to be removed without excessive impact on the hardened, exposed area. Baking or other processes may be used to further harden the remaining, exposed portions, if desired. 
     Significantly, it can be seen that the entire sidewall of aperture  51  covered with the second conductive layer and protected by photoimaging layer  31  will provide (after removal of the photoresist) a complete and uninterrupted conductive layer in aperture  51 . Previous techniques to accomplish this required multiple steps to metallize the cavity whereas in the present invention it can be accomplished in only one metallizing step. This is enabled by protection of the entire aperture sidewall with the photoimaging layer during subsequently described etching steps. 
     In FIG. 11, base member  13  is shown following the above exposure and removal (developing) operations. As such, only portions of photoresist layer  31  remain. These portions are represented by the numeral  33 . It is understood that the removed portions of the photoresist in turn result in openings  35  which, in turn, expose preselected areas on the respective surfaces on which circuitization is to eventually occur. Thus a predetermined pattern on both surfaces is provided. 
     Although a negative-acting photoresist procedure has been described, the invention is not limited thereto. It is also possible to instead use positive-acting photoresists in which the exposed areas thereof under the photomask, when immersed in the developing solution, are removed. It is thus seen that the present invention is adaptable to more than one accepted technology. 
     In FIG. 12, member  13  has been subjected to a metallization process in which copper or similarly conductive metal is removed in the exposed portions (e.g., site  35 ) remaining following photoresist development. In a preferred embodiment, the exposed portions are removed by wet etching. Wet etching can be performed by known techniques in the art, preferably using cupric chloride or ferric chloride. Wet etching is well known in the art and further description is not believed necessary. Wet etching of the exposed areas  35  substantially removes the exposed second electrically conductive layer  30 , the first electrically conductive layer  29  directly under the exposed second electrically conductive layer  30 , and conductive layers  1  and  3 , also directly under the exposed second electrically conductive layer  30 , leaving exposed portions of the first dielectric layer  15  and the second dielectric layer  17 . Non-exposed portions  33  define a circuitized pattern on first dielectric layer  15  and the second dielectric layer  17 . 
     In FIG. 13, portions  33  of photoresist layer  31  are removed, preferably by stripping the photoresist with a suitable solvent known in the art, such as propylene carbonate, sodium carbonate, or sodium hydroxide. Other removal techniques such as laser ablation and mechanical removal or combinations thereof, may also be employed to remove the photoresist layer. In one example, the exposed areas of the second electrically conductive layer  30  on the surfaces of base member  13  serve as one or more contact pad areas  37 . In addition to the exposed contact pad areas, it is also possible to expose one or more areas  39  on the surface of the second conductive layer  30  around opening  5 , depending on operational requirements for the final product. This area  39  is a land segment and may serve to interconnect upper and lower layers of circuitry and also internal conductive planes such as plane  19 , if desired. The exposed areas of the second electrically conductive layer on sidewalls  7  of aperture  51  serve to substantially cover the entire sidewall. 
     It is understood that the exposed areas illustrated in FIG. 13 are shown for illustration purposes only and do not limit the invention to those as shown. Specifically, in one example of the invention, a total of about 600 pad sites  37  were provided, in addition to about 200 through-hole sites  38 . 
     At this point, it may also be desirable to selectively apply precious metal (e.g., gold, nickel or combinations thereof) material to various parts of the respective circuit layers formed on the upper and lower surfaces of member  13  and on the sidewall  7  of aperture  51 . Such application is preferably performed by a plating process, several types of which are known in the art. Further description is not believed necessary. Such additional plating is particularly desired for those surfaces of the circuitry designed to receive the highly conductive, fine wires which may eventually couple a chip (described below) to this circuitry. In FIG. 14, the layer of nickel  39  is shown coated with a layer of gold  40  to form conductive members  41 . 
     In the event that it is desired to provide a heat sinking and/or stiffening member, such a member, represented by the numeral  61  in FIG. 15, may be simply bonded to the bottom surface of member  13 . In one embodiment, this member  61  was comprised of a 14 mil thick copper sheet which was secured to member  13  using an epoxy-based adhesive, represented by the numeral  63 . The heat sink and/or stiffener  61  can be directly attached to the lower surface of dielectric layer  17  or the upper surface of dielectric surface  15  in the case where either lower surface  17  or upper surface  15  are without circuitry. 
     The member  13  in FIG. 15 is now ready to receive a chip, such as shown in FIG. 16 (the chip represented by the numeral  71 ). Preferably, chip  71  is bonded to the heat sinking and/or stiffening member  61  using a second adhesive  73 , a preferred adhesive being of the thermally conducting type which, in a preferred embodiment, is a commercially available silver-impregnated epoxy sold under the trade designation Ablebond 9651-L by Ablestick Corporation. Chip  71  is thus thermally coupled to member  61  to assure enhance heat removal from the final package structure as produced in accordance with the teachings herein. Bond wires  75  may now be provided to electrically couple contact sites  77  on the chip&#39;s upper surface to corresponding respective ones of the conductive members  41  which form the upper layer of circuitry for member  13 . As seen in FIG. 16, these wires extend from the chip outwardly to this circuitry. The wires  75  are preferably provided using a wire bond process, well known in the art. Wires  75  can be comprised of gold or aluminum, preferably gold. 
     If desired, an encapsulant material (not shown) may be provided over the wires and associated pads to provide protection from the occasionally harsh environment in which the product produced by the invention may be exposed. One suitable encapsulant is an epoxy molding material sold by the Dexter-Hysol Company under the product name Hysol 4450. 
     FIG. 16 thus illustrates a chip carrier structure  79  which is now capable of being electrically coupled to additional circuit structures (e.g., printed circuit boards) which form part of the larger information handling system (computer) for which the product produced by the invention is particularly suited. One such form of coupling may include solder ball attach in which solder balls (e.g., 90:10 lead:tin) are used to couple respective parts of member  13 &#39;s circuitry to the circuitry on one/more of such additional circuit structures. Other techniques are of course readily possible for achieving this end. 
     Thus there have been shown and described a facile method for producing a circuitized substrate for use as part of a chip carrier assembly which is capable of being readily performed using many established processes of the art. The invention thus represents a relatively inexpensive yet effective process for producing chip carrier structures on a mass scale. While the invention has been described with respect to organic dielectric materials, this is not meant to limit the invention in that even inorganic (e.g., ceramic) may be utilized to provide the dielectric function. As stated above, it is also readily possible to utilize alternative procedures (e.g., additive circuitization) which are also known in the art, to accomplish the invention. 
     While there have been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.