Abstract:
A through hole, and associated method of formation, through a layered structure that includes one or more layers having photoimageable dielectric (PID) material. The method forms a via within each such layer in isolation and then stacks the layers in a way that registers the vias over one another such that the through hole is formed as the sequentially registered vias. A sticker layer of the layered structure includes a cylindrical volume, an annular volume circumscribing the cylindrical volume, and a remaining volume surrounding the annular volume. The sticker layer preferentially includes a power plane of continuous metalization having a hole, wherein a perimeter of the hole surrounds the fully cured volume and circumscribes a portion of the remaining volume. During processing of the sticker layer, the sticker layer is photolithographically masked and exposed to ultraviolet radiation in a manner that leaves the cylindrical volume uncured, the annular volume fully cured, and the remaining volume partially cured. Then the PID material within the cylindrical volume is chemically developed away so as to leave a via in the sticker layer. During the stacking of the layers, the sticker layer is sandwiched between two dielectric layers. Subsequent pressurization of the stack causes the two dielectric layers to adhesively bond with the layer. During such pressurization, the fully cured annular volume prevents liquified and partially cured PID material in the remaining volume from flowing into the via of the layer.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Technical Field  
           [0002]    The present invention relates to a method of forming a through hole in a layered structure that includes a layer having a photoimageable dielectric material.  
           [0003]    2. Related Art  
           [0004]    An electrical structure, such as a printed circuit board, typically includes a stack of cores. A core is a dielectric layer with metalization on either side. Such an electrical structure may include cores, such as 2 to 15 cores, laminated together with a layer of dielectric material between each pair of cores. Following lamination, a though hole may be formed through the thickness of the overall structure, such as by mechanical drilling or laser ablation, and then plated with metal to facilitate electrical coupling between various layers of the structure. Alternatively, the through hole may be formed incrementally by forming a via in a layer after the layer has been laminated onto the stack, such that the via thus formed is properly registered over the corresponding via in the preceding layer of the stack. Thus, the through hole may formed in either in one step or in a sequence of steps.  
           [0005]    Drilling a through hole through a layered structure, such as by mechanical or laser drilling, is a very expensive step of the overall process and is often the most costly step. Moreover, it is not unusual for some of such drilled holes to generate a defect in the structure that necessitates discarding the structure, resulting in a yield loss coupled with loss of processing time. For example, the drilling may cause an unwanted pinhole or crack to form such that subsequent metallic plating of the structure results in plating of the pinhole which becomes a source of unwanted electrical shorting between conductive portions of the structure. Even greater costs may result from using the sequential method because a yield loss will occur at each step in which a via is formed with the cumulative cost growing nonlinearly as more layers are added.  
           [0006]    A less costly method is needed to form a through hole in a layered dielectric structure.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention provides a method for forming an electronic structure, comprising the steps of:  
           [0008]    providing a layer that includes: a cylindrical volume of a photoimageable dielectric (PID) material, an annular volume of the PID material circumscribing the cylindrical volume, and a remaining volume of the PID material circumscribing the annular volume;  
           [0009]    photolithograhically exposing the layer to radiation;  
           [0010]    fully curing the annular volume by said radiation;  
           [0011]    partially curing the remaining volume by said radiation; and  
           [0012]    preventing curing of the cylindrical volume, wherein the PID material in the cylindrical volume remains uncured.  
           [0013]    The present invention provides a method for forming an electronic structure having a through hole, comprising the steps of:  
           [0014]    forming a layer that includes a via and an internal power plane having a hole therethrough, wherein a fully cured volume of a photoimageable dielectric (PID) material circumscribes the via, wherein a partially cured remaining volume of the PID material circumscribes the fully cured volume, and wherein a perimeter of the hole in the power plane surrounds the fully cured volume and circumscribes a portion of the remaining volume;  
           [0015]    forming a first dielectric layer having a first via, wherein a cross-sectional area and shape of the first via is about the same as a cross-sectional area and shape of the via;  
           [0016]    forming a second dielectric layer having a second via, wherein a cross-sectional area and shape of the second via is about the same as the cross-sectional area and shape of the via;  
           [0017]    forming a layered stack, wherein the layer is nonadhesively sandwiched between the first dielectric layer and the second dielectric layer, and wherein the via is registered between the first via and the second via; and  
           [0018]    fully curing the remaining volume, wherein the PID material of the partially cured volume is prevented by the fully cured volume from entering the via, wherein the layer becomes adhesively sandwiched between the first dielectric layer and the second dielectric layer, and wherein the electronic structure is formed such that the through hole comprises the first via, the via, and the second via.  
           [0019]    The present invention provides a layer, comprising:  
           [0020]    a cylindrical volume;  
           [0021]    a fully cured annular volume of a photoimageable dielectric (PID) material circumscribing the cylindrical volume; and  
           [0022]    a partially cured remaining volume of the PID material circumscribing the annular volume.  
           [0023]    The present invention provides an electronic structure, comprising:  
           [0024]    a layer that includes: a via, a fully cured volume of a photoimageable dielectric (PID) material circumscribing the via, and a partially cured remaining volume of the PID material circumscribing the fully cured volume; and  
           [0025]    a power plane between a first surface of the layer and a second surface of the layer, wherein the power plane includes a hole therethrough, wherein a perimeter of the hole in the power plane surrounds the fully cured volume and circumscribes a portion of the remaining volume.  
           [0026]    The present invention provides a method forming an electronic structure, comprising the steps of:  
           [0027]    providing a layer that includes:  
           [0028]    a cylindrical volume of a photoimageable dielectric (PID) material,  
           [0029]    a first annular volume of the PID material circumscribing the cylindrical volume,  
           [0030]    a second annular volume of the PID material circumscribing the first annular volume,  
           [0031]    a remaining volume of the PID material circumscribing the second annular volume, and  
           [0032]    a power plane between a first surface of the layer and a second surface of the layer, wherein the power plane includes a hole therethrough, and wherein a perimeter of the hole in the power plane circumscribes the second annular volume;  
           [0033]    photolithograhically exposing the layer to radiation;  
           [0034]    partially curing the first annular volume by said radiation;  
           [0035]    fully curing the second annular volume by said radiation;  
           [0036]    partially curing the remaining volume by said radiation; and  
           [0037]    preventing curing of the cylindrical volume.  
           [0038]    The present invention provides an electronic structure, comprising:  
           [0039]    a layer that includes: a via, a first partially cured volume of a photoimageable dielectric (PID) material circumscribing the via, a fully cured volume of the PID material circumscribing the first partially cured volume, and a second partially cured remaining volume of the PID material circumscribing the fully cured volume; and  
           [0040]    a power plane between a first surface of the layer and a second surface of the layer, wherein the power plane includes a hole therethrough, wherein a perimeter of the hole in the power plane circumscribes the fully cured volume.  
           [0041]    The present invention advantageously forms a through hole in a layered structure having a layer that includes PID material, by a method which forms each layer and its via in isolation from the other layers, wherein a defect generated by formation of the via may result in discarding the layer without discarding the layered structure.  
           [0042]    The present invention has the advantage of providing a fully cured annulus around a via within a layer of PID material, so that partially cured PID material cannot move into the via when the layered structure that includes the layer is subject to pressurization and/or elevated temperature.  
           [0043]    The present invention has the advantage of forming photovias, which is a less expensive process than that of forming laser-drilled vias.  
           [0044]    The preceding advantages facilitate lower fabrication costs, reduced cycle time, and improved quality assurance. Thus, the present invention has the overall advantage of providing an inexpensive method of forming a through hole in a layered dielectric structure having PID material in at least one layer. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0045]    [0045]FIG. 1 depicts a front cross-sectional view of a layer that includes photoimageable dielectric (PID) material, in accordance with preferred embodiments of the present invention.  
         [0046]    [0046]FIG. 2 depicts FIG. 1 with the layer divided into distinct volumes, including a cylindrical volume.  
         [0047]    [0047]FIG. 2A depicts the axial structure of the cylindrical volume of FIG. 2.  
         [0048]    [0048]FIG. 3 depicts the layer of FIG. 2 showing a first photolithographic masking and exposure, in accordance with a first preferred embodiment of the present invention.  
         [0049]    [0049]FIG. 4 depicts the layer of FIG. 2 showing a second photolithographic masking and exposure, in accordance with the first preferred embodiment of the present invention.  
         [0050]    [0050]FIG. 5 depicts the layer of FIG. 2 showing a photolithographic masking and exposure, in accordance with a second preferred embodiment of the present invention.  
         [0051]    [0051]FIG. 6 depicts the layer of FIG. 2 after the photolithographic masking and exposure shown in FIGS. 3 and 4, or in FIG. 5.  
         [0052]    [0052]FIG. 7 depicts FIG. 2 with a modification of the volume structure and showing a photolithographic masking and exposure, in accordance with a third preferred embodiment of the present invention.  
         [0053]    [0053]FIG. 8 depicts the layer of FIG. 7 after the photolithographic masking and exposure shown in FIG. 7.  
         [0054]    [0054]FIG. 9 depicts FIG. 2 with a modification of the volume structure and showing a photolithographic masking and exposure, in accordance with a fourth preferred embodiment of the present invention.  
         [0055]    [0055]FIG. 10 depicts the layer of FIG. 9 after the photolithographic masking and exposure shown in FIG. 9.  
         [0056]    [0056]FIG. 11 depicts FIG. 6 after the photolithographically masked and exposed layer of FIG. 6 is sandwiched between two 2S/1P layers to form a layered stack.  
         [0057]    [0057]FIG. 12 depicts FIG. 11 after additional layers having PID material are added to opposite sides of the layered stack. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0058]    [0058]FIG. 1 illustrates a front cross-sectional view of a layer  10  that includes photoimageable dielectric (PID) material  20 , in accordance with preferred embodiments the present invention. Any PID material known to one skilled in the art may be used in the resent invention, such as improved photoimagable cationically polymerizable epoxy based coating materials whose compositions are described in U.S. Pat. No. 5,026,624 (Day et al., Jun. 25, 1991) and U.S. Pat. No. 5,300,402 (Card, Jr. et al., Apr. 5, 1994). The PID material  20 , if uncured, flows when subject to pressurization and/or elevated temperature. The propensity of the PID material  20  to flow diminishes as it undergoes a curing process. For this invention, a given specimen of PID material may exist in one of the following states of cure: uncured, partially cured, and fully cured. A specimen of PID material is “uncured” if the specimen has experienced no curing or negligible curing. A specimen of PID material is “partially cured” if the specimen has been cured to an extent that it will flow or deform, so as to nonadhesively couple with a contacting dielectric layer when subject to atmospheric pressure at ambient temperature, and adhesively bond with the contacting dielectric layer under subsequent pressurization and/or elevated temperature. A dielectric material that has been partially cured in the preceding manner is known to one skilled in the art as B-staged material. A specimen of PID material is “fully cured” if the specimen has been cured to such an extent that the PID material will not substantially flow, or substantially deform, if subject to subsequent pressurization and/or elevated temperature. The magnitude of pressurization and/or elevated temperature needed to effectuate adhesive bonding depends on, inter alia, such factors as: the degree of partial curing achieved prior to the pressurization and/or elevated temperature, the particular PID material that has been partially cured, and the roughness of the surface to which the partially cured PID material will be subsequently bonded. The elevated temperature(s) may be achieved in various ways such as with multiple heating cycles. Pressures in a range of about 100 psi to about 700 psi, coupled with elevated temperatures in a range of about 80° C. to about 250° C., have been found to be effective for full curing the B-staged materials.  
         [0059]    For the present invention, partial curing is accomplished by limited exposure of the PID material to radiation, such as ultraviolet radiation, and may be improved by accompanying and/or following the radiation exposure with heating such as at a temperature in a range of about 100° C. to about 150° C. for a period of time between about 3 minutes and about 15 minutes. Also for the present invention, full curing is accomplished either by exposure to radiation such as ultraviolet radiation of sufficient intensity and time to effectuate full curing, or by subjecting partially cured PID material to a combination of pressurization and temperature elevation. Partial curing and full curing by exposure of the PID material to radiation is differentiated by the amount of radiant energy absorbed by the PID material, which is determined by such variables as the energy flux F (in such units as milliwatts/cm 2 ) of the radiation passing through the PID material and the total time T of exposure to the radiation, or more particularly on the dose FT. The range of FT that distinguishes partial curing from full curing depends on the specific PID material used inasmuch as each different PID material has its own characteristic chemical response to the incident radiation. One skilled in the art may determine practical ranges of FT for effectuating either full curing or partial curing, without undue experimentation, by varying FT through control of F and T for individually cured PID samples, followed by testing to determine whether the cured PID samples undergo liquification and flow upon subsequent pressurization and exposure to elevated temperatures.  
         [0060]    The layer  10  preferably includes a power plane  30  having a hole  32  therethrough. A power plane is a layer of metal, such as copper, having one or more holes. The hole  32  is bounded by its perimeter, which is the cylindrical surface  34  of the power plane  30 . The hole  32  is filled with the PID material  20 . Thus, the PID material  20  is continuously distributed from the upper portion  12  to the lower portion  13  of the layer  10 . While FIG. 1 shows the power plane  30  as approximately equidistant from a surface  15  and a surface  16  of the layer  10 , the power plane  30  may be located at any distance from the surface  15  and the surface  16 . The power plane  30  is required for some embodiments and is optional for other embodiments. Unless otherwise stated, the power plane  30  is assumed to be present.  
         [0061]    An important characteristic of PID material is that negatively acting PID material, if not exposed to the radiation that it is sensitive to such as ultraviolet radiation, may be chemically developed away by any method known to one of ordinary skill in the art. Note that if the PID material is positively acting, the PID material actually exposed to the radiation would be developed away, which would necessitate an-inversion of the masking schemes described herein in which portions of a given mask shown and described herein as opaque would be instead transparent and portions of the given mask shown and described herein as transparent would be instead opaque. The specific method and the chemicals that may be used for developing away the PID material, including wet chemicals and dry chemicals, depends on the chemical composition of the PID material. In contrast, radiation exposure of PID material causes chemical cross-linking reactions in the PID material, which renders the PID material resistant to being chemically washed away by a developer solution. Thus, photovias may be formed in the layer  10  by photolithographic masking schemes that prevent the radiation from reaching those volumes of the layer  10  in which photovias are to be formed, but which allow radiation to interact with the other volumetric portions of the layer  10  which may be subsequently exposed to the developer solution. The present invention includes, inter alia, four such photolithographic embodiments, which are described infra herein.  
         [0062]    [0062]FIG. 2 illustrates FIG. 1, wherein the space of the PID material  20  is divided into distinct volumes: a cylindrical volume  70 , an annular volume  60  circumscribing the cylindrical volume  70 , and a remaining volume  50  circumscribing the annular volume  60 . Definitionally, circumscribing includes surrounding and contacting. Also definitionally, a cylindrical volume is a three-dimensional volumetric shape having an axis therethrough such that a cross section of the cylindrical volume has a shape and area that are each invariant to position along the axis. FIG. 2A illustrates the axial structure of the cylindrical volume  70 , wherein the cross section  77  of the cylindrical volume  70  is invariant to a position P of the cross section  77  in the direction  75  along the axis  78  of the cylindrical volume  70 . The direction  75  also appears in FIG. 2 to clarify the orientation of the cylindrical volume  70  in FIG. 2A relative to the layer  10  in FIG. 2. While the shape of the cross section, such as the cross section  77  of FIG. 2A, of a cylindrical volume may be that of a circle, the shape may also be that of, inter alia, an ellipse or a square.  
         [0063]    Returning to FIG. 2, the remaining volume  50  includes the portion  51 , which is a volume between the power plane  30  and the annular volume  60 . As the portion  51  of the remaining volume  50  diminishes in size and approaches a null (i.e., zero) volume, the portion  51  disappears such that the power plane  30  approaches circumscribing the annular volume  60 . This limiting case is an optional form of the first and second embodiments of the present invention, whereas this limiting case is required for the third and fourth embodiments of the present invention.  
         [0064]    The first preferred embodiment of the present invention utilizes two masking schemes in succession. FIG. 3 illustrates FIG. 2 showing a first photolithographic masking and exposure, in accordance with the first preferred embodiment of the present invention. In FIG. 3, a radiation source  120  directs radiation  130 , such as ultraviolet radiation, of energy flux F 1  for a time duration T 1  through a mask  100  located over the surface  15  of the layer  10  and then through the layer  10 . In relation to the radiation  130 , the mask  100  includes an opaque portion  102  over the cylindrical volume  70 , a transparent portion  104  over the annular volume  60 , and an opaque portion  106  over the remaining volume  50 . Definitionally, a material is opaque or transparent if opaque or transparent, respectively, to an incident radiation. Thus, the opaque portion  102  and the transparent portion  104  are respectively opaque and transparent to the radiation  130 . The radiation source  140  directs radiation  150 , such as ultraviolet radiation, of energy flux F 2  for a time duration T 2  through a mask  110  located over the surface  16  of the layer  10  and then through the layer  10 . In relation to the radiation  150 , the mask  110  includes an opaque portion  112  over the cylindrical volume  70 , a transparent portion  114  over the annular volume  60 , and an opaque portion  116  over the remaining volume  50 . F 1  T 1  and F 2  T 2  are preferentially about equal and should not differ by more than about 10%. The radiation source  120  may be operated before, after, or concurrent with the radiation source  140 . Alternatively, either the radiation source  120  or the radiation source  140  may be omitted since the annular volume  60  can be accessed by either the radiation  130  or the radiation  150 , regardless of whether the power plane  30  is present or absent. The energy absorbed by the annular volume  60  from the radiation  130  and/or the radiation  150  should be high enough to fully cure the annular volume  60 , or high enough to initiate a full cure of the annular volume  60  followed by heating to effectuate the full cure of the annular volume  60  if the radiation is accompanied with, or followed by, heating. This necessitates that F 1 T 1 +F 2 T 2  be of a sufficiently high magnitude that can be determined without undue experimentation, as explained supra.  
         [0065]    [0065]FIG. 4 illustrates FIG. 2 showing a second photolithographic masking and exposure, in accordance with the first preferred embodiment. In FIG. 4, the radiation source  120  directs radiation  130 , such as ultraviolet radiation, of energy flux F 3  for a time duration T 3  through a mask  200  located over the surface  15  of the layer  10  and then through the layer  10 . In relation to the radiation  130 , the mask  100  includes an opaque portion  202  over the cylindrical volume  70 , and a transparent portion  204  over the annular volume  60  and over the remaining volume  50 .  
         [0066]    With the power plane  30  present, the radiation  130  cannot access a portion of the remaining volume  50  situated between the power plane  30  and the surface  16  of the layer  10 , so that the radiation source  140  must be used. The radiation source  140  directs radiation  150  of energy flux F 4  for a time duration T 4 , such as ultraviolet radiation, through a mask  210  located over the surface  16  of the layer  10  and then through the layer  10 . In relation to the radiation  150 , the mask  210  includes an opaque portion  212  over the cylindrical volume  70 , and a transparent portion  214  over the annular volume  60  and over the remaining volume  50 . F 3  T 3  and F 4  T 4  are preferentially about equal and should not differ by more than about 10%. The radiation source  120  may be operated before, after, or concurrent with the radiation source  140 . If the power plane  30  is absent, the radiation source  140  and associated radiation  150  are not required and may be omitted. The energy absorbed by the remaining volume  50  from the radiation  130  and/or the radiation  150  should be bounded so to partially cure, but not fully cure, the remaining volume  50 . This necessitates that F 3 T 3  and F 4 T 4  be of a sufficiently low magnitude that can be determined without undue experimentation, as explained supra.  
         [0067]    For the first preferred embodiment, the first photolithographic masking and exposure (see FIG. 3) may be executed either before or after the second photolithographic masking and exposure (see FIG. 4). FIG. 6 shows an appearance of the layer  10  after execution of the first photolithographic masking and exposure and the second photolithographic masking and exposure. In FIG. 6, the cylindrical volume  70  is represented as an uncured volume  72 , the annular volume  60  has become a fully cured volume  62 , and the remaining volume  50  has become a partially cured volume  52 . The uncured volume  72  is a consequence of the opaque portion  102 ,  112 ,  202 , and  212  of the masks  100 ,  110 ,  200 , and  210 , respectively. The uncured volume  72  may be chemically developed away to form a via. For example, FIG. 11 shows the via  73  which results from a developing away of the PID material in the uncured volume  72  of FIG. 6.  
         [0068]    [0068]FIG. 5 illustrates the layer of FIG. 2 showing a photolithographic masking and exposure, in accordance with the second preferred embodiment of the present invention. In FIG. 5, the radiation source  120  directs radiation  130 , such as ultraviolet radiation, of energy flux F 5  for a time duration T 5  through a mask  300  located over the surface  15  of the layer  10  and then through the layer  10 . In relation to the radiation  130 , the mask  300  includes a portion  302  having an optical density D 1  over the cylindrical volume  70 , a portion  304  having an optical density D 2  over the annular volume  60 , and a portion  306  having an optical density D 3  over the remaining volume  50 , wherein D 1 &gt;D 3 &gt;D 2 . Optical density, which is defined as  31  log 10  of the transmissivity, relates to a fraction of incident radiation  130  transmitted through the mask  300 ; i.e., the fraction of radiation  130  transmitted through a given portion of the mask  300  decreases as the optical density of the given portion increases. A purely transparent material has an optical density of zero, while a purely opaque material has an optical density of infinity.  
         [0069]    With the power plane  30  present, the radiation  130  cannot access a portion of the remaining volume  50  situated between the power plane  30  and the surface  16  of the layer  10 , so that the radiation source  140  must be used. The radiation source  140  directs radiation  150  of energy flux F 6  for a time duration T 6 , such as ultraviolet radiation, through a mask  310  located over the surface  16  of the layer  10  and then through the layer  10 . In relation to the radiation  150 , the mask  310  includes a portion  312  having an optical density D 4  over the cylindrical volume  70 , a portion  314  having an optical density D 5  over the annular volume  60 , and a portion  316  having an optical density D 6  over the remaining volume  50 , wherein D 4 &gt;D 6 &gt;D 5 . F 5 T 5  and F 6 T 6  are preferentially about equal and should not differ by more than about 10%. If the power plane  30  is absent, the radiation source  140  and associated radiation  150  are unnecessary and may be omitted.  
         [0070]    For given values of F 3 T 3  and F 4 T 4  associated with the radiation  130  and the radiation  150 , respectively, the optical densities D 1  and D 4  should be sufficiently high that the cylindrical volume  70  remains uncured, the optical densities D 2  and D 5  should be sufficiently low that the annular volume  60  becomes fully cured (or low enough to initiate a full cure of the annular volume  60  followed by heating to effectuate the full cure of the annular volume  60  if the radiation is accompanied with, or followed by, heating), and the optical densities D 3  and D 6  should be in a range that ensures partial curing and prevents full curing. For given values of F 3 T 3  and F 4 T 4 , one skilled in the art may determine practical values of D 1 , D 2 , D 3 , D 4 , D 5  and D 6  without undue experimentation by parametrically varying D 1 , D 2 , D 3 , D 4 , D 5 , and D 6  until the aforementioned curing configuration of the layer  10  is achieved. Alternatively, one skilled in the art may use his or her experience to estimate practical values of D 1 , D 2 , D 3 , D 4 , D 5 , and D 6 , and then, without undue experimentation, parametrically vary F 3 T 3  and F 4 T 4  until the aforementioned curing configuration of the layer  10  is achieved. In accordance with the preceding methodology, D 1 , D 2 , D 3 , D 4 , D 5 , and D 6  may be adjusted such that the portion  302  of the mask  300  is opaque over the cylindrical volume  70 , the portion  304  of the mask  300  is transparent over the annular volume  60 , the portion  306  of the mask  300  is partially transparent over the remaining volume  50 , the portion  312  of the mask  310  is opaque over the cylindrical volume  70 , the portion  314  of the mask  310  is transparent over the annular volume  60 , and the portion  316  of the mask  310  is partially transparent over the remaining volume  50 . A portion of a mask is partially transparent if the portion of the mask transmits a portion of the total incident radiative flux that partially cures a portion of the layer  10  that is exposed to the portion of the radiative flux.  
         [0071]    [0071]FIG. 6, which was discussed infra in connection with the first embodiment, also shows the appearance of the layer  10  after execution of the photolithographic masking and exposure for the second embodiment. As with the first embodiment, the cylindrical volume  70  is represented as an uncured volume  72 , the annular volume  60  has become a fully cured volume  62 , and the remaining volume  50  has become a partially cured volume  52 . The uncured volume  72  may be chemically developed away to form a via. For example, FIG. 11 shows the via  73  which results from developing away the PID material in the uncured volume  72  of FIG. 6.  
         [0072]    [0072]FIG. 7 illustrates FIG. 2 with a modification of the volume structure and showing a photolithographic masking and exposure, in accordance with a third preferred embodiment of the present invention. In FIG. 7, the portion  51  of the remaining volume  50  of FIG. 2 has been eliminated such that the remaining volume  50  has been replaced by the remaining volume  55 , and an annular volume  60  has been replaced by the annular volume  65  such that the power plane  30  circumscribes the annular volume  65  at the cylindrical surface  34  of the power plane  30 . In FIG. 7, the radiation source  120  directs radiation  130  of energy flux F 7  for a time duration T 7 , such as ultraviolet radiation, through a mask  400  located over the surface  15  of the layer  10  and then through the layer  10 . In relation to the radiation  130 , the mask  400  includes an opaque portion  402  over the cylindrical volume  70 , and a transparent portion  404  over the annular volume  65  and over the remaining volume  55 .  
         [0073]    Due to the presence of the power plane  30 , the radiation  130  cannot access a portion of the remaining volume  55  situated between the power plane  30  and the surface  16  of the layer  10 , so that the radiation source  140  must be used. The radiation source  140  directs radiation  150 , such as ultraviolet radiation, of energy flux F 8  for a time duration T 8  through a mask  410  located over the surface  16  of the layer  10  and then through the layer  10 . In relation to the radiation  150 , the mask  410  includes an opaque portion  412  over the cylindrical volume  70 , and a transparent portion  414  over the annular volume  65  and over the remaining volume  55 . F 7  T 7  and F 8  T 8  are preferentially about equal and should not differ by more than about 10%. The radiation source  120  may be operated before, after, or concurrent with the radiation source  140 . Note that the power plane  30  must be present in the third embodiment. The energy absorbed by the remaining volume  55  from the radiation  130  and the radiation  150  should be bounded so as to partially cure, but not fully cure, the remaining volume  55 . This necessitates that F 7 T 7  and F 8 T 8  be of a sufficiently low magnitude. On the other hand, F 7 T 7 +F 8 T 8  must be high enough to fully cure the annular volume  65 , or high enough to initiate a full cure of the annular volume  65  followed by heating to effectuate the full cure of the annular volume  65  if the radiation is accompanied with, or followed by, heating. For the case in which F 7 T 7  is equal to about F 8 T 8 , the time-integrated radiant energy flux absorbed by the annular volume  65  (i.e., 2F 7 T 7 ) is about twice the time-integrated radiant energy flux absorbed by the remaining volume  55  (i.e., F 7 T 7 ). Practical values of F 7 T 7  and F 8 T 8  that satisfy the preceding curing requirements can be determined without undue experimentation by parametric studies involving F 7 , T 7 , F 6 , and T 8 , as explained supra.  
         [0074]    [0074]FIG. 8 shows the appearance of the layer  10  after execution of the photolithographic masking and exposure for the third embodiment. The cylindrical volume  70  is represented as an uncured volume  71 , the annular volume  65  has become a fully cured volume  66 , and the remaining volume  55  has become a partially cured volume  56 . The uncured volume  71  is a consequence of the opaque portions  402  and  412  of the masks  400  and  410 , respectively. The uncured volume  71  in FIG. 8 may be chemically developed away to form a via in the same manner as the uncured volume  72  in FIG. 6 may be chemically developed away to form a via as was explained supra.  
         [0075]    [0075]FIG. 9 illustrates FIG. 2 with a modification of the volume structure and showing a photolithographic masking and exposure, in accordance with a fourth preferred embodiment of the present invention. In FIG. 9, the portion  51  of the remaining volume  50  of FIG. 2 has been eliminated such that the remaining volume  50  has been replaced by the remaining volume  58 , and an annular volume  68  has replaced the annular volume  60  of FIG. 2 such that the power plane  30  circumscribes the annular volume  68  at the cylindrical surface  34  of the power plane  30 . Additionally, the cylindrical volume  70  of FIG. 2 has been replaced by a cylindrical volume  85  and an annular volume  80  circumscribing the cylindrical volume  85 , such that the annular volume  68  circumscribes the annular volume  80 . In FIG. 9, the radiation source  120  directs radiation  130  of energy flux Fg for a time duration T 9 , such as ultraviolet radiation, through a mask  450  located over the surface  15  of the layer  10  and then through the layer  10 . In relation to the radiation  130 , the mask  450  includes an opaque portion  452  over the cylindrical volume  85 , and a transparent portion  454  over the annular volume  80 , over the annular volume  68 , and over the remaining volume  58 .  
         [0076]    Due to the presence of the power plane  30 , the radiation  130  cannot access a portion of the remaining volume  58  situated between the power plane  30  and the surface  16  of the layer  10 , so that the radiation source  140  must be used. The radiation source  140  directs radiation  150  of energy flux F 10  for a time duration T 10 , such as ultraviolet radiation, through a mask  460  located over the surface  16  of the layer  10  and then through the layer  10 . In relation to the radiation  150 , the mask  460  includes an opaque portion  462  over the cylindrical volume  85  and over the annular volume  80 , and a transparent portion  464  over the annular volume  68  and over the remaining volume  58 . F 9 T 9  and F 10 T 10  are preferentially about equal and should not differ by more than about 10%. The radiation source  120  may be operated before, after, or concurrent with the radiation source  140 . Note that the power plane  30  must be present in the fourth embodiment. The energy absorbed by the remaining volume  58  from the radiation  130  and the radiation  150  should be bounded so to partially cure, but not fully cure, the remaining volume  58 . This necessitates that F 9 T 9  and F 10 T 10  be of a sufficiently low magnitude. On the other hand, F 9 T 9 +F 10 T 10 , must be high enough to fully cure the annular volume  68 , or high enough to initiate a full cure of the annular volume  68  followed by heating to effectuate the full cure of the annular volume  68  if the radiation is accompanied with, or followed by, heating. Moreover, since the opaque portion  462  prevents the radiation  150  from reaching the annular volume  80 , the annular volume  80  will be partially cured if the remaining volume  58  is partially cured. For the case in which F 9 T 9  is equal to about F 10 T 10 , the time-integrated radiant energy flux absorbed by the annular volume  68  (i.e., 2F 9 T 9 ) is about twice the time-integrated radiant energy flux absorbed by the remaining volume  58  as well as by the annular volume  80  (i.e., F 9 T 9 ). Practical values of F 9 T 9  and F 10 T 10  that satisfy the preceding curing requirements can be determined without undue experimentation by parametric studies involving F 9 , T 9 , F 10 , and T 10  as explained supra.  
         [0077]    [0077]FIG. 10 shows the appearance of the layer  10  after execution of the photolithographic masking and exposure for the fourth embodiment. The cylindrical volume  85  is represented as an uncured volume  87 , the annular volume  80  has become a partially cured volume  82 , the annular volume  68  has become a fully cured volume  69 , and the remaining volume  58  has become a partially cured volume  59 . The uncured volume  87  is a consequence of the overlapping portions of the opaque portions  452  and  462  of the masks  450  and  460 , respectively. The uncured volume  87  in FIG. 10 may be chemically developed away to form a via in the same manner as the uncured volume  72  in FIG. 6 may be chemically developed away to form a via as was explained supra.  
         [0078]    Note that a via thus formed in place of the uncured volume  87  is adjacent to the partially cured volume  82 . Thus, during subsequent pressurization and/or elevated temperature, partially cured PID material may flow from the partially cured volume  82  into the via thus formed from the uncured volume  87 . This is potentially advantageous in cases where a small crevice or space may develop between layers of a layered stack, such as the layered stack  999  described infra in conjunction with FIGS. 11 and 12, that includes the layer  10  of FIG. 10. The partially cured PID material that flows from the partially cured volume  82  into the via formed from the uncured volume  87  may advantageously fill the unwanted crevice or space between layers, which insulatively protects against electrical shorting that may occur between subsequent plating of the via and nearby conductive material located within the layered stack. Noting that the PID material within the via may cause subsequent metallic plating thickness variability, it is desirable to control the volume of the uncured volume  87  to be small enough to reduce any such plating thickness variability to levels that can be tolerated. Noting that the volume of the uncured volume  87  is proportional to the differential in cross-section area of the opaque portion  452  of the mask  450  and the opaque portion  462  of the mask  460 , the volume of the uncured volume  87  may be controlled by adjusting the cross-section area of the portions  452  and  462 . The cross-section area of the portion  452  is the area of the portion  452  that is exposed to the radiation  130 . The cross-section area of the portion  462  is the area of the portion  462  that is exposed to the radiation  150 .  
         [0079]    [0079]FIG. 11 depicts FIG. 6 after the photolithographically masked and exposed layer  10  is sandwiched between a 2S/1P layer  500  and a 2S/1P layer  600 , to form a layered stack  999 , wherein the uncured volume  72  of FIG. 6 has been chemically developed away and is replaced by a via  73  as shown in FIG. 11. A 2S/1P layer generally comprises a dielectric layer with an internal power layer, a signal layer on a bounding surface of the dielectric layer, and another signal layer on another bounding surface of the dielectric layer. A signal plane is a layer of conductive circuit lines. The 2S/1P layer  500  and the 2S/1P layer  600  may each comprise any dielectric material such as, inter alia, a PID material or a filled dielectric material containing a filler such as, inter alia, silica, alumina, dolomite, mica, and talc. The 2S/1P layer  500  includes a dielectric layer  510 , a power plane  520 , a signal plane  540 , and a signal plane  550 . Additionally, the 2S/1P layer  500  includes a via  530  that is registered over the via  73 , wherein the via  530  includes a cross section of about the same size and shape as a cross section of the via  73 . As shown, the dielectric layer  510  includes a fully cured material, wherein the dielectric layer  510  could include a drilled hole with or without metal plating. Alternatively, the dielectric layer  510  could include a fully cured ring of dielectric material (analogous to the fully cured volume  62 ) surrounding the via  530  and a partially cured volume of dielectric material (analogous to the partially cured volume  52 ) circumscribing the fully cured ring. The  2 S/ 1 P layer  600  includes a dielectric layer  610 , a power plane  620 , a signal plane  640 , and a signal plane  650 . Additionally, the 2S/1P layer  600  includes a via  630  that is registered over the via  73 , wherein the via  630  includes a cross section of about the same size and shape as a cross section of the via  73 . As shown, the dielectric layer  610  includes a fully cured material, wherein the dielectric layer  610  could include a drilled hole with or without metal plating. Alternatively, the dielectric layer  610  could include a fully cured ring of dielectric material (analogous to the fully cured volume  62 ) surrounding the via  630  and a partially cured volume of dielectric material (analogous to the partially cured volume  52 ) circumscribing the fully cured ring. FIG. 11 shows a through hole  940  that includes the sequential arrangement of the via  530 , the via  73 , and the via  630 . The partially cured volume  52  of the layer  10  will become fully cured upon subsequent pressurization and/or elevated temperature, which will cause both the 2S/1P layer  500  and the 2S/1P layer  600  to become adhesively bonded to the layer  10 . During the subsequent final lamination step of pressurization and/or elevated temperature, the fully cured volume  62  will prevent liquified PID material from the partially cured volume  52  from flowing into the via  73 , the fully cured ring (if it exists) of dielectric material in the dielectric layer  510  will prevent liquified PID material from the circumscribing partially cured volume of dielectric material in the dielectric layer  610  from flowing into the via  530 , and the fully cured ring (if it exists) of dielectric material in the dielectric layer  610  it will prevent liquified PID material from the circumscribing partially cured volume of dielectric material in the dielectric layer  610  from flowing into the via  630 . The layer  10  is called a “sticker layer,” because the layer  10  serves to interfacially bond the 2S/1P layer  500  and the 2S/1P layer  600  together in conjunction with the final lamination step of pressurization and/or elevated temperature.  
         [0080]    [0080]FIG. 12 depicts FIG. 11 after additional layers  700  and  800  are added to opposite sides of the layered stack  999  prior to the final lamination step of pressurization and/or elevated temperature. The layer  700  is stacked on the 2S/1P layer  500  and includes a partially cured volume  710  of PID material, a via  730  that is registered over the via  530  wherein the via  730  includes a cross section of about the same size and shape as a cross section of the via  73 , and a fully cured volume  720  of PID material that circumscribes the via  730 . The layer  800  is stacked on the 2S/1P layer  600  and includes a partially cured volume  810  of PID material, a via  830  that is registered over the via  630  wherein the via  830  includes a cross section of about the same size and shape as a cross section of the via  73 , and a fully cured volume  820  of PID material that circumscribes the via  830 . FIG. 12 shows the through hole  940  as an elongated variant of the through hole  940  in FIG. 11 such that the through hole  940  of FIG. 12 includes the sequential arrangement of the via  730 , the via  530 , the via  73 , the via  630 , and the via  830 . The partially cured volumes  710 ,  810 , and  52 , along with any partially cured volumes that may exist in the 2S/1P layers  500  and  600 , will become fully cured upon a subsequent final lamination step of pressurization and/or elevated temperature. The final lamination step which will cause the layers  700  and  800  to respectively bond adhesively with the 2S/1P layers  500  and  600 , in addition to causing the 2S/1P layers  500  and  600  to each bond adhesively with the layer  10 . During the subsequent final lamination step of pressurization and/or elevated temperature, the fully cured volume  720  will prevent liquified PID material from the partially cured volume  710  from flowing into the via  730 , the fully cured volume  820  will prevent liquified PID material from the partially cured volume  810  from flowing into the via  830 , the fully cured volume  62  will prevent liquified PID material from the partially cured volume  52  from flowing into the via  73 , the fully cured ring (if it exists) of dielectric material in the dielectric layer  510  will prevent liquified PID material from the circumscribing partially cured volume of dielectric material in the dielectric layer  610  from flowing into the via  530 , and the fully cured ring (if it exists) of dielectric material in the dielectric layer  610  it will prevent liquified PID material from the circumscribing partially cured volume of dielectric material in the dielectric layer  610  from flowing into the via  630 . While FIG. 12 depicts a five-layer structure, the invention embodied by FIG. 12 could include any number of layer, such as  17  or more layers, wherein all layers each include a partially cured ring of dielectric material or alternating layers each include a partially cured ring of dielectric material.  
         [0081]    While preferred and particular embodiments of the present invention have been described herein for purposes of illustration, many modifications and changes will become apparent to those skilled in the art. Accordingly, the appended claims are intended to encompass all such modifications and changes as fall within the true spirit and scope of this invention.