Patent Document

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is generally in the field of inductor fabrication. More specifically, the present invention is in the field of inductor fabrication on a package substrate of a semiconductor chip. 
     2. Background Art 
     The requirement of smaller, more complex, and faster devices operating at high frequencies, such as wireless communications devices and Bluetooth RF transceivers, has also resulted in an increased demand for small size inductors with high inductance. These small wireless communication devices and Bluetooth RF transceivers require small size inductors with high inductance for use in resonator circuits, filters, and switch regulators. For example, highly efficient switch regulators that need to work in the high KHz to low MHz range require inductors in a range of 100.0 nano henries (“nH”) to 10.0 micro henries (“μH”). Also, the highly efficient switch regulators require inductors to have an inductance value with a tolerance of +/−10%. 
     One attempt to satisfy the demand for the small size inductors with a high inductance discussed above has been to integrate the inductor on a substrate that houses a chip. Inductors with an inductance on the order of 1.0 to 3.0 nH, and even as high as 10.0 nH can be integrated on a substrate that houses a chip. However, inductors with an inductance in the range of 100.0 nano henries (“nH”) to 10.0 micro henries (“μH”) discussed above are too large to be integrated on a substrate that also houses a chip. 
     Another attempt to satisfy the demand for inductors with a small size and high inductance discussed above has been to use discrete inductors. However, discrete inductors suffer from various disadvantages not shared by inductors that are integrated on a substrate the houses a chip. For example, the discrete inductor requires the assembly of at least two components, i.e. the chip itself and the discrete inductor. The required assembly of two or more components introduces corresponding reliability issues and also results in a greater manufacturing cost. 
     Additionally, a discrete inductor typically has a fixed inductance that is not tunable or adjustable. Thus, a discrete inductor must have the specific inductance required in a particular circuit. If the value of the required inductance changes, the discrete inductor must be removed from the circuit and replaced with another discrete inductor having the new required inductance. For example, to obtain a specific resonance frequency in the development phase of a LC test circuit, the determination of exact value of the required inductance could require the removal and replacement of numerous discrete inductors before arriving at a discrete inductor with the required inductance. 
     Thus, there exists a need in the art for a structure for integrating an inductor on a package substrate of a chip that provides an inductor with a small size and an inductance in the range of 100.0 nH to 10.0 μH. Moreover, there exists a need in the art for a structure for integrating an inductor on a package substrate of a chip that allows the value of the inductance to be tuned to meet a specific requirement. Further, there exists a need in the art for a structure for integrating an inductor on a package substrate of a chip that provides the flexibility to meeting different size requirements. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a high inductance inductor in a semiconductor package. According to one embodiment, a number of trace metal segments or conductors are patterned onto a top surface of a substrate suitable for receiving and housing a semiconductor die. In one embodiment, an insulator layer covers the trace metal segments and separates them from a high permeability core which is mounted on top of the insulator layer. The insulator layer can comprise, for example, solder mask while the high permeability core can comprise, for example, a ferrite rod. 
     In one embodiment, a number of bonding wires are passed over the high permeability core and make connections to respective trace metal segments under the core so as to create an inductor winding around the core. The terminals of the inductor so formed can be connected to a substrate bond pad and/or to a semiconductor die bond pad. Due to the high permeability of the core, the inductance value of the inductor so formed can be quite high while the inductor has a relatively small size. Moreover, the present invention&#39;s inductor can be fine-tuned by adjusting the number of bonding wires in the inductor winding and also by adjusting the length of the high permeability core. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a top view of an exemplary structure in accordance with one embodiment of the present invention. 
     FIG. 2 illustrates a perspective view of an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is directed to a high inductance inductor in a semiconductor package. The following description contains specific information pertaining to various embodiments and implementations of the invention. One skilled in the art will recognize that the present invention may be practiced in a manner different from that specifically discussed in the present application. Moreover, some of the specific details of the invention are not discussed in order not to obscure the invention. The specific details not described in the present application are within the knowledge of a person of ordinary skills in the art. 
     The drawings in the present application and their accompanying detailed description are directed to merely example embodiments of the invention. To maintain brevity, other embodiments of the invention that use the principles of the present invention are not specifically described in the present application and are not specifically illustrated by the present drawings. 
     Structure  100  in FIG. 1 illustrates a top view of an exemplary structure in accordance with one embodiment of the present invention. Structure  100  includes semiconductor die  102 , which can be attached to top surface  104  of substrate  106  in a manner know in the art. It is noted that a “semiconductor die,” such as semiconductor die  102 , is also referred to as a “chip” or a “semiconductor chip” in the present application. Substrate  106  “houses” semiconductor die  102 , and can comprise, for example, an organic laminate material or a ceramic material. It is also noted that a “substrate,” such as substrate  106 , is also referred to as a “package substrate” in the present application. However, in one embodiment, substrate  106  may be a printed circuit board (“PCB”). 
     Structure  100  also includes inductor  108 , which is situated, or “housed,” on top surface  104  of substrate  106 . In other embodiments, inductor  108  may be housed in a pin grid array package, a ball grid array package, a land grid array package, or on a laminate PCB. The package or laminate materials might comprise, for example, various ceramic or organic materials known in the art. Inductor  108  comprises winding  110 , core  112 , insulator  114 , substrate bond pad  116 , also referred to as a “terminal” of inductor  108  in the present application, and substrate bond pad  118 , also referred to as a “terminal” of inductor  108  in the present application. 
     Winding  110  further comprises bonding wires, such as bonding wire  120 , and trace metal segments, such as trace metal segment  122 . It is also noted that a “trace metal segment,” such as trace metal segment  122 , is also referred to as a “conductor” in the present application. Trace metal segment  122  is fabricated on top surface  104  of substrate  106 . For example, a mask can be used to pattern conductors on a copper metallization layer on top surface  104  of substrate  106 . The excess copper can be etched away, resulting in a defined metal trace pattern that can include, for example, trace metal segment  122 . Winding  110  is also referred to as an “inductor winding” in the present application. 
     In structure  100 , trace metal segment  122  can comprise nickel-plated copper. Trace metal segment  122  can further comprise a layer of gold plating over the nickel-plated copper to provide a surface for wire bonding. A first end of trace metal segment  122  is connected to substrate bond pad  116 , and a second end of trace metal segment  122  is connected to bonding wire  120 . Similar to trace metal segment  122 , substrate bond pad  116  can be fabricated on top surface  104  of substrate  106 , and can comprise nickel-plated copper. Substrate bond pad  116  can also further comprise a layer of gold plating over the nickel-plated copper to provide a surface for wire bonding. 
     Bonding wire  120  can comprise gold or can comprise other metals such as aluminum. The diameter of bonding wire  120  can be approximately 1.0 mil to 6.0 mils. For example, in an application where inductor  108  provides filtering for a high-current voltage regulator, the diameter of bonding wire  120  can be approximately 6.0 mils. By way of further example, in an application where inductor  108  is used with a low-current micro module, the diameter of bonding wire  120  can be approximately 1.0 mil. Winding  110  will be discussed in greater detail in relation to FIG.  2 . 
     Continuing with FIG. 1, insulator  114 , also referred to as an “insulator layer” in the present application, is situated under core  112  so as to electrically insulate core  112  from trace metal segments such as trace metal segment  122 . Insulator  114  can be a nonconducting material such as solder mask. In one embodiment, insulator  114  can be solder mask comprised of AUS-5. As shown in FIG. 1, bonding wires, such as bonding wire  120 , pass over core  112  and do not make contact with core  112 . In the present embodiment, core  112  can comprise a high permeability material such as a ferrite rod. By way of background, ferrite is a powdered, compressed, and sintered magnetic compound composed of iron oxide, a metallic oxide such as zinc, nickel, cobalt, or iron, and ceramic. Instead of a ferrite rod, any other high or medium permeability material suitable for increasing inductance can also be used. 
     The particular metallic oxide (for example, zinc, nickel, cobalt, or iron) that is used to form the ferrite rod affects the permeability of the ferrite rod, which can be, for example, approximately 40.0 to 100.0. Since the inductance of an inductor is proportional to the permeability of its core, the inductance of inductor  108  can be increased approximately 40.0 times if core  112  comprises a ferrite rod with a permeability of 40.0. Core  112  will be discussed in greater detail in relation to FIG.  2 . 
     Continuing with FIG. 1, a first end of bonding wire  124  is bonded to substrate bond pad  116  of inductor  108 , and a second end of bonding wire  124  is bonded to semiconductor die bond pad  126 . Bonding wire  124  can be gold or can comprise other metals such as aluminum. The diameter of bonding wire  124  can be 30.0 microns or other diameter of choice. Bonding wire  124  electrically connects substrate bond pad  116  of inductor  108 , i.e. a terminal of inductor  108 , to semiconductor die bond pad  126 . In to another embodiment, a bonding wire can electrically connect substrate bond pad  116  of inductor  108  to another substrate bond pad on the periphery of top surface  104 , such as substrate bond pad  128 . 
     As shown in FIG. 1, a first end of bonding wire  130  is bonded to substrate bond pad  118  of inductor  108 , and a second end of bonding wire  130  is bonded to substrate bond pad  132 . Bonding wire  130  can be comprised of similar material as bonding wire  124  discussed above. Substrate bond pads  118 ,  128 , and  132  can be fabricated on top surface  104  of substrate  106  in a similar manner as substrate bond pad  116  discussed above. Substrate bond pads  118 ,  128 , and  132  can also comprise the same material as substrate bond pad  116 . 
     Bonding wire  130  electrically connects substrate bond pad  118  of inductor  108 , i.e. a terminal of inductor  108 , to substrate bond pad  132 , which “abuts” via  134 . Thus, bonding wire  130  can, in one embodiment, electrically connect substrate bond pad  118  of inductor  108  to a land (not shown in FIG. 1) that is connected to via  134  on the bottom surface of substrate  106  by way of substrate bond pad  132  and via  134 . In a different embodiment, a bonding wire can electrically connect substrate bond pad  118  of inductor  108  to a semiconductor die bond pad, such as semiconductor die bond pad  136  on semiconductor die  102 . In another embodiment, a bonding wire can connect substrate bond pad  116  or substrate bond pad  118  to a component on top surface  104  of substrate  106 , such as a capacitor. It is noted that in FIG. 1, only trace metal segment  122 , bonding wire  120 , substrate bond pads  128  and  132 , via  134 , and semiconductor die bond pads  126  and  136  are specifically discussed herein to preserve brevity. 
     Referring now to FIG. 2, inductor  208  illustrates a perspective view of an exemplary inductor in accordance with one embodiment of the present invention. Inductor  208  corresponds to inductor  108  in FIG.  1 . In particular, core  212 , winding  210 , insulator  214 , substrate bond pad  216 , substrate bond pad  218 , trace metal segment  222 , and bonding wire  220 , respectively, correspond to core  112 , winding  110 , insulator  114 , substrate bond pad  116 , substrate bond pad  118 , trace metal segment  122 , and bonding wire  120  in FIG.  1 . 
     Now discussing FIG. 2 in more detail, winding  210  comprises trace metal segments  222 ,  224 ,  226 ,  228 ,  230 ,  232 ,  234 , and  236 , and bonding wires  220 ,  238 ,  240 ,  242 ,  244 ,  246 ,  248 , and  250 . Trace metal segments  222 ,  224 ,  226 ,  228 ,  230 ,  232 ,  234 , and  236  are similar to trace metal segment  122  in FIG.  1  and are fabricated on top surface  204  of substrate  206  in a similar manner as trace metal segment  122  described above. Winding  210  is also referred to as an “inductor winding” in the present application. 
     Continuing with FIG. 2, the first ends of bonding wires  220 ,  238 ,  240 ,  242 ,  244 ,  246 ,  248 , and  250 , respectively, are connected to the first ends of trace metal segments  222 ,  224 ,  226 ,  228 ,  230 ,  232 ,  234 , and  236 . The second ends of bonding wires  220 ,  238 ,  240 ,  242 ,  244 ,  246 ,  248 , and  250 , respectively, are connected to the second ends of trace metal segments  224 ,  226 ,  228 ,  230 ,  232 ,  234 , and  236 , and substrate bond pad  218 , also referred to as a “terminal” of inductor  208  in the present application. 
     In the present embodiment, first ends of bonding wires  220 ,  238 ,  240 ,  242 ,  244 ,  246 ,  248 , and  250 , respectively, can be connected to the first ends of trace metal segments  222 ,  224 ,  226 ,  228 ,  230 ,  232 ,  234 , and  236  by bonding. Similarly, the second ends of bonding wires  220 ,  238 ,  240 ,  242 ,  244 ,  246 ,  248 , and  250 , respectively, can be connected to the second ends of trace metal segments  224 ,  226 ,  228 ,  230 ,  232 ,  234 , and  236 , and substrate bond pad  218  by bonding. 
     Bonding wires  220 ,  238 ,  240 ,  242 ,  244 ,  246 ,  248 , and  250  are similar to bonding wire  120  in FIG. 1, and comprise the same material as bonding wire  120 , such as gold or aluminum. The diameter of bonding wires  220 ,  238 ,  240 ,  242 ,  244 ,  246 ,  248 , and  250  can be approximately 1.0 mil to 6.0 mils. Trace metal segments  222 ,  224 ,  226 ,  228 ,  230 ,  232 ,  234 , and  236  can comprise nickel-plated copper. Trace metal segments  222 ,  224 ,  226 ,  228 ,  230 ,  232 ,  234 , and  236  can further comprise a layer of gold plating over the nickel-plated copper to provide a surface for wire bonding. 
     Continuing with FIG. 2, each trace metal segment of winding  210  and the bonding wire connected to the first end of the trace metal segment form a “turn” of winding  210 . For example, trace metal segment  222  and bonding wire  220  that is connected to the first end of trace metal segment  222  as discussed above form one “turn” of winding  210 . The inductance of an inductor is generally proportional to the square of the number of “turns” in the inductor&#39;s winding. Thus, the inductance of inductor  208  can be increased or decreased by increasing or decreasing the number of “turns” in winding  210 . For example, adding trace metal segments and bonding wires to winding  4   210  can increase the number of “turns” in winding  210 , and thus increase the inductance of inductor  208 . By way of further example, the inductance of inductor  208  can be decreased by removing bonding wires to decrease the number of “turns” in winding  210 . 
     Thus, by increasing or decreasing the number of “turns” in winding  210 , the inductance of the invention&#39;s inductor  208  can be “fine tuned” to more closely match a required inductance in a particular application. For example, in the development phase of an LC resonance circuit, bonding wires can be removed or added to “fine tune” the inductance of inductor  208  to obtain a particular resonance frequency. Thus, the present invention&#39;s inductor  208  provides the flexibility to allow the number of “turns” in winding  210  to vary as required to produce an inductance in a range of approximately 1.0 nH to 100.0 μH. 
     As shown in FIG. 2, substrate bond pad  216 , also referred to as a “terminal” of inductor  208  in the present application, is connected to trace metal segment  222  to provide a connection to a first end of winding  210 . As discussed above, a second end of bonding wire  250  is bonded to substrate bond pad  218  to provide a connection to a second end of winding  210 . Substrate bond pads  216  and  218  are fabricated on top surface  204  of substrate  206  in a similar manner as substrate bond pads  116  and  118  described above. Substrate bond pad  216  can be wire bonded to a semiconductor die bond pad, such as semiconductor die bond pad  126  in FIG. 1, or a substrate bond pad, such as substrate bond pad  128 . Similarly, substrate bond pad  218  can be wire bonded to a semiconductor die bond pad, such as semiconductor die bond pad  136  in FIG. 1, or a substrate bond pad, such as substrate bond pad  132 . In another embodiment, substrate bond pad  216  or substrate bond pad  218  can be connected to a component on top surface  204  of substrate  206 , such as a capacitor. 
     Continuing with FIG. 2, core  212  is situated over insulator  214  (or “insulator layet”  214 ) but under bonding wires  220 ,  238 ,  240 ,  242 ,  244 ,  246 ,  248 , and  250 . Core  212  can be secured to top surface  204  of substrate  206  by glue. However, other methods known in the art may be used to attach core  212  to top surface  204  of substrate  206 . In the present embodiment, core  212  is housed on top surface  204  of substrate  206 , which also houses a semiconductor die, such as semiconductor die  102  in FIG.  1 . In other embodiments, core  212  may be housed in a pin grid array package, a ball grid array package, a land grid array package, or on a laminate PCB. In the present embodiment, length  252  of core  212  can be approximately 20.0 mils, width  256  can be approximately 10.0 mils, and thickness  254  can be approximately 10.0 mils. In another embodiment, length  252  can be approximately 40.0 mils, width  256  can be approximately 15.0 mils, and thickness  254  can be approximately 10.0 mils. 
     Core  212 , as discussed above, can comprise a ferrite rod that can have a permeability of approximately 40.0 to 100.0. Also, as discussed above, core  212  can increase the inductance of inductor  208  in proportion to the increase in the value of the permeability of core  212 . Therefore, inductor  208  can decrease in length and still maintain the same inductance by proportionally increasing the permeability of core  212 . Moreover, in the manner described in relation to FIG. 1, inductor  208  in FIG. 2 can be fine-tuned to meet a required inductance in a particular application. FIG. 2 further illustrates an inductor that can provide an inductance in a range of approximately 1.0 nH to 100.0 μH while maintaining a relatively small size. 
     From the above description of the invention it is manifest that various techniques can be used for implementing the concepts of the present invention without departing from its scope. Moreover, while the invention has been described with specific reference to certain embodiments, a person of ordinary skill in the art would recognize that changes can be made in form and detail without departing from the spirit and the scope of the invention. For example, in one embodiment, two inductors, each one similar to inductor  208 , can be mounted on a top surface of a substrate to form a transformer. In such instance, the core, i.e. the ferrite rod, of the first inductor can be mounted in close proximity to the core of the second inductor to form a transformer by coupling the magnetic fields generated by the windings of each inductor. As such, the described embodiments are to be considered in all respects as illustrative and not restrictive. It should also be understood that the invention is not limited to the particular embodiments described herein, but is capable of many rearrangements, modifications, and substitutions without departing from the scope of the invention. 
     Thus, a high inductance inductor in a semiconductor package has been described.

Technology Category: h