Abstract:
A multi-layer micro-printed circuit board (PCB) is disclosed, which defines a magnetic component, such as a transformer, using planar technology. Instead of using the traditional twelve-layer PCB incorporating both a primary and a secondary winding, this invention stacks multiple PCBs, each having four or six layers and each including a single winding (either the primary or the secondary). The PCBs are stacked in an offset arrangement such that the pins penetrating the PCB or PCBs including the primary winding or windings do not penetrate the PCB or PCBs including the secondary winding or windings. Additionally, this offset arrangement prevents the pins penetrating the secondary PCBs from penetrating the primary PCBs in the same manner. This offset configuration thereby avoids significant flashover problems associated with current planar components. Moreover, the invention describes an arrangement whereby a jumper or other connection can be used to connect the windings in a series or in a parallel configuration allowing the user to configure the component according to user-required parameters.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to miniature printed circuit boards (PCB) for microelectrical applications. More particularly, the invention relates to multi-layer, user configurable and stackable miniature printed circuit boards for static electromagnetic components such as transformers. 
     DESCRIPTION OF THE RELATED TECHNOLOGY 
     Transformers are widely known electromagnetic components used in electrical devices and power supply units. In general, static magnetic components such as transformers have traditionally been constructed using windings of ordinary conducting wire having a circular cross section. The conventional transformer comprises an insulator gap between a primary coil and a secondary coil, and the voltage generated in the secondary coil is determined by the voltage applied to the primary coil multiplied by the winding ratio between the primary coil and the secondary coil. Manufacture of these traditional structures involves winding the wire around a core or bobbin structure, a process that often involves considerable amounts of expensive hand labor. Furthermore, high power applications often require a magnetic component having a bulky core and large wire sizes for the windings. Even though the transformer is often an essential component of an electrical apparatus, it has been historically the most difficult to miniaturize. 
     New operational requirements with respect to circuit size and power density and the increasing necessity to reduce circuit manufacturing costs have made the traditional static magnetic component very unattractive as a circuit component. Newly designed circuits, for example, need low profiles to accommodate the decreasing space permitted to power circuits. Attaining these objectives has required the redesign of magnetic components to achieve a low profile and a low cost component assembly. 
     Planar magnetic components fabricated with flexible circuit and multi-layer printed circuit board (PCB) technologies offer an alternative to address the new operational and cost requirements. With planar technology, transformers have been formed from single or multi-layered printed circuit boards. FIG. 1A illustrates an example of a typical planar transformer constructed from printed circuit boards. Specifically, FIG. 1A depicts a side view of such a component  100  attached to the main board  110  of an electrical device. The component  100  includes a PCB  130  with multiple internal layers. Windings of the PCB  130  are connected to the main board by connecting pins  140 . FIG. 1B illustrates the manner in which the component  100  is assembled and FIG. 2 schematically depicts the individual layers of the PCB  130 . 
     The basic construction of the component  100  comprises a spiral conductor on each layer of the PCB  130  forming one or more inductor “turns.” As shown in FIG. 1B, the core  120  can comprise two separate and identical E-shaped sections  122  and  124 . Each E-shaped section  122 ,  124  includes a middle leg  126  and two outer legs  128 . A hole  132  is drilled in the center of the PCB  130 . The middle leg  126  of the E-shaped section  122 ,  124  can be supported within the hole  132  to form part of the core  120 . The middle leg  126  has a circular cross-section and each of the outer legs  128  has a circular or rectangular cross-section. The remaining section of the E-shaped sections  122 ,  124  is formed by a ferrite bar, which is bonded to the legs  126 ,  128 . The E-shaped sections  122 ,  124  are assembled so that the legs  126 ,  128  of each E-shaped section are bonded together. Primary and secondary pins connecting the primary and secondary windings, respectively, can penetrate the PCB via terminal holes  134  drilled near the outer edges of the PCB as will be explained below. 
     The width of the spiral conductor depends on the current carrying requirement. That is, the greater the current carrying requirement, the greater the width of the conductor. Typically, a predetermined area is reserved for the inductor and the one or more turns are printed on each layer according to well known printed circuit board technology. (See, for example, U.S. Pat. No. 5,521,573.) After each layer is so printed, the layers are bonded together into a multi-layer PCB by glass epoxy. Through-hole “vias” or blind “vias” are used to interconnect the turns of the different layers. 
     A through-hole via is formed by drilling a hole through the layers at a position to intersect ends of two of the spiral conductors and then “seeding” the inner surface of the holes with a water soluble adhesive. Next, copper is electrolessly plated on the adhesive to interconnect the conductors. Next, additional copper is electrically plated over the electroless copper plate to the desired thickness. Finally, the holes are filled with solder to protect the copper plate. A separate via is required for each pair of spiral conductors on adjacent layers to connect all of the turns in series. Each such through-hole via is positioned not to intersect the other conductors. 
     Drilling holes in selected layers before the layers are bonded together forms a “blind” via. Then, the layers are successively bonded together and, while exposed, the inner surface of the holes is seeded with nickel, electrolessly plated with copper and then filled with solder. The resultant vias extend between the two layers sought to be electrically connected. Thus, the hole does not pass through other layers, and no area is required on these other layers to clear the via. However, the blind via fabrication process is much more expensive than the through-hole fabrication process. As shown in FIG. 1A, primary pins  140  connecting the primary windings and secondary pins  150  connecting the secondary windings are then positioned to penetrate the multi-layer PCB  130 . 
     FIG. 2 illustrates a process for manufacturing a printed coil with conventional planar technology in a PCB. In the layers of the PCB of FIG. 2, a primary winding and secondary winding can be formed by connecting multiple coil traces from five layers  200 ,  220 ,  240 ,  260 , and  280 . The primary winding, for example, can have an outside terminal  202  connected to a coil trace  204  on layer  200 . The inside terminal of the coil trace  204  can be connected to an inside terminal of a connection trace  242  on layer  240  by an inner peripheral terminal  208  through a via. The outside terminal of the connection trace  242  is connected by a primary terminal  210  through a via to an outside terminal  282  of a coil trace  284  on layer  280 . The inner terminal of the coil trace  284  is connected to the inner terminal of connection trace  244  on layer  240  by a peripheral terminal  286  through a via. Connection trace  244  is connected to outside terminal  246 , thereby forming a primary winding between outside terminals  202  and  246  from coil traces  204  and  284  on layers  200  and  280 , respectively. 
     A secondary winding can be formed by connecting a coil trace  224  on layer  220  and a coil trace  264  on layer  260  in a similar fashion. An outside terminal  262  of coil trace  264  can be connected through a via to a corresponding outside terminal  222  of coil trace  224  by a primary terminal  266 . The inside terminal of coil trace  224  is connected to the inside terminal of coil trace  284  through a via by peripheral terminal  226 . Because the inside terminal of each coil trace  224  and  264  is connected and the outside terminals of each coil trace  224  and  264  is connected, the coil trace  224  and the coil trace  264  are connected in parallel. 
     FIG. 3 illustrates a typical twelve-layer layout where each individual layer is shown separately. These layers can be connected in a fashion similar to that described above with reference to FIG. 2 to form a PCB having a primary winding and a secondary winding. In this conventional layout, a twelve layer PCB includes traces of both the primary and secondary windings as similarly described with reference to FIG.  2 . However, as a result, the primary and secondary windings are physically positioned near one another, creating significant risks of electrical flashover. 
     FIG. 4 schematically illustrates how a primary winding and a secondary winding from a PCB can be arranged as a transformer. Referring again to FIG. 2, the windings traced on the layers of a PCB can form a primary winding with external terminals  202  and  282  and a secondary winding with external terminals  226  and  262 . As shown in FIG. 4, a primary winding  420  can be connected to the main board  110  by pins  430  and  440  at terminals  202  and  282 . A secondary winding  460  can be connected to the main board  110  by pins  470  and  480  at terminals  226  and  262 . The primary winding  420  is configured across from the secondary winding  460  with the dielectric material of the core  120  positioned therebetween and represented by lines  490 . 
     While a considerable improvement over traditional construction of magnetic components, these arrangements still fail to meet the performance and cost objectives of contemporary circuit designs. In particular, this conventional planar arrangement poses significant design, cost, and operational disadvantages. 
     As discussed above, applications today are increasingly demanding space restrictions for their design. Consequently, efforts are continuing to further reduce the size of electrical components. Power supplies, for example, have been significantly reduced in size over the past few years. As a result, the space available for the planar magnetic component is extremely limited. Therefore, the current twelve layer arrangement in conventional planar technology offers a significant obstacle to miniaturizing circuit designs. 
     Closely tied to the current and ongoing size constraints are the ever-increasing demands for less expensive and more reliable applications. The conventional twelve-layer planar components also prove to be extremely costly. The conventional planar magnetic component must be customized for each circuit design depending on the parameters required (e.g., the turn ratio). If the parameters change, then a new planar magnetic component must be custom manufactured. Manufacture of the magnetic components using conventional planar technology therefore requires substantial costs associated with each new PCB configuration built for each and every circuit parameter change. 
     Moreover, the current planar technology raises serious operational problems associated with high potential (HIPOT) applications as well. The pins in the conventional boards penetrate the PCB layers in various locations and generally propagate through the thickness of most or all of the layers; however, only certain pins are electrically bonded to certain layers. Because of the manner in which the pins in the conventional planar components fully penetrate the boards in various locations, with only certain pins electrically bonded to certain layers, significant risks of failure due to an electrical flashover exist. Lastly, such many layer boards require significant pressure to laminate them together, thereby generally creating higher shear forces on the layers during manufacture. The resulting lateral movement of each individual layer relative to the layers above and below can cause significant defects to the operation of the component and, in particular, can infringe the minimum space needed between primary and secondary windings. 
     Accordingly, there is a need for a static electro-magnetic component which not only satisfies demanding operational and size requirements of current electronic technology but also avoids the flashover problems and high costs of the current planar technology. Furthermore, there is a need for an electrical device which offers the additional benefit of providing a configurable and customizable capability allowing a user to change parameters of the component to suit the needs of a particular application. 
     SUMMARY OF THE INVENTION 
     The embodiments of the invention described below offer a multi-layer and user-configurable PCB device which can function as a transformer. The novel arrangement of this invention along with its customizable configuration overcome the disadvantages and problems associated with the prior art, which were discussed above. 
     The invention generally comprises a series of discrete stackable PCBs having predetermined trace layouts, such as those used for a cylindrical transformer core. These predetermined boards can be standardized, thereby eliminating the designer layout process. The user may configure the boards using variable position vias (pins) and jumpers such that the vias do not penetrate boards to which they are not electrically connected. 
     One embodiment of the invention comprises a plurality of core members and a plurality of printed circuit boards stacked into a multi-layer configuration between the core members. A first printed circuit board is configured to define a primary winding of a transformer. A second set of printed circuit boards is configured to define a secondary winding of a transformer. A connection member is configured to selectively connect the printed circuit boards of the secondary winding in either a parallel or a series electrical configuration depending on the needs of the user. Connector pins are configured to electrically connect the plurality of printed circuit boards to the main circuit board. Each connector pin penetrates only printed circuit boards containing the primary winding or the printed circuit boards containing the secondary winding. 
     In another embodiment, the invention comprises a method of manufacturing an electrical device including printing at least one coil on each of a plurality of printed circuit boards, configuring electrical connections on the plurality of printed circuit boards to include the coils on the printed circuit boards so as to define a primary winding and a secondary winding. The printed circuit boards are configured in a stacked arrangement, and the primary winding on the printed circuit boards and the secondary winding on the printed circuit boards are connected to a main circuit board with connector pins in such a manner that the connector pins connecting the primary winding only penetrate printed circuit boards containing the primary winding and connector pins connecting the secondary winding only penetrate printed circuit boards containing the secondary winding. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a side sectional view of a magnetic component employing the conventional planar technology. 
     FIG. 1B is an exploded perspective view of the magnetic component of FIG.  1 A. 
     FIG. 2 is an exploded perspective view of layers of a PCB used in a magnetic component. 
     FIG. 3 is a top view of the multiple layers of the magnetic component of FIG.  1 A. 
     FIG. 4 is a schematic diagram of the equivalent circuit of the magnetic component of FIG.  1 A. 
     FIG. 5 is an exploded perspective view of a magnetic component showing an upper core portion removed. 
     FIG. 6 is an exploded perspective view of a primary PCB including a primary winding and a secondary PCB including a secondary winding. 
     FIG. 7 is a perspective view of the primary PCB of FIG. 5 positioned between two secondary PCBs. 
     FIG. 8 is a schematic diagram of the equivalent circuit of the primary windings and secondary windings of the PCB of FIG.  6 . 
     FIG. 9A is a schematic diagram of the equivalent circuit of the magnetic component of FIG. 5 configured in a series connection. 
     FIG. 9B is a schematic diagram of the equivalent circuit of the magnetic component of FIG. 5 configured in a parallel connection. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is best understood by reference to the figures wherein like parts are designated with like numerals throughout. 
     FIG. 5 is an exploded perspective view of a magnetic component  500  with an upper core portion  510  separated from a lower core portion  540 . The magnetic component  500  is configured as a transformer. One primary PCB  525  and two secondary PCBs  530  and  535 , are laid onto the lower core portion  540 . The three PCBs  525 ,  530 , and  535  each have hollow centers to accommodate a cylindrical member (not shown) of the upper core portion  510  and a cylindrical member (not shown) of the lower core portion  540 . Therefore, as the PCBs  525 ,  530 , and  535  are placed on the lower core portion  540 , the cylindrical member of the lower core portion  540  fits into the hollow centers of the PCBs  525 ,  530 , and  535 . Similarly, as the upper core portion  510  is placed on top of the lower core portion  540 , the cylindrical member of the upper core portion  510  passes through the hollow centers of the PCBs  525 ,  530 , and  535 . In one embodiment, the core portions  510  and  540  and the cylindrical members passing through the hollow centers of the PCBs  525 ,  530 , and  535  are manufactured from a ferrite material. Alternatively, the core portions  510  and  540  can be manufactured from other suitable materials. 
     The upper core portion  510  is configured with a flat outer surface  512 . The surface opposite the flat outer surface  512  is configured with two support members  514  on opposing ends of the upper core portion  510  thereby forming a gap  516  therebetween. The support members  514  run the width of the upper core portion  510  and consequently, the gap  516  also runs the width of the upper core portion  510 . The cylindrical member (not shown) of the upper core portion is centered in the gap  516  of the surface opposite the flat outer surface  512 . This configuration resembles the “E-shape” of the cores used in the conventional planar technology described above and depicted in FIG.  1 B. Edges  518  of the upper core portion  510  and lower core portion  540  are configured with a cornered indent  520  (not shown in lower core portion  540 ) to accommodate connecting pins described below. 
     The lower core portion  540  is configured to substantially define a mirror image of the upper core portion  510 . The upper core portion  510  can then be secured to the lower core portion  540  by an adhesive placed on surfaces  542  of the support members of the lower core portion  540 . When the support members  514  of the core portions  510  and  540  are mated together at surfaces  542 , the cylindrical member (not shown) of the upper core portion is then positioned to pass through the hollow centers of the PCBs  525 ,  530 , and  535 . 
     As shown in FIG. 6, the primary PCB  525  and the secondary PCB  530  each are generally formed as flat boards. Each of the PCBs  525  and  530  has a circular portion  615  which is substantially circular in shape with a hollow center  610 . As described above, the diameters of the hollow centers  610  of the PCBs  525  and  530  are substantially equal and can accommodate the diameter of the cylindrical member of the upper core portion  510 . Each of the PCBs  525  and  530  has a rectangular portion  620  which is substantially rectangular in shape with a leading edge  625  parallel to a tangent of the outer edge of the circular shape. The rectangular portion  620  has a width substantially as wide as the annuli of the circular portions of the PCBs  525  and  530 . The rectangular portion  620  of each PCB  525 ,  530  also preferably includes a plurality of holes  630  to accommodate connecting pins. Moreover, each rectangular portion  620  provides a conductive surface through which pins connecting the PCBs  525 ,  530  can attach in order to connect winding traces. 
     Referring to FIG. 7, six electrical conducting pins  501 ,  502 ,  503 ,  503 A,  504 , and  504 A, can penetrate the stacked PCB layers  525 ,  530  and  535 . Alternatively, more or fewer pins can be employed. The pins labeled  501  and  502  penetrate the primary PCB  525 ; pins  503 ,  503 A,  504 , and  504 A penetrate the secondary PCBs,  530  and  535 . The primary PCB  525  is positioned so that the rectangular portion  620  of the primary PCB  525  is directly opposite the rectangular portion  620  of the secondary PCBs  530  and  535 . As a result of this configuration, the pins  501  and  502  only penetrate the primary PCB  525  and the pins  503 ,  503 A,  504 , and  504 A only penetrate the secondary PCBs  530  and  535 . Therefore, no physical or electrical connection exists between the primary windings and the secondary windings. As a result, the significant risks of failure due to an electrical flashover can be minimized. The pins  501 ,  502 ,  503 ,  503 A,  504 , and  504 A act to connect the various outside terminals of the windings embedded in each PCB to a main circuit board  590 . 
     A schematic circuit diagram of the configuration of the magnetic component of FIG. 5 is illustrated in FIG.  8 . In particular, pins  501  and  502  connect the windings of the primary PCB  525  which consists of six turns in this diagram. Pins  503  and  503 A connect the windings of the secondary winding  430 , which consists of three turns in this diagram. Lastly, pins  504  and  504 A connect the windings of the secondary PCB  535 , which also consists of three turns in this diagram. The dielectric of the core portions  510 ,  540  is represented by lines  820  passing in-between the turns of the primary PCB  520  and the primary PCBs  530  and  535 . A user could easily re-configure this arrangement by replacing any one of these PCBs with another PCB wired with a different number of turns, thereby easily adjusting the turn ratio. 
     The magnetic component of FIG. 5 can be configured to define various turn ratios for a transformer. For example, FIGS. 9A and 9B illustrate a series configuration and a parallel configuration of the secondary PCBs  530  and  535 . 
     Each PCB can comprise single or multiple layers such as, for example, four or six layers. Each PCB includes an individual winding (either primary or secondary) with a predetermined number of turns. These windings are formed on the layers and can be formed using the conventional technology described above with reference to FIG.  2 . As a result, new designs with different turn ratios can be configured in a short time by simply replacing a particular four or six layer PCB with another PCB with different turn ratios. Alternatively, with additional traces etched on the main board  590 , the secondary windings can be connected in series or in parallel as described below to further configure the turn ratio according to user-defined needs. This flexibility in permitting user-configuration with a reduced number of layers of PCBs helps to reduce the overall cost of the component. 
     As shown in FIGS. 9A and 9B, several terminals can be used to connect the pins of the secondary PCBs  530  and  535 . Specifically, for example, pin  503  can be used to connect a terminal  903  to the main board  590 , pin  503 A can be used to connect a terminal  903 A to the main board  590 , pin  504  can be used to connect a terminal  904  to the main board  590 , and pin  504 A can be used to connect a terminal  904 A to the main board  590 . The terminals  903 ,  903 A,  904 , and  904 A can be connected to the various outside terminals of the windings embedded in secondary PCBs  530  and  535 . Additional traces  910 ,  912 ,  914  and  916  are etched on the main board  590  and connect pins  503 ,  503 A,  504 , and  504 A to output terminals  918  and  920  as shown in FIGS. 9A and 9B. 
     In FIG. 9A, a series configuration is depicted whereby by a connection in the form of a jumper  920  joins the windings of secondary PCB  530  with the windings of secondary PCB  535  by connecting terminals  903 A and  904 A. Pins  503  and  504  connect terminals  903  and  904  (of secondary PCB&#39;s  530  and  535 , respectively) to the main board  590  (pins  503 A and  504 A are not connected in this configuration). Due to the jumper  920  connection, the secondary windings  530  and  535  are electrically connected in series and offer double the turn ratio for the transformer. In FIG. 9B, the jumper  820  is disconnected. Pins  503 A and  504 A connect terminals  903 A and  904 A (of secondary PCB&#39;s  530  and  535 , respectively) to the main board  590 . As a result the secondary windings are electrically in parallel. 
     Alternatively, the jumper  920  can be replaced or enhanced by a hardware or software configuration on the main board. For example, an electronic switch can be configured to control the jumper  920  connection or the jumper  920  could be replaced by a hardwired jumper on the main board  110 . 
     Recall that the conventional planar technology included both the primary and secondary winding in a single twelve layer PCB. Moreover, the configuration of conventional windings (e.g., whether in parallel or in series) was predetermined by the particular connections used for the traces. Consequently, in order to change the turn ratios or parameters of the conventional magnetic component, a new PCB would need to be designed and manufactured. The stackable and user-configurable layout of the above embodiment overcomes this longstanding problem in the industry by providing several distinct advantages. For example, as described above, the arrangement allows a user to configure the component in such a way as to alter its turn ratios and thereby avoid the high costs of re-design and re-fabrication of a brand new component. Moreover, the offset configuration effectively eliminates the opportunity for flashover common in the current planar technology. Additionally, this arrangement replaces the traditional twelve layer board previously described by using a combination of a three, four, and six layer boards, which are much easier and less costly to make than the twelve layer board. This arrangement can be accomplished using the standardized, conventional designs of FIG.  3  and as a result, several different configurations can be made without invoking the design layout process. 
     While the above detailed description has shown, described, and pointed out novel features of the invention as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the device or process illustrated may be made by those skilled in the art without departing from the spirit of the invention. For example, the embodiment described contained a device with three PCBs; more or fewer PCBs are envisioned as within the scope of the invention.