Abstract:
A device for electrically interconnecting and packaging electronic components. A non-conducting base member having a component recess and a plurality of specially shaped lead channels formed therein is provided. At least one electronic component is disposed within the recess, and the wire leads of the component routed through the lead channels. A plurality of lead terminals, adapted to cooperate with the specially shaped lead channels, are received within the lead channels, thereby forming an electrical connection between the lead terminals and the wire leads of the electronic component(s). The special shaping of the lead channels and lead terminals restricts the movement of the lead terminals within the lead channels in multiple directions during package fabrication, thereby allowing for the manufacture of larger, more reliable devices. In another aspect of the invention, the device includes a series of specially shaped through-holes are provided within the base member to allow the routing of wire leads there through. The bottom surface of the base member is chamfered to facilitate “wicking” of molten solder up the wire leads during soldering, thereby allowing for a stronger and more reliable joint. A method of fabricating the device is also disclosed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention. 
     The present invention relates generally to non-semiconductor electrical and electronic elements used in printed circuit board applications and particularly to an improved package and method of packaging microminiature electronic components. 
     2. Description of Related Technology 
     Dual in-line chip carrier packages (DIPs) are well known in the field of electronics. A common example of a DIP is an integrated circuit, which is typically bonded to a ceramic carrier and electrically connected to a lead frame providing opposed rows of parallel electrical leads. The integrated circuit and ceramic carrier are normally encased in a black, rectangular plastic housing from which the leads extend. 
     The continuing miniaturization of electrical and electronic elements and high density mounting thereof have created increasing challenges relating to electrical isolation and mechanical interconnection. In particular, substantial difficulty exists in establishing reliable and efficient connections between fine gauge (AWG 24 to AWG 50) copper wire leads associated with various electronic elements within a given DIP. One particularly useful prior art method of connecting element leads to the lead frame terminals (or interconnecting the leads of two or more electronic elements) is disclosed in U.S. Pat. No. 5,015,981, which is illustrated herein in FIG.  1 . Commonly known as “interlock base” technology, this method involves routing the wire lead(s)  2  to an unused lead frame slot or channel  3  located at the edge of the non-conducting base member  10 , as shown in FIGS. 1 and 2. Each of these channels is designed to receive a single conductive lead frame terminal  4 , which when assembled asserts an inward bias on the package thereby forcing contact between the conductive terminals  4  of the lead frame and the electronic element lead(s)  2 ; see FIG.  2 . This method has also typically utilized a locking mechanism, such as a small tab  12  or extension on the four corner lead terminals  14 ,  15 ,  16 ,  17 , which locks into a plastic protrusion  18  of similar dimensions using the spring tension associated with the individual lead terminals  4  of the lead frame  34 . Refer again to FIG.  2 . 
     However, while simple, this locking mechanism design suffers from three primary disabilities: (i) the relatively low amount of normal force that the package can sustain during manufacture without dislodging or deforming the locking tabs; (ii) the localization of the resistive or reaction force provided by the locking tabs on the four corners of the package; and (iii) the ability of the tabs to provide resistive force in only one direction. These limitations ultimately translate to restrictions relating to the size of the package that can be reliably assembled. For example, the use of a prior art lead frame  34  and base member  10  as described above works well for 16 pin packages, which typically have a surface area (measured across the top of the package) on the order of 0.1 square inches. When larger packages with more surface area and leads are manufactured, however, the lead frame often dislocates and separates from the base member, thereby allowing for movement and/or loss of contact of the lead frame terminals with the component leads. This reduces the reliability of the final package as a whole, and increases the cost of manufacturing, since more defective or non-conforming devices are manufactured in a given production run. This dislocation and separation is largely a result of the increased downward force associated with transfer molding the larger package. Additionally, as previously noted, the distribution of force in the larger package with respect to the leads is less desirable, since the spacing between the four locking tabs on the corners of the package is increased, thereby allowing greater flexing and distortion of the leads interposed there between. The ability of the lead frame terminals  4  to move in one direction also contributed to device failure in that the potential for misalignment and separation of the lead frame and base. 
     One “work-around” solution for these problems has comprised the use of an adhesive or epoxy placed between the lead frame terminals  4  and the base member  10  so as to maintain a rigid contact between the two. However, this solution obviates many of the benefits of the interlock base technology by introducing additional process steps, materials, and curing times. 
     In a somewhat unrelated aspect, the aforementioned interlock base technology suffered from another disability; namely, a significant potential for shearing off of the soldered leads after formation. Specifically, one prior design of the interlock base used a series of “through-holes”  13  designed to accommodate multiple wire leads  2  and facilitate their bonding via a soldering process, as shown in FIGS. 3 a  and  3   b . See also Applicant&#39;s pending U.S. patent application Ser. No. 08/791,247, entitled “Through-Hole Interconnect Device With Isolated Wire Leads and Component Barriers” filed Jan. 30, 1997, which is incorporated herein by reference in its entirety. Basically, the wire leads to be joined were twisted and routed through the through-hole so as to protrude from the bottom of the package as shown in FIG. 3 a  herein. Through-holes having an essentially flat or unchamfered bottom surface were used. During soldering, there was a tendency for the molten solder  19  to form a bubble  20  around the egress point of the leads from the feed-through hole at the bottom surface. This bubble effectively displaced solder from the leads as shown in FIG. 3 b , thereby making the formation of the solder joint occur at a position lower on the leads than would occur if the bubble were not present. When the extensive portion of leads was subsequently trimmed, the entire solder joint would sometimes be inadvertently trimmed off as well, thereby potentially resulting in failure of the joint. 
     Based on the foregoing, it would be highly desirable to provide an improved apparatus and method for connecting a lead frame to a package of any size such that the physical forces associated with molding of the package and soldering of the leads would not result in movement or separation of the lead frame from the interlock base or wire leads disposed within the lead channels. Additionally, such an improved apparatus and method would allow for more complete soldering of any electrical joints located within feed-through holes within the interlock base, thereby reducing or eliminating failure of these joints due to inadvertent removal during processing. 
     SUMMARY OF THE INVENTION 
     The present invention satisfies the aforementioned needs by providing an improved microelectronic component package and interconnect device having a plurality of specially shaped lead channels which allow lead terminals to be more rigidly captured therein. 
     In a first aspect of the invention, an improved microelectronic device base member is disclosed which is fabricated from non-conductive material and includes at least one electronic component recess and a plurality of specially shaped lead channels. These lead channels are adapted to receive specially shaped lead terminals associated with a lead frame such that the lead frame and terminals are restricted from any significant movement within the lead channels during device fabrication. In one embodiment, the shapes of the lead channels and lead terminals is such so as to prevent longitudinal movement of the lead terminals within the channels in either direction, yet facilitate easy assembly. Such an arrangement allows the device to be easily assembled without additional labor or process steps, and also allows the fabrication of larger packages with a high degree of reliability. The disclosed base member also optionally includes a plurality of chamfered through-holes which permit more secure joining of the wire leads of the electronic component(s) when installed within the base member. 
     In a second aspect of the invention, an improved microelectronic device is disclosed utilizing the aforementioned base member and lead terminals. The device includes at least one electronic component having wire leads which is disposed within the base member, and a plurality of shaped lead terminals received within the shaped lead channels of the base member. The shape of the lead terminals and corresponding channels is such to restrict the movement of the lead terminals (and associated lead frame) within the channels during device fabrication, thereby allowing for constant and firm contact between the component wire leads disposed within the lead channels and the lead terminals. This design accordingly allows the reliable manufacturing or larger devices with a minimum of process steps. The device is also encapsulated in a polymer overmolding. 
     In a third aspect of the invention, an improved method for fabricating the aforementioned device is disclosed. In one embodiment of the method, the aforementioned base member is formed from a non-conductive material using a molding process. The electronic component(s) and lead frame are also formed. The electronic component is inserted in the recess of the base member, and its wire leads routed through one or more of the lead channels in the base member. Additionally, any wire leads desired to be joined with those of other components are twisted and inserted in the through-holes such that they protrude from the bottom of the base member. Next, the lead frame is mounted on the base member such that the shaped lead terminals are received and locked within the corresponding shaped lead channels, thereby forming a rugged electrical contact between the lead terminals and any wire leads routed in the channels. The base member, wire leads, and lead terminals are then dip-soldered to form permanent electrical joints. The wire leads are trimmed, and the device encapsulated in a polymer overmolding using a transfer molding process. The extensive portions of the lead terminals are then trimmed from the lead frame and formed to the desired shape. 
    
    
     These and other objects and features of the present invention will become more fully apparent from the following description and appended claims taken in conjunction with the following drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a prior art microelectronic packaging device illustrating the relationship between the lead terminals and lead channels. 
     FIG. 2 is perspective view of the prior art device of FIG. 1, illustrating the electrical interconnection between the component lead and lead terminals within a single lead channel, and the locking mechanism associated therewith. 
     FIGS. 3 a  and  3   b  are side cross-sectional views of the prior art device of FIG. 1, illustrating the prior art wire lead through-hole configuration before and after soldering, respectively. 
     FIG. 4 is a perspective view of a first embodiment of the base member and associated lead terminals of the present invention 
     FIG. 4 a  is detail plan view of the lead channels and lead terminals of FIG.  4 . 
     FIG. 4 b  is a detail perspective view of one of the second lead channels of the base member of FIG. 4, illustrating the “T-bar” arrangement. 
     FIG. 5 is a plan view of a second embodiment of the lead channels and associated lead terminals according to the present invention. 
     FIG. 6 is a plan view of a third embodiment of the lead channels and associated lead terminals according to the present invention. 
     FIG. 7 is a cross-sectional view of the first embodiment of FIG. 4, taken along line  7 - 7 , illustrating the through-hole arrangement of the present invention. 
     FIG. 8 is a perspective view of the electronic packaging device of the present invention prior to encapsulation, illustrating the placement of the various components with respect to the base member of FIG.  4 . 
     FIG. 9 is a perspective view of the electronic packaging device of the present invention, after encapsulation. 
     FIG. 10 is a flow chart illustrating one embodiment of the method of manufacturing the electronic packaging device according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference is now made to the drawings wherein like numerals refer to like parts throughout. 
     FIGS. 4 and 4 a  illustrate a first embodiment of the base member  100  and associated lead terminals  102  according to the present invention. As illustrated in FIG. 4, the base member  100  is comprised generally of a three-dimensional base body  104  having one or more electronic component recesses  106  formed at least partly therein. The body  104  includes a top surface  110 , side surfaces  112   a - 112   d , and a bottom surface  114 . The body  104  also includes a plurality of first lead channels  116  and a plurality of second lead channels  118  formed within the body  104 , described in greater detail below. The base body  104  is ideally fabricated from a non-conductive material such as a liquid crystal polymer using an injection molding process, although other materials and processes may be used. One or more wire lead through-holes  105  are also optionally formed in the base body  104 , as described below with reference to FIG.  7 . In the present embodiment, the lead channels  116 ,  118  are disposed on the opposing, elongate side surfaces  112   a ,  112   c  of the base body, and oriented in a vertical direction such that the channels  116 ,  118  run generally from the top surface  110  to the bottom surface  114 , and are parallel to one another. This orientation facilitates the routing of wire leads associated with the electronic components disposed in the recesses  106  into the lead channels  116 ,  118  when the packaging device is assembled; see FIG.  8 . The individual recesses  106  are shaped to receive any one of a variety of different electronic elements, such as toroidal induction coils also as shown in FIG.  8 . While the discussion presented herein is specific to the illustrated toroidal induction coils, it can be appreciated that a variety of different electronic components may be used in conjunction with the invention with equal success. 
     As shown in FIG. 4, a plurality of first and second lead terminals  120 ,  122  are received within the lead channels  116 ,  118  when the packaging device is assembled. These lead terminals  120 ,  122  are part of a larger lead frame  130  before being separated therefrom during manufacturing. The use of a lead frame allows all of the lead terminals to be places within their respective lead channels in one processing step, as is described further below. The lead frame  130  (and attached lead terminals  120 ,  122 ) of the present embodiment are fabricated from an electrically conductive metal alloy, although other materials may conceivably be used. 
     Referring again to FIG. 4 a , the structure and operation of the first and second lead channels  116 ,  118  and their associated lead terminals  120 ,  122  are described. The first lead channels  116  are formed so as to include a first retention element  134 . In the present embodiment, the retention elements  134  comprise a shape  136  formed in each or a subset of the first lead channels  116 . The shape  136  comprises a narrow portion  140  at the top end  142  of the channel  116 , and a wider portion  144  adjacent to and below the narrow portion  140 , hereinafter referred to as a “bayonet” shape. A complementary shape  150  in the corresponding first lead terminal  120 , having a narrow portion  152  atop a wider portion  154 , is formed to permit the lead terminal  120  to engage the lead channel  116  to prevent the lead terminal  120  from moving in a first longitudinal direction  156  beyond a desired point within the lead channel  116  when the terminal  120  and base member  100  are joined. 
     Similarly, as shown in FIGS. 4 a  and  4   b , the second lead channels  118  include a retention element  160  in the form of a shape  162 , the latter designed to engage the second lead terminals  122  when received within the channels  118 . The shape  162  employed in the second lead channels  118 , however, is different than that used in the first lead channels  116 , so as to allow the lead terminals  120 ,  122  to be inserted into their respective lead channels  116 ,  118  from the same direction, yet prevent the movement of the second lead terminals  122  in a second longitudinal direction  164  once inserted. Specifically, the second lead channels  118  use a modified “bayonet” shape having a ramp portion  165  proximate to the top portion  167  of the channel  118 , as shown in FIG. 4 b . This ramp portion  165  receives and urges a “T-bar” shape  169  formed on the distal end  170  of all or a subset of the second lead terminals  122  in a direction away from the base body  104  when the terminals  122  are inserted into the second channels  118 . When fully inserted, the T-bar shape  169  of each terminal  122  engages a shoulder region  174  on the top surface of the base body  104 , so as to prevent the withdrawal of the second lead terminals from the second lead channels  118 . Since the first and second lead terminals  120 ,  122  are rigidly connected via the lead frame  130  (prior to severance) as previously described, the interaction of the first lead channels  116  and their corresponding lead terminals  120 , and the second lead channels  118  and their corresponding terminals  122 , prevent the lead frame from moving substantially in either the first or second longitudinal directions  156 ,  164  when the terminals  120 ,  122  are mated to the base member  100 . In this manner, the lead terminals (and lead frame) are “locked” to the base member  100  via both the first and second lead channels. Furthermore, the lead terminals  120 ,  122  are precluded from moving laterally within the lead channels  116 ,  118  by the close tolerance fit between the terminals and the side walls of the channels. 
     It is noted that since the lead frame  130  and lead terminals  120 ,  122  of the present embodiment are constructed of a metallic alloy having some degree of resiliency, the outward deflection of the T-bar shape  169  of the second lead terminals  122  produces an inward bias force resisting such deflection. In this fashion, as the lead frame  130  is being mounted on the base member  100 , and the terminals  120 ,  122  inserted into their respective lead channels  116 ,  118 , a resistive force opposing the movement of the lead terminals  120 ,  122  longitudinally within the channels is created until the leads (and lead frame) are in their “locked” position, at which point the T-bar shapes  169  are received within the shoulder region  174  of the base body  104 . Hence, the lead frame and terminals are designed to “snap” onto the base member in a frictional manner. 
     Note also that the width of the base body (or alternatively, the depth of the lead channels) may also be varied as a function of vertical position on the base body so as to provide a variable interference fit with the lead terminals. Such a variable fit may be useful, for example, during assembly, so as to permit an assembler to more easily place and align the ends of the lead terminals  120 ,  122  within the lead channels  116 ,  118  before sliding the lead frame  130  fully into position. 
     It is further noted that while the embodiment of FIGS. 4-4 b  utilizes nine first lead channels  116  which are interleaved or interspersed with three second lead channels  118  on each of the elongate sides of the body  104  in a predetermined pattern, other patterns and combinations of lead channels and associated terminals may be used. For example, first and second lead channels/terminals could be dispersed in on alternating basis (i.e., one first channel, one second channel, one first channel, etc.). Alternatively, the orientation of each of the lead channels could be inverted (i.e., rotated 180 degrees) with respect to the base body  104  such that the lead frame  130  and terminals  120 ,  122  are inserted onto the top of the body  104  rather than the bottom. Many such variations are possible, and all being considered within the scope of the invention. 
     Referring now to FIG. 5, a second embodiment of the present invention is disclosed. In this second embodiment, a series of rectangular retention elements  200  are formed within all or a subset of the lead channels  202  of the base member  206 . These retention elements  200  are arranged at a given vertical elevations along the sides of the base member for simplicity of manufacturing, although other arrangements may be used. As in the embodiment of FIG. 4, a ramp portion  208  is included within each of the lead channels  202  to facilitate guiding and biasing the lead terminals  210  during mounting of the lead frame  212 . When the lead frame  212  is properly positioned on the base member  206 , the shapes  214  formed in the lead terminals  210  engage the retention elements  200  in the lead channels  202  so as to restrict movement of the lead terminals within the lead channels in both longitudinal directions  220 ,  222 . As with the embodiment of FIG. 4, the lead frame  212  and base member  206  “snap” together when the lead frame  212  is properly positioned due to the biasing force on the lead terminals  202  and the physical relationship between the components. 
     FIG. 6 illustrates a third embodiment of the base member and lead terminals of the present invention. In this third embodiment, a series of “notch” recesses  300  are formed within all or a subset of the lead channels  302  of the base member  304 . The lead terminals  306  include a corresponding shape  308  formed therein which cooperates with the recess  300  within the respective lead channel  302  to retain the lead terminals  306  in a fixed position when the lead frame  310  is mounted on the base member  304 . The fit between the lead channel recess  300  and the shape  308  of the lead terminals is such that the lead terminals again “snap” into their recesses at a desired position, aided by a plurality of ramp portions  311  disposed within the lead channels  302 . Longitudinal movement of the lead terminals  306  is restricted by the cooperation of the shapes  308  and the recesses  300 . 
     FIG. 7 is a cross-sectional view of the first embodiment of FIG. 4, illustrating the through-hole arrangement of the present invention. The base body  104  includes at least one through-hole  105  disposed within the body  104  so as to facilitate the routing and bonding of the wire leads  402  associated with the electronic component(s)  404  contained within the base member  100 . The individual wire leads  402  of the components  404  are joined, such as by twisting them together, and disposing them within the through-hole(s)  105  such that the distal portion  405  of the joined leads extends below the bottom surface  114  of the base body  104 . This arrangement facilitates mass soldering of several such joined leads, such as by dip soldering or wave soldering. The through-holes  105  are further provided with a chamfered region  406  disposed adjacent to the bottom surface  114  as shown in FIG.  7 . This chamfered region  406  helps preclude the formation of solder bubbles in the area of the through-hole (or alternatively, if a bubble does form, allows the bubble to rise above the plane of the bottom surface  114 ), thereby allowing solder  407  to “wick” up the joined leads  402  further and above the plane of the bottom surface as well. This approach dramatically reduces the occurrence of inadvertent trimming of the solder joint during subsequent process steps, since the solder joint now extends well into the through-hole  105 . 
     It will be readily appreciated that the number, size, location, and orientation of the through-holes  105  of the present invention may be varied as desired. Furthermore, such through-holes may be used with any of other embodiments of the invention, such as those described with reference to FIGS. 5 and 6 above. 
     Referring now to FIG. 8, the electronic packaging device of the present invention is now described. As shown in FIG. 8, the device  500  comprises the base member  100  previously discussed with respect to FIGS. 4-4 b , lead terminals  120 ,  122  mounted on a lead frame  130 , as well as one or more electronic components  404  having wire leads  402 . Note that the device shown in FIG. 8 is in a state of partial completion, prior to encapsulation, and is inverted from that shown in FIG. 4, to better illustrate the relationship between the electronic components  404 , wire leads  402 , lead channels  116 ,  118 , and lead terminals  120 ,  122 . It will be recognized that while the base member  100  and leads  120 ,  122  of FIGS. 4-4 b  are utilized in the device  500  of FIG. 8, other base member and lead terminal combinations may be used with equal success. The embodiment of FIG. 8 is therefore merely illustrative. 
     The electronic component  404  of the present embodiment comprise an induction coil having a doughnut shaped iron core member  522  around which are wrapped coils of thin gauge wire, with the ends of the wire extending outward and forming terminal ends or leads  402 . The components  404  of the present embodiment are disposed within their respective recesses  106  of the base body  104  in such a manner that the central axis of each coil element is aligned with that of all other coil elements as shown in FIG. 8, although it will be appreciated that other orientations and configurations may be used. This arrangement is desirable in that a minimum of space is required to accommodate a given number of components, and field interactions between each component  404  and its neighboring component(s) are generally spatially uniform and consistent from component to component. This assists in distributing any potential (voltage) generated by alternating magnetic or electric fields present during operation more evenly along the windings of each element, thereby increasing overall device longevity and permitting “tuning” of the electrical response of the package as a whole. Note that silicone or adhesive may optionally be used within the recesses  106  to maintain the components  404  in the desired position during assembly of the device  500 . 
     Through-holes  105  of the type described with reference to FIG. 7 herein are also provided in each of the component barriers  526 . These through-holes allow the interconnection of leads from the various electronic components  404  installed in the recesses, thereby providing great flexibility in the routing and interconnection of leads during both the design and assembly phases. 
     In addition to being joined in the through-holes  105 , some of the wire leads  402  of the components  404  are routed into the lead channels  116 ,  118  of the base member  100  prior to installation of the lead terminals  120 ,  122  so as to form an electrical contact with the lead terminals  120 ,  122  when the device  500  is assembled. Both the wire lead/electrical terminal contacts  530 , and the joined wire leads  402  disposed within the through-holes, are soldered in order to form a more permanent electrical joint. Ultimately, the device  500  is encapsulated in a polymer encapsulant  550  of the type well known in the electronic arts, and the lead terminals  120 ,  122  trimmed from the leadframe and deformed to the desired profile as illustrated in FIG.  9 . 
     Method of Manufacturing 
     The method of assembling the electronic packaging device of the present invention is now described with reference to FIG.  10 . In the first process steps  602 ,  604 ,  606  of the method  600 , the base member  100 , lead frame  130 , and electronic component(s)  404  are formed using processes well understood in the art. For example, the base member  100  may be formed using an injection molding process, and the lead frame formed from a metal alloy using a stamping and bending process. Many different methods of forming these components are known and may be used with equal success. 
     Next, the electronic components  404  are placed within the recesses formed within the base member  100  in step  608 . A silicone gel or other adhesive may optionally be used to aid in retaining the components  404  in their recesses during subsequent processing. The wire leads  402  of the electronic components are then routed into the lead channels  116 ,  118  in the next step  610 . If the base member  100  includes through-holes  105  such as those previously described, certain of the wire leads of the components  404  are then mechanically joined together (typically, using a twisting or comparable process) in step  612 , and then routed into the through-holes in step  614  such that the distal portion  405  of the leads  402  extends below the bottom surface of the base member  100  as shown in FIG.  7 . In the next step  616 , the formed lead frame  130  is placed on the base member  100  in the proper orientation, and the lead terminals  120 ,  122  “locked” into their respective lead channels  116 ,  118  in the following step  618  as previously described. The partially assembled device is then soldered, such as by a dip soldering process, in step  620 . When the aforementioned solder process is completed, the flux is then cleaned with an isopropyl alcohol using an ultrasonic cleaner or comparable means per step  622 . The wire leads (both those routed through the lead channels  116 ,  118 , and those routed into the through-holes  105 ) are then tried as necessary in step  624 . In the next step  626 , the device is encapsulated in a suitable plastic or polymer material, which material forms a smooth rectangular package as illustrated in FIG.  9 . The device is preferably encapsulated in an IC grade thermoset epoxy  550 , such as that available from Dexter under the Trademark HYSOL MG25F-05, or equivalent thereof. Thereafter, in steps  628  and  630  respectively, the lead frame is trimmed and formed in a die press or the like to finish the lead terminals  120 ,  122  in a suitable form, for either surface mounting or pin mounting as desired. 
     It will be recognized that while the aforementioned method  600  is described in terms of a specific sequence of steps, the order of certain of these steps may be permuted if desired. For example, while the method  600  of FIG. 10 routes the lead wires into the lead channels per a first step  610  prior to joining and routing the lead wires per subsequent steps  612 ,  614 , the order of these two operations may be reversed. Similarly, the formation of the base member, lead frame, and electronic components may occur in series, rather than parallel as shown in FIG.  10 . Additionally, it is noted that other process steps may be added, such as for inspection and/or testing of certain components, and other steps optionally deleted (such as those relating to joining and routing the joined the wire leads if no through-holes are employed within the device). Many such permutations and combinations are possible, all being considered within the scope of the present invention. 
     While the above detailed description has shown, described, and pointed out the fundamental 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 or essential characteristics of the invention. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalence of the claims are to be embraced within their scope.