WO2001045254A1

WO2001045254A1 - Planar wideband inductive devices and method

Info

Publication number: WO2001045254A1
Application number: PCT/US2000/033174
Authority: WO
Inventors: Joseph H. Kiser; Robert L. Reynolds; Larry M. Romero
Original assignee: Vari-L Company, Inc.
Priority date: 1999-12-14
Filing date: 2000-12-07
Publication date: 2001-06-21

Abstract

The planar inductive devices (10) have one or more turns (16) and are operable at a wide range of frequencies on the order of 20 to 4000 MHz. The devices include a thin dielectric layer (15), formed conductors on opposite sides of the electric layer (15), a stiffener board (14) and a core (17). The turns (16) are configured for mutually aiding magnetic coupling and electric transmission line coupling to perform as the windings of transmission line inductive devices (10). The devices (10) are automatically assembled and the method includes making the devices (10) in an array of typically several hundred.

Description

PLANAR WIDEBAND INDUCTIVE DEVICES AND METHOD

This application claims the benefit under 35 U.S.C. § 119(e) of the U.S. provisional patent application no. 60/170,609 filed December 14, 1999.

Technical Field

The present invention relates to inductive devices, and more particularly to planar inductive devices operable at a very wide range of frequencies and a method of making.

Background Art

Prior known inductive devices such as inductors or transformers have been made by winding wire around various iron or ferrite core shapes. These core shapes include solenoidal, cup or pot, toroidal, binocular, multihole, and E and I. The steps of winding, lead stripping, and lead attachment required to make these devices are low reliability and labor intensive operations. The winding of these cores is usually fairly random causing unit to unit performance variations with negative yield impacts. These devices tend ro be tall, making the devices unsuitable for mounting on circuit boards with maximum height limitations.

In inductive devices with one or more conductors wound as single wire coils, the conductors are coupled by magnetic coupling such that the flux linkages of the turns overlap. Such devices are tigh ly coupled if the turns are very close. These devices generally require a large number of turns for each winding. The magnetic coupling decreases as the frequency increases, limiting the upper frequency and the frequency band width of devices coupled only by magnetic coupling.

Transmission lines are generally lines with two conductors spaced a uniform distance apart. Examples of transmission lines include coaxial cable, twin lead ribbon and twisted pair wire. The two conductors in a transmission line are mainly coupled by electric coupling. This electric coupling increases as the frequency increases, as long as the length of the windings is much less than one quarter of the wavelength.

Transmission line transformers are inductive devices that use transmission line for the windings. Ruthroff type transmission line transformers, as described in "Some Broadband Transformers", C. L. Ruthroff (Proc. IRE, vol 47, pp 1337-1342, August 1959), use twisted pair or multistrand wire. Transmission line transformers fully utilize a composite of magnetic coupling and electric coupling to provide a relatively uniform coupling of the windings over a very wide frequency range. Generally, transmission line transformers are used at radio frequencies and require few turns .

Transmission line transformers are also known to work at very high frequencies. Transmission lines look like an open circuit when the length of the transmission line approaches one fourth of the wavelength. The length of the windings provides the upper frequency limit for a transmission line transformer connected in a shorted transmission line configuration, and decreasing the length of the windings increases this upper frequency limit. The minimum length of wire wound transmission line windings is limited by the cost and technology of repeatably winding very short wire windings on very small cores .

Transmission line transformers are suitable for wide band and high frequency applications such as in modern communications apparatus. The high profile of twisted wire devices is not suitable for circuit board mounting with height limitations and the variations of wire wound devices are not acceptable.

Other inductive devices have a plurality of planar windings. Planar windings are low profile, making planar windings suitable for circuit board mounting, and planar windings do not suffer the variations of wire wound devices. The known planar windings generally have a spiral configuration. U.S. Patent 5,781,093 to Grandmont et al . discloses a planar transformer with stamped or etched multi-turn spiral windings laminated between insulative sheets. Other planar inductive devices have spiral windings formed on a substrate by circuit board manufacturing methods such as metalization or etching copper clad as disclosed in U.S. Patent 5,353,001 to

Meinel et al. or U.S. Patent 5,386,206 to Iwatani et al., respectively.

Each of these prior known planar inductive devices includes a core and depends exclusively on magnetic coupling. These devices have a limited frequency band width and are best suited for use in lower frequency applications. The prior known planar inductive devices do not have a physical configuration that allows the electric coupling of a transmission line transformer and therefore do not have the high frequency capability or the wide frequency range of transmission line transformers . Disclosure of the Invention

Planar inductive devices operating in a frequency range on the order of 20 - 4000 MHz and particularly suitable for automated surface mount assembly to a printed circuit board are disclosed. The inductive devices include a dielectric layer with uniformly spaced planar formed conductors made by plating, etching and/or deposition. In one embodiment the dielectric layer is a thin substrate and a stiffener board is electrically and mechanically attached thereto. A magnetic core, including an E core portion and an I core portion, provides increased inter-turn coupling for enhanced low frequency operation. The formed conductors are the turns of the inductive device and only one or two turns per conductor are typically required. The turns are configured and positioned relative to one another and connected to provide mutually aiding magnetic coupling as well as electric transmission line coupling to provide performance characteristics as transmission line transformers. The inductive device is assembled in a fully machine automated fashion. The method of making an inductive device includes the steps of providing an array of stiffener boards, attaching a substrate with an array of circuits to the array of stiffener boards to form a composite array, attaching an E core portion to each circuit, attaching an I core portion to each circuit and separating the composite array into individual inductive devices. A second embodiment and method of making includes inductive devices made by direct deposition of dielectric and insulating layers, and formed conductors onto a ferrite core base portion. The inductive devices incorporate the benefits of planar inductive devices and transmission line transformers. Brief Description of the Drawings

Details of this invention are described in connection with the accompanying drawings that bear similar reference numerals in which:

Figure 1 is a perspective view of an inductive device embodying features of the present invention, shown mounted on a portion of a printed circuit board.

Figure 2 is a cutaway perspective view of the inductive device of Figure 1 with the shield cover removed.

Figure 3 is an exploded view of the inductive device of Figure 1.

Figure 4 is an exploded detailed view of the circuitry of the device of Figure 1.

Figure 5 is a schematic circuit diagram of the inductive device of Figure 3.

Figure 6 is a sectional view along line 6 - 6 of Figure 2 showing an alternative circuit arrangement.

Figure 7 is a schematic circuit diagram of the inductive device of Figure 6.

Figure 8 is a sectional view along line 6 - 6 of Figure 2 showing an alternative circuit arrangement.

Figure 9 is a schematic circuit diagram of the inductive device of Figure 8.

Figure 10 is an exploded perspective view of the core of the inductive device of Figure 1. Figure 11 is a schematic diagram of the equivalent circuit of the core of Figure 10.

Figure 12 is an exploded perspective view of an alternative configuration of a substrate of an inductive device embodying features of the present invention.

Figure 13 is a sectional view along line 13 - 13 of Figure 12, with an alternative core and a stiffener board added.

Figure 14A is a top view of a first portion of an alternative core for an inductive device embodying features of the present invention.

Figure 14B is an end view of the first portion of Figure 14A.

Figure 14C is a top view of a second portion of the core of Figure 14A.

Figure 14D is an end view of the second portion of Figure 14C.

Figure 15A is a top view of a first portion of an alternative core for an inductive device embodying features of the present invention.

Figure 15B is an end view of the first portion of Figure 15A.

Figure 15C is a top view of a second portion of the core of Figure 15A.

Figure 15D is an end view of the second portion of Figure 15C. Figure 16 is an exploded perspective view of an alternate embodiment inductive device embodying features of the present invention.

Figure 17 is an exploded perspective view of an alternate configuration of the inductive device of Figure 16.

Detailed Description Of The Invention

Referring to Figures 1, 2, 3 and 4, an inductive device 10, and specifically a transformer, embodying features of the present invention is shown mounted on a printed circuit board 11 having conductive paths 12 and pads 13. The inductive device 10 includes a stiffener board 14, a dielectric layer in the form of substrate 15, formed circuitry 16, a core 17 and a shield cover 18.

Describing the specific embodiments herein chosen for illustrating the invention, certain terminology is used which will be recognized as being employed for convenience and having no limiting significance. For example, the terms "up" and "down" refer to the illustrated embodiment in its normal position during mounting to a circuit board. Further, all of the terminology above-defined includes derivatives of the word specifically mentioned and words of similar import.

The stiffener board 14 is generally box shaped with a lower surface 19 and a spaced, oppositely facing upper surface 20. A first side face 21 and a spaced, oppositely facing second side face 22 are connected by a third side face 23 and a spaced, oppositely facing fourth side face 24 at opposite ends to form a rectangular configuration with the first, second, third and fourth side faces 21, 22, 23 and 24 extending between peripheral edges of the lower surface 19 and the upper surface 20. An aperture 25, sized and shaped to receive core 17, extends through stiffener board 14 from the lower surface 19 to the upper surface 20. A plurality of conductive half vias 26 extend along the first and second side faces 21 and 22 from the lower surface 19 to the upper surface 20. The inductive device 10 is mounted on the circuit board 11 with the lower surface 19 against the circuit board 11 and with the half vias 26 solder reflowed to the pads 13 to provide the electrical connection between the inductive device 10 and the circuit board 11.

The substrate 15 is a relatively thin dielectric layer with a lower face 28 and a spaced, oppositely facing upper face 29. The substrate is sized and shaped to fit over the upper surface 20 of the stiffener board 14, and mounts thereon with a first edge 30 adjacent to first face 21, and a spaced second edge 31 adjacent to second face 22. The thickness of the substrate 15 is selected to simulate the insulation between the twisted wires of a transmission line type inductive device and is about 0.001" to 0.003". The substrate 15 also includes a first end aperture 32, an intermediate aperture 33 and a second end aperture 34 spaced respectively between the third and fourth side faces 23 and 24 of the stiffener board 14, and sized and shaped to receive the core 16 as will be described hereinafter.

The formed circuitry 16 is formed on the lower and upper faces 28 and 29 of substrate 15. The term "formed" in relation to conductors and circuitry as used herein is intended to cover plating, deposition, etching and/or any other similar planar forming or conductor printing method. Circuitry 16 includes a formed first conductor 35, a formed second conductor 36 and a formed third conductor 37. The first conductor 35 includes a planar first turn 39 on the lower face 28 that extends around the intermediate aperture 33 inside of the first and second end apertures 32 and 34, and has a first end 40 and a second end 41 opposite the first end 40. The first turn 39 extends down, around and back, and is herein referred to as generally U shaped. The first conductor 35 also includes a planar generally U shaped second turn 43 on the upper face 29 that is aligned at a uniform distance over the first turn 39. The alignment at a uniform distance of the first turn 39 and the second turn 43 provides electric transmission line coupling of the first turn 39 and the second turn 43. The second turn 43 has a first end 44 over the first end 40 of the first turn 39 and a second end 45 opposite the first end 44 and over the second end 41 of the first turn 39. The second end 41 of the first turn 39 connects to the first end 44 of the second turn 43 through a first through hole or via 42, so that the first turn 39 and second turn 43 are mutually aiding magnetically coupled. The first conductor 35, without the second and third conductors 36 and 37, is a two turn coil or inductor.

The second conductor 36 includes a planar generally U shaped third turn 47 on the lower face 28 spaced a uniform selected distance outside of the first turn 39, and having a first end 48 and a second end 49 opposite the first end 48. The second conductor 36 also includes a planar generally U shaped fourth turn 51 on the upper face 29 spaced a uniform selected distance inside of the second turn 43, and having a first end 52 and a second end 53 opposite the first end 52. The second end 49 of the third turn 47 connects to the first end 52 of the fourth turn 51 through a second through hole or via 50, so that the third turn 47 and fourth turn 51 are mutually aiding magnetically coupled. The alignment at a uniform distance of first turn 39 and third turn 47, and the alignment at a uniform distance of the second turn 43 and the fourth turn 51 provides electric transmission line coupling of first conductor 35 and second conductor 36. The first conductor 35 and second conductor 36, without the third conductor, can form various inductive devices such as transformers or baluns, examples of which are discussed hereinafter.

The third conductor 37 includes a planar generally U shaped fifth turn 55 on the lower face 28 spaced a uniform selected distance inside of the first turn 39, and having a first end 56 and a second end 57 opposite the first end 56. The third conductor 37 also includes a planar generally U shaped sixth turn 59 on the upper face 29 spaced a uniform selected distance outside of the second turn 43 and having a first end 60 and a second end 61 opposite the first end 60. The second end 57 of the fifth turn 55 connects to the first end 60 of the sixth turn 59 through a third through hole or via 58, so that the fifth turn 55 and sixth turn 59 are mutually aiding magnetically coupled.

The spacing between the first, third and fifth turns 39, 47 and 55 on the lower face 28 is selected, in the same manner as the thickness of the substrate 15, to simulate the insulation between the twisted wires of a transmission line type inductive device and is about

0.001" to 0.003". The spacing between the second, fourth and sixth turns 43, 51 and 59 on the upper face 29 is also selected to simulate the insulation between the twisted wires of a transmission line type inductive device and is about 0.001" to 0.003". The uniform spacing between the first, third and fifth turns 39, 47 and 55 and the uniform spacing between the second, fourth and sixth turns 43, 51 and 59 provides electric transmission line coupling between the first conductor 35, the second conductor 36 and the third conductor 37.

The circuitry 16 includes half via first lower pad 63, second lower pad 64 and third lower pad 65 spaced along the first edge 30 on the lower face 28, half via fourth lower pad 66, fifth lower pad 67, and sixth lower pad 68 spaced along the second edge 31 on the lower face 28, and half via first, second, third, fourth, fifth and sixth upper pads 70, 71, 72, 73, 74 and 75 on the upper face 29, each over and connected to the respective lower pad by the plated through half vias. The substrate 15 and circuitry 16 are assembled to the stiffener board 14 with each lower and upper pad pair over a half via 26 on the stiffener board, and the pad pairs are solder reflowed to the half vias 26 to electrically and mechanically attach the circuitry 16 to the stiffener board 14.

The first end 40 of the first turn 39 connects to the fourth lower pad 66 and the second end 45 of the second turn 43 connects through a fourth via 76 to the sixth lower pad 68. The first end 48 of the third turn 47 connects to the first lower pad 63 and the second end 53 of the fourth turn 51 connects to the second upper pad 71. The first end 56 of the fifth turn 55 connects to the second lower pad 64, connecting the second conductor 36 to the third conductor 37, and the second end 61 of the sixth turn 59 connects to the third upper pad 72. Circuitry 16 may also include other components such as the trim capacitance 78, to offset stray inductance, connected to the sixth lower pad 68 and the trim inductance 79, as a path length equalizer, connected between the fourth turn 51 and the second upper pad 71.

In the illustrated embodiment, as shown in the circuit schematic of Figure 5, circuitry 16 forms a DC isolated transformer with the first conductor 35 forming a two turn primary winding, and the second conductor 36 and the third conductor 37 forming a four turn secondary winding with a center tap. This transformer has a turns ratio of 2:1 and an impedance ratio of Z_S/Z_P = (2/1)² = 4.

This transformer, because of the alignment of and uniform spacing between the windings, is a transmission line transformer with mutually aiding magnetic coupling and electric transmission line coupling, and this transformer therefore has a high frequency capability and a wide frequency range. The formed conductors that form the windings of the inductive devices of the present invention can be manufactured in shorter lengths with greater uniformity than prior known wire wound devices, so that the inductive devices of the present invention can have a higher frequency capability and more consistent performance characteristics than prior known inductive devices.

Alternately, other configurations for the circuitry 16 with the first, second and third conductors 35, 36 and 37 can be provided. For example, the second end 45 of the second turn 43 may be connected to the first end 48 of the third turn 47 to form a six turn coil and a tap may be further connected between turns to form an autotransformer . Such an autotransformer would have a turns ratio of 6:1, 3:1, 2:1, 6:5 or 3:2, depending on where the tap is connected. Figures 6 and 7 show an alternative configuration for circuitry 16, without the third conductor 37, that forms a two conductor, two turns per conductor, DC isolated transformer. This transformer has a turns ratio of 1:1 and an impedance ratio of Z_S/Z_P = (2/2) ² = 1. Figures 8 and 9 show an another alternative configuration for circuitry 16, without the third conductor 37, with the second end 45 of the second turn 43 connected to the first end 48 of the third turn 47 and a tap connected between the third turn 47 and the fourth turn 51 to form an autotransformer. This transformer has a turns ratio of 4:1 or 4:3 and an impedance ratio of Z_s/Zp = (4/1)² = 16 or Z_S/Z_P = (4/3)² = 16/9.

The above descriptions of configurations of circuitry 16 are by way of example and not limitation. Additional specific configurations for the inductive devices include DC isolated wideband transformers (inverting and non-inverting) , impedance matching transformers, balanced to unbalanced DC isolated and non DC isolated, double and single balanced mixers, balanced switches, power dividers, directional couplers, inductors, and other similar inductive circuit components .

Referring to Figure 10, the core 17 is shown, including an E shaped first portion 82 and an I shaped second portion 83. The first portion 82 has a bar section 85, and spaced first end leg 86, intermediate leg 87 and second end leg 88, each extending perpendicular to the bar section 85. The first portion 82 of the core 17 is assembled to the substrate 15 with the first end leg 86, intermediate leg 87 and second end leg 88 extending through the first end aperture 32, the intermediate aperture 33 and the second end aperture 34, respectively, and the second portion 83 is assembled across the first end leg 86, intermediate leg 87 and second end leg 88 opposite the bar section 85.

Figure 11 shows the equivalent circuit of the core 17. The equivalent circuit includes the generator impedance Z_G, the load impedance Z_L, the core 17, represented by the dotted section, with L_P, the inductance of a winding on the core, and R_P, the equivalent shunt resistance of a winding on the core. The units of L_P are nano henries per turns squared (nH/TRN²) , and the units R_P are ohms per turns squared (Ω/TRN²) .

The total inductive reactance, X_Lp total, and the total shunt resistance, R_P total, should each be much greater than the load impedance, Z , for good core operation at the low frequency end of the band. In a device with Z_L = 50 Ω, values of 200 to 300 Ω for X_Lp total and R_P total work well with reasonable input to output loss and return loss. Using a value of 250 Ω, a two turn (TRN) winding and a frequency (F) of 40 MHz:

X_Lp total = 250 = 2ΠFL_P total = 6.28 (40 x 10⁶) L_P total L_P total = 250/(6.28 x 40 x 10⁶) _* 1000 nh

L_P = L_P total/ (2) ² = 1000 nH/4 TRN² = 250 nh/TRN² R_P = R_P total/ (2) ² = 250 Ω/4 TRN² = 62.5 Ω/TRN²

These represent typical minimum values for good operation at 40 MHz. The actual physical length of transformer windings when they begin to approach λ/4 at the upper frequency end begin to look like an open circuit with associated poor transmission loss and return loss as well as poor transformer interwinding coupling. Thus the ideal core shape would result in high R_P and L_P at the lowest frequency along with the shortest possible winding length. Referring again to Figure 10, the core 17 is designed to contain an L_P of at least 250 nh/TRN² and an

R_P of at least 62.5 Ω/TRN², at 40 MHz, with a minimum conductor path length. As shown, the width of the first portion 82 is 3^:/₃ X/ the width of the intermediate leg 87 is X, the widths of the first and second end legs 86 and 88 are each 1/2 X, and the first and second end legs 86 and 88 are each spaced from the intermediate leg 87 by a distance of 2/3 X. The total height of the first portion 82 is Y, the height of the bar section 85 is 3/4 Y, and the first end leg 86, intermediate leg 87 and second end leg 88 extend from the bar section 85 a height of 1/4 Y. The depth of the first portion 82 is Z. The second portion 83 of core 17 has a width of the 10/3 X, a height of 5/8 Y and a depth of Z. In the preferred embodiment of the present invention the relationship among the height, width and depth is X = Y and Z = 7/4 X.

Figures 12 and 13 show an alternative configuration for the substrate 15 and the core 17. The substrate 15 is the same as described above except that the substrate 15 does not include the first end aperture 32, the intermediate aperture 33 and the second end aperture 34. The core 17 has an E shaped first portion 90 and an E shaped second portion 91. The first portion 90 includes a bar section 93, and spaced first end leg 94, intermediate leg 95 and second end leg 96, each extending perpendicular to the bar section 93. The second portion 91 has a bar section 98, and spaced first end leg 99, intermediate leg 100 and second end leg 101, each extending perpendicular to the bar section 98. The first end leg 94, intermediate leg 95 and second end leg 96 of the first portion 90 are assembled to the lower face 28 of substrate 15 with the intermediate leg 95 surrounded by the first, second, and third conductors 35, 36 and 37 of circuitry 16 and the first and second end legs 94 and 96 outside the first, second, and third conductors 35, 36 and 37. The first end leg 99, intermediate leg 100 and second end leg 101 of the second portion 91 are assembled to the upper face 29 of the substrate 15 opposite the first end leg 94, intermediate leg 95 and second end leg 96 of the first portion 90.

Referring to Figures 14A, 14B, 14C and 14D, an alternative core 17 is shown, including a D shaped first portion 103 and a D shaped second portion 104. The first portion 103 has a D shaped base 105, a U shaped wall 106 extending along the curved portion of the periphery of the base 105, a D shaped leg 107 extending from the base 105 within the wall 106 and a U shaped channel 108 between the wall 106 and the leg 107. Figures 15A, 15B, 15C, and 15D shows another alternative core 17 including a cup or pot shaped first portion 110 and a cylindrical second portion 111. The first portion 110 has a cylindrical base 112, semicircular first and second wall sections 113 and 114 extending along the periphery of the base 112 and separated at opposite ends by first and second gaps 115 and 116, a cylindrical center leg 117 extending from the base 112 within the first and second wall sections 113 and 114, and a donut shaped channel 118 between the first and second wall sections 113 and 114 and the center leg 117.

The core 17 provides increased inter-turn coupling for enhanced low frequency operation of the inductive devices 10 of the present invention. Inductive devices 10 for use exclusively at high frequencies do not require the core 17. Such high frequency inductive devices 10 include a substrate 15, as shown in Figure 12, without the first end aperture 32, the intermediate aperture 33 and the second end aperture 34, and do not include a core 17. These high frequency inductive devices 10 can be manufactured at a lower cost, since the cost of the core 17 and the cost of forming the apertures are eliminated. However, the operational band width of such inductive devices 10 is not a great as the preferred embodiment of the present invention described above.

Figure 16 shows a second embodiment of an inductive device 120 with features of the present invention, including a core 121, a first insulating layer 122, a dielectric layer 123, a second insulating layer 124 and circuitry 125.

The core 121 has a base portion 127 and an E shaped portion 128. The base portion 127 is generally box shaped with a lower surface 130 and a spaced, oppositely facing upper surface 131. A first side face 132 and a spaced, oppositely facing second side face 133 are connected by a third side face 134 and a spaced, oppositely facing fourth side face 135 at opposite ends to form a rectangular configuration with the first, second, third and fourth side faces 132, 133, 134 and 135 extending between peripheral edges of the lower surface 130 and the upper surface 131. A plurality of conductive half vias 136 extend along the first and second side faces 132 and 133 from the lower surface 130 to the upper surface 131. The inductive device 120 is adapted to be mounted on a circuit board, as shown in Figure 1, with the lower surface 130 against the circuit board and with the half vias 136 solder reflowed to the pads on the circuit board to provide the electrical connection between the inductive device 120 and the circuit board.

The E shaped portion 128 includes a bar section 138, and spaced first end leg 139, intermediate leg 140 and second end leg 141, each extending perpendicular to the bar section 138. The first insulating layer 122 is formed by direct deposition on the upper surface 131 and includes a first end aperture 143, an intermediate aperture 144 and a second end aperture 145, sized, shaped and positioned to receive the first end leg 139, the intermediate leg 140 and the second end leg 141 of the E shaped portion 128, respectively.

Circuitry 125 includes a first conductor 147, a second conductor 148 and a third conductor 149. The first conductor 147 includes a first turn 151 and second turn 152. The first turn 151 is formed by direct deposition onto the first insulating layer 122. The first turn 151 is generally U shaped, extending around the intermediate aperture 144 inside of the first and second end apertures 143 and 145, and has a first end 153 and a second end 154 opposite the first end 153.

The second conductor 148 includes a third turn 156 and fourth turn 157. The third turn 156 is formed by direct deposition onto the first insulating layer 122.

The third turn 156 is generally U shaped, is spaced at a uniform selected distance outside of the first turn 151, inside of the first and second end apertures 143 and 145, and has a first end 158 and a second end 159 opposite the first end 158. The third conductor 149 includes a fifth turn 161 and sixth turn 162. The fifth turn 161 is formed by direct deposition onto the first insulating layer 122. The fifth turn 161 is generally U shaped, is spaced at a uniform selected distance inside of the first turn 151, and has a first end 163 and a second end 164 opposite the first end 163.

The circuitry 125 includes spaced half via first lower pad 166, second lower pad 167 and third lower pad 168 on the upper surface 131 of the base portion 127 adjacent to the first side face 132, and spaced half via fourth lower pad 169, fifth lower pad 170, and sixth lower pad 171 on the upper surface 131 of the base portion 127 adjacent to the second side face 133. The first through sixth lower pads 166 to 171 are formed by direct deposition at the same time as the first, third and fifth turns 151, 156 and 161.

The dielectric layer 123 is formed by direct deposition over the first insulating layer 122 and the first, third and fifth turns 151, 156 and 161. The directly deposited dielectric layer may be as thin as about 0.00025". The dielectric layer 123 includes a first end aperture 173, an intermediate aperture 174 and a second end aperture 175, sized, shaped and positioned match to the first end aperture 143, the intermediate aperture 144 and the second end aperture 145, respectively, of the first insulating layer 122. The second turn 152, fourth turn 157 and the sixth turn 162 are each formed by direct deposition onto the dielectric layer 123.

The second turn 152 is generally U shaped, is aligned at a uniform distance over the first turn 151, and has a first end 177 and a second end 178 opposite the first end 177. The fourth turn 157 is generally U shaped, is spaced at a uniform selected distance inside of the second turn 152, and has a first end 180 and a second end 181 opposite the first end 180. The sixth turn 162 is generally U shaped, is spaced at a uniform selected distance outside of the second turn 152, and has a first end 183 and a second end 184 opposite the first end 183.

The first conductor 147 includes a first via 186 that extends through the dielectric layer 123 and connects the second end 154 of the first turn 151 to the first end 177 of the second turn 152. The second conductor 148 includes a second via 187 that extends through the dielectric layer 123 and connects the second end 159 of the third turn 156 to the first end 180 of the fourth turn 157. The third conductor 149 includes a third via 188 that extends through the dielectric layer 123 and connects the second end 164 of the fifth turn 161 to the first end 183 of the sixth turn 162.

The circuitry 125 includes a first upper pad

191, a second upper pad 192, a third upper pad 193, a fourth upper pad 194, a fifth upper pad 195, and a sixth upper pad 196, with each of the first through sixth upper pad 191 to 196 being formed by direct deposition onto the respective one of the first through sixth lower pads 166 to 171 at the same time as the second, fourth and sixth turns 152, 157 and 162 are formed by direct deposition.

The first end 153 of the first turn 151 connects to the fourth lower pad 169 and the second end 178 of the second turn 152 connects through a fourth via 189 to the sixth lower pad 171. The first end 158 of the third turn 156 connects to the first lower pad 166 and the second end 181 of the fourth turn 157 connects to the second upper pad 192. The first end 163 of the fifth turn 161 connects to the second lower pad 167, connecting the second conductor 148 to the third conductor 149, and the second end 184 of the sixth turn 162 connects to the third upper pad 193.

The second insulating layer 124 is formed by direct deposition over the dielectric layer 123 and the second, fourth and sixth turns 152, 157 and 162. The second insulating layer 124 includes a first end aperture 198, an intermediate aperture 199 and a second end aperture 200, sized, shaped and positioned to match the first end apertures 143 and 173, the intermediate apertures 144 and 174, and the second end apertures 145 and 175, respectively, of the first insulating layer 122 and the dielectric layer 123. The first end leg 139, intermediate leg 140 and second end leg 141 of the E shaped portion 128 of the core 121 extend through first end apertures 143, 173 and 198, the intermediate apertures 144, 174 and 199, and the second end apertures 145, 175 and 200, respectively, of the second insulating layer 124, the dielectric layer 123 and first insulating layer 122 and attach to the base portion 127, with the bar section 138 extending over the second insulating layer 124.

The circuitry 125 of the inductive device 120 as described forms the DC isolated transformer of the circuit schematic shown in Figure 5. Other circuit configurations, as discussed above, can be implemented within the structure of this second embodiment.

Referring to Figure 17, an alternative to the inductive device 120 of the second embodiment is shown, in which the first, second, third and fourth vias 186, 187, 188 and 189 are replaced by a first lower tab 202, a second lower tab 203, a third lower tab 204 and a fourth lower tab 205, and a first upper tab 207, a second upper tab 208, a third upper tab 209 and a fourth upper tab 210. The first through fourth lower tabs 202 to 205 are formed by direct deposition onto the first insulating layer 122 at the same time as the first, third and fifth turns 151, 156 and 161 are formed. The first through fourth upper tabs 207 to 210 are formed by direct deposition respectively onto the first through fourth lower tabs 202 to 205 at the same time as the second, fourth and sixth turns 152, 157 and 162 are formed.

The inductive devices 10 of the present invention are designed to be produced automatically in an array of typically several hundred. First an array of substrates 15 with circuitry 16 is provided. An array of stiffener boards 14 including aperture 25 and plated through hole vias between adjacent stiffener boards 14 is provided. Solder balls are placed over the vias on the upper surface 29 of the substrates 15. The array of substrates 15 is accurately positioned and placed over array of stiffener boards 14. The solder balls are reflowed to mechanically and electrically attach the array of substrates 15 to the array of stiffener boards 14 to form a composite array. The E shaped first portions 82 of the cores 17 are pick and placed, and staked with adhesive, to the composite array. The adhesive is cured. The composite array is inverted and the I shaped second portions 83 of the cores 17 are pick and placed, and staked with adhesive, to the E shaped first portions 82. The shield covers 18 are pick and placed, and reflow soldered or staked with adhesive, over each inductive device 10. The adhesive is cured. The composite array is singulated into individual inductive devices 10 through the vias to form the half vias 26.

Similarly, the inductive devices of the second embodiment of the present invention are designed to be produced automatically in an array of typically several hundred. An array of base portions 127 of the core 121 is provided with plated through vias between adjacent base portions 127. The first insulating layer 122 is formed by deposition on the base portions 127. Next, the first, third and fifth turns 151, 156 and 162, and the first through sixth lower pads 166 to 171 are formed by deposition on the insulating layer 122 and base portions 127. Then the dielectric layer 123 is formed by deposition. The second, fourth and sixth turns 152, 157 and 162, and the first through sixth upper pads 191 to

196 are formed by deposition. The second insulating layer 124 is formed by deposition next. E shaped portions 128 are pick and placed, and staked with adhesive, onto the base portions 127. The composite array is singulated into individual inductive devices 120 through the vias to form the half vias 136.

Although the present invention has been described with a certain degree of particularity, it is understood that the present disclosure has been made by way of example and that changes in details of structure may be made without departing from the spirit thereof.

Claims

What is Claimed is:

1. An inductive device comprising: a formed first conductor including a planar first turn and a planar second turn of similar size and shape as said first turn aligned at a selected uniform distance opposite said first turn, said first and second turns being electrically connected to pass current in the same direction in said turns whereby said first turn and said second turn are coupled by mutually aiding magnetic coupling and electric transmission line coupling.

2. The device as set forth in claim 1 further comprising a formed second conductor including a third turn coplanar with and spaced a selected uniform distance from said first turn, and a fourth turn coplanar with and spaced a selected uniform distance from said second turn, said third and fourth turns being electrically connected to pass current in the same direction in said turns whereby said first conductor and said second conductor are coupled by mutually aiding magnetically coupling and electric transmission line coupling.

3. The device as set forth in claim 2 wherein said second and third turns are electrically connected to pass current in the same direction in said turns to form a four turn coil.

4. The device as set forth in claim 3 further comprising a tap between said third turn and said fourth turn to form an autotransformer.

5. The device as set forth in claim 2 further comprising a formed third conductor including a fifth turn coplanar with and spaced a selected uniform distance from said first and third, and a sixth turn coplanar with and spaced a selected uniform distance from said second and fourth turns, said fifth turn and said sixth turn being electrically connected to pass current in the same direction in said turns whereby that said first, second and third conductors are coupled by mutually aiding magnetically coupling and electric transmission line coupling.

6. The device as set forth in claim 5 wherein said fourth turn and said fifth turn are electrically connected to pass current in the same direction in said turns to form a DC isolated transformer.

7. The device as set forth in claim 5 wherein said distance from said first turn to said third turn is about 0.001" to 0.003", said distance from said first turn to said fifth turn is about 0.001" to 0.003", said distance from said second turn to said fourth turn is about 0.001" to 0.003", and said distance from said second turn to said sixth turn is about 0.001" to 0.003".

8. The device as set forth in claim 1 further comprising a planar dielectric layer of a selected thickness having a lower face and a spaced, oppositely facing upper face, with said first turn on said upper face and said second turn on said lower face so that said selected thickness equals the said selected uniform distance from said first turn to said second turn.

9. The device as set forth in claim 8 wherein said dielectric layer is a dielectric substrate.

10. The device as set forth in claim 9 wherein said substrate is a thin flexible film.

11. The device as set forth in claim 10 further comprising a stiffener board attached to said substrate for stiffening and supporting said substrate.

12. The device as set forth in claim 11 wherein said stiffener board includes a first side wall extending perpendicular to said lower face of said dielectric substrate and a second side wall spaced from and opposite first side wall, said first and second side walls having at least one conductive half via extending perpendicular to said lower face of said dielectric substrate.

13. The device as set forth in claim 8 wherein said selected thickness of said dielectric layer is about 0.00025" to 0.003".

14. The device as set forth in claim 8 further comprising a ferrite core extending around said first conductor.

15. The device as set forth in claim 14 wherein said core includes an E shaped first portion and an I shaped second portion, said first portion having a bar section and spaced first end, intermediate and second end legs each extending perpendicular to said bar section, and said dielectric layer includes spaced first end, intermediate and second end apertures sized and shaped to receive said first end, intermediate and second end legs with said first end and second end apertures outside said first and second turns and said intermediate aperture inside said first and second turns, said first end, intermediate and second end legs extending through said first end, intermediate and second end apertures and said second portion of said core being attached to said first portion of said core at said first end, intermediate and second end legs.

16. The device as set forth in claim 15 wherein said first end and second end legs are each half as wide as said intermediate leg, said bar section is three quarters of the total height of said first portion and said legs are the other one quarter of the height of said first portion, and said second portion is five eighths the height of said first portion.

17. The device as set forth in claim 14 wherein said core includes E shaped first and second portions each having a bar section and spaced first end, intermediate and second end legs each extending perpendicular to said bar section, said first portion attaching to said lower face with said first end and second end legs outside said first and second turns and said intermediate leg inside said first and second turns, and said second portion attaching to said upper face opposite said first portion.

18. The device as set forth in claim 14 wherein said core includes D shaped first and second portions, said first portion having a D shaped base with a U shaped wall extending therefrom and a D shaped inner leg within and spaced from said wall to form a U shaped channel, and said dielectric layer includes an aperture therethrough inside said first and second turns and sized and shaped to receive said inner leg, said inner leg extending through said aperture and attaching to said second portion, said wall surrounding said dielectric layer and attaching to said second portion.

19. The device as set forth in claim 14 wherein said core includes a cup shaped first portion and a cylindrical second portion, said first portion having an outer wall and an inner leg within and spaced from said wall, and said dielectric layer includes an aperture therethrough inside said first and second turns and sized and shaped to receive said inner leg, said inner leg extending through said aperture and attaching to said second portion, said wall surrounding said dielectric layer and attaching to said second portion.

20. The device as set forth in claim 14 wherein said core includes a base portion and an E shaped portion, said base portion having a surface and an insulating layer deposited on said surface with said first turn being deposited over said insulating layer, said dielectric layer being deposited over said first turn and said second turn being deposited over said dielectric layer, said E shaped portion having a bar section and spaced first end, intermediate and second end legs each extending perpendicular to said bar section, said insulating layer and said dielectric layer each having spaced first end, intermediate and second end apertures therethrough sized and shaped to receive said first end, intermediate and second end legs with said first end and second end apertures outside said first and second turns and said intermediate aperture inside said first and second turns, said first end, intermediate and second end legs extending through said first end, intermediate and second end apertures of said insulating and dielectric layers and attaching to said base portion.

21. The device as set forth in claim 20 wherein said first turn is connected to said second turn by a conductive via in said dielectric layer.

22. The device as set forth in claim 20 wherein said first turn is connected to said second turn by direct deposition of an end of said second turn on an end of said first turn.

23. A planar wideband inductive device comprising: a dielectric substrate of thin flexible film having a lower face, a spaced, oppositely facing upper face, and spaced first end, intermediate and second end apertures extending between said first and upper faces, a stiffener board laminated to said substrate for stiffening and supporting said substrate, said stiffener board having a single aperture therethrough around said first end, intermediate and second end apertures of said substrate, said stiffener board having a first side wall extending perpendicular to said lower face of said dielectric substrate and a second side wall spaced from and opposite first side wall, said first side wall having a half via extending perpendicular to said lower face of said dielectric substrate, a formed first conductor including a generally U-shaped first turn on said lower face around said intermediate aperture having a first end and a second end opposite said first end and a generally U-shaped second turn on said upper face, aligned at a uniform distance over said first turn, having a first end over said first end of said first turn and a second end opposite said first end, said second end of said first turn being electrically connected to said first end of said second turn, said first end of said first turn being electrically connected to said half via, a formed second conductor including a generally U-shaped third turn on said lower face extending around said intermediate aperture spaced a uniform selected distance from said first turn and having a first end and a second end opposite said first end and a generally U- shaped fourth turn on said upper face spaced a uniform selected distance from said second turn and having a first end and a second end opposite said first end, said second end of said third turn being electrically connected to said first end of said fourth turn, a formed third conductor including a generally U-shaped fifth turn on said lower face spaced a uniform selected distance from said first and third turns and having a first end and a second end opposite said first end and a generally U-shaped sixth turn on said upper face spaced a uniform selected distance from said second and fourth turns and having a first end and a second end opposite said first end, said second end of said fifth turn being electrically connected to said first end of said sixth turn, and a ferrite core having an E shaped first portion with a bar section and spaced first end, intermediate and second end legs each extending perpendicular to said bar section, and an I shaped second portion, said first end, intermediate and second end legs extending through said first end, intermediate and second end apertures, respectively, of said substrate and attaching to said second portion.

24. A method of making inductive devices comprising the steps of: providing an array of planar substrates, each said substrate including a dielectric layer and a formed first conductor, said dielectric layer having a lower face and a spaced, oppositely facing upper face, said first conductor having a generally U-shaped first turn on said lower face and a generally U-shaped second turn on said upper face aligned at a uniform distance over said first turn, said first turn and said second turn being electrically connected to pass current in the same direction in said turns, providing an array of stiffener boards, mechanically and electrically attaching said substrates to said stiffener boards to form a composite array, and separating said composite array into individual inductive devices.

25. The method as set forth in Claim 24 wherein said step of attaching said substrates to said stiffener boards includes the step of reflowing solder spheres.

26. The method as set forth in Claim 25 wherein said step of reflowing is in a vacuum oven that has nitrogen periodically introduced so said reflowing is fluxless .

27. The method as set forth in Claim 24 further comprising the steps of: providing a ferrite core for each substrate, and attaching said cores to said composite array before said step of separating.

28. The method as set forth in Claim 27 wherein each said core has an E shaped portion with a bar section and spaced first end, intermediate and second end legs each extending perpendicular to said bar section, and an I shaped portion, each said stiffener board has an aperture therethrough sized and shaped to receive at least one said core, each said substrate has spaced first end, intermediate and second end apertures therethrough sized and shaped to receive said first end, intermediate and second end legs of said E shaped portion with said first end and second end apertures outside said first and second turns and said intermediate aperture inside said first and second turns, and said step of attaching said cores includes the substeps of: picking and placing one said E shaped portion onto each substrate with said first end, intermediate and second end legs extending through said first end, intermediate and second end apertures, respectively, staking said E shaped portions to said composite array with an adhesive, inverting said composite array, picking and placing one said I shaped portion across said first end, intermediate and second end legs of said E shaped portion, and staking said I shaped portions to said E shaped portions with an adhesive to attach said E shaped and I shaped portions to form said ferrite core around said first and second turns.

29. The method as set forth in Claim 28 wherein said step of staking said E shaped portions includes curing said adhesive and said step of staking said I shaped portions includes curing said adhesive.

30. The method as set forth in Claim 27 wherein each said core includes E shaped first and second portions each having a bar section and spaced first end, intermediate and second end legs each extending perpendicular to said bar section, with said intermediate leg being sized and shaped to fit within said first and second turns and said first and second end legs being sized and spaced to fit outside said first and second turns, each said stiffener board has an aperture therethrough sized and shaped to receive one said first portion, and said step of attaching said cores includes the substeps of: picking and placing a first portion onto each substrate with said intermediate leg within said first and second turns and said first and second end legs outside said first and second turns, staking said first portions to said composite array with an adhesive, inverting said composite array, picking and placing a second portion onto each substrate with said intermediate leg within said first and second turns and said first and second end legs outside said first and second turns, and staking said second portions to said composite array with an adhesive to form said ferrite core around said first and second turns.

31. The method as set forth in Claim 24 further comprising the step of attaching a shield cover over each substrate before said step of separating.

32. The method as set forth in Claim 24 wherein said array of support boards includes vias between said support boards and said step of separating includes dicing said composite array through said vias to form half vias on each support board with one of said half vias electrically connecting to said first turn, said half vias providing means for reflow soldering each said inductive device to a circuit. .

33. The method as set forth in Claim 24 further comprising the step of automatically loading said individual inductive devices into EIA compliant Surface Mount Carrier tape.

34. A method of making inductive devices comprising the steps of: providing an array of planar substrates, each said substrate including a dielectric layer and a formed first conductor, said dielectric layer having a lower face and a spaced, oppositely facing upper face, said first conductor having a generally U-shaped first turn on said lower face and a generally U-shaped second turn on said upper face substantially parallel to said first turn, said first turn being electrically connected to said second turn to pass current in the same direction in said turns, each said substrate including an intermediate aperture within said first and second turns and first and second end apertures oppositely spaced from said intermediate aperture outside said first and second turns, providing an array of stiffener boards with vias between said stiffener boards and each said stiffener board having an aperture therethrough, placing said array of substrates over said array of stiffener boards with solder sphere therebetween, reflowing said solder spheres in a vacuum oven that has nitrogen periodically introduced to mechanically and electrically attach said substrates to said stiffener boards to form a composite array with said first turn on each substrate being electrically connected to one said via, providing an E shaped core first portion for each said substrate, each said first portion having a bar section and spaced first end, intermediate and second end legs each extending perpendicular to said bar section and sized and shaped to fit through said first end, intermediate and second end aperture, respectively, picking and placing an E shaped ferrite portion onto each substrate with said first end, intermediate and second end legs extending through said first end, intermediate and second end apertures, respectively, staking said E shaped ferrite portions to said composite array with an adhesive, and curing said adhesive, inverting said composite array, providing an I shaped ferrite portion for each said substrate, picking and placing one said I shaped ferrite portion across said first end, intermediate and second end legs of said E shaped ferrite portion, and staking said I shaped ferrite portions to said E shaped ferrite portions with an adhesive and curing said adhesive to form a ferrite core around said first and second turns, attaching a shield cover over each substrate, separating said composite array into individual devices by dicing through said vias to form half vias on each support board, said half vias providing means for reflow soldering each said inductive device to a circuit, and automatically loading said individual inductive devices into EIA compliant Surface Mount Carrier tape.

35. A method of making inductive devices comprising the steps of: providing an array of ferrite base portions, each said base portion having a planar surface, providing a ferrite E shaped portion for each said base portion, each said E shaped portion having a bar section and spaced first end, intermediate and second end legs each extending perpendicular to said bar section depositing a first insulating layer on said planar surface of each said base portion, each said first insulating layer having spaced first end, intermediate and second end apertures therethrough sized and shaped to receive said first end, intermediate and second end legs of said E shaped portion, depositing a conductive generally U-shaped first turn on each said first insulating layer around said intermediate aperture and inside said first and second end apertures of said first insulating layer, depositing a dielectric layer on each said first insulating layer over said first turn, each said dielectric layer having spaced first end, intermediate and second end apertures therethrough sized, shaped and located to match said first end, intermediate and second end apertures of said first insulating layer, depositing a conductive generally U-shaped second turn on each said dielectric layer aligned over said first turn, electrically connecting each said first turn to each said second turn to pass current in the same direction in said turns whereby said first turn and said second turn form a mutually magnetically coupled first conductor, depositing a second insulating layer on said dielectric layer over said second turn, each said second insulating layer having spaced first end, intermediate and second end apertures therethrough sized, shaped and located to match said first end, intermediate and second end apertures of said first insulating layer and said dielectric layer, attaching one said E shaped portion to each said base portion with said first end, intermediate and second end legs extending through said first end, intermediate and second end apertures, respectively, of said first insulating, dielectric and second insulating layers and directly contacting said base portion, and separating said array into individual inductive devices. .

36. The method as set forth in Claim 35 wherein said step of electrically connecting includes forming a via in said dielectric layer between each said first turn and each said second turn

37. The method as set forth in Claim 35 wherein said step of electrically connecting includes forming a cutout portion along an edge of said dielectric layer with an end said first turn extending on said first insulating layer beyond said cutout portion in said dielectric layer, and directly depositing an end of said second turn onto said end of said first turn.

38. The method as set forth in Claim 35 further comprising the steps of: before depositing said dielectric layer, depositing a conductive generally U-shaped third turn on each said first insulating layer around said intermediate aperture and inside said first and second end apertures of said first insulating layer parallel to and spaced from said first turn, after depositing said dielectric layer, depositing a conductive generally U-shaped fourth turn on each said dielectric layer parallel to and spaced from said second turn, and electrically connecting each said third turn to each said fourth turn to pass current in the same direction in said turns whereby said third turn and said fourth turn form a mutually magnetically coupled second conductor.