WO2001037296A1

WO2001037296A1 - Solid state capacitors and methods of manufacturing them

Info

Publication number: WO2001037296A1
Application number: PCT/GB2000/004355
Authority: WO
Inventors: David Huntington
Original assignee: Avx Limited
Priority date: 1999-11-15
Filing date: 2000-11-15
Publication date: 2001-05-25
Also published as: DE60010505T2; EP1230656A1; EP1230656B1; GB9926975D0; CN1423821A; KR100675958B1; CN1272816C; US6813140B1; KR20020079733A; DE60010505D1; ATE266247T1; IL149541A0; AU1402801A; JP2003514385A; JP4405126B2

Abstract

The present invention relates to the field of solid state capacitors. The present invention seeks to provide improved capacitors and improved methods of manufacturing such capacitors. According to one aspect of the present invention there is provided a method of manufacturing solid state capacitors comprising: providing an electrically conducting substrate (109); forming a plurality of porous bodies (105) comprising valve action material on a surface of the substrate, the bodies each having an upper surface distal to the substrate; forming an electrically insulating layer over the bodies; forming a conducting cathode layer over the insulating layer applied to the bodies; and dividing the substrate into capacitor portions, each portion comprising a body and a portion of substrate, characterised in that an end region of each body portion distal from the substrate is provided with a platform (106) which is locally raised with respect to the rest of the end region, the platform providing a cathode terminal site in the final capacitor, and the substrate portion providing an anode site.

Description

Solid State Capacitors and

Methods of Manufacturing Them

The present invention relates to the field of solid state capacitors. The invention particularly relates to capacitors of the type in which a powder-formed valve action metal forms a highly porous anode body portion of a capacitor, an electrically insulating dielectric layer is formed though the porous structure of the anode body, and a conducting cathode layer is formed on the dielectric layer which layer is then electrically connected to a cathode terminal, the anode body being electrically connected to an anode terminal.

US patent specification no. 5,357,399 (Salisbury) describes a method for simultaneously manufacturing multiple such capacitors from a porous tantalum layer sintered to a tantalum substrate. The layer is machined to form anode body portions of each capacitor. After processing a top plate (substrate lid) is bonded to the processed anode body top ends. The plate forms a lid which, after machining of the substrate/anode body/plate sandwich, becomes the cathode terminal of each capacitor. United Kingdom patent application no. 9824442.9 concerns a modified version of the Salisbury method in which the volumetric efficiency of the capacitors produced is optimized by removing the need for a substrate lid as the cathode terminal of each capacitor, thereby, increasing the specific capacitive volume.

The foregoing methods permit the manufacture of very small but highly efficient capacitors. However the continued pressure of electronic circuit board design towards miniaturisation of components and ease of assembly of such boards maintains a continued need for capacitors of improved volumetric efficiency and reduced component windows (or footprint) on the circuit board. There is a particular requirement for a method of producing capacitors which have a low profile on a circuit board, in some cases having a thickness of less than 1 mm.

The present invention seeks to provide improved capacitors and improved methods of manufacturing such capacitors.

According to one aspect of the present invention there is provided a method of manufacturing solid state capacitors comprising: providing an electrically conducting substrate; forming a plurality of porous bodies comprising valve action material on a surface of the substrate, the bodies each having an upper surface distal to the substrate; forming an electrically insulating layer over the bodies; forming a conducting cathode layer over the insulating layer applied to the bodies; and dividing the substrate into capacitor portions, each portion comprising a body and a portion of substrate, characterised in that an end region of each body portion distal from the substrate is provided with a platform which is locally raised with respect to the rest of the end region, the platform providing a cathode terminal site in the final capacitor, and the substrate portion providing an anode site.

The platform may consist of or be comprised of the porous valve action material from which the bodies are made. In this case the platform may be formed by green or post- sintered forming of the bodies integrally with the platform. Preferably the platform is formed by green moulding of the bodies.

Alternatively the platform may be formed by machining of the sintered bodies. In yet another method the platform is formed by green forming of the platform onto pre- formed bodies. In another aspect of the invention the platform comprises a solid conducting material. In this case the platform may be applied as a planar frame or lattice applied to upper end regions of the bodies, which frame or lattice is subsequently formed into individual platforms for each body.

In yet another aspect, the platform is formed from a conductive material applied as a coating or paste which solidifies to form the platform.

The method of the present invention will almost always further comprise encapsulating each capacitor body portion with a protective insulating material, leaving exposed an outer surface portion of the substrate and an outer surface portion of the platform.

It may be desired to form a capacitor with anode and cathode poles on a common face or side of the capacitor. Hence in yet another aspect of the invention a conducting bridge is applied to each capacitor, extending the anode terminal site over at least a portion of the encapsulation layer. Preferably the portion of the encapsulation layer to which is applied the conducting bridge includes a region adjacent the cathode site platform, whereby electrical anodic and cathodic terminal contact with the capacitors may be made on a common side of each capacitor at terminals corresponding to the platform and the encapsulated region adjacent the platform. The conducting bridge may be formed by a conducting end cap applied to a sidewall of the capacitor portion, which end cap overlaps the substrate end of the capacitor and encapsulated portion of the platform end of the capacitor. In a preferred arrangement the conducting bridge comprises two end caps applied to opposite sidewalls, thereby to form two anode terminal contacts, one at side of the capacitor and overlapping the platform end of the capacitor.

Typically, the platforms take the form of rectilinear, circular or oval tabs or steps, usefully, the platform is generally centrally located on an substrate-distal end of each body. In one embodiment the platform is located at one side region of the substrate-distal end of each body .

In another aspect of the invention, two or more locally raised platforms are formed on the distal end of each anode body, thereby to form two or more cathode terminal sites on each body. Generally, the bodies are arranged on the substrate in an array of rows and columns, and the dividing comprises cutting along the rows and columns as is conventional in the art

The final processing step is usually a termination process. This applies solder-compatible coatings onto the cathode terminal sites on each platform and the cathode terminal sites. The termination process may comprise liquid coating of each terminal contact surface with conducting paste, and allowing the coating to solidify. In addition, or in the alternative, the termination treatment comprises metal plating to form a layer of metal or metals on the respective terminal sites.

The present invention also seeks to provide structurally novel and inventive capacitors, which may be manufactured according to the method of the present invention.

Hence according to a further aspect of the invention there is provided a solid state capacitor comprising: an electrically conducting substrate member; a porous body comprising valve action metal provided on a surface of the substrate; an electrically insulating layer formed over the free surface of the cathode and anode; a conducting cathode layer formed over the electrically insulating layer on the anode body and the cathode body; wherein the body has an upper surface distal to the substrate, which surface is formed with a locally raised platform with respect to the adjacent upper surface of the body, the locally raised portion providing a cathode terminal site and the substrate providing an anode terminal site.

Preferably the body is encapsulated by a sleeve of protective insulating material, leaving exposed an outer surface portion of the substrate as the anode site and an outer surface portion of the platform as the cathode site .

A conducting bridge may extend between the anode site to an encapsulated surface portion of body, thereby to form an anode terminal extension contact on the encapsulated body portion. Preferably, the encapsulated surface portion at which the anode terminal contact is formed is located adjacent the cathode site corresponding to the platform, whereby both anode and cathode terminal contacts to a printed circuit board may be made on a common side of the capacitor. The conducting bridge may comprise one or more conducting end caps applied to one side of each capacitor. The caps may be applied as a liquid conductive paste coating, by for example dipping.

The raised platform portion may be formed by moulding of the porous bodies on the substrate. The moulding may comprise pressing with a female die and punch arrangment. Alternatively, or in addition the raised portion may be formed by machining of pre-formed bodies.

In a preferred embodiment, the bodies each have a generally flat upper surface and the raised portion takes the form of a step in on the surface. The step may be generally centrally located on the upper surface. Alternatively the step may be located at one -side region of the upper surface.

The method may further comprise providing a termination treatment to the exposed anode and cathode terminal contacts, the treatment facilitating soldered electrical connection of the capacitor with an electrical circuit.

Typically, the bodies are arranged on the substrate an array of rows and columns, and the dividing comprises cutting along the rows and columns.

The termination treatment may comprise liquid coating of each terminal contact surface with conducting paste, and allowing the coating to solidify. The .termination treatment may further comprise electro-plating, sputter coating or vapour phase deposition on each solidified coating to form a layer of metallic material the respective terminals.

The method may include providing termination means on the terminal portions of the capacitors, thereby to facilitate electrical connection of the anode and cathode bodies to an electrical circuit.

The anode bodies may be arranged on the substrate in rows and columns, and the dividing may comprise cutting along rows and colums to separate the capacitors. The cutting is preferably carried out through a plane or planes perpendicular or substantially perpendicular to the plane of the substrate. The cutting may comprise grinding by for example a grinding wheel.

The capacitor bodies may each be formed from a pre-form layer of porous valve action material that has been applied to the substrate. The pre-form layer may be machined to form the bodies .

Preferably, before dividing, the substrate treated with a protective insulating material which infiltrates in between the bodies to encapsulate sidewalls of the bodies. The dividing process comprises cutting along the channels filled with protective material, thereby to leave a sidewall of protective material around each anode and cathode body of each cathode portion. The insulating material preferably also covers the upper surface of the bodies, other than the raised portion. Alternatively the encapsulation material may be allowed to completely cover the bodies. In this case a top layer of the encapsulation material is removed (by for example machining) to reveal the platform cathode sites.

The protective material may be a resin material which is infiltrated as a liquid and subsequently allowed to set. One suitable material is epoxy resin.

The termination coating may comprise a layer of material comprising a solid dispersion of conductive particles within a carrier matrix. The termination coating may further comprise a layer of metallic plate, such as nickel and tin layers.

Preferably respective exposed terminal sites on capacitors having common side terminals are generally coplanar so that the capacitor may stand on a flat surface with the cathode terminal and anode terminal contacting the flat surface. This makes the capacitor very well adapted for placement on and attachment to a circuit board.

The anode terminal body and the anode body may each be formed from a pre-form layer of porous valve action material that has been applied to the substrate. The preform may be applied by laying a green, un-sintered mixture of valve action metal powder and binder/lubricant on the substrate. The green mixture may then be sintered to fuse the powder into a solid highly porous pre-form, the binder/lubricant being removed by washing/dissolution of binder from the bodies before sintering.

The pre-form layer may be machined to form the anode terminal body and the anode body. Typically longitudinal and lateral grinding cuts may be employed in order to produce a network of rectilinear anode and cathode bodies on the substrate, separated by ^streetsξjjjξ corresponding to the path of the grinding cut. Naturally more complex shapes can be produced by conventional machining techniques, as required.

The insulating layer may be a dielectric layer of an oxide of the valve action metal, applied for example by conventional anodization techniques in order to build up gradually an oxide of the required thickness and integrity. In one example in which the valve action layer is tantalum, a layer of tantalum pentoxide is built up on the bodies.

The cathode layer may be applied by dipping of the anode and cathode bodies into a precursor solution of, for example manganese nitrate solution. The layer of manganese nitrate formed on the bodies may be heated to oxidise the nitrate to manganese dioxide. Repeated dipping steps may be necessary in order to build-up the optimum cathode layer.

Isolation cutting is typically carried out to^' remove all cathode layer material bridging the anode and cathode terminal portions of each capacitor. This may conveniently be achieved which the capacitors are undivided on the substrate by a machining cut along the channels separating individual bodies which extends through the cathode layer, and inevitably through the insulating dielectric layer also. To avoid the cutting process a masking resist layer may be laid in the region of the substrate between anode and cathode bodies, before the cathode layer is applied. Subsequent removal of the masking resist also removes unwanted excess cathode layer material.

Typically the termination process involves the application of a first layer of conducting carbon paste which is then cured. Next a second layer of conducting silver paste is applied, and cured. A further layer of metal plate may be applied, for example by electrodeposition. Typically layers of nickel and tin; a layer of tin/lead alloy; or a layer of gold is applied. This provides a solder-compatible surface for electrical connection.

Dividing of the substrate may be achieved by machining by for example a grinding cut. If necessary a rigid backing support may be provided for the substrate to as to provide the necessary structural rigidity to permit cutting without damaging the capacitors. The material from which the capacitor is made is typically a valve action metal, especially tantalum. However other valve action materials are not excluded from the invention, and these may include metal oxide materials or other materials which the skilled person will recognise as being suitable for use in the processes of the present invention.

Following is a description by way of example only and with reference to the accompanying drawings of methods of putting the present invention into effect.

In the drawings : -

Figure 1A is a side view of a portion of a substrate according to the present invention.

Figure IB is a side view of a portion of the substrate after encapsulation.

Figure 2 is a perspective view of a small area of the substrate portion shown in figure 1.

Figures 3A, 3B and 4A, 4B show an unfinished and finished capacitor made according to the present invention. Figures 5A, 5B, 5C and 5D show, respectively, underside, top face, side view and sectional views of a finished capacitor according to one embodiment of the present invention.

Figures 6A, 6B, 6C and 6D show, respectively, underside, top face, side view and sectional views of a finished capacitor according to another embodiment of the present invention .

Figures 7A to 7C are plan views of a substrate under processing according to a second embodiment of the present invention.

Figure 8 is a sectional view through a capacitor formed by the method of figure 7.

Figures 9A and 9B are sectional views from one side of a substrate undergoing processing according to a third embodiment of the present invention.

Figures 10A to 10D are plan views of the substrate of figure 9 during the processing sequence.

Figure 11 is a sectional view through a capacitor produce according to the third embodiment of the invention.

Figure 12 shows plan, side and sectional AA' views through the capacitor of figure 11.

Figure 13 is a sectional view through a capacitor produced according to a fourth embodiment of the present invention.

Figure 14 is a perspective view of a capacitor according to the present invention attached to a printed circuit board.

Figure 15 is a plan view of a PCB provided with a prior art capacitor and a capacitor according to a fifth embodiment of the invention.

First embodiment

A solid substrate of, for example, 0.25 mm thick tantalum wafer 10 is shown in figure 1. A top surface 9 of the substrate is covered with a dispersion of tantalum grains (not shown). The grains are fused to the tantalum wafer by sintering, thereby to form a seed layer (not shown). A conventional mixture of tantalum powder and binder/lubricant is then pressed onto the seed layer. The seed layer provides mechanical keying and enhances the bond between the green (un-sintered) powder and the substrate. The green powder mixture is then sintered to form an inter-connecting highly porous matrix of fused tantalum powder particles. The binder is burned off during the sintering process. This leaves a uniform layer of porous tantalum on the solid wafer.

The porous layer mixture is machined to form an orthogonal pattern of channels in rows 11 and columns

(not shown) . The effect of this is to produce an array of upstanding rectilinear bodies 15 on the substrate.

The bodies 15 will form capacitive bulk in the final capacitors, so are termed anode bodies hereafter. The bodies are further machined to form a step' 17 on each body upper surface region 16. The step is an oblong feature which will form the cathode terminal in each capacitor produced. The step may be produced by other methods, such as pressing/moulding of the green flowable pre-from, although machining is described for this embodiment .

The substrate and its array of upstanding bodies 15 is then subjected to a conventional anodization treatment which forms a thin dielectric layer (not shown) of tantalum pentoxide on the tantalum of the substrate and through the porous network of the powder-formed bodies. Anodization may be repeated several times in order to build-up the required depth and integrity of dielectric layer. The dielectric layer forms an electrically insulating layer for providing capacitance in the final devices .

Next the substrate 10 and bodies 15 are coated with a cathode layer-forming solution of manganese nitrate. The solution enters into the porous network to form a manganese nitrate layer on the dielectric layer. The manganese nitrate is heated in an oxygen-containing atmosphere that oxidises the manganese nitrate, forming manganese dioxide. The coating and heating process may be repeated in order to build up the required conductive layer thickness and integrity. The manganese dioxide layer is electrically conducting and provides a layer providing electrical contact with a cathode terminal in the final capacitors.

Respective layers of carbon and silver paste (shown as

38 in figure 3) are applied to the exposed top ends of the steps 17 and bodies in general. These layers provide a good electrical contact for the formation of cathode terminals on the final capacitors.

An epoxy resin liquid is infiltrated into the rows and columns to occupy the space in between bodies on the substrate. A lid (not shown) is placed on the body top ends, juxtaposed the steps 17, in order to constrain the resin to below the top ends of the steps. The resin is allowed to flow over the top surface 16 of each body, but prevented from covering the steps 17. The resin is allowed to set, and the lid layer removed, to produce the arrangement shown in figure IB, in which the resin is shown as 18.

The substrate is now divided, as shown in figure 2, to provide a plurality of individual capacitor portions. The division is conducted by means of a linear array of fine grinding wheels 20. Each cut follows along the centre line of each row 11, through a plane perpendicular to the plane occupied by the substrate. Each column cut similarly follows the centre-line of the column.

Once cutting is complete, a plurality of unfinished capacitor bodies is left, one of which 34 is shown in figure 3. Figure 3A is a top view of the unfinished capacitor, simply showing the diced substrate portion 35 of the capacitor. Figure 3B is a sectional side view along the line AA' . The cathode body 15 is surrounded by a sleeve of resin material 37. Each body is shown with the silver and carbon paste layers 38.

One end face 36 of the capacitor 34 is dipped into a liquid silver paste to coat the face and local region of the capacitor with an end cap 39, as shown in figure 4A and 4B. The coating provides a conductive bridge between the substrate 35 and the under-face 40 of the capacitor.

In order to finish the capacitor a metal plate layer is applied to the exposed surfaces 39,41 of the respective anode and cathode bodies. This can be applied by known methods such as electro-deposition and sputter coating. In a preferred arrangement a layer of nickel is applied followed by a tin-lead layer. The metal plate layer provides a solder compatible surface permitting soldering of the component to a printed circuit board. Figure 5 shows the final capacitor.

Second Embodiment

Figure 6 shows an alternative capacitor 100 according to the present invention. Each capacitor is formed with two anode terminals 101,102. In between these two anode terminals is a cathode terminal 103. It will be appreciated that the alteration to the process will involve forming the step in a central region of the body upper surface 104. In addition two end-caps are formed on each end of the capacitor by dipping of the capacitor ends in silver paste, and preferably also final (Ni/Sn) metal plating to form a solderable contact.

An advantage of this design configuration is that the capacitor has a central underside cathode terminal contact, and an anode terminal contact at each end region. This means that the capacitor is not prone to placement on a PCB in an incorrect orientation because both end regions have the same polarity. This makes automated capacitor attachment to a PCB more simple as the component is effectively polarity insensitive.

The steps involved in the manufacture of this embodiment are illustrated in figures 7A to 7C. Figure 7 A is a plan view of a tantalum substrate 109. The array is formed with a layer of sintered porous tantalum, in much the same manner as for example 1. Again, this is machined into an array of bodies 105. In this case the array is a four by four matrix of rectilinear upstanding bodies 105. Each body is further machined to remove material from two side regions 107 of each upstanding end of the bodies, thereby leaving an oblong central platform 106 on each body end. The substrate an its array of bodies is then processed by anodization to form a dielectric layer, followed by manganisation to form^' a cathode conductive layer, isolation cutting, reformation of the dielectric, and then carbon and silver coating of the end region of the bodies (as per example 1). This leaves a coated array as shown in figure 7B. A lid layer (not shown) is then applied to the upper ends of the bodies, and clamped in position. The space in between the bodies sandwiched between the substrate and the lid is then infiltrated with a liquid resin 110 (epoxy) which is then allowed to solidify. After solidification the lid is removed to leave an array of encapsulated bodies, for each of which two side regions 107 are covered with a film of encapsulation material, and the central platform is left un-encapsulated.

The substrate is then divided into individual capacitor units, one of which is shown in section in figure 8. Each unit undergoes a termination process in which terminals are applied to the anode and cathode portions to form solderable contacts. The exposed substrate surface 115 is sputter coated with Ni & Sn layers to provide a protective coat. At each end 111 and 112 an end cap 113 of adhesive paste (e.g. silver paste) is applied. The end cap provides a conductive bridge between the tantalum substrate 109 and the underside 116 of the capacitor device, so that anode terminals 117 are formed on a common side with the cathode terminal 103. The end caps and the platform 106 are each coated with nickel/tin layers to form a solderable contact to facilitate connection to a PCB.

Third embodiment

The third embodiment, shown in figure 9A et seq., is an alternative method of forming the cathode platform feature. As with embodiments 1 & 2 a solid substrate of, for example, 0.25 mm thick tantalum wafer 310 has a top surface 309, which surface is covered with a dispersion of tantalum grains (not shown). The grains are fused to the tantalum wafer by sintering, thereby to form a seed layer (not shown). A conventional mixture of tantalum powder and binder/lubricant is then pressed onto the seed layer. The seed layer provides mechanical keying and enhances the bond between the green (un-sintered) powder and the substrate. The green powder mixture is then sintered to form an inter-connecting highly porous matrix of fused tantalum powder particles. The binder is removed by a wash/dissolution process such as is descrribed in our PCT application GB98/00023 (inventor Ian Bishop) before the sintering process. This leaves a uniform layer of highly porous tantalum 313 on the solid wafer.

The porous layer mixture is machined to form an orthogonal pattern of channels in rows 312 and columns 311, as shown in figure 10A. The effect of this is to produce an array of upstanding rectilinear bodies 315 on the substrate. The bodies 315 will form capacitive bulk in the final capacitors, and are termed anode bodies hereafter.

As for the examples 1 & 2, the substrate and its array of upstanding bodies 315 is then subjected to a conventional anodization treatment which forms a thin dielectric layer (not shown) of tantalum pentoxide on the tantalum of the substrate and through the porous network of the powder-formed bodies. Anodization may be repeated several times in order to build-up the required depth and integrity of dielectric layer. The dielectric layer forms an electrically insulating layer for providing capacitance in the final devices.

Next the substrate 310 and bodies 315 are coated with a cathode layer-forming solution of manganese nitrate. The solution enters into the porous network to form a manganese nitrate layer on the dielectric layer. The manganese nitrate is heated in an oxygen-containing atmosphere that oxidises the manganese nitrate, forming manganese dioxide. The coating and heating process may be repeated in order to build up the required conductive layer thickness and integrity. The manganese dioxide layer is electrically conducting and provides a layer providing electrical contact with a cathode terminal in the final capacitors. After application of the manganisation layer, conventional isolation cuts are made along the bottom of the channels between anode bodies, which cuts (by for example shallow sawing/grinding) remove any stray manganese dioxide bridging between the anode body and the tantalum substrate. If left these would cause a short in the final capacitors, making them useless. The cuts also inevitably remove the underlying insulating dielectric layer, so a "reformation" process is carried out to reform the tantalum pentoxide layer in the region of the isolation cuts.

Respective cap layers of carbon and silver paste (shown as 338 in figure 10B) are applied (by for example dipping) to the exposed top end regions of the bodies. These layers provide a good electrical contact for the formation of cathode terminals on the final capacitors.

In the present embodiment, rather than machining the bodies to form a step 17 (figure IB) or platform 106 (figure 7A) as per embodiments 1 & 2 on each body upper surface, the steps 317 are formed en masse by attachment of a planar alloy frame 320 to the upper surface. The frame may be made for example from alloy 42 (nickel/iron). The frame is made up of four lateral portions 321 and two orthogonal edge portions 322. One surface of each lateral portion is coated with silver adhesive paste 323 along its length. This adhesive surface is then juxtaposed the top ends of the anode bodies, as shown in figure IOC. The lateral portions are aligned over a central region of each body top end as shown in the figure. The adhesive is allowed to set, bonding the frame to the anode bodies. A lid layer ( nt shown) is then applied and clamped to the alloy frame. An epoxy resin encapsulation resin is then infiltrated between the bodies and coating the exposed upper surfaces of each anode body. On removal of the lid layer the frame 320 is the only portion left un-coated with resin, as shown in figure 10D. The substrate is then divided into individual capacitors, in which the alloy frame portions 321 form the cathode platforms, as shown in figure 11. The termination process is completed as per example 3 to produce a capacitor of outwardly identical configuration.

In order to finish the capacitor a metal plate layer is be applied to the exposed surfaces of the respective anode and cathode portions. This can be applied by known methods such as electro-deposition and sputter coating. In a preferred arrangement a layer of nickel is applied followed by a tin-lead layer. The metal plate layer provides a solder compatible surface permitting soldering of the component to a printed circuit board.

The final configuration is shown in figure 12

Fourth Embodiment

An alternative process for forming the cathode platform involves building up a layer of conductive paste on each anode body of the array. The process proceeds as per example 3 until a frame is applied to the array of bodies. At this point a conductive pad of adhesive silver paste is applied by stencilling to a central portion of each anode end surface. Several layers of adhesive may be applied to form the desired height of cathode platform. Once the pads have cured, the process continues as per example 3 to produce a capacitor in which the conductive paste pad replaces the alloy platform of example 3. Figure 13 shows a capacitor 400 in which the adhesive pad is labelled 401.

Figure 14 is a perspective view of a capacitor 501 produced by any of examples 2 to 4 in place on a section of printed circuit board PCB 500. The PCB has a U-plan positive rail 502 and an elongate negative rail 503. The U-plan rail contacts each of the end anode regions of the capacitor 504,505. The elongate rail 503 contacts the cathode platform contact surface (obscured) of the capacitor.

Fifth Embodiment

The foregoing examples have shown methods of manufacturing capacitors, each having a single cathode terminal and one or two anode terminals. It is within the scope of the present invention to provide a capacitor having an array of cathode terminals by forming a plurality of platforms on the anode body by the same methods, mutatis mutandis, as are described in the foregoing specific description. Figure 15 shows a PCB 549 upon which are mounted such a capacitor 550 next to a conventional prior art solid state tantalum anode capacitor 551. The capacitor has two anode terminals 552,553 at opposite sides thereof. These contact corresponding PCB anode tracks 554,555 on the PCB. There are four cathode terminals 556 formed on t e underside of the capacitor. Each of these terminals may be formed by the methods of any of examples 1 to 4 of the foregoing, viz: machining of the anode body, application of a solid metal plate to the anode body, application of a conductive paste tab. These terminals are aligned with four separate cathode terminal tracks 557 on the PCB.

The invention described herein provides, inter alia, methods particularly useful for producing low-profile (thin) capacitors having terminals which may be arranged on a common face of the capacitor.

Claims

1. A method of manufacturing solid state capacitors comprising: providing an electrically conducting substrate; forming a plurality of porous bodies comprising valve action material on a surface of the substrate, the bodies each having an upper surface distal to the substrate; forming an electrically insulating layer over the bodies; forming a conducting cathode layer over the insulating layer applied to the bodies; and dividing the substrate into capacitor portions, each portion comprising a body and a portion of substrate, characterised in that an end region of each body portion distal from the substrate is provided with a platform which is locally raised with respect to the rest of the end region, the platform providing a cathode terminal site in the final capacitor, and the substrate portion providing an anode site.

2. A method as claimed in claim 1 wherein the platform comprises the porous valve action material from which the bodies are made.

3. A method as claimed in claim 2 wherein the platform is formed by green or post-sintered forming of the bodies .

4. A method as claimed in claim 3 wherein the platform is formed by green moulding of the bodies.

5. A method as claimed in claim 3 or 4 wherein the platform is formed by machining of the sintered bodies.

6. A method as claimed in any of claims 3 to 5 wherein the platform is formed by green forming of the platform onto pre-formed bodies.

7. A method as claimed in claim 1 wherein the platform comprises a solid conducting material.

8. A method as claimed in claim 4 wherein the platform is applied as a planar frame or lattice applied to upper end regions of the bodies on the substrate, which frame or lattice is subsequently formed into ^' individual platforms for each body.

9. A method as claimed in claim 8 wherein the frame or lattice comprises a solid metal or metal alloy planar sheet.

10. A method as claimed in claim 1 wherein the platform is formed from a conductive material applied as a coating or paste which solidifies to form the platform.

11. A method as claimed in any preceding claim and further comprising encapsulating each capacitor body portion with a protective insulating material, leaving exposed an outer surface portion of the substrate and an outer surface portion of the platform.

12. A method as claimed in any preceding claim wherein a conducting bridge is applied to each capacitor, extending from the anode terminal site to form an extension of the anode site disposed on a portion of the encapsulation layer.

13. A method as claimed in claim 12 wherein the portion of the encapsulation layer to which is applied the conducting bridge includes a region adjacent, the cathode site platform, whereby electrical anodic and cathodic terminal contact with the capacitors may be made on a common side of each capacitor at terminals corresponding to the platform and the encapsulated region adjacent the platform.

14. A method as claimed in claim 12 or claim 13 wherein the conducting bridge is formed by a conducting end cap applied to a sidewall of the capacitor portion, which end cap overlaps the substrate end of the capacitor and encapsulated portion of the platform end of the capacitor.

15. A method as claimed in claim 14 wherein the conducting bridge comprises two end caps applied to opposite sidewalls, thereby to form two anode terminal contacts, one at side of the capacitor and overlapping the platform end of the capacitor.

16. A method as claimed in any preceding claim wherein the platforms take the form of rectilinear, circular or oval tabs or steps.

17. A method as claimed in any preceding claim wherein the platform is generally centrally located on an substrate-distal end of each body.

18. A method as claimed in any of claims 1 to 16 wherein the platform is located at one side region of the substrate-distal end of each body.

19. A method as claimed in any preceding claim wherein the bodies are arranged on the substrate in an array of rows and columns, and the dividing comprises cutting along the rows and columns.

20. A method as claimed in any preceding claim wherein a termination process applies solder-compatible coatings onto the anode terminal sites on each platform and the cathode terminal sites.

21. A method as claimed in claim 20 wherein the termination process comprises liquid coating of each terminal contact surface with conducting paste, and allowing the coating to solidify.

22. A method as claimed in claim 20 or claim 21 wherein the termination treatment comprises metal coating to form a layer of metal or metals on the respective terminal sites .

23. A method as claimed din any preceding claim wherein two or more locally raised platforms are formed on the distal end of each anode body, thereby to form two or more cathode terminal sites on each body. J-5

24. A solid state capacitor comprising: an electrically conducting substrate member; a porous body comprising valve action metal provided on a surface of the substrate; an electrically insulating layer formed over the free surface of the cathode and anode; a conducting cathode layer formed over the electrically insulating layer on the anode body and the cathode body; wherein the body has an upper surface distal to the substrate, which surface is formed with a locally raised platform with respect to the adjacent upper surface of the body, the locally raised portion providing a cathode terminal site and the substrate providing an anode terminal site.

25. A capacitor as claimed in claim 24 wherein encapsulating the body is encapsulated by a protective insulating material, leaving exposed an outer surface portion of the substrate as the anode site and an outer surface portion of the platform as the cathode site.

26. A capacitor as claimed in claim 25^' wherein a conducting bridge extends between from the anode site to an encapsulated surface portion of body, thereby to form an anode terminal contact extension on the encapsulated body portion.

27. A capacitor as claimed in claim 26 wherein the encapsulated surface portion at which the anode terminal contact is formed is located adjacent the cathode site corresponding to the platform, whereby both anode and cathode terminal contacts to a printed circuit board may be made on a common side of the capacitor.

28. A capacitor as claimed in claim 26 or 27 wherein the conducting bridge comprises a conducting end-cap applied to one side of each capacitor.

29. A capacitor as claimed in claim 28 wherein the conducting bridge comprises two or more end caps applied to opposite sides of each capacitor.

30. A capacitor substantially as hereinbefore described with reference to the drawings.

29. A method substantially as hereinbefore described with reference to the accompanying drawings .