Field of the Invention

The present invention relates to a circuit board assembly.

Background

Electronic components are increasingly being incorporated into printed articles, such as books, posters and greeting cards, to allow printed articles to become more interactive. Examples of interactive printed articles are described in GB 2 464 537 A, WO 2004 077286 A, WO 2007 035115 A and DE 1993 4312672 A.

Conventionally, discrete devices (such as capacitors) and packaged devices (such as microcontrollers) are mounted to a printed wiring board and the printed wiring board is mounted to or inserted into the printed article.

GB 2 453 765 A describes a problem which can arise when conductive glue is used to attach a device, such as a light emitting diode, to conductive tracks supported on a substrate. Separate regions of conductive glue deposited on the conductive tracks can be drawn together by capillary action and so form a short circuit between the tracks. GB 2 453 765 A also describes a solution to the problem, namely forming a physical barrier, such as a slot, between the tracks which prevents flow of conductive glue.

Summary

The present invention seeks to facilitate incorporation of devices into articles, such as games, books, greeting cards, product packaging and posters. According to a first aspect of the present invention there is provided a circuit board assembly comprising a module which comprises a first substrate having first and second opposite faces, a first conductive region disposed on the first face of the first substrate and a hole in or adjacent to the first conductive region and passing through the first substrate between the first and second faces, a circuit board which comprises a second substrate having first and second opposite faces, a second conductive region disposed on the first face of the second substrate and conductive ink or conductive glue disposed in the hole and between the first and second substrates. The module is mounted to the circuit board and is arranged such that the hole lies over or adjacent to the second conductive region and the conductive ink or conductive glue provides an electrical connection between first and second conductive regions.

Thus, liquid conductive ink or conductive glue can be used to help facilitate mounting the module (which may include a device) to the circuit board, for example, using capillary action.

The conductive ink may include a non-conductive adhesive. The conductive ink or glue may be water based. The conductive ink or glue may be solvent based. The conductive ink may be curable, for example using ultraviolet (UV) light. The conductive ink or glue can take the form of paste, i.e. a conductive paste.

The circuit board assembly may comprise a plurality of first conductive regions disposed on the first face of the first substrate, a plurality of second conductive regions disposed on the first face of the second substrate, a plurality of holes in or adjacent to the first conductive regions and passing through the first substrate between the first and second faces, such that at some of the first conductive regions has a corresponding hole, and conductive ink or conductive glue disposed in at least some of the holes and between the first and second substrates. At least some of the holes having conductive ink or conductive glue lie over or adjacent to a

corresponding second conductive region and the conductive ink provides an electrical connection between first and second conductive regions. The first conductive region(s) may comprise conductive ink, such as silver-, copper- or carbon-based conductive ink. The conductive ink may be printed, for example, by flexographic printing. The conductive ink may include a non-conductive adhesive. The conductive ink may be water based. The conductive ink may be solvent based. The conductive ink may be curable, for example using ultraviolet (UV) light. The first conductive region(s) may comprise conductive foil. The conductive foil may be stamped.

The second conductive region(s) may comprise conductive ink, such as silver-, copper- or carbon-based conductive ink. The conductive ink may be printed, for example, by flexographic printing. The conductive ink may include a non- conductive adhesive. The conductive ink may be water based. The conductive ink may be solvent based. The conductive ink may be curable, for example using ultraviolet (UV) light. The first conductive region(s) may comprise conductive foil. The conductive foil may be stamped.

The first substrate and/or the second substrate may be flexible. The first substrate and/or the second substrate may comprise paper, card, cardboard or other similar fibre-based material . The paper or card may comprise formable paper or card. The first substrate and/or the second substrate may be shaped (or "moulded") . For example, the first substrate and/or the second substrate may be embossed. The first and/or the second flexible substrate may comprise plastic. For example, a substrate may comprise polyethylene terephthalate (PET), polypropylene (PP) or polyethylene naphthalate (PEN) . The first flexible substrate may comprise a laminate, for example comprising a layer of fibre-based material covered by a layer of plastic or sandwiched between and one or two layers of plastic. By using a fibre- based material, less material can be used which can be environmentally friendly. The fibre-based material may comprise recycled material. The first substrate and/or the second substrate may be rigid. The hole (s) may be configured to promote capillary action. For example, the hole(s) may have a maximum diameter or width of 1 mm. The hole(s) may have a diameter or width no less than 50 μηι. The holes (s) may be configured to receive a large volume of ink or glue. For example, the hole(s) may have a minimum diameter or width of 1 mm.

The module may further comprise a device mounted on the first substrate, for example, using conductive glue, ink or tape. The device may comprise a semiconductor die. The device may comprise a microcontroller.

The second substrate may support one or more capacitive touch switches, for example in the form a finger-tip-sized (e.g. having an area of between 0.2 mm2 to 2 mm2) and/or an array of touch electrodes for a touch panel. Thus, a

microcontroller and other devices may be directly mounted or mounted via one or more other substrates to form an enhanced printed matter (such as poster or greeting card) which a user can provide input using touch.

The circuit board assembly may comprise a printed article or a part of printed article (such as a cover) . The printed article may be a greeting card, poster, book, product packaging, point of sale display, map or pamphlet.

A water-based conductive ink or glue may have an application viscosity between 90 to 300 centipoise (cP) . A UV-cured conductive ink or glue may have an application viscosity of about 250 to 600 cP. A solvent-based conductive ink or glue may have an application viscosity of 100 to 500 cP.

A water- or solvent-based conductive ink may have a solid content of 15 to 80% solids by volume and/or up to 95% by weight. A UV-cured conductive ink may be considered effectively to be 100% by volume or weight.

Conductive ink or glue, for example the first and/or second contact pads and/or bonding material, may have a thickness of at least 1 μιτι or at least 2 μηι. The conductive ink or glue may have a thickness of at least 5 μιτι or at least 10 μηι. The conductive ink or glue may have a thickness no more than 100 μιτι or no more than 50 μηι. The conductive ink or glue may have a thickness of no more than 20 μιτι or no more than 10 μηι. Dry conductive ink, for example applied by flexography, may have a thickness of between 1 and 10 μηι.

According to a second aspect of the present invention there is provided a method of fabricating a circuit board assembly, the method comprising providing a module comprising a first substrate having first and second opposite faces, a first conductive region on the first face of the first substrate and a hole in or adjacent to the first conductive region and through the first substrate between the first and second faces, providing a circuit board comprising a second substrate having first and second opposite faces and a second conductive region on the first face of the second substrate. The method may comprise adding a volume of liquid conductive ink or conductive glue on and/or adjacent to the second conductive region. The method may comprise adding conductive ink or conductive glue on the second face of the first substrate adjacent to the hole. The method comprises bringing together the first and second substrates so as to form a conductive path between the first and second conductive regions. The volume of liquid conductive ink is sufficiently large to form the conductive path.

According to a third aspect of the present invention there is provided a method of fabricating a circuit board assembly, the method comprising providing a module comprising a first substrate having first and second opposite faces, a first conductive region on the first face of the first substrate and a hole in or adjacent to the first conductive region and through the first substrate between the first and second faces and providing a circuit board comprising a second substrate having first and second opposite faces, and a second conductive region on the first face of the second substrate. The method comprises providing conductive ink or conductive glue in the hole and bringing together the first and second substrates. Providing the conductive ink or conductive glue may occur before or after bringing together the first and second substrates. Providing the conductive ink may comprise dipping the module into the conductive ink or conductive glue. Providing the hole through the first substrate may occur before providing the first conductive region on the first face of the first substrate.

The method may comprise curing the conductive ink or conductive glue, for example, by allowing the conductive ink or conductive glue to dry.

According to a fourth aspect of the present invention there is provided a circuit board assembly comprising a circuit board which comprises a substrate having first and second opposite faces, a conductive region disposed on the first face of the first substrate and a hole in or adjacent to the conductive region and passing through the substrate between the first and second faces, a device comprising a contact pad, and conductive ink or conductive glue disposed in the hole and between the device and substrate. The device is mounted to the circuit board and is arranged such that the hole lies over or adjacent to the contact pad and the conductive ink or conductive glue provides an electrical connection between contact pad and conductive region.

This can help to bond a device, such as a semiconductor die or module, onto the substrate.

The substrate may be flexible. The substrate may comprise paper, card, cardboard or other similar fibre-based material. The substrate may comprise plastic. For example, the substrate may comprise PET, PP or PEN. The flexible substrate may comprise a laminate, for example comprising a layer of fibre-based material covered by a layer of plastic or sandwiched between two layers of plastic.

The contact pad may be a bond pad. The device may comprise a plurality of contact pads, e.g. twenty or more, and the substrate may be provided with corresponding conductive regions, e.g. contact pads or conductive tracks. The conductive region(s) may comprise conductive ink, glue or foil.

The substrate may support one or more capacitive touch switches, for example in the form a finger-tip-sized (e.g. having an area of between 0.2 mm2 to 2 mm2) and/or an array of touch electrodes for a touch panel. Thus, a microcontroller and other devices may be directly mounted or mounted via one or more other substrates to form an enhanced printed matter (such as poster or greeting card) which a user can provide input using touch.

Brief Description of the Drawings

Figure 1 is a simplified, perspective view of part of a circuit board assembly;

Figure 2 is a cross section of the circuit board assembly shown in Figure 1 ;

Figure 3 illustrates a first method mounting the module to a flexible circuit board; Figure 4 illustrates a second method mounting the module to a flexible circuit board; and

Figures 5a and 5b illustrate a third method mounting the module to a flexible circuit board. Detailed Description of Certain Embodiments

Figure 1 shows part of flexible circuit board assembly 1.

Referring also to Figures la and 2, the circuit board assembly 1 comprises a module 2 and a circuit board 3. The circuit board 3 includes a flexible substrate 4 having a face 5 which supports a set of contact pads 6 (herein also referred to as "conductive regions") . The substrate 4 is formed from an insulating material, such as card, paper or plastic. The substrate 4 may take the form of a sheet of card or paper. The substrate 4 may be a laminate. In this example, only two contact pads 6 are shown. However, many contact pads 6, for example twenty or more, can be provided.

The contact pads 6 comprise conductive ink, such as silver-based conductive ink, and may be formed directly on the circuit board substrate 4. The contact pads 6 may be discrete pads which are connected to a set of conductive tracks (not shown) . However, the contact pads 6 may be provided by sections or ends of conductive tracks. In some examples, the contact pads 6 may be provided by metallic foil, for example formed directly on the circuit board substrate 4. The contact pads 6 may have dimensions (e.g. width and/or length) of at least 100 μηι. For example, the contact pads 6 have width of between 1 and 10 mm.

The module 2 comprises a flexible substrate 7, for example a sheet of card or plastic, having first and second faces 8, 9, a device 10 and a set of contact pads 11 (herein also referred to as "conductive regions") supported on a first face 8 of the substrate 7. The module 2 may include a protective cover 12 which covers the device. The contact pads 11 comprise conductive ink, such as silver-based conductive ink, and may be formed directly on the module substrate 7. In some examples, the contact pads 11 may be provided by metallic foil. The contact pads 11 may have dimensions (e.g. width and/or length) of at least 100 μηι. For example, the contact pads 11 have width of between 1 and 10 mm.

The device 10 includes a set of terminals 13, such as bond pads. Typically, terminals 13 have dimensions of about 100 μηι. However, the terminals 13 can be bigger. In this example, a simple two-terminal device 10 is shown. However, the device 10 may have many terminals, for example twenty terminals or more. The terminals 13 are electrically connected to the contact pads 11. For example, each terminal 13 fully or partially overlaps a respective contact pad 1 1 and is attached using conductive glue, ink or tape (not shown) .

Suitable modules and a method of making such modules are described in GB 2 472 047 A which is incorporated herein by reference. The modules and processes are modified, however, by punching holes 14 in the substrate either before or after forming the contact pads 1 1.

The module 2 is on the circuit board 3 such that the module substrate 7 is interposed between the device 10 and circuit board substrate 4.

Each contact pad 11 includes one or more holes 14. The holes 14 pass through the module substrate 7 between the faces 8, 9. Each hole 14 is filled with conductive ink or glue 15 which reaches (and may even extend onto) the module contact pad 11 and fills space between the module 2 and the circuit board 3 to reach a

corresponding circuit board contact pad 6. The conductive ink 15 may include a non-conductive adhesive, such as polyvinyl acetate (PVA), silicone or epoxy resin, to increase adhesion. Another set of contact pads (not shown) can be formed on the second face 9 (or "underside") of the module substrate 7. This can be used to increase contact area and, thus, lower contact resistance. The conductive ink or glue 15 can be introduced into the circuit board assembly 1 in one of several different ways.

Referring to Figures 1, la, 2 and 3, liquid conductive ink or glue 15' capable of flowing can be dropped, applied using a blade (or "squeegee") or printed, for example by flexographic printing, inkjet printing, lithographic printing, screen printing or gravure printing, onto the circuit board contact pads 6 before bringing the module 2 and circuit board 3 together. Once the conductive ink or glue 15' has been dropped, applied or printed onto the circuit board contact pads 6, the module 2 and circuit board 3 are aligned and brought into contact.

As the conductive ink or glue 15' touches the underside 9 of the module 2, it drawn or squeezed between the module 2 and circuit board 3 and into the hole 14. In some embodiments, the ink or glue 15' may be drawn into the hole by capillary action. In certain embodiments, the conductive ink or glue 15' may be forced into the hole 14. The volume of conductive ink or glue 15' and viscosity is chosen so that sufficient conductive ink 15' reaches the module contact pads 11.

The conductive ink or glue 15' can additionally or alternatively be dropped, applied or printed adjacent to the circuit board contact pads 6, for example, within a few millimetres of the circuit board contact pads 6. In this case, the conductive ink or glue 15' can be drawn or directed sideways onto the circuit board contact pads 6 as well as upwards into the hole 14. This can allow greater freedom when applying the conductive ink or glue 15'. One or more slots (not shown) and/or barriers (not shown) may be provided in the circuit board substrate 4 as described in GB 2 453 765 A to control unwanted flow of ink or glue 15' and prevent short circuits. The conductive ink or glue 15' is cured, for example by allowing it dry or by using IR or UV radiation.

The (cured) conductive ink or glue 15 provides a conductive path between the circuit board pads 6 and module contact pads 1 1. The conductive ink or glue 15 may also mechanically bond the module 2 and circuit board 3. However, additional adhesive (which may be non-conductive) may be provided.

Referring to Figures 1, la, 2 and 4, liquid conductive ink or glue 15' capable of flowing can be dropped, applied or printed onto the module contact pads 6 before or after bringing together the module 2 and circuit board 3.

The conductive ink or glue 15' is drawn or directed into the hole 14. If the module 2 and circuit board 3 are already in contact or close enough for the gap between the module 2 and board 3 to be bridged, then the conductive ink or glue 15' can continue to be drawn to and/or spread over the contact pad 6.

If the module 2 and circuit board 3 are not sufficiently close, then a film or meniscus of conductive ink or glue 15' may remain on the underside of the module 2 until the module 2 and board 3 are close enough, in which case, the conductive ink or glue 15' is drawn or directed onto the contact pad 6.

One or more slots (not shown) may be provided in the circuit board substrate 4, for example, between contact pads 5, as described in GB 2 453 765 A to control flow and prevent unwanted short circuits.

The two method of applying conductive ink or glue 15' involve dropping, applying or printing conductive ink 15' in specific points or regions of the module 2 and/or circuit board 3. This can help to control the amount of ink used and its position. However, other methods of applying the conductive ink or glue 15' can be used

Referring to Figures 1, la, 2, 5a, the module 2 is dipped into a pool 16 of liquid conductive ink or glue. Once the module 2 is removed, liquid conductive ink or glue 15' can coalesce in the holes 14, while excess ink may run off the rest of the module 2.

Referring to Figures 1, la, 2, 5b, the module 2 and circuit board 3 are aligned and brought into contact, whereupon the conductive ink or glue 15' is drawn between the module 2 and circuit board 3.

If necessary, suitable ink- or glue-repellent layers may be formed on the module 2 and/or circuit board 3 to help locate the conductive ink or glue 15'.

Flow by capillary action or viscous flow can be promoted by adjusting the viscosity and/or surface energy of the ink or glue. Together with the diameter of hole, an ink or glue having suitable flow behaviour can be found by routine experiment. The module 2 and the circuit board assembly 1 can be assembled in substantially the same way, for example, using a continuous sheet process or other high-volume process which can be carried out using printing and/or converting processes (such that as described in GB 2 472 047 A) . A flexographic printing process may be used. Pick-and-place robots can be used.

The module 2 and circuit board assembly 1 (including the module 2) can be assembled in the same plant and even in the same manufacturing line. This can help to simply manufacturing the circuit board assembly 1. Furthermore, the same or similar types of materials can be used for the first and second substrates which can help to reduce mechanical stress.

It will be appreciated that many modifications may be made to the embodiments hereinbefore described.

Conductive ink need not be used for contact pads and/ or tracks. For example, de- metallised film may be used wherein a layer of metal (such as aluminium) which coats a plastic film (such as PET) is partially removed (i.e. de-metallised) by masking and then etching to leave electrodes and tracks.

The holes may be provided in the circuit board and a device, such as a

semiconductor die or module (without holes), may be mounted on circuit board.

Conductive ink or glue is provided to the circuit board in the same or similar way to that described earlier.

The first and/or second substrate need not be flat. A substrate may be shaped (or "moulded"), for example to be embossed and/or to be contoured. Thus, the device can take the form of three-dimensional (i.e. non-flat) article, such as a computer mouse. A substrate may be formed from formable paper or card, such as Billerud FibreForm (RTM) . The first and/or second substrates may have different outline shapes. For example, the substrates need not have straight edges, but can have curved edges. The first and/or second substrates may include slots, slits, holes (which are relatively small compared to the size of a substrate) and/or apertures (which are relatively large compared to the size of a substrate) .