Printed circuit board

Abstract

Printed circuit board A printed circuit board, wherein the printed circuit board comprises an upper surface and a lower surface and a plurality of cavities which extend from the upper surface into the printed circuit board The plurality of cavities are arranged in a grid array for receiving a plurality of connectors arranged in a grid array on a device. The printed circuit board further comprises a plurality of conductive traces. Each of the plurality of cavities extend from an opening in the upper surface and have a conductive adhesive therein for mechanically and electrically coupling a connector to a conductive trace of the plurality of conductive traces.

Description

[0001] Printed circuit board

[0002] The invention disclosed herein relates to a printed circuit board; a printed circuit board assembly comprising a printed circuit board and a grid array device; and a method of manufacturing a printed circuit board assembly.

[0003] It is convention to mechanically and electrically couple a component such as a grid array device to a printed circuit board by soldering. Connectors (for example, solder balls) arranged in a grid array and coupled to conductive pads on a lower surface of the grid array device are aligned with conductive pads arranged in a grid array on an upper surface of the printed circuit board. The connectors are then melted and cooled to form bonds between the conductive pads of the grid array device and those of the printed circuit board. The connectors may be melted and cooled by passing the grid array device and printed circuit board, once aligned, through a reflow oven.

[0004] A high temperature (typically up to 260°C) is required to melt the connectors. Therefore, it is necessary for the substrate of the printed circuit board to be able to withstand this high temperature without being degraded and / or deformed. In some examples, the material from which the substrate is formed must have a sufficiently high glass transition temperature to retain its rigidity under this high temperature, thereby limiting the materials from which the substrate can be formed to, for example, polyamide and FR4.

[0005] Furthermore, it can be challenging to correctly bond the conductive pads of the grid array device to those of the printed circuit board. Misalignment of the connectors with the conductive pads of the printed circuit board can result in incorrect bonds forming between the conductive pads of the grid array device and those of the printed circuit board. Also, unconstrained movement of the melted connectors may also result in, for example, inadequate bonds forming between the conductive pads of the grid array device and those of the printed circuit board, bridges forming between two or more of the printed circuit board conductive pads, or connectors merging, which may result in electrical short circuits.

[0006] It can also be challenging to recycle the grid array device and / or printed circuit board. To decouple the grid array device from the printed circuit board, often moisture must first be evaporated (typically requiring a temperature of around 125°C). The connectors must then be re-melted (typically requiring a temperature of 210°C to 260°C) and removed from the conductive pads. Any remaining residue from the connectors must then be cleaned from the conductive pads, without damaging them. For the grid array device, new connectors must thenbe added to the conductive pads. The complexity of this process and the energy required means often only the most valuable of devices are recycled.

[0007] A first aspect of the claimed invention is a printed circuit board, wherein the printed circuit board comprises:

[0008] an upper surface and a lower surface;

[0009] a plurality of cavities extending from the upper surface into the printed circuit board, wherein the plurality of cavities are arranged in a grid array for receiving a plurality of connectors arranged in a grid array on a device; and

[0010] a plurality of conductive traces,

[0011] wherein each of the plurality of cavities extend from an opening in the upper surface and have a conductive adhesive therein for mechanically and electrically coupling a connector to a conductive trace of the plurality of conductive traces.

[0012] Thus, this printed circuit board allows a standard grid array device to be mechanically and electrically coupled to the conductive traces by receiving each connector of the grid array device into a cavity with a conductive adhesive therein which functions to electrically and mechanically couple the connector to a conductive trace.

[0013] A second aspect of the claimed invention is a printed circuit board assembly, wherein the printed circuit board assembly comprises:

[0014] the printed circuit board as described in the first aspect; and

[0015] a grid array device, wherein the grid array device comprises:

[0016] a device, wherein the device comprises an upper surface and a lower surface; and

[0017] a plurality of connectors arranged in a grid array, wherein the plurality of connectors extend from the lower surface of the device,

[0018] wherein a connector of the plurality of connectors is received within each of the plurality of cavities and mechanically and electrically coupled to the conductive traces by the conductive adhesive.

[0019] As this printed circuit board assembly uses conductive adhesive as opposed to solder to mechanically and electrically couple the grid array device and printed circuit board, and conductive adhesive can typically electrically and mechanically couple a connector to a conductive trace without the high temperatures required by soldering, then not only does the process require less energy, but as the range of materials which are able to withstand this temperature is higher, this makes a wider range of materials suitable for forming the substrateof the printed circuit board. Examples of materials which would be suitable for use in this method, but not the soldering method, include bioplastics (for example, polyethylene terephthalate (PET) and polyethylene naphthalate (PEN)) and polycarbonates.

[0020] The cavities may also function to correctly align the connectors with the conductive traces and maintain that alignment whilst the conductive adhesive mechanically and electrically couples the connectors to the conductive traces. This alignment mechanism reduces the likelihood of incorrect bonds forming between the conductive pads of the printed circuit board and those of the grid array device. Also, containing the conductive adhesive within the cavities constrains movement of the conductive adhesive, thereby reducing the likelihood of incorrect bonds forming, which can lead to electrical short circuits.

[0021] Furthermore, recycling the printed circuit board and / or grid array device is less complex, not least because it may not be necessary to evaporate any moisture present and, as the connectors are kept intact, it is not necessary to add new connectors (for example, solder balls) to restore the grid array device for re-use. The process of removing the grid array device from the circuit board also requires less energy, at least because for some conductive adhesives the temperature required to soften the conductive adhesive is significantly less (typically 80°C) than is required to re-melt the solder (often in excess of 210°C). This results in a more efficient recycling process, thereby making more devices commercially viable for recycling.

[0022] The grid array device may be any type of surface-mount packaging. For example, a ball grid array (BGA) device, column grid array device (CGA), or pin grid array device (PGA). In such examples, the connectors are solder balls, solder columns, and pins, respectively. The device may be, for example, an integrated circuit. The plurality of connectors may comprise any number of connectors arranged in a grid array. For example, four or more connectors. The grid array may be a regular shape, such as a square or rectangle, or an irregular shape. Square-shaped grid arrays may comprise 8x8 to 45x45 connectors. Spacing between the connectors may be from 0.1 mm to 1 ,5mm, for example, 0.3mm to 1 ,3mm, for example, 0.3mm to 1 ,27mm. A diameter or width of the connector, where it extends from the lower surface of the grid array device, may be 0.1 mm to 0.6mm, for example, 0.2mm to 0.5mm, for example, 0.2mm to 0.46mm.

[0023] Similarly, the plurality of cavities may comprise any number of cavities arranged in a grid array. For example, four or more cavities. The grid array may be a regular shape, such as a square or rectangle, or an irregular shape. The plurality of cavities may consist of a number of cavitiesthat may be equal to or more than the number of connectors in the plurality of connectors. Alternatively, the plurality of cavities may consist of a number of cavities that may be less than the number of connectors in the plurality of connectors. The printed circuit board may comprise additional cavities with non-conductive adhesive therein for mechanically coupling a connector to a conductive trace when it is not necessary to electrically couple the connector to the conductive trace. Spacing between the cavities may be less than, equal to, or more than, spacing between the connectors.

[0024] The substrate of the printed circuit board may be formed of any material, or composition of materials, able to withstand the conditions required (for example, temperature and / or radiation) for the conductive adhesive to sufficiently adhere the connector to the conductive trace. The substrate may be formed of more than one layer formed of the same or different materials. The material, or composition of materials, may have a glass transition temperature equal to or greater than 80°C. The distance between the upper and lower surfaces of the printed circuit board, which may also be referred to as the depth of the substrate, may be from 1pm to 5mm, for example, 1 m to 2mm, 1 pm to 1.6mm, or 2pm to 120pm. Accordingly, the distance the cavities extend from the upper surface may be less than the depth of the substrate, or equal to the depth of the substrate such that they extend through the substrate. The substrate may be relatively rigid or flexible. Examples of suitable materials include conventional printed circuit board materials, such as polyamide and FR4, and other materials, such as bioplastics (for example, polyethylene terephthalate (PET) and polyethylene naphthalate (PEN)), composite epoxy materials (CEM), aluminium, and polycarbonates, in new and recycled forms.

[0025] The conductive traces may form pathways for electrical signals between components affixed to the printed circuit board. For example, where the grid array device is an integrated circuit, the conductive traces may function to electrically couple components of the integrated circuit to other components on the printed circuit board via the connectors. The conductive traces may be formed of any conductive material, for example, copper (for example, copper etching or copper ink), silver (for example, silver ink), and gold (for example, gold ink). The conductive material may be etched or printed onto the substrate, for example onto surfaces of one or more layers of the substrate.

[0026] The conductive adhesive may be any adhesive capable of both mechanically and electrically coupling the connectors to the conductive traces. The conductive adhesive must be able to both adhere the connectors to the printed circuit board and provide a conductive path between the connector and the conductive trace. The conductive adhesive may be inserted into theplurality of cavities as a fluid and then hardened and / or cured to form a solid. The hardening and / or curing may be carried out using heat and / or radiation. In comparison to the soldering method, a lower temperature (typically from 90°C to 150°C, for example, 120°C) may be used to harden and / or cure the conductive adhesive to couple the connectors to the conductive traces. Similarly, to aid the recycling of the printed circuit board assembly, the adhesive properties of the conductive adhesive may be reduced or eliminated such that the grid array device and printed circuit board can be decoupled at a lower temperature (for example, 200°C or less, 150°C or less, or 100°C or less, or 80°C or less, for example, from 80 to 100 °C) than is required to re-melt solder. This may be achieved by exposing the printed circuit board assembly to water and / or another solvent. For example, by bathing the printed circuit board assembly in a hot bath of water and / or solvent, or exposing it to a jet of hot water and / or solvent. Additionally, or alternatively, the adhesive properties of the conductive adhesive may be reduced or eliminated using an adhesive reversal agent, such as a chemical solvent. Such a chemical solvent may be an organic, environmentally safe solvent. The adhesive reversal agent may be brought into contact with the conductive adhesive (for example, inserted into the openings of the cavities) to reduce or eliminate the adhesive properties of the conductive adhesive (for example, to induce a chemical change in the conductive adhesive that weakens the adhesive strength). Examples of suitable conductive adhesives include a polymer based thermoplastic adhesive and / or cross-link thermosetting cyclic amine based adhesives. Examples of suitable conductive adhesives and reversal agents are disclosed in European patent EP2621254. Loctite Ablestick CE 3103 by Henkel may be suitable for use as a non-reversable conductive adhesive.

[0027] The volume of conductive adhesive in the cavity may be less than the volume of the cavity. The volume of conductive adhesive in the cavity may be such that the conductive adhesive does not extend through the opening in the upper surface of the printed circuit board when the connector is received within the cavity. In a fluid form some conductive adhesives can flow more easily than a melted solder. Therefore, constraining the conductive adhesive within a cavity can be beneficial as it can prevent the conductive adhesive from spreading across the upper surface of the printed circuit board and forming incorrect bonds between the connectors and / or the conductive traces. The volume of conductive adhesive in the cavity may be, for example, 0.1 mm to 2mm, for example, 0.3mm to 1 mm.

[0028] The printed circuit board assembly may have a gap between the lower surface of the device and the upper surface of the printed circuit board. This gap may be beneficial where the conductive adhesive used is configured such that its adhesive properties can be reduced or eliminated using an adhesive reversal agent, as it may facilitate access to the conductiveadhesive for the adhesive reversal agent. Thus, the gap can be beneficial for recycling purposes. The size of the gap may be from 10pm to 300pm, for example, 50 to 250pm.

[0029] To create the gap, at least one of the plurality of cavities may be configured such that the connector cannot fully enter the cavity.

[0030] For example, the cavity may include stepped, or shaped, side walls or may extend from the upper surface of the printed circuit board into the printed circuit board by a first depth, and the connector received within the cavity may extend from the lower surface of the device by a first length, wherein the first depth is less than the first length. For example, the connector may rest on a base of the cavity to create the gap between the lower surface of the device and the upper surface of the printed circuit board.

[0031] Alternatively, or additionally, to create the gap, at least one of the plurality of cavities may be dimensioned such that a portion of the at least one connector received with the at least one cavity rests on the opening of the at least one cavity. For example, a diameter and / or width of the base of the connector, where it extends from the lower surface of the device, may be greaterthan the diameter and / or width of the opening. For example, the diameter and / or width of the opening may be 90% or less that of the base of the connector. For example, for a connector with a base having a diameter of 0.45mm the diameter of the cavity opening may be 0.36mm.

[0032] The printed circuit board may have no gap between the lower surface of the device and the upper surface of the printed circuit board. In this example, the plurality of connectors may be entirely received within the plurality of cavities. This may increase contact between the conductive adhesive and the connector, thereby strengthening the mechanical coupling.

[0033] To ensure there is no gap, the plurality of cavities may extend from the upper surface into the printed circuit board by a second depth, and the plurality of connectors may extend from the lower surface of the device by a second length, wherein the second depth is equal to or more than the second length.

[0034] Additionally, to ensure there is no gap, the diameter and / or width of the base of the connectors, where they extend from the lower surface of the device, may be equal to or less than the diameter and / or width of the openings of their respective cavities. For example, the diameter and / or width of the base of the connectors may be 90% or less that of the openings.Where the connector is received into the cavity such that it is in contact with the cavity, the cavity may act to resist, in addition to the conductive adhesive, movement of the grid array device relative to the printed circuit board in a direction parallel to the upper surface of the printed circuit board. This resistance may be increased the further the connector is received into the cavity, as the contact area between the connector and the cavity is increased. A force of 80N or more may be resisted.

[0035] The cavities may have any shape. The shape of the cavities may be configured according to the shape of the connectors they are designed to receive, for example, to make it easier for the cavities to receive the connectors and thereby correctly align the connectors with the conductive traces of the printed circuit board. The cavities may be tubular or cuboid shaped.

[0036] A portion of at least one of the plurality of cavities may be tapered from its opening in the upper surface towards the lower surface of the printed circuit board. This may encourage the connector to nestle into the cavity, and assist with the mechanical coupling between the connector and the cavity. Furthermore, it enables the connector and conductive trace to be electrically coupled, even if the connector and cavity are not perfectly aligned. The portion may be any shape, for example cone shaped or semi-spherical. A base of the portion may be from 50 to 100% the diameter / width of the connector, and the opening may be from 100 to 150% the diameter / width of the connector. A wider opening may aid installation and / or alignment. There may be a space between the openings, or the openings may abut one another. The portion may be shaped using a countersink or counterbore drill. The cavities may all have the same shape and / or size. Alternatively, one or more of the cavities may have a different shape and / or size.

[0037] At least one, some, or all the plurality of cavities may extend from their opening / s in the upper surface through the printed circuit board to closed ends. In these examples, the conductive adhesive is inserted into the cavities via the openings in the upper surface.

[0038] Alternatively, or additionally, at least one, some, or all the plurality of cavities may extend from their opening / s in the upper surface through the printed circuit board to openings in the lower surface of the printed circuit board. The conductive adhesive may be inserted into the cavities via the openings in the upper surface and / or the openings in the lower surface. Openings in the lower surface of the printed circuit board may enable any excess conductive adhesive to escape when the connector is received therein, and allow the escape of any gasses that may arise during a curing process.A portion of at least some of the plurality of cavities may be tapered from the opening in the lower surface towards the upper surface of the printed circuit board, such that the portion is widest at the opening. For example, to form a cone shape.

[0039] The plurality of conductive traces may extend to other regions of the printed circuit boardto provide electrical connections thereto. The plurality of conductive traces may be located anywhere throughout the printed circuit board. For example, on the upper surface or lower surface of the printed circuit board, or at any location between the upper surface or lower surface of the printed circuit board. The plurality of connectors may be connected to the plurality of conductive traces either directly, or via a conductive pad in and / or a plating of the plurality of cavities.

[0040] The printed circuit board may have a plurality of layers with at least one conductive trace located between each of the layers, and at least one cavity extending through one or more of the layers to enable a connector received in the cavity to be electrically coupled to at least one of the conductive traces. At least one of the layers may have at least one conductive trace in its upper surface, and the multi-layered printed circuit board may be formed by laminating the layers together.

[0041] The printed circuit board may have two layers — a first layer and a second layer — with a conductive trace located between the first layer and the second layer. At least one cavity may extend through the first layer to enable a connector received in the cavity to be electrically coupled to the conductive trace by the conductive adhesive. For example, the at least one cavity may extend through the first layer and terminate at a conductive pad of the conductive trace, and the conductive adhesive may then electrically couple the connector received in the cavity to the conductive pad. A plurality of cavities may extend through the first layer, each terminating at a different pad of the conductive trace or different conductive traces. A single cavity could also connect to a plurality of conductive traces.

[0042] The printed circuit board may have more than two layers. The printed circuit board may have three layers — a third layer in addition to the first and second layers, with a conductive trace located between the second layer and the third layer. At least one cavity may extend through the first and second layers to enable a connector received in the cavity to be electrically coupled to the conductive trace by the conductive adhesive. For example, the at least one cavity may extend through the first and second layers and terminate at a conductive pad of the conductive trace, and the conductive adhesive may then electrically couple the connector received in the cavity to the conductive pad. A plurality of cavities may extend through the firstand second layers, each terminating at a different pad of the conductive trace or different conductive traces.

[0043] At least one of the plurality of cavities may be plated with a conductive material. Examples of such conductive materials include copper, hot air levelling (HAL or HASL), and electroless nickel immersion gold (ENIG). However, it is not necessary to plate the cavities where the conductive adhesive is in direct contact with the connector and the conductive trace. For example, where a conductive trace is located between layers of a printed circuit board and a cavity terminates at a conductive pad of the conductive trace, plating is not required.

[0044] The grid array device may be further mechanically coupled to the printed circuit board via an adhesive. The adhesive may be non-conductive.

[0045] A third aspect of the claimed invention is a method of manufacturing a printed circuit board assembly, wherein the printed circuit board assembly comprises a printed circuit board and a grid array device,

[0046] wherein the printed circuit board comprises:

[0047] an upper surface and a lower surface;

[0048] a plurality of cavities arranged in a grid array, wherein each of the plurality of cavities extend from an opening in the upper surface into the printed circuit board; and a plurality of conductive traces, and

[0049] wherein the grid array device comprises:

[0050] a device, wherein the device comprises an upper surface and a lower surface; and a plurality of connectors arranged in a grid array, wherein each of the plurality of connectors extend from the lower surface of the device,

[0051] wherein the method comprises:

[0052] inserting the plurality of connectors into the plurality of cavities;

[0053] inserting conductive adhesive into the plurality of cavities; and

[0054] curing the conductive adhesive to mechanically and electrically coupling the plurality of connectors to the plurality of conductive traces.

[0055] The conductive adhesive may be cured using heat or radiation, such as UV.

[0056] The printed circuit board may further comprise:

[0057] a carrier layer and a primary layer, wherein the carrier layer comprises:

[0058] the upper surface of the printed circuit board and a carrier layer lower surface, andthe plurality of cavities, wherein each of the plurality of cavities extend from the respective opening in the upper surface through the carrier layer to an open end in the carrier layer lower surface, and the primary layer comprises:

[0059] a primary layer upper surface and the lower surface of the printed circuit board, and

[0060] the plurality of conductive traces,

[0061] wherein the method may further comprise, after inserting the plurality of connectors and the conductive adhesive into the plurality of cavities, and before curing the conductive adhesive:

[0062] aligning the plurality of cavities with the plurality of conductive traces; and placing the carrier layer lower surface in contact with the primary layer upper surface.

[0063] Thus, conductive adhesive that passes through the cavities and out of the openings in the carrier layer lower surface can be used to adhere the carrier layer to the primary layer. The openings in the carrier layer lower surface may be tapered to increase the contact area of the conductive adhesive and the primary layer upper surface. Accordingly, the primary layer may be a standard printed circuit board, and the carrier layer can be used to adapt the standard printed circuit board to comprise a plurality of cavities for receiving the plurality of connectors. Alternatively, the primary layer may comprise a plurality of cavities arranged in a grid array for receiving a plurality of connectors extending through the plurality of cavities in the carrier layer.

[0064] The depth of the carrier layer may be such that there is a gap of 0.1mm or less, preferably 0.06mm, between the end of the connectors and the upper surface of the primary layer. For example, if the connector extends 0.4mm from the lower surface of the grid array device, then then depth of the cavity would not be more than 0.5mm. Similarly, if a gap of 0.2mm is required between the lower surface of the grid array device and the upper surface of the printed circuit board, a gap of 0.2mm, if the height of the connector is 0.4mm, the depth of the carrier layer would be no more than 0.3mm.

[0065] The conductive adhesive may be inserted into the openings in the upper surface of the printed circuit board before or after inserting the plurality of connectors into the plurality of cavities.

[0066] Where a cavity extends from its opening in the upper surface through the printed circuit board to an opening in the lower surface of the printed circuit board, the method may comprise — in addition, or as an alternative, to inserting conductive adhesive into the opening in the upper surface — inserting the conductive adhesive into the opening in the lower surface to mechanically and electrically couple the connector received therein to a conductive trace. The conductive adhesive may be inserted into the opening in the lower surface before or afterreceiving the connector within the cavity. Inserting the adhesive into both the openings in the upper and lower surfaces may help to strengthen the mechanical and electrical coupling between the connector and the conductive trace.

[0067] The method may further comprise using a non-conductive adhesive to strengthen the mechanical coupling between the grid array device and the printed circuit board. A non-conductive adhesive may be inserted into a cavity where an electrical connection between a connector and the conductive trace which the cavity is exposed to is not required. A non-conductive adhesive may be inserted into a cavity in addition to conductive adhesive to strengthen the mechanical coupling between the connector and the conductive trace. For example, a cavity with an opening in the lower surface of the printed circuit board may receive the conductive adhesive in the opening in the upper surface of the printed circuit board to form an electrical coupling and non-conductive adhesive in the opening in the lower surface of the printed circuit board to form a mechanical coupling.

[0068] Furthermore, a non-conductive adhesive may be used outside of the cavities to further strengthen the mechanical coupling between the connectors and the conductive traces. This may be particularly advantageous where the printed circuit board is relatively flexible (for example, one made of polyethylene terephthalate (PET)), and it is required to strengthen the mechanical coupling between the grid array device and the printed circuit board such that it can withstand flexing of the printed circuit board. The adhesive may be applied to strengthen the mechanical coupling directly between the grid array device and the printed circuit board — for example, by applying the adhesive between the lower surface of the grid array device and the upper surface of the printed circuit board. Or the adhesive may be applied such that it extends over the grid array device and adheres to the printed circuit board — for example, the adhesive may be applied such that it encapsulates the grid array device. The adhesive may be adhered to the lower surface of the printed circuit board to provide additional rigidity to the printed circuit board. For example, the adhesive may extend under the grid array device. Where cavities are open in the lower surface of the printed circuit board, the non-conductive adhesive may contact the connectors and / or conductive adhesive to provide rigidity thereto.

[0069] The invention is further described by way of example only with reference to the following figures:

[0070] Figure 1 A shows a top view of a portion of a printed circuit board with closed cavities;Figure 1B shows a cross-section of the printed circuit board shown in Figure 1A;

[0071] Figures 2A-C show a printed circuit board assembly including different examples of a printed circuit board with closed cavities;

[0072] Figure 3A-C show exemplary shapes of closed cavities;

[0073] Figure 4A shows a printed circuit board with open cavities;

[0074] Figure 4B shows a printed circuit board assembly including the printed circuit board shown in Figures 4A;

[0075] Figure 5A-F show exemplary shapes of open cavities;

[0076] Figure 7 shows a printed circuit board having a plurality of layers;

[0077] Figure 8A shows a printed circuit board assembly, the printed circuit board having a carrier layer and a primary layer, before adhering the carrier layer to the primary layer; and

[0078] Figure 8B shows the printed circuit board assembly shown in Figure 8A, after adhering the carrier layer to the primary layer.

[0079] Figure 1 A shows a top view of a portion of a printed circuit board 100. The printed circuit board has a plurality of cavities 102 arranged in a grid array. In this example, the grid array is an 8 x 8 grid array having eight rows and eight columns. Figure 1 B shows a cross-section of the printed circuit board 100 shown in Figure 1 through one of the rows or columns.

[0080] The printed circuit board 100 has an upper surface 104 and a lower surface 106. Each of the plurality of cavities 102 extend from an opening 108 in the upper surface 104 into the printed circuit board 100. The printed circuit board 100 includes a plurality of conductive traces 110, and each of the plurality of cavities 102 have a closed end 112 and are exposed to one of the plurality of conductive traces 110 which extend to other regions of the printed circuit board 100 to provide electrical connections thereto, for example to electrically connect the cavity 102 to an electrical component or connector. Each of the plurality of cavities 102 have a conductive adhesive 114 therein. Accordingly, the plurality of cavities 102 are configured for receiving a plurality of connectors arranged in a grid array on a device, and the conductive adhesive 114in each of the plurality of cavities is configured to mechanically and electrically couple a connector to one of the plurality of conductive traces 110.

[0081] Figure 2A shows a printed circuit board assembly 20, including a printed circuit board 200 and a grid array device 118. The printed circuit board 200 is akin to the printed circuit board 100 described in Figures 1A and 1 B, and so similar features will be referred to using the same reference numerals. The grid array device 118 includes a device 116. The device 116 has an upper surface 120 and a lower surface 122, and a plurality of connectors 124 arranged in a grid array extending from the lowersurface 122. Aconnectorofthe plurality of connectors 124 is received within each of the plurality of cavities 102 and mechanically and electrically coupled to a conductive trace of the plurality of conductive traces 110 by the conductive adhesive 116.

[0082] There is a gap 125 between the lower surface 122 of the device 116 and the upper surface 104 of the printed circuit board 200. In this example, to create the gap 125, the plurality of cavities 102 are dimensioned such that a portion of the plurality of connectors 124 received within the plurality of cavities 102 rests on the openings 108 of the plurality of cavities 102.

[0083] Figure 2B shows a printed circuit board assembly 30, including a printed circuit board 300 and the grid array device 118 shown in Figure 3A. The printed circuit board 300 is akin to the printed circuit board 100, and so similar features will be referred to using the same reference numerals. In this example, to create the gap 125, the plurality of cavities extend from the upper surface 104 into the printed circuit board 200 by a depth, and the plurality of connectors 124 do not contact the opening 108, but extend from the lowersurface 122 of the device 116 by a length which is greater than the depth of the cavities 102 so the connectors 124 contact the closed end of the cavities 102.

[0084] Figure 2C shows a printed circuit board assembly 40, including a printed circuit board 400 and the grid array device 118 shown in Figure 2A. The printed circuit board 400 is akin to the printed circuit board 100, and so similar features will be referred to using the same reference numerals. Contrary to the printed circuit board assemblies 20,30 shown in Figures 2A,2B, there is no gap between the lowersurface 122 ofthe device 116 and the uppersurface 104 of the printed circuit board 102. In this example, the plurality of cavities 102 extend from the upper surface 104 into the printed circuit board 102 by a depth which is equal to the length by which the plurality of connectors 124 extend from the lower surface 122 of the device 116 to ensure there is no gap. In other examples, the depth of the plurality of cavities 102 may be greater than the length of the plurality of connectors 124 to ensure there is no gap.Figures 3A, 3B, and 3C show different examples of closed cavity shapes. In figure 3A, the cavity is tubular. In this example, the diameter of the base is greater than the depth of the cavity. In other examples, the diameter of the base may be equal to or less than the depth of the cavity. Alternatively, the cavity may be cuboid shaped. In this example, the width of the base of the cavity is greater than the depth of the cavity. In other examples, the width of the base may be equal to or less than the depth of the cavity.

[0085] In Figures 3B and 3C, the cavity is tapered from the opening 108 in the upper surface 104 toward the lower surface 106 of the printed circuit board 100. In Figure 3B, the cavity is semi-spherical. In Figure 3C, the cavity is cone shaped.

[0086] In all the examples shown in Figures 1-3C, the plurality of cavities 102 extend from openings 108 in the upper surface 104 of the printed circuit board to closed ends 112. However, in the examples provided by Figures 4, 5, and 6A-F, the plurality of cavities 102 extend from openings 108 in the upper surface 104 through the printed circuit board to open ends 126 in the lower surface 106 of the printed circuit board. In these examples, adhesive can also be inserted into the open ends 126.

[0087] Figures 6A-F, show different examples of open cavity shapes. The upper portion of the cavity extending from the upper surface 104 of the printed circuit board in Figures 6Aand 6B has the same shape as the closed cavity shown in Figure 3A. In Figure 6A, the lower portion of the cavity which extends from the upper portion to the lower surface 106 of the printed circuit board has a smaller diameter than the upper portion. In Figure 6B, the diameter of the upper portion and the lower portion is the same. In Figures 6D and 6F, the upper portion of the cavity extending from the upper surface 104 of the printed circuit board has the same shape as the closed cavity shown in Figure 3B. In Figure 6D, the lower portion of the cavity which extends from the upper portion to the lower surface 106 of the printed circuit board has a tubular shape. In Figure 6F, the upper portion and lower portion are separated by a middle portion. The middle portion is tubular, and the lower portion is cone shaped and tapers from the opening 126 in the lower surface 106 of the printed circuit board to meet the middle portion. In figures 6C and 6E, the upper portion of the cavity extending from the upper surface 104 of the printed circuit board has the same shape as the closed cavity shown in Figure 3C. In Figure 6C, the lower portion of the cavity which extends from the upper portion to the lower surface 106 of the printed circuit board has a tubular shape. In Figure 6E, the upper portion and lower portion are separated by a middle portion. The middle portion is tubular, and the lower portion is cone shaped and tapers from the opening 126 in the lower surface 106 of the printed circuit board to meet the middle portion.Figure 7 shows a printed circuit board 600, having three layers: a first layer 128, a second layer 130, and a third layer 132. A conductive trace of the plurality of conductive traces 110 is located between the first layer 128 and the second layer 130, and a cavity of the plurality of cavities 102 extends through the first layer 128 such that a connector received within the cavity is electrically coupled to the conductive trace by the conductive adhesive.

[0088] Figure 8A and 8B show two steps of manufacturing a printed circuit board assembly 60 having a grid array device 118 and a printed circuit board 700, wherein the printed circuit board 700 has a carrier layer 134 and a primary layer 136. The carrier layer 134 has upper surface 104 and a lower surface 138, and the primary layer has an upper surface 140 and a lower surface 106. The plurality of cavities 102 extend from openings 108 in the upper surface 104 of the carrier layer 134 through the carrier layer 134. To assemble the printed circuit board assembly 60, the grid array device 118 and the carrier layer 134 are oriented such that the upper surface 104 of the carrier layer 134 faces the lower surface 122 of the device 116. The plurality of connectors 124 are then inserted into the plurality of cavities 102, and conductive adhesive 114 is inserted into the plurality of cavities 102. The carrier layer 134 and the primary layer 136 are then oriented such that the lower surface 138 of the carrier layer faces the upper surface 140 of the primary layer 136, and the surfaces are brought into contact with one another to mechanically couple the carrier layer 134 to the primary layer 136.

Claims

Claims1. A printed circuit board, wherein the printed circuit board comprises:an upper surface and a lower surface;a plurality of cavities extending from the upper surface into the printed circuit board, wherein the plurality of cavities are arranged in a grid array for receiving a plurality of connectors arranged in a grid array on a device; anda plurality of conductive traces,wherein each of the plurality of cavities extend from an opening in the upper surface and have a conductive adhesive therein for mechanically and electrically coupling a connector to a conductive trace of the plurality of conductive traces.

2. A printed circuit board assembly, wherein the printed circuit board assembly comprises:the printed circuit board as claimed in claim 1 ; anda grid array device, wherein the grid array device comprises:a device, wherein the device comprises an upper surface and a lower surface; anda plurality of connectors arranged in a grid array, wherein the plurality of connectors extend from the lower surface of the device,wherein a connector of the plurality of connectors is received within each of the plurality of cavities and mechanically and electrically coupled to the conductive trace by the conductive adhesive.

3. A printed circuit board assembly as claimed in claim 2, wherein there is a gap between the lower surface of the device and the upper surface of the printed circuit board.

4. A printed circuit board assembly as claimed in claim 3, wherein at least one of the plurality of cavities extends from the upper surface into the printed circuit board by a first depth, and the at least one connector received within the at least one cavity extends from the lower surface of the device by a first length, wherein the first depth is less than the first length.

5. A printed circuit board assembly as claimed in claims 3 or 4, wherein at least one of the plurality of cavities is dimensioned such that a portion of the at least one connector received within the at least one cavity rests on the opening of the at least one cavity.

6. A printed circuit board assembly as claimed in claim 2, wherein there is no gap between the lower surface of the device and the upper surface of the printed circuit board.

7. A printed circuit board assembly as claimed in claim 6, wherein the plurality of cavities extend from the upper surface into the printed circuit board by a second depth, and the plurality of connectors extend from the lower surface of the device by a second length, wherein the second depth is equal to or more than the second length.

8. A printed circuit board assembly as claimed in any one of claims 2 to 7, wherein at least one of the plurality of cavities is tubular or cuboid shaped.

9. A printed circuit board assembly as claimed in any one of claims 2 to 8, wherein a portion of at least some of the plurality of cavities are tapered from the respective opening in the upper surface towards the lower surface of the printed circuit board.

10. A printed circuit board assembly as claimed in any one of claims 2 to 9, wherein a portion of at least some of the plurality of cavities are cone shaped.

11. A printed circuit board assembly as claimed in any one of claims 2 to 10, wherein a portion of at least some of the plurality of cavities are semi-spherical.

12. A printed circuit board assembly as claimed in any one of claims 2 to 11 , wherein at least some of the plurality of cavities extend from the respective opening in the upper surface through the printed circuit board to a closed end.

13. A printed circuit board assembly as claimed in any one of claims 2 to 11 , wherein at least some of the plurality of cavities extend from the respective opening in the upper surface through the printed circuit board to an open end in the lower surface of the printed circuit board.

14. A printed circuit board assembly as claimed in claim 13, wherein a portion of at least some of the plurality of cavities are tapered from the opening in the lower surface towards the upper surface of the printed circuit board.

15. A printed circuit board assembly as claimed in anyone of claims 2 to 14, wherein a portion of at least some of the plurality of cavities are tapered from the opening in the lower surface towards the upper surface of the printed circuit board to form a cone shape.

16. A printed circuit board assembly as claimed in any one of claims 2 to 15, wherein the printed circuit board comprises a first layer and a second layer, wherein the conductive trace is located between the first layer and the second layer, and at least some of the plurality of cavities extend through the first layer such that the respective connector is electrically coupled to the conductive trace by the conductive adhesive.

17. A printed circuit board assembly as claimed in any one of claims 2 to 16, wherein at least some of the plurality of cavities are plated.

18. A printed circuit board assembly as claimed in any one of claims 2 to 17, wherein the grid array device is further mechanically coupled to the printed circuit board via a non-conductive adhesive.

19. A printed circuit board as claimed in any one of claims 2 to 18, wherein the grid array device is a ball grid array device and the plurality of connectors is a plurality of solder balls.

20. A method of manufacturing a printed circuit board assembly, wherein the printed circuit board assembly comprises a printed circuit board and a grid array device,wherein the printed circuit board comprises:an upper surface and a lower surface;a plurality of cavities arranged in a grid array, wherein each of the plurality of cavities extend from an opening in the upper surface into the printed circuit board; and a plurality of conductive traces, andwherein the grid array device comprises:a device, wherein the device comprises an upper surface and a lower surface; and a plurality of connectors arranged in a grid array, wherein each of the plurality of connectors extend from the lower surface of the device,wherein the method comprises:inserting the plurality of connectors into the plurality of cavities;inserting conductive adhesive into the plurality of cavities; andcuring the conductive adhesive to mechanically and electrically coupling the plurality of connectors to the plurality of conductive traces.

21. A method of manufacturing a printed circuit board assembly as claimed in claim 20, wherein the printed circuit board further comprises:a carrier layer and a primary layer, wherein the carrier layer comprises:the upper surface of the printed circuit board and a carrier layer lower surface, andthe plurality of cavities, wherein each of the plurality of cavities extend from the respective opening in the upper surface through the carrier layer to an open end in the carrier layer lower surface, and the primary layer comprises:a primary layer upper surface and the lower surface of the printed circuit board, andthe plurality of conductive traces,wherein the method further comprises, after inserting the plurality of connectors and the conductive adhesive into the plurality of cavities, and before curing the conductive adhesive:aligning the plurality of cavities with the plurality of conductive traces; and placing the carrier layer lower surface in contact with the primary layer upper surface.

22. A method of manufacturing a printed circuit board assembly as claimed in any one of claims 20 to 21 , wherein the conductive adhesive is inserted into the openings of the plurality of cavities prior to inserting the plurality of connectors into the plurality of cavities.

23. A method of manufacturing a printed circuit board assembly as claimed in any one of claims 20 to 22, wherein at least some of the plurality of cavities extend from the respective opening in the upper surface through the printed circuit board to an open end in the lower surface of the printed circuit board, and the method comprises inserting the conductive adhesive into the open ends in the lower surface to mechanically couple the plurality of connectors to the plurality of conductive traces.

24. A method of manufacturing a printed circuit board assembly as claimed in any one of claims 20 to 23, the method further comprising applying a non-conductive adhesive to mechanically couple the lower surface of the device to the upper surface of the printed circuit board.

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