WO2012089275A1

WO2012089275A1 - Multi board module with implant

Info

Publication number: WO2012089275A1
Application number: PCT/EP2010/070948
Authority: WO
Inventors: Andrew KINSELLA
Original assignee: Option Wireless Limited
Priority date: 2010-12-30
Filing date: 2010-12-30
Publication date: 2012-07-05

Abstract

A multi board module is manufactured by forming (100) a first multilayer circuit board so as to have an aperture, providing (110) a second multilayer circuit board (50) to fit within at least part of the aperture, and inserting (120) the second multilayer circuit board into the aperture so that surfaces of the boards are coplanar. Circuit components are mounted (130) on the coplanar surfaces and in the same step, a passive component is mounted between the respective conductors across a perimeter of the aperture to form one or more electrical connections between the boards. This can avoid the need for a separate manufacturing step for the electrical connections. A lug and recess can be provided to enable the insertion to be a press fit. The second board can be thinner so that its backside is recessed and thus provide a better foundation for a glued joint.

Description

MULTI BOARD MODULE WITH IMPLANT

Field of the invention:

This invention relates to methods of manufacturing multi board modules in which a second multilayer board is implanted into a first multilayer board, and to corresponding multi board modules and electronic or communication devices including the multi board module.

Description of the Related Art:

It is known to implant a second multilayer circuit board into a recess in a first multilayer board. It is known to cut the recess by a laser cutting step and have it recessed sufficiently accurately that the two boards have coplanar top surfaces. US2009290318 shows this and mentions that the number of wiring layers per unit thickness can be the same and also that the boards differ in the number of wiring layers, which will result in the boards being of different thickness. It also mentions that an electrical connection between the boards can be made by a flip chip connection with solder reflow, or by a wire bonding step.

This implant is useful to enable different densities of interconnect to be combined for example, as shown in US 2009283312.

However in practice some difficulties remain unresolved, or are relatively costly to resolve, in manufacturing such multi board modules.

Summary of the Invention:

An object of the invention is to provide a method of manufacturing of a multi board module in which a second multilayer board is implanted into a first multilayer board, and/or corresponding multi board modules and/or electronic or communication devices including the multi board module.

According to a first aspect, the invention provides a method of manufacturing a multi board module having the steps of forming a first multilayer circuit board so as to have an aperture, forming a second multilayer circuit board to fit within at least part of the aperture, inserting the second multilayer circuit board into the aperture so that at least one surface of the second multilayer circuit board is coplanar with a corresponding surface of the first multilayer circuit board, and mounting circuit components on the coplanar surfaces and in the same step, mounting one or more additional components, such as passive and/or active components, between the respective conductors across a perimeter of the aperture to form one or more electrical connections between respective conductors on the coplanar surfaces of the first and second multilayer circuit boards. The one or more passive and/or active components can be described as bridging components. They are preferably electronic components. They can be surface mount devices. Such passive devices can be resistors, inductors, capacitors, and combinations of these such as filters. Such active devices can be transistors, integrated circuits, diodes, ADC or DAC, digital filters, DSP's, microprocessor cores, etc.

An effect of mounting the one or more bridging components, e.g. passive components and/or active components such as surface mount devices. in the same step as mounting circuit components, is that the electrical connections between the boards can be created without the need for a separate manufacturing step for the electrical connections. The cost of a number of additional bridging components such as passive components and/or active components is typically much less than the cost of making these electrical connections in a separate step by a flip chip or wire bonding process.

According to a second aspect, the invention provides a method of manufacturing a multi board module having the steps of forming a first multilayer circuit board so as to have an aperture, the aperture having an outline with at least one lug or recess, forming a second multilayer circuit board to fit within at least part of the aperture, and having an outline having a corresponding lug or recess and inserting the second multilayer circuit board into the aperture so that at least one surface of the second multilayer circuit board is coplanar with a corresponding surface of the first multilayer circuit board, while engaging the corresponding lug and recess, to provide a press fit in the aperture.

An effect of using a press fit is to enable easier automation and enable a subsequent gluing step to be made simpler and more reliable if the press fit means the inserted board is less likely to slip out of position before gluing. An effect of having the lug and recess is to enable the press fit to be achieved more easily with less need for precise tolerances on all dimensions of the outlines.

According to a third aspect, the invention provides a method of manufacturing a multi board module having the steps of forming a first multilayer circuit board so as to have an aperture, forming a second multilayer circuit board to fit within at least part of the aperture, inserting the second multilayer circuit board into the aperture so that at least one surface of the second multilayer circuit board is coplanar with a corresponding surface of the first multilayer circuit board, and screen printing the coplanar surfaces with solder after the inserting step.

An effect of screen printing after rather than before insertion is that it can enable the step to be carried out once rather than carrying out the same step twice on the boards before insertion. Also it helps avoid the need for a frame around the second multilayer board, to grip the board if processing it before insertion.

According to a fourth aspect, the invention provides a method of manufacturing a multi board module having the steps of forming a first multilayer circuit board so as to have an aperture, forming a second multilayer circuit board to fit within at least part of the aperture, and inserting the second multilayer circuit board into the aperture so that at least one surface of the second multilayer circuit board is coplanar with a corresponding surface of the first multilayer circuit board, the second multilayer circuit board being formed by cutting from an array of similar boards without providing a surrounding frame for each of the boards.

An effect of this is to increase a number or boards in the array of a given size and hence reduce costs.

According to a fifth aspect, the invention provides a method of manufacturing a multi board module having the steps of forming a first multilayer circuit board so as to have an aperture, forming a second multilayer circuit board, thinner than the first multilayer circuit board, and having an outline to fit within at least part of the aperture, inserting the second multilayer circuit board into the aperture by placing one surface of the first multilayer circuit board against a reference surface then pressing the second multilayer circuit board into the aperture from an opposite side of the first multilayer circuit until the second multilayer circuit abuts the reference surface, so that one surface of the second multilayer circuit board is coplanar with a corresponding surface of the first multilayer circuit board, and a second surface of the second multilayer board is recessed, and fixing the second multilayer board by applying glue where the recessed surface of the second multilayer board meets the first multilayer board.

An effect of the second board being thinner is to provide a better foundation for a glued joint, (where glued is intended to encompass using resins or any similar fixing material) as the surfaces to be joined meet at a right angle. This means the strength of the joint is less dependent on a gap size, or on ability of the glue to flow into a gap. Also, it is easier to ensure the glue does not protrude above the surface, to interfere with subsequent handling of the multi board module, without needing additional manufacturing steps to provide a specific groove to accommodate the glue.

According to other aspects, the invention provides corresponding multi board modules. Any additional features may be added to these features, and some such additional features are described below. Any of the additional features can be combined together and combined with any of the aspects. Other effects or advantages will be apparent to those skilled in the art, especially over other prior art. Numerous variations and modifications can be made without departing from the claims of the present invention. Therefore, it should be clearly understood that the form of the present invention is illustrative only and is not intended to limit the scope of the present invention.

Brief Description of the Drawings:

How the present invention may be put into effect will now be described by way of example with reference to the appended drawings, in which:

Figs 1 and 2 show views of a multilayer motherboard,

Fig. 3 shows a plan view of an array of such motherboards,

Fig. 4 shows a cross section view of the two boards before insertion,

Fig.5 shows an array of HDI boards with frames,

Fig.6 shows an array of HDI boards without frames,

Fig 7 shows a cross section view of the boards before and after insertion,

Fig. 8 shows a cross section view of the boards after insertion and with glue applied,

Fig 9 shows a plan view of the boards after glueing,

Fig. 10 shows a cross section view of another embodiment in which the boards are of the same thickness and showing a groove cut for the glue,

Fig. 11 shows a cross section view of the embodiment of figure 10, after glueing, Fig. 12 shows a plan view of an array of modules after implanting,

Fig. 13 shows a plan view of the module showing pads for electrical connections between boards,

Fig. 14 shows a cross section view of the embodiment of figure 8 after mounting components and passives (optionally or alternatively active components) as electrical connections between the boards,

Fig. 15 shows a plan view of an outline of a board showing lugs for making a press fit, and

Figs 16 to 20 show method steps of embodiments according to various aspects.

Description of the Preferred Embodiments:

The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. Where the term "comprising" is used in the present description and claims, it does not exclude other elements or steps. Where an indefinite or definite article is used when referring to a singular noun e.g. "a" or "an", "the", this includes a plural of that noun unless something else is specifically stated.

The term "comprising", used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. Thus, the scope of the expression "a device comprising means A and B" should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.

References to multilayer boards are intended to encompass circuit boards with one or more conductive layers below a surface of the circuit board, not including single sided or double sided boards.

Figures 1-3 Multilayer Board Figure 1 shows a cross section of a first multilayer circuit board in the form of a lower density Multilayer mother board, having various layers of conductive interconnect and some vias 10 between the layers, or vias 20 from one surface to another. The board is designed with a "keep out" area 30 specifically dimensioned to receive the High Density Interconnect (HDI) implant, as shown in the plan view of figure 2. Conductive connection pads 40 are provided near the aperture for making electrical connections to the implant. The term "keep out" refers to an area of the board that does not contain any electrical connections on any of the layers. This motherboard can be manufactured using industry standard techniques and can be manufactured separately from the HDI implant. For later production processing, multiple boards can be manufactured in an array forming a panel, as shown in figure 3 in plan view. This shows three of the boards, separated by a frame, there can be any number of the boards in the array.

Figure 1 X- Section

Figure 4 shows the Multilayer board with the keep out area removed to form the aperture. There are a number of techniques for removing sections of PCB (printed circuit board), the most common being Routing/Milling or Punching. This routing out of this area can be part of the Multilayer board manufacturing process. Notably, since there is no depth measurement of the aperture, this step need not be carried out with a laser, to achieve an accurate depth, and so can be carried out at the same time as shaping or cutting out an outline of the board from the panel, thus avoiding the costs of an extra step.

Figure 4 also shows a cross section of a second multilayer board in the form of an HDI board 50. This board can be manufactured separately, to be thinner and have more dense interconnect, requiring a different process to the Multilayer board. Because the HDI board will be implanted into the first Multilayer board, it is not necessary to be manufactured in panels surrounded by support frames for later production processing. This can reduce the board production waste by 15-20%, translating into reduced HDI board cost.

HDI

HDI (High Density Interconnect) technology is a packaging technology for a three- dimensional hybrid wafer scale integration packaging technology where, rather than place the wafers perfectly (as in wafer scale integration) wafer position is corrected for in the direct-write process. By using a laser to direct-write patterns of interconnect layouts and drill micro-via holes, individual chips can be connected to each other using standard semiconductor fabrication methods. To take the packaging to the third dimension, wafer- scale components are stacked like a deck of cards and connected by patterning interconnects at their edges. The result is an electronic assembly that used to be spread out over a large circuit board can now be packaged into a small cube.

The technology uses a polyimide overlay as the insulating layer over bare chips on a ceramic (or plastic) substrate. Integrated circuit chips are connected in three dimensions through micro-via holes to the individual bonding pads. High-speed via-hole formation and interconnect metallization were accomplished using a laser-assisted direct-write adaptive lithography system. In laser-assisted patterning, a computer-driven laser writes the integrated circuit pattern on the polyimide overlay. Conducting paths are patterned on the edges to electrically interconnect the layers. Once patterned, the wafers are overlaminated with glue and then the microholes are drilled. After the chips are coated with metal, the layers of photoresist and pattern lines are applied.

Direct writing by laser allows selective deposition of metal into patterns, bypassing the traditional photolithography and etching steps that limit the amount of miniaturization possible when forming interconnects on integrated circuits. By also using a laser to drill micro via holes between insulating layers, the process further increases the interconnect density. Notably it eliminates wire bonding, which is a thermomechanical process, with a direct metallurgical connection to the integrated circuit pad.

Figures 5, 6, array of HDI boards

An example of a current HDI production format is shown in plan view in Figure 5, with a frame 60 around each board to enable it to be clamped for processing. Each board has features such as connection pads 65 for later connection of components such as one or more active and/or passive components. They are preferably electronic components. They can be surface mount devices. An example of the HDI implant PCB production format is shown in Figure 6, manufactured without the support frame, which is feasible if further processing such as screen printing with solder and mounting of components, is carried out after implanting by inserting into the aperture.

Figure 7 Implant of HDI Board

The HDI board is inserted into the now vacant Keep Out area of the Multilayer board so that the top of each board is perfectly flat. This is essential for later screen printing of solder paste and placement of electronic components. They can be surface mount devices. This insertion can be from either side of the motherboard, but if from the side away from the surfaces to be made coplanar, then it can be easier to achieve accurate coplanarity by placing the motherboard against a reference surface (not shown here) covering the aperture. Then the implant can be inserted up to the reference surface.

Figure 8 Heat Cure Epoxy X-Section

Figure 8 shows a cross section view of the multi board module. The HDI board is mechanically secured in place by applying Heat Cure Epoxy 70 between the circumference of the underneath of the HDI board and the circumference of the Keep Out area of the Multilayer board. The under surface of the implant is recessed since the implant is thinner than the mother board. This means the surfaces of the two boards meet at a right angle, which provides a better foundation for a glued joint, and makes it easier to ensure that the glue does not protrude.

Figure 9 Plan View showing Heat Cure Epoxy

Figure 9 shows a plan view of the underside of the example of figure 8, showing where the glue in the form of a heat cure epoxy is applied to the circumference of the multi board module.

Figure 10 Same Thickness PCBs

Where the HDI PCB is the same thickness as the Multilayer PCB, one way to achieve a smooth surface on both sides is to cut a groove or channel 80 in both boards to receive the epoxy.

Figure 11 Epoxy Bead

The epoxy is applied in the groove ensuring the epoxy bead is at or below the surface of the PCBs. This is to ensure that there is no interference with the solder stencil use for screen printing during component placement.

Figure 12 Multilayer Production Panel with implant

Figure 12 shows a plan view of an example of the panel of figure 3 following insertion and following the step of mounting the one or more circuit components. The components can be passive and/or active components. They are preferably electronic components. This can be carried out by screen printing the panel with solder so that the solder is applied to both first and second boards at the same time. The electronic components are then placed for both boards at the same time, simplifying the production process. Then a conventional reflow solder step can be carried out for the panel.

Figure 13 Electrical Connections

Figure 13 shows a plan view of an example of an arrangement of conductive pads for electrical connections between the first and second boards. As can be seen, for the example of a wireless application, there are two RF connections 84 on one side and six baseband connections 82 on another side of the multi board module.

Currently, the most common method of embedding Wireless modules in devices is to use an industry standard PCI mini card. This standard utilises RF connectors and Co- axial cables to connect the Wireless Module antenna output to the Device antenna.

With the Implanted module according to embodiments of the present invention it is possible to make these RF connections with one or more far less expensive bridging components such as passive components and/or active components. They are preferably electronic components. Likewise, the PCI mini card BaseBand connections are conventionally made using multi pin moulded PCI connectors mounted on the mother board. With the Implanted module according to embodiments of the present invention it is possible to make these BaseBand connections with one or more far less expensive bridging components such as passive components and/or active components. They are preferably electronic components. The bridging components such as passive

components and/or active components can be in the form of surface mount components which take up little space and do not need holes, and are more tolerant of some height mismatch across the gap than using a flip chip process with an array of pads. SMT (surface mount technology) component placement systems, sometimes called pick-and- place machines are robotic machines which are used to place surface mount devices (SMDs) onto a proted circuit borad (PCB). They are used for high speed, high precision placing of broad range of electronic components, like capacitors, resistors, inductors, integrated circuits, transistors, diodes, filters, ADC's or DAC's onto the PCBs.

Figure 14 X-Section with components placed

Figure 14 shows a cross section of a completed multi board module, showing placed circuit components 90, and surface mount passive devices 95 for the electrical connections to the multi board module.

Figure 15 Outline with lugs Figure 15 shows an example of an outline of an insert with lugs 600 for fitting with corresponding recesses on the outline of an aperture. In this example, three lugs are shown on three different sides of the outline. Of course the lugs could be on the aperture outline and corresponding recesses on the outline of the insert. Many other arrangements are possible. The lugs and corresponding recesses make it easier to implement a press fit without needing precise tolerances on larger dimensions of the overall outline.

Figure 16 method steps

Figure 16 shows some of the principal method steps of some embodiments according to an aspect of the invention. At step 100, a first multilayer circuit board is formed with an aperture. This can be part of a panel as described above or a stand alone board. At step 110 a second multilayer board is provided, to fit the aperture. This can be a standard part bought in, or can be manufactured or shaped in house. Clearly the order of these two steps is not important. At step 120, the second multilayer circuit board can be inserted in to the aperture to provide coplanar surfaces. Then in step 130, circuit components can be mounted on the coplanar surfaces in various ways, and in the same step or at the same time, one or more bridging components such as passive components and/or active components can be mounted across a gap between the boards to provide electrical connections between the boards. They are preferably electronic components. They can be surface mount devices. Other steps can be added.

Figure 17 method steps

Figure 17 shows some of the principal method steps of embodiments according to another aspect. At step 200, a first multilayer circuit board is formed with an aperture, the aperture having an outline with one or more lugs or recesses. Again this can be part of a panel as described above or a stand alone board. At step 210 a second multilayer board is provided, to fit the aperture, and thus having an outline with a corresponding lug or recess to engage with the lug or recess on the outline of the aperture. This can be a standard part bought in, or can be manufactured or shaped in house. Clearly the order of these two steps is not important. At step 220, the second multilayer circuit board can be inserted in to the aperture to provide coplanar surfaces, while engaging the corresponding lug and recess to give a press fit. Then in step 230, circuit components can be mounted on the coplanar surfaces in various ways to complete the multi board module. For example one or more bridging components can be mounted between the boards. The bridging components can be passive and/or active components. They are preferably electronic components. They can be surface mount devices. Other steps can be added.

Figure 18 method steps

Figure 18 shows some of the principal method steps of embodiments according to another aspect. At step 100, a first multilayer circuit board is formed with an aperture. This can be part of a panel as described above or a stand alone board. At step 110 a second multilayer board is provided, to fit the aperture. This can be a standard part bought in, or can be manufactured or shaped in house. As before, the order of these two steps is not important. At step 120, the second multilayer circuit board can be inserted in to the aperture to provide coplanar surfaces. Then in step 330, the implant is glued in place to enable processing of the module. The coplanar surfaces of both boards are screen printed in the same step with solder. Then circuit components can be mounted on the coplanar surfaces in various ways to complete the module. For example one or more bridging components can be mounted between the boards. The bridging components can be passive and/or active components. They are preferably electronic components. They can be surface mount devices. Other steps can be added.

Figure 19 method steps

Figure 19 shows some of the principal method steps of embodiments according to another aspect. At step 100, a first multilayer circuit board is formed with an aperture. This can be part of a panel as described above or a stand alone board. At step 410 a second multilayer board is formed, to fit the aperture, by cutting from an array of similar boards without providing a surrounding frame for each board. This array can be a standard part bought in, or can be manufactured or shaped in house. As before, the order of these two steps is not important. At step 120, the second multilayer circuit board can be inserted in to the aperture to provide coplanar surfaces. Then in step 230, circuit components can be mounted on the coplanar surfaces in various ways to complete the multi board module. For example one or more bridging components can be mounted between the boards. The bridging components can be passive and/or active components. They are preferably electronic components. They can be surface mount devices. Other steps can be added.

Figure 20 method steps

Figure 20 shows some of the principal method steps of embodiments according to another aspect. At step 100, a first multilayer circuit board is formed with an aperture. This can be part of a panel as described above or a stand alone board. At step 510 a second multilayer board is formed, to fit the aperture, the board being thinner than the first board. Again this can be a standard part bought in, or can be manufactured or shaped in house. As before, the order of these two steps is not important. At step 520, the second multilayer circuit board can be inserted into the aperture to provide coplanar surfaces, by placing one side of the first board against a reference surface covering the aperture, then inserting the second board into the aperture from the other side of the first board. The second board can be pushed against the reference surface to ensure coplanarity, up to the degree of planarity of the reference surface.

Then at step 530, glue can be applied to fix the implant, to a corner where the backside of the implant meets a perpendicular surface of the aperture. Then the circuit components can be mounted on the coplanar surfaces in various ways to complete the multi board module. For example one or more bridging components can be mounted between the boards. The bridging components can be passive and/or active components. They are preferably electronic components. They can be surface mount devices. Other steps can be added.

Summary of some additional features and their effects:

The one or more additional bridging component such as a passive component and/or an active component can comprise a surface mount package. They can be surface mount devices. This type of package is compact and does not need holes in the boards for pins. Hence it is suited to spanning a joint between the boards without taking much board space and without the need for such holes near the edges of the boards, which might add some structural weakness and add costs. The additional passive component can comprise an inductor suitable for RF impedance matching for example. This can help minimize the impact of the passive component on the circuit design, particularly for RF applications. The step of forming the second multilayer circuit board can comprise forming it to be a press fit in the aperture. This can make automation easier and enable a subsequent gluing step to be made simpler and more reliable if the press fit means the inserted board is less likely to slip out of position before gluing.

The outlines of the aperture and of the second multilayer circuit board respectively can be formed with one or more cooperating lugs and recesses to provide the press fit. This can enable the press fit to be achieved more easily with less need for precise tolerances on all dimensions of the outline.

The mounting step can have a step of screen printing the coplanar surfaces with solder after the inserting step. This can enable both boards to be processed together after insertion, to reduce costs compared to carrying out the same step twice on the boards before insertion. Also it helps avoid the need for a frame around the second multilayer board, to grip the board when processing it. Hence in some cases the second multilayer circuit board can be formed by cutting from an array of similar boards without a surrounding frame for each of the boards. This can increase a number or boards in the array of a given size and hence reduce costs.

The inserting of the second multilayer circuit board can comprise placing the coplanar surface of the first multilayer circuit board against a reference surface then pressing the second multilayer circuit board into the aperture from an opposite side of the first multilayer circuit until the second multilayer circuit abuts the reference surface, then applying glue to a joint at the opposite side of the joint away from the coplanar surface. This can help ensure the coplanarity, in a fashion which is much simpler and cheaper than trying to control a depth of a recess for example.

The forming of the first multilayer circuit board can comprise forming the aperture in the same step as forming an outline of the board. This can reduce the number of processing steps and save costs, and follows from no longer needing a precision cut to control the depth of a recess.

The second multilayer circuit board can be an HDI board, which has effects set out above, such as enabling a higher density of interconnect and reducing a need for wire bonds.

Other variations can be envisaged within the scope of the claims.

Claims

Claims:

1. A method of manufacturing a multi board module having the steps of:

forming (100) a first multilayer circuit board so as to have an aperture,

providing (110) a second multilayer circuit board (50) to fit within at least part of the aperture,

inserting (120) the second multilayer circuit board into the aperture so that at least one surface of the second multilayer circuit board is coplanar with a corresponding surface of the first multilayer circuit board, and

mounting (130) circuit components on the coplanar surfaces and in the same step, mounting one or more additional passive components between the respective conductors across a perimeter of the aperture to form one or more electrical connections between respective conductors on the coplanar surfaces of the first and second multilayer circuit boards.

2. The method of claim 1, the additional passive component comprising a surface mount package.

3. The method of claim 1 or 2, the additional passive component comprising an inductor suitable for RF impedance matching.

4. The method of any preceding claim, the step of forming the second multilayer circuit board comprising forming it to be a press fit in the aperture.

5. The method of claim 4, wherein outlines of the aperture and of the second multilayer circuit board respectively are formed with one or more cooperating lugs and recesses to provide the press fit.

6. The method of any preceding claim, the mounting step having the step of screen printing the coplanar surfaces with solder after the inserting step.

7. The method of any preceding claim, the second multilayer circuit board being formed by cutting from an array of similar boards without a surrounding frame for each of the boards.

8. A method of manufacturing a multi board module having the steps of: forming (200) a first multilayer circuit board so as to have an aperture, the aperture having an outline with at least one lug or recess

providing (210) a second multilayer circuit board to fit within at least part of the aperture, and having an outline having a corresponding lug or recess and

inserting (220) the second multilayer circuit board into the aperture so that at least one surface of the second multilayer circuit board is coplanar with a corresponding surface of the first multilayer circuit board, while engaging the corresponding lug and recess, to provide a press fit in the aperture.

9. The method of any preceding claim, having the step of screen printing the coplanar surfaces with solder after the inserting step.

10. The method of any preceding claim, the second multilayer circuit board being formed by cutting from an array of similar boards without a surrounding frame for each of the boards.

11. A method of manufacturing a multi board module having the steps of:

forming (100) a first multilayer circuit board so as to have an aperture,

providing (110) a second multilayer circuit board to fit within at least part of the aperture,

inserting the second multilayer circuit board into the aperture so that at least one surface of the second multilayer circuit board is coplanar with a corresponding surface of the first multilayer circuit board, and

screen printing (330) the coplanar surfaces with solder after the inserting step.

12. The method of any preceding claim, the step of forming the second multilayer circuit board comprising forming it to be a press fit in the aperture.

13. The method of claim 12 wherein outlines of the aperture and of the second multilayer circuit board respectively are formed with one or more cooperating lugs and recesses to provide the press fit.

14. The method of any preceding claim, the second multilayer circuit board being formed by cutting from an array of similar boards without a surrounding frame for each of the boards.

15. A method of manufacturing a multi board module having the steps of:

forming (100) a first multilayer circuit board so as to have an aperture,

providing (410) a second multilayer circuit board to fit within at least part of the aperture, and

inserting (120) the second multilayer circuit board into the aperture so that at least one surface of the second multilayer circuit board is coplanar with a corresponding surface of the first multilayer circuit board,

the second multilayer circuit board being formed (410) by cutting from an array of similar boards without providing a surrounding frame for each of the boards.

16. The method of claim 15, having the step of screen printing the coplanar surfaces with solder after the inserting step.

17. The method of any preceding claim, the inserting of the second multilayer circuit board comprising placing the coplanar surface of the first multilayer circuit board against a reference surface then pressing the second multilayer circuit board into the aperture from an opposite side of the first multilayer circuit until the second multilayer circuit abuts the reference surface, then applying glue to a joint at the opposite side of the joint away from the coplanar surface.

18. A method of manufacturing a multi board module having the steps of:

forming (100) a first multilayer circuit board so as to have an aperture,

providing (510) a second multilayer circuit board, thinner than the first multilayer circuit board, and having an outline to fit within at least part of the aperture,

inserting (520) the second multilayer circuit board into the aperture by placing one surface of the first multilayer circuit board against a reference surface then pressing the second multilayer circuit board into the aperture from an opposite side of the first multilayer circuit until the second multilayer circuit abuts the reference surface, so that one surface of the second multilayer circuit board is coplanar with a corresponding surface of the first multilayer circuit board, and a second surface of the second multilayer board is recessed, and

fixing the second multilayer board by applying glue where the recessed surface of the second multilayer board meets the first multilayer board.

19. The method of any preceding claim wherein the forming of the first multilayer circuit board comprises forming the aperture in the same step as forming an outline of the board.

20. The method of any preceding claim, the second multilayer circuit board being an HDI board.

21. A multi board module having:

a first multilayer circuit board with an aperture,

a second multilayer circuit board shaped to fit within at least part of the aperture, and inserted into the aperture so that at least one surface of the second multilayer circuit board is coplanar with a corresponding surface of the first multilayer circuit board, and circuit components placed and soldered on the coplanar surfaces and one or more additional passive components making one or more electrical connections between respective conductors on the coplanar surfaces of the first and second multilayer circuit boards across a perimeter of the aperture.

22. The board of claim 21, the additional passive component comprising a surface mount package.

23. The board of claim 21 or 22, the additional passive component comprising an inductor suitable for RF impedance matching.

24. A multi board module having:

a first multilayer circuit board with an aperture, and

a second multilayer circuit board shaped to fit within at least part of the aperture, and inserted into the aperture so that at least one surface of the second multilayer circuit board is coplanar with a corresponding surface of the first multilayer circuit board, wherein outlines of the aperture and of the second multilayer circuit board respectively are formed with one or more cooperating lugs and recesses to provide a press fit.