GB2577211A

GB2577211A - Opto-electronic assembly

Info

Publication number: GB2577211A
Application number: GB1917589.2A
Authority: GB
Inventors: Carley Carl
Original assignee: Hilight Semiconductor Ltd
Current assignee: Hilight Semiconductor Ltd
Priority date: 2019-12-02
Filing date: 2019-12-02
Publication date: 2020-03-18
Also published as: GB201917589D0

Abstract

An optical transceiver for fibre optic communication is disclosed, which includes a bi-directional optical sub-assembly (BOSA) 101, a first circuit board 306 and a second circuit board 302. The BOSA includes a laser 103, a photodiode 104, photodiode connectors (110/111 Fig. 2) on a first side of the BOSA and laser connectors (109, Fig. 2) on a second side of the BOSA. The first side of the BOSA (the bottom in Figure 3) is mounted on a first circuit board 306. The first circuit board includes laser driver circuitry (107, Fig. 1)/303, amplifier circuitry (108 Fig. 1)/303 and a receive path 307 which connects the amplifier circuitry with the BOSA’s photodiode connectors. A second side of the BOSA is mounted on a second circuit board 302. The second circuit board is mounted on the first circuit board. The second circuit board includes circuitry 304 for providing impedance matching or modification between the laser driver and the laser. An electrical path 310 couples the impedance matching circuit with the first circuit board 306. The first and second circuit boards may be rigid and orthogonal.

Description

(71) Applicant(s):

HiLight Semiconductor Limited

Delta House, Enterprise Road, Southampton Science Park, Southampton, Hampshire, SO16 7NS, United Kingdom (72) Inventor(s):

Carl Carley (74) Agent and/or Address for Service:

Page White & Farrer

Bedford House, John Street, London, WC1N 2BF, United Kingdom (56) Documents Cited:

CN 103957057 A

JP 2009210696 A

JP 2011238848 A US 20030142929 A1

HiLight Semiconductor, Datasheet: HLC10V0, 1.25 to 11.3 Gbps Combined VCSEL / LASER Driver and Limiting Amplifier, March 2018. Downloaded from https://hilight-semi.com/drivers-receiverstransceivers/ on 4 February 2020.

(58) Field of Search:

INT CL G02B, H04B, H05K

Other: WPI, EPODOC, Patent Fulltext (54) Title ofthe Invention: Opto-electronic assembly

Abstract Title: An optical transceiver comprising a BOSA mounted on two orthogonal and interconnected circuit boards, one of which has impedance matching circuitry (57) An optical transceiver for fibre optic communication is disclosed, which includes a bi-directional optical subassembly (BOSA) 101, a first circuit board 306 and a second circuit board 302. The BOSA includes a laser 103, a photodiode 104, photodiode connectors (110/111 Fig. 2) on a first side ofthe BOSA and laser connectors (109, Fig. 2) on a second side of the BOSA. The first side of the BOSA (the bottom in Figure 3) is mounted on a first circuit board 306. The first circuit board includes laser driver circuitry (107, Fig. 1)/303, amplifier circuitry (108 Fig. 1)/303 and a receive path 307 which connects the amplifier circuitry with the BOSA’s photodiode connectors. A second side ofthe BOSA is mounted on a second circuit board 302. The second circuit board is mounted on the first circuit board. The second circuit board includes circuitry 304 for providing impedance matching or modification between the laser driver and the laser. An electrical path 310 couples the impedance matching circuit with the first circuit board 306. The first and second circuit boards may be rigid and orthogonal.

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Figure 2

102

101

Fsbre

110,111

Laser Drive

Receive Raw Data, Power, Contro!

109

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Figure

Figure 5

310

505

Figure 6

601

302

505

7/9

Figure 7

701

8/9

Figure 8

9/9

Fiuure 9

901

902

903

904

905

906

907

908

Attach daughter board to main board with plated recesses over coresponding signal traces

Form solder joints between daughter board and main board at recess locations

Opto-Electronic Assembly

Field of the Invention

The present application relates to opto-electronic assemblies and optical subassembly construction with a combination of circuit board assemblies.

Background of the Invention

High speed optical communication links comprise many optical, electronic and optoelectronic components and assemblies wherein electrical signals are converted into optical 15 signals for transmission over a fibre; and where optical signals conveyed by means of a fibre are converted to an electrical signal and subject to amplification and further processing. Common requirements for the components and assemblies used in such links are that the cosf be minimised, while at the same time the performance is to be maximised.

2.0 This invention is concerned with that part of an optical communications system wherein an optical signal is received and converted into an electrical signal and subject to amplification and possibly aiso subject to other signal processing functions before being conveyed to other components of the complete signal chain, and also wherein an electrical signal is converted into an optical signal. The elements of such an optical communications 25 system considered in this invention are where said transmit and said receive functions are combined into a single sub-assembly.

A component wherein the optical to electrical and electrical to optical conversion functions are combined for both the receive and transmit paths is commonly called a 30 Bidirectional Optical Sub-Assembly or BOSA. This may comprise a laser, a photodiode and an associated amplifier, typically a trans-impedance amplifier, possibly with an associated internal limiting amplifier. The amplifier associated with the receive photodiode is typically mounted close to the photodiode in order to maximise the bandwidth of the complete system. The driving circuitry for the laser diode is typically external to the BOSA.

Conventionally the laser, photodiode and the amplifier are mounted in a metal enclosure which provides an optical port and locating position to couple the electro-optical components to the fibre, and wherein the external electrical connections are provided by means of wire leads that feed through insulating regions in the sides of the enclosure, to 40 addition to the receive signal path, there may also be connections for power, monitoring, and control signals for the amplifier and the photodiode. The receive path connections are typically located on a side of the enclosure that is not the same as those for the transmit path connections to the laser. The drive to the laser is typically provided directly from the driver electronic circuitry, often in terms of a directly modulated current. The electrical path between 45 the driver electronic circuitry and the laser diode itself becomes a critical design issue at high data rates, due to the possibility of parasitic impedances on circuit nodes and impedance discontinuities in the electrical paths giving rise to distortion in the transmitted optical signal. Such distortions will typically reduce the observable differences between different data signalling levels, commonly referred to as eye-opening. These levels may be binary in 50 nature, or defined by some multi-level signalling scheme, for example, 4-level pulseamplitude-modulation (PAM4). In order to minimise distortion of the transmitted optical signals, it is commonly necessary to add matching components to the signal path between the driver circuitry and the BOSA package. The nature and complexity of the matching network will depend on the characteristics of the laser and the BOSA package, and aiso on 55 the signal path through the circuit boards on which said components are mounted, to order for the matching network to be as effective as possible, it is desirable to be able to mount said matching components as closely as possible to the BOSA to avoid long circuit board traces between them.

Further, if a manufacturer of an optical communications terminal chooses to change the type of BOSA being used, it will imply a complete re-design of the circuit board and the matching network. Since the circuit board is likely to comprise many other components and functions in addition to the BOSA, this can represent a significant cost.

Summary of the Invention to

It is an object of the invention to provide means of construction and configuration for the reception and transmission functions of a high speed optical communication system wherein improved performance can be achieved compared with prior art. It is a further object of the invention to provide a construction and configuration for the reception and transmission 15 functions of a high speed optical communication system wherein improved performance can be achieved and overall manufacturing cost can reduced compared with prior art.

A benefit of the invention is that matching components present in the signal path between the driving circuitry in the transmit function can be mounted closer to the BOSA and 20 its internal laser so as to minimise parasitic impedances present between same, thereby providing the capability to improve the eye opening in the transmitted optical signal.

A further benefit of the invention is that changes to the specific BOSA employed or to the matching circuitry employed can be made by redesign of a small daughter board rather 25 than the main circuit board of the optical communication terminal.

According to a first aspect of the invention there is provided an assembly of electronic components providing means for ths transmission and reception of data using an optical fibre wherein said assembly comprises: a bi-directional optical sub-assembly, the bi-directional 30 optical sub-assembly comprising: a laser configured to generate a suitable optical output for the transmission of data: a photodiode and associated electronic circuitry configured to receive a suitable optical input and provide signals associated with the reception of data; a first circuit board, a first side of the bi-directional optical sub-assembly being physically mounted on the first circuit board wherein connections from the first side of the bi-directional 35 optical sub-assembly are coupled to the photodiode and associated electronic circuitry, and on the first circuit board are located: laser driver circuitry configured to drive the laser; and amplification and processing circuitry configured to receive the signals associated with the reception of data, and wherein the first circuit board comprises at least one receive path electrical connection to couple the photodiode and associated electronic circuitry to the 40 amplification and processing circuitry; a second circuit board, the second circuit board being physically mounted on the first circuit board and a second side of the bi-directional optical sub-assembly is physically mounted on a first side of the second circuit board, wherein connections from the second side of the bi-directional optical sub-assembly are coupled to the laser, the second circuit board further comprises at least one electrical connection configured 45 to couple the laser driver circuitry on the first circuit board to the laser of the bi-directional optical sub-assembly, wherein the tit least one electrical connection on the second circuit board is coupled to the at least one electrical connection on the first circuit board via at least one area of conductive material on the second circuit board and physically located on an opposite side to the first side of the second circuit board is at least one component coupled to 50 the at least one electrical connection and configured to provide impedance modification or matching between the laser driver circuitry on the first circuit board and the laser of the bidirectional optical sub-assembly.

The second circuit board may comprise at least one mechanical lug configured to slot 55 into at least one slot within the first circuit board.

The second circuit board may be affixed to the first circuit board by a fixing agent.

The fixing agent may be solder.

The af least one electrical connection on the second circuit board may be coupled to the at least one electrical connection on the first circuit board via at least one solder joint.

The at least one area of conductive material on the second circuit board rnay comprise at least one conductive edge region configured to couple the at least one electrical connection of the second circuit board to the at least one electrical connection of the first circuit board when the second circuit board is physically mounted on the first circuit board.

The at least one conductive edge region may comprise at least a part of a throughplated-via.

The second circuit board may comprise electrical connections configured to couple the laser of the bi-directional optical sub-assembly to the at least one component configured to provide impedance modification or matching such that the path distance is approximately a thickness of the second circuit board.

According to a second aspect there is provided a method for providing an assembly of electronic components providing means for the transmission and reception of data using an optical fibre wherein said method comprises: providing a bi-directional optical sub-assembly, the bi-directional optical sub-assembiy comprising: a laser configured to generate a suitable optical output for the transmission of data; a photodiode and associated electronic circuitry configured to receive a suitable optical input and provide signals associated with the reception of data; providing a first circuit board; physically mounting a first side of the bi-directional optical sub-assembly on the first circuit board, the first side of the bi-directional optical subassembly comprising connections which couple to the photodiode and associated electronic circuitry configured to receive a suitable optical input; locating on the first circuit board laser driver circuitry configured to drive the laser; locating on the first circuit board amplification and processing circuitry configured to receive the signals associated with the reception of data; coupling, using at least one receive path electrical connection, the photodiode and associated electronic circuitry to the amplification and processing circuitry; providing a second circuit board; physically mounting the second circuit board on the first circuit board; physically mounting a second side of the bi-directional optical sub-assernbly on a first side of the second circuit board, the second side of the bi-directional optical sub-assembly comprising connections which couple to the laser; coupling, using at least one area of conductive material on the second circuit board and at least one electrical connection on the second circuit board the laser driver circuitry on the first circuit board to the laser of the bi-directional optical sub-assembly; and physically locating, on an opposite side to the first side of the second circuit board, at least one impedance modification or matching component coupled to the at least one electrical connection and configured to provide impedance modification or matching between the laser driver circuitry on the first circuit board to the laser of the bidirectional optical sub-assembly.

Providing the second circuit board may comprise providing at least one mechanical lug on the second circuit board, the at least one mechanical lug configured to slot into at least one slot within the first circuit board.

The method may further comprise affixing the second circuit board to the first circuit 50 board by a fixing agent.

Affixing the second circuit board to the first circuit board may comprise soldering the second circuit board to the first circuit board.

Coupling, using the at least one area of conductive material on the second circuit board and the at least one electrical connection, the laser driver circuitry on the first circuit board to the laser of the bi-directional optical sub-assembly mounted on the second circuit board may comprise forming at least one solder joint coupling the first circuit board to the second circuit board.

The method may further comprise forming on the second circuit board at least one 5 conductive edge region, the at least one conductive edge region coupling the at least one electrical connection on the second circuit board to the at least one electrical connection on the first circuit board when the second circuit board is physically mounted on the first circuit board.

The method may further comprise coupling the laser of the bi-directional optical subassembly mounted on the second circuit board to the at least one component configured to !5 provide impedance modification or matching such that a distance between the laser of the bidirectional optical sub-assembly and the at least one component is approximately a thickness of the second circuit board.

According to a third aspect there is provided a method for manufacturing an assembly 20 of electronic components providing means for the transmission and reception of data using an optical fibre wherein said method comprises: manufacturing a first circuit board, wherein on the first circuit board are located at least one receive path electrical connection; physically mounting a first side of a bi-directional optical sub-assembly on the first circuit board, the bidirectional optical sub-assembly comprising: a laser configured to generate a suitable optical 2.5 output for the transmission of data; a photodiode and associated electronic circuitry configured to receive a suitable optical input and provide signals associated with the reception of data and the first side of the bi-directional optical sub-assembly comprising at least one connection which couples to the photodiode and associated electronic circuitry configured to receive a suitable optical input; physically locating on the first circuit board laser driver 30 circuitry configured to drive the laser; physically locating on the first circuit board amplification and processing circuitry configured to receive the signals from the bi-directional optica! assembly associated with the reception of data; coupling via the at least one receive path electrical connection, the photodiode and associated electronic circuitry to the amplification and processing circuitry; manufacturing a second circuit board, wherein on the second circuit 35 board are located at least one area of conductive material and at least one electrical connection: physically mounting the second circuit board on the first circuit board; physically mounting a second side of the bi-directional optical sub-assembly on a first side of the second circuit board, the second side of the bi-directional optical sub-assembly comprising at least one connection which couples to the laser; coupling, using at least the at least one area of conductive material and the at least one electrical connection on the second circuit board, and at least one electrical connection on the first circuit board the laser driver circuitry on the first circuit board to the laser of the bi-directional optical sub-assembly; and physically locating, on an opposite side to the first side of the second circuit board, at least one impedance modification or matching component coupled to the at least one area of conductive material and configured to provide impedance modification or matching between the laser driver circuitry on the first circuit board and the laser of the bi-directional optical sub-assembly.

Coupling, using the at least one area of conductive material on the second circuit board, the laser driver circuitry on the first circuit board to the laser of the bi-directional optical 50 sub-assembly, said coupling may comprise forming a solder joint between the at least one area of conductive material of the second circuit board and the at least one area of conductive material of the first circuit board.

Manufacturing a second circuit board, wherein on the second circuit board is located 55 at least one area of conductive material may comprise plating at least one edge region of the second circuit board, wherein the at least one edge region plating couples the at least one area of conductive material on the first circuit board and the at least one electrical connection on the second circuit board.

Manufacturing a second circuit board, wherein on the second circuit board is located at least one area of conductive material may comprise creating at least one electrical connection configured to couple the laser to the at least one component mounted on the 5 second side of the second circuit board when the bi-directional optical sub-assembly is physically located on the first side of the second circuit board; creating at least one thoughplated hole electrically connected to at least one component mounted on the second side of the second board at an edge of the said second board, cutting the at least one throughplated-via to expose the through plating and create the at least one area of conductive 10 material on an edge of the second circuit board configured to couple the at least one impedance modification or matching component to the first circuit board when the second circuit board is physically mounted on the first circuit board.

Manufacturing a second circuit board may comprise creating an electrical connection 15 to couple the first side and the opposite side of the second circuit board, wherein the electrical connection couples the bi-directional optical sub-assembly on a first side of the second circuit board and the at least one impedance modification or matching component such that the distance between the bi-directional optical sub-assembly and the at least one impedance modification or matching component is substantially the thickness of the second circuit board. 20

Manufacturing a first circuit board may comprise creating receive path electrical connections configured to couple the photodiode and associated electronic circuitry to the amplification and processing circuitry when the first side of the bi-directional optical subassembly is physically located on the first circuit board.

2.5

Manufacturing a first circuit board and manufacturing a second circuit board may comprise: manufacturing a single circuit board; patterning the single circuit board with the receive path electrical connections; populating the single circuit board with the laser driver circuitry configured to drive the laser, the first circuit board amplification and processing 30 circuitry, and the at 'east one impedance modification or matching component; separating the single circuit board into the first circuit board and the second circuit board.

Physically mounting the second circuit board on the first circuit board may comprise: slotting at least one mechanical lug on the second circuit board into at least one slot within the 35 first circuit board; and affixing the second circuit board to the first circuit board by a fixing agent.

Summary of the Figures

The invention will now be described solely by way of example and with reference to the accompanying drawings, in which:

Figure 1 shows a fibre optical communications system according to prior art.

Figure 2 shows a view of a BOSA for use in a fibre optical communications transmitter and receiver according to prior art.

Figure 3 shows an assembly of a ROSA and associated components configured according to an embodiment of the present invention.

Figure 4 shows a view of an assembly of circuit boards configured according to an 55 embodiment of the present invention.

Figure b shows a circuit board configured according to an embodiment of the present invention.

Figure 6 shows a circuit board configured according to an embodiment of the present 5 invention.

Figure 7 shows a circuit board configured according to an embodiment of the present invention.

Figure 8 shows a circuit board configured according to an embodiment of the present invention.

Figure 9 shows a procedure for the method of configuring components according to some aspects of the invention.

The description is not to be taken in a limiting sense but is made merely for the purposes of describing the general principles of the embodiments of the invention.

Embodiments of the Application

Figure 1 shows the basic system level configuration of a generic optical communications physical link, wherein electrical data signals 109 containing information are converted to optical signals for transmission over a fibre 102 and received optical data signals from the said fibre are converted to electrical signals, said conversions being performed within 25 a Bi-directional Optical Sub-Assembly (BOSA) 101.

The BOSA may be comprised of a photodiode 104 to perform the basic conversion of the optical signal into an electrical signal, where said photodiode is coupled to an amplifier 105, typically, though not exclusively, a transimpedance amplifier (TIA), in order to deliver a 30 usefully large raw data signal 110 that may be conveyed to electronic components and systems for further processing. The amplifier 105 is typically mounted very close to the photodiode 104 in order to minimise stray capacitance and inductance effects that could have detrimental impacts on the speed of operation. The BOSA may also have additional connections 111 to provide power supplies and may have control and monitoring inputs and 35 outputs for the receiving path. The output 110 of said amplifier is typically passed to a limiting amplifier in the associated receiver circuits 108, wherein the magnitude of the signal is raised and compensation made for variations in the strength of the optical signal in order to make it suitable for further processing, often by digital circuits. Said receiver circuits 108 are typically mounted on a main circuit board 106.

The said BOSA may also be comprised of a iaser, typically a semiconductor laser diode 103, whose optical output intensify is controlled by an electrical signal 109 modulated in a mariner so as to be able to convey data over the optical fibre, said signal being supplied by laser drive circuits 107 external to the BOSA. Said laser drive circuits are typically mounted 45 on a main circuit board 106. In many embodiments the said receiver circuits 108 and the said laser driver circuits 107 may be implemented in circuitry contained within a single integrated circuit (IC) mounted on said main circuit board 106.

The laser driver circuits 107 may provide the signai 109 to the laser either in the form 50 of a controlled current or a controlled voltage. It will be obvious to one of ordinary skill in the art that at very high data rates there will be significant challenges in ensuring that the optical intensity modulation is a faithful representation of the desired data signals. Significant challenges are often associated with the electrical path between the laser driver circuits and the laser itself. Depending on the physical nature of the electrical connections, there may be 55 parasitic impedances present at critical circuit nodes, and where there is an attempt to construct constant impedance lines, there may be changes in impedance at physical junctions. These factors may lead to distortions in the transmit drive signals to the extent that the laser’s optical output has reduced clear distinctions between the defined signalling modulation levels. Said desired signalling modulation levels may be simply two levels for binary signalling, or multiple levels such as in PAM4 signalling.

In order to mitigate problems associated with the electrical behaviour of the combination of the laser driver circuitry, the connections across the circuit board(s), the BOSA package and the laser itself, it is common to employ additional electronic matching components in the electrical path between the laser driver circuits and the BOSA. Said matching components are typically a small number of passive elements. Due to the sensitivity to the design(s) of the circuit board(s) and to the configuration and nature of ihe tO matching components in terms of the effects in the optical signal, it is common to require several iterations in the design of the boards and the matching network. Where the implementation is attempted using a single circuit board for the BOSA and for the associated transmit and receive circuitry, it will be apparent that each redesign will incur significant cost and potentially result in delay in completion of the final design.

Figure 2 shows a view of a typical BOSA 101 as used in many fibre optical transmission and reception systems. In the example BOSA shown, there is provided an optically transparent port on one side to allow coupling of transmitted and received light signals travelling in the fibre 102 to the internal electro-optical components, the laser 103 and 20 the photodiode 104. On another side of the BOSA are provided electrical connection wires which carry the transmit data signal 109 which is used to drive the laser. On a yet further side of the BOSA are provided electrical connection wires which carry the received data signals 110 as well as any required power supply and control signals 111. It is common for the sides carrying the said transmit and receive electrical connections to be adjacent and separated by 25 an included right angle.

Figure 3 shows an exemplar arrangement for an arrangement of components configured to provide transmission and reception of optical data over a fibre wherein said arrangement seeks to improve on some of the shortcomings of the previously described prior 30 art according to some embodiments of the invention.

The arrangement provides for the mounting of the BOSA 101 on a small daughter board 302 such that the transmit path electrical connections 109 are connected to the daughter board 302. The daughter board is in turn mounted on the main (mother) board 301, 35 said main board having mounted thereon the transmit and receive circuitry 303 commonly required in such systems, for example, the transmit laser driver circuits, the receive path limiting amplifier, timing circuits and control circuits. These circuits may be constructed from discrete components or may be constructed from one or more integrated circuits. The main board 301 will also comprise circuit traces 307 intended to convey power and electrical 40 signals from the receive path of the BOSA. The main board 301 will also comprise circuit traces 308 intended to convey electrical signals to the laser in the BOSA. Due to the veryhigh frequencies of the electrical signals typical in such applications, it is common to configure these circuit traces 307, 308 so as to present defined impedances and propagation characteristics in order to minimise distortion of the electrical signal waveforms. The main 45 board will also comprise further circuit traces 305, 306, intended to convey electrical signals between the transmit and receive circuitry 303 on the main board, to the host system requiring the conveyance of data.

In this example, the daughter board 302 is mounted so as to be perpendicular to the 50 main board 301. However in some embodiments the daughter board 302 is mounted in any suitable plane with respect to the main board 301. For example in some embodiments the daughter board 302 is at an angle other than perpendicular with respect to the main board 301 and mechanically supported by supports between the main board 301 and the daughterboard 302.

The position of the BOSA 101 mounted on the daughter board 302 with the transmit path 109 electrical connections is such that it is possible and convenient to connect the receive signal path 110, power and control 111 electrical connections directly to the main board 301. it is then possible to further connect the receive path signals, power and control connections to the circuitry 303 on the main board by means of appropriately configured circuit traces 307 that are located at suitable distances from other components on the main board so as to respect any interference considerations.

On an opposite side of the daughter board 302 from that on which the BOSA 101 is mounted, it is convenient to mount components 304 required to provide impedance modification or matching functions between the laser driver circuitry 107 comprised within the transmit and receive circuitry 303 mounted on the main board 301 and the laser 103 iO comprised within the BOSA 101. By mounting said impedance modification and matching components 304 on the daughter board 302 in this way it is possible to minimise the length of the electrical path between said components and the laser, so that this electrical path length is effectively only the thickness of the daughter board 302 plus the internal connection within the BOSA package 101 itself, in this way, it is possible to achieve more accurate and reliable 15 control of the circuit impedances affecting the electrical signals provided to the laser.

The electrical connections between the daughter board 302 and the main board 301 are formed where the transmit path traces 308 on the main board are aligned with corresponding traces 310 on the daughter running from the connections to the matching 20 components 304 and the BOSA laser and the edge of the daughter board. Where these traces are in contact, solder connections 309 can be made in a conventional manufacturing process. However, with simple abutment of the traces 309. 310 on the surfaces of each board, there is some risk that a reliable joint my not be achieved.

There is a further requirement that there is a sufficient degree of mechanical rigidity in the mounting of the daughter board 302 on the main board 301. This may be advantageously provided by additional solder joints between the boards. Additional rigidity may be achieved if the daughter board 302 is provided with lugs that locate in holes in the main board. However it would be appreciated that any suitable mounting element may be used io support the daughter board or provide sufficient mechanical rigidity.

Figure 4 shows a cross sectional view of an exemplar arrangement for some of the components comprised within a larger arrangement configured to provide transmission and reception of optical data over a fibre wherein said arrangement seeks to improve on some of 35 the shortcomings of the previously described prior art according to some embodiments of the invention. The daughter board 302 is shown mounted on the main board 301. Mechanical rigidity is assisted by solder joints at holes 311 in the main board. The connections between the circuit traces 310 on the daughter board 302 and the circuit traces 308 on the main board are advantageously formed by providing recesses 401 on an edge of the daughter board at 40 locations that correspond with the locations of the circuit traces 308, 310, and wherein the said recesses have metallic plating along the edge of the daughter board, and wherein the said plating is connected to the corresponding circuit trace 310. Further, the circuit traces on the main board 308 are configured to run in the recesses 401 underneath the full width of the edge of the daughter board 302 when the daughter board is correctly positioned. Thus when 45 the daughter board is positioned correctly on the main board, there is a sufficient area of metal on both the trace on the main board and on the edge of the daughter board for there to be a robust solder joint for each circuit trace.

Figure 5 shows a representation of the stages in the fabrication of the daughter board 50 which pertain to the formation of the recesses 401 in a convenient manner using conventional manufacturing processes. The daughter board is initially fabricated in a larger form 501 than is required in its final form 301 so that holes 502 may be formed in the board at the locations of the desired recesses 401. The holes are then plated through with metal in the conventional manner used to provide vias between a side of a board and another side of a board. The 55 plating process provides that there is an electrical connection between the circuit traces 310 on the daughter board and the plating within the holes 502. The board is then cut along the line denoted 503 so that the remaining board is left with recesses 401, each recess having metallic plating across the edge of the daughter board 301 and each plating area within each recess being electrically connected to the corresponding circuit trace 310, and where the regions 505 ot the edge of the daughter board between the said recesses has no conducting materia! such that each electrical path is appropriately isolated.

It may be advantageous to construct the daughter board initially as part of the main board, wherein an area of a larger board is defined as being used for the main board and an area defined for use as the daughter board. In this situation, it is possible to place the matching components on the daughter board before any cutting process is performed in order to separate the daughter board 302 from the main board 301 and form the plated recesses 10 401.

Figure 6 shows a further representation of the stages in the fabrication of the daughter board which pertain to the formation of the recesses 401 in a convenient mariner using conventional manufacturing processes. It may be that due to the requirements for the 15 size of the daughter board and the limitations of the manufacturing process or for other reasons that the holes provided in the formation of the recesses 504 are too large to be able to be separately formed in the circuit board; and that their circumferences 'will overlap if the recesses are to align correctly with the circuit traces 310 on the daughter board. In this case the cutting line 603 for the starting size 601 of the daughter board may be positioned so that 20 the recesses 504 are still formed with insulating regions 505.

Figure 7 shows a yet further representation of the stages in the fabrication of the daughter board in a convenient manner using conventional manufacturing processes. In order to provide additional rigidity to the complete assembly of the SOSA 101 with the 25 daughter board 302 and the main board 301 it may be advantageous to provide lugs 701 on the daughter board 302, to locate in suitably positioned holes in the main board 301. These lugs may have metallic plating in order to be able to provide a solder joint between said lugs and corresponding regions on the main board. Alternatively, a fixing agent may be used to attach the lugs to the main board.

As an alternative to or addition to the use of lugs 701 to provide mechanical rigidity, an insulating fixing agent may be used at the joint between the daughter board 302 and the main board 301 where there are insulating regions 505 on the daughter board and suitable corresponding regions on the main board.

in the examples shown in Figures 4 to 7 the holes are circular and the recesses are arcs of the circular holes. However it would be appreciated that the holes may be any suitable shape and the formed recesses a portion of the periphery of the shape. Additionally the holes may be formed by any suitable process such as drilling, punching etc.

Figure 8 shows a plan view of a circuit board used in an exemplar process for fabricating both the main and daughter board in a manner referred to with reference to figure

5. A piece of unprocessed circuit board 801 is patterned to provide the conducting electrical traces, interconnections, component locations and vias as required by both the circuits to be 45 implemented on both the main board area 802 and the daughter board area 803. Cutting lines are defined for the trajectory of a router in order to cut the boards as desired. The main board area can be cut away using a router following the line denoted 804. The daughter board area can be cut to shape along the line denoted 805. It may be convenient to retain small areas of board 806 intact to facilitate handling in the assembly point which may be 50 snapped off to release the daughter circuit boEtrd in its final form.

Figure 9 shows an exemplar method for the assembly of components according to some embodiments of the invention. It will be understood that many variations of this method and other different methods are possible to achieve the objectives of the invention.

Thus there is a first operation of fabricating one or more (for example a multiple of) instances of both the main circuit board and the daughter circuit board on a rectangular panel as shown in figure 9 by step 901.

Then the holes are drilled or formed by other convenient means to provide electrical connection between layers of conducting traces and also to form the holes that will become the plated recesses as shown in figure 9 by step 902.

Then the holes formed to provide electrical connection between layers of conducting traces and also io form the holes that will become the recesses are plated with a conducting metal layer as shown in figure 9 by step 903.

Then the boards are cut using a router or other convenient tool leaving snapping points for final separation as shown in figure 9 by step 904.

Then the electronic components are mounted on the main board and the daughter board as shown in figure 9 by step 905.

Then the outline of the daughter board is cut along lines that will intersect the holes provided for the formation of the plated recesses and the daughter board is snapped away from the redundant materia! as shown in figure 9 by step 906

Then the daughter board is attached to the main board with the plated recesses aligned over the corresponding conducting metal signal traces on the main board as shown in figure 9 by step 907.

Then the joints between the daughter board and the main board are soldered at the .5 plated recesses and any other desired locations using any convenient manufacturing process as shown in figure 9 by step 908.

Whilst this invention has been described with reference to particular examples and possible embodiments thereof, these should not be interpreted as restricting the scope of the 0 invention in any way. It is to be made clear that many other possible embodiments, modifications and improvements may be incorporated into or with the invention without departing from the scope and spirit of the invention as set out in the claims.

1!

Claims

What is claimed is:

5 1. An assembly of electronic components providing means for the transmission and reception of data using an optical fibre wherein said assembly comprises:

a bi-directionai optical sub-assembly, the bi-directional optical sub-assembly comprising:

a laser configured to generate a suitable optical output for the transmission of 10 data;

a photodiode and associated electronic circuitry configured to receive a suitable optical input and provide signals associated with the reception of data;

a first circuit board, a first side of the bi-directional optical sub-assembly being physically mounted on the first circuit board wherein connections from the first side of the Dili directional optical sub-assembly are coupled to the photodiode and associated electronic circuitry, and on the first circuit board are located:

laser driver circuitry configured to drive the laser; and amplification and processing circuitry configured to receive the signals associated with the reception of data, and wherein the first circuit board comprises at 20 least one receive path electrical connection to couple the photodiode and associated electronic circuitry to the amplification and processing circuitry;

a second circuit board, the second circuit board being physically mounted on the first circuit board and a second side of the bi-directional optical sub-assembly is physically mounted on a first side of the second circuit board, wherein connections from the second side 25 of the bi-directional optical sub-assembly are coupled to the laser, the second circuit board further comprises at least one electrical connection configured to couple the laser driver circuitry on the first circuit board to the laser of the bi-directional optical sub-assembly, wherein the at least one electrical connection on the second circuit board is coupled to the at least one electrical connection on the first circuit board via at least one area of conductive 30 material on the second circuit board and physically located on an opposite side to the first side of the second circuit board is at least one component coupled to the at least one electrical connection and configured to provide impedance modification or matching between the laser driver circuitry on the first circuit board and the laser of the bi-directional optical subassembly.
2. The assembly as claimed in claim 1. wherein the second circuit board comprises at least one mechanical lug configured to slot into at least one slot within the first circuit board.
3. The assembly as claimed in claim 2, where the second circuit board is affixed to the 40 first circuit board by a fixing agent.
4. The assembly as claimed in claim 3, wherein the fixing agent is solder.
5. The assembly as claimed in any of claims 1 to 4, wherein the at least one electrical

5 connection on the second circuit board is coupled to the at least one electrical connection on the first circuit board via at least one solder joint.
6. The assembly as claimed in any of claims 1 to 5, wherein the at least one area of conductive material on the second circuit board comprises at. least one conductive edge

10 region configured to couple the at least one electrical connection of the second circuit board to the at least one electrical connection of the first circuit board when the second circuit board is physically mounted on the first circuit board.
7. The assembly as claimed in claim 6, wherein the at least one conductive edge region 15 comprises at least a part of a through-plated-via.
8. The assembly as claimed in any of claims 1 to 7, wherein the second circuit board comprises electrical connections configured to couple the laser of the bi-directional optical sub-assembly to the at least one component configured to provide impedance modification or

20 matching such that the path distance is approximately a thickness of the second circuit board.
9. A method for providing an assembly of electronic components providing means for the transmission and reception of data using an optical fibre wherein said method comprises:

providing a bi-directional optical sub-assembly, the bi-directional optical sub25 assembly comprising: a laser configured to generate a suitable optical output for the transmission of data; a photodiode and associated electronic circuitry configured to receive a suitable optical input and provide signals associated with the reception of data;

providing a first circuit board:

physically mounting a first side of the bi-directional optical sub-assembly on the first 30 circuit board, the first side of the bi-directional optica! sub-assembly comprising connections which couple to the photodiode and associated electronic circuitry configured to receive a suitable optical input:

locating on the first circuit board laser driver circuitry configured to drive the laser; locating on the first circuit board amplification and processing circuitry configured to

35 receive the signa's associated with the reception of data;

coupling, using at least one receive path electrical connection, the photodiode and associated electronic circuitry to the amplification and processing circuitry;

providing a second circuit board:

physically mounting the second circuit board on the first circuit board;

physically mounting a second side of the bi-directional optical sub-assembly on a first side of the second circuit board, the second side of the bi-directional optical sub-assembly comprising connections which couple to the laser;

coupling, using at least one area of conductive material on the second circuit board

5 and at least one electrical connection on the second circuit board the laser driver circuitry on the first circuit board to the laser of the bi-directional optical sub-assembly; and physically locating, on an opposite side to the first side of the second circuit board, at least one impedance modification or matching component coupled to the at least one electrical connection and configured to provide impedance modification or matching between 0 the laser driver circuitry on the first circuit board to the laser of the bi-directional optica! subassembly.
10. The method as claimed in claim 9, wherein providing the second circuit board comprises providing at least one mechanical lug on the second circuit board, the at least one

5 mechanical lug configured to slot into at least one slot within the first circuit board.
11. The method as claimed in claim 10, further comprising affixing the second circuit board to the first circuit board by a fixing agent.

’0
12. The method as claimed in claim 11, wherein affixing the second circuit board to the first circuit board comprises soldering the second circuit board to the first circuit board.
13. The method as claimed in any of claims 9 to 12, wherein coupling, using the at least one area of conductive material on the second circuit board and the at least one electrical ’5 connection, the laser driver circuitry on the first circuit board to the laser of the bi-directional optical sub-assembly mounted on the second circuit board comprises forming at ieast one solder joint coupling the first circuit board to the second circuit board.
14. The method as claimed in any of claims 9 ίο 13, further comprising forming on the »0 second circuit board at least one conductive edge region, the at least one conductive edge region coupling the at least one electrical connection on the second circuit board to the at ieast one electrical connection on the first circuit board when the second circuit board is physically mounted on the first circuit board.
15. The method as claimed in claim 14, wherein the at least one conductive edge region comprises at ieast a part of a through-plated-via.
16. The method as claimed in any of claims 9 to 15, further comprising coupling the laser of the bi-directional optical sub-assembly mounted on the second circuit board to the at least one component configured to provide impedance modification or matching such that a distance between the laser of the bi-directional optical sub-assembly and the at least one component is approximately a thickness of the second circuit board.

5
17. A method for manufacturing an assembly of electronic components providing means for the transmission and reception of data using an optical fibre wherein said method comprises:

manufacturing a first circuit board, wherein on the first circuit board are located at least one receive path electrical connection:

IO physically mounting a first side of a bi-directional optical sub-assembly on the first circuit board, the bi-directional optical sub-assembly comprising: a laser configured to generate a suitable optical output for the transmission of data; a photodiode and associated electronic circuitry configured to receive a suitable optical input and provide signals associated with the reception of data and the first side of the bi-directional optical sub15 assembly comprising at least one connection which couples to the photodiode and associated electronic circuitry configured to receive a suitable optical input;

physically locating on the first circuit board laser driver circuitry configured to drive the laser:

physically locating on the first circuit board amplification and processing circuitry

20 configured to receive the signals from the bi-directional optical assembly associated with the reception of data;

coupling via the at least one receive path eiectrical connection, the photodiode and associated electronic circuitry to the amplification and processing circuitrymanufacturing a second circuit board, wherein on the second circuit board are

25 located at least one area of conductive material and at least one electrical connection; physically mounting the second circuit board on the first circuit board;

physically mounting a second side of the bi-directional optical sub-assembly on a first side of the second circuit board, the second side of the bi-directional optical sub-assembly comprising at least one connection which couples to the laser;

30 coupling, using at least the at least one area of conductive material and the at least one electrical connection on the second circuit board, and at least one electrical connection on the first circuit board the laser driver circuitry on the first circuit board to the laser of the bidirectional optical sub-assembly: and physically locating, on an opposite side to the first side of the second circuit board, at

35 least one impedance modification or matching component coupled to the at least one area of conductive material and configured to provide impedance modification or matching between the laser driver circuitry on the first circuit board and the laser of the bi-directional optical subassembly.
18. The method as claimed in claim 17, wherein coupling, using the at least one area of conductive material on the second circuit board, the laser driver circuitry on the first circuit board to the laser of the bi-directional optical sub-assembly, said coupling comprising forming a solder joint between the at least one area of conductive material of the second circuit board and the at least one area of conductive material of the first circuit board.
19. The method as claimed in any of claims 17 or 18, wherein manufacturing a second circuit board, wherein on the second circuit board is located at least one area of conductive material comprising plating at least one edge region of the second circuit board, wherein the at least one edge region plating couples the at least one area of conductive material on the first circuit board and the at least one electrical connection on the second circuit board.
20. The method as claimed in any of claims 17 to 19, wherein manufacturing a second circuit board, wherein on the second circuit board is located at least one area of conductive material comprising creating at least one electrical connection configured to couple the laser to the at least one component mounted on the second side of the second circuit board when the bi-directional optical sub-assembly is physically located on the first side of the second circuit board;

creating at least one though-plated hole electrically connected to at least one component mounted on the second side of the second board at an edge of the said second board, cutting the at least one through-plated-via to expose the through plating and create the at least one area of conductive material on an edge of the second circuit board configured to couple the at least one impedance modification or matching component to the first circuit board when the second circuit board is physically mounted on the first circuit board.
21. The method as claimed in any of claims 17 to 20, wherein manufacturing a second circuit board comprises creating an electrical connection to couple the first side and the opposite side of the second circuit board, wherein the electrical connection couples the bidirectional optical sub-assembly on a first side of the second circuit board and the at least one impedance modification or matching component such that the distance between the bidirectional optical sub-assembly and the at least one impedance modification or matching component is substantially the thickness of the second circuit board.
22. The method as claimed in any of claims 17 to 21, wherein manufacturing a first circuit board comprises creating receive path electrical connections configured to couple the photodiode and associated electronic circuitry to the amplification and processing circuitry when the first side of the bi-directional optical sub-assembly is physically located on the first circuit board.
23. The method as claimed in any of claims 17 to 22, wherein manufacturing a first circuit board and manufacturing a second circuit board comprises:

manufacturing a single circuit board:

patterning the single circuit board with the receive path electrical connections:

5 populating the single circuit board with the laser driver circuitry configured to drive the laser, the first circuit board amplification and precessing circuitry, and the at least one impedance modification or matching component;

separating the single circuit board into the first circuit board and the second circuit board.
24. The method as claimed in any of claims 17 to 23, wherein physically mounting the second circuit board on the first circuit board comprises:

slotting at least one mechanical lug on the second circuit board into at least one slot within the first circuit board; and

15 affixing the second circuit board to the first circuit board by a fixing agent.
25. The method as claimed in claim 24, wherein affixing the second circuit board to the first circuit board comprises soldering the second circuit board to the first circuit board.

Intellectual

Property

Office

Application No: GB1917589.2