WO2017005704A1

WO2017005704A1 - An optoelectronic device

Info

Publication number: WO2017005704A1
Application number: PCT/EP2016/065743
Authority: WO
Inventors: Patrick Doyle; John D. LAMBKIN; Michael O'gorman; Thomas Moriarty
Original assignee: Firecomms Limited
Priority date: 2015-07-08
Filing date: 2016-07-04
Publication date: 2017-01-12

Abstract

An optoelectronic device (30) has a lead frame (31) and a circuit board (34) on the lead frame. A moulded body (32) forms a lens (33) over an optoelectronic component (39). The component is placed on the lead frame (31) within an aperture (37) of the circuit board. The aperture may include a conductor on the inward-facing surface to contribute to screening of the optoelectronic component, and there may additionally be wires (51) over the aperture to contribute to screening. By virtue of being within an aperture the optoelectronic component may be physically further from the lens (33) surface, there is additional space for conductors, and there may be additional electromagnetic interference screening.

Description

"An Optoelectronic Device"

Introduction Field of the Invention

The invention relates to optoelectronic devices. Prior Art Discussion

It is known to build optoelectronic devices by mounting an optoelectronic component, such as a photodiode or LED, on a metal lead frame and to encapsulate the component and part of the metal frame in an over moulded transparent material, such as a thermoset epoxy. This moulded body may include a lens formed in the moulding process, and aligned with the component, so as to guide the light coming from or going to the component. The metal leads protruding from the body serve to provide electrical connections to the device and any other electronic components that may also be mounted on the metal frame.

This is illustrated in Fig 1, in which an optoelectronic device 10 is made with a metal lead frame 11 and a transparent moulded body 12 incorporating a moulded lens 13. Mounted on the lead frame is an optoelectronic component 14 and there may be one or more other electronic components, such as an integrated circuit 15. Wires 16 serve to connect the optoelectronic component and the other electronic components, if present, to one another or to elements of the metal lead frame. In some cases electronic components are electrically connected to the lead frame on which they are mounted by conductive glue, solder or other such means. This style of construction limits the complexity of the circuit that can be incorporated.

An additional disadvantage is that the optoelectronic component and the wires connecting it are exposed to surrounding electromagnetic fields. In the case of optoelectronic devices designed to receive optical signals, this is a particular disadvantage, as the optoelectronic component produces a very feeble electronic signal in response to a pulse of light: the optoelectronic component is usually connected to an amplifying element, either within the optoelectronic device or external to it, to amplify this feeble signal. If the optoelectronic component and the wires connecting it pick up electronic signals from an electromagnetic field, these signals will be amplified along with the intended signal, and may interfere with it. In the case of optoelectronic devices designed to transmit optical signals, the lack of shielding may not cause a problem to the device itself. However, such devices typically work by having pulses of current pass through the optoelectronic element at high frequency, and this can cause electromagnetic radiation to be emitted, potentially causing problems to other nearby equipment if it is not effectively shielded.

To build more complex devices it is known, for example in US Patent number 8,175,462, to mount the components on a printed circuit board which is fixed to a metal lead frame. The entire printed circuit board with the components on it, and part of the lead frame, are over moulded with transparent material to form a body, with a lens formed in the moulded material as before.

An advantage of using a printed circuit board is that more components may be included, and / or more complex circuits may be constructed, as the individual conducting tracks on the printed circuit may be many times smaller than the smallest practical dimensions for the elements of the metal lead frame. However, a disadvantage of this construction is that the thickness of the printed circuit board moves the opto-electronic component further towards the front of the device: this can reduce the effectiveness of the lens, as the distance between the lens and the component is reduced. Also it can give rise to difficulties with the wire or wires used to make electrical connection to the optoelectronic component, as there is not much space for these wires and they may be damaged in the moulding process or may have to be formed with tight curves which impose strains and may reduce the reliability of the connection. Whereas signals travelling in the circuit board may be shielded from EMC fields by techniques such as multi-level layers of conductors, the optoelectronic element and the wires connecting to its top surface are still exposed to electromagnetic fields and may receive or transmit interference as before.

Summary of the Invention

According to the invention, there is provided an optoelectronic device comprising:

a lead frame supporting a circuit board having one or more electronic components, a moulded body including a lens, and

one or more optoelectronic components aligned with the lens,

wherein at least one optoelectronic component is mounted directly on the lead frame. In one embodiment, the circuit board has an aperture, and said optoelectronic component is within said aperture.

In one embodiment, the device further comprises a conductive coating on the board adjacent the optoelectronic component.

In one embodiment, the circuit board has an aperture, the optoelectronic component is on the lead frame within said aperture, and the aperture has a conductive coating. In one embodiment, the circuit board has at least one aperture which is shaped so that the optoelectronic component may be guided into a correct location on the lead frame as it is inserted through the aperture.

In one embodiment, the device includes one or more wires, such that:

(a) each wire is connected to two conductors on the circuit board, which conductors are electrically connected to each other by means other than said wire, and (b) each wire passes over the circuit board aperture to provide electromagnetic screening of the optoelectronic component within the aperture. In one embodiment, the device further comprises electrical links between said optoelectronic component and a conductor and/or a component on the circuit board.

In one embodiment, the device comprises electrical connections between a component on the board, the optoelectronic component on the lead frame, and the lead frame, to form a circuit to which external electrical connections may be made through the lead frame.

In one embodiment, the device further comprises at least one integrated circuit mounted on the circuit board with at least one conductive pad on the integrated circuit electrically connected to at least one conductive pad on the circuit board by wire bonding.

In one embodiment, the device further comprises at least one integrated circuit mounted on the circuit board with at least one conductive pad on the integrated circuit electrically connected to at least one conductive pad on the circuit board by solder or flip chip conductors. In one embodiment, the device further comprises at least one integrated circuit mounted on the circuit board with at least one conductive pad on the integrated circuit electrically connected to at least one conductive pad on the circuit board by conductive epoxy. In one embodiment, the moulded body encapsulates the board.

In one embodiment, the moulded body forms an optical element such as a lens.

Additional Statements

According to the invention, there is provided an optoelectronic device comprising a lead frame supporting a circuit board, a moulded body, and one or more optoelectronic components, wherein at least one optoelectronic component is mounted directly on the lead frame.

In one embodiment, the circuit board has an aperture, and said optoelectronic component is within said aperture.

In one embodiment, the device further comprises electrical links between said optoelectronic component on the lead frame and a conductor and/or component on the circuit board.

In one embodiment, the device comprises electrical connections between a component on the board, the component on the lead frame, and the lead frame, to form a circuit to which external electrical connections may be made through the lead frame.

In one embodiment, the device comprises at least one integrated circuit mounted on the circuit board with at least one conductive pad on the integrated circuit electrically connected to at least one conductive pad on the circuit board by wire bonding. In one embodiment, the device comprises at least one integrated circuit mounted on the circuit board with at least one conductive pad on the integrated circuit electrically connected to at least one conductive pad on the circuit board by solder or similar "flip chip" technology

In one embodiment, the device comprises at least one integrated circuit mounted on the circuit board with at least one conductive pad on the integrated circuit electrically connected to at least one conductive pad on the circuit board by conductive epoxy. In one embodiment, the device comprises a conductive coating on the board adjacent the optoelectronic component. In one embodiment, the circuit board has an aperture, the optoelectronic component on the lead frame is within said aperture, and the aperture has a conductive coating.

In one embodiment, the board has at least one aperture which is arranged to be larger than the optoelectronic component on the lead frame so that the optoelectronic component may be guided into a correct location on the lead frame as it is inserted through the aperture.

In one embodiment, the device comprises one or more wires, such that:

(c) each wire is connected to two points on the circuit board, which points are electrically connected to each other by means other than said wire, and

(d) each wire passes over the hole containing the optoelectronic element.

In one embodiment, the moulded body encapsulates the board.

In one embodiment, the moulded body forms an optical element such as a lens.

DETAILED DESCRIPTION OF THE INVENTION

Brief Description of the Drawings The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings in which :-

Fig. 1 is a diagram representative of prior art, as described above;

Fig. 2 is a diagrammatic front view and a side cross-sectional view of a device of the invention; Fig. 3 is a set of front, side cross-sectional and rear views of a device of another embodiment, having a shield around an optical element;

Fig. 4 is a similar set of views of a further device, having a Faraday Cage; and

Fig. 5 is a set of a cross-sectional front and side views of a device of a further embodiment.

Description of the Embodiments

A device of the invention has an optical component, a lead frame, and a circuit board. There is a hole or aperture in the circuit board such that the optical component may be mounted directly on the lead frame within the aperture. The terms "optical component" and "optoelectronic component" are interchangeable as this component either receives and/or transmits light and has electrical conductivity and possibly also electronic signal processing. It may for example be an integrated circuit with integrated photodetector.

In one embodiment of the invention, one or more electronic and possibly also optical, components are mounted on the circuit board, which has conductive tracks on the circuit board to form a circuit. This is illustrated in Fig 2, in which an optical device 30 is made with a metal lead frame 31 and a transparent moulded body 32 incorporating a moulded lens 33.

Mounted on the lead frame 31 is a circuit board 34 on which one or more electronic components are mounted, such as an integrated circuit 35. The circuit board 34 has conductive tracks including a track 36 to complete a circuit with the electronic components. The circuit board has metal plated apertures (not shown), to connect the circuit to the metal leads of the lead frame 31 and so permit external electrical connections.

Within the circuit board 34 there is an aperture 37 and at least one of the elements 38 of the metal lead frame is formed to be accessible through this aperture. An optoelectronic component 39 is mounted on the lead frame element 38, and a bond wire 40 connects the optoelectronic component 39 to the circuit board 34. It will be appreciated that the optical component 39 is further away from the lens (33) than is the situation in the prior art. This allows more versatility in the optical characteristics, especially in choice of lens radius for desired optical properties. Also, because the optical component 39 is directly mounted to, and electrically connected to, the lead frame 31 (at the lead frame element 38) there is less risk of EMI interference adversely affecting the signal from the optical component 39. As can be seen in the diagram, the highest point of the bond wire 40 is comfortably clear of the surface of the transparent moulded body 32: If the optical component 39 were mounted on the printed circuit board, the highest point of the wire would be very near the surface and, with the normal variations of manufacturing tolerances it might become exposed or damaged during the moulding process.

In another embodiment of the invention, at least part of the inner surface of the aperture is metal or other conducting material, so as to additionally provide an electromagnetic shield around the optoelectronic element. It is preferred to connect this electromagnetic shield to one of the elements of the metal lead frame, and so arrange for the shield to be connected to the signal ground.

Referring to Fig 3 a device 40 comprises a metal lead frame 41 and a transparent moulded body 42 incorporating a moulded lens 43. For reference, the four parts of the lead frame 41 have been labelled "AN", "N/C", "CA" and "GND". Mounted on the lead frame 41 is a circuit board 44, in which there are two apertures, 45 and 46. Both circuit board apertures are coated with metal 47 on their inner (radially- inward facing) surfaces, and the conductor 47 extends along the top planar surface of the board 44. On the back of the circuit board there is a smaller conductive area 48, only part of which can be seen. The conductive area 48 is also electrically connected to the conductor 47 and hence to the inner surface of aperture 46. The purpose of the small aperture, 46, is to connect this small conductive area on the back of the printed circuit board to the larger conductive area on the front; the purpose of the aperture 45 is to allow the optoelectronic component to be mounted on the lead frame. This conductive area is fixed to the lead frame element identified as "GND", so that the inner surfaces of both apertures are electrically connected to this element. An optoelectronic component 49 is fixed on the element of the lead frame labelled "CA" using conductive epoxy, so that the cathode of the optoelectronic element is electrically connected to this lead frame element. Wire 50 serves to connect the anode of the optoelectronic component to the lead frame element labelled "AN". Optionally, the conductive screen may be continued on part at least of the surface of the circuit board, and wires may be added to loop over an aperture, so providing a complete Faraday Cage around the optoelectronic component. This is illustrated in Fig 4, in which all of the elements of Fig 3 remain in place and additional wires 51 are shown bridging the larger aperture 45. In one example the wires 51 have a diameter of 25 μιη, while the aperture 45 will be in the order of 1000 μιη in diameter, so the shadow of the wires will not be a significant problem.

It will be appreciated that the manner in which the optical component is mounted provides the above-mentioned advantages and additionally the screening advantages of this embodiment. These additional benefits are achieved with little additional complexity or parts.

In another embodiment, the use of electronic components attached to the circuit board, and shielding may be further combined. The circuit board has:

a conductive surface on the circuit board inside of the aperture surrounding the optoelectronic component,

one or more electronic components mounted on the circuit board,

conductive tracks on the board, and

wires which together form the electrical connections between the electronic components, the optoelectronic component and elements of the lead frame and additional wires which s form a Faraday Cage around the optoelectronic component and some of the other components connected to it.

This is illustrated in Fig 5, in which an optical component 60 is made with a metal lead frame 61 and a transparent moulded body 62. Mounted on the lead frame is a circuit board 63 on which one or more electronic components are mounted, such as an integrated circuit 65. The circuit board has conductive tracks including a track 66 to complete a circuit with the electronic component(s). It also has a conductive track 67 surrounding the aperture 64, and being an integral part of the conductor of the aperture 64. Provision is also made, for example by metal plated apertures through the circuit board (not shown), to connect the circuit to the metal leads, and so permit external electrical connections. At least one of the elements of the metal lead frame is formed to be accessible through the aperture 64 and on this lead frame element an optoelectronic component 68 has been mounted. A wire 69 connects this optoelectronic component to the circuit board. Additional wires 70 bridge the space over the aperture, being connected at each end to the conductive track 67. In this embodiment the feeble electronic signals from the optoelectronic component are protected from interference within the Faraday cage formed by the aperture 64 and the wires 70. Immediately the signals emerge from the Faraday cage on wire 69 they are connected to the printed circuit board, where they may be protected by a ground plane technique until they enter the integrated circuit. Within the integrated circuit the signals are amplified to a level much stronger than the interference signals, so that interference is no longer a problem.

Whereas the diagrams show integrated circuits with discrete leads, it may be advantageous to use an integrated circuit with conductive pads for making connections. These may be connected to the appropriate points on the circuit board or on other components by wire bonding, or the integrated circuit may be inverted, so that the conductive pads on it are connected directly to conductive pads on the circuit board by solder bumps or other "flip chip" technology.

It will be appreciated that, in the manufacture of this type of device, it is important to ensure alignment between the lens and the optoelectronic component. To achieve this, it may be appropriate to form the aperture in the printed circuit board so that it is only just larger than the optoelectronic component, and so forms a guide to ensure the component is correctly placed.

The invention is not limited to the embodiments described but may be varied in construction and detail. For example, it is envisaged that the optical component is mounted directly on the lead frame outside of the circuit board. In the illustrated embodiments the lens is near the centre of the transparent moulded body, however it could be placed nearer to the edge such as near the top.

Also, it is envisaged that the optoelectronic component mounted on the lead frame may be an integrated circuit incorporating a photodiode, providing a photodiode with an attached amplifier circuit. In such an embodiment there may or may not be another integrated circuit on the printed circuit board, and/or other electronic components, such as resistors or capacitors, on the board.

Claims

1. An optoelectronic device comprising:

a lead frame (31) supporting a circuit board (34) having one or more electronic components (35),

a moulded body (32) including a lens (33), and

one or more optoelectronic components (39) aligned with the lens,

wherein at least one optoelectronic component is mounted directly on the lead frame

(31).

2. An optoelectronic device as claimed in claim 1, wherein the circuit board has an aperture (37), and said optoelectronic component (39) is within said aperture.

3. An optoelectronic device as claimed in claims 1 or 2, further comprising a conductive coating (47, 67) on the board adjacent the optoelectronic component (49).

4. An optoelectronic device as claimed in claim 3, wherein the circuit board has an aperture (37, 45), the optoelectronic component (39, 49) is on the lead frame within said aperture, and the aperture has a conductive coating (47, 67).

5. An optoelectronic device as claimed in any of claims 2 to 4, wherein the circuit board has at least one aperture which is shaped so that the optoelectronic component may be guided into a correct location on the lead frame as it is inserted through the aperture.

6. An optoelectronic device as claimed in any of claims 2 to 5, including one or more wires, such that:

(a) each wire (51, 70) is connected to two conductors on the circuit board, which conductors are electrically connected to each other by means other than said wire, and

(b) each wire (51, 70) passes over the circuit board aperture (45) to provide electromagnetic screening of the optoelectronic component (49) within the aperture.

7. An optoelectronic device as claimed in any preceding claim, further comprising electrical links between said optoelectronic component (39, 49) and a conductor and/or a component (35) on the circuit board (34).

An optoelectronic device as claimed in claim , wherein the device comprises electrical connections between a component (35) on the board, the optoelectronic component (39) on the lead frame, and the lead frame (31), to form a circuit to which external electrical connections may be made through the lead frame.

An optoelectronic device as claimed in any preceding claim, further comprising at least one integrated circuit (35) mounted on the circuit board (34) with at least one conductive pad on the integrated circuit electrically connected to at least one conductive pad on the circuit board by wire bonding (40).

An optoelectronic device as claimed in any preceding claim, further comprising at least one integrated circuit mounted on the circuit board with at least one conductive pad on the integrated circuit electrically connected to at least one conductive pad on the circuit board by solder (66) or flip chip conductors. 11. An optoelectronic device as claimed in any preceding claim, comprising at least one integrated circuit (65) mounted on the circuit board (63) with at least one conductive pad on the integrated circuit electrically connected to at least one conductive pad on the circuit board by conductive epoxy. 12. An optoelectronic device as claimed in any preceding claim, wherein the moulded body encapsulates the board.

An optoelectronic device as claimed in any preceding claim, wherein the moulded body forms an optical element such as a lens.