Patent Application
20170215305
Head mounted display devices used for example in augmented reality environments often use a depth sensor for sensing distances to objects within the field of view of a head mounted display device. Such depth sensors often employ one or more laser diode assemblies and associated electronic components mounted on a printed circuit board for emitting laser light. Emitted light bounces of objects and is reflected back in the depth sensor, to indicate distances to the objects, for example using time of flight between light emission and receipt of reflected light.
The laser diode assemblies and associated electronic components in such devices emit electromagnetic interference (EMI), which must be shielded in order to comply with FCC regulations. One difficulty in providing EMI shielding in depth sensors such as used on head mounted display devices is that the shielding must not cover the aperture(s) through which the laser light is emitted. A further difficulty is that shielding applied over the laser diode assembly cannot be surface mounted to the printed circuit board, as the heat required for such surface mounting may damage the laser diode assembly. Another difficulty in providing shielding for depth sensors used for example in head mounted display devices is that space is at a premium, and conventional EMI shields tend to be bulky.
Embodiments of the present technology relate to an EMI shield and method of its manufacture. Embodiments of the EMI shield may be used in a light emitting optical device having a compact design, such as for example a depth sensor used in a head mounted display device presenting an augmented reality environment. The EMI shield may have a dual-piece construction. A first piece, referred to herein as the fence, may be surface mounted to a printed circuit board to cover electronic components that may also be surface mounted to the printed circuit board. The fence includes one or more openings to allow top-down connection of a light emitter such as a laser diode onto the printed circuit board. The one or more openings also allow light to leave the light emitter without obstruction.
After connection of the light emitter, a second piece of the EMI shield, referred to herein as the cover, may be affixed to the fence over portions of the light emitter and electronic components to shield EMI from the light emitter and components. The light emitter may be sensitive to high temperatures. Thus, the cover may be affixed to the fence by methods other than surface mounting which use high temperatures for solder reflow, such as for example using an adhesive. The shield is provided to allow light to leave the light emitter without obstruction.
This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
Embodiments of the present technology will now be described with reference to the figures, which in general relate to an EMI shield used to prevent electromagnetic radiation from an electronic device such as a compact, light-emitting optical device. Embodiments of the EMI shield may comprise two pieces: a fence and a cover. The fence may be surface mounted to a printed circuit board to cover electronic components also surface mounted to the printed circuit board. The fence may include one or more openings which provide top-down access to the printed circuit board for mounting of additional electronic components. The cover may be affixed to the fence after mounting of the additional electronic components, for example by an adhesive.
In embodiments explained below, the EMI shield may be used in association with a laser diode assembly of a depth sensor for a head mounted display device presenting an augmented reality environment. In such embodiments, optical driver circuitry may be surface mounted to a printed circuit board. Thereafter, a laser diode may be connected to the printed circuit board. As the laser diode assembly is heat sensitive, surface mounting an EMI shield to the printed circuit board after mounting the laser diode may damage the laser diode. Thus, in accordance with aspects of the present technology, the EMI shield may be assembled in a two-step process. The fence may be surface mounted over the driver circuitry after surface mounting of the driver circuitry. The opening(s) in the fence provide access to the printed circuit board to allow for gluing and wire bonding of the laser diode. Thereafter, EMI cover may be affixed to the fence using an adhesive to shield the laser diode while preventing damage to the laser diode.
The fence and cover are configured to block EMI from the driver circuitry and laser diode, while allowing emission of light from the laser diode unimpeded. Additionally, the fence may be surface mounted in the same process as the surface mounting of the driver circuitry.
In one example, the EMI shield according to the present technology may be used in a depth sensor of a head mounted display device for presenting an augmented reality experience.
As shown in
The head mounted display device may further include a room facing camera 112 which may be or include a depth sensor, as explained in greater detail below. Additional components of the head mounted display device used to generate an augmented reality experience but not directly related to the EMI shield of the present technology are omitted. However, such additional components are described for example in U.S. Patent Publication No. 2013/0326364 entitled “Position Relative Hologram Interactions,” published on Dec. 5, 2013.
In an example embodiment, the depth sensor 120 may be configured to capture a depth image of an area in the field of view of the sensor 120. The depth image may include a two-dimensional (2-D) pixel array of the captured area where each pixel in the 2-D pixel array may represent a distance of an object in the captured area from the depth sensor 120. The depth image may capture depth values of the area via any suitable technique including, for example, time-of-flight, structured light, stereo image, or the like. According to one embodiment, the depth sensor 120 may organize the calculated depth information into “Z layers,” or layers that may be perpendicular to a Z axis extending from the depth sensor along its line of sight.
The light emitters 130 and driver circuitry 134 emit electromagnetic radiation which can interfere with the operation of other electronics in the vicinity. Therefore, in accordance with aspects of the present technology, each edge portion 128 may include an EMI shield 140 (shown shaded in
In general, a first set of electronic components may be surface mounted to the PCB 124 using heat, while a second set of electronic components such as the light emitters 130 are heat sensitive and are mounted using an adhesive after the first set of components. The EMI shield 140 may be affixed in two parts—one part being surface mounted using heat before the heat-sensitive components are affixed, and a second part being affixed using adhesive after the heat-sensitive components are affixed. In this way, the overall EMI shield 140 shields electromagnetic radiation from the first and second sets of electronic components without impeding the mounting or functionality of the heat-sensitive components.
In step 200, a first set of electronic components are surface mounted to electrical contacts of the PCB 124, using a heat-bonding material such as for example solder. The solder may be reflowed in a heating process in step 202. The first set of electronic components are those which are able to withstand surface mounting in the heating process and include for example the driver circuitry 134, one electronic component of which is marked in
In step 206, a first part of the EMI shield 140—fence 150—may be surface mounted to contact pads or other metal portions of the PCB 124, as shown in
The fence 150 is shown in
It is understood that the fence 150 may have a wide variety of other configurations in further embodiments. In general the fence may have a shape so that it covers at least some of the surface mounted, electromagnetic radiating components from the first set of electronic components, while having one or more openings or spaces to allow top-down mounting of the components from the second set of components on the PCB 124.
The configuration of the PCB 124 for receiving the first and second set of electronic components may vary greatly in different embodiments, and the configuration of the fence 150 may vary accordingly. In one such further embodiment, the widths of one or more of the portions 150a, 150b and/or 150c may vary to increase or decrease the size of one or both openings 152, 154. In another such further embodiment including a single light emitter 130 instead of the two shown in the figures, one of the openings 152, 154 may be omitted from the fence 150 altogether.
The fence 150 may have edges 156 which extend at an angle down from a major planar surface of the fence 150. It is the edges 156 (or portions of the edges 156) that may be surface mounted to contact pads on the PCB 124, for example by soldering. The height of the edges 156 (i.e., how far the edges 156 extend from a major planar surface of the fence 150) defines how high the fence extends above the surface of the PCB 124.
In one embodiment, a surface of the fence (150c,
Thus, the height of the EMI shield 140 above the PCB 124 is equal to the height of the surface 150c above the PCB 124, plus the thicknesses of the fence 150 and cover 160. As explained below, the cover may be a flat, planar plate. In embodiments, the fence 150 and cover 160 may each have thicknesses of between 100 to 150 μm, though one or both may be thicker or thinner than that in further examples. This provides an overall height of the EMI shield above the tallest component beneath the fence 150 of 200 μm to 450 μm, though the EMI shield 140 may be at a height which is greater or smaller than this in further embodiments. This provides an EMI shield 140 having a lower profile above the PCB 124 than is known in the prior art. Prior art EMI shields include mechanical clamps for mounting on the PCB, which mechanical clamps result in a profile above the PCB that is larger than 150 μm.
The fence 150 may be formed of a variety of materials that shield EMI, including by absorbing and/or reflecting EMI. In embodiments, the fence may for example be formed of Nickel plated Aluminum, Nickel plated Copper, or other conductive materials that do not oxidize or have a low rate of oxidation.
The first set of electronic components may be surface mounted in step 200 and reflowed in step 202, and then the fence 150 may be surface mounted over at least some of the first set of electronic components in step 206 and reflowed in step 208. In further embodiments, step 202 may be omitted so that the first set of electronic components may be surface mounted in step 200, the fence 150 may be surface mounted over at least some of the first set of electronic components in step 206, and then the solder mounting the first set of electronic components and the fence may be reflowed in step 208. In either event, use of the fence 150 according to embodiments of the present technology provides fabrication efficiencies, in that it may be mounted in the same process, or at least at the same processing stations, as the first set of surface mounted components.
In step 212, the second set of components may be mounted to the PCB 124. As noted above, in embodiments, the second set of components may be one or more electronic components that would be adversely affected during the surface mount and reflow process steps 200 and 202 described above. However, in further embodiments, there may be reasons unrelated to heat sensitivity for affixing the second set of components after the first set of components and fence have been mounted. For example, the second set of component may be affixed to the PCB 124 at a different location than the first set of components.
Additionally, it is conceivable that the second set of components, including for example light emitters 130, be glued to a sub-mount circuit board (not shown), which may in turn be surface mounted to the PCB 124 using heat. The sub-mount may be mounted to the PCB 124 in a second step, after the first set of components and fence are mounted on the PCB 124.
In one embodiment, the second set of components comprise one or more light emitters 130. The one or more light emitters 130 may be mounted to contact pads 142 in step 212 and as shown in
Thereafter, the adhesive bonding the light emitters may be cured in step 214. Additionally, at least certain light emitters 130, such as laser diodes, are wire bonded to the PCB 124. If the light emitters get wire bonded, they may be wire bonded in step 218. Again, the openings 152, 154 in the fence 150 allow the wire bonding capillary access to bond the light emitters to contact pads on the PCB 124. Where a light emitter 130 is wire bonded to the PCB 124, the light emitter 130 may be adhesively bonded to non-conductive portion on the PCB 124, and may be bonded using a non-conductive adhesive.
In step 220, a second part of the EMI shield 140—cover 160—may be mounted to the fence 150 as shown in
The cover 160 is shown with a rectangular shape in
In the embodiment shown in
As noted, given the heat sensitivity of a light emitter such as a laser diode, the electronic components of the depth sensor 120 may be assembled in a two-step process as described above. First, components are surface mounted to the PCB 124, then the light emitter may be glued to the PCB 124 using an epoxy or other adhesive. The present technology is compatible with such a two-step process in that the fence may be surface mounted to the PCB 124 with the first set of surface mounted components, and then the cover may be glued to the fence using an epoxy or other adhesive.
Additionally, the fence and cover of the present technology are compatible with an electronic, light emitting device where EMI shielding is required, without the EMI shield interfering or blocking the emitted light. The opening(s) left in the shield allow light from the light emitters to travel unimpeded from the depth sensor 120.
In embodiments, the EMI shield 140 including the fence and cover may having openings of about 1 mm, through which the light from the light emitters may radiate. At openings of these sizes, the EMI shield 140 may block EMI down to about 2 GHz. However, it is understood that the EMI shield 140 may have openings of other sizes and block EMI from about 50 MHz to 8 Ghz, though the range of frequencies blocked may be above or below this range in further embodiments.
Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims. It is intended that the scope of the invention be defined by the claims appended hereto.
