Abstract:
A mount for a semiconductor device, the mount comprising: an insulating substrate having first and second parallel face surfaces, an edge surface that connects the parallel surfaces and having formed therein a recess having an opening on the first face surface; an electrically conductive plug seated in the recess and having a first exposed surface on or near the edge surface and a second exposed surface on or near the first face surface.

Description:
RELATED APPLICATIONS 
       [0001]    The present application claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Application 61/376,281 filed on Aug. 24, 2010, the disclosure of which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    Embodiments of the invention relate to methods and device for supporting a semiconductor light source and providing electrical connections to the light source. 
       BACKGROUND 
       [0003]    Semiconductor light sources, such as light emitting diodes (LEDs) and laser diodes (LDs) are used to provide illumination, optical radar and signaling in optical communication networks. They are used to transduce electrical signals to optical signals that carry information via optical fibers in the physical infrastructures of the various local and global communications networks to support the rich menu of voice, video, text, and data services that is the backbone of modern society and its activities. 
         [0004]    The amount of information transferred over the communication networks is growing at a staggering rate. A white paper published in 2008 by Cisco Systems Inc. entitled “Approaching the Zettabyte Era” predicted that global IP traffic will increase from about 10 exabytes per month in 2008 to over 40 exabytes per month in 2012. The rapid increase in global communication traffic has generated a need for communications equipment that can not only support the increased traffic rates with greater optical signaling rates, but can provide the support in ever smaller physical packaging. 
         [0005]    As optical signaling rates provided by communication equipment increase and size of the equipment shrinks, the LEDs and LDs, hereinafter generically referred to as LDs, that generate optical communication signals are required to operate at ever higher frequencies and to be packaged in ever increasing spatial densities. The increasing operating frequencies and packaging densities results in continually increasing severity of constraints to be met by mounts that physically support the LDs. The mounts are advantageously configured to provide the LDs with appropriate electrical connections to circuits that drive and control them in an increasingly crowded component environment, to dissipate increasing amounts of heat they generate during operation, and to provide for convenient alignment of the LDs with optical fibers that receive optical signal they generate. Commercial constraints generally require that the mounts, conventionally referred to as “sub-mounts”, also be relatively easy to produce in large quantities and to be relatively inexpensive. 
       SUMMARY 
       [0006]    An aspect of an embodiment of the invention relates to providing a semiconductor light source mount, hereinafter referred to as a “smart mount”, comprising a substrate having two parallel face surfaces, an edge surface connecting and optionally perpendicular, to the face surfaces and an electrically conductive contact plug secured in a recess of the substrate. The contact plug has a first surface exposed on, or near, one of the face surfaces, and a second surface, hereinafter a “mounting surface”, exposed on the edge surface to which an LD to be supported by the smart mount can be mounted and electrically connected. The LD may be mounted to the contact plug mounting surface using any of various materials and techniques, such as bonding with a conductive epoxy or soldering with a suitable solder alloy. Not only does the contact plug provide convenient support and electrical connectivity for an LD mounted to the plug but the mass of the plug conducting material also functions as an advantageous heat sink for heat generated by the LD during operation. In an embodiment of the invention the substrate is formed from a heat conducting ceramic, such as AlN (Aluminum Nitride) and the contact plug is formed form a metal such as Gold, Copper, Silver, or Aluminum or an alloy thereof. 
         [0007]    A smart mount, in accordance with an embodiment of the invention, is robust and relatively easy and inexpensive to produce. 
         [0008]    An aspect of an embodiment of the invention relates to providing a method of manufacturing a plurality of smart mounts. In an embodiment of the invention, a relatively large wafer of a substrate material having parallel face surfaces is processed to form an array of rows and columns of holes, hereinafter “contact plug holes”, that extend into and optionally through, the substrate wafer from a face surface of the wafer. A cross section of each of the contact plug holes parallel to the face surfaces is configured having two relatively large areas, referred to as “wing areas” connected by a relatively narrow neck. The holes are filled with a conductive material to form the contact plugs of the smart mounts. 
         [0009]    Following formation of the contact plugs the substrate wafer is diced to provide the smart mounts. Dicing is done by cutting the substrate wafer along lines, referred to as “row cutting lines”, parallel to the rows of holes and along cutting lines, referred to as “column cutting lines”, parallel to and between columns of holes. A row cutting line may pass substantially through the necks but not through the wing areas of the cross sections of contact plug holes in a row of contact plug holes, through only one of the wing areas of each of the contact plug holes in the row, or between rows of contact plug holes. Row cutting lines that pass through contact plug holes are referred to as “contact plug cutting” lines or “plug cutting lines”. Row cutting lines that pass between rows of contact plug holes and column cutting lines are also referred to as die partition lines. Cutting the substrate wafer along the row contact plug cutting lines creates the exposed mounting surfaces of the smart mount contact plugs. Each smart mount conductive contact plug is held securely in place in its plug hole by the narrowing of the hole in the region of the neck, which operates to grip and lock the contact plug in place. 
         [0010]    In the discussion, unless otherwise stated, adjectives such as “substantially” and “about” modifying a condition or relationship characteristic of a feature or features of an embodiment of the invention, are understood to mean that the condition or characteristic is defined to within tolerances that are acceptable for operation of the embodiment for an application for which it is intended. 
         [0011]    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 to limit the scope of the claimed subject matter. 
     
    
     
       BRIEF DESCRIPTION OF FIGURES 
         [0012]    Non-limiting examples of embodiments of the invention are described below with reference to figures attached hereto that are listed following this paragraph. Identical structures, elements or parts that appear in more than one figure are generally labeled with a same numeral in all the figures in which they appear. Dimensions of components and features shown in the figures are chosen for convenience and clarity of presentation and are not necessarily shown to scale. 
           [0013]      FIG. 1A  schematically shows a wafer formed from a substrate material suitable for forming smart mounts and having contact plug holes formed therein in accordance with an embodiment of the invention; 
           [0014]      FIG. 1B  schematically shows the substrate wafer shown in  FIG. 1A  with the contact plug holes filled with a conductive material in accordance with an embodiment of the invention; 
           [0015]      FIG. 2A  schematically shows the substrate wafer having filled contact plug holes shown in  FIG. 1B  after the substrate wafer has been diced, in accordance with an embodiment of the invention; 
           [0016]      FIG. 2B  schematically shows an LD mounted to a contact plug of a single smart mount formed by dicing the substrate wafer shown in  FIG. 2A , in accordance with an embodiment of the invention; 
           [0017]      FIG. 3A  schematically shows a substrate wafer similar to the substrate wafer shown in  FIG. 1B , but having conducting tracks formed on a face surface of the substrate wafer, in accordance with an embodiment of the invention; 
           [0018]      FIG. 3B  schematically shows the substrate wafer shown in  FIG. 3A , after dicing, in accordance with an embodiment with an embodiment of the invention; 
           [0019]      FIG. 4A  schematically shows a smart mount resulting from dicing a substrate wafer having contact tracks, in accordance with an embodiment with an embodiment of the invention; 
           [0020]      FIG. 4B  schematically shows the smart mount shown in  FIG. 4A  mounted to a support pedestal, in accordance with an embodiment of the invention; 
           [0021]      FIG. 5A  schematically shows a substrate wafer formed having contact plug holes different from those shown in  FIG. 1A , in accordance with an embodiment of the invention; 
           [0022]      FIG. 5B  schematically shows a portion of the substrate wafer shown in  FIG. 4A  after it has been cut along a row cutting line, in accordance with an embodiment of the invention; and 
           [0023]      FIG. 6  schematically shows an alternative method for forming smart mounts in accordance with an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    In the following paragraphs of the detailed description, a description of a process for manufacturing a plurality of smart mounts in accordance with an embodiment of the invention is discussed with reference to  FIGS. 1A-2C . A method of forming smart mounts having conducting tracks formed in a lithography process is discussed with reference to  FIGS. 3A-3D . A variation of the method of manufacturing smart mounts schematically illustrated in  FIGS. 1A-2C  is shown in and discussed with reference to  FIGS. 4A and 4B .  FIG. 5  schematically shows another method of manufacturing smart mounts in accordance with an embodiment of the invention. 
         [0025]      FIG. 1A  schematically shows a substrate wafer  20  having top and bottom parallel face surfaces  21  and  22  for manufacturing smart mounts in accordance with an embodiment of the invention. Substrate wafer  20  is formed from an insulating material having a relatively high thermal conductivity, such as an insulating ceramic, and may, by way of example, have thickness in a range from about 0.5 mm to 5 mm and have a square perimeter having a side length of about 100 mm. In an embodiment of the invention substrate wafer  20  may be formed from AlN (Aluminum Nitride). AlN has a thermal conductivity that may range from about 70 W/m/K (Watts per meter per degree Kelvin) to about 210 W/m/K. 
         [0026]    In an embodiment of the invention substrate wafer  20  has formed therein rows  31  and columns  32  of optionally through holes  30 , also referred to as contact plug holes,  30 . To prevent clutter, only some of rows  31  and columns  32  are labeled with numerals. The rows of contact plug holes are optionally configured in pairs of closely spaced rows, with adjacent pairs of rows separated by relatively large distances. Similarly, the columns of contact plug holes are optionally configured in pairs of closely spaced columns, with adjacent pairs of columns separated by relatively large distances. An inset  34  shows an enlarged view of contact plug holes  30 . A cross section  36  parallel to face surface  21  of a contact plug hole  30  is shown in an inset  37 . Cross section  36  has two wing areas  38  connected by a relatively narrow neck  39  and optionally has a figure eight shape. 
         [0027]    Contact plug holes  30  may be formed by any of various methods known in the art such as laser cutting, etching, ablating, or drilling. Forming the holes by drilling may be accomplished by drilling circular holes at a pitch less than a diameter of the holes so that the holes overlap and share a common chord parallel to face surface  21  having length less than the circular hole diameter. Whereas relatively large overlapping holes may be formed in a substrate relatively easily, for example by mechanical drilling and/or laser ablation, a minimum diameter and pitch of the holes are generally determined by wafer thickness and constraints of a process used in forming the holes. For example, minimum diameter and pitch of holes formed by mechanical drilling of a wafer may be constrained to be no less than about 0.8 and about 1.5 times the wafer thickness respectively. 
         [0028]    After formation contact plug holes  30  are filled with a conducting material such as a metal, which may be Gold, Copper, Silver or Aluminum or an alloy thereof to form conducting contact plugs embedded in substrate wafer  20 . Contact plug holes  30 , if large enough or characterized by a small enough ratio (aspect ratio) of hole height to hole diameter, may for example be filled by pouring molten metal onto face surface  21  of substrate wafer  20  so that the metal flows into and fills the holes. Excess metal that remains on face surface  21  may be removed by a suitable etching, abrasion, and/or polishing process, such as a dry or a wet etching process or chemical-mechanical planarization. 
         [0029]      FIG. 1B  schematically shows substrate wafer  20  shown in  FIG. 1A  after having contact plug holes  30  filled with a conducting material to form contact plugs  40 . An inset  41  schematically shows an enlarged view of filled contact plug holes  30 .  FIG. 1B  also shows row cutting lines  51  and  53  and column cutting lines  52 , shown in dashed lines. Row cutting lines  51  are contact plug cutting lines and row cutting lines  53  are row die partition cutting lines. Substrate wafer  20  is diced to form smart mounts, in accordance with an embodiment of the invention, by cutting the substrate wafer along the cutting lines. 
         [0030]    Each contact plug cutting line  53  optionally lies between contact plug holes  30  in a pair of closely spaced rows of contact plugs  40 . In an embodiment of the invention, when substrate wafer  20  is cut along a contact plug cutting line  53 , an amount of material removed from the wafer and each contact plug  40  along the cutting line is sufficient to form an exposed surface of the plug that lies on a surface of the substrate material formed by the cut. The exposed surface is configured to have dimensions so that it may function as a mounting surface of the contact plug to which, by way of example, an LD may be mounted to physically support the LD and provide it with electrical connections to a driving circuit. Neck region  39  of the contact plug hole in which the contact plug is formed is displaced from the mounting surface and functions to prevent the contact plug from separating from the substrate material after substrate wafer is cut. 
         [0031]    By way of numerical example, assuming that contact plug holes  30  are formed in wafer  20  having thickness equal to about 0.5 mm by drilling overlapping circular holes having a diameter equal to about 0.4 mm in the wafer, contact plug mounting surfaces may have a width in a direction parallel to contact plug cutting lines  51  equal to about 0.2 mm. And neck region  39  of the plug may be displaced about 0.1 mm from the mounting surface. 
         [0032]    A portion of substrate wafer  20  after the substrate wafer is diced is shown in  FIG. 2A . The figure shows individual smart mounts  60  resulting from the dicing and features of the smart mounts, in accordance with an embodiment of the invention. Mounting surfaces of contact plugs  40  formed during the dicing process and comprised in each smart mount  60  are labeled with a numeral  62 . Contact plug mounting surfaces  62  are exposed on edge surfaces  64  of the smart mounts that are formed when substrate wafer  20  is cut along plug cutting lines  51  ( FIG. 1B ). 
         [0033]    Portions of top and bottom surfaces  21  and  22  of substrate wafer  20  ( FIG. 1A ) that are comprised in a smart mount  60  are referred to as top and bottom surfaces  66  and  67  respectively of the smart mount shown in  FIG. 2B . In the perspective of  FIG. 2A  bottom surfaces  67  of smart mounts  60  are not shown. Bottom surface  67  is indicated in  FIG. 2B . A surface  70 , also referred to as a contact pad  70 , of a contact plug  40  comprised in each smart mount  60  is exposed on top surface  66 . Optionally, contact pad  70  has a mirror image contact pad on bottom surface  67 . 
         [0034]    In an embodiment of the invention, following forming, referred to as “singulation”, of individual smart mounts  60  by dicing wafer  20 , contact plugs  40  are plated with a metal or metal alloy to prepare surfaces of the plugs for electrical bonding to an LD or other electrical component or circuit. Optionally, the plugs are plated using any of various plating methods known in the art, with tin or nickel, which metals are often used to facilitate various reflow and/or wire bonding procedures. Plating may be performed by an electroless plating process. 
         [0035]      FIG. 2B  schematically shows an LD  80  mounted to mounting surface  64  of a first contact plug  40  in smart mount  60 . LD  80  may be mounted and electrically connected to the mounting surface using a conductive adhesive or epoxy to bond a cathode (not shown) of the LD to the mounting surface. A bond wire  82  may be used to connect an anode (not shown) of the LD to a second contact plug  40  in smart mount  60 . 
         [0036]    Smart mount  60 , and its LD  80 , may relatively easily be mounted to a printed circuit board (PCB, not shown) comprising or providing electrical connection to circuitry (not shown) for powering and controlling LD  80 . Electrically connecting the circuitry to contact pads  70  connects the circuitry to the LD. Optionally LD  80  is connected to the circuitry by surface mounting the smart mount to the PCB contact pads on bottom surface  67  that are mirror images of contact pads  70  so that the minor image contact pads make electrical contact with power traces on the PCB. 
         [0037]      FIG. 3A  schematically shows a substrate wafer  120 , similar to wafer  20  shown in  FIGS. 1A and 1B  that has been processed to form, in addition to an array of rows  131  and columns  132  of contact plugs  140 , conductive tracks  150 , in accordance with an embodiment of the invention. Each conductive track  150  makes electrical contact with each of two contact plugs  140  in a same column  132  of contact plugs. 
         [0038]    Wafer  120  is diced by cutting along cutting lines  151 ,  152  and  153  to produce smart mounts  160  schematically shown in  FIG. 3B . An inset  155  shows an enlarged image of a portion of diced wafer  120 . Conductive tracks  150  may be formed by any of various lithography processes. The tracks provide convenient to use electrical contacts for electrically connecting a smart mount  160  to circuitry that may be used to power and/or control an LD mounted to the smart mount. 
         [0039]    It is noted that whereas  FIGS. 3A and 3B  show contact tracks on a top surface  121  of wafer  120 , in an embodiment of the invention, a wafer may be provided with contact tracks on both a top and bottom face surface so that electrical contact to resultant smart mounts may be made on both top and bottom surface of the smart mounts. It is also noted that whereas  FIGS. 1A-3B  show smart mounts having only two contact plugs, a smart mount in accordance with an embodiment of the invention is not limited to smart mounts having only two contact plugs.  FIG. 4A  schematically shows a smart mount  200  in accordance with an embodiment of the invention comprising three contact plugs  202  and associated contact tracks  204 . 
         [0040]    Nor are smart mounts in accordance with an embodiment of the invention limited to having contact plugs only along a same edge of the smart mount. For example, if wafers  20  and  120  are not cut along row cutting lines  53  and  153  in a dicing process of the wafers, smart mounts in accordance with an embodiment of the invention will have contact plugs on two opposite edges. 
         [0041]    A smart mount in accordance with an embodiment of the invention may also be mounted on a pedestal to adjust height of the smart mount and an LD mounted to the smart mount to position the LD relative to optical and/or electrical components with which it is used and/or to provide the LD with a large heat sink. For example, if an LD is to be coupled to an optic fiber at a given fixed position a smart mount to which it is mounted may be required to be supported by a suitable pedestal to register position of the LD with an input aperture of the fiber.  FIG. 4B  schematically shows smart mount  200  supported by a pedestal  206  in accordance with an embodiment of the invention. 
         [0042]    Practice of the invention is of course not limited to contact plug holes having a shape of plug holes  30  shown in  FIG. 1A . Plug holes may have any shape suitable for locking contact plugs, which are formed by filling holes in a substrate wafer with a conductive material to the wafer. 
         [0043]    For example,  FIG. 5A  schematically shows a portion of a wafer  300  having plug holes  302  having an “hourglass” shape cross section, in accordance with an embodiment of the invention. Dashed lines  310  and  312  indicate a plug cutting line and column cutting lines respectively in the portion of the wafer shown in the figure. It is noted that unlike plug cutting lines  53  ( FIG. 1B) and 153  ( FIG. 3A ) which pass between plug holes in their associated wafers, plug cutting line  310  passes through a narrow neck  304  of hourglass plug holes  302 . 
         [0044]      FIG. 5B  schematically shows wafer  300  after contact plug holes  302  have been filled with a conducting material and the wafer has been cut along plug cutting line  310  in a dicing process. Cutting wafer  300  along the plug cutting line forms contact plugs  320  having a trapezoidal cross section. Dicing of wafer  300  and singulation of smart mounts from the wafer is optionally completed by cutting the wafer along cutting lines  312 . Were it desired to have a smart mount having, by way of example, ten contact plugs  320 , cutting along cutting lines  312  shown in  FIG. 5B  may be foregone. 
         [0045]    It is noted that smart mounts in accordance with an embodiment of the invention may be manufactured by methods that are different from, or that are variations of, the methods described above. For example,  FIG. 6  schematically shows a laser system  400  generating a laser beam  402  to cut contact plug “slots”  420  along an edge  422  of an, optionally ceramic, substrate “bar”  430 . After cutting the slots, the substrate bar is held in a mold (not shown) with the slots at the top. A molten conductive metal or alloy is poured into the mold to cover and fill the slots and form contact plugs. After cooling, the substrate bar is removed and excess metal milled or abraded away to remove excess metal form edge  422  and planarize mounting surfaces of the contact plugs. By way of another example, rather than pour a molten metal or metal alloy into plug holes, such as plug holes  30  ( FIG. 1A ) or plug holes  302  ( FIG. 5A ) preformed contact plugs may be press fit into plug holes. 
         [0046]    In the description and claims of the present application, each of the verbs, “comprise” “include” and “have”, and conjugates thereof, are used to indicate that the object or objects of the verb are not necessarily a complete listing of components, elements or parts of the subject or subjects of the verb. 
         [0047]    Descriptions of embodiments of the invention in the present application are provided by way of example and are not intended to limit the scope of the invention. The described embodiments comprise different features, not all of which are required in all embodiments of the invention. Some embodiments utilize only some of the features or possible combinations of the features. Variations of embodiments of the invention that are described, and embodiments of the invention comprising different combinations of features noted in the described embodiments, will occur to persons of the art. The scope of the invention is limited only by the claims.