Abstract:
The present invention relates generally to laser/detector packages, and particularly to laser/detector packages with components that increase the accuracy and ease of laser diode positioning. In particular, the laser/detector package of the present invention includes an attachment plate having a reference surface; a header post that is perpendicular to the reference surface when attached to the reference surface; sub-mount that houses a laser diode and abuts the reference surface or a spacer, which abuts the reference surface. By abutting the reference surface or the spacer, the laser diode attached to the sub-mount is easily and precisely positioned a proper distance from the reference surface. Additionally, preferred embodiments of the invention include a marking on the sub-mount that is parallel to the reference surface and a marking that is perpendicular to the reference surface on the spacer or sub-mount. These markings further improve the ease and accuracy of positioning and repositioning the laser diode and/or sub-mount.

Description:
This application claim the benefit of Provisional Application No. 60/275,402 filed Mar. 13, 2001. 
    
    
     The present invention relates generally to laser/detector packages, and particularly to laser/detector packages with components that increase the accuracy of positioning components of a laser/detector package. 
     BACKGROUND OF THE INVENTION 
     A prior art laser/detector package is illustrated in FIG.  1 . Laser diode  7  and sensitive photo diode  9  (“SPD”) are attached to circular attachment plate  1 . In particular, laser diode  7  is attached to sub-mount  8 , which is attached to header post  6 . Also included is cap  4 , which has laser light transparent window  5  and is attached to circular attachment plate  1 . Attached to cap  4  is window  5 . Header post  6 , which functions as a heat sink, is provided on the portion of circular attachment plate  1  covered by cap  4 . Semiconductor laser chip  7  is coupled to cathode terminal  2  and anode terminal  12  and SPD  9  is coupled to anode terminal  3 . Typically, wires  11  connect semiconductor laser chip  7  to cathode terminal  2  and SPD chip  9  to anode terminal  3 . 
     A drawback of prior art laser/detector packages includes the positioning of laser diode  7  on sub-mount  8 . In these systems, the sub-mount is positioned by reference to the top of header post  6 . However, header posts  6  are not manufactured with enough accuracy to reliably ensure that laser diode  7 , which is mounted on sub-mount  8 , is a proper distance from circular attachment plate  1 . 
     Additionally, a reflow sub-process included in various stages of the manufacturing process often causes laser diode  7  and sub-mount  8  to move from their initial position. The reflow sub-process includes placing a laser/detector package in a furnace to reflow solder used to bind laser diode  7  to sub-mount  8  and sub-mount  8  to header plate  6 . 
     When laser diode  7  and sub-mount  8  move from their initial position during the reflow sub-process, the laser/detector package is discarded because there is no accurate way to reposition these components. 
     SUMMARY OF THE INVENTION 
     There is needed in the art therefore a system and method for manufacturing laser/detector packages that enables a more accurate manufacturing process. In particular, a system and method by which precise positioning of laser/detector package components is possible, movement of laser/detector package components during a reflow sub-process is minimized, and laser/detector package components that do move during a reflow sub-process may be accurately repositioned. 
     One embodiment of the invention is a laser/detector package comprising an attachment plate having a reference surface; a header post that is perpendicular to the reference surface; a spacer that abuts the reference surface when attached to the header post; a sub-mount that abuts the spacer when attached to the header post; and a laser diode attached to the sub-mount. 
     Additionally, preferred embodiments of the invention include on the spacer a marking that is perpendicular to the reference surface. This marking permits a more precise and easier positioning and repositioning of the sub-mount and laser diode. A line that is an inherent part of the laser diode and also perpendicular to the reference surface is aligned with the marking. 
     Further, preferred embodiments of the invention include on the sub-mount a marking that is parallel to the reference surface when the sub-mount is attached to header post. When positioning the laser diode on the sub-mount, the laser diode is positioned such that it abuts the marking on the sub-mount. 
     In another embodiment of the invention, the laser/detector package comprises an attachment plate having a reference surface; a header post that is perpendicular to the reference surface; a sub-mount that abuts the reference surface when attached to the header post; and a laser diode attached to the sub-mount. Instead of including a separate spacer as in the above described embodiment, the size of the sub-mount is increased so that the laser diode is a proper distance from the reference surface when the sub-mount abuts the reference surface. 
     Further, preferred embodiments of the invention include on the sub-mount a marking that is parallel to the reference surface and a marking that is perpendicular to the reference surface when the sub-mount is attached to header post. The laser diode is positioned on the sub-mount such that an edge of the laser diode abuts the marking parallel to the reference surface and a line on the laser diode aligns with the marking perpendicular to the reference surface. 
     Another aspect of the invention includes a method of assembling a laser/detector package that comprises attaching a spacer to the header post so that the spacer abuts the reference surface of the attachment plate; attaching a laser diode to the sub-mount so that the laser diode emits laser beams in a direction parallel to the sub-mount; and attaching the sub-mount to the header post so that the sub-mount abuts the spacer. 
     Additionally, preferred embodiments of the invention include a) marking the spacer so that the spacer includes a mark that is perpendicular to the reference surface and b) positioning the laser diode with reference to the mark. 
     Further, preferred embodiments of the invention include marking the sub-mount so that the sub-mount includes a mark that is parallel to the reference surface. When positioning the laser diode on the sub-mount, this mark serves as a guideline to ensure that the laser diode is a precise distance from the circular attachment plate. 
     Another method of assembling a laser/detector package comprises attaching a laser diode to the sub-mount so that the laser diode emits laser beams in a direction parallel to the front surface of the sub-mount and attaching the sub-mount to the header post so that the sub-mount abuts the reference surface of the attachment plate. 
     Further, preferred embodiments of the invention include marking the sub-mount so that the sub-mount includes a mark that is parallel to the reference surface and a mark that is perpendicular to the reference surface. When positioning the laser diode on the sub-mount, these marks serve as guidelines to ensure precise positioning of the laser diode. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Additional objects and features of the invention will be more readily apparent from the following detailed description and appended claims when taken in conjunction with the drawings, in which: 
     FIG. 1 is a perspective view showing a prior art laser/detector package partially broken away. 
     FIG. 2 is a perspective view showing a laser/detector package, which is partially broken away, according to an embodiment of the present invention. 
     FIG. 3 illustrates various components of a variation of the embodiment of the present invention illustrated in FIG.  2 . 
     FIG. 4 illustrates steps used in a preferred embodiment of the invention to construct a laser/detector package. 
     FIG. 5 is a perspective view showing a laser/detector package, which is partially broken away, according to another embodiment of the present invention. 
     FIG. 6 illustrates steps used in a preferred embodiment of the invention to construct a laser/detector package. 
     FIG. 7 illustrates various components of a variation of the embodiment of the present invention illustrated in FIG.  5 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A laser/detector package manufactured in accordance with an embodiment of the present invention is illustrated in FIG.  2 . Laser diode  7  and sensitive photo diode  9  (“SPD”) are attached to circular attachment plate  1 . Laser diode  7  emits laser beams in two directions. One beam is emitted from laser diode  7  directly to SPD  9 , which captures the beam for analysis. In particular, this be am provides information about the second laser beam, which is emitted from laser diode  7  in the opposite direction of the first beam. In other words, in a direction away from SPD  9  that is roughly perpendicular to circular attachment plate  1 . 
     Also included in FIG. 2 is cap  4 , which has laser light transparent window  5  and is attached to circular attachment plate  1 . Attached to cap  4  is window  5 . Header post  6  is provided on the portion of circular attachment plate  1  covered by cap  4 . Semiconductor laser chip  7  is connected to cathode terminal  2  and anode terminal  12  and SPD  9  is connected to anode terminal  3  by wires  11 . Additionally, wires  11  also connect SPD chip  9  to anode terminal  3 . 
     Also included in FIG. 2 is spacer  200 . Spacer  200  is attached to header post  6  by silver epoxy. Spacer  200  ensures that sub-mount  8  is a precise distance from reference surface  330  of circular attachment plate  1 , which is the flat surface to which cap  4  is attached as illustrated in FIG.  2 . 
     More specifically, laser diode  7  is attached to sub-mount  8 , which is soldered to header post  6 . Header post  6  functions as a heat sink for laser diode  7 . Sub-mount  8  comprises silicon, so sub-mount  8  electrically isolates laser diode  7  from header post  6 , but does not prevent header post  6  from absorbing heat from laser diode  7 . 
     In preferred embodiments, sub-mount  8  is marked before attaching laser diode  7  to sub-mount  8  as illustrated in FIG.  3 . Mark  300  is positioned a precise distance from the edge of sub-mount  8  that abuts spacer  200  (distance Y of FIG.  3 ). After attaching sub-mount  8  to header post  6 , mark  300  is parallel with reference surface  330  of circular attachment plate  1 . An edge of laser diode  7  is positioned along mark  300  when attaching laser diode  7  to sub-mount  8 . By controlling the size of the spacer  200  and the distance of mark  300  from the edge of sub-mount  8 , the distance of laser diode  7  from reference surface  330  of circular attachment plate  1  (distance Z of FIG. 3) is precisely controlled without using header post  6  as a positioning reference. 
     Mark  300  also permits accurate repositioning of laser diode  7  after subjecting the laser/detector package to a reflow sub-process during a stage of the manufacturing process. Without mark  300 , accurate repositioning of laser diode  7  is not feasible because there would be no reliable guideline by which to reposition laser diode  7 . 
     Mark  300  is preferably a metal pattern created by a photolithography process. Briefly, photolithography involves imprinting a pattern on silicon that is coated with a photoresist mask containing the pattern and spinning ultraviolet light through the mask. However, mark  300  can be created using other means without departing from the scope of the present invention. In a preferred embodiment, mark  300  indicates the position of the front facet of laser diode  7 . In an alternative embodiment, mark  300  can indicate the position of the back facet of laser diode  7 . 
     As noted above, the reflow sub-process can also cause sub-mount  8  to move from its initial position, but spacer  200  minimizes movement of sub-mount  8  and the silver epoxy prevents movement of spacer  200 . Again, sub-mount  8  is attached to header post  6  so that it abuts spacer  200 , which abuts reference surface  330  of circular attachment plate  1 . 
     In preferred embodiments, spacer  200  is marked as illustrated in FIG.  3 . Partial cut  310  is usually positioned along the axis of spacer  200  that is perpendicular to circular attachment plate  1 . Laser diode line  320 , which is also illustrated in FIG. 3, is aligned with partial cut  310  in order to precisely position laser diode  7  and sub-mount  8  (to which laser diode  7  is attached). 
     Partial cut  310 , which is preferably created by a dicing saw, also permits repositioning of laser diode  7  and/or sub-mount  8  after subjecting the laser/detector package to a reflow sub-process during a stage of the manufacturing process. Without partial cut  310 , accurate repositioning of laser diode  7  and/or sub-mount  8  is not feasible because there would be no reliable guideline by which to position laser diode  7  and/or sub-mount  8 . 
     Laser diode line  320  is an inherent feature in laser diodes suitable for use in the present invention. In terms of horizontal positioning with reference to circular attachment plate  1 , it is laser diode line  320  that is critical rather than the edges of laser diode  7 . The reason is that the laser beams emitted by laser diode  7  emanate from the area of laser diode line  320 . 
     A method for manufacturing a laser/detector package that is consistent with the embodiment illustrated in FIG.  2  and that includes marking sub-mount  8  and spacer  200  is illustrated in FIG.  4 . The process begins with creating spacer  200  with a precisely measured height (step  400 ). This may be accomplished using a dicing saw. 
     Next, spacer  200  is marked with a vertical line to create partial cut  310  (step  405 ). As described above, partial cut  310  is preferably created with a dicing saw. Partial cut  310  permits precise positioning of laser diode  7  and/or sub-mount  8 . In alternative embodiments, a vertical line may be made on spacer  200  using other techniques such as photolithography or using a cutting tool other than a dicing saw. 
     The marked spacer  200  is then attached to header post  6  using a silver epoxy (step  410 ). 
     Additionally, sub-mount  8  is marked (step  420 ) to create mark  300 . As described above, mark  300  is preferably created by photolithography. The distance of mark  300  from the edge of sub-mount  8  that abuts spacer  200  (distance Y of FIG. 3) is dictated by the size of spacer  200  and the precise distance that the front facet of laser diode  7  must be from reference surface  330  of circular attachment plate  1  (distance Z of FIG.  3 ). Again, mark  300  permits precise positioning of laser diode  7  on sub-mount  8 . Importantly, mark  300  is not affected by the reflow process described above. Similarly, the size and shape of spacer  200  and sub-mount  8  are not affected by the reflow process. Accordingly, mark  300  and partial cut  310  remain viable means for repositioning sub-mount  8  and laser diode  7  after a reflow process. 
     After sub-mount  8  is marked, laser diode  7  is positioned on sub-mount  8  so that laser diode  7  abuts mark  300 . Thus, a plane of laser diode  7  is parallel with mark  300 , spacer  200 , and reference surface  330  of circular attachment plate  1 . 
     More specifically, solder paste is applied to sub-mount  8  and then laser diode  7  is positioned on sub-mount  8  using placement equipment (e.g., pick-and-place machines, chip shooters, etc.). The laser/detector package is then subjected to a reflow sub-process, which includes heating the laser/detector package until the solder paste is liquidus. The laser/detector package is then cooled until the solder hardens and creates a permanent connection between laser diode  7  and sub-mount  8 . Before the solder cools however, laser diode  7  is repositioned as needed by reference to mark  300 —thus completing step  430 . 
     Sub-mount  8  is then positioned on header post  6  by reference to partial cut  310 . Specifically, sub-mount  8  is positioned on header post  6  so that laser diode line  320  is aligned with partial cut  310 . Additionally, sub-mount  8  is positioned on header post  6  so that the bottom surface of sub-mount  8 , the surface facing reference surface  330  of circular attachment plate  1 , abuts the top surface of spacer  200 . Further, the laser/detector package is subjected to another reflow sub-process, as described above in detail. As with laser diode  7 , sub-mount  8  is repositioned as necessary after the reflow process—thus completing step  440 . 
     Laser diode  7  need not be repositioned after the reflow sub-process in step  440  because the solder (e.g., gold and tin solder) used to attach laser diode  7  to sub-mount  8  has a higher melting temperature than the solder (e.g., lead and tin solder) used to attach sub-mount  8  to header post  6 . 
     A laser/detector package manufactured in accordance with another embodiment of the present invention is illustrated in FIG.  5 . Laser diode  7  and sensitive photo diode  9  (“SPD”) are attached to circular attachment plate  1 . Laser diode  7  emits a laser beam towards SPD  9  and away from SPD  9  in a direction roughly perpendicular to circular attachment plate  1 . 
     Also included in FIG. 5 is cap  4 , which has laser light transparent window  5  and is attached to circular attachment plate  1 . Attached to cap  4  is window  5 . Header post  6  is provided on the portion of circular attachment plate  1  covered by cap  4 . Semiconductor laser chip  7  is connected to cathode terminal  2  and anode terminal  12  and SPD  9  is connected to anode terminal  3  by wires  11 . Additionally, wires  11  also connect SPD chip  9  to anode terminal  3 . 
     More specifically, laser diode  7  is attached to enlarged sub-mount  500 , which is soldered to header post  6 . Header post  6  functions as a heat sink for laser diode  7 . Sub-mount  500  comprises silicon, so sub-mount  500  electrically isolates laser diode  7  from header post  6 , but does not prevent header post  6  from absorbing heat from laser diode  7 . 
     Additionally, sub-mount  500  is sized to precisely position laser diode  7  a predetermined distance from reference surface  330  of circular attachment plate  1 , with a bottom surface of sub-mount  500  abutting reference surface  330  of circular attachment plate  1 . FIG. 7 better illustrates a sub-mount  500  consistent with this embodiment of the invention. 
     In preferred embodiments, sub-mount  500  is marked before attaching laser diode  7  to sub-mount  500  as illustrated in FIG.  7 . Mark  300  is positioned a precise distance from the edge of sub-mount  500  (distance Z in FIG. 7) that abuts reference surface  330  of circular attachment plate  1 . After attaching sub-mount  500  to header post  6 , mark  300  is parallel with reference surface  330  of circular attachment plate  1 . The front facet edge of laser diode  7  is positioned along mark  300 . Thus, by controlling the distance of mark  300  from the edge of sub-mount  500  that abuts circular attachment plate  1 , the distance of the front facet of laser diode  7  from reference surface  330  of circular attachment plate  1  is precisely controlled without relying on header post  6  as a positioning reference. In alternative embodiments, a vertical line may be made on sub-mount  500  using other techniques such as photolithography or using a cutting tool other than a dicing saw. 
     Mark  300  also permits repositioning of laser diode  7  after subjecting the laser/detector package to a reflow sub-process during the manufacturing process. Without mark  300 , accurate repositioning of laser diode  7  is not feasible because there is no reliable guideline by which to reposition laser diode  7 . The mark is preferably created by a photolithography process as described above. 
     As noted above, the reflow sub-process can also cause sub-mount  500  to move from its initial position, but abutting sub-mount  500  against reference surface  330  of circular attachment plate  1  minimizes movement of sub-mount  500 . 
     In preferred embodiments, sub-mount  500  is also partially cut to create partial cut  310  as illustrated in FIG.  7 . Partial cut  310  is usually positioned along the axis of sub-mount  500  that is perpendicular to circular attachment plate  1 . Laser diode line  320 , which is also illustrated in FIG. 7, is aligned with partial cut  310  in order to precisely position laser diode  7  on sub-mount  500 . 
     Partial cut  310 , which is preferably created by a dicing saw, also permits repositioning of laser diode  7  after subjecting the laser/detector package to a reflow sub-process during a stage of the manufacturing process. 
     As noted above, laser diode line  320  is an inherent feature in laser diodes suitable for use in the present invention. 
     A method for manufacturing a laser/detector package that is consistent with the embodiment illustrated in FIG.  5  and that includes marking sub-mount  500  is illustrated in FIG.  6 . The claimed process begins making partial cut  310  with a dicing saw on sub-mount  500  and creating mark  300  on sub-mount  500  with a photolithography process (step  600 ). Again, partial cut  310  and mark  300  permit precise positioning of laser diode  7  on sub-mount  500 . 
     After sub-mount  500  is marked, laser diode  7  is positioned on sub-mount  500  so that laser diode  7  abuts mark  300  and laser diode line  320  aligns with partial cut  310 . 
     More specifically, solder paste is applied to sub-mount  500  and then laser diode  7  is positioned on sub-mount  500  using placement equipment (e.g., pick-and-place machines, chip shooters, etc.). The laser/detector package is then subjected to a reflow sub-process, which includes heating the laser/detector package until the solder paste is liquidus. The laser/detector package is then cooled until the solder hardens and creates a permanent connection between laser diode  7  and sub-mount  500 . Before the solder cools however, laser diode  7  is repositioned as needed by reference to mark  300  and partial cut  310 —thus completing step  610 . 
     Sub-mount  500  is then positioned on header post  6 . Specifically, sub-mount  500  is positioned on header post  6  so that the bottom surface of sub-mount  500  abuts reference surface  330  of circular attachment plate  1 . Additionally, the laser/detector package is subjected to another reflow sub-process, as described above in detail—thus completing step  620 . 
     Laser diode  7  need not be repositioned after the reflow sub-process in step  620  because the solder used to attach laser diode  7  to sub-mount  500  has a higher melting temperature than the solder used to attach sub-mount  500  to header post  6 .