Abstract:
An electrode pattern for wire-bonding includes: a wire-bonding reference pattern indicating a reference position for determination of a wire-bonding position; and a wire-bonding recognition pattern. The distance between the reference position and a wire-bonding metal portion bonded to the electrode pattern and the distance between the wire-bonding recognition pattern and the wire-bonding metal portion satisfy predetermined relationships.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an electrode pattern for wire bonding to an electrode of a semiconductor device, a substrate, or the like and to a wire bonding method. 
   2. Background Art 
   For wire-bonding metal wires to electrodes, it is necessary to teach a bonding position to a bonding apparatus. When wire bonding is performed by using an Au ball, for example, usually a design is made so that each Au ball is within a wire-bonding electrode with sufficient margins. A technique for allowing a wire bonding apparatus to recognize a bonding position in a wire bonding process of manufacture of a semiconductor device is disclosed in JP-A-2001-326241. 
   A wire-bonding electrode pattern of a laser diode has a long and narrow shape. In recording laser diodes, whereas the optical output that is required for laser diodes increases as the recording speed increases, there is strong demand for price reduction. Some attempts have being made to meet these requirements. To attain a high output power, laser diodes are elongated in the longitudinal direction. To attain price reduction, laser diodes are shortened in the lateral direction so that the number of chips taken from one wafer is increased. For example, in high-output-power (350-mW-class) recording laser diode has very long and narrow shape which is more than 2,000 μm in the longitudinal direction and less than 150 μm in the lateral direction. 
   A high-output-power recording laser diode is mounted in a package in the following manner. A submount and a laser diode are bonded to an eyelet with AuSn solder or the like. The electrode of the laser diode is wire-bonded to a lead or the eyelet. To form an Au ball at a prescribed position on the electrode, a characteristic pattern of an electrode end portion is recognized and an Au ball is then bonded to the electrode at a position that is shifted from the characteristic pattern by a prescribed length. It is known that when the submount and the laser diode are bonded to the eyelet, the center line of the laser diode can be inclined from that of the eyelet by about 2° at the maximum due to the accuracy of an assembling apparatus. 
   SUMMARY OF THE INVENTION 
   If the center line of the laser diode is not inclined at all from that of the eyelet, an Au ball can be bonded to the electrode on its center line. However, there is a problem that an Au ball bulges out of the electrode when an inclination exists. When the electrode is long in the longitudinal direction and short in the shorter-axis direction (i.e., the electrode width is small), a large deviation occurs in the shorter-axis direction and the bulging length of an Au ball becomes large. The bulging length of an Au ball can be made small if it is formed in the vicinity of an electrode end portion. However, this leads to a problem that the density of current that can be supplied to the laser diode at a position that is distant from the Au ball is made different from that in the vicinity of the Au ball. In this case, the laser diode hardly operates normally. Therefore, it is necessary that an Au ball be formed near the center of the laser diode. This phenomenon is more remarkable in the case where an Au ball is formed on a long and narrow electrode pattern as in the case of high-output-power recording laser diodes. 
   An aspect of the present invention has been made in view of the above mentioned circumstances and provides an electrode pattern and a wire bonding method which make it possible to perform wire bonding with high accuracy. 
   An aspect of the present invention provides an electrode pattern for wire-bonding including: 
   a shorter sideline; 
   a longer sideline; 
   a wire-bonding reference pattern indicating a reference position for determination of a wire-bonding position; and 
   a wire-bonding recognition pattern, 
   wherein the following relationships are satisfied,
 
L 3 14.3(W−3d/4), and
 
Lb£14.3(W−3d/4),
 
   where 
   L indicates a distance between (i) the reference position and (ii) a line that is parallel with the shorter sideline of the electrode pattern and passes through a position where a wire-bonding metal portion bonded to the electrode pattern has a maximum width in a direction parallel with the shorter sideline of the electrode pattern, 
   Lb indicates a distance between (i) a line that passes through a center, in a direction parallel with the longer sideline of the electrode pattern, of the wire-bonding recognition pattern and is parallel with the shorter sideline of the electrode pattern and (ii) the line that is parallel with the shorter sideline of the electrode pattern and passes through the position where the wire-bonding metal portion has the maximum width in the direction parallel with the shorter sideline of the electrode pattern, 
   d indicates a maximum width of the wire-bonding metal portion bonded to the electrode pattern in the direction parallel with the shorter sideline of the electrode pattern, and 
   W indicates a width of the electrode pattern in the direction parallel with the shorter sideline of the electrode pattern. 
   According to the above configuration, it is possible to obtain a long and narrow electrode pattern which allows a wire-bonding wire to be bonded to the electrode pattern at an arbitrary position. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the present invention will be described in detail based on the following figures, wherein: 
       FIG. 1  is a schematic diagram of an electrode pattern according to a first embodiment of the present invention; 
       FIGS. 2A and 2B  are schematic diagrams of a semiconductor device using the electrode pattern according to the first embodiment; 
       FIG. 3  is a schematic diagram of an electrode pattern according to a second embodiment of the present invention; 
       FIG. 4  is a schematic diagram of another electrode pattern according to the second embodiment; and 
       FIGS. 5A ,  5 B and  5 C are schematic diagrams of further electrode patterns according to the second embodiment. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   First Embodiment 
     FIG. 1  is a schematic diagram of a wire-bonding electrode pattern according to a first embodiment of the present invention.  FIGS. 2A and 2B  are schematic diagrams of a semiconductor device using the wire-bonding electrode pattern according to the first embodiment. A description will be made with reference to  FIGS. 1 ,  2 A and  2 B. The first embodiment of the present invention is directed to a semiconductor device which is formed by performing wire-bonding on a long and narrow laser diode chip. A wire-bonding electrode pattern  103  is formed in the laser diode chip. Wire bonding is performed by forming an Au ball  109  having a diameter d in a wire-bonding area  111  on the electrode pattern  103 . In the bonding, if the center line of the laser diode  205  is not inclined at all from that of an eyelet  201  (i.e., θ=0; see  FIG. 2B ), the Au ball  109  is formed so that the center thereof is located on a line that is parallel with the longer sideline of the electrode pattern  103  and passes through a center, in a direction parallel with the shorter sideline of the electrode pattern  103 , of the electrode pattern  103 . The electrode pattern  103  is formed with a wire-bonding recognition pattern  107  as a characteristic pattern. In this embodiment, the wire-bonding recognition pattern  107  is a rectangular cut that is formed adjacent to one longer sideline of the electrode pattern  103 . Individual dimensions are defined as follows. 
   L: The shortest distance between an edge (electrode edge  105 ) of the electrode pattern  103  and the center of the Au ball  109  formed in the wire bonding area  111 . 
   Lb: The shortest distance between the center line, in the direction parallel with the longer sideline of the electrode pattern  103 , of the wire-bonding recognition pattern  107  which is parallel with the shorter sidelines of the electrode pattern  103  and the center of the Au ball  109  formed in the wire bonding area  111 . 
   d: The diameter of the Au ball  109 . 
   W: The width of the electrode pattern  103  in the shorter-axis direction thereof. 
   The inclination (deviation) θ of the center line of the laser diode  205  from that of the eyelet  201  can be 2° at the maximum and depends on the accuracy of an assembling apparatus. A length x by which the Au ball  109  bulges out of the wire bonding area  111  when the Au ball  109  is formed in the wire bonding area  111  is given by the following equation:
 
 x=d/ 2 −W/ 2 +L  tan θ
 
   If the maximum allowable value of the bulging length x is set at d/8, corresponding values of L and Lb are given by the following equations since tan 2°=0.0349:
 
 L =14.3( W −3 d/ 4)
 
 Lb =14.3( W −3 d/ 4)
 
   In this embodiment, the electrode edge  105  is employed as a wire bonding reference pattern which is a reference for determination of a wire bonding position. Wire bonding is performed at such a position that the distance L between this wire bonding reference pattern and the center of the Au ball  109  having the diameter d and formed in the wire bonding area  111  satisfies a relationship:
 
 L ≧14.3( W −3 d/ 4).
 
   At this time, positioning is performed so that the distance Lb between the center line, in the direction parallel with the longer sideline of the electrode pattern  103 , of the wire-bonding recognition pattern  107  (formed in the electrode pattern  103 ) which is parallel with the shorter sidelines of the electrode pattern  103  and the center of the Au ball  109  satisfies a relationship
 
 Lb ≦14.3( W −3 d/ 4).
 
   For example, in a high-output-power recording laser diode in which the longitudinal length is 2,000 μm, the width is 120 μm, and the electrode width is 80 μm, if the Au ball diameter is 80±10 μm, the distance L is about 286 μm. Therefore, without the wire-bonding recognition pattern, an Au ball can be formed only near the edge of the long and narrow electrode. As a result, the density of current injected in an electrode top portion is made different from that of current injected in an electrode bottom portion, and the operation of the laser diode is rendered unstable. According to this embodiment, since the wire-bonding recognition pattern  107  is provided at a desired position, it possible to easily prevent non-uniformity of the density of current injected. 
   Although in this embodiment the electrode edge  105  is used as the wire bonding reference pattern, characteristic patterns of the electrode other than the electrode edge can be used as the wire-bonding reference pattern. For example, a cut, which is formed in the electrode pattern  103  at one of the four corners to enable, for example, discrimination between the front portion and the rear portion of the chip, can be used as the wire-bonding reference pattern. In this embodiment, this cut is a combination of rectangles, it may have other shapes such as a circle and a triangle. Although in this embodiment wire bonding is performed by forming an Au ball  109 , in the case of wedge bonding, Au ball is not formed and, instead, a tip portion of a wire is subjected to ultrasonic pressure bonding. In this case, the end portion of a wire is crushed and bonded to the electrode pattern  103 . 
   In the first embodiment, d indicates the diameter of the Au ball  109 . However, when the Au ball  109  has not a circular shape, d is defined as a maximum width of the Au ball  109  in the direction parallel with the shorter sideline of the electrode pattern. L is defined as a distance between the wire bonding reference pattern and a line that is parallel with a shorter sideline of the electrode pattern  103  and passes through a position where the Au ball  109  has the maximum width in a direction parallel with the shorter sideline of the electrode pattern  103 . Lb is defined as a distance between a line that passes through a center, in a direction parallel with the longer sideline of the electrode pattern, of the wire-bonding recognition pattern  107  and is parallel with the shorter sideline of the electrode pattern and the line that is parallel with the shorter sideline of the electrode pattern  103  and passes through a position where the Au ball  109  has the maximum width in a direction parallel with the shorter sideline of the electrode pattern  103 . 
   Second Embodiment 
     FIGS. 3 and 4  are schematic diagrams of wire-bonding electrode patterns according to a second embodiment of the present invention. Whereas in the first embodiment the wire-bonding recognition pattern  107  is a rectangular cut (see  FIG. 1 ), this embodiment employs a circular wire-bonding recognition pattern shown in  FIG. 3  or a triangular wire-bonding recognition pattern shown in  FIG. 4 . In the case of the circular wire-bonding recognition pattern  307 , even if it is made small or etching-induced rounding occurs when an etching method that is low in working accuracy is used, the shape of the wire-bonding recognition pattern  307  is kept circular and hence a recognition error can be avoided. In the case of the triangular wire-bonding recognition pattern  407 , the straight portions can be made longer than those of a rectangular shape having the same size, which provides an advantage that the influence of pattern deterioration by etching-induced rounding or the like can be reduced. 
   Since each of the wire-bonding recognition patterns  307  and  407  is formed adjacent to one longer sideline of the electrode pattern  303  or  304 , it can be formed easily by a lift-off method. Where etching or a like method is used, a wire-bonding recognition pattern  507  may be formed inside an electrode pattern  503  as shown in  FIGS. 5A ,  5 B and  5 C. 
   Third Embodiment 
   This embodiment is directed to a method for performing wire-bonding by recognizing a wire-bonding recognition pattern. 
   Referring to  FIG. 2 , an approximate position of the wire-bonding recognition pattern  107  can be recognized by recognizing the external shape of the eyelet  201 . Then, the wire-bonding recognition pattern  107  of the electrode pattern  103  is recognized to determine a wire-bonding position. At this time, if necessary, the wire-bonding recognition pattern  107  is recognized with the magnification of the camera changed. Finally, wire bonding is performed by using wires  211  and  213  and connections are thereby made to a lead  207  and the ground based on the determined wire-bonding position. This method makes it possible to immediately find the laser diode  205  being deviated from the prescribed position due to miss-setting, a pre-alignment failure, a failure of a positioning jig, or the like. That is, since it is found after recognition of the external shape of the eyelet  201  that no wire-bonding recognition pattern exists at the expected position, the operation of the apparatus is stopped upon the finding. This minimizes the number of defective products having positional errors which are produced in the laser diode bonding process, and hence provides an advantage that a loss caused by continuing production of defective products is prevented. 
   Fourth Embodiment 
   This embodiment is directed to another method for performing wire-bonding by recognizing a wire-bonding recognition pattern. 
   As in the third embodiment, an approximate position of the wire-bonding recognition pattern  107  can be recognized by recognizing the external shape of the eyelet  201 . Then, the wire-bonding reference pattern as the reference of a wire-bonding position is recognized. In this embodiment, the electrode edge  105  is used as the wire-bonding reference pattern. Then, the wire-bonding recognition pattern  107  of the electrode pattern  103  is recognized to determine a wire-bonding position. At this time, if necessary, the wire-bonding recognition pattern  107  is recognized with the magnification of the camera changed. Finally, wire bonding is performed based on the determined wire-bonding position. Since the chip position is recognized beforehand, this method makes it possible to recognize the position of the wire-bonding recognition pattern  107  more accurately than in the third embodiment. Furthermore, the cut that is formed in the electrode pattern  103  at one of the four corners can be used for position recognition as the wire-bonding reference pattern. Although in this embodiment this cut is a combination of rectangles, it may have other shapes such as a circle and a triangle. 
   Fifth Embodiment 
   This embodiment is directed to a further method for performing wire-bonding by recognizing a wire-bonding recognition pattern. 
   First, an approximate position of the wire-bonding recognition pattern  107  can be recognized by recognizing the external shape of the eyelet  201  (see  FIG. 1 ). Then, the wire-bonding recognition pattern  107  of the electrode pattern  103  is recognized to determine a wire-bonding position. At this time, if necessary, the wire-bonding recognition pattern  107  is recognized with the magnification of the camera changed. Then, the pattern of the electrode edge  105  which should be located at the expected position is recognized. Finally, wire bonding is performed based on the determined wire-bonding position. In addition to being capable of detecting a positional error occurring in the bonding process as in the third embodiment, this embodiment can immediately detect a failure that a laser diode chip of another type has been bonded. Laser diode chips have different longitudinal lengths depending on the optical output power. Therefore, the pattern of the electrode edge of the chip of a different type cannot be recognized and hence the apparatus is stopped. As such, this method has an advantage that a loss that is caused by continuing to produce products having a failure that a different chip is mounted. Furthermore, the cut that is formed in the electrode pattern  103  at one of the four corners can be used for position recognition. Although in this embodiment this cut is a combination of rectangles, it may have other shapes such as a circle and a triangle. 
   The present invention relates to an electrode pattern having shorter sideline and longer sideline. The effect of the inclined displacement of the center line of a laser diode relative to the center line of an eyelet is increased when the width W of the electrode pattern in the shorter sideline direction is smaller. Although the margin to the displacement becomes greater when W is larger, the margin substantially disappears when W is not more than 100 μm. Therefore, the present invention especially exerts the effect when W is not more than 100 μm. 
   Although several embodiments according the present invention has been described above as being directed to the high-output-power recording laser diodes, the present invention can also be applied to electrode patterns to be subjected to wire bonding such as wiring patterns of red laser diodes, bluish-purple laser diodes, communications laser diodes, LEDs, other semiconductor devices, packages, substrates, etc. 
   Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described. 
   The entire disclosure of a Japanese Patent Application No. 2007-070684, filed Mar. 19, 2007 and a Japanese Patent Application No. 2008-008066, filed on Jan. 17, 2008 including specification, claims, drawings and summary, on which the Convention priority of the present application is based, are incorporated herein by reference in its entirety.