Integrated circuit or circuit board with bump electrode and manufacturing method thereof

Abstract: A method of forming a bump electrode (300) on an electrode includes the steps of forming a ball bond on an IC electrode by a wire bonding apparatus, moving up a bonding capillary, moving the bonding capillary sideway and then downward, bonding an Au wire to the ball bond portion, and cutting the Au wire. The bump electrode (300) has a particular form, with a bump portion (40) having a vertex (7) at a first height above the electrode and a tail portion (50) extending from the bump portion (300) and having a vertex (52) at approximately the same height as the vertex of the bump portion (40). Both vertices have a flattened surface (31a).

Description: BACKGROUND OF THE INVENTION The present invention relates to an integrated circuit or a circuit board comprising an electrode and a bump electrode according to claim 1, and a method for forming a bump electrode according to claim 7. In recent years, electronic equipment has been developed to have a compact size, a light weight and a high function, and this has also required electronic components to have a compact size, a light weight and a high function. From this point of view, in regard to a method of forming a bump electrode on an IC electrode relevant to the present invention, a mounting method by means of a wire bonding technique is used. The method of forming a bump electrode on an IC electrode by the aforementioned prior art wire bonding technique will be described below with reference to the drawings. Figs. 12A-12D show schematic views of a prior art bump electrode forming method. In the figure are shown an Au wire 101, an Au ball 102, a bonding capillary 103, an IC electrode 104 on a board 170, a ball bond portion 105 and a bump electrode 106. The method of forming the bump electrode on the IC electrode will be described next. In Fig. 12A, the Au ball 102 formed at the tip end of the Au wire 101 is supplied onto the IC electrode 104 as shown in Fig. 12B and bonded onto the IC electrode 104 by the bonding capillary 103. Subsequently, the bonding capillary 103 moves up, sideway and then downward, thereby connecting the Au wire to the ball bond portion 105 as shown in Fig. 12C. Subsequently, the capillary 103 moves up and cut the Au wire 101, thereby forming a bump electrode as shown in Fig. 12D. That is, the above operation is described below in detail. A method of forming a bump on a semiconductor element by a prior art ball bonding method and a method of connecting the semiconductor element provided with the bump are disclosed in United States Patent No. 4,661,192. The methods will be described. As shown in Fig. 13A, a high voltage of several thousand volts is applied from a torch 160 which serves as a discharge electrode to the tip end 101a of a wire 101 protruding from the tip end of a capillary 103. By the application of this high voltage, the wire 101 comes to be increased in temperature and melted from the tip end 101a while a discharge current is flowing between the torch 160 and the wire tip end 101a, so that a ball-shaped melted portion as shown in Fig. 13B is formed. After the ball 102 is formed, the capillary 103 is moved down to the semiconductor element side, so that the ball 102 is made to abut against an electrode 104 of the semiconductor element 170. By further moving down the capillary 103 with respect to the ball 102 that has abutted against the electrode 104, the ball 102 is bonded to the electrode 104 and the ball 102 is formed by the tip end portion 103a of the capillary 103, so that a bump base portion 8 as shown in Fig. 13C is formed. Next, as shown in Fig. 13D, by moving up the capillary 103 to the side opposite to the semiconductor element while clamping the wire 101 by means of the capillary 103, the wire 101 is torn off in the vicinity of the bump base portion 8, thereby forming a bump 30 on the electrode 104 of the semiconductor element 170. Consequently, a protruding portion 30a is formed upright on the bump base portion 8 of the bump 30 as shown in Fig. 13D. In the semiconductor element 1 where the bump 30 is thus formed on the electrode 104, as shown in Fig. 14A, the bump 30 is pressed against a base material 21 on which a flat surface 21a is formed, so that a bump 31 having a flat surface 31a formed by flattening the protruding portion 30a is formed. Subsequently, as shown in Fig. 14B, the bump 31 having the flat surface 31a is brought in contact with a conductive adhesive 18 formed on a stage 41, thereby transferring the conductive adhesive 18 onto the flat surface 31a of the bump 31 and its periphery. Subsequently, as shown in Fig. 14C, by aligning in position the bump 31 onto which the conductive adhesive 18 has been transferred with an electrode 20 on a circuit board 19 and thereafter making the bump 31 abut against the electrode 20, the bump 31 is bonded to the electrode 20 for the achievement of electrical connection between the semiconductor element 170 and the circuit board 19. However, according to the bump electrode.forming method as described above, the Au wire 101 comes in contact with the IC electrode portion 104 when the Au wire 101 is cut by the capillary 103. Consequently, as shown in Fig. 15A and 15B, the electrode 106a, 106b exhibits an abnormal shape and an IC electrode material adheres to the tip end of the Au wire 101, causing the issue that the Au ball 102a cannot be normally formed as shown in Fig. 15C. From patent abstracts of Japan vol. 1996, No. 06, 28 June 1996 a capillary for a bump bonding apparatus can be inferred which is used to manufacture an IC in which the shape of a stud bump is stable. As a tip shape of that capillary, a swelled part which is swelled in the axial direction is formed at the outer circumferential part of the tip. Thereby, when a gold wire is cut and torn, the gold wire is cut and tom in a prescribed part, and the shape of a stud bump becomes stable. Moreover, EP patent application 0 320 244 discloses an electrical contact bump and a package provided with the same. A substrate provided with conductive terminals and another substrate provided with electrode pads and two-stepped electrical contact bumps formed respectively on the electrode pads and each consisting of a first raised portion and a second raised portion formed on the first raised portion, are joined securely by bonding the second raised portions coated respectively with droplets of conductive adhesive and the corresponding conductive terminals by the droplets of the conductive adhesive. The ratio of the area of a section of the first raised portion in a plane parallel to the surface of the electrode pad is greater than the area of a section of the second raised portion parallel to the section of the first raised portion at a predetermined ratio. In an exemplary method of forming the electrical contact bump, the second raised portion is formed by bending a conductive wire in a loop by a ball bonding apparatus. SUMMARY OF THE INVENTION In view of the aforementioned issues, the present invention has an object to provide a bump electrode and a method of forming said bump electrode on an IC electrode causing no abnormality in the shape of the electrode as well as to provide a semiconductor element, a method of fabricating said semiconductor element, a semiconductor device and a method of fabricating said semiconductor device. The aforementioned technical problem is solved by a bump electrode defined in claims 1 to 4, a method of forming a bump electrode defined in claims 5 to 10, a semiconductor element defined in claims 11 to 13, a method of fabricating a semiconductor element defined in claims 14 to 16, a semiconductor device defined in claim 17 and a method of fabricating a semiconductor device defined in claims 18 to 24. According to an aspect of the present invention, there is provided a semiconductor element in which the bump electrode is bonded to the IC electrode on a circuit forming surface of a semiconductor element, said bump being defined by claim 1 attached. In particular, said bump comprises: a first protrusion which is comprised of a portion formed by once melting and solidifying a wire and its periphery and is bonded to said electrode; and a second protrusion which is formed of an unmelted portion of said wire and extended from said first protrusion beyond a planar area defined by projecting said first protrusion on said electrode to a height approximately equal to that of said first protrusion with respect to said electrode, wherein said first protrusion and said second protrusion are brought in contact with or put close to one.electrode on said circuit board when the semiconductor element is mounted on the circuit board and wherein the first and the second protrusion have each a flat surface portion. According to a further aspect of the present invention, there is provided a semiconductor element as defined above, wherein said first protrusion is provided with a formed portion formed by forming a melted portion of said wire by a capillary and solidifying the same and a wire material portion which is comprised of the wire in a vicinity of said melted portion, extended from a vertex portion of said formed portion downwardly of said vertex portion and bonded to said formed portion. According to another aspect of the present invention, there is provided a semiconductor element as defined above, wherein said second protrusion extends toward an outer end surface side of said semiconductor element without exceeding said outer end surface. According to a yet further aspect of the present invention, there is provided a semiconductor element as defined above, wherein said second protrusion extends outwardly of said semiconductor element beyond an outer end surface of said semiconductor element. According to a further aspect of the present invention, there is provided a semiconductor device in which an electrode on a circuit board and said bump of the semiconductor element as defined above are electrically connected to each other. According to a further aspect of the present invention, there is provided a method of fabricating a semiconductor element as defined above, wherein, after the formation of said formed portion, said wire continued to said formed portion is bonded after said capillary describes an approximately rectangular shape in a plane parallel to a vertical direction above said formed portion when said first protrusion is formed. According to still another aspect of the present invention, there is provided a method of fabricating a semiconductor element as defined above, wherein, a region of said wire recrystallized by heat has a length extending to an end of said second protrusion when said melted portion is formed. According to a yet further aspect of the present invention, there is provided a method of fabricating a semiconductor element as defined above wherein the length of said recrystallized region is controlled by an application time of a voltage to be applied to said wire for the formation of said melted portion. According to another aspect of the present invention, there is provided a method of fabricating a semiconductor device comprising: fabricating a semiconductor element by the fabricating method described above; providing a conductive adhesive at each of said first protrusion and second protrusion; and electrically connecting said bump of the semiconductor element to an electrode on the circuit board. According to a further aspect of the present invention, there is provided a method of fabricating a semiconductor device comprising: fabricating a semiconductor element by the fabricating method as defined above; providing a conductive adhesive at the vertex portions of each of said first protrusion and second protrusion; electrically connecting said bump of the semiconductor element to an electrode on the circuit board; and checking the performance of electrical connection between said bump and said electrode for a good-or-bad test by picking up an image of an outwardly protruding portion extending outwardly of said semiconductor element beyond the periphery of said semiconductor element by means of an image pick-up device. According to a still further aspect of the present invention, there is provided a method of fabricating a semiconductor device as defined above, wherein said good-or-bad test of said electrical connection is executed by presence or absence of the conductive adhesive based. on pick-up image information of said outwardly protruding portion picked up by said image pick-up device. According to a yet another aspect of the present invention, there is provided a method of fabricating a semiconductor device as defined above, wherein said good-bad-test of said electrical connection is executed by confirming the operation of said semiconductor element by electrically bringing a contact in contact with said outwardly protruding portion instead of said image pick-up device. According to a yet further aspect of the present invention, there is provided a method of fabricating a semiconductor device as defined above, wherein confirmation of operation of said semiconductor element is executed by a diode characteristic test. According to still another aspect of the present invention, there is provided a method of fabricating a semiconductor device as defined above, wherein a flat surface portion is formed at the vertex portion of each of said first protrusion and second protrusion before said conductive adhesive is provided, and then said conductive adhesive is provided on the flat surface portion. According to a last aspect of the present invention, there is provided a method of fabricating a semiconductor device as defined above, wherein solder is used in place of said conductive adhesive. With the above-mentioned arrangement of the present invention, the wire does not come in contact with the periphery of the ball bond portion except for the ball bond portion when the wire is bonded to the ball bond portion, so that a bump electrode can be formed on the IC electrode. BRIEF DESCRIPTION OF THE DRAWINGS These and other aspects and features of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which: Fig. 1 is a side view showing an example of the shape of a bump and being used for producing an inventive bump shown in Fig. 5A to 5D and formed on a semiconductor element; Figs. 2A, 2B, 2C, 2D, 2E, and 2F are views for explaining the operation of forming the bump as shown in Fig. 4 and being used for producing an inventive bump shown in Fig. 5A to 5D and; Fig. 3 is a flowchart of a fabricating process of a bump of Fig. 1 and 2 provided for a semiconductor element; Fig. 4 is a side view showing another example of the shape of the bump shown in Fig. 1; Figs. 5A, 5B, 5C, and 5D are views for explaining a procedure for forming an inventive semiconductor device by connecting an inventive semiconductor element having bumps according to the invention; Fig. 6 is a graph showing a relationship between the size of a vertex portion of a bump and the amount of transfer of a conductive adhesive transferred to the bump; Fig. 7 is a side view of the bump shown in Fig. 4 at which the other end of the second protrusion is made to protrude from an end surface of the semiconductor element; Fig. 8 is a flowchart of a process for fabricating a semiconductor device with the semiconductor element of the present invention; Fig. 9 is a view showing an example of the method of testing a semiconductor device fabricated with a semiconductor element having the bump shown in Fig. 7; Fig. 10 is a view showing another example of the method of testing a semiconductor device fabricated with a semiconductor element having the bumps shown in Fig. 7; Figs. 11A and 11B are views showing the case where bumps are connected to board electrodes of a circuit board by means of solder in fabricating a semiconductor device with a semiconductor element of a tenth embodiment of the present invention; Figs. 12A, 12B, 12C, and 12D are sectional views showing a prior art method of forming a bump electrode on an IC electrode; Figs. 13A, 13B, 13C, and 13D are views for explaining the operation of forming a prior art bump; Figs. 14A, 14B, and 14C are views for explaining a procedure for forming a semiconductor device by connecting a semiconductor element having a prior art bump to a circuit board; and Figs. 15A, 15B, and 15C are sectional views showing an abnormal shape of a bump electrode formed on an IC electrode. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings. A semiconductor element together with a bump according to an embodiment of the present invention, a semiconductor device employing the semiconductor element as well as a method of fabricating the semiconductor element and a method of fabricating the semiconductor device will be described below with reference to the drawings. The above-mentioned semiconductor element will be described first. One bump being used for forming an inventive bump 300 described later is bonded onto each electrode 2 on a circuit forming surface 1a of a semiconductor element 1. In the semiconductor element 1 of this embodiment, a bump 3 having two protruding portions of a first protrusion 40 and a second protrusion 50 is bonded to at least one electrode 2 as shown in Fig. 1. It is to be noted that this kind of bump 3 is preferably provided on all the electrodes 2 of the semiconductor element 1. The second protrusion 50 extends beyond a planar area III defined by projecting the first protrusion 40 on the electrode 2, and the other end 52 which is a terminal end portion of the second protrusion 50 extends from one end 51 to a height approximately equal to that of the vertex portion 41 of the first protrusion 40 in the direction of height from the electrode 2. It is to be noted that Fig. 1 shows the case where the other end 52 extends to a position located slightly higher than the height of the vertex portion 41 of the first protrusion 40. The other end 52 of the second protrusion 50 comes in contact with no adjacent electrode 2 of the semiconductor element 1. By thus providing the first protrusion 40 and the second protrusion 50 at one bump 3, the area of the vertex portions 7 of the bump 3 can be increased, and as described in detail later, the connection area when connecting the above-mentioned bump 3 to the electrode of the circuit board by means of a conductive adhesive can be increased, so that the connection resistance value can be reduced. Furthermore, the amount of transfer of the conductive adhesive onto the bump 3 can be increased, and this eliminates the possible occurrence of a defective electrical conduction, allowing the connection reliability to be improved. The bump 3 of the above-mentioned type is formed approximately through the processes in Steps (each indicated by "S" in the figure) 1 through 3 as shown in Fig. 3, mostly in accordance with the ball bonding method. That is, in Step 1, the length of a recrystallization region as described later is controlled by controlling the discharge time, thereby melting the wire 10. In Step 2, the first protrusion 40 is formed of the melted wire on the electrode 2. In Step 3, the second protrusion 50 is further formed. These operations will be described in more detail below. As shown in Fig. 2A, a wire 10 which has a wire diameter of, for example, 25 µm and is made of a material . of, for example, gold is extended by about a length II from the tip end portion 9a of the capillary 9. It is to be noted that the above-mentioned length II is 450 µm, i.e., the projection length in the prior art. The material of the wire 10 is not limited to the above-mentioned gold, and it may be provided by copper, aluminum, nickel, solder or the like so long as the ball bonding method can be effected. Depending on the diameter of the wire 10, bump dimensions such as a base diameter and a height can be changed according to the purpose. A high voltage is applied to the tip end portion 10a of the wire 10 similarly to the prior art, and as shown in Fig. 2B, the tip end portion 10a is melted by an electric discharge between a discharge electrode and the tip end portion 10a, thereby forming a ball 11. It is to be noted that the diameter of the ball 11 can be controlled by the value of the application voltage, and the diameter of the ball 11 increases as the application voltage is increased. In the ball 11 and a portion having a certain length of the wire 10 continued to the ball 11, the crystal grain of the wire 10 is increased by heat generated by the above-mentioned electric discharge. This portion having the great crystal grain is served as a recrystallized region 16, and its length VI becomes 120 µm when the discharge time is 5 ms. For the reason that the crystal grain size differs in a boundary portion between a normal crystal region 17 having the initial crystal grain size and the above-mentioned recrystallized region 16, there is formed a crystal grain interface 15 at which the breaking strength of the wire 10 is weak. For the reason that the other end 52 of the second protrusion 50 is located at the crystal grain interface 15 or its vicinity, the length VI of the recrystallized region 16 becomes an important factor for the formation of the second protrusion 50. The length VI of the recrystallized region i6 as described above can be controlled by the discharge time in which the electric discharge is effected. Next, as shown in Fig. 2C, the ball 11 formed at the tip end portion 10a of the wire 10 is bonded onto the electrode 2 of the semiconductor element 1 by means of a pressure, heat or supersonic vibration applied from the capillary 9. The shape of the formed portion 42 of the first protrusion 40 formed on the electrode 2 by the ball 11 formed by thus melting the wire 10 is determined by the shape of the tip end portion 9a of the capillary 9. Therefore, the formed portion 42 is allowed to have an approximately conical shape as shown in Fig. 1 or a shape having a two-step protrusion comprised of a base portion 421 at which a shoulder portion 422 is formed and a protruding portion 424 provided upright on the base portion 421 as shown in Fig. 4. In a bump 300 having the base portion 421 of the above-mentioned type, due to the provision of the shoulder portion 422, the conductive adhesive is transferred only to the protruding portion 424 in transferring the conductive adhesive to the bump 300, and this produces the effect that the conductive adhesive can be prevented from spreading to the circuit forming surface 1a of the semiconductor element 1 by virtue of the shoulder portion 422 and the base portion 421. It is to be noted that this bump 300 is taken as an example in the following description. In the wire 10, a proximate portion 10b in the vicinity of the ball 11 is subjected to looping by the capillary 9 as indicated by a course 14 in a plane parallel to the vertical direction above the base portion 421 as, shown in Fig. 2D. In Fig. 2D, the distance of the movement of the capillary 9 is slightly exaggerated for the looping, and the looping is practically performed above a planar area III of the base portion 421. It is to be noted that the planar area III has a dimension of about 80 µm in the present embodiment. By the last motion 14a of the movement of the above-mentioned looping, the proximate portion 10b continued to the protruding portion 424 extends downwardly from the vertex portion 41 of the formed portion 42, and as shown in Fig. 2E, the proximate portion 10b is bonded to the peripheral portion 423 of the base portion 421 by pressure, heat or supersonic vibration. Thus the first protrusion 40 is formed. Therefore, the first protrusion 40 is comprised of the formed portion 42 and the wire material portion 43 which has been formed of the proximate portion 10b, extended from the vertex portion 41 and bonded to the peripheral portion 423. The above-mentioned looping is performed for the purpose of preventing the vertex portion 41 from falling to the semiconductor element side in accordance with the downward movement of the proximate portion 10b from the vertex portion 41 of the formed portion 42. Next, a clamper 12 provided for the capillary 9 clamps the wire 10 extending inside the capillary 9, and thereafter, the wire 10 bonded to the peripheral portion 423 of the base portion 421 is orientated upwardly with the elevation of the capillary 9 as shown in Fig. 2F and then torn off at the crystal grain interface 15 with the further elevation of the capillary 9. Thus the aforementioned second protrusion 50 is formed. By the operation of the capillary 9 as described above, the other end 52 of the second protrusion 50 extends beyond the aforementioned planar area III of the first protrusion 40 to a height positioned between the one end 51 bonded to the aforementioned peripheral portion 423 and the approximate vertex portion 41 of the first protrusion 40. It is to be noted that the position of the crystal grain interface 15 is controlled in the direction in which the wire 10 extends by controlling the aforementioned discharge time as described above so that the other end 52, i.e., the portion approximately identical to the crystal grain interface 15 is arranged in height in.a position between the above-mentioned one end 51 and the approximate vertex portion 41. Thus, one bump having two protrusions on one electrode 2 is obtained. The wire 10 is continued from the wire material portion 43 of the first protrusion 40 to the second protrusion 50 in the aforementioned embodiments. However, it is acceptable to bond the end portion of the wire material portion 43 to, for example, the peripheral portion 423 of the base portion 421, cut it once, bond the one end 51 of the second protrusion 50 to, for example, the peripheral portion 423 and extend the other end 52 as described above. The looping of the wire 10 is performed so that the vertex portion 41 of the first protrusion 40 is arranged in a position approximately in the vertical direction with respect to the electrode 2 in the aforementioned embodiments. However, the looping may not be performed so long as the vertex portion 41 can be arranged in a position in the vertical direction without performing the looping. The bumps 300 and 3 are each formed on the electrode 2 of the semiconductor element 1 in the aforementioned embodiments. However, the bumps 300 and 3 may be each formed on the boards electrode on the circuit board on which the semiconductor element 1 is mounted. Next, the following will describe the case where a semiconductor device is formed by mounting the semiconductor element 1 provided with the aforementioned bump 300 or bump 3 on a circuit board via the above-mentioned bump 300 etc. It is to be noted that the following description will be made taking the bump 300 as an example. It is to be noted that the above-mentioned mounting operation is similar to the operation described with reference to Figs. 14A through 14C. In regard to the semiconductor element 1 provided with the aforementioned bump 300, by pressing the semiconductor element 1 to the base material side as shown in Fig. 5A, the vertex portions 7 of the first protrusion 40 and the second protrusion 50 of the bump 300 are pressed against the flat surface 21a of the board 21, thereby forming flat surfaces 31a at the respective vertex portions 7. Next, as shown in Fig. 5B, by bringing the flat surface side of the bump 300 in contact with the conductive adhesive 18 formed on the flat surfaces of a stage 41, the conductive adhesive 18 is transferred onto the first protrusion 40 and the second protrusion 50. Next, as shown in Fig. 5D, the bump 300 on which the conductive adhesive 18 has been transferred is aligned with the board electrode 20 of the circuit board 19, and the first protrusion 40 and the second protrusion 50 of each bump 300 are fixed on the board electrode 20 by the conductive adhesive 18. Thus a semiconductor device 600 is fabricated. By virtue of the provision of the two protrusions of the first protrusion 40 and the second protrusion 50, the amount of transfer of the conductive adhesive 18 onto the vertex portions 7, i.e., the height IV of the conductive adhesive 18 as shown in Fig. 5C is increased. Further, by forming the flat surfaces 31a on the vertex portions 7 of the first protrusion 40 and the second protrusion 50, the area of the vertex portions 7 is further increased. As shown in Fig. 6, the above-mentioned amount of transfer increase as the area of the vertex portions 7 increases, and therefore, the amount of transfer can be increased by forming the flat surface 31a. In the above-mentioned manner, the conductive adhesive 18 can be transferred onto the bump 300 by the height IV of 10 µm or greater as shown in Fig. 5C. Furthermore, the warp of the circuit board 19 in the case where the semiconductor element 1 is connected to the circuit board 19 is absorbed by the above-mentioned amount of transfer of the conductive adhesive 18, and therefore, the increase in amount of transfer as described above allows the amount of absorption of the warp to be increased. Therefore, the specification of the warp at the portion in which the semiconductor element 1 is connected to the circuit board 19 can be alleviated to 10 µm from the conventional specification of 4 µm, also allowing the circuit board 19 to be reduced in cost. Furthermore, the connection area of the bump 300 and the board electrode 20 on the circuit board 19 as well as the amount of the conductive adhesive 18 are increased, so that the strength of connecting the bump 300 to the electrode 20 can be increased and the connection resistance value can be suppressed to a low value. A direction in which the other end 52 of the second protrusion 50 is orientated will be described next. The other end 52 of the second protrusion 50 at the bump 300 formed as described above can be orientated to the peripheral side of the semiconductor element 1, or as further shown in Fig. 7, the other end 52 can be also extended beyond an extension line of the outer end surface ib of the periphery of the semiconductor element 1. It is to be noted that the orientation of the other end 52 is executed by the operation of the capillary 9. In regard to the bump 300, a bump at which the other end 52 is extended beyond of the extension line of the outer end surface 1b of the periphery of the semiconductor element 1 is denoted by a bump 310 as shown in Fig. 7. Further, the portion which belongs to the wire 10 and extends beyond the extension line of the outer end surface 1b is denoted by an outwardly protruding portion 53. By thus orientating the other end 52 to the peripheral side of the semiconductor element 1, the other end 52 does not extend toward the adjacent electrode 2 in the semiconductor element 1. Therefore, the other end 52 is not brought in contact or short-circuited with the adjacent electrode 2 when the conductive adhesive 18 is transferred to the bump 310. Therefore, the orientation of the other end 52 to the peripheral side of the semiconductor element 1 can assure the amount of transfer of the conductive adhesive 18 and prevent the possible occurrence of the short circuit as described above by virtue of the provision of the second protrusion 50 in addition to the first protrusion 40. Further, a semiconductor device can be also fabricated by forming the bump 310 on the electrode 2 of the semiconductor element 1 as described above in Step 11 shown in Fig. 8 and connecting the bump 310 onto the electrode 20 of the circuit board 19 in a face-down mounting manner in Step .12. When fabricating the semiconductor device as described above, the other end 52 is neither brought in contact or short-circuited with the adjacent electrode 2 in the semiconductor element 1 having the bump 310. Furthermore, the second protrusion 50 of the bump 310 has the outwardly protruding portion 53. For the above reason, when the bump 310 is connected to the electrode 20 on the circuit board 19, its connection area is greater than that of, for example, the bump 300. Therefore, the connection strength can be made higher and the connection resistance value can be made lower. Furthermore, in a semiconductor device 610 in which the semiconductor element 1 having the bump 310 is connected to the circuit board 19, a test process for testing the performance of the electrical connection of the bump 310 to the electrode 20 on the circuit board 19 can be provided as one fabricating process of the semiconductor device 610 as shown in Step 13 in Fig. 8. This test will be described below. For example, when the semiconductor element 1 having the bump 300 is mounted on the circuit board 19 in the face-down mounting manner, the other end 52 of the second protrusion 50 is not protruding from the outer end surface 1b of the periphery of the semiconductor element 1. Therefore, the portion in which the bump 300 is connected to the electrode 20 on the circuit board 19 cannot be visually checked. When the semiconductor element 1 having the bump 310 is mounted on the circuit board 19 in the face-down mounting manner, the outwardly protruding portion 53 is protruding from the outer end surface 1b of the periphery of the semiconductor element 1. Therefore, the portion in which the bump 310 is connected to the electrode 20 on the circuit board 19 can be viewed via the outwardly protruding portion 53 and subjected to a visual test. Furthermore, it is acceptable to automatically execute the above-mentioned visual test by means of a camera 25 and a visual tester 26 connected to the camera 25 as shown in Fig. 9. That is, the electrical connection of the bump 310 to the electrode 20 can be checked for a good-or-bad test by picking up the image of the portion in which the outwardly protruding portion 53 is connected to the electrode 20 by the camera 25, taking in the image into the visual tester 26, and detecting the presence or absence of the conductive adhesive 18 in the connection portion by means of the visual tester 26. Furthermore, in the semiconductor device 610 employing the semiconductor element 1 having the bump 310, a contact probe 26 can be brought in contact with the outwardly protruding portion 53 or the conductive adhesive 18 which covers the outwardly protruding portion 53 as shown in Fig. 10. The contact probe 26 is connected to a semiconductor element performance tester 27 which can check the state of connection of the bump 310 to the electrode 20 of the circuit board 19 or the operation of the semiconductor element 1. Therefore, by executing, for example, a diode characteristic test, it can be checked in a short time whether the connection of the electrode 2 of the semiconductor element 1 to the electrode 20 of the circuit board 19 is in a non-conductive state or short-circuited. It is to be noted that the above-mentioned diode characteristic test is to test the diode formed in the circuit of the semiconductor element 1 for the purpose of preventing an excessive current from flowing through the circuit of the semiconductor element 1. The connection of the bump to the electrode 20 of the circuit board 19 is achieved by the conductive adhesive 18 according to the description of the above-mentioned embodiment. However, as shown in Figs. 11A and 11B, solder 28 can be used instead of the conductive adhesive 18. It is to be noted that the bump 300 is taken as an example in Figs. 11A and 11B. Similarly to the case described with reference to Figs. 5A-5D, the vertex portions 7 of the first protrusion 40 and the second protrusion 50 of the bump 300 of the semiconductor element 1 are provided with respective flat surfaces 31a. On the other hand, as shown in Fig. 11A, solder 28 is provided on the electrode 20 of the circuit board 19. Then, as shown in Fig. 11B, by aligning in position the bump 300 of the semiconductor element 1 with the electrode 20 of the circuit board 19, bringing the flat surfaces 31a of the bump 300 into contact with the solder 28 and heating the same, the two protrusions of the first protrusion 40 and the second protrusion 50 of the bump 300 are connected to the electrode 20 of the circuit board 19 via the. solder 28. By thus connecting the electrode 20 of the circuit board 19 with the bump 300 having the first protrusion 40 and the second protrusion 50 by means of solder, a solder fillet is formed. By virtue of the provision of this fillet, the strength against a stress effected on the circuit board 19 is increased and the connection reliability is improved. Furthermore, the connection area is increased and the connection resistance value is reduced. The bump having two protrusions is formed by the ball bonding method in the aforementioned embodiment. However, it is a matter of course that a method capable of forming two protrusions on at least one bump can be used instead of the ball bonding method. As described in detail above, according to the semiconductor elements of the aspects as well as the semiconductor element fabricating method of the aspect of the present invention, two protrusions are provided on one bump wherein the vertex portions of these two protrusions have each a flat surface. Therefore, the area of contact of the bump with the board electrode on the circuit board is increased. Accordingly, the connection strength and the connection reliability can be made high and the connection resistance value can be made low and stable in connecting the semiconductor element to the circuit board. Furthermore, according to the semiconductor device of the aspect and the semiconductor device fabricating method of the aspect of the present invention, the semiconductor element having two protrusions at one bump wherein the vertex portions of these two protrusions have each a flat surface, as described above, is used and the bump is connected to the board electrode of the circuit board. With this arrangement, the area of contact of the bump with the board electrode on the circuit board is increased, and accordingly, the connection strength and the connection reliability of the semiconductor element and the circuit board can be made high and the connection resistance value can be made low and stable in the semiconductor device. Furthermore, according to the semiconductor device fabricating method of the aspect of the present invention, the end portion of the second protrusion is extended outwardly of the semiconductor element beyond the periphery of the semiconductor element at the bump having two protrusions being provided each with a flat surface. This arrangement of course enables the improvement of the connection strength and the connection reliability and the reduction and stabilization of the connection resistance value as described above and allows the semiconductor device to be tested by means of the second protrusion extended outwardly of the semiconductor element. Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.

Claims: An integrated circuit (1) or a circuit board (19) comprising an electrode (20) and a bump electrode formed thereon and being used for connecting said semiconductor element (1) to said circuit board (19), said bump electrode comprising: a base portion (421) provided on said electrode (2, 20) of said semiconductor element (1) or said circuit board (19), the base portion (421) having a first protrusion (40) extending away from the electrode (2, 20) to define a first vertex (41) and a second protrusion (50) having a first end attached to the periphery of the base portion (421) and a second end defining the second vertex (25), characterized in that the height of the second protrusion (50) is approximately equal to that of said first protrusion (40) above said electrode and that said vertex portions (7) of the first protrusion (40) and the second protrusion (50) have each a flat upper surface portion (31a). An integrated circuit or circuit board according to claim 1, characterized in that said first protrusion (40) is comprised of a formed portion (42) which has an approximately conical shape. An integrated circuit or circuit board according to claim 2, characterized in that said formed portion (42) has a shape of a two-step protrusion comprising said base portion (421) with a shoulder portion (422) and a protruding portion (424) defining said first protrusion (40). An integrated circuit or circuit board according to any of claims 1 to 3, characterized in that a conductive adhesive (18) or a solder (28) is provided on said flat surface portions (31a) of the first and second protrusions (40, 50). An integrated circuit according to any of claims 1 to 4, characterized in that said second protrusion (50) extends toward an outer end surface side (1b) of said integrated circuit (1) without exceeding said outer end surface side (1b). An integrated circuit according to claim 5, characterized in that said second protrusion (50) extends outwardly of said integrated circuit (1) beyond an outer end surface (1b) of said integrated circuit (1). A method of forming a bump electrode (300; 310) on an electrode (2) of an integrated circuit (1) or on an electrode (20) of a circuit board (19), comprising the following steps: forming a base portion (421) on the electrode (2, 20) of said integrated circuit (1) or said circuit board (19), from a wire (10) using a capillary (113) wherein said base portion is provided with a first protrusion (40) extending away from the electrode (2, 20) to define a first vertex (41 ), and a second protrusion (50) having a first end attached to the periphery of said base portion (421) and the second end defining a second vertex (52) characterized in that the height of said second protrusion (50) is made approximately equal to that of said first protrusion (40) above said electrode and that said first and second vertex portions (41,52) are each provided with a flat upper surface portion (31a). The method according to claim 5, characterized in that said first protrusion (40) is formed by forming a portion (42) formed by solidifying a melted portion of a wire (101) and its periphery, and that said second protrusion (50) is formed of an unmelted portion of said wire (101). The method according to claim 8, characterized in that said first protrusion (40) is formed by forming the melted portion of said wire (10) into said formed portion (42) by a capillary (113) and extending the wire (10) in a vicinity of said melted portion from the first vertex portion (41) of said formed portion (42) downwardly of said first vertex portion (41) and bonding the wire (10) to a periphery of said formed portion (42). The method according to claim 9, characterized in that , after the formation of said formed portion (42), said first protrusion (40) is formed by looping said wire and bonding said loop to a peripheral portion of said formed portion (42), said capillary moving in an approximately rectangular shape in a plane that includes the direction orthogonal to the surface of the integrated circuit or circuit board. The method according to any of claims 8 to 10, characterized in that a region of said wire (10) recrystallized by heat has a length extending to an end of said second protrusion (50) when said melted portion is formed. The method according to claim 11, characterized in that the length of said recrystallized region is controlled by an application time of a voltage to be applied to said wire (10) for the formation of said melted portion. The method according to claim 7, wherein said bump electrode (300,310) is formed on said integrated circuit, characterized in that said second protrusion (50) is formed such that it extends to the peripheral side (1b) of said integrated circuit (1). The method according to claim 13, characterized in that said second protrusion (50) is formed such that it extends beyond the periphery of said integrated circuit (1) to the outside of said integrated circuit (1). A semiconductor device in which an electrode (20) of a circuit board (19) and an integrated circuit (1) according to any of claims 5 to 6 are electrically connected to each other. A method of fabricating a semiconductor device, comprising the following steps: fabricating an integrated circuit (1) by the fabricating method of any of claims 13 to 14, providing a conductive adhesive (18) or solder (28) at each side of said first protrusion (40) and the second protrusion (50), and electrically connecting said bump electrode (3; 300; 310) of the integrated circuit (1) to an electrode (20) of said circuit board (19). A method of fabricating a semiconductor device, comprising the following steps: fabricating an integrated circuit (1) by the fabricating method according to claim 14, providing a conductive adhesive (18) or solder (28) at the vertex portions (7, 41) of each of said first protrusion (40) and the second protrusion (50), electrically connecting said bump electrode (310) of the integrated circuit (1) to an electrode (20) of said circuit board (19), and checking the performance of electrical connection between said bump electrode (310) and said electrode (20) for a good-or-bad test by picking up an image of an outwardly protruding portion (53) of said bump (310) extending outwardly of said integrated circuit (1) beyond the periphery of said integrated circuit (1) by means of an image pick-up device (25, 26). The method according to claim 17, characterized in that said good-or-bad test of said electrical connection is executed by presence or absence of the conductive adhesive (18) based on a pick-up image information of said outwardly protruding portion (53) picked up said image pick-up device (25, 26). The method according to claim 17, characterized in that said good-or-bad test of said electrical connection is executed by confirming the operation of said integrated circuit (1) by electrically bringing a contact in contact with said outwardly protruding portion (53) instead of said image pick-up-device (25, 26). The method according to claim 19, characterized in that the confirmation of operation of said integrated circuit (1) is executed by a diode characteristic test. The method according to any of claims 19 to 22, characterized in that a flat surface portion (31a) is formed at the vertex portions (7, 41) of each of said first protrusion (40) and said second protrusion (50) before said conductive adhesive (18) is provided, and then said conductive adhesive (18) is provided on the flat surface portion (31a).

Inventors: HIGASHI KAZUSHI, KITAYAMA YOSHIFUMI, OTANI HIROYUKI, TSUKAHARA NORIHITO, YAGI YOSHIHIKO, YONEZAWA TAKAHIRO, HIGASHI, KAZUSHI, KITAYAMA, YOSHIFUMI, OTANI, HIROYUKI, TSUKAHARA, NORIHITO, YAGI, YOSHIHIKO, YONEZAWA, TAKAHIRO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1997
Main classification: H01L21
IPC codes: H01L23, H01L21