Method and tool for making an electronic circuit having uniform solder residues after solder paste transfer

Abstract: A method for producing an electronic circuit device includes a repair step in which, in a case where a semiconductor device once mounted on a wiring board is defective, the defective semiconductor device is removed from the wiring board and a new semiconductor device is mounted on the wiring board. The repair step includes the steps of: removing an excessive residue of a brazing metal residue remaining on lands of the wiring board from which the defective semiconductor device has been removed and leaving a uniform amount of the brazing metal residue on the lands; aligning the new semiconductor device with the wiring board; and melting the brazing metal residue which is made uniform and remains on the lands and projecting electrodes of the new semiconductor device by heating, thereby connecting the new semiconductor device to the wiring board.

Description: BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION: The present invention relates to a method for producing an electronic circuit device in accordance with the precharacterizing part of claim 1 and to an apparatus for producing an electronic circuit device in accordance with the precharacterizing part of claim 16. A method and an apparatus of that kind are respectively known from EP-A-0 307 574. 2. DESCRIPTION OF THE RELATED ART: During a repair step of an electronic circuit device, when a defective semiconductor device (electronic component) is removed from a wiring board (i.e., substrate for mounting a semiconductor device), a solder residue, for example, made of brazing metal remains on connecting portions (i.e., lands) of the wiring board. Since the height of the solder residue is not uniform, when a new semiconductor device is mounted on the wiring board in this state, a connection failure may occur, leading to disconnection or the like. According to the conventional repair method, in order to prevent the connection failure, the following steps (1) and (2) have been performed. (1) First, a solder-wettable metal plate (i.e., a metal plate over which solder can spread well) is pressed against a solder residue and heated in this state so that the solder residue adheres to the metal plate, whereby the solder residue on the wiring board is completely removed. (2) A flux is coated onto lands of the wiring board for the purpose of preventing the lands from being oxidized. Solder projecting electrodes of a semiconductor device to be newly mounted melt by heating in an atmosphere furnace or in an air-oven, whereby the semiconductor device is connected to the wiring board. For example, Japanese Laid-open Publication Nos. 1-209736 and 8-46351 disclose conventional examples as described above. In the case where a semiconductor device is bonded to a wiring board, using solder projecting electrodes by flip chip bonding, when there is a difference in thermal expansion coefficient between the semiconductor device and the wiring board, there is the following problem. The difference between the temperature at which the solder projecting electrodes melt by heating and room temperature, or the difference between the temperature during operation of the semiconductor device and the temperature when the semiconductor device is not being operated causes a difference in expansion and contraction between the semiconductor device and the wiring board (i.e., thermal stress). This may strain connecting portions of the solder projecting electrodes to induce a connection failure. Thus, strain on the connecting portions of the solder projecting electrodes caused by the difference in thermal expansion coefficients of the parts decreases the reliability of a product. In the case where nothing fills between the semiconductor device and the wiring board, the strain of the connecting portions of the solder projecting electrode is in good agreement with a value calculated from the Coffin·Manson connection fatigue life expression represented by the following Formulae (1) and (2). In order to decrease the maximum strain γ max in the connecting portions, as is understood from Formula (2), the height H j of the connecting portions should be increased. For this purpose, the amount of solder is increased. Nf = C·f 1/3 ·1/γ max 2 ·exp(ΔE/KT max ) γ max = 1/(D min/2 ) 2/β ·(V j /π·H j (1+β) ) 1/β ·ΔT·Δα·d where N f : number of cycles until a connection failure occurs C: proportionality factor β: solder material constant K: Boltzmann's constant f: frequency of temperature cycle T max : maximum temperature of temperature cycle D min : minimum diameter of connecting portions (i.e., smaller value of upper and lower diameters D B1 and D B2 of connecting portions in Figure 13 ) Δα: difference in thermal expansion coefficient between wiring board and semiconductor device d: distance between focused solder joint and the neutral point of thermal stress ΔE: activating energy leading to fatigue For reference, Figure 13 illustrates representative elements among those shown above. As described above, according to the conventional repair method, the solder residue is completely removed, and the semiconductor device is connected to the wiring board by using the solder in the solder projecting electrodes alone. Therefore, the amount of solder is small. This makes it impossible to increase the height Hj of the connecting portions so as to improve the reliability of the product. EP-A-0 307 574 disclosing the features of the precharacterizing parts of the independent claims 1 and 17 describes method steps producing an electronic circuit device including a repair step of removing the faulty device after melting the brazing metal; aligning a replacement semiconductor device with the substrate and melting the brazing metal residue remaining on the lands on the substrate and on projecting electrodes of the new semiconductor device by heating thereby connecting the new semiconductor device to the substrate. SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing an electronic circuit device which is capable of efficiently securing the amount of solder for connecting a semiconductor device to a wiring board thereby increasing the height of the connecting portions to improve the reliability of a product and to provide an apparatus for producing an electronic circuit device which is usable for performing that production method. According to a first aspect of the present invention, a method for producing an electronic circuit device includes a repair step during a process of producing an electronic circuit device by aligning projecting electrodes made of brazing metal and formed on one principal plane of a semiconductor device with a substrate (30) for mounting a semiconductor device having lands for connection corresponding to the projecting electrodes, and melting the projecting electrodes by heating, thereby mounting the semiconductor devices on the substrate, the repair step including, in a case where the semiconductor device once mounted is defective, removing the defective semiconductor device from the substrate and mounting a new semiconductor device on the substrate, the repair step comprising the steps of: aligning the new semiconductor device with the substrate; and melting the brazing metal residue which remains on the lands and projecting electrodes of the new semiconductor device by heating, thereby connecting the new semiconductor device to the substrate, wherein the repair step is characterized by removing an excessive residue of a brazing metal residue remaining on the lands of the substrate from which the defective semiconductor device has been removed and leaving a uniform amount of the brazing metal residue on the lands by means of a heating iron, which moves at a predetermined speed while keeping in contact with the brazing metal residue or by a jig for making a solder residue uniform, including a plurality of pins on an outer peripheral portion thereof. In one embodiment of the present method, the uniform amount of the brazing metal residue remaining on the lands has a height corresponding to surface tension of the brazing metal residue. In another embodiment of the present invention, the brazing metal residue which is made uniform and remains on the lands and the projecting electrodes of the new semiconductor device are heated to melt with light emitted by a lamp. In another embodiment of the present invention, a near-infrared lamp is used as the lamp. According to another embodiment, the step of removing an excessive residue of a brazing metal residue remaining on the lands of the substrate from which the defective semiconductor device has been removed and leaving a uniform amount of the brazing metal residue on the lands is performed by placing the jig in form of a plate made of a solder-wettable metal over the brazing metal residue on the lands with a predetermined gap kept therebetween and heating the plate, said gap being provided by the plurality of pins. In another embodiment of the present invention, the predetermined gap is about 1/4 to about 1/10 of a land diameter of the lands. In another embodiment of the present invention, in a case where the land diameter of the lands is about 150 µm to about 800 µm, the heating iron is moved manually. In another embodiment of the present invention, in a case where the land diameter of the lands is about 150 µm to about 550 µm, the heating iron is moved manually. In another embodiment of the present invention, the brazing metal is eutectic solder or solder whose strength is increased by adding a slight amount of additive to eutectic solder. In another embodiment of the present invention, the semiconductor device is a semiconductor package having projecting electrodes in an area-array. In another embodiment of the present invention, the repair step additionally comprises, if necessary, supplying brazing metal paste to tip ends of projecting electrodes of the new semiconductor device and melting also the brazing metal paste by heating to connect the new semiconductor device to the substrate. In another embodiment of the present invention, the step of supplying the brazing metal paste to the tip ends of the projecting electrodes is performed by a transfer method. In another embodiment of the present invention, the brazing metal paste is obtained by dispersing metal powders which are the same kind as that of brazing metal in a binder. In another embodiment of the present invention, the projecting electrodes of the new semiconductor device and the brazing metal paste are heated to melt with light emitted by a lamp. According to a further aspect, the present invention is directed to an apparatus for producing an electronic circuit device by aligning projecting electrodes made of brazing metal and formed on one principal plane of a semiconductor device with a substrate for mounting a semiconductor device having lands for connection corresponding to the projecting electrodes, and melting the projecting electrodes by heating, thereby mounting the semiconductor device on the substrate, wherein, in a case where the semiconductor device once mounted is defective, the apparatus is designated to remove the defective semiconductor device from the substrate and to mount a new semiconductor device on the substrate, the apparatus comprising: a holder holding the substrate; a holder holding the defective semiconductor device or the new semiconductor device; an alignment unit aligning the substrate with the defective semiconductor device or the new semiconductor device; and a heating unit melting the projecting electrodes of the aligned new semiconductor device by heating, thereby connecting the new semiconductor device to the substrate; said apparatus being characterized by a unit removing an excessive residue of a brazing metal residue remaining on connecting portions of the substrate from which the defective semiconductor device has been removed and leaving on the connecting portions a uniform amount of the brazing metal residue having a height corresponding to surface tension of the brazing metal residue on the connecting portions by means of a heating iron which moves at a predetermined speed while keeping in contact with the brazing metal residue or by a jig for making a solder residue uniform including a plurality of pins on an outer peripheral portion thereof. In one embodiment, the apparatus of the present invention further comprises the jig for transferring brazing metal paste to tip ends of the projecting electrodes of the new semiconductor device as described above. In one embodiment of the present apparatus, the heating unit is a near-infrared lamp. Hereinafter, the function of the present invention will be described. As described above, only a uniform amount of solder residue in accordance with the surface tension of the solder is left, and a new semiconductor device is provided with solder paste by a transfer step. Therefore, a sufficient amount of solder can be secured for a repaired semiconductor device. As is understood from the Coffin·Manson connection fatigue life expression, this increases the height H j of the connecting portions and decreases the maximum strain γ max in the connecting portions, so that a connection failure (i.e., disconnection) does not occur. Thus, the reliability of the semiconductor device can be improved. Depending upon the kinds of products (i.e., kinds of semiconductor devices and wiring boards to be connected), the transfer step as described above is not required. According to the experimental result of the inventors of the present invention, for example, in the case where a semiconductor device having a land pitch L P of about 0.6 mm is mounted on a wiring board having a land diameter L D of about 200 µm, the height of the printed solder (i.e., height of the solder residue after being shaped) is about 70 µm. Therefore, it was confirmed that a reliable semiconductor device may be obtained without performing a transfer step. According to the present invention, the solder residue remaining on a wiring board from which a defective semiconductor device has been removed is left on purpose, instead of being completely removed, whereby a sufficient amount of solder is secured. In this case, the solder residue remaining on the wiring board from which the defective semiconductor device has been removed is left in a nonuniform amount. However, by utilizing the surface tension of the molten solder, the solder residue can be controlled to a uniform amount and a uniform height. This control can be easily performed by heating the solder residue by using the above-mentioned jig for making the solder residue uniform. According to the transfer method, a uniform amount of solder paste can be easily supplied to a semiconductor device, which is convenient. More specifically, the use of the above-mentioned jig for transferring brazing metal paste facilitates the transfer of solder paste. In accordance with the Coffin·Manson connection fatigue life expression, in order to increase the height of the connecting portions, solder paste should be transferred as much as possible. Considering the relationship between the amount of the solder residue remaining on the wiring board and the surface tension thereof, the transfer amount is preferably about 1/3 or more of the height of the solder projecting electrodes. If too great an amount of solder paste is transferred, as shown in Figure 3A (described later), solder paste 12 may adhere to a semiconductor device 20 to form a bridge 23 between solder projecting electrodes 21 . When such a bridge 23 is formed, as shown in Figure 3B , the bridge 23 reflows together with the solder projecting electrodes 21 when the semiconductor device 20 is mounted and heated. Then, the molten solder is integrated due to its surface tension, forming a solder projecting electrode 24 with a large diameter. In order to prevent such a solder projecting electrode from being formed, the transfer amount should be limited to about 1/2 of the height of the solder projecting electrodes 21 , i.e., a value not exceeding an equator surface of the solder projecting electrodes 21 . The depth of the groove of the jig for transferring brazing metal paste is prescribed to be about 1/2 to about 1/3 of the height of the solder projecting electrodes, whereby the transfer amount is prescribed to be about 1/2 to about 1/3 of the height of the solder projecting electrodes 21. A heating device for re-connecting a new semiconductor device to a wiring board should not involve an excessive external force. More specifically, without an excessive external force, a semiconductor device and a wiring board which have been aligned with each other will not be shifted in position. Thus, the repair step can be more easily and efficiently performed. Because of this, according to the present invention, a lamp which does not involve an external force is used. As the lamp, a near-infrared lamp (IR lamp) is preferably used for the following reason. In a semiconductor device, Si is used as a material mainly for a circuit board. Si transmits light in a near-infrared region (wavelength: about 1 to about 5 µm). When the light with a wavelength of about 1 to about 5 µm is used, the light passes through Si to directly and efficiently heat the solder projecting electrodes and solder paste. Thus, an IR lamp capable of emitting light with a wavelength of about 1 to about 5 µm is preferably used. The use of eutectic solder or eutectic solder with a slight amount of additive added thereto as brazing metal can improve solder strength. Thus, the invention described herein makes possible the advantages of: (1) providing a method for producing an electronic circuit device which is capable of securing the amount of solder sufficient for connecting a semiconductor device to a wiring board, thereby increasing the height of the connecting portions to improve the reliability of a product (2) providing an apparatus for producing an electronic circuit device used for performing the production method. These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a flow chart showing a repair process in a method for producing an electronic circuit device according to the present invention. Figure 2A is a perspective view showing a jig for transferring solder paste used for performing the method according to the present invention; and Figure 2B is a perspective view showing a state in which the jig is filled with transfer paste. Figures 3A and 3B illustrate inconvenience in the case where the amount of transfer paste is excessive. Figures 4A and 4B show steps of transferring solder paste. Figure 5A is a perspective view showing another jig for transferring solder paste used for performing the method according to the present invention; and Figure 5B is a perspective view showing a state in which the jig is filled with transfer paste. Figure 6 is a perspective view showing a jig for making a solder residue uniform. Figures 7A through 7C show steps of making a solder residue on a wiring board uniform using the jig shown in Figure 6 . Figures 8A through 8C show steps of making a solder residue uniform using another jig for making a solder residue uniform. Figures 9A and 9B respectively show a semiconductor device and a wiring board to which the present invention is applied. Figure 10 is a graph illustrating a range of a land diameter of a wiring board to which the present is applied. Figure 11 is a perspective view of an apparatus for producing an electronic circuit device according to the present invention. Figure 12 is a perspective view of another apparatus for producing an electronic circuit device according to the present invention. Figure 13 illustrates the Coffin·Manson connection fatigue life expression. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described by way of illustrative embodiments with reference to the drawings. Embodiment 1 Figures 1 through 7 show a method for producing an electronic circuit device in Embodiment 1 according to the present invention. The method according to the present invention is characterized by a repair step which will be outlined with reference to Figure 1. First, at Step S1, it is confirmed that a semiconductor device on a wiring board is defective. At Step S2, the defective semiconductor device is heated by a lamp so as to melt solder projecting electrodes, whereby the semiconductor device is removed from the wiring board. At Step S3, after the defective semiconductor device is removed, an excessive solder residue remaining on the wiring board is removed so that only a uniform amount thereof is left. At Step S4, a new semiconductor device is prepared. At Step S5, solder paste is provided by a transfer method to tip ends of solder projecting electrodes of the device, whereby the device is ready to be mounted. At Step S6, the new semiconductor device to which the solder paste has been transferred is aligned with the wiring board on which a uniform amount of solder residue remains. At Step S7, the new semiconductor device which has been mounted on the wiring board is heated by a lamp, whereby the solder projecting electrodes and the solder paste melt. Thus, the semiconductor device is connected to the wiring board. At Step S8, the repair is completed. During the repair step, a near-infrared lamp (IR lamp) is preferably used for the following reason. As a material of choice for wiring boards, Si is used. Si transmits light in a near-infrared region (wavelength: about 1 to about 5 µm). When the light with a wavelength of about 1 to about 5 µm is used, the light passes through Si to directly heat the solder projecting electrodes and solder paste with efficiency. Thus, the IR lamp which emits light with a wavelength of about 1 to about 5 µm is preferable. The step of transferring solder paste at Step 5 is performed, for example, by using a solder paste transfer jig 10 shown in Figure 2 . The jig 10 is a rectangular solid which has a groove 11 in the shape of an expanding slot at a center portion of its surface. The groove 11 is provided for the purpose of allowing solder paste 12 to have constant thickness. It is appropriate that the depth of the groove 11 is about 1/2 to about 1/3 of the height of solder projecting electrodes 21 of a semiconductor device 20 (see Figure 3 ) for the following reason. According to the above-mentioned Coffin·Manson connection fatigue life expression, in order to increase the height of the connecting portions, the solder paste 12 may be transferred as much as possible. Considering the relationship between the amount of a solder residue remaining on the wiring board and the surface tension thereof, the depth of the groove 11 is preferably at least about 1/3 of the height of the solder projecting electrodes 21 . When the transfer amount is excessive, there is a possibility that the solder paste 12 may adhere to a semiconductor device 20 to form a bridge 23 between the solder projecting electrodes 21, as shown in Figure 3A . When such a bridge 23 is formed, as shown in Figure 3B, the bridge 23 reflows together with the solder projecting electrodes 21 when the semiconductor device 20 is mounted and heated. Then, the molten solder is integrated due to its surface tension, forming a solder projecting electrode 24 with a large diameter. In order to prevent such inconvenience, the transfer amount should be set at about 1/2 of the height of the solder projecting electrodes 21 , i.e., at a value not exceeding an equator surface of the solder projecting electrodes 21 . In Embodiment 1, the depth of the groove 11 of the jig 10 is set to be about 1/2 to about 1/3 of the height of the solder projecting electrodes 21 , whereby the transfer amount is set to be about 1/2 to about 1/3 of the height of the solder projecting electrodes 21 . Next, referring to Figures 4A and 4B , the step of transferring solder paste using the jig 10 will be described in detail. First, the solder paste 12 is put in the groove 11 of the jig 10 , and the surface of the solder paste 12 is flattened out by a squeegee or the like (not shown) so that the groove 11 is filled with the solder paste 12 . Thereafter, the semiconductor device 20 is pressed against the jig 10 (see Figure 4A ), whereby the solder paste 12 is allowed to adhere to the tip ends of the solder projecting electrodes 21 . The semiconductor device 20 is lifted up. Thus, the step of transferring the solder paste 12 is completed (see Figure 4B ). Figures 5A and 5B show another example of a solder paste transfer jig. A jig 10' is in the shape of a disk which has a circular groove 11' in a center portion. A projection 13 whose surface is as high as the surface of the jig 10' is disposed in a center portion of the circular groove 11' . The depth of the groove 11' is set to be about 1/2 to about 1/3 of the height of the solder projecting electrodes 21 in the same way as the above. Figure 6 shows a jig for making the amount of the solder residue on the wiring board uniform at Step 3. A jig 40 is composed of a solder-wettable metal plate 41 in the shape of a rectangular solid provided with pins 42 at four corners. The pins 42 have the function of keeping a constant gap with respect to a wiring board 30 (see Figure 7 ). Next, the step of making a solder residue 31 on the wiring board 30 uniform by using the jig 40 will be described with reference to Figures 7A through 7C . As shown in Figure 7A , the jig 40 is pressed against the wiring board 30 from which a defective semiconductor device has been removed, with the pins 42 facing downward. In this condition, the jig 40 is heated. The solder residue 31 on the wiring substrate 30 melts and spreads over the metal plate 41 (see Figure 7B ). In Figure 7B , for simplicity, the solder residue spreading over the metal plate 41 is not shown. Due to the surface tension of the solder, the solder stops spreading over the jig 40 , with a predetermined amount of solder remaining on lands 33 for connection of the wiring board 30 . At this time, if required, a flux or the like may be coated on the jig 40 or the wiring board 30 . Thereafter, the jig 40 is removed, and,a uniform amount of solder 32 remains on the lands 33 of the wiring board 30 (see Figure 7C). In order to make the solder residue 31 uniform by utilizing the surface tension of the solder, the height of the pins 42 is important. It has been confirmed that the height of the pins 42 is preferably about 1/4 to about 1/10 of the diameter of the lands 33 . As a semiconductor device to which the present invention is applied, a semiconductor package having solder projecting electrodes in an area array is used. Embodiment 2 Figures 8A through 8C show a method for producing an electronic circuit device in Embodiment 2 according to the present invention. Embodiment 2 is characterized by a method for making a solder residue uniform during a repair step. In Embodiment 2, the solder residue is made uniform by using a soldering iron. The step of making the solder residue uniform will be described in detail. First, as shown in Figure 8A , a soldering iron 50 is positioned above a wiring board 30. More specifically, the soldering iron 50 is positioned at such a height that its tip end can come into contact with the solder residue 31 . Next, as shown in Figure 8B , the heated soldering iron 50 is moved in the horizontal direction at a constant speed. Herein, the soldering iron 50 is desirably coated with a flux. When the soldering iron 50 is moved, the solder residue 31 is heated by the soldering iron 50 to melt, thereby spreading over the soldering iron 50 and lands 33 . In Figure 8B , for simplicity, the solder spreading over the soldering iron 50 is not shown. However, due to the surface tension of the solder, the solder stops spreading with a predetermined amount of solder remaining on the lands 33 of the wiring board 30 (see Figure 8C ). It was confirmed that the soldering iron 50 is preferably moved at such a speed as to pass by the lands 33 at about 1/10 to about 1 second. Although the soldering iron 50 is manually moved in the present embodiment, it may be automatically moved by an apparatus (described later) according to the present invention . As described above, in the case where the solder residue 31 is scraped by manually moving the soldering iron 50 to be shaped, it is required to consider a land diameter L D . More specifically, depending upon the size of the land diameter L D of the wiring board 30, such a shaping method causes variation or the like of the solder residue 31 , resulting in an undesirable state. A preferable range of the land diameter L D will be described below. Referring to Figures 9A and 9B , a solder projecting electrode size H D of a semiconductor device 20 , a solder projecting electrode pitch H P thereof, and a land pitch L P of a wiring board 30 (same as the solder projecting electrode pitch H P ) will be described. The solder projecting electrode size H D is about 0.2 mm to about 0.8 mm, and the solder projecting electrode pitch H P and the land pitch L P of the wiring board 30 are respectively about 0.5 mm to about 1.27 mm. An experiment was conducted using the semiconductor device 20 and the wiring board 30 in the above-mentioned ranges. Figure 10 shows the result. The preferable height of the solder residue after being shaped varies depending upon the land diameter L D (for example, as shown in Figure 10, the preferable height of the solder residue in the case of the land diameter L D of about 150 µm is about 55 µm to about 90 µm; and the preferable height of the solder residue in the case of the land diameter L D of about 250 µm is about 60 µm to about 100 µm). According to the experimental result, the preferable land diameter L D was confirmed to be in the range of about 150 µm to about 550 µm. With the wiring board 30 having a land diameter L D of about 800 µm or more, it is not preferable to shape the solder residue 31 by scraping it with a soldering iron. It was confirmed that dispensing solder paste is preferable in this case. When the land diameter L D exceeds about 1 mm, the minimum value of the distribution of the solder residue 31 tends to decrease and the variation thereof tends to increase. Thus, it was confirmed that the land diameter exceeding about 1 mm is not preferable. Embodiment 3 Embodiment 1 adopts a process for transferring solder paste to the solder projecting electrodes 21 of the new semiconductor device 20 , thereby increasing the height of the connecting portions. However, depending upon the kinds of products (i.e., the kinds of the semiconductor device 20 and the wiring board 30 to be connected), such a transfer step is not required. More specifically, a repair method omitting Step S5 (transfer step) in Embodiment 1 can be performed. According to the experimental results of the inventors of the present invention, for example, in the case where the semiconductor device 20 having a land pitch L P of about 0.6 mm is mounted on the wiring board 30 having a land diameter L D of about 200 µm, the height of the printed solder (i.e., height of the solder residue after being shaped) is about 70 µm. Therefore, as is understood from Figure 10 , it was confirmed that a reliable repair step can be performed even without performing Step S5. The following Table 1 shows a test result of temperature cycle reliability evaluation of a semiconductor device repaired in accordance with the method of the present invention and of a semiconductor device which is not defective. The land pitch of the semiconductor device used herein was 0.6 mm. It was confirmed that the repaired semiconductor device has the same reliability as that of the device which is not defective. The following Table 2 shows a comparison result of the occurrence of disconnection in a semiconductor device which has been repaired in accordance with the present invention and a semiconductor device which has been repaired by the conventional repair method (i.e., a semiconductor device which has been repaired by completely removing a solder residue without transferring solder paste). The land pitch of the semiconductor device used herein was 0.8 mm. Temperature cycle 100 200 300 400 500 Method of Present Invention Good Good Good Good Good Conventional method 4/5poor 5/5 poor As is understood from Table 2, according to the method of the present invention, a connection failure which would occur according to the conventional method can be completely eliminated. The experiment according to the present invention was conducted as follows: The wiring board 30 including the lands with a land diameter L D of about 0.3 mm was used. The lands were coated with about 2 to about 3 µm of electroless Ni plating and flush Au plating. As the IR lamp, a near-infrared lamp with a power of 225 watts made of tungsten filaments produced by Phoenix Elect. was used. Light emitted by the IR lamp was condensed by a parabolic mirror so as to have a focal point in the vicinity of the surface of the wiring board and the semiconductor device. The semiconductor device was heated to 250°C by the IR lamp in about one minute. Solder paste (RMA501-88-3-30, produced by Alphametals Co., Ltd.) having a viscosity of 300,000 centipoises (cP) was used in the experiment, which was obtained by kneading minute solder powders (average size: 30 µm) of eutectic solder (Sn 63% and Pb 37%) with a RMA type flux. The solder paste was placed in the jig 10 shown in Figures 2A and 2B which was obtained by forming a groove with a depth of about 150 µm in an SUS 301 plate (thickness: about 6 mm) by milling. The solder paste was squeegeed with a glass plate (7027, produced by Corning) having a thickness of about 1.1 mm so as to be flattened in the groove. The semiconductor device 20 was attached to a vacuum pincette (392, produced by Hakko Kinzoku Co., Ltd.). The semiconductor device 20 was manually pressed against the solder paste flattened to a thickness of about 50 µm. The semiconductor device 20 was allowed to stand for at least 2 minutes so as to be intimately contacted by the solder paste. The solder residue was removed by using the jig 40 in which four female threads (ISO·M2 threads) are provided on a brass plate (thickness: about 1.0 mm) so as to allow tip ends thereof to project from the brass plate by about 0.1 mm to form pins 42 (see Figure 6 ). The brass plate was thinly soldered by a dip soldering method. The soldered brass plate was further coated with a flux (RF-350-RMA, produced by Nihon Alumit Co., Ltd.) by a brush. The jig 40 was placed over the solder residue and heated by the IR lamp at about 1225 watts/min. The solder residue assumed a shape of a hill such as shown in Figures 7C and 8C with a thickness of about 50 to about 70 µm. Instead of using the jig 40 , a flux (RF-350-RMA) was coated onto the solder residue by a brush, and the solder residue was rubbed with a soldering iron (926M, produced by Hakko Kinzoku Co., Ltd.) having an iron tip (900M-TI-C) at 300°C to 320°C. In this case, the solder residue similar to the above was also obtained. The semiconductor device 20 to which the solder paste has been transferred was attached to a vacuum pincette and placed on the wiring board 30 by visual alignment marks. The semiconductor device 20 placed on the wiring board 30 was heated by the IR lamp so as to allow the solder residue, the solder projecting electrodes 21 and the transferred solder paste to melt. Thus, the semiconductor device 20 was connected to the wiring board 30. When the solder melts, it returns to a normal position due to the surface tension even if it is displaced (self-alignment effect). Therefore, in the case of lands with a diameter of about 0.3 mm, the lands can be adjusted by up to about ±0.15 mm. Because of this, it was confirmed that the semiconductor device 20 was able to be mounted on the wiring board 30 by visual alignment. Embodiment 4 Figure 11 shows an apparatus for producing an electronic circuit device in Embodiment 4 according to the present invention. The apparatus includes a substrate stage 130 which holds a wiring board 30 and is capable of precisely moving for alignment, a solder paste transfer jig 10 , a heating lamp 160 (IR lamp) for removing a defective semiconductor device 20' , making a solder residue uniform, and mounting a new semiconductor device 20 , a pickup tool 170 for holding and moving the semiconductor device 20 , an optical system 190 for alignment, and a monitor TV 191 for confirming alignment. The pickup tool 170 , the heating lamp 160 , and the optical system 190 for alignment can be moved horizontally. They can be moved, for example, by a linear motor (not shown). In the above-mentioned apparatus, during the repair step, the lamp 160 is moved onto the defective semiconductor device 20' . The lamp 160 is lit up to heat the defective semiconductor device 20'. As a result, the solder of the connecting portions is heated to melt, which enables the defective semiconductor device 20' to be removed. Next, the pickup tool 170 is moved to be positioned above the defective semiconductor device 20' and attaches to it, whereby the defective semiconductor device 20' is removed. The above-mentioned jig 40 is placed over the solder residue 31 remaining on the wiring board 30 and heated by the lamp 160 , whereby the solder residue is made uniform. Next, the new semiconductor device 20 is attached to the pickup tool 170 . At this time, solder paste 12 is placed in the groove 11 of the solder paste transfer jig 10 and flattened with a squeegee or the like. The semiconductor device 20 attached to the pickup tool 170 is pressed against the groove 11 of the solder paste transfer jig 10 filled with the solder paste 12, whereby the solder paste 12 is transferred to tip ends of the solder projecting electrodes 21 of the semiconductor device 20 . Then, the pickup tool 170 is moved to be positioned above the wiring board 30 , attaching to the semiconductor device 20 . Using the optical system 190 for alignment and the monitor TV 191 for confirming alignment, the substrate stage 130 is moved so as to align the wiring board 30 with the semiconductor device 20 , whereby the semiconductor device 20 is mounted on the wiring board 30 . Thereafter, the semiconductor device 20 is heated by the lamp 160 , thereby heating and melting the solder to connect the semiconductor device 20 with the wiring board 30 . Embodiment 5 Figure 12 shows an apparatus for producing an electronic circuit device in Embodiment 5 according to the present invention. This apparatus is different from that in Embodiment 4 only in that a soldering iron 50 and a movement mechanism 51 for horizontally moving the soldering iron 50 are provided. Therefore, like reference numerals refer to like parts. The description of the parts which have been described in Embodiment 4 will be omitted here. The movement mechanism 51 is operated, for example, by a linear motor. In the apparatus of the present embodiment, during the repair step, the lamp 160 is moved to be positioned above the defective semiconductor device 20' and heats it, whereby the solder of the connecting portions is heated to melt. The pickup tool 170 is moved to be positioned above the defective semiconductor device 20' and attaches to it, whereby the defective semiconductor device 20' is removed. Then, a soldering iron 50 is brought into contact with the wiring board 30 . The movement mechanism 51 is operated under this condition, whereby the solder residue 31 on the wiring board 30 is made uniform. Next, the new semiconductor device 20 is attached to the pickup tool 170 . The semiconductor device 20 is pressed against the groove 11 of the solder paste transfer jig 10 filled with solder paste 12 . Thus, the solder paste 12 is transferred to tip ends of the solder projecting electrodes 21 of the semiconductor device 20 . Hereinafter, in the same way as in the above, the wiring board 30 is aligned with the semiconductor device 20 , whereby the semiconductor device 20 is mounted on the wiring board 30 . Then, the semiconductor device 20 is heated with the lamp 160 so as to be connected with the wiring board 30 . In the apparatus in Embodiment 5, it is critical that the movement mechanism 51 of the soldering iron 50 is in contact with the soldering iron 50 . However, since the margin of the movement speed is large, the soldering iron 50 may be manually moved without using the movement mechanism 51 . In this case, the apparatus may have the same structure as that in Embodiment 4. According to the present invention, only a uniform amount of solder residue is left on a wiring board in accordance with the surface tension thereof, and a new semiconductor device is provided with solder paste. Therefore, a sufficient amount of solder can be secured for a repaired semiconductor device. As is understood from the Coffin·Manson connection fatigue life expression, this increases the height H j of the connecting portions and decreases the maximum strain γ max in the connecting portions, so that a connection failure (i.e., disconnection) does not occur. Thus, the reliability of a semiconductor device can be improved. Depending upon the kinds of products (i.e., kinds of a semiconductor device and a wiring board to be connected), the transfer step as described above is not required. According to the present invention, the solder residue remaining on the wiring board from which a defective semiconductor device has been removed is left on purpose, instead of being completely removed, whereby a sufficient amount of solder is secured. In this case, the solder residue remaining on the wiring board from which the defective semiconductor device has been removed is left in a nonuniform amount. However, by utilizing the surface tension of the molten solder, the solder residue can be controlled to a uniform amount and a uniform height. This control can be easily performed by heating the solder residue, using the jig for making the solder residue uniform according to the present invention. According to the transfer method, a uniform amount of solder paste can be easily supplied to the semiconductor device, which is convenient. More specifically, the use of the above-mentioned jig for transferring brazing metal paste facilitates the transfer of solder paste. In accordance with the Coffin·Manson connection fatigue life expression, in order to increase the height of the connecting portions, solder paste should be transferred as much as possible. Considering the relationship between the amount of the solder residue remaining on the wiring board and the surface tension thereof, the transfer amount is preferably about 1/3 or more of the height of the solder projecting electrodes. If too much amount of solder paste is transferred, a bridge may be formed between the solder projecting electrodes. When such a bridge is formed, the molten solder is integrated due to the surface tension thereof to form a solder projecting electrode having a large diameter. In order to prevent such a solder projecting electrode from being formed, the transfer amount should be limited to about 1/2 of the height of the solder projecting electrodes, i.e., a value not exceeding an equator surface of the solder projecting electrodes. The depth of the groove of the jig for transferring brazing metal paste is prescribed to be about 1/2 to about 1/3 of the height of the solder projecting electrodes, whereby the transfer amount is prescribed to be about 1/2 to about 1/3 of the height of the solder projecting electrodes. A heating device for re-connecting a new semiconductor device to the wiring board should not involve any excessive external force. More specifically, without an excessive external force, the semiconductor device and the wiring board which have been aligned with each other will not be shifted in position. Thus, the repair step can be more easily and efficiently performed. Because of this, according to the present invention, a lamp which does not involve an external force is used. As the lamp, a near-infrared lamp (IR lamp) is preferably used for the following reason. In a semiconductor device, Si is used as a material of choice for a circuit board. Si transmits light in a near-infrared region (wavelength: about 1 to about 5 µm). When the light with a wavelength of about 1 to about 5 µm is used, the light passes through Si to directly heat solder projecting electrodes and solder paste with efficiency. Thus, the IR lamp which is capable of emitting light with a wavelength of about 1 to about 5 µm is preferably used. The use of eutectic solder or eutectic solder with a slight amount of additive added thereto as brazing metal can improve solder strength.

Claims: A method for producing an electronic circuit device including a repair step during a process of producing an electronic circuit device by aligning projecting electrodes (21) made of brazing metal and formed on one principal plane of a semiconductor device (20) with a substrate (30) for mounting a semiconductor device having lands (33) for connection corresponding to the projecting electrodes (21), and melting the projecting electrodes (21) by heating, thereby mounting the semiconductor device (20) on the substrate (30), the repair step including, in a case where the semiconductor device (20') once mounted is defective, removing the defective semiconductor device (20') from the substrate (30) and mounting a new semiconductor device (20) on the substrate (30), the repair step comprising the steps of: aligning the new semiconductor device (20) with the substrate (30); and melting the brazing metal residue (32) which remains on the lands (33) and projecting electrodes (21) of the new semiconductor device (20) by heating, thereby connecting the new semiconductor device (20) to the substrate (30), wherein the repair step is characterized by removing an excessive residue (31) of a brazing metal residue remaining on the lands (33) of the substrate (30) from which the defective semiconductor device (20') has been removed and leaving a uniform amount of the brazing metal residue (32) on the lands (33) by means of a heating iron (50), which moves at a predetermined speed while keeping in contact with the brazing metal residue or by a jig (40) for making a solder residue (31) uniform, including a plurality of pins (42) on an outer peripheral portion (41) thereof. The method for producing an electronic circuit device according to claim 1, wherein the uniform amount of the brazing metal residue (32) remaining on the lands (33) has a height corresponding to surface tension of the brazing metal residue. The method for producing an electronic circuit device according to claim 1, wherein the brazing metal residue (32) which is made uniform and remains on the lands (33) and the projecting electrodes (21) of the new semiconductor device (20) are heated to melt with light emitted by a lamp (160). The method for producing an electronic circuit device according to claim 3, wherein a near-infrared lamp is used as the lamp (160). The method for producing an electronic circuit device according to claim 1, wherein the step of removing an excessive residue (31) of a brazing metal residue remaining on the lands of the substrate (30) from which the defective semiconductor device (20) has been removed and leaving a uniform amount of the brazing metal residue on the lands (33) is performed by placing the jig (40) in form of a plate made of solder-wettable metal over the brazing metal residue on the lands (33) with a predetermined gap kept therebetween and heating the plate, said gap being provided by said plurality of pins (42). The method for producing an electronic circuit device according to claim 5, wherein the predetermined gap is about 1/4 to about 1/10 of a land diameter (LD) of the lands (33). The method for producing an electronic circuit device according to claim 1, wherein, in a case where the land diameter (LD) of the lands (33) is about 150 µm to about 800 µm, the heating iron (50) is moved manually. A method for producing an electronic circuit device according to claim 1, wherein, in a case where the land diameter (LD) of the lands (33) is about 150 µm to about 550 µm, the heating iron (50) is moved manually. The method for producing an electronic circuit device according to claim 1, wherein the brazing metal is eutectic solder or solder whose strength is increased by adding a slight amount of additive to eutectic solder. The method for producing an electronic circuit device according to claim 1, wherein the semiconductor device is a semiconductor package having projecting electrodes in an area-array. The method for producing an electronic circuit device according to one of- claims 1 and 5-10, wherein the repair step additionally comprises supplying brazing metal paste (22) to tip ends of projecting electrodes (21) of the new semiconductor device (20); and melting also the brazing metal paste (22) by heating, to connect the new semiconductor device (20) to the substrate (30). The method for producing an electronic circuit device according to claim 11, wherein the step of supplying the brazing metal paste (22) to the tip ends of the projecting electrodes (21) is performed by a transfer method. The method for producing an electronic circuit device according to claim 11, wherein the brazing metal paste (22) is obtained by dispersing metal powders which are the same kind as that of brazing metal in a binder. The method for producing an electronic circuit device according to claim 11. wherein the projecting electrodes of the new semiconductor device (20) and the brazing metal paste are heated to melt with light emitted by a lamp (160). The method for producing an electronic circuit device according to claim 14, wherein a near-infrared lamp is used as the lamp (160). An apparatus for producing an electronic circuit device by aligning projecting electrodes (21) made of brazing metal and formed on one principal plane of a semiconductor device (20) with a substrate (30) for mounting a semiconductor device having lands (33) for connection corresponding to the projecting electrodes (21), and melting the projecting electrodes (21) by heating, thereby mounting the semiconductor device (20) on the substrate (30), wherein, in a case where the semiconductor device (20') once mounted is defective, the apparatus is designated to remove the defective semiconductor device (20') from the substrate (30) and to mount a new semiconductor device (20) on the substrate (30), the apparatus comprising: a holder (130) holding the substrate (30); a holder (170) holding the defective semiconductor device (20') or the new semiconductor device (20); an alignment unit (130; 170) aligning the substrate (30) with the defective semiconductor device (20') or the new semiconductor device (20); and a heating unit melting the projecting electrodes (21) of the aligned new semiconductor device (20) by heating, thereby connecting the new semiconductor device to the substrate; said apparatus being characterized by a unit removing an excessive residue (31) of a brazing metal residue remaining on connecting portions (33) of the substrate (30) from which the defective semiconductor device (20') has been removed and leaving on the connecting portions (33) a uniform amount of the brazing metal residue having a height corresponding to surface tension of the brazing metal residue (32) on the connecting portions (33) by means of a heating iron (50) which moves at a predetermined speed while keeping in contact with the brazing metal residue or by a jig (40) for making a solder residue uniform including a plurality of pins (42) on an outer peripheral portion (41) thereof. The apparatus for producing an electronic circuit device according to claim 16, wherein the heating unit is a near-infrared lamp (160). The apparatus for producing an electronic circuit device according to ond of claims 16 and 17, wherein said apparatus further comprises a jig (10; 10') for transferring brazing metal paste to tip ends of the projecting electrodes (21) of the new semiconductor device (20), a groove (11) in a shape of an expanding slot or a circular concave groove (11') being formed in a center portion of the jig (10'), and a depth of the groove being prescribed to be about 1/3 to about 1/2 of a height of the projecting electrodes (21) of the semiconductor device (20).

Inventors: SATO TOMOTOSHI, SATO, TOMOTOSHI
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1997
Main classification: H01L21
IPC codes: H05K3, H01L21, B23K1