JP5500117B2 - Al-Cu bonding ribbon and manufacturing method thereof - Google Patents

Description

  The present invention relates to a bonding ribbon used as a connection material for a semiconductor package or the like, and more particularly to an Al—Cu bonding ribbon having a two-layer structure in which two kinds of materials of Al and Cu are clad.

  Conventionally, bonding by an Au wire has been mainly used for the connection of a semiconductor package due to metallic characteristics such as high electrical conductivity and suppression of surface oxidation. However, in the case of bonding with an Au wire, when a relatively large current flows, a plurality of Au wires are often connected to avoid a short circuit due to an overcurrent. Since a large amount of Au material must be used, this is a cause of high cost.

  In addition, IC chips mounted on semiconductor packages that require high functions often have a laminated structure, but in recent years, there has been a demand for lighter, thinner, and smaller devices by downsizing IC chips. For this reason, since the space for connection in the IC chip is also limited, improvement in the accuracy of wire bonding is required.

  However, in the connection pattern according to the design of the IC chip, for example, when the wiring space between adjacent wires is a distance of about one Au wire, or in order to realize a low loop, it is greatly increased from the position closest to the 1st bonding position. In some cases, a curved loop shape must be taken. Under such circumstances, it is necessary to perform process design such as composition and annealing conditions of the Au wire itself.

  In order to cope with such a situation, for example, Patent Document 1 (Japanese Patent Laid-Open No. 2008-140983) proposes an improvement of a bonding apparatus that can cope with a fine pitch, and wire bonding in which the stage and its peripheral members are improved. An apparatus is described. However, in order to implement this technique, wire followability that can follow the operation of the capillary is indispensable. If the flexibility of the wire itself is insufficient, short-circuit failure is likely to occur due to contact between adjacent wires.

  Further, matching and selection with a jig are important to reduce non-bonding defects at the time of wire bonding. However, in order to solve this problem, Patent Document 2 (Japanese Patent Application Laid-Open No. 2007-095963) discloses the inside of a capillary. The idea of designing the hole diameter and the chamfer diameter according to the wire diameter is shown. Thus, in order to realize a fine pitch, not only thinning of the wire but also optimization of the apparatus and the jig is required, and much time and labor are required for the design and the like.

  Furthermore, since Au wires are expensive, they tend to be thinned to reduce costs. Advances in thinning technology in recent years have been remarkable, and it has become possible to accurately realize the wire diameter according to requirements. However, when resin-sealing Au wires bonded at high density, it is necessary to control the injection direction and flow rate with high accuracy, as well as selecting the resin. In some cases, productivity is significantly reduced.

  In order to deal with such a problem, for example, Patent Document 3 (Japanese Patent Application Laid-Open No. 2004-155857) discloses an epoxy resin composition in which the occurrence of electrical property defects such as deformation of the Au wire and defective disconnection leakage is small, and the resin. An electronic component device sealed with is described. However, as a premise of the technique of Patent Document 3, sufficient strength of the Au wire is required for the resin sealing, and even if it is a high strength Au wire, if the interval between adjacent wires is narrow, a short circuit occurs at the time of resin injection. Cases are likely to occur.

  In recent years, instead of a bonding wire having such a problem, a bonding ribbon has been proposed as a connection material as described in, for example, Japanese Patent Application Laid-Open No. 2006-196629. Bonding ribbons are widely used mainly in power devices because they have the advantage of high resistance to stress from the lateral direction during resin injection because bonding between flat surfaces is realized unlike wires. . Patent Document 5 (Japanese Patent Laid-Open No. 2004-336043) describes an Al—Cu bonding ribbon, but only describes the superiority due to the difference in shape between the wire and the ribbon.

  The bonding method using the bonding ribbon uses an ultrasonic wire bonding method. By applying a load and ultrasonic vibration to the bonding ribbon, an oxide film of about several nanometers formed naturally on the surface of the bonding ribbon. To bond metal atoms on the bonding ribbon by exposing them and bonding them between atoms while gradually increasing the new surfaces that adhere to each other by generating plastic flow at the interface between the bonding pad and bonding ribbon, such as aluminum or nickel. It is.

JP 2008-140983 A JP 2007-095963 A JP 2004-155857 A JP 2006-196629 A JP 2004-336043 A

  As described above, in the conventional bonding ribbon, since the bonding ribbon has high rigidity between the 1st bonding and the 2nd bonding, so-called bonding non-bonding that is repelled from bending and unbonded easily occurs. Also, when the bonding ribbon is unwound from the end of the first bonding to the 2nd bonding position, the bonding ribbon may generate a strong friction with the inner wall of the bonding tool. Non-delivery occurred.

  Furthermore, as described above, there has been a problem that the bonding ribbon surface becomes wrinkled due to excessive rubbing between the tip of the bonding tool and the bonding ribbon in the loop formation process after the first bonding. The wrinkles on the surface cause various problems, but in particular, the new surface of a metal surface such as Cu is partially exposed, and eventually the oxidation of the bonding ribbon proceeds. In particular, for Al-Cu bonding ribbons, the bonding strength between Al and Cu is often insufficient, and there is a problem that peeling is likely to occur at the bonding interface between Al and Cu in the loop formation process after the first bonding. there were.

  The present invention has been made in view of such problems in the conventional bonding ribbon. By providing flexibility to the Al-Cu bonding ribbon, peeling at the bonding interface between Al and Cu in the loop formation process is achieved. An object of the present invention is to provide an Al—Cu bonding ribbon and a method of manufacturing the same that can prevent bonding non-bonding and surface wrinkling due to repulsion against bending and unsuccessful feeding.

  In order to solve the above-described problems of the conventional Al-Cu bonding ribbon, the present inventor eliminates peeling at the bonding interface between Al and Cu, and has excellent looping properties without bending repulsion and feeding failure. As a result of intensive studies on Al-Cu bonding ribbons that can be wired in a limited area with downsizing of IC chips, the result of cold rolling when joining Al and Cu materials The present inventors have found that it is effective to relax the stress by heat treatment and impart flexibility to the Al—Cu bonding ribbon, and have reached the present invention.

  That is, in order to solve the above problems, the Al—Cu bonding ribbon provided by the present invention is a two-layer bonding ribbon in which an Al material and a Cu material are joined, and the hardness of the Al material layer is 20 to 30 Hv and Cu. The material layer has a hardness of 40 to 50 Hv. The Al—Cu bonding ribbon of the present invention is characterized in that it is heat-treated at a temperature of 250 to 350 ° C. after the cold bonding of the Al material and the Cu material.

The method for manufacturing an Al—Cu bonding ribbon provided by the present invention is a method for manufacturing a bonding ribbon having a two-layer structure in which an Al material and a Cu material are bonded, and the surfaces to be bonded of the Al material and the Cu material are polished. Then, after joining both polished surfaces together by cold rolling, heat treatment is performed at a temperature of 250 to 350 ° C., so that the hardness of the Al material layer is in the range of 20 to 30 Hv and the hardness of the Cu material layer is 40 to 50 Hv. It is characterized by being in the range .

  In the method for producing an Al—Cu bonding ribbon of the present invention, it is preferable that the surfaces to be joined of the Al material and the Cu material are polished so that the surface roughness is less than 5 μm in Rmax. In addition, the polished Al material and Cu material may be cold-rolled to a predetermined thickness, joined, slit processed to a predetermined width, and then heat-treated in an inert gas atmosphere for 1 hour or longer. preferable.

  According to the present invention, it is possible not only to eliminate peeling at the bonding interface between Al and Cu in the loop formation process, but also to relieve the residual stress by heat treatment after bonding by cold rolling, thereby reducing the Al-Cu bonding ribbon. Therefore, it is possible to eliminate bonding non-sticking due to repulsion against bending and unsuccessful feeding, and to prevent surface wrinkling.

It is a schematic sectional drawing which shows the loop formation process in the semiconductor package which uses an Al-Cu bonding ribbon.

  The Al—Cu bonding ribbon of the present invention is a two-layer structure formed by bonding an Al material and a Cu material, that is, a bonding ribbon composed of an Al material layer and a Cu material layer. The Al material used for joining is not particularly limited in composition, and a wide range of Al alloys such as high-purity Al and Al—Ni can be used. Moreover, although it does not specifically limit about a copper material, It is desirable to use 99.99% or more pure copper from a viewpoint of maintaining desired electroconductivity.

  In the Al-Cu bonding ribbon of the present invention having the above two-layer structure, the residual stress generated by rolling is alleviated by heat treatment in a temperature range of 250 to 350 ° C. after joining the Al material and the Cu material by cold rolling. In addition to being removed, the crystal structure is made uniform, the hardness of the Al material layer and the Cu material layer having a two-layer structure is lowered, and the flexibility is improved. Specifically, it is necessary to adjust the hardness (Vickers hardness) of the Al material layer and the Cu material layer to be in the range of 20 to 30 Hv for the Al material layer and in the range of 40 to 50 Hv for the Cu material layer. is there.

  When the hardness of the Al material layer exceeds 30 Hv and / or the hardness of the Cu material layer exceeds 50 Hv, bonding non-bonding and surface wrinkling increase rapidly, and at the bonding interface between Al and Cu in the loop formation process. Peeling easily occurs. The lower the hardness of the Al material layer and the Cu material layer, the better. However, even if the hardness of the Al material layer is less than 20 Hv and / or the hardness of the Cu material layer is less than 40 Hv, the above-described flexibility improvement effect is achieved. This is not preferable because further improvement of the thickness is reduced and bonding non-bonding is likely to occur.

  Next, the method for producing the Al—Cu bonding ribbon of the present invention will be specifically described. First, with respect to the Al material, at least one surface to be joined is polished with an abrasive. By this surface polishing, the oxide film formed on the surface of the Al material can be removed to expose the new surface. On the other hand, the surface of the Cu material is similarly polished to remove the oxide film on the surface and expose the new surface. Since the surface area joined by this surface polishing is increased, the joining of the Al material and the Cu material can be strengthened by rolling and joining the surfaces having the increased surface area.

  In the surface polishing step, polishing is preferably performed so that the surface roughness of the Al material and the Cu material is Rmax of 5 μm or less. When the surface roughness of both or one of the polished Al material and Cu material is larger than 5 μm in Rmax, it is possible to join the Al material and the Cu material in the next cold rolling process. Since the bonding strength is not sufficient, the obtained bonding ribbon is not preferable because peeling easily occurs at the bonding interface between Al and Cu in the loop formation process.

  The Al material and the Cu material whose surfaces are polished as described above are quickly supplied to the next cold rolling process, and rolled to a predetermined thickness at room temperature using a roll rolling machine, whereby the Al material and the Cu material are It can be firmly joined. In order to avoid surface oxidation of the Al material and the Cu material, it is desirable to perform the steps from the surface polishing to the cold bonding as quickly as possible. The thickness after rolling, that is, the thickness of the Al—Cu bonding material can be changed according to the target Al—Cu bonding ribbon. The thicknesses of the Al material layer and the Cu material layer of the Al-Cu bonding ribbon can be changed by changing the thicknesses of the Al material and the Cu material to be used.

  The Al—Cu bonding member obtained in the cold rolling step is slitted to a width used for bonding using a slitter or the like, and then heat-treated in a temperature range of 250 to 350 ° C. In general, the Cu material can be subjected to annealing at a temperature of 200 ° C. or higher to remove the inherent processing strain. And if it heat-processes on the said 250-350 degreeC temperature conditions, while the crystal structure of Cu material will be homogenized, while spreading | diffusion to the Al surface of Cu is accelerated | stimulated, one layer of Al material and Cu material Strong bonding is realized.

  In addition, by adjusting the temperature and time during the heat treatment, the relaxation of residual stress and the homogenization of the crystal structure are promoted as described above, and the hardness of the Al material layer and the Cu material layer forming the two-layer structure are bonded. The hardness can be lowered to an optimum hardness as a material, and excellent flexibility can be imparted to the Al—Cu bonding ribbon. The heat treatment time is not particularly limited, but is preferably 1 hour or longer in order to obtain a necessary effect. The heat treatment is preferably performed in an inert gas atmosphere such as nitrogen in order to suppress surface oxidation of the bonding ribbon.

  When the heat treatment temperature is less than 250 ° C., it is difficult to adjust the hardness of the Al material layer to a range of 20 to 30 Hv and the hardness of the Cu material layer to a range of 40 to 50 Hv, which gives sufficient flexibility to the Al—Cu bonding ribbon. I can't. For this reason, non-bonding due to bending repulsion or unsuccessful feeding and surface wrinkling occur, and peeling at the bonding interface between Al and Cu is likely to occur during the loop formation process. On the contrary, if the temperature during the heat treatment exceeds 350 ° C., the hardness of the Al material layer and the Cu material layer becomes too low and bonding non-bonding is likely to occur.

  The Al—Cu bonding ribbon of the present invention thus obtained has both the lightness of Al and the conductivity of Cu, and at the same time has excellent flexibility and interfacial bonding strength. Therefore, not only can the peeling at the bonding interface between Al and Cu be eliminated during the loop formation process, but it can also be suitably used as, for example, a bonding material for forming a loop shape as shown in FIG.

  That is, the Al-Cu bonding ribbon 1 composed of the Al material layer 1a and the Cu material layer 1b is first bent in the first bonding so that the tip portion is placed over a bonding tool (not shown), and an IC is applied while applying a load. The Al material layer 1 a side is pressure-bonded to the Al plate surface 3 of the chip 2. Thereafter, the bonding ribbon 1 is unwound to the position of 2nd bonding via a bonding tool, and 2nd bonding is performed on the lead frame terminal 4 in the same manner as described above.

  The bonding ribbon of the present invention having excellent flexibility can eliminate peeling at the bonding interface between Al and Cu in the process from the first bonding to the second bonding, and the tip can be easily bent and bonded. Since it is possible to prevent insufficient feeding (insufficient supply) due to friction with the inner wall of the tool, it is possible to eliminate bonding failure.

  An Al-0.005 wt% Ni alloy plate (width 30 mm, thickness 0.32 mm) was prepared as an Al material, and one surface of the non-woven abrasive material (“Scotch Bright” manufactured by Sumitomo 3M Co., Ltd.) # 240 to # 1000). On the other hand, a Cu plate having a purity of 99.99% (width 22 mm, thickness 0.38 mm) was prepared as a Cu material, and one surface thereof was polished using the same nonwoven fabric abrasive as described above. In the above polishing, the Al material and the Cu material were both polished so that the surface roughness was Rmax of 5 μm or less.

  The Al material and Cu material whose one surface was polished as described above were supplied to a roll mill immediately after polishing, and rolled at room temperature so that the width was about 22 mm and the thickness was 0.2 mm. By this cold rolling, an Al material and a Cu material were joined, and a joining member having a two-layer structure of an Al material layer and a Cu material layer was obtained. The thicknesses of the Al material layer and the Cu material layer of this Al—Cu bonding member were both 0.1 mm.

  Next, the Al—Cu bonding member was slit to have a width of 0.2 mm to produce an Al—Cu bonding ribbon material, and then heat treatment was performed in a nitrogen gas atmosphere. As shown in Table 1 below, the heat treatment conditions were changed for each sample, and the heat treatment time was 1 hour for all samples. Thus, the bonding ribbons of Samples 1 to 5 were obtained by performing the heat treatment while changing the heat treatment temperature. Regarding the bonding ribbons of these samples 1 to 5, the hardness (Hv) of the Al material layer and the Cu material layer is shown in Table 1 below.

  For each of the 30 bonding ribbons of the obtained samples 1 to 5, bonding in a loop shape as shown in FIG. 1 was performed, bonding non-bonding, Cu material layer surface wrinkles, interface at the Al-Cu bonding interface The number of peeling defects was examined. For reference, the same evaluation was performed on the sample 6 on which the heat treatment was not performed with the above-described joining member. The obtained results are shown in Table 1 below. The hardness was measured with a Vickers hardness meter, and the number of defects generated was confirmed by visual observation.

  As can be seen from the above results, in Samples 1 to 3 according to the present invention heat-treated at 250 to 350 ° C. × 1 hour, the hardness of the Al material layer is in the range of 20 to 30 Hv and the hardness of the Cu material layer is 40 to 50Hv, no bonding failure, wrinkles on the surface of the Cu material layer, and defects of peeling of the Al—Cu interface did not occur, and normal loop-shaped bonding was possible.

  On the other hand, in the sample 4 of the comparative example in which the heat treatment temperature is 380 ° C., the hardness decrease of the Al material layer and the Cu material layer becomes too large, so that the surface of the Cu material layer does not wrinkle and the Al—Cu interface peeling occurs. Although it did not occur, bonding failure was confirmed in 2 out of 30 wires. Further, in Sample 5 in which the heat treatment temperature was 200 ° C. and Sample 6 in which the heat treatment was not performed, the hardness of the Al material layer and the Cu material layer did not decrease, and bonding failure occurred in 27 of 30 samples, and all 30 samples In addition to wrinkles on the surface of the Cu material layer, peeling of the Al—Cu interface occurred in 25 out of 30.

  In such a bonding ribbon that does not have a sufficient heat treatment effect, strong friction occurs due to contact with the inner wall of the bonding tool. Therefore, when the bonding tool moves from the 1st bonding position to the 2nd bonding position, the bonding ribbon is not fed out as much as necessary. Since it tries to stay inside, it is considered that non-sticking occurs immediately after the first bonding. Al-Cu interface peeling occurred from the 1st bonding to the top of the loop, but there was little diffusion of Al and Cu and the adhesion of the joint surface was weak, and the hardness difference between the Al and Cu surfaces. Therefore, it is considered to occur during loop formation.

DESCRIPTION OF SYMBOLS 1 Bonding ribbon 1a Al material layer 1b Cu material layer 2 IC chip 3 Al plate surface 4 Lead frame terminal

Claims (5)

  A bonding ribbon having a two-layer structure in which an Al material and a Cu material are bonded, wherein the Al material layer has a hardness of 20 to 30 Hv and the Cu material layer has a hardness of 40 to 50 Hv.   2. The Al—Cu bonding ribbon according to claim 1, wherein the Al—Cu bonding ribbon is heat-treated at a temperature of 250 to 350 ° C. after the cold rolling of the Al material and the Cu material. ribbon. A manufacturing method of a bonding ribbon having a two-layer structure in which an Al material and a Cu material are bonded, the surfaces to be bonded of the Al material and the Cu material are polished, and both polished surfaces are joined together by cold rolling, A method for producing an Al-Cu bonding ribbon, characterized in that the hardness of the Al material layer is in the range of 20-30 Hv and the hardness of the Cu material layer is in the range of 40-50 Hv by heat treatment at a temperature of 250-350 ° C. .   4. The method for producing an Al—Cu bonding ribbon according to claim 3, wherein the surfaces of the Al material and the Cu material to be joined are polished so that the surface roughness is Rmax of 5 μm or less.   The polished Al material and Cu material are rolled and joined to a predetermined thickness while being cold-rolled, slitted to a predetermined width, and then heat-treated in an inert gas atmosphere for 1 hour or longer. The manufacturing method of the Al-Cu bonding ribbon of Claim 3 or 4.

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