JP2010272884A - Bonding wire for semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bonding wire which improves forming property and bondability of a ball part, has excellent loop controllability, as well, increases the bonding strength of wedge connection, secures industrial productivity, and mainly includes copper less expensive than a gold wire. <P>SOLUTION: The bonding wire for the semiconductor device includes a core material whose main component is copper and a cover layer of the conductive metal of a composition different from the core material on the core material. The main component of the cover layer is one or more kinds selected from among gold, palladium, platinum, rhodium, silver or nickel, a region having the concentration gradient of at least one of the main component metals and copper in a wire-diameter direction is present inside the cover layer, and the forefront area of an alloy containing at least two kinds of gold, palladium, platinum, rhodium, silver or nickel in the uniform concentration of 0.1 mol% or higher is present on the surface side of the cover layer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a bonding wire for a semiconductor device used for connecting an electrode on a semiconductor element and a wiring of a circuit wiring board (lead frame, substrate, tape).

  Currently, fine wires (bonding wires) having a wire diameter of about 20 to 50 μm are mainly used as bonding wires for bonding between electrodes on semiconductor elements and external terminals. Bonding wires are generally joined by ultrasonic thermocompression bonding, and a general-purpose bonding apparatus, a capillary jig used for connecting the wires through the inside, or the like is used. After the wire tip is heated and melted by arc heat input and a ball is formed by surface tension, this ball portion is pressure bonded to the electrode of the semiconductor element heated within the range of 150 to 300 ° C. Are joined to the external lead side by ultrasonic pressure bonding.

  In recent years, the structure, materials, connection technology, etc. of semiconductor mounting have been diversified rapidly. For example, in the mounting structure, in addition to QFP (Quad Flat Packaging) using the current lead frame, a substrate, polyimide tape, etc. are used. New forms such as BGA (Ball Grid Array) and CSP (Chip Scale Packaging) have been put into practical use, and there is a demand for bonding wires with improved loop characteristics, bondability, mass production usability, and the like. In such wire connection technology, in addition to the current mainstream ball / wedge joints, wedge / wedge joints suitable for narrow pitches join the wires directly at two locations, so it is necessary to improve the jointability of fine wires. It is done.

  The materials to which bonding wires are bonded are diversified, and in addition to conventional Al alloys, Cu suitable for finer wiring has been put to practical use as wiring and electrode materials on silicon substrates. Also, Ag plating, Pd plating, etc. are applied on the lead frame, and Cu wiring is applied on the resin substrate, tape, etc., and a film of a noble metal element such as gold and its alloy is formed thereon. Is often applied. It is required to improve the bondability of the wire and the reliability of the joint according to these various joining partners.

  As a material for the bonding wire, gold of high purity 4N (purity> 99.99 mass%) has been mainly used so far. However, since gold is expensive, a bonding wire of another kind of metal having a low material cost is desired.

  In the demand from the wire bonding technology, it is important to form a ball having good sphericity when forming the ball and obtain a sufficient bonding strength at the bonding portion between the ball portion and the electrode. Further, in order to cope with a decrease in the bonding temperature, thinning of the wire, etc., it is necessary to have a bonding strength, a tensile strength, and the like at a portion where the wire is wedge-connected to the wiring portion on the circuit wiring board.

  In the resin sealing process in which high-viscosity thermosetting epoxy resin is injected at high speed, the wire deforms and comes into contact with the adjacent wire, and further, while narrow pitch, long wire, and thinning are progressing, It is required to suppress even a little wire deformation during resin sealing. Although the deformation can be controlled to some extent by increasing the wire strength, it is difficult to put it to practical use unless problems such as loop control becomes difficult and the strength at the time of bonding decreases.

  As a wire characteristic that satisfies these requirements, loop control in the bonding process is easy, and bondability to the electrode and lead parts has also been improved, suppressing excessive wire deformation in the resin sealing process after bonding. It is desirable to satisfy comprehensive characteristics such as

  In order to increase material costs at low cost, excellent electrical conductivity, ball bonding, wedge bonding, and the like, a bonding wire using copper as a raw material has been developed, and Patent Document 1 is disclosed. However, copper bonding wires have problems in that the bonding strength is reduced due to the oxidation of the wire surface, and that the wire surface is easily corroded when sealed with a resin. This is also the reason why the practical application of copper bonding wires has not progressed.

  Therefore, as a method for preventing the surface oxidation of the copper bonding wire, Patent Document 2 proposes a wire in which copper is coated with a noble metal such as gold, silver, platinum, palladium, nickel, cobalt, chromium, titanium, or a corrosion-resistant metal. Yes. Further, from the viewpoints of ball formability, prevention of deterioration of the plating solution, and the like, Patent Document 3 describes a core material mainly composed of copper, a dissimilar metal layer made of a metal other than copper formed on the core material, and There has been proposed a wire formed on the dissimilar metal layer and having a covering layer structure made of an oxidation-resistant metal having a melting point higher than that of copper.

JP-A-56-21254 JP-A-62-97360 JP 2004-64033 A

  As practical problems of the copper bonding wire, it can be mentioned that the surface of the wire is likely to be oxidized and the bonding strength is likely to be lowered. In addition, due to insufficient wire strength, high-purity copper bonding wires have problems such as large wire deformation during resin sealing, low pull strength at the neck, and difficulty in lowering the loop. It is also a problem that there are few semiconductor products that can be applied. Therefore, as a means for preventing the surface oxidation of the copper bonding wire, it is possible to coat the wire surface with a noble metal or an oxidation resistant metal.

  The present inventors evaluated in consideration of needs such as high density, miniaturization, and thinning of semiconductor packaging, and the conventional multilayer copper wire having a structure in which the surface of the copper bonding wire is covered with a metal different from copper. In the following (hereinafter referred to as conventional multilayer copper wire), it has been found that many practical problems as described later remain.

  Conventionally, when a ball is formed at the tip of a multilayer copper wire, there is a problem that a flat ball deviated from a true sphere is formed, or an unmelted wire remains in the ball. If such an abnormal ball portion is bonded onto the electrode, it may cause problems such as a decrease in bonding strength and chip damage. Further, along with severe loop control such as lowering the loop, damage to the neck portion is likely to occur, and the pull strength may decrease.

  When complex loop control is performed with conventional multilayer copper wires, the loop shape becomes unstable due to peeling at the interface between the coating layer and copper, etc., and adjacent wires cause electrical shorts in narrow pitch connections There is concern.

  Conventionally, when a multilayer copper wire is wedge-connected to an electrode such as a circuit board, the interface between the coating layer and the core material is peeled off, the coating layer is discharged from the wire-electrode joint, and the copper is directly joined Therefore, there is a concern that the bonding strength becomes unstable or decreases.

  As a factor for improving the problems of the conventional multilayer copper wire described above, it is conceivable to control the thickness of the coating layer. However, thickening the coating layer is expected to improve wedge connection, etc., but forming a thick coating layer by plating or vapor deposition has problems in industrial production, such as a decrease in productivity and an increase in material costs. Arise. Further, when the coating layer is thickened, the concentration of elements other than copper is increased in the melted ball portion, so that the ball portion is cured, and there is a problem that chip damage is caused at the time of ball bonding.

  On the other hand, if the coating layer of the conventional multilayer copper wire is only made thin, peeling at the interface between the coating layer and the core material occurs, and it becomes difficult to prevent oxidation and improve wedge connection.

  The present invention solves the above-mentioned problems of the prior art, improves the ball section formability and bondability, has good loop controllability, increases the wedge connection joint strength, and improves industrial productivity. An object of the present invention is to provide a bonding wire mainly composed of copper, which is less expensive than a gold wire.

The gist of the present invention for solving the above problems is as follows.
(1) A bonding wire having a core material mainly composed of copper and a conductive metal skin layer having a composition different from that of the core material on the core material, the main component of the skin layer being gold, palladium 2 or more selected from platinum, rhodium, silver or nickel, and a portion having a concentration gradient of one or both of the main component metal and copper in the wire radial direction exists in the skin layer Bonding wire for equipment.
(2) A bonding wire having a core material mainly composed of copper and a conductive metal skin layer having a composition different from that of the core material on the core material, the main component of the skin layer being gold, palladium 2 or more selected from platinum, rhodium, silver or nickel, and a portion having a concentration gradient of one or both of the main component metal and copper in the wire radial direction is present in the skin layer. A bonding wire for a semiconductor device, wherein at least one of the components has both an increase and a decrease in the wire radial direction.
(3) The bonding wire for a semiconductor device according to (1) or (2), further having a single metal region of gold, palladium, platinum, rhodium, silver or nickel on the surface side of the skin layer.
(4) The bonding wire for a semiconductor device according to (1) or (2), which has a single metal region of gold, palladium, platinum, rhodium, silver or nickel inside the skin layer.
(5) A bonding wire having a core material mainly composed of copper and a conductive metal skin layer having a composition different from that of the core material on the core material. The outermost layer is made of an alloy containing one or more than 30 mol% copper, and the main component of the skin layer is at least one selected from gold, palladium, platinum, rhodium, silver or nickel, and the skin layer A bonding wire for a semiconductor device, characterized in that there is a region having at least one kind of main component metal in the wire radial direction and a concentration gradient in which both copper increases and decreases in the wire radial direction.
(6) A bonding wire having a core material mainly composed of copper and a conductive metal skin layer having a composition different from that of the core material on the core material, the main component of the skin layer being gold, palladium One or more selected from platinum, rhodium, silver or nickel, and a region having a concentration gradient of at least one main component metal and copper in the wire radial direction exists in the skin layer, and the surface of the skin layer A bonding wire for a semiconductor device, characterized in that an outermost region of an alloy containing two or more of gold, palladium, platinum, rhodium, silver or nickel at a uniform concentration of 0.1 mol% or more exists on the side.
(7) The bonding wire for a semiconductor device according to any one of (1) to (6), wherein the skin layer contains an intermetallic compound.
(8) Any one of (1) to (7), wherein the core containing copper as a main component contains 1 to 300 mass ppm in total of at least one selected from Ca, Sr, Be, Al, or a rare earth element A bonding wire for a semiconductor device as described in 1.
(9) The semiconductor device according to any one of (1) to (8), wherein the core material containing copper as a main component contains 0.1 to 10% by mass in total of one or more of silver, tin, and gold. Bonding wire.

  The bonding wire for a semiconductor device of the present invention is low in material cost, excellent in ball bondability, wire bondability, etc., and in good loop formation, for narrow pitch thinning, and for thickening power IC applications. It becomes possible to provide a copper-based bonding wire that is also adaptable.

  The bonding wire of the present invention is composed of a core material mainly composed of copper and a conductive metal skin layer having a composition different from that of the core material. However, the simple two-layer structure of the copper core material and the skin layer does not have sufficient ball formation, bondability, loop control, and the like, and may cause characteristic deterioration as compared with a single-layer copper wire. Therefore, in order to improve the characteristics comprehensively over the single-layer copper wire, the skin layer of the present invention has a concentration gradient region of one or both of copper and the conductive metal.

  Further, the productivity of the bonding wire process may be lower than the current mainstream gold bonding wire only with the copper concentration gradient. Therefore, as a structure of the skin layer that improves productivity to the same level or more as that of the gold bonding wire, a skin layer in which the main component of two or more kinds of conductive metals other than copper has a concentration gradient, and a single metal region of the main component includes It has been found that it is effective to characterize a skin layer formed on the surface or inside, a skin layer having an alloy region of a constant concentration of the main component in the outermost surface region, and the like. Furthermore, a technique of using a copper alloy having a specific element in the core material is also effective.

  The boundary between the skin layer and the core material is an area where the detected concentration of the conductive metal constituting the skin layer is 5 mol% or more. This is based on the fact that the effect of improving the characteristics can be expected from the structure of the skin layer of the present invention, and the conductive metal concentration often changes continuously for the expression of characteristics. The accuracy of quantitative analysis and the like were comprehensively determined, and the region where the concentration of the conductive metal was 5 mol% or more was determined. Preferably, in the region of 10 mol% or more, the accuracy of quantitative analysis is improved, and the measurement becomes simpler.

  When the concentration gradient is classified by constituent elements, there are two types according to the presence or absence of copper elements constituting the core. That is, a concentration gradient composed of a copper element and a conductive metal element constituting the core (hereinafter referred to as A-type concentration gradient), and a concentration composed only of the conductive metal element without including the copper element constituting the core It is divided into gradients (hereinafter referred to as B-type concentration gradients).

  As for the definition of the concentration gradient, it is desirable that the degree of concentration change in the depth direction is 5 mol% or more per 1 μm. If this change is exceeded, the improvement effect as the skin layer having the above-described concentration gradient can be expected, and the result of good reproducibility can be obtained in terms of the accuracy of quantitative analysis. However, the case where the element concentration in the wire locally fluctuates is distinguished from the case where it is unevenly distributed. Preferably, if it is 10 mol% or more per 1 μm, the production is easy. More preferably, if it is 20 mol% or more per 1 μm, a high effect of mutual use can be expected without impairing the different properties of the skin layer and the core material.

  From the standpoints of productivity and quality stability, it is preferable that the concentration gradient in the epidermis layer changes continuously. That is, the degree of the gradient of the concentration gradient is not necessarily constant in the epidermis layer, and may change continuously. For example, good characteristics can be obtained even when the gradient of concentration change at the interface between the coating layer and the core material or near the outermost surface is different from the inside of the coating layer or when the concentration changes exponentially.

  The concentration gradient region is preferably a region formed by atomic diffusion. This is because a layer formed by diffusion has many advantages such as low possibility of defects such as local peeling and cracks, and easy formation of a continuous concentration change.

  A technique for optimizing the skin layer with the alloy composition, concentration distribution, and the like will be specifically described.

  It is composed of a core material mainly composed of copper, and a conductive metal skin layer having a composition different from that of the core material on the core material, and the skin layer is made of gold, palladium, platinum, rhodium, silver, or nickel. A bonding wire containing a metal of more than seeds and having a concentration gradient of one or both of the main component metal and copper inside the skin layer is desirable.

  This is because the skin layer has two or more types of conductive metal elements other than copper, and an A-type concentration gradient containing copper element in the core, and only the conductive metal element does not contain copper element in the core. B-type concentration gradient consisting of the following improvements in ball formability, wire strength, loop control, joint strength, etc., while suppressing an increase in electrical resistance, etc., compared to alloying where the element distribution in the skin layer is almost homogeneous can do. Regarding the effect of the concentration gradient, the A-type concentration gradient in the vicinity of the boundary between the skin layer and the core portion improves the stability of loop formation composed of the bent portion of the wire, and the B-type concentration gradient formed inside the skin layer is It is effective for improving ball formability and wire strength.

  When the main element of the skin layer is only one of gold, palladium, platinum, rhodium, silver and nickel, the loop shape and resin flow control are improved compared to the conventional copper wire without the skin layer, but the current Compared with the gold wire, it is difficult to improve the ball bonding shape, the loop shape, the bonding strength and the like at a mass production level because the proper bonding conditions are different. It is found that the skin layer is composed of two or more metals of gold, palladium, platinum, rhodium, silver and nickel, so that the required characteristics are comprehensively improved and have the same characteristics as general-purpose gold bonding wires. It was. Furthermore, by having a copper element concentration gradient near the skin layer / core interface by diffusion, etc., it is possible to suppress peeling of the skin layer and obtain a stable loop shape even by forced bending during loop formation. Can do.

  Regarding the combination of elements constituting the skin layer, the improvement in wedge bondability is remarkable in the system of gold-palladium, gold-platinum, gold-rhodium, gold-silver, gold-nickel, palladium-platinum, palladium-nickel, It was confirmed that palladium-rhodium or the like has a very good ball-like sphericity. Regarding the average alloy ratio of the skin layer for improving these functions, in the gold-palladium, gold-platinum, gold-rhodium, gold-silver, and gold-nickel systems, the composition ratio of gold is 50 to 90%. The high effect which improves wedge bondability compared with the conventional copper wire is acquired. In the case of palladium-platinum and palladium-nickel, the arc discharge is stabilized and the effect of improving ball-shaped sphericity and dimensional variation is enhanced by setting the palladium composition ratio to 40 to 90%. . Considering the control of the loop shape and the like, a combination of the above-exemplified elements is also possible.

  When the skin layer is composed of three or more elements, it is possible to further improve the above characteristics, and examples thereof include gold-palladium-platinum, gold-palladium-silver, and gold-platinum-nickel.

  The total thickness of the concentration gradient region is preferably 10% to 100% of the thickness of the skin layer, which is 10% or more compared to the case of average alloying. This is because the effect of improving the function is obtained. Moreover, if it is preferably 20% to 80%, the effect of improving electrical characteristics can be enhanced. If the concentration change in the depth direction is 2 mol% or more per 1 μm, the effect of increasing the productivity of the bonding process can be secured.

  The skin layer contains two or more main metals (hereinafter referred to as skin main metals) of gold, palladium, platinum, rhodium, silver and nickel, and the main metal or copper in the wire radial direction in the skin layer. It is desirable that there is a site having one or both of the concentration gradients, and that there is both an increase and a decrease in the concentration gradient of at least one epidermal main metal in the depth direction. Here, a case where the concentration decreases in the depth direction from the surface is a negative concentration gradient, and a case where the concentration increases is a positive concentration gradient. For comparison, when the main skin metal has only a negative concentration gradient, such as a concentration gradient exists only at the boundary between the skin layer and the core material, the loop shape and wedge bondability are further stabilized. It is difficult to do. Therefore, the presence of positive and negative concentration gradients of the same element at the same time improves the adhesion between the skin layer and the core material, stabilizes the loop shape, such as reducing the variation in loop height, and further provides wedge bonding. It is possible to improve the stabilization of the deformed shape and the reduction of the turning failure of the joint. This is presumably because positive and negative concentration gradients interfere with each other to promote the stabilization of deformation even when non-uniform external force or impact is applied to the wire.

  As an example of the positive and negative concentration gradient of the same element, when the main component of the skin layer is gold and palladium, and there is a lot of gold on the surface side, the concentration gradient of palladium element is composed of gold and palladium in the skin layer. There is a positive concentration gradient of palladium in the region of the B type concentration gradient, and palladium in the region of the A type concentration gradient composed of palladium and copper in the core near the boundary between the skin layer and the core. A bonding wire having a negative concentration gradient can be produced.

  When the skin layer is composed of only an alloy, there is a concern about an increase in electrical resistance in high frequency IC applications. Thus, it has been found that the electrical characteristics and the like can be improved by forming a single metal region. Here, the single metal region has one main element, and the total concentration of other metal elements is less than 0.01 mol%. In both the single metal region and the alloy layer, surface contamination such as C, S, and Na on the extreme surface, and elements such as O, N, and H are not considered. About the site | part of a single metal area | region, it distinguishes into the outermost surface and the inside of an outer skin layer, and each mentions later.

  It is composed of a core material mainly composed of copper and a skin layer formed on the core material, and the skin layer contains two or more kinds of skin main metals such as gold, palladium, platinum, rhodium, silver and nickel. Further, it is desirable that the bonding wire has a portion having a concentration gradient between the main skin metal and copper inside the outer skin layer, and has a single metal region made of one kind of main skin metal on the outermost surface. This has a single metal region consisting of one of gold, palladium, platinum, rhodium, silver, and nickel on the outermost surface of the wire, thereby improving electrical characteristics and further promoting a uniform structure of the ball part. This is because the effect of stabilizing the press-bonded ball shape is obtained.

  It is composed of a core material mainly composed of copper and a skin layer formed on the core material, and the skin layer contains two or more kinds of skin main metals such as gold, palladium, platinum, rhodium, silver and nickel. Further, it is desirable that the bonding wire has a single metal region made of one kind of epidermal main metal and a portion having a concentration gradient of the epidermal main metal and copper inside the epidermis layer. This is because a single metal region is formed inside the skin layer, and in addition to improving electrical characteristics, controlling the heat-affected tissue in the neck near the ball increases pull strength and lowers the loop. It is an advantage that it can respond. Here, when the neck is affected by heat, the internal single metal region acts as a source of diffusion, forming a diffusion layer on both sides of the single metal region to increase the pull strength, and recrystallization It is considered that the loop can be reduced by suppressing the noise.

  By making the outermost surface alloy of the main skin metal, the surface alloy part contributes to high rigidity, which is effective in preventing wire sag in long span, improving linearity, reducing wire surface scraping, etc. is there. Further, by forming a single metal region both on the outermost surface and inside the skin layer, it is possible to increase electrical characteristics, wedge bondability, pull strength, and the like.

  With respect to the wire including a single metal region, the internal structure of the skin layer will be specifically described using the above-described palladium-gold system as an example. From the surface of the wire to the center of the wire, represented by a single metal region of gold / (concentration gradient layer of palladium and gold) / (concentration gradient layer of gold, palladium, copper) / (concentration gradient layer of palladium, copper) A first configuration having a concentration gradient layer in which three elements are mixed, a second configuration having a single metal region in the middle, such as (palladium and gold alloy) / gold / (gold and copper concentration gradient region) / core material. A third configuration having a single metal region in the middle represented by the configuration, gold single metal region / (palladium and gold concentration gradient layer) / palladium single metal region / (palladium and copper concentration gradient layer); Etc.

  In the first and third configurations, the single metal region such as gold on the outermost surface promotes the diffusion of the bonding interface, so that the bonding strength of the wedge bonding portion is high, which is advantageous in improving the productivity in the low temperature connection. In addition, in the first configuration, an increase in wire strength or a reduction in resin flow is expected by effectively using a larger number of concentration gradient layers than a ternary system or the like. In the second configuration, the alloy portion on the surface is advantageous in preventing wire drooping in a long span, improving linearity, and the like. In the third configuration, since both the palladium and gold have a single metal region, if the concentration gradient region is thinned, the effect of improving electrical characteristics can be further enhanced.

  Paying attention to the concentration gradient, as a further characteristic improvement, palladium, which is the main metal of the skin in both the first and third configurations, has a positive and negative concentration gradient. Promotes stabilization. In the second and third configurations, a single metal region is provided between the positive and negative concentration gradients of the skin main metal. By adopting such a three-layer structure of positive concentration gradient / single metal region / negative concentration gradient, wire deformation is stable against non-uniform external forces such as bending of loop formation and excessive plastic deformation of wedge joints. It is more effective for conversion.

  With the illustrated combination, the function can be improved even with a structure in which palladium and gold are replaced. The purity of the single metal in the skin layer is the case where one of gold, palladium, platinum, rhodium, silver and nickel is 99.9 mol% or more, and other impurities are suppressed to less than 0.1 mol%. It is desirable.

  A core material mainly composed of copper, a conductive metal skin layer having a composition different from that of the core material on the core material, and a bonding wire having an outermost surface region, wherein the main component of the skin layer is: One or more selected from gold, palladium, platinum, rhodium, silver or nickel, and there is a portion having a concentration gradient of at least one main component metal and copper in the wire radial direction in the skin layer. The surface region is desirably a bonding wire in which an alloy containing two or more of gold, palladium, platinum, rhodium, silver or nickel at a uniform concentration of 0.1 mol% or more exists. Here, the presence of an alloy containing two or more of the main component metals at a uniform concentration of 0.1 mol% or more on the surface further increases the rigidity of the surface and further suppresses the wire flow during resin sealing. There are advantages such as an increase, and since it is not necessary to control the concentration gradient on the surface, manufacturing management becomes easy. Here, when the concentration of the alloy is less than 0.1 mol%, the effect of improving the characteristics is small.

  The reason why the concentration on the surface of two or more elements of gold, palladium, platinum, rhodium, silver, nickel, and copper is 0.1 mol% or more is advantageous in suppressing wire flow at the time of resin sealing by increasing strength. Based on being.

  Regarding the internal structure of the skin layer, the change from the wire surface to the wire center direction is exemplified by the platinum / gold system: (platinum and gold concentration gradient region) / gold / (gold and copper concentration gradient region) / core Fourth configuration having a single metal region in the middle like a material, (concentration gradient region of platinum and gold) / (concentration gradient region containing three elements of platinum, gold, and copper) / (concentration gradient of gold and copper) 5th structure which consists of an area | region) etc. are mentioned. The fourth configuration corresponds to the case where the surface is a concentration gradient region in the above-described second configuration, and improvement effects such as ball bonding by surface modification and reduction of scratches on the wire surface during loop control are also obtained. In the fifth configuration, a significant improvement in strength can be achieved by effectively utilizing a concentration gradient containing three elements. With these exemplary combinations, the function can be improved even with a structure in which platinum and gold are replaced. In the above example, the concentration distribution of the gold element has positive and negative concentration gradients, promotes stabilization of the characteristics, and controls the length, amount of change, etc. of these concentration gradients. It is also possible to improve characteristics, wedge bondability, and the like.

The structure of the skin layer contains one or more kinds of skin main metals of gold, palladium, platinum, rhodium, silver and nickel, and is separated from the copper constituting the core material on the outermost surface by plating or the like. It has a single metal region formed of copper element formed on the surface or an alloy layer containing 30 mol% or more of copper element, and has a skin main metal and copper concentration gradient inside the skin layer, Bonding wires in which concentration gradients both increase and decrease in the depth direction are also effective. Hereinafter, the copper element in the vicinity of the outermost surface is represented by “copper _out ”, and the copper element constituting the core material is represented by “copper _in ”.

A specific structure of the skin layer will be described with reference to a copper / gold component system. When a single metal region of copper _out is exposed on the outermost surface, the structure of the skin layer from the surface to the depth direction is as follows: copper _out single metal region / (copper _out and gold concentration gradient layer 1) / gold Single metal region / (concentration gradient layer 2 of copper _in and gold). Focusing on the copper element, the outer (copper _out and gold concentration gradient layer 1) and the inner (copper _in and gold concentration gradient layer 2) are separated through a single gold layer. When the concentration gradient of copper element in the depth direction is compared, copper is negative concentration gradient in (copper _out and gold concentration gradient layer 1), and copper is positive _in (copper _in and gold concentration gradient layer 2). Conflicts with concentration gradient. Gold elements also have a mixture of positive and negative concentration gradients. These two elements, copper and gold, contain a total of four concentration gradients, with positive and negative concentration gradients, respectively, so that it is highly effective to improve wedge bondability, wire strength, bending rigidity, etc. It is done. By having these four types of concentration gradients, it is possible to express advantages that are superior to the above-described skin layer having a simple structure composed only of the gold element and the copper element of the core material. The same improvement effect can be obtained even when the gold single metal region disappears.

In addition, (copper _out and gold concentration gradient layer 1) / gold single metal region / (copper _in and gold concentration gradient layer 2), one or more of copper _out , palladium, platinum, and nickel Even when an alloy layer having a concentration gradient layer with the above element is exposed on the outermost surface, improvement in bondability with gold plating and the like can be imparted. As an example of the manufacturing method of these wire structures, it is possible to first create an initial structure of copper _out / gold / copper _in core material, and then form a positive and negative concentration gradient of copper element by diffusion heat treatment, etc. is there.

  Regarding the structure of the skin layer described above, a structure composed of two types of elements has been described. However, if the number of elements is increased and the structure has a larger number of concentration gradient layers, the complex loop shape and fine connection in the new type mounting will be described. It is possible to further improve the applicability to the above.

  The third technique is a technique for optimizing the composition of the copper alloy of the core material. Specifically, copper is the main component, and at least one of silver, tin, and gold is 0.1 to 30 in total. A core material containing mass% and a skin layer formed on the core material, wherein the skin layer is mainly composed of at least one metal selected from gold, palladium and platinum, and the inside of the skin layer. It is desirable that the bonding wire has a copper concentration gradient. By using a copper alloy containing silver, tin, and gold as the core material, it is possible to suppress deformation of the ball part, etc., compared to the case of only a single copper, and the perfect circle of the joined ball part It is possible to achieve improvement in properties and increase in bonding strength. Here, if the addition amount is 0.1% by mass or more, the above-described improvement in ball bondability can be stably achieved at the mass production level, and if it exceeds 30% by mass, the ball part is bonded by curing. This is because damaging the chips directly underneath is a problem.

  The thickness of the skin layer is desirably 0.05 μm or more. If it is 0.05 μm or more, it can be uniformly formed on the entire wire, there are few surface irregularities, and there is no problem such as peeling of the skin layer, so that sufficient effects such as oxidation inhibition and bondability are obtained. Because of the reason. Moreover, if it is 70% or less of a wire diameter, industrial mass productivity is also high and quality control etc. can fully respond | correspond. As for the lower limit of the thickness, preferably 0.1 μm or more, the effect of suppressing oxidation when exposed to high temperature is enhanced, and more preferably 0.2 μm or more, quality can be assured because it can be analyzed relatively easily. There are many advantages such as being easy. At one upper limit, it is easy to form a concentration-change layer uniformly within 50% of the wire diameter, and more preferably within 30% of the wire diameter, the increase in electrical resistance is reduced. There are advantages such as being suppressed.

  Concentration analysis of the skin layer is effective by analyzing the surface of the wire while digging in the depth direction by sputtering or the like, or by line analysis or point analysis at the wire cross section. The former is effective when the skin layer is thin, but if it is thick, it takes too much measurement time. The latter analysis is effective when the epidermis layer is thick, and it is advantageous that the concentration distribution over the entire cross-section and reproducibility confirmation at several locations are relatively easy. If the layer is thin, the accuracy decreases. It is also possible to measure by increasing the thickness of the diffusion layer by obliquely polishing the wire. Line analysis is relatively simple in the cross section, but it is also effective to narrow the analysis interval of line analysis or to perform point analysis focusing on the region to be observed near the interface when improving the accuracy of analysis. EPMA, EDX, Auger spectroscopic analysis, a transmission electron microscope (TEM), etc. can be utilized in the analysis apparatus used for these concentration analyses. Further, for the investigation of the average composition, etc., it is possible to dissolve in acid or the like stepwise from the surface portion, and obtain the composition of the dissolution site from the concentration contained in the solution.

It is also effective that the skin layer contains an intermetallic compound phase mainly composed of copper and a conductive metal in addition to the concentration gradient. That is, it is composed of a core material mainly composed of copper and a skin layer of a conductive metal. Inside the skin layer, a portion having a concentration gradient of copper and an intermetallic compound having copper and a conductive metal are 1 Excellent properties can be obtained with bonding wires containing more than one layer. By including the intermetallic compound phase in the skin layer, the mechanical properties such as the strength and elastic modulus of the wire are increased, which is effective in improving the linearity of the loop and suppressing the flow of the wire during sealing. The intermetallic compound phase is mainly composed of copper and conductive metal, and it is desirable that the total concentration thereof is 80 mol% or more. However, even if the alloying element contained in the core material and the skin layer is partially contained I do not care. For example, when the conductive metal is gold, palladium, platinum or the like, the intermetallic compound phase formed is CuAu ₃ , CuAu, Cu ₃ Au, Cu ₃ Pd, CuPd, Cu ₃ Pt, CuPt, CuPt ₃ , CuPt _7. Etc. are candidates, and these intermetallic compound phases are formed in the skin layer or the skin layer / core material interface, and are effective in improving the characteristics. The thickness of these intermetallic compound phases is preferably from 0.001 μm to half the thickness of the skin layer.

  When the skin main metal forming the skin layer is gold, palladium, platinum, silver, or copper, it further contains 1 to 300 ppm by mass in total of at least one of Ca, Sr, Be, Al, and rare earth elements. Thus, the strength, structure, and plastic deformation resistance of the skin layer can be adjusted, so that the effect of controlling the deformation of the wire and the electrode material (Ag, Au, Pd, etc.) at the time of wedge bonding can be promoted. It has been found that when the above-mentioned skin main metal has a concentration gradient, the effect of adding these elements is highly effective. Furthermore, since Ca, Sr, Be, Al, and rare earth elements have a concentration gradient, a higher effect can be obtained.

  By adjusting the structure of the wire and the plastic deformation resistance, the core material mainly composed of copper contains at least one of Ca, Sr, Be, Al, and rare earth elements in a total amount of 1 to 300 ppm by mass. The effect of controlling the deformation of the wire and the electrode material (Ag, Au, Pd, etc.) at the time of wedge bonding can be promoted. In addition, it has been found that when the above-mentioned skin main metal has a concentration gradient, the effect of adding these elements is high. Here, when the content is 1 mass ppm or more, the above effect appears, and when the content is less than 300 mass ppm, adverse effects on oxidation or the like during ball formation can be suppressed. Furthermore, since Ca, Sr, Be, Al, and rare earth elements have a concentration gradient, a higher effect can be obtained.

  The core material mainly composed of copper contains one or more of silver, tin, or gold in a total amount of 0.1 to 10% by mass, so that the strength of the wire can be increased and the wire deformation during resin sealing can be reduced. . In addition, it has been found that when the above-mentioned skin main metal has a concentration gradient, the effect of adding these elements is high. Here, the above effect appears when the content is 0.1% by mass or more, and when the content exceeds 10% by mass, the electrical resistance of the wire is increased. Furthermore, since Ca, Sr, Be, Al, and rare earth elements have a concentration gradient, a higher effect can be obtained.

  In producing the wire of the present invention, a step of forming a core material and a skin layer, and a concentration gradient in the skin layer of copper element and a heat treatment step exposed to the outermost surface are required.

  Methods for forming the skin layer on the surface of the copper core include plating, vapor deposition, and melting. As the plating method, either electrolytic plating or electroless plating can be used. Electrolytic plating called strike plating or flash plating has a high plating speed and good adhesion to the substrate. Solutions used for electroless plating are classified into substitutional type and reduction type. If the film is thin, substitutional plating alone is sufficient, but when forming a thick film, reduction type plating is used after substitutional plating. It is effective to apply stepwise. The electroless method is simple and easy to use, but requires more time than the electrolysis method.

  In the vapor deposition method, physical adsorption such as sputtering, ion plating, and vacuum deposition, and chemical adsorption such as plasma CVD can be used. All of them are dry-type, and cleaning after film formation is unnecessary, and there is no concern about surface contamination during cleaning.

  Regarding the stage of plating or vapor deposition, either the method of forming a conductive metal film with a target wire diameter or the method of forming a film on a thick core material and then drawing multiple times to the target wire diameter Is also effective. In the former film formation with the final diameter, manufacturing, quality control and the like are simple, and the latter film formation and wire drawing are advantageous in improving the adhesion between the film and the core material. As a specific example of each forming method, a method of forming a film while continuously sweeping a wire into an electrolytic plating solution on a copper wire of a target wire diameter, or thick copper in an electrolytic or electroless plating bath For example, a method of drawing the wire to reach the final diameter after immersing the wire to form a film is possible.

  When the skin layer forms a plurality of layers composed of two or more kinds of skin main metals, a plurality of different skin main metal layers are formed stepwise by plating, vapor deposition, melting, or the like. In that case, a method of performing heat treatment after forming all different skin main metals, and a method of alternately performing formation of one layer of skin main metal and heat treatment are effective.

  A diffusion heat treatment by heating is effective as a step of forming a concentration gradient of one or both of the main component metal and copper in the skin layer using the skin layer and the core material formed by the above method. This is a heat treatment for promoting mutual diffusion between copper and a conductive metal at the interface between the skin layer and the core material. The method of performing heat treatment while continuously sweeping the wire is excellent in productivity and quality stability. However, simply heating the wire does not control the distribution of copper on and within the skin layer. Even if the processing strain relief annealing used in normal wire manufacturing is applied as it is, loop control becomes unstable due to a decrease in adhesion between the skin layer and the core material, or wire scraps accumulate inside the capillary and clog. It is difficult to completely solve problems such as the occurrence of oxidization and the oxidation of copper exposed on the surface to decrease the bonding strength. Therefore, it is important to control the temperature, speed, time, etc. of the heat treatment.

As a preferred heat treatment method, the heat treatment is performed while continuously sweeping the wire, and the temperature in the furnace is not constant, which is a general heat treatment. It becomes easy to mass-produce a wire having an outer skin layer and a core material. Specific examples include a method of introducing a temperature gradient locally and a method of changing the temperature in the furnace. In order to suppress the surface oxidation of the wire, it is also effective to heat while flowing an inert gas such as N ₂ or Ar into the furnace.

  In the temperature gradient method, positive temperature gradient near the furnace inlet (temperature rises with respect to the wire sweep direction), stable temperature range Negative temperature gradient near the furnace outlet (temperature falls with respect to the wire sweep direction) For example, it is effective to incline the temperature in a plurality of regions. This improves adhesion without causing separation of the skin layer and core material in the vicinity of the furnace inlet, promotes diffusion of copper and conductive metal in a stable temperature region, and forms a desired concentration gradient, Further, by suppressing excessive oxidation of copper on the surface in the vicinity of the furnace outlet, it is possible to improve the bondability and loop controllability of the obtained wire. In order to obtain such an effect, it is desirable to provide a temperature gradient at the entrance / exit of 1 ° C./mm or more.

  In the method of changing the temperature, it is also effective to create a temperature distribution by dividing the furnace into a plurality of regions and performing different temperature control in each region. For example, the inside of the furnace is divided into three or more places, temperature control is performed independently, and the both ends of the furnace are set to a temperature lower than that of the central portion, whereby the same improvement effect as in the case of the temperature gradient can be obtained. Moreover, in order to suppress the surface oxidation of a wire, the joint strength of a wedge-joint part can be increased by setting both ends of the furnace or the outlet side to a low temperature at which the oxidation rate of copper is low.

  Heat treatment with such a temperature gradient or temperature distribution is preferably performed at the final wire diameter in terms of productivity, but on the other hand, the surface oxide film is removed by performing wire drawing after the heat treatment to bond at a low temperature. In addition, the effect of reducing wire scraping inside the capillary can be obtained by using wire drawing and strain relief annealing in combination.

  In addition, the melting method is a technique in which either the skin layer or the core material is melted and cast, and it is excellent in productivity by drawing after connecting the skin layer and the core material with a large diameter of about 1 to 50 mm. Compared to plating and vapor deposition methods, the alloy component design of the skin layer is easy, and there are advantages such as easy improvement of properties such as strength and bondability. In a specific process, a melted conductive metal is cast around a prefabricated core wire to form a skin layer, and a prefabricated conductive metal hollow cylinder is used, and a melted copper is formed in the center portion thereof. Or it is divided into the method of forming a core wire by casting a copper alloy. Preferably, it is easier to stably form a copper concentration gradient or the like in the skin layer by casting a copper core into the latter hollow cylinder. Here, if a small amount of copper is contained in the skin layer prepared in advance, the copper concentration on the surface of the skin layer can be easily controlled. Further, in the melting method, it is possible to omit the heat treatment work for diffusing Cu in the skin layer, but further improvement in characteristics can be expected by performing the heat treatment to adjust the Cu distribution in the skin layer. .

  Further, when such a molten metal is used, at least one of the core wire and the skin layer can be manufactured by continuous casting. By this continuous casting method, the process is simplified as compared with the above casting method, and the wire diameter can be reduced to improve the productivity.

  As a method of forming a single metal region of the main skin metal of gold, palladium, platinum, rhodium, silver or nickel on the surface or inside of the skin layer, a single metal region of two layers made of different skin main metals is used as a core material. It is effective to optimize the heat treatment conditions so that a single metal region remains on the surface or inside by using the diffusion heat treatment for forming the concentration gradient described above.

  As another method for forming a single metal region on the surface of the skin layer, it is also possible to newly form a single metal region by the above-described plating method, vapor deposition method, etc. after performing diffusion heat treatment. . In order to improve the adhesion of the single metal region to the base, it is also effective to appropriately perform a heat treatment after the formation of the single metal region.

  A layer composed of one or more selected from gold, palladium, platinum, rhodium, silver or nickel on the surface of the core material as a method for forming the outermost region made of a single copper alloy or an alloy containing copper of 30 mol% or more It is effective to form a copper layer on the surface, and then form a two-layer single metal region consisting of different main skin metals on the surface of the core material and perform diffusion heat treatment under appropriate conditions. is there. The gold, palladium, platinum, rhodium, silver or nickel layer and the copper layer are formed by using the above-described plating method, vapor deposition method, melting method or the like.

  Examples will be described below.

  As the raw material of the bonding wire, the copper used for the core material is a high-purity material having a purity of about 99.99 mass% or more, and the purity of the Au, Pt, Pd, Cu, Ag, Ni, and Rh materials on the outer periphery The raw material of 99.9 mass% or more was prepared.

  To form a concentration gradient by using an electroplating method, electroless plating method, vapor deposition method, melting method, etc. to form a different metal layer on the surface of a copper wire that has been thinned to a certain wire diameter. Also heat-treated. A method was used in which the skin layer was formed with the final wire diameter, and after the skin layer was formed with a certain wire diameter, it was further thinned to the final wire diameter by wire drawing. As the electrolytic plating solution and the electroless plating solution, a plating solution commercially available for semiconductor applications was used, and the sputtering method was used for vapor deposition. Prepare a wire with a diameter of about 50 to 200 μm in advance, coat the wire surface by vapor deposition, plating, etc., draw the wire to a final diameter of 15 to 25 μm, remove the processing strain, and have an elongation value of about 4%. Heat treatment was applied so that As needed, after wire drawing to a wire diameter of 30 to 100 μm, diffusion heat treatment was performed, and then wire drawing was further performed.

  When utilizing the melting method, a method of casting a molten metal around a core wire prepared in advance and a method of casting molten copper or a copper alloy in the central portion of a hollow cylinder prepared in advance were employed. The diameter of the core wire was about 3 to 8 mm, and the diameter of the outer peripheral portion was about 5 to 10 mm. Thereafter, forging, roll rolling, die drawing and the like, and heat treatment were performed to produce a wire. In addition, in order to form a plurality of layers, a composite method of forming another layer on the surface of an intermediate product formed by a melting method by an electrolytic plating method, an electroless plating method, a vapor deposition method, or the like was also performed.

Regarding the heat treatment of the wire of the example of the present invention, the wire was heated while continuously sweeping. A method of introducing a temperature gradient locally, a method of changing the temperature in the furnace, and the like were used. This temperature difference was set in the range of 30 to 200 ° C., and the temperature distribution, the wire sweep speed, etc. were optimized and adjusted so that the tensile elongation was around 4%. In the atmosphere of the heat treatment, in addition to the air, an inert gas such as N ₂ or Ar was used for the purpose of suppressing oxidation. Regarding the heat treatment process of the comparative example, when the plated layer was formed after the heat treatment was performed on the drawn Cu wire (Comparative Examples 2, 4, 7, and 8), after the heat treatment was drawn, and after the plating layer was formed The sample was prepared when applied twice in (Comparative Examples 3 and 6).

  The tensile strength and elastic modulus of the wire were obtained by carrying out a tensile test of five wires having a length of 10 cm and calculating the average value.

For connection of the bonding wire, a commercially available automatic wire bonder was used to perform ball / wedge bonding. A ball (initial ball diameter: 35 to 50 μm) was produced at the tip of the wire by arc discharge, and it was joined to the electrode film on the silicon substrate, and the other end of the wire was wedge joined to the lead terminal. In order to suppress oxidation during ball melting, discharging was performed while N ₂ gas was blown onto the tip of the wire.

  As a bonding partner, an Al alloy film (Al-1% Si-0.5% Cu film, Al-0.5% Cu film) having a thickness of 1 μm, which is a material of an electrode film on a silicon substrate, was used. On the other hand, a lead frame whose surface was Ag-plated (thickness: 1 to 4 μm) or a resin substrate having an electrode structure of Au plating / Ni plating / Cu was used as a partner for wedge bonding.

  Regarding the loop shape stability in the bonding process, two types of bonding samples with a wire length of 3 mm and 5 mm were prepared, and 500 wires were observed with a projector, and the linearity of the wire, variation in loop height, etc. were observed. Judged. The condition with a long wire length of 5 mm is a stricter evaluation. If the wire length is 3 mm and there are 5 or more defects such as linearity and loop height, it is judged that there is a problem and is indicated by x, the wire length is 3 mm, 2 to 4 defects, and the wire length is 5 mm. In the case where the number of defects is 5 or more, it is determined that improvement is necessary, and is represented by a Δ mark. Since the loop shape is relatively good, it is indicated by a circle, and when the wire length is 5 mm and the number of defects is 1 or less, the loop shape is determined to be stable and is indicated by an ◎. As one of the causes of defects, the adhesion between the interface between the core wire and the outer peripheral portion is not sufficient, and the characteristic variation in the cross section is assumed.

  Measurement of wire flow (resin flow) at the time of resin sealing is performed using a soft X-ray non-destructive inspection device after preparing a bonding sample with a wire length of 5 mm and sealing with a commercially available epoxy resin. The amount of flow in this part was measured, and the average value divided by the span length of the wire (percentage) was taken as the wire deformation rate at the time of sealing. If this wire deformation rate is 6% or more, it is judged as defective, and if it is 4% or more and less than 6%, improvement is necessary. Is marked as o, and if it is less than 2.5%, the wire deformation is excellently reduced, and is marked as o.

  In the observation of the initial ball shape, 20 balls before bonding were observed to determine whether the shape was a true sphere or whether the dimensional accuracy was good. If there are two or more abnormally shaped balls, the mark is bad because it is defective, and the number of irregular shapes is two or less. If there are 2 to 4 misalignments, it is judged that there is no major problem in practical use. If the misalignment is less than 1 and the dimensional accuracy is good, the ball formation is good. Indicated.

  In determining the bonded shape of the press-bonded ball portion, 500 bonded balls were observed to evaluate the roundness of the shape, dimensional accuracy, and the like. The conditions for the ball crimp diameter to be in the range of 2 to 3 times the wire diameter were selected. If there are 5 or more defective ball shapes such as anisotropy and ellipse with a large deviation from the perfect circle, it is judged as defective, x mark, 2 to 4 defective ball shapes, or petal-shaped ball crimping part If the number of outer peripheral parts is 8 or more, improvement is necessary. Therefore, Δ mark, less than 1 defective ball shape, and 3 to 7 petal-like deformations, it is determined that there is no problem in practical use. Since it is good if the number of petal-like deformations is 2 or less, it is indicated by ◎.

  For the strength evaluation of the neck portion, 20 breaking loads (pull strength) were measured by a pull test method in which the breaking strength was read by moving a hook hung on the lower portion of the loop upward. The hook position can be changed according to the measurement site, and in order to evaluate the strength of the neck part, a pull test (neck pull strength) is performed in the vicinity of the ball joint part. Pull strength was measured near about 1/4 of the wire span. If the neck pull strength is 60% or more of the wire strength, it is good because it is good. If it is less than 40%, it needs to be improved.

  Judgment of wedge bondability for bonding wires to the lead side makes bonding difficult at lower temperatures. Therefore, 1000 pieces of bonding are performed at a stage temperature of 220 ° C. and 180 ° C. The deformation shape, etc. were investigated. When there are two or more complete peels at the joint at 220 ° C, X mark, less than two at 220 ° C, and improvement when partial peel near the wire breakage occurs △ mark, there is no defect at 220 ° C, and when complete peeling at 180 ° C is 1 or less, ○ mark, no complete peeling at 180 ° C, and partial peeling is less than 3 In some cases, it is indicated by ◎.

  In the measurement of the pull strength of the wedge joint, a pull test was performed in the vicinity of the wedge joint with a sample having a wire length of 3 mm in order to determine the adhesion at the joint interface, and the average value of 20 pieces was obtained.

  Tables 1 to 4 and 6 show the evaluation results of the copper bonding wires according to the present invention, and Table 5 shows comparative examples.

  The bonding wires according to the first claim are Examples 1 to 55, the bonding wires according to the second claim are Examples 1 to 51, and the bonding wires according to the third claim are Examples 1 to 40, The bonding wires according to claim 4 are Examples 1-29, 41-46, the bonding wires according to claim 5 are Examples 56-69, the bonding wires according to claim 6 are Examples 52-55, The bonding wires according to the claims are examples 3, 7, 10, 32, 43, 50, 59, 61, the bonding wires according to the eighth claim are the examples 74 to 78, and the bonding wires according to the ninth claim are the examples. Corresponds to examples 70-75. Comparative Examples 1 to 8 in Table 5 show the results of bonding wires not corresponding to the claims of the present invention.

  A part of the evaluation results will be described for representative examples of each claim.

  The bonding wires of Examples 1 to 55 include two or more main component metals selected from gold, palladium, platinum, rhodium, silver, or nickel in the skin layer according to the present invention, and the wire is formed in the skin layer. By having a concentration gradient of one or both of the main component metal and copper in the radial direction, it was confirmed that the ball part formability and the wire strength were sufficiently high. These characteristics are not sufficient for Cu wires in which films of elements other than copper of Comparative Examples 1 to 8 are simply formed on the surface, but are improved in Examples 1 to 55 having a concentration gradient in the wire radial direction. It became clear.

  The bonding wires of Examples 1 to 51 have concentration gradients in which at least one of gold, palladium, platinum, rhodium, silver and nickel has both an increase and a decrease in the depth direction in the skin layer according to the present invention. As a result, it was confirmed that the loop controllability and wedge bondability were good.

  The bonding wires of Examples 1 to 40 have a good wedge bondability and a crimped shape by having a single metal region of gold, palladium, platinum, rhodium, silver or nickel in the skin layer according to the present invention. It was confirmed.

  The bonding wires of Examples 1 to 29 and 41 to 46 have high pull strength by having a single metal region of gold, palladium, platinum, rhodium, silver or nickel inside the skin layer according to the present invention. It was confirmed that the neck damage was reduced and it was possible to cope with the low loop.

  The bonding wires of Examples 56 to 69 are gold, palladium, platinum, rhodium, silver in the outermost surface region composed of a single copper alloy or an alloy containing copper of 30 mol% or more, and the skin layer according to the present invention. Or the presence of at least one kind of nickel and copper having concentration gradients both increasing and decreasing in the wire radial direction results in good ball formation, high pull strength, and improved wedge bondability. It was confirmed.

  The bonding wires of Examples 52 to 55 have a concentration gradient of at least one of gold, palladium, platinum, rhodium, silver, or nickel as a main component metal and a main component metal in the skin layer according to the present invention. It was confirmed that by having an alloy layer containing two or more of these at a uniform concentration of 0.1 mol% or more, the pull strength is high, and it is possible to cope with a low loop by reducing neck damage, increasing pull strength, and the like.

  The bonding wires of Examples 3, 7, 10, 32, 43, 50, 59, 61 were confirmed to form an intermetallic compound in the skin layer, and the wires were strengthened, and the straight line during use was confirmed. Property, resin flow suppression, etc. were improved.

  The bonding wires of Examples 74 to 78 have improved wedge bondability by containing a predetermined amount of Ca, Sr, Be, Al, or rare earth elements in the core according to the present invention. In the bonding wires of ˜75, the resin flow was improved by containing a predetermined amount of silver, tin or gold in the core.

Claims (9)

  A bonding wire having a core material mainly composed of copper and a skin layer of a conductive metal having a composition different from that of the core material on the core material, the main component of the skin layer being gold, palladium, platinum, Bonding for semiconductor devices, wherein there are at least two kinds selected from rhodium, silver or nickel, and a portion having a concentration gradient of one or both of the main component metal and copper in the wire radial direction exists in the skin layer Wire.   A bonding wire having a core material mainly composed of copper and a skin layer of a conductive metal having a composition different from that of the core material on the core material, the main component of the skin layer being gold, palladium, platinum, It is at least two selected from rhodium, silver, or nickel, and there is a portion having a concentration gradient of one or both of the main component metal and copper in the wire radial direction in the skin layer, and at least the main component of the skin layer One type has both an increase and a decrease in the wire radial direction, a bonding wire for a semiconductor device.   The bonding wire for a semiconductor device according to claim 1, further comprising a single metal region of gold, palladium, platinum, rhodium, silver or nickel on the surface side of the skin layer.   The bonding wire for a semiconductor device according to claim 1 or 2, wherein a single metal region of gold, palladium, platinum, rhodium, silver or nickel is provided inside the skin layer.   A bonding wire having a core material mainly composed of copper and a conductive metal skin layer having a composition different from that of the core material on the core material, the surface of the skin layer having a single or 30 mol of copper % Of the outermost layer made of an alloy containing copper, and the main component of the skin layer is at least one selected from gold, palladium, platinum, rhodium, silver, or nickel, and a wire is formed in the skin layer. A bonding wire for a semiconductor device, characterized in that there is a region in which at least one kind of main component metal and copper have both concentration gradients of increase and decrease in the wire radial direction.   A bonding wire having a core material mainly composed of copper and a skin layer of a conductive metal having a composition different from that of the core material on the core material, the main component of the skin layer being gold, palladium, platinum, It is at least one selected from rhodium, silver or nickel, and there is a region having a concentration gradient of at least one main component metal and copper in the wire radial direction in the skin layer, on the surface side of the skin layer, A bonding wire for a semiconductor device, wherein there is an outermost region of an alloy containing two or more of gold, palladium, platinum, rhodium, silver or nickel at a uniform concentration of 0.1 mol% or more.   The bonding wire for a semiconductor device according to claim 1, wherein the skin layer contains an intermetallic compound.   The semiconductor device according to claim 1, wherein the copper-based core material contains 1 to 300 ppm by mass in total of one or more selected from Ca, Sr, Be, Al, or rare earth elements. Bonding wire.   The bonding wire for a semiconductor device according to any one of claims 1 to 8, wherein the core containing copper as a main component contains at least 0.1 to 10% by mass of one or more of silver, tin, and gold.