JP2005183462A - Wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a bonding wire in the diameter of 100 μm or more cannot be rigidly deposited on the surface of the wiring layer. <P>SOLUTION: The wiring board 4 is formed of a board 1 formed of an electrical insulating material, a wiring layer 2 which is formed of at least one from among Au, Ag, Cu, Pd, and Pt on the board 1 with simultaneous baking, and includes a region to which the bonding wire 5 in diameter of 100 μm or more is bonded, and a covering layer 9 formed of an Ni layer 6 deposited to the region to which at least the bonding wire 5 of the wiring layer 2 is bonded in the thickness of 4 μm to 13 μm with content of Bi of 0.005 mass% to 0.03 mass%, a Pd layer 7 in the thickness of 0.03 μm to 0.3 μm, and an Au layer 8 in the thickness of 0.005 μm to 0.3 μm. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a wiring board on which electronic components such as a semiconductor element, a capacitive element, and a resistor are mounted, and more particularly to a wiring board in which a bonding wire having a large diameter that allows a large current flow is connected to a wiring layer. It is.

  Conventionally, wiring boards on which electronic components such as semiconductor elements, capacitive elements, resistors and the like are mounted are made of an electrically insulating material such as an aluminum oxide sintered body, and a substrate having an electronic component mounting portion on the surface and formed on the substrate. Wiring layers made of refractory metal materials such as tungsten, molybdenum, etc., and mounting electronic components such as semiconductor elements, capacitive elements, resistors, etc. on the mounting part of the substrate and wiring the electrodes of each electronic component The layers are electrically connected via bonding wires.

  Such a wiring board is mounted on the external electric circuit board by connecting a part of the wiring layer to the wiring conductor of the external electric circuit board via a low melting point brazing material such as tin-lead solder, and is simultaneously mounted on the wiring board. Each electrode of the electronic component is electrically connected to a predetermined external electric circuit.

  In addition, as a material of the bonding wire for connecting each electrode of the electronic component to the wiring layer, aluminum and gold are generally used, and it is particularly necessary to increase the diameter of the bonding wire in order to flow a large current. In many cases, aluminum bonding wires are frequently used with an emphasis on economy, and gold bonding wires are frequently used when bonding speed is important.

  In addition, the connection between the wiring layer and the electrode of the electronic component via a bonding wire is generally performed by using an ultrasonic bonder. Specifically, one end of the bonding wire is brought into contact with the surface of the wiring layer. The bonding wire is connected to the wiring layer by sliding and generating friction energy between the bonding wire and the surface of the wiring layer and causing the friction energy to cause metal diffusion between the bonding wire and the surface portion of the wiring layer. The

  In this case, the diameter of the conventional bonding wire is about 30 μm, and the bonding wire is pressed against the surface of the wiring layer with a load of about 30 gf to 50 gf (0.294 N to 0.49 N), and friction energy is generated by sliding. Is designed to occur efficiently.

  Further, the wiring layer of the wiring substrate is usually coated with a coating layer comprising a Ni layer having an average thickness of about 3 μm and an Au layer having an average thickness of about 1.5 μm or more on the surface by plating or the like. It has good bonding wire connectivity using an ultrasonic bonder.

  When the coating layer is formed by a plating method, an electroless method that does not require a lead wire for supplying a plating current is increasingly used. In this case, the wiring layer is formed by electroless Ni, Pd, or Au. By immersing in a plating solution such as a predetermined time, a metal component such as Ni in the plating solution adheres to the surface of the wiring layer to form a coating layer. In addition, the electroless Ni plating solution contains a reducing agent such as sodium hypophosphite and a stabilizer such as a Pb (lead) compound in addition to the Ni compound serving as the Ni supply source. The coating layer such as the Ni layer contains a small amount of Pb which is a decomposition product of these components.

  By the way, in this conventional wiring board, the electric resistance value of the wiring layer formed of tungsten, molybdenum, or the like is high, and a voltage drop is caused in the electric signal transmitted through the wiring layer so as to be connected to the wiring layer. There is a drawback that it is not possible to accurately input and output electrical signals to and from such electronic components. In particular, this defect becomes more prominent as the current value of the electrical signal transmitted through the wiring layer increases.

  Therefore, in order to eliminate the above-described drawbacks, a wiring board is proposed in which the wiring layer is formed of a metal material having a low electric resistance value such as Cu (copper), Ag (silver), or Au (gold).

  According to such a wiring board, since the wiring layer is formed of Cu, Ag, Au or the like having a low electric resistance value, when an electric signal is propagated to the wiring layer, a large voltage drop is caused in the electric signal in the wiring layer. This makes it possible to accurately transmit an electrical signal to the electronic component.

  In recent years, however, wiring boards have been increasingly used in applications where it is necessary to flow an electric signal of a large current of about 5 A or more, such as boards for ECUs (Electronic Control Units). In order to flow a large current to the electronic component, the diameter of the bonding wire for connecting the wiring layer and the electronic component needs to be very large, such as 100 μm or more. Such a bonding wire having a large diameter is formed by an ultrasonic bonder. When trying to connect to the wiring layer, there is a new defect that a defect such as a crack or peeling occurs between the wiring layer and the substrate.

  The reason for the occurrence of defects such as cracks and peeling between the wiring layer and the substrate is that when a large bonding wire having a diameter of 100 μm or more is connected to the wiring layer, there is a large gap between the bonding wire and the wiring layer. It is necessary to generate friction energy, and in order to generate this large friction energy, a very large load of about 90 gf to 600 gf (0.882 N to 5.88 N) must be applied to the bonding wire on the surface of the wiring layer. The large load acts on the interface between the wiring layer and the substrate, and the large mechanical stress generated by the sliding of the bonding wire and the wiring layer acts on the interface between the wiring layer and the substrate. Since the thickness of the Ni layer covering the surface of the layer is about 3 μm on average, it is relatively thin and has a small effect of absorbing mechanical stress, the load It is considered that the mechanical stress generated due to heavy or sliding between the bonding wire and the wiring layer acts on the interface between the wiring layer and the substrate as it is without being absorbed or relaxed by the Ni layer.

  In addition, since the average thickness of the Au layer covering the surface of the wiring layer is as thick as about 1.5 μm, when connecting a bonding wire made of aluminum having a large diameter of 100 μm or more to the wiring layer, bonding with the Au layer A large amount of brittle aluminum and gold intermetallic compounds are formed at or around the joint with the wire, and as a result, when an external force is applied to the bonding wire, the bonding wire is easily detached from the wiring layer, and the electronic component It also induces a drawback that the reliability of the electrical connection with the wiring layer is low.

In response to various drawbacks of such a conventional wiring board, the applicant of the present invention consists of a board made of an electrically insulating material and at least one of Au, Ag, Cu, Pd, and Pt, and is formed on the board by co-firing. A wiring layer having a region to which an aluminum bonding wire having a diameter of 100 μm or more is connected, and a Ni layer having a thickness of 4 μm to 13 μm, which is deposited on at least a region of the wiring layer to which the bonding wire is connected; A wiring board formed of a 0.03 μm to 0.3 μm Pd layer and a coating layer composed of a 0.005 μm to 0.3 μm Au layer was proposed. (Japanese Patent Application No. 2002-247388)
According to this wiring board, the wiring layer is composed of at least one of Au (gold), Ag (silver), Cu (copper), Pd (palladium), and Pt (platinum), and therefore has a low electrical resistance. When the electrical signal is propagated to the electrical signal, the electrical signal can be accurately transmitted without causing a large voltage drop in the electrical signal in the wiring layer.

  In addition, a region of the wiring layer to which the bonding wires are connected includes a Ni layer having a thickness of 4 μm to 13 μm, a Pd layer having a thickness of 0.03 μm to 0.3 μm, and an Au layer having a thickness of 0.005 μm to 0.3 μm. When the coating layer is deposited and the Ni layer thickness is increased to 4 μm to 13 μm, when connecting a large bonding wire with a diameter of 100 μm or more to the wiring layer, the load for pressing the bonding wire against the wiring layer surface, The mechanical stress generated by sliding with the wiring layer is absorbed and relaxed by the Ni layer and becomes smaller. As a result, a large force does not act on the interface between the wiring layer and the substrate. It is possible to effectively prevent the occurrence of defects such as cracks or peeling between the wiring layer and firmly bond the wiring layer to the substrate.

Further, according to the wiring board, the Ni layer and the Pd layer having a strong bonding strength to the Au layer are interposed between the Ni layer and the Au layer, and the Ni layer is prevented from being oxidized in the Pd layer, and the bonding wire. As a result, the Au layer can be made as thin as 0.005 μm to 0.3 μm. As a result, the wiring layer has a large aluminum bonding wire with a diameter of 100 μm or more. When connecting the wire, a large amount of fragile aluminum and gold metal compound is not generated at or around the bonding portion between the Au layer and the bonding wire, and even if an external force is applied to the bonding wire, the bonding wire Does not easily disengage from the wiring layer, and the electrical connection between the electronic component and the wiring layer can be made highly reliable. Than it is.
JP 2002-124590 A

However, in the wiring board configured as described above, the wiring layer has a low electrical resistance, and the wiring layer is firmly attached to the board so as not to cause defects such as cracks and peeling when a large bonding wire having a diameter of 100 μm or more is connected. Can be joined to
When forming the covering layer, since the Ni layer or the like is not deposited on the surface of the substrate, the Ni, Pd, Au layers 23, 24, 25 are formed at the end portion of the wiring layer 22, as shown in FIG. The thickness of the wiring layer 22 gradually decreases from the upper surface to the vicinity of the lower end of the side surface, and the cross-sectional shape is inclined toward the inside, so that a fine gap is likely to be generated between the coating layer 22 and the substrate 21. The Ni layer 23 cannot be completely covered with the thin Pd layer 24 or the Au layer 25 at the end portion, and a portion where Ni is locally exposed is likely to occur, and a large current of about 5 A or more flows repeatedly to the wiring layer 22. For example, when moisture in the outside air enters the gap between the coating layer 26 and the substrate 21, a battery action occurs between the exposed portion of the Ni layer 23 and the Pd layer 24 and the Au layer 25. Ni layer 2 due to action The so-called migration in which the Ni component forming the elution occurs causes a problem such as an electrical short circuit between adjacent wiring layers 22, and the defect that the long-term reliability as a wiring board is inferior is newly revealed. It was.

  In this case, the Ni layer 23 contains a Pb component, and the migration resistance of Pb is inferior to that of Ni. Therefore, it is difficult to suppress the above migration, and the migration is more remarkable due to segregation of Pb and the like. There was also a risk of becoming.

  Moreover, since the Pb component is contained in the Ni layer 23 that occupies a large portion of the coating layer 26, there is a drawback in that the environment and the human body may be adversely affected such as toxicity.

  The present invention has been devised in view of the above-mentioned drawbacks. The purpose of the present invention is to provide an aluminum bonding wire having a diameter as large as 100 μm or more in the wiring layer, such as a crack or peeling between the wiring layer and the substrate. An object of the present invention is to provide a wiring board that can be firmly connected without causing defects, has excellent migration resistance of the coating layer, is excellent in long-term reliability, and has a small environmental load.

  The wiring board of the present invention is connected to a substrate made of an electrically insulating material and a bonding wire made of at least one of Au, Ag, Cu, Pd, and Pt, formed by simultaneous firing, and having a diameter of 100 μm or more. A wiring layer having a region to be formed, and at least a region of the wiring layer to which a bonding wire is connected, having a thickness of 4 μm to 13 μm and a Bi content of 0.005 mass% to 0.030 mass% It is characterized in that it is formed of a Ni layer, a Pd layer of 0.03 μm to 0.3 μm, and a coating layer composed of an Au layer of 0.005 μm to 0.3 μm.

  The wiring board of the present invention is characterized in that the coating layer has a Vickers hardness of 200 Hv or more.

The wiring board of the present invention is characterized in that the internal stress of the Ni layer is 98 N / mm ² or less.

  In the wiring board of the present invention, the Ni layer has a particle size of 5 μm to 30 μm.

  The wiring board according to the present invention is characterized in that the surface roughness of the Au layer is 0.1 μm to 0.3 μm in terms of arithmetic average roughness (Ra).

  According to the wiring board of the present invention, the wiring layer is composed of at least one of Au (gold), Ag (silver), Cu (copper), Pd (palladium), and Pt (platinum), and has low electrical resistance. When an electric signal is propagated to the wiring layer, the electric signal can be accurately transmitted without causing a large voltage drop in the electric signal in the wiring layer.

  According to the wiring board of the present invention, the Ni layer having a thickness of 4 μm to 13 μm, the Pd layer having a thickness of 0.03 μm to 0.3 μm, and the 0.005 μm to 0 in the region to which the bonding wire of the wiring layer is connected. . When a coating layer composed of an Au layer of 3 μm is deposited and the Ni layer is thickened to 4 μm to 13 μm, a bonding wire having a diameter of 100 μm or more is connected to the wiring layer. The load applied to the surface and the mechanical stress generated by the sliding between the bonding wire and the wiring layer are absorbed and relaxed by the Ni layer and become smaller. As a result, a large force acts on the interface between the wiring layer and the substrate. In other words, it is possible to effectively prevent the occurrence of defects such as cracks or peeling between the wiring layer and the substrate, and to firmly bond the wiring layer to the substrate.

  Further, according to the wiring board of the present invention, the thick Ni layer contains 0.005 mass% to 0.030 mass% of Bi having migration resistance equal to or higher than that of Ni. Even if a large current of about 5 A or more flows repeatedly in the wiring layer, migration of the Ni component of the Ni layer is effectively prevented, and electrical insulation between adjacent wiring layers is achieved. Can be maintained over a long period of time, and a wiring board excellent in long-term reliability can be provided.

  Further, when such a Ni layer is formed by a plating method, it is not necessary to add a Pb component to the plating solution or the like by adding a Bi component as a stabilizer to the plating solution. Can be prevented, adverse effects such as toxicity to the environment and the human body can be suppressed, and a wiring board with a low environmental load can be provided.

  Furthermore, according to the wiring board of the present invention, the Ni layer and the Au layer are interposed between the Ni layer and the Au layer, and the Pd layer having a strong bonding strength with respect to the Au layer, and the Ni layer is prevented from being oxidized and bonded to the Pd layer. The Au layer can be made as thin as 0.005 μm to 0.3 μm because it assists the connectivity of the wire, and as a result, the wiring layer has a large diameter aluminum bonding of 100 μm or more. When connecting wires, a large amount of fragile aluminum-gold intermetallic compound is not generated at or around the joint between the Au layer and the bonding wire, and even if an external force is applied to the bonding wire, etc. The bonding wire is not easily detached from the wiring layer, and the reliability of the electrical connection between the electronic component and the wiring layer can be increased.

  In the wiring board of the present invention, when the hardness of the coating layer is set to 200 Vv or more in terms of Vickers hardness, when the bonding wire is connected to the wiring layer with an ultrasonic bonder, the ultrasonic energy is applied to the vibration of the coating layer. It is not absorbed by deformation and is efficiently converted into friction energy at the interface between the bonding wire and the coating layer, and the bonding wire can be more firmly connected to the wiring layer by this friction energy.

Further, in the wiring board of the present invention, when the internal stress of the Ni layer is 98 N / mm ² or less, the internal stress of the Ni layer is small, so that a large bonding wire having a diameter of 100 μm or more is connected to the wiring layer. At this time, it is assumed that a very large load of about 90 gf to 600 gf (0.882 N to 5.88 N) is applied to the surface of the wiring layer in order to generate a large frictional energy between the bonding wire and the wiring layer. However, this load and internal stress combine to prevent an extremely large force from acting on the Ni layer, and mechanical damage such as cracks occurs in the Ni layer or at the interface between the Ni layer and the Pd layer. Therefore, it is possible to more effectively and firmly connect a large bonding wire having a diameter of 100 μm or more to the wiring layer.

  Further, in the wiring board of the present invention, when the size of the Ni particles forming the Ni layer is 5 μm to 30 μm, the Ni particles have an appropriate size and there are few grain boundaries of the Ni particles, When a large bonding wire having a diameter of 100 μm or more is connected to the wiring layer, the bonding wire is about 90 gf to 600 gf (0.882 N) relative to the wiring layer surface in order to generate a large frictional energy between the bonding wire and the wiring layer. Even if a very large load (˜5.88 N) is applied, it is possible to effectively prevent fracture at the grain boundary between the Ni particles, and as a result, a large bonding wire having a diameter of 100 μm or more is more reliably formed in the wiring layer. It can be firmly connected.

  In the wiring board of the present invention, when the roughness of the surface of the uppermost Au layer of the coating layer is 0.1 μm to 0.3 μm in terms of arithmetic average roughness (Ra), the surface of the coating layer Therefore, when connecting a large bonding wire with a diameter of 100 μm or more to the wiring layer with an ultrasonic bonder, the coating layer and the bonding wire are brought into close contact with each other on the entire surface of the bonding layer. It is possible to generate a large amount of frictional energy uniformly over the entire surface of the wire to allow sufficient metal diffusion between the bonding wire and the wiring layer, thereby further improving the connection reliability of the bonding wire to the wiring layer. Can be made.

  Next, the present invention will be described in detail with reference to the accompanying drawings.

  1 and 2 show an embodiment in which the wiring board of the present invention is applied to a substrate for mounting a semiconductor element such as an ECU (Electronic Control Unit) board, where 1 is a board and 2 is a wiring layer. The substrate 1 and the wiring layer 2 form a wiring substrate 4 for mounting the semiconductor element 3.

  The substrate 1 of the wiring board 4 acts as a support member for supporting the semiconductor element 3, and the semiconductor element 3 is attached and fixed to a substantially central portion of the upper surface via an adhesive material such as glass, brazing material, and resin.

  The substrate 1 is made of an electrically insulating material such as an aluminum oxide sintered body that can be sintered at a low temperature of 1200 ° C. by adding a glass ceramic sintered body, crystalline glass, a manganese compound, or the like. If it is made of a sintered body, add appropriate organic binder, solvent, etc. to glass ceramic raw material powder consisting of glass powder such as silicon oxide, boron oxide and calcium oxide and ceramic powder such as aluminum oxide and mullite. The slurry is made into a glass ceramic green sheet (glass ceramic green sheet) by adopting a doctor blade method or a calender roll method, and then the glass ceramic green sheet is appropriately punched. And if necessary, stack several sheets to obtain about 9 It is manufactured by firing at a temperature of 0 ° C..

  Further, the substrate 1 has a plurality of wiring layers 2 formed on the upper surface from the periphery of the region where the semiconductor element 3 is mounted and mounted to the lower surface, and the portion of the wiring layer 2 exposed on the upper surface of the substrate 1 has the semiconductor element 3. The electrode is connected via a bonding wire 5 and the portion leading to the lower surface of the substrate 1 is connected to an external electric circuit substrate via a conductive connecting material such as solder.

  The wiring layer 2 acts as a conductive path for connecting each electrode of the semiconductor element 3 to an external electric circuit. By connecting each electrode of the semiconductor element 3 to the wiring layer 2 via the bonding wire 5, the wiring layer 2 Each electrode is connected to an external electric circuit through the wiring layer 2.

  The wiring layer 2 is made of at least one of Au, Ag, Cu, Pd, and Pt. Since the wiring layer 2 made of Au, Ag, Cu, Pd, Pt, and the like has a small electric resistance value, the wiring layer 2 When the electrical signal is propagated to 2, the electrical signal can be accurately transmitted to the semiconductor element 3 without causing a large voltage drop in the electrical signal in the wiring layer 2.

  For example, if the wiring layer 2 is made of Ag, a metal paste is prepared by adding an appropriate organic binder and solvent to Ag powder, and this metal paste is used as the substrate 1 on the surface of the glass ceramic green sheet. Then, a predetermined pattern is formed from the upper surface to the lower surface of the substrate 1 by printing and coating in a predetermined pattern.

  The wiring layer 2 has an electrode of the semiconductor element 3 connected to a region exposed on the upper surface of the substrate 1 through a bonding wire 5 having a diameter of 100 μm or more. It will be electrically connected to the wiring layer 2 through the wiring.

  Since the bonding wire 5 has a diameter as large as 100 μm or more, when a large current signal of about 5 A or more flows from the wiring layer 2 to the semiconductor element 3 through the bonding wire 5, the large current signal is no problem. It can be propagated to the semiconductor element 3 without causing any damage.

  When the diameter of the bonding wire 5 is less than 100 μm, it becomes difficult to propagate a large current electric signal. Therefore, the bonding wire 5 is specified to have a diameter of 100 μm or more.

  The bonding wire 5 is connected to the wiring layer 2 by sliding one end of the bonding wire 5 against the surface of the wiring layer 2 with a large load of about 90 gf to 600 gf (0.882 N to 5.88 N), Friction energy is generated between the bonding wire 5 and the wiring layer 2 surface, and metal diffusion is performed between the bonding wire 5 and the wiring layer 2 surface portion by the friction energy.

  Further, the wiring layer 2 is further at least in a region to which the bonding wire 5 is connected, as shown in FIG. 2, a Ni layer having a thickness of 4 μm to 13 μm and a Bi content of 0.005 mass% to 0.030 mass%. 6, a coating layer 9 composed of a Pd layer 7 of 0.03 μm to 0.3 μm and an Au layer 8 of 0.005 μm to 0.3 μm is deposited, and the coating layer 9 is formed by oxidizing the wiring layer 2. This effectively prevents the bonding wire 5 from being firmly connected to the wiring layer 2.

  The Ni layer 6 has good adhesion and adhesion strength between the wiring layer 2 made of at least one of Au, Ag, Cu, Pd, and Pt and the Pd layer 7 to be described later. 2 acts as a base layer to be firmly attached to 2 and absorbs / relaxes stress, and is formed by a plating method such as an electroless method or an electrolytic method, or a sputtering method, for example, by an electroless plating method. If present, the wiring layer 2 is formed by immersing it in an electroless Ni plating solution using a phosphorus reducing agent such as sodium hypophosphite or a boron reducing agent such as dimethylamine borane for a predetermined time.

  Since the Ni layer 6 has a thickness of 4 μm to 13 μm, the wiring layer 2 can be completely covered to effectively prevent the wiring layer 2 from being oxidized, and the wiring layer 2 has a large bonding diameter of 100 μm or more. When the wire 5 is connected, the load that presses the bonding wire 5 against the surface of the wiring layer 2 and the mechanical stress generated by the sliding of the bonding wire 5 and the wiring layer 2 are absorbed and relaxed by the Ni layer 6 and are extremely small. As a result, a large force does not act on the interface between the wiring layer 2 and the substrate 1, and it is possible to effectively prevent defects such as cracks and peeling between the wiring layer 2 and the substrate 1. Thus, the wiring layer 2 can be firmly bonded to the substrate 1.

  When the Ni layer 6 has a thickness of less than 4 μm, the load that presses the bonding wire 5 against the surface of the wiring layer 2 and the mechanical stress generated by the sliding of the bonding wire 5 and the wiring layer 2 are sufficient. Absorption cannot be mitigated, and defects such as cracks and cracks occur at the interface between the wiring layer 2 and the substrate 1, and if it exceeds 13 μm, the internal stress of the film becomes very large and the Ni layer 6 and the wiring The bonding strength between the layer 2 and between the wiring layer 2 and the substrate 1 deteriorates, and the Ni layer 6 peels off from the wiring layer 2 or the wiring layer 2 peels off from the substrate 1. Therefore, the thickness of the Ni layer 6 is specified in the range of 4 μm to 13 μm.

  Further, when the thickness of the Ni layer 6 is set in the range of 5 μm to 10 μm, the bonding wire 5 can be more securely and firmly connected to the wiring layer 2 and the Ni layer 6 is separated from the wiring layer 2. In addition, it is possible to completely prevent the wiring layer 2 from being peeled off from the substrate 1 and to further improve the reliability as the wiring substrate. Therefore, it is more preferable that the Ni layer 6 has a thickness in the range of 5 μm to 10 μm.

Further, according to the wiring board of the present invention, the thick Ni layer 6 contains 0.005 mass% to 0.030 mass% Bi, and the migration resistance of Bi is equal to or higher than Ni.
While a gap is generated between the covering layer 9 and the substrate 1, even if a large current of about 5 A or more flows repeatedly in the wiring layer 2, it is effectively prevented that migration occurs in the Ni component of the Ni layer 6, It is possible to provide a wiring board excellent in long-term reliability that can maintain electrical insulation between adjacent wiring layers 2 over a long period of time.

  In order to contain the Bi component in the Ni layer 6, for example, when the Ni layer 6 is formed by a plating method using an electroless Ni plating solution, a Bi compound such as chloride or organic sulfonic acid is added to the plating solution. A method such as addition may be used.

  When the Bi component is added to the Ni plating solution, the Bi component has a certain inhibitory action on the reaction between the reducing agent and the Ni component in the plating solution, so the reaction between the Ni component and the reducing agent is abrupt. Therefore, it can act as a stabilizer for preventing Ni from adhering to unnecessary portions other than the wiring layer 2.

  Therefore, when such a Ni layer 6 is formed by a plating method, it is not necessary to add a Pb component as a stabilizer to the plating solution by adding a Bi component to the plating solution. Provided is a wiring board that can prevent the Pb component from being contained, can prevent Ni migration more effectively, can suppress adverse effects such as toxicity to the environment and the human body, and has a low environmental load. be able to.

  In this case, if the Bi content in the Ni layer 6 is less than 0.005% by mass, the migration resistance of the Ni layer 6 cannot be effectively improved, and if it exceeds 0.030% by mass, the Ni layer 6 And the reliability of deposition on the wiring layer 2 decreases, and the content of the Bi component in the plating solution for containing the Bi component in the Ni layer 6 also increases, and this Bi component is a catalyst poison. As a result, defects such as chipping and unevenness occur in the Ni layer 6. Therefore, the Ni layer 6 needs to have a Bi content in the range of 0.005 mass% to 0.030 mass%.

  Since the Bi content in the Ni layer 6 is proportional to the Bi component content in the plating solution, the Bi content in the Ni layer 6 is adjusted by adjusting the Bi component content in the plating solution. Control within a predetermined range is possible.

  The content of Bi in the Ni layer 6 can be measured by dissolving the Ni layer in nitric acid or the like, and analyzing and quantifying the solution by an analytical method such as emission spectroscopic analysis.

  If a Bi component is added to the electroless nickel plating solution, Bi has a property as a catalyst poison against the precipitation by the reducing agent of Ni, so that excessive precipitation of the Ni component in the plating solution is prevented. The Ni layer 6 can be formed stably over a long period of time without adding a Pb component as a stabilizer to the plating solution.

Further, in the wiring substrate 4 of the present invention, when the internal stress of the Ni layer 6 is 98 N / mm ² or less, the internal stress of the Ni layer 6 is small, so that a large bonding wire 5 having a diameter of 100 μm or more is wired. When connecting to the layer 2, in order to generate a large frictional energy between the bonding wire 5 and the wiring layer 2, the bonding wire is about 90 gf to 600 gf (0.882 N to 5.88 N) with respect to the surface of the wiring layer 2. Even when a very large load is applied, the load and internal stress combine to prevent an extremely large force from acting on the Ni layer 6, and mechanical damage such as cracks occurs in the Ni layer 6. This makes it possible to more effectively prevent and prevent the bonding layer 5 having a diameter of 100 μm or more to be more reliably and firmly connected to the wiring layer 2.

The internal stress of the Ni layer 6 can be measured by a conventionally known measurement method, for example, a simple average stress measurement method using a device shown in JIS H8626, a spiral contractometer method, or the like. When the stress or compressive stress exceeds 98 N / mm ² , when connecting a large bonding wire 5 having a diameter of 100 μm or more to the wiring layer 2, the internal stress and the load for connection are combined to generate a large force. It acts on the layer 6 and mechanical breakage such as cracks is likely to occur. Therefore, the Ni layer 6 preferably has an internal stress of 98 N / mm ² or less.

In order to set the internal stress of the Ni layer 6 to 98 N / mm ² or less, for example, the Ni layer 6 is formed by electroless Ni plating, and about 300 ° C. for 120 to 180 minutes with respect to the Ni plating layer. It is possible to use a method such as heat treatment under moderate heating conditions to remove internal stress.

  Further, in the wiring board 4 of the present invention, when the size of the Ni particles forming the Ni layer 6 is 5 μm to 30 μm, the Ni particles have an appropriate size and there are few Ni particle grain boundaries. When the bonding wire 5 having a diameter of 100 μm or more is connected to the wiring layer 2, the bonding wire 5 is brought into contact with the surface of the wiring layer 2 in order to generate large frictional energy between the bonding wire 5 and the wiring layer 2. Even if a very large load of about 90 gf to 600 gf (0.882 N to 5.88 N) is applied, it is possible to effectively prevent the grain boundary between Ni particles from being broken. As a result, the diameter is as large as 100 μm or more. The bonding wire 5 can be more securely and firmly connected to the wiring layer 2.

  In order to set the size of the Ni particles of the Ni layer 6 to 5 μm to 30 μm, for example, the Ni layer 6 is formed by electroless Ni plating, and about 300 ° C. for 120 minutes with respect to the Ni plating layer. A method such as heat treatment under heating conditions of about 180 minutes to cause Ni particles to grow can be used.

  When the Ni layer 6 has a Ni particle size of less than 5 μm, there are many grain boundaries between the Ni particles, and due to the load when connecting a large bonding wire 5 having a diameter of 100 μm or more to the wiring layer 2. There is a tendency that cracks or the like are likely to occur in the Ni layer 6, and when it exceeds 30 μm, the chemical and physical bonding force between the grain boundaries between the Ni particles is extremely small, and thus a large bonding wire 5 having a diameter of 100 μm or more. Is pressed with a large load, the Ni particles themselves are detached from the Ni layer 6 made of Ni, or peeling occurs between the Ni layer 6 and a Pd layer 7 described later. The strength of the connection to the layer 2 tends to be deteriorated.

  Therefore, the Ni layer 6 preferably has a Ni particle size of 5 μm to 30 μm.

  Further, a Pd layer 7 is deposited on the surface of the Ni layer 6. The Pd layer 7 prevents the Ni layer 6 from being oxidatively corroded, and firmly adheres the Au layer 8 to the Ni layer 6. In addition, even if the thickness of the Au layer 8 is reduced, the bonding wire 5 is assisted to be firmly connected.

  The Pd layer 7 can be formed by a plating method such as an electrolytic method or an electroless method. For example, the Pd layer 7 can be formed by using a phosphorus-based reducing agent such as sodium hypophosphite or a boron-based reducing agent such as dimethylamine borane. It is formed by immersing the wiring layer 2 on which the Ni layer 6 is deposited in the electrolytic Pd plating solution for a predetermined time.

  If the thickness of the Pd layer 7 is less than 0.03 μm, the oxidative corrosion of the Ni layer 6 cannot be effectively prevented. If the thickness exceeds 0.3 μm, the coating layer 9 with respect to the wiring layer 2 is affected by the plating film stress. Deposition strength is deteriorated. Therefore, the thickness of the Pd layer 7 is specified in the range of 0.03 μm to 0.3 μm.

  Further, the Au layer 8 is deposited on the surface of the Pd layer 7. The Au layer 8 prevents oxidation corrosion of the Ni layer 6 and the Pd layer 7, and metal diffuses between the bonding wire 5. The bonding wire 5 is firmly bonded to the wiring layer 2.

  The Au layer 8 can be formed by a plating method such as an electrolysis method or an electroless method. For example, when the Au layer 8 is formed by an electroless method, potassium gold cyanide is the main component and EDTA (ethylenediaminetetraacetic acid) is used. ) And the like, a substitution-type electroless Au plating solution formed by adding a complexing agent, a pH adjusting agent, etc., or a reduction-type electroless Au plating solution using a reducing agent such as potassium borohydride or dimethylamine borane. The wiring layer 2 having the Ni layer 6 and the Pd layer 7 deposited thereon is immersed in a known electroless Au plating solution for a predetermined time.

  Since the Au layer 8 is provided with a Pd layer 7 for assisting the connection of the bonding wire 5 underneath, the thickness can be reduced to 0.005 μm to 0.3 μm. As a result, the wiring layer 2 When a bonding wire 5 made of aluminum having a large diameter of 100 μm or more is connected to the wire, a large amount of fragile aluminum and gold intermetallic compound is generated at or around the bonding portion between the Au layer 8 and the bonding wire 5. Thus, even when an external force is applied to the bonding wire 5 or the like, the bonding wire 5 is not easily detached from the wiring layer 2, and the electrical connection between the semiconductor element 3 and the wiring layer 2 is highly reliable. Can be

  If the thickness of the Au layer 8 is less than 0.005 μm, the oxidative corrosion of the Ni layer 6 or the like cannot be effectively prevented, and when Ni oxide is formed, this precipitates on the surface of the Au layer 8. An oxide layer is formed and the connection of the bonding wire 5 becomes weak, or the metal diffusion between the bonding wire 5 and the Au layer 8 becomes insufficient, and the connection of the bonding wire 5 becomes weak. If the thickness exceeds 0.3 μm, a large amount of brittle aluminum-gold intermetallic compound is generated at or around the bonding portion between the Au layer 8 and the bonding wire 5, and as a result, when an external force is applied to the bonding wire 5 or the like. The bonding wire 5 is easily detached from the wiring layer 2 and the reliability of the electrical connection between the semiconductor element 3 and the wiring layer 2 becomes low. Therefore, the thickness of the Au layer 8 is specified in the range of 0.005 μm to 0.3 μm.

  When the thickness of the Au layer 8 is reduced to less than about 0.05 μm (0.005 μm or more), the Pd layer 7 is made of a plating solution using a phosphorus reducing agent such as sodium hypophosphite. It is preferable that the Pd layer 7 is formed and contained in an amount of 0.5% by mass or more by external addition of the P component. If the P component is added to the Pd layer 7 by adding 0.5% by mass or more by external addition, the oxidation of the Ni component can be more reliably prevented by the action of the P component, so the Au layer 8 is made less than about 0.05 μm. Even when it is thin (0.005 μm or more), oxidation of the Ni layer 6 can be prevented more effectively, and the bonding wire 5 can be more reliably connected to the wiring layer 2. In this case, if the P component exceeds 5 mass% by external addition, the internal stress of the P layer 7 increases, and there is a possibility that peeling occurs between the Pd layer 7 and the Au layer 8 or the like. Therefore, when the P component is added to the Pd layer 7, the amount added is more preferably in the range of 0.5 mass% to 5 mass% by external addition.

  In the wiring substrate 4 of the present invention, when the roughness of the surface of the uppermost Au layer 8 in the coating layer 9 is 0.1 μm to 0.3 μm in terms of arithmetic average roughness (Ra), Since the surface of the layer 9 becomes moderately smooth, when the bonding wire 5 having a diameter of 100 μm or more is connected to the wiring layer 2 with an ultrasonic bonder, the covering layer 9 and the bonding wire 5 are connected to the entire bonding surface. Can be made to adhere well and generate a large amount of frictional energy uniformly over the entire surface between them to allow sufficient metal diffusion between the bonding wire 5 and the wiring layer 2, thereby bonding to the wiring layer 2. The connection reliability of the wire 5 can be further increased.

  The Au layer 8 becomes smooth when its surface roughness is less than 0.1 μm in arithmetic mean roughness (Ra), and therefore, a large frictional energy may be generated between the Au layer 8 and the bonding wire 5. It becomes difficult, and it becomes difficult to cause sufficient metal diffusion between the bonding wire 5 and the wiring layer 2, and the connection reliability between the wiring layer 2 and the bonding wire 5 tends to decrease. When the surface roughness exceeds 0.3 μm in arithmetic mean roughness (Ra), when connecting a bonding wire 5 having a diameter of 100 μm or more to the wiring layer 2 with an ultrasonic bonder, the Au layer 8 and the bonding wire 5 are used. It is difficult to adhere both of them well and uniformly over the entire surface of the wide bonding surface, and the friction energy is partially insufficient, so that sufficient metal diffusion is achieved on the entire surface between the bonding wire 5 and the Au layer 8. It is difficult to cause the bonding wire 5 to be firmly connected to the wiring layer 2. Therefore, the Au layer 8 preferably has a surface roughness of 0.1 μm to 0.3 μm in terms of arithmetic average roughness (Ra).

  In order to set the surface of the Au layer 8 to an arithmetic average roughness (Ra) in the range of 0.1 μm to 0.3 μm, for example, when the Ni layer 6 is formed on the wiring layer 2 by the electroless plating method as described above. Phosphorus (P) and boron, which are decomposition products of reducing agents that co-deposit with Ni and Ni, or add appropriate amounts of sulfur compounds, Se, Te, etc. as crystal modifiers (brighteners) to the electroless Ni plating solution Combine two or three complexing agents with different stability constants (complexing power) with (B), and adjust plating conditions such as pH, liquid temperature, and stirring speed according to the surface condition of the wiring layer 2 and the like. As a result, Ni is deposited and deposited so as to fill and smooth the unevenness on the surface of the wiring layer 2, and thereby the surface roughness of the Ni layer 6 is set to an arithmetic average roughness (Ra) of 0. The range is set to 1 μm to 0.3 μm, and the surface of the Ni layer 6 Methods such as for 0.1μm to a range of 0.3μm in roughness of each surface arithmetic average roughness of the Pd layer 7 and the Au layer 8 is deposited (Ra) can be used.

  Thus, according to the above-described wiring substrate, the semiconductor element 3 is mounted and fixed on the upper surface of the substrate 1, and the electrodes of the semiconductor element 3 are connected to the wiring layer 2 via the bonding wires 5 having a diameter of 100 μm or more. If the element 3 is sealed with a sealing material (not shown) such as a lid or a sealing resin, an ECU (Electronic Control Unit) substrate or the like is completed.

  Next, the function and effect of the present invention will be described based on the following experimental examples.

[Experimental example]
First, glass powder, filler powder (ceramic powder), an organic binder, a plasticizer, an organic solvent, and the like are mixed and formed into a sheet to produce a glass ceramic green sheet.

  The components of the glass powder include, for example, SiO2-B2O3-based, SiO2-B2O3-Al2O3-based, SiO2-B2O3-Al2O3-MO-based (where M represents Ca, Sr, Mg, Ba or Zn), SiO2-Al2O3- M1O-M2O system (wherein M1 and M2 are the same or different and each represents Ca, Sr, Mg, Ba or Zn), SiO2-B2O3-Al2O3-M1O-M2O system (where M1 and M2 are the same as above) ), SiO 2 —B 2 O 3 —M 32 O (where M 3 represents Li, Na or K), SiO 2 —B 2 O 3 —Al 2 O 3 —M 32 O (where M 3 is the same as above), Pb glass, Bi glass, etc. Any SiO2-based material may be used, and in this experimental example, a SiO2-B2O3-based material was used.

  Examples of the filler powder include at least one selected from Al2O3, SiO2, ZrO2 and alkaline earth metal oxide, TiO2 and alkaline earth metal oxide, Al2O3 and SiO2. A composite oxide containing spinel, mullite, cordierite, etc. is used, and Al2O3 is used in this experimental example.

  The mixing ratio of the glass powder and filler powder is preferably 40:60 to 99: 1 by mass ratio.

  Further, as the organic binder, those conventionally used for ceramic green sheets can be used. For example, acrylic (acrylic acid, methacrylic acid or their homopolymers or copolymers, specifically, Is acrylic acid ester copolymer, methacrylic acid ester copolymer, acrylic acid ester-methacrylic acid ester copolymer, etc.), polyvinyl butyral, polyvinyl alcohol, acrylic-styrene, polypropylene carbonate, cellulose Homopolymers or copolymers such as these are used, and in this experimental example, an acrylic type was used.

  In addition, as a method of forming into a sheet shape, a conventionally known forming method such as a doctor blade method, a rolling method, a calender roll method, or a die brace method can be used, which is necessary for the glass powder, filler powder, and organic binder. According to the above, a predetermined amount of plasticizer and solvent (organic solvent, water, etc.) are added to obtain a slurry, which is obtained by molding to a thickness of about 50 to 500 μm by the above molding method. In this experimental example, the doctor blade method was used.

  Next, Ag paste is printed on the surface of the glass ceramic green sheet thus produced, and six linear test patterns (adjacent to each other) having a width and an adjacent interval (line and space) of 100 μm / 100 μm are printed by screen printing. The number of intervals = 5) was printed as a wiring layer and baked to produce a wiring board for a sample.

  Next, a coating layer composed of a Ni layer, a Pd layer, and an Au layer is applied to this sample by an electroless plating method using a phosphorus-based reducing agent such as sodium hypophosphite and adding Bi chloride as a stabilizer. Was attached to the test pattern surface with the thickness shown in Table 1, and various bonding wires made of Heraeu aluminum having different diameters shown in Table 1 were connected using an M360C ultrasonic bonder manufactured by Orthodyne. The Bi content of the coating layer was adjusted by the concentration of the Bi component in the plating solution.

  In addition, the connection conditions using an ultrasonic bonder are as follows.

・ Ultrasonic frequency: 60 kHz
Bonding time: 25-150ms
Bonding power: 110-130 steps
Bonding load: 4.275N-5.88N
・ Loop height: 6-8mm
・ Loop length: 6-8mm
Then, a tensile test was performed on the bonding wire connected next, and the connection strength and the fracture mode of the bonding wire were measured.

  In addition, the breakage mode of the bonding wire is good for breakage (wire breakage) in the middle of the bonding wire, between the test pattern and the substrate, between the wiring layer and the Ni layer, between the Ni layer and the Pd layer, Those in which breakage occurred between the Pd layer and the Au layer (pad peeling) were judged as defective.

  In addition, the measurement made the number of samples 5 about each item, and the connection strength of the bonding wire has described the arithmetic mean value.

  In addition, the migration resistance is measured by performing a high temperature and high humidity bias test (temperature: 85 ° C., humidity: 85%, load voltage: 10 VDC) on the above sample and measuring the time when migration occurs (time when the wiring layers are electrically short-circuited). It was evaluated by.

  As a result of this test, those in which migration did not occur over 100 hr (hours) were shown as acceptable (O), and those in which migration occurred in less than 100 hr were shown as unacceptable (x) in Table 1. A case in which migration did not occur for 100 hours or more indicates that no practical problem occurs. The measurement of the Bi content and the migration resistance test were carried out only for the samples in which no abnormality was observed in the bonding strength and the fracture mode.

The results are shown in Table 1.

  As can be seen from the results shown in Table 1, when the thickness of the Ni layer is less than 4 μm (sample number 1), the Ni layer cannot absorb and relieve stress, and cracks or peeling between the wiring layer and the substrate can occur. If the Pd layer is less than 0.03 μm (sample number 2) and the thickness of the Au layer is less than 0.005 μm (sample number 3), the Ni layer is oxidized and deposited on the Au layer surface. A Ni oxide layer is formed, or metal diffusion between the bonding wire and the Au layer is insufficient, so that the bonding wire and the Au layer cannot be firmly connected. When the Ni layer thickness exceeds 13 μm or the Pd layer thickness exceeds 0.3 μm (sample numbers 31, 32, 49, 50, 76), the internal stress of the Ni layer or Pd layer Increases, peeling occurs between the wiring layer and the Ni layer, between the Ni layer and the Pd layer, and the thickness of the Au layer exceeds 0.3 μm (sample numbers 74 and 75). In this case, a large amount of fragile aluminum-gold intermetallic compound is generated at the connection between the Au layer and the bonding wire, and the bonding wire is easily detached from the wiring layer. Accordingly, in any of these samples, the bonding strength of the bonding wire is 0.39 (N) or less, and the bonding wire is detached from the wiring layer or the wiring layer is peeled off from the substrate with a small force.

  In addition, when the Bi content in the coating layer is less than 0.005% by mass (sample numbers 4, 15, 26, 43, 58, 69), migration occurs, and the Bi content is 0.030% by mass. When exceeding (Sample Nos. 8, 19, 30, 47, 62, 73), defects such as uneven plating were observed in the Ni coating layer.

  In contrast, the Ni layer has a thickness of 4 μm to 13 μm, the Bi content is 0.005 mass% to 0.030 mass%, the Pd layer thickness is 0.03 μm to 0.3 μm, and the Au layer thickness is The product of the present invention having a thickness of 0.005 μm to 0.3 μm has a bonding wire connection strength of 0.64 (N) or more, bonding of the wiring layer to the substrate, deposition of the coating layer on the wiring layer, bonding to the wiring layer Wire connection can be made extremely strong, and problems such as migration between wiring layers can be effectively prevented.

  The present invention is not limited to the above-described embodiments and experimental examples, and various modifications are possible without departing from the gist of the present invention. For example, in the above-described embodiments, the wiring layer 2 can be changed. If the corner (ridgeline) portion at the upper end of the outer periphery is chamfered in an arc shape, stress concentrates on the adhesion interface between the wiring layer 2 and the coating layer 9 at this corner portion, and a mechanical problem such as a crack occurs in the coating layer 9 Can be effectively prevented from occurring. Therefore, the wiring layer 2 is preferably chamfered in a circular arc shape at the corner (ridge line) at the outer peripheral upper end.

It is sectional drawing which shows one Example of the wiring board of this invention. It is a principal part expanded sectional view of one Example of the wiring board of this invention. It is an expanded sectional view of the wiring layer part of the conventional wiring board.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... substrate 2 ... wiring layer 3 ... semiconductor element 4 ... wiring substrate 5 ... bonding wire 6 ... Ni layer 7 ... Pd layer 8 ... ... Au layer 9 ... Coating layer

Claims (5)

  A wiring layer having a substrate made of an electrically insulating material and a region made of at least one of Au, Ag, Cu, Pd, and Pt, formed by simultaneous firing, and connected to a bonding wire having a diameter of 100 μm or more A Ni layer having a thickness of 4 μm to 13 μm and a Bi content of 0.005 mass% to 0.030 mass%, and 0.03 μm. A wiring board formed of a Pd layer having a thickness of 0.3 μm to a coating layer made of an Au layer having a thickness of 0.005 μm to 0.3 μm.   The wiring board according to claim 1, wherein the coating layer has a Vickers hardness of 200 Hv or more. The wiring board according to claim 1, wherein an internal stress of the Ni layer is 98 N / mm ² or less.   The wiring board according to claim 1, wherein the particle size of the Ni layer is 5 μm to 30 μm.   The wiring board according to claim 1, wherein the surface roughness of the Au layer is 0.1 μm to 0.3 μm in terms of arithmetic average roughness (Ra).

Images