JP2017084866A - Bonding wire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bonding wire having a core material including Ag as a primary component, which can prevent the sulfurization of a wire surface before and after boding.SOLUTION: Used is a bonding wire comprising: a core material 12 including 75 mass% or more of Ag; and a metal coating layer 14 covering the outer peripheral face of the core material 12. The metal coating layer 14 includes 90 mass% or more of at least one element selected from a group consisting of Sn, Zn and In. The metal coating layer is 0.01 μm or more in thickness.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a bonding wire for connecting an electrode of a semiconductor element and an electrode of a substrate, and more particularly to a bonding wire including a core material mainly composed of Ag.

  Since bonding wires used for connecting electrodes on a semiconductor element and electrodes on a substrate are generally very thin, they are manufactured from a metal material having good conductivity and excellent workability. In particular, Au bonding wires have been widely used in the past because of their chemical stability and ease of handling in the atmosphere. However, since a conventional Au bonding wire has a mass of 99% or more and is very expensive, a bonding wire made of a cheaper material is awaited.

  In addition to being cheaper than Au bonding wires, Ag bonding wires are more effective in improving the light emission efficiency of LEDs and the like because their light reflectance is higher than that of Au.

  However, the bonding wire made of Ag has a problem that the surface is easily sulfided and easily discolored. A bonding wire made of Ag having a sulfurized surface is liable to cause poor bonding to the electrode, and also causes a problem that the light reflectance is lowered and the luminous efficiency is deteriorated.

  On the other hand, in order to suppress discoloration due to sulfuration on the Ag surface, a bonding wire has been proposed in which a discoloration prevention layer containing an organic compound and a surfactant is formed on the outer peripheral surface of a core material mainly composed of Ag. (For example, Patent Document 1 below).

JP-A-2015-164186

  However, in the Ag bonding wire having the above-described anti-discoloration layer, the anti-discoloration layer is composed of an organic compound and a surfactant, and thus has an antisulfurization effect in a normal environment. There is a problem that the anti-discoloring layer easily scatters from the surface of the material, and the effect of preventing sulfidation after bonding is reduced.

  The present invention has been made in view of the above problems, and provides a bonding wire that can prevent sulfidation of the wire surface before and after bonding in a bonding wire including a core material mainly composed of Ag. With the goal.

  In order to solve the above problems, a bonding wire of the present invention includes a core material containing 75% by mass or more of Ag and a metal coating layer that covers the outer peripheral surface of the core material. And 90% by mass or more of one or more elements selected from the group consisting of In, and the thickness of the metal coating layer is 0.01 μm or more.

  The thickness of the metal coating layer of the bonding wire according to the present invention can be 1% or less of the diameter of the bonding wire.

  The thickness of the metal coating layer of the bonding wire according to the present invention can be less than 0.1 μm.

  The metal coating layer of the bonding wire according to the present invention preferably contains Sn.

  According to the present invention, the metal coating layer covering the outer peripheral surface of the core material containing Ag as a main component does not contain an organic compound as a main component unlike the prior art, so that it is scattered from the surface of the core material by heat applied during bonding. Therefore, discoloration of the bonding wire surface can be prevented before and after bonding.

It is sectional drawing of the bonding wire which concerns on one Embodiment of this invention.

  Hereinafter, a bonding wire 10 according to an embodiment of the present invention will be described.

  As shown in FIG. 1, the bonding wire 10 according to this embodiment includes a core material 12 mainly composed of Ag, and a metal coating layer 14 that covers the entire outer peripheral surface of the core material 12 so that there is no exposed portion. Prepare.

  Specifically, the core material 12 preferably contains 75% by mass or more of Ag in order to make the light reflectivity Au or more. The specific resistance of the bonding wire 10 is preferably equal to or lower than the specific resistance (3.0 μΩ · cm) of 2N (99%) Au bonding wire. From this viewpoint, the purity is 99.9% by mass or more. It is preferable to produce an Ag alloy that constitutes the core material 12 using Ag.

  The wire diameter (diameter) φ of the core material 12 can be set as appropriate according to the application of the bonding wire 10, but can be set to 5 μm or more and 150 μm or less, for example.

  As long as the core material 12 does not contradict the object of the present invention, in addition to Ag, one or more elements selected from Au and Pd, Ca, Y, Sm, La, Ce, Be, B And one or more elements selected from Ge and at least one element of Cu and Ni may be contained.

  Au can be added to improve the sphericity of a free air ball (hereinafter abbreviated as FAB) formed at the tip of the bonding wire by discharge heating or the like. Usually, when a FAB is produced using a pure Ag wire, it is difficult to stably obtain a FAB having a high sphericity. However, it becomes easy to obtain FAB with high sphericity by adding a certain amount of Au.

Pd can be added in order to improve the corrosion resistance of the part (first joint part) joined by pressing the FAB formed at the tip of the bonding wire against the electrode. An electrode of a semiconductor package such as a BGA (Ball Grid Array) is often coated with aluminum or an aluminum alloy. The electrode of the LED is often gold-coated, but an aluminum or aluminum alloy coating material may be used. When silver and aluminum are bonded, an intermetallic compound layer of silver and aluminum is formed at the bonding interface. When Ag ₂ Al grows in this compound layer, the corrosion resistance in a wet environment deteriorates. When a certain amount of Pd is added to the Ag wire, a Pd enriched layer is formed on the outer peripheral portion of the FAB, which can suppress the formation of Ag ₂ Al and suppress the deterioration of the corrosion resistance in a wet environment.

  Even if Au and Pd are added alone, the effect can be obtained. However, when Pd and Au are added in combination, the melting point of the wire is increased and the heat resistance is further improved.

  When Au and / or Pd are contained in the core material 12 from the above viewpoint, the content is the total amount (that is, when Au or Pd is added alone, the amount of Au or Pd is combined with Au and Pd). When added, the total amount of Au and Pd) is preferably 0.1 to 20% by mass, and more preferably 0.5 to 4.0% by mass. If it is 0.1% by mass or more, a spherical FAB is easily formed by discharge heating, and if it is 10% by mass or less, the specific resistance of the wire is maintained in an appropriate range, and further 0.5% by mass or more. Thus, a FAB having a more stable shape is obtained, and if it is 4.0% by mass or less, the specific resistance of the wire is 3.0 μΩ · cm or less, and a wire with better characteristics is obtained.

  When one or more elements selected from Ca, Y, Sm, La, Ce, Be, B and Ge are added to the core material 12, the total amount of these elements is 5 It is preferable that it is -500 mass ppm. When the content is 5 ppm by mass or more, the strength of the obtained wire can be further improved, and the occurrence of a wire flow in which the bonded wire is moved by the flow of the mold resin at the time of resin molding after bonding can be prevented. When the mass is less than or equal to ppm, the shape of the FAB obtained by discharge heating is stable, and a good spherical FAB is obtained.

  Here, among Ca, Y, Sm, La, Ce, Be, B, and Ge, Y is preferable from the point of being effective in improving the heat resistance and strength of the wire by adding a very small amount, La and Ce are also preferable in that the compound is dispersed in the matrix Ag by making the compound of Ag and contributes to the enhancement of the strength of the wire. However, addition of Ca, Be, B or Ge is preferable from the viewpoint of availability, and addition of Ca is most preferable from the viewpoint of usability and effect.

  Furthermore, in order to further improve the strength, in addition to the addition of Ca, Y, Sm, La, Ce, Be, B or Ge, the addition of Cu and Ni is effective. Cu, Ni is easily alloyed with Ag of the matrix without reacting with Ca, Y, Sm, La, Ce, Be, B and Ge, so Ca, Y, Sm, La, Ce, Be, B and This contributes to increasing the strength of the matrix without impairing the effect of adding Ge. When high strength is required, Cu or Ni may be added together with Ca, Y, Sm, La, Ce, Be, B, and Ge as described above, but Ca, Y, Sm, La may be added. Even if Cu or Ni is added instead of Ce, Be, B and Ge, the strength of the wire can be improved.

  Moreover, when adding 1 type or 2 types of elements selected from Cu and Ni to the core material 12, it is preferable that the total amount of these elements is 100-10000 mass ppm. When it is 100 mass ppm or more, the strength of the obtained wire can be further improved, and the occurrence of wire flow in which the bonded wire moves by the flow of the molding resin can be prevented at the time of resin molding after bonding. When the mass is less than or equal to ppm, the shape of the FAB obtained by discharge heating is stable, and a good spherical FAB is obtained.

  Next, the metal coating layer 14 contains 90% by mass of one or more elements selected from the group consisting of Sn, Zn, and In in order to suppress sulfidation on the surface of the core material 12 and obtain a significant discoloration preventing effect. It is preferable to contain above, and it is more preferable to contain 99 mass% or more. The metal coating layer 14 is preferably made of one or more of Sn, Zn, and In, and any of Sn, Zn, In, Sn and Zn alloys, and Sn and In alloys. More preferably, it consists of one of them. Among Sn, Zn, In, an alloy of Sn and Zn, and an alloy of Sn and In, Sn is preferable in terms of excellent workability. The metal coating layer 14 may contain elements other than Sn, Zn, and In as long as the object of the present invention is not adversely affected. Examples of such metals include Ti, Cu, Ni, Al, Mg, Pd, Au, Pt are mentioned.

  The thickness t of the metal coating layer 14 is preferably 0.01 μm or more and less than 0.1 μm. When the thickness t of the metal coating layer 14 is 0.01 μm or more, sulfidation of the surface of the core material 12 can be suppressed, and a significant discoloration preventing effect can be obtained. If the thickness t of the metal coating layer 14 is less than 0.1 μm, cracking of the metal coating layer 14 is less likely to occur even when wire drawing is performed after the metal coating layer 14 is provided on the outer peripheral surface of the core material 12. The metal coating layer 14 preferably covers the entire surface of the core material 12 without any gaps, but there may be uncovered portions as long as the object of the present invention is not adversely affected.

  Further, in order to improve the sphericity of the FAB obtained by discharge heating, it is preferable to reduce the thickness t of the metal coating layer 14 as the wire diameter φ of the bonding wire 10 becomes smaller, and the wire diameter φ of the bonding wire 10. In contrast, the ratio ρ (t / φ) of the thickness t of the metal coating layer is preferably 1% or less, and more preferably 0.2% or less. If the ratio ρ is 1% or less, the shape of the FAB obtained by discharge heating is stable and a good spherical FAB is easily obtained, and if it is 0.2% or less, the FAB having a more stable shape is easily obtained.

  Next, an example of a method for manufacturing the bonding wire 10 having such a configuration will be described.

  First, Ag having a purity of 99.9% by mass or more, if necessary, one or more selected from Au, Pd, Ca, Y, Sm, La, Ce, Be, B, Ge, Cu and Ni After adding the above element and casting an Ag alloy containing 95% by mass or more of Ag, a rod-shaped ingot having a predetermined diameter is produced by a continuous casting method.

  Next, the rod-shaped ingot is drawn to reduce the diameter until the core material 12 has a predetermined diameter. Thereafter, a metal coating layer 14 containing one or more elements selected from Sn, Zn, and In is formed on the entire outer periphery of the core material 12. The metal coating layer 14 can be formed by known means such as electroplating, electroless plating, and vapor deposition.

  Then, the core material 12 on which the metal coating layer 14 is formed is further drawn to reduce the diameter until a predetermined wire diameter φ (for example, 5 μm to 150 μm) is reached. Thereby, the bonding wire 10 which covered the whole outer peripheral surface of the core material 12 with the metal coating layer 14 whose thickness t is 0.01 micrometer or more can be obtained.

  The thickness t of the metal coating layer 14 is changed to the thickness t of the metal coating layer 14 of the finally obtained bonding wire 10 by changing the thickness of the metal coating layer 14 formed on the core material 12 during the wire drawing process. Can be adjusted.

  In addition, you may heat-process the bonding wire 10 as needed in the middle of a wire drawing process, or after completion | finish of a wire drawing process. If an example of heat processing is given, a continuous annealing process can be performed for 0.1 to 60 second at 300-1000 degreeC in air | atmosphere atmosphere or nitrogen gas atmosphere.

  In the bonding wire 10 obtained as described above, the core is formed by the metal coating layer 14 containing 90% by mass or more of one or more elements selected from Sn, Zn and In and having a thickness t of 0.01 μm or more. Since the outer peripheral surface of the material 12 is covered, sulfidation of the core material 12 can be suppressed, and thus discoloration of the bonding wire 10 can be suppressed. In addition, the metal coating layer 14 is made of a metal such as Sn and remains on the outer peripheral surface of the core material 12 without being scattered by heat applied when the bonding wire 10 is bonded. Discoloration due to sulfuration can be prevented.

  As mentioned above, although embodiment of this invention was described, these embodiment was shown as an example and is not intending limiting the range of invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and modifications thereof are included in the invention described in the claims and equivalents thereof as well as included in the scope and gist of the invention.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to these Examples.

An Ag alloy containing 95% by mass or more of Ag was melted, and a rod-shaped ingot was produced by a continuous casting method. Then, the rod-shaped ingot is drawn to reduce the diameter until the core material 12 has a diameter of 488 μm, and then the outer peripheral surface of the core material 12 is coated with Sn by electroplating, and Sn is 99.5% by mass. The containing metal coating layer 14 was formed. Thereafter, the core material 12 on which the metal coating layer 14 is formed is further drawn to reduce the diameter until the wire diameter φ reaches 25 μm, and then subjected to continuous annealing treatment (heat treatment) at 460 ° C. for 1 second in an air atmosphere. The bonding wires 10 of Examples 1 to 5 and Comparative Examples 1 to 3 were obtained.

  Examples 1 to 5 and Comparative Examples 1 to 3 all included the wire diameter φ of the bonding wire 10 and the composition of the core material 12 and the metal coating layer 14 except that the thickness t of the metal coating layer 14 was changed. Identical.

  For the obtained bonding wires 10 of Examples 1 to 5 and Comparative Examples 1 to 3, measurement of the thickness t of the metal coating layer 14, presence or absence of cracks in the metal coating layer 14, sulfidation resistance, and FAB true ball performance Evaluation was performed. The specific evaluation method is as follows. The results are shown in Table 1.

1. Thickness measurement of metal coating layer The bonding wires 10 of Examples 1 to 5 and Comparative Examples 1 to 3 were scanned with a scanning Auger Electron Spectrometer (PHI-700, ULVAC-PHI Co., Ltd.) in the depth direction with Ar ions. Sputtering was carried out for a unit time (inward in the radial direction), and the Sn concentration was measured each time, and the thickness of the metal coating layer was determined up to the point where the concentration was ½ of the Sn concentration in the outermost layer. For the thickness conversion, SiO ₂ conversion was used.

2. Evaluation of cracks in the metal coating layer The bonding wire 10 in which the metal coating layer 14 is formed on the outer peripheral surface of the core material 12 by electroplating is drawn until the wire diameter reaches 250 μm, and then a general-purpose electron microscope ( The surface appearance is observed with JEOL Co., Ltd. (JSM-6510LA), and an energy dispersive X-ray spectrometer (EDX: Energy Dispersive X-ray Spectroscopy) (EX-37001, manufactured by JEOL Ltd.) The surface state was analyzed at 1 to evaluate the presence or absence of cracks (plating cracks) in the metal coating layer 14 caused by wire drawing.

3. Sulfide resistance evaluation After bonding wires 10 of Examples 1 to 5 and Comparative Examples 1 to 3 were cut to a length of 200 mm to prepare an evaluation sample, the evaluation sample was exposed to vapor generated from an aqueous ammonium sulfide solution for 20 minutes. The external appearance was observed with the general-purpose electron microscope, and the sulfur mass was measured with the energy dispersive X-ray spectrometer.

  With respect to the sulfur mass quantitative value of the bonding wire of Comparative Example 1 in which the metal coating layer 12 is not formed, a sulfur mass quantitative value of 70% or less is judged to have sulfurization resistance, and is more than 70%. The product was judged not to have sulfurization resistance.

4). Evaluation of FAB True Sphericality For the bonding wires of Examples 1 to 5 and Comparative Examples 1 to 3, FABs were prepared using a wire bonder (Iconn, manufactured by K & S). FAB preparation conditions were as follows: discharging was performed in an N ₂ gas atmosphere at a gas flow rate of 0.5 mL / min, a spark current of 40 mA, and a spark time of 1200 μsec.

  For evaluation of FAB sphericity, 40 FABs were prepared for each of the bonding wires of Examples and Comparative Examples, and the appearance was observed with the general-purpose electron microscope. And the length in the vertical direction were measured. The ratio (X / Y) of the length X of the FAB in the wire parallel direction to the length Y in the vertical direction is used as an index of true sphericity. The number of FABs judged to be spherical was counted.

  The results are as shown in Table 1. In Examples 1 to 5, even after heat treatment at 460 ° C., the sulfur mass was 70% or less of Comparative Example 1 in the sulfidation resistance evaluation test, and sulfidation performance was recognized. It was. That is, since the metal coating layer 14 does not scatter due to heat, sulfidation of the wire surface can be prevented not only before but also after bonding.

  In particular, in Examples 1 to 3, no cracks occurred in the metal coating layer 14 due to the wire drawing performed after the metal coating layer 14 was formed. Moreover, in Examples 1-3, FAB with favorable sphericity could be produced.

  On the other hand, in Comparative Examples 1-3, the sulfur mass in the sulfidation resistance evaluation test was greater than 70% of Comparative Example 1, and no significant sulfidation performance was obtained.

DESCRIPTION OF SYMBOLS 10 ... Bonding wire, 12 ... Core material, 14 ... Metal coating layer

Claims (4)

A core material containing 75% by mass or more of Ag, and a metal coating layer covering the outer peripheral surface of the core material,
A bonding wire in which the metal coating layer contains 90% by mass or more of one or more elements selected from the group consisting of Sn, Zn, and In, and the thickness of the metal coating layer is 0.01 μm or more.   The bonding wire of Claim 1 whose thickness of the said metal coating layer is 1% or less of the wire diameter of a bonding wire.   The bonding wire according to claim 1, wherein the metal coating layer has a thickness of less than 0.1 μm.   The bonding wire according to claim 1, wherein the metal coating layer contains Sn.

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