JP2009030108A - Member having lead-free plated layer and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a plated member 3 having a lead-free plated layer 2 which suppresses generation of acicular whisker 10. <P>SOLUTION: A plating material of the plated layer 2 is a Sn based plating material and the plated layer 2 is formed so that the ratio occupied by (001) plane of the Sn crystalline particles is the largest on the surface of the plated layer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  In an electronic component such as a semiconductor device, copper, copper alloy, brass, 42 alloy, or the like is used as a base material for an external terminal. However, if the substrate is left as it is, the terminal surface is oxidized to cause poor conduction due to poor soldering or the like. There is a fear. For this purpose, a protective film (plating layer) is usually formed on the terminal surface by plating or the like to prevent oxidation.

  When using an Sn alloy or Zn alloy as a material for the plating layer, an alloy containing lead (Pb) has been used. In recent years, there has been a demand for lead-free from the viewpoint of reducing the environmental burden, and for the plating layer material of the terminal, for example, a material containing no lead such as Sn alloy and Zn alloy is used. It has become. However, when the surface of the terminal of the electronic component is plated with a lead-free material, whiskers that are needle-like single crystals of Sn or Zn are generated from the plating layer.

  In recent years, for example, electronic components such as a semiconductor device in which an IC chip is mounted on a lead frame have been required to be further reduced in size, and as a result, the distance between the terminals has been reduced to about several hundred μm. The whisker may grow to a length of several hundred μm. If the distance between the terminals is as narrow as several hundred μm as described above, a short circuit between the terminals may occur due to the generated whisker. Measures for suppressing the occurrence of whiskers are required.

  Although the mechanism of whisker generation and growth has not been fully elucidated, the residual stress in the plating layer or the compressive stress applied to the plating layer is considered to be a factor, so the residual stress is actively released or plating is performed. Many solutions have been proposed that reduce the compressive stress on the layer. On the other hand, it has been found that the generation of whiskers can be suppressed by controlling the crystal orientation plane and the orientation index of the plating layer, and solutions from that approach have already been proposed. For example, Patent Document 1 describes that the crystal orientation plane of the Sn plating film is preferentially oriented to the (220) plane, and the film stress after forming the Sn plating film is -7.2 MPa or more and 0 MPa or less. . Patent Document 2 describes that whisker can be suppressed by increasing the (220) / (200) plane orientation ratio of the Sn plating surface. Patent Document 3 discloses a technique for suppressing the generation of whiskers by forming an Sn alloy phase at the crystal grain boundary of the Sn plating layer. In order to facilitate the formation of the Sn alloy phase, the (220) plane in the plating layer is disclosed. And increasing the orientation index of the (321) plane.

JP 2006-70340 A JP 2006-322014 A JP 2006-249460 A

  As a technique for suppressing the generation of whiskers in the lead-free plating layer, the technique for controlling the crystal orientation plane and the orientation index of the plating layer as described above is considered effective. The present inventors have also conducted many experiments and researches on this method, but it is difficult to say that all of the methods proposed heretofore have achieved sufficient results, and there are still points to be improved. Have experienced that.

  The present invention has been made in the circumstances as described above, the present invention is a plating member that can suppress the generation of whiskers more completely using a technique for controlling the crystal orientation plane of the plating layer, It is another object of the present invention to provide a manufacturing method thereof.

  In order to solve the above-mentioned problems, the present inventors have performed X-ray diffraction by the EBSP method on the surface of a large number of lead-free plating layers, and have analyzed the crystal orientation plane in which acicular whiskers are generated. The needle whisker has a higher probability of growing from a crystal orientation plane with a high atomic density in the crystal grains of the plating material than a probability of growth from a crystal orientation plane with a low atomic density. It has been found that the occurrence of whiskers that grow outward from the surface of the plating layer can be suppressed by having many orientations on the surface of the plating layer.

  The present invention is based on the above findings, and the plated member according to the present invention is a plated member having a lead-free plated layer on the surface of a base material, and has a crystal orientation plane with low atomic density in crystal grains of the plated material. It is characterized in that the plating layer is formed in such a manner that more is exposed on the surface as compared with the crystal orientation plane having a high atomic density.

  In the lead-free plating layer according to the present invention, more of the crystal orientation plane with a high electron density with a high probability of growing needle-like whiskers is arranged inside the plating layer, and even if whiskers are generated, they are The probability of growing as a needle-like whisker from the surface toward the outside can be reduced. In the plated member according to the present invention, the ratio of the crystal orientation plane having the lowest atomic density in the crystal grains of the plating material on the surface of the plating layer is preferably 100% or a value close to 100%. If the low crystal orientation plane occupies a larger area on the surface of the plating layer, the intended purpose can be achieved.

  In a more specific aspect of the plating material according to the present invention, when the plating material is an Sn-based plating material, the plating layer is formed so that the ratio of the (001) plane of the Sn crystal grains is the largest on the plating layer surface. Has been. Here, “Sn-based plating material” means a plating material that includes not only pure Sn but also Sn alloys such as Sn—Cu, Sn—Bi, and Sn—Ag.

  In the Sn crystal grains, the (100) plane and the (010) plane are planes with higher atomic density, and the (001) plane is the plane with the lowest atomic density. Therefore, when the plating material is an Sn-based plating material as described above, the plating layer is formed so that the proportion of the (001) plane in the crystal grains is maximized, so that the plating layer surface is directed outward. It is possible to suppress the growth of acicular whiskers. In this case as well, the proportion of the (001) plane on the plating layer surface is preferably 100% or a value close to 100%, but the (001) plane is more in comparison with other crystal orientation planes. If it occupies the area, the intended purpose can be achieved. In the lead-free plating layer made of Sn-based plating material formed by current electrolytic plating or the like, the proportion of the (001) plane of crystal grains on the plating layer surface is several percent or less.

  In order to produce a large number of (001) planes on the surface of the plating layer, that is, to preferentially orient the (001) planes over other planes, it can be performed by an artificial method such as heat treatment. As another method, a method of preferentially orienting the surface to be plated on the surface of the base material to the (001) plane and forming an Sn-based plating layer thereon by epitaxial growth can also be mentioned.

  In another more specific aspect of the plating material according to the present invention, when the plating material is a Zn-based plating material, the plating layer is formed so that the proportion of the (1100) plane of Zn crystal grains is the largest in the plating layer surface. Is formed. Here, the “Zn-based plating material” means a plating material containing not only pure Zn but also a Zn alloy such as Zn—Ni alloy plating as in the case of the “Sn-based plating material”. .

  In the Zn crystal grains, the (0001) plane is a plane having a higher atomic density than the (0001) plane, and the (1100) plane is a plane having a low atomic density. Therefore, when the plating material is a Zn-based plating material as described above, the plating layer is formed so that the proportion of the (1100) plane in the crystal grains is maximized, whereby acicular whiskers from the surface of the plating layer are formed. Growth can be suppressed.

  In order to increase the number of (1100) planes on the surface of the plating layer, that is, to preferentially orient the (1100) planes over other planes, it can be performed by a technique such as heat treatment. As another method, a method of preferentially orienting the surface to be plated on the surface of the base material to the (1100) plane and forming a Zn-based plating layer thereon by epitaxial growth can also be mentioned.

  FIG. 1 is a schematic view of a plated member according to the present invention, and FIG. 2 schematically shows an EBSP analysis result at a location where a whisker is generated in a lead-free plated layer performed by the present inventors.

  As shown in FIG. 1, a plating member 3 according to the present invention has a lead-free plating layer 2 formed on the surface of a base material 1. And in the plating layer 2, the plating layer is formed so that the crystal orientation plane with low atomic density in the crystal grains of the plating material comes out on the surface more than the crystal orientation plane with high atomic density. Thereby, it is suppressed that the acicular whisker 10 grows outward from the plating layer 2.

  The reason will be explained. The present inventors formed a thin plating layer 2 made of pure Sn on the surface of the Cu alloy base material which is the base material 1 by electrolytic plating, and analyzed the surface by EBSP analysis. The EBSP analysis is performed in the ND direction, RD direction, and TD direction of the OIM coordinate system, and the combined result is shown in FIG. 2 in relation to the growth direction of the whisker 10 and the crystal grain surface of the Sn crystal grain 2a. Yes. As shown in the drawing, the surface of the plating layer was the (110) plane, and the crystal orientation of the cross section at the base of the needle-like whisker was the (001) plane. Therefore, the needle-like whisker 10 is generated from the (100) plane or the (010) plane. Therefore, it can be seen that by forming the plating layer so that the (001) plane of the Sn crystal grains is more oriented on the plating surface, it is possible to suppress the growth of the needle-like whisker 10 outward from the plating layer. .

  In the Sn crystal grain, the (100) plane and the (010) plane are planes with higher atomic density, and the (001) plane is the plane with the lowest atomic density. Therefore, in a plating member having a lead-free plating layer on the surface of the base material, the crystal orientation plane with low atomic density in the crystal grains of the plating material is more exposed to the surface than the crystal orientation plane with high atomic density. By forming the plating layer, it is possible to suppress the growth of acicular whiskers outward from the plating layer.

  In the case of Sn-based plating, the plating layer is formed so that the crystal orientation plane with a low atomic density appears on the surface more than the crystal orientation plane with a high atomic density, that is, the (001) plane of the Sn crystal grains is plated. In order to form the plating layer so as to be more oriented on the surface, for example, a technique such as heat treatment may be employed.

  As another method, the Sn-based plating layer may be formed by liquid phase epitaxial growth that is conventionally known by preferentially orienting the surface to be plated of a base material (for example, a Cu alloy base material) to the (001) plane.

The schematic diagram of the plating member by this invention. The figure which shows typically the EBSP analysis result in the whisker generation | occurrence | production location in the lead free plating layer which the present inventors performed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Base material, 2 ... Plating layer, 2 ... Sn crystal grain, 3 ... Plating member, 10 ... Acicular whisker

Claims (5)

  A plating member having a lead-free plating layer on the surface of the base material, so that the crystal orientation plane with low atomic density in the crystal grains of the plating material appears more on the surface than the crystal orientation plane with high atomic density A plating member, wherein a plating layer is formed.   2. The plating layer according to claim 1, wherein the plating material is an Sn-based plating material, and the plating layer is formed so that the ratio of the (001) plane of the Sn crystal grains is the largest on the surface of the plating layer. Plating member.   The method for producing a plated member according to claim 2, wherein the surface to be plated of the base material is preferentially oriented to the (001) plane, and an Sn-based plating layer is formed thereon by epitaxial growth. Manufacturing method of member.   2. The plating layer according to claim 1, wherein the plating material is a Zn-based plating material, and the plating layer is formed such that the proportion of the (1100) plane of the Zn crystal grains is the largest on the surface of the plating layer. Plating member.   5. The method for producing a plated member according to claim 4, wherein the surface to be plated of the base material is preferentially oriented to the (1100) plane, and a Zn-based plated layer is formed thereon by epitaxial growth. Manufacturing method of member.

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