JP2006249460A - Sn PLATING OR Sn ALLOY PLATING HAVING EXCELLENT SUPPRESSION OF WHISKER GENERATION - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an Sn plating or Sn alloy plating structure free from the generation of whiskers, to provide its production method, and particularly, to provide an Sn plating or Sn alloy plating structure where the generation of whiskers is suppressed even when being subjected to external stress such as bending, and to provide its production method. <P>SOLUTION: The Sn plating or Sn alloy plating is characterized in that an alloy phase of Sn is formed on the grain boundaries of Sn plating or Sn alloy plating, and particularly, an alloy phase of Sn in which the ratio to be occupied in the length of the grain boundaries is ≥50% is formed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to the technical field of Sn plating or Sn alloy plating, and more particularly to Sn plated copper plates and copper alloy plates used for connector terminals of semiconductor lead frames and electronic components, and Sn plating that suppresses the occurrence of whiskers causing short circuits. The present invention also relates to a structure of Sn alloy plating and a manufacturing method of Sn plating or Sn alloy plating structure.

  Semiconductor lead frames and connector terminals of electronic devices are usually plated with Sn—Pb alloy in order to improve solderability. However, in recent years, Sn plating that does not use Pb is required due to environmental problems.

  However, whisker which is a single crystal of needle-like Sn having a diameter of several μm and a length of several μm to several mm is spontaneously generated from the surface of Sn plating, resulting in a short circuit problem. To do. As for this whisker, a fast one occurs within a few days after plating, and a slow one occurs several months after plating.

  The growth mechanism of this Sn whisker is not completely understood, but it is said that when compressive stress is applied to the Sn plating layer, this will be the driving force and induce whisker diffusion. .

  Therefore, in order to prevent the generation of Sn whiskers, there is a method for preventing the Sn plating layer from being subjected to compressive stress.

  Here, as the compressive stress applied to the Sn plating layer, the plating residual compressive stress generated by plating, the Cu of the substrate reacts after plating, and the alloy phase of Sn and copper (Cu3Sn or Cu6Sn5) at the interface between the plating and the Cu substrate There is a compressive stress generated due to the generation of compressive stress due to the formation of, and bending after plating.

  For this reason, as a method of reducing the compressive stress and preventing whisker generation, (1) Reduction of plating residual stress by studying plating conditions and plating method, (2) Sn and Cu alloy phase cannot be at the substrate and plating interface As described above, there is a base plating on a copper or copper alloy substrate, and (3) residual stress relaxation by performing a heat treatment after Sn plating.

  As a method of (1), for example, as shown in Patent Document 1, there is a method of relaxing internal stress of Sn plating by performing pulse plating. However, even if the initial plating residual stress is reduced, after the plating, Sn and the copper of the substrate react gradually, and a compressive stress is generated due to the formation of an alloy phase of Sn and copper at the interface. Occurs.

  In the method (2), for example, as reported in Non-Patent Document 1, Dittes et al. Suppress the generation of stress due to the formation of an alloy layer of Cu and Sn by performing Ni or Ag base plating on a Cu substrate. This shows that whisker generation is suppressed. However, whiskers are generated if there is residual compressive stress after plating. Therefore, a combination with (1) is required, but if processing is performed after plating, a whisker is generated because compressive stress is generated.

  The method (3) includes, for example, a method of heat-treating an Sn plating material in the range of 180 ° C. to a melting point temperature as shown in Patent Document 2 and a Sn-Cu alloy plating of 227 ° C. as shown in Patent Document 3. There is a method of performing heat treatment at 270 ° C. or lower and within 15 minutes. In these methods, an alloy phase is rapidly formed at the substrate-plating interface by heat treatment, but since it is in a heated state, the generated compressive stress is rapidly relieved, and once the alloy phase is formed, Since the diffusion rate of Sn and Cu becomes very slow, the growth of the alloy phase is suppressed and the generation of new stress is suppressed when the temperature is returned to room temperature. In addition, after stress relaxation occurs due to heating, tensile stress is generated due to the difference in thermal expansion coefficient between Sn and Cu due to cooling after heating, and thus whisker generation is suppressed. However, whisker is generated when external compressive stress is generated by processing.

In addition to reducing compressive stress, whisker prevention methods using Sn alloy plating have been reported. For example, Patent Document 4 describes Sn—Bi alloy plating, Patent Document 5 describes Sn—Zn alloy plating, Patent Document 6 describes Sn—Cu alloy plating, and Patent Document 7 describes Sn—Ag alloy plating. . The reason for whisker suppression is not specified for Sn-Cu, but Sn-Bi and Sn-Zn inhibit the diffusion of Sn by Bi and Zn, and Sn-Ag has an Ag alloy phase in the Sn plating layer. It is described that whisker generation is suppressed due to the formation. However, even with these methods, it is difficult to completely suppress whisker generation, and there is a demand for Pb-free Sn plating that suppresses whisker generation.
JP2003-129276 JP 57-126992 JP2003-193289 JP2004-169073 JP2003-253470 JP2000-87204 JP2002-220682 Tin Whisker Formation-Results, Test Methods and Countermeasures, IEEE (2003) pp822-826

  The present invention has been made paying attention to such circumstances, and an object thereof is to provide Sn plating or Sn alloy plating in which no whisker is generated, and a method for manufacturing the same. In particular, the present invention provides an Sn plating or Sn alloy plating in which the generation of whiskers is suppressed even when an external stress such as bending is applied, and a method for manufacturing the same.

  In order to achieve the above object, the present inventors have intensively studied, and as a result, completed the present invention. According to the present invention, the above object can be achieved.

  The present invention thus completed and capable of achieving the above object relates to Sn plating or Sn alloy plating, and has the following configuration.

  Claim 1 is Sn plating or Sn alloy plating characterized in that an Sn alloy phase is formed at the grain boundary of Sn plating or Sn alloy plating (first invention).

  A second aspect of the present invention is characterized in that the ratio of the Sn alloy phase formed at the grain boundaries of Sn plating or Sn alloy plating to the grain boundaries is 50% or more. Alloy plating (second invention).

  Claim 3 is characterized in that the Sn alloy phase formed at the grain boundary of Sn plating or Sn alloy plating is any one of Sn and Cu, Sn and Fe, Sn and Co, Sn and Ni alloy The Sn plating or the Sn alloy plating according to claim 1 or 2 (third invention).

  Claim 4 is the Sn alloy plating according to any one of claims 1 to 3, wherein the alloy element of the Sn alloy plating is at least one selected from Cu, Co, Fe, and Ni. (Fourth invention).

  In claim 5, on the copper or copper alloy substrate, there is any one of Cu, Fe, Co, Ni, Ni-P plating layer as the first layer, and Sn plating or Sn alloy as the second layer thereon. 5. The Sn plating or Sn alloy plating according to claim 1, further comprising a plating layer (fifth invention).

  Claim 6 is Sn plating or Sn alloy plating according to claim 3, wherein the Sn alloy phase formed at the grain boundaries of Sn plating or Sn alloy plating is Sn and Cu. Six inventions).

According to a seventh aspect of the present invention, among the Sn peaks of an X-ray diffraction spectrum obtained by measuring 2θ from 30 ° to 80 ° by a θ-2θ method of an X-ray diffraction method using a Cu X-ray source ( 220) The peak intensity I (220) of the plane and the peak intensity I (321) of the (321) plane satisfy the formula (1), or Sn plating or Sn according to any one of claims 1 to 6 Alloy plating,
[I (220 / I ₀ 220) + I (321 / I ₀ 321)] / [ΣI (hkl) / I ₀ (hkl)] ≧ 0.5 (1)
Here, I ₀ (hkl) represents the peak intensity of the (hkl) plane described in the JCPDS card, and I (hkl) represents the peak height of the measured Sn (hkl) plane (seventh invention).

  Claim 8 is a copper or copper alloy plated product to which the Sn plating or Sn alloy plating according to any one of claims 1 to 7 is applied. (Eighth invention).

  Claim 9 is a crystal of Sn plating or Sn alloy plating by performing a step of performing Sn plating or Sn alloy plating on a Cu or Cu alloy substrate and then a step of performing a heat treatment at a temperature of 100 ° C. to 180 ° C. This is a method of forming a Sn—Cu alloy phase at the grain boundary (ninth invention).

  Claim 10 is a step of plating any one of Fe, Co, Ni, Ni-P, Cu plating layers as a first layer on a substrate, a step of performing Sn plating or Sn alloy plating thereon, and thereafter The method of forming an alloy phase of Sn and the metal element contained in the first plating layer at the grain boundary of Sn plating or Sn alloy plating by performing a heat treatment step at a temperature of 100 ° C. to 180 ° C. Yes (tenth invention).

  According to the present invention, it is possible to provide an excellent Sn plating or Sn alloy plating structure that does not generate whiskers even when an external stress such as bending is applied, and a method for manufacturing the same. It makes a useful contribution.

  Although the mechanism of whisker generation from Sn plating is not completely understood, it is considered that whisker is generated by compressive stress acting on plating inducing diffusion of Sn atoms as described above.

  In the prior art, an effort has been made to prevent the generation of compressive stress. However, if mechanical processing such as bending is applied to the plating from the outside, the compressive stress cannot be avoided, leading to the generation of whiskers.

  On the other hand, the present inventors paid attention to the diffusion of Sn atoms, and as a result of intensive research, the formation of whiskers by forming an alloy phase in which the diffusion rate of Sn atoms becomes slow at the grain boundaries of Sn or Sn alloy plating Found to suppress.

  That is, the diffusion of Sn atoms is dominated by grain boundary diffusion that diffuses Sn grain boundaries rather than body diffusion that diffuses within Sn crystal grains, and the grain boundaries of Sn or Sn alloy are important for whisker generation It is thought that it plays a role. Therefore, the idea has been reached that the formation of whiskers can be suppressed by forming an alloy phase that inhibits the diffusion of Sn atoms at the grain boundaries of Sn or Sn alloy.

  Examples of such alloy phases include combinations of Sn and Cu, Sn and Fe, Sn and Ni, Sn and Co, and the like. Specifically, Cu6Sn5, FeSn2, FeSn, Fe3Sn2, Ni3Sn4, Ni3Sn2, CoSn2, CoSn, and the like.

  In order to sufficiently inhibit the diffusion of Sn atoms and suppress the generation of whiskers, it is preferable that the ratio of the grain boundary length of the Sn alloy phase formed at the grain boundaries is 50% or more.

  Of course, it is preferable that the thickness of these Sn alloy phases is thick. This is because the Sn diffusion coefficient in the Sn alloy phase is small, but if the thickness is small, Sn atoms penetrate through the alloy phase and the effect as a diffusion barrier is reduced. Therefore, the thickness of the Sn alloy phase should preferably be 0.05 μm or more, more preferably 0.1 μm or more, and most preferably 0.2 μm or more. Further, the Sn alloy phase is preferably as continuous as possible. This is because, when intermittently present, Sn diffuses from the part where the alloy phase is broken. Therefore, it is most preferable that an alloy phase is continuously formed over the entire crystal grain boundary of Sn plating or Sn alloy plating connected from the substrate surface to the plating surface. Furthermore, it is considered that Sn atoms forming whiskers are also involved in Sn atoms several tens of μm or more away from the whiskers, so even if an alloy phase is not formed at all grain boundaries, for example, the thickness direction of plating and Of the grain boundaries of the plating that reach the plating surface from the substrate surface crossing the vertical direction, for example, the entire grain boundary from the substrate surface to the plating surface at a ratio of 30 μm in the direction perpendicular to the thickness direction of the plating There may be a crystal grain boundary in which an alloy layer is continuously formed.

  Among these, when Sn alloy plating is Sn-Cu alloy plating, or when the substrate to be plated is Cu or Cu alloy, Cu in Sn-Cu alloy or Cu in substrate is Sn or Sn alloy plating crystal By diffusing into the grain boundary, an alloy phase of Sn and Cu can be formed at the grain boundary. In this case, Cu base plating may be performed on the Cu or Cu alloy base material. In particular, when the base material does not contain copper such as 42 alloy (Fe—Ni alloy), it is effective to perform Cu base plating.

  In the case of Sn—Cu alloy plating, Cu does not dissolve in Sn and the diffusion coefficient of Cu in Sn is large, so Cu tends to precipitate at the grain boundaries of Sn—Cu alloy plating. For this reason, the Sn—Cu alloy phase is precipitated at the crystal grain boundary of the Sn—Cu alloy plating, but the structure of the crystal grain boundary influences the precipitation of the alloy phase at the crystal grain boundary. That is, when the energy of the crystal grain boundary is low, the Sn—Cu alloy is not sufficiently precipitated, and whisker generation cannot be suppressed. In addition, when the substrate does not contain Cu, the supply of Cu is only Cu in Sn-Cu alloy plating, so if the Cu composition in Sn-Cu is low, a sufficient alloy phase is precipitated at the grain boundaries. Can not do it. Therefore, the Cu composition in the Sn—Cu alloy plating needs to be 1 wt% or more. Preferably it is 2 wt% or more, and most preferably 3 wt% or more. On the other hand, if there is too much Cu, Cu-Su alloy phase will precipitate in the crystal grains of Sn-Cu alloy plating, Cu will not precipitate at the grain boundaries, and Cu-Sn alloy phase will not be formed at the grain boundaries Therefore, it is preferably 10 wt% or less. More preferably, it is 9 wt%, and most preferably 8 wt% or less.

  Moreover, when performing Cu base plating, it is preferable that the thickness of Cu plating shall be 0.1 micrometer or more. If the thickness is smaller than this, the diffusion of Cu into the Sn plating or Sn alloy plating grain boundary is not sufficiently performed. Preferably it is 0.2 μm or more, most preferably 0.5 μm or more. Although Cu diffusion can be spontaneously formed by adjusting the crystal orientation of Sn or Sn alloy plating described later, more alloy layers can be formed by heat treatment.

  When heat treatment is performed, the treatment temperature is desirably 100 ° C. or higher and 180 ° C. or lower. If it is not higher than 100 ° C, the effect of promoting diffusion cannot be obtained. In addition, the body diffusion that diffuses within the Sn crystal of Cu becomes more prevalent, and the Cu and Sn alloy layer at the interface between the Sn or Sn alloy plating and the substrate before Cu diffuses at the grain boundary. This is because this layer acts as a barrier layer for Cu grain boundary diffusion and hinders alloy phase formation at the Sn grain boundary. Further, the treatment time is preferably 10 minutes or more and 60 minutes or less. If it is less than 10 minutes, Cu does not diffuse sufficiently, and if it is more than 60 minutes, the Cu-Sn alloy phase precipitated at the crystal grain boundaries aggregates and collects in the crystals of a certain Cu-Sn alloy. This is because the proportion of the Cu—Sn alloy that is being used decreases.

  In addition, if you want to form an alloy phase of Sn and Fe, Sn and Ni, Sn and Co, perform an underplating of Fe, Ni, Ni-P, Co on the substrate and perform heat treatment, or Sn An alloy phase can be formed at the grain boundary of Sn or Sn alloy plating by performing heat treatment after performing -Ni plating, Sn-Co plating, and Sn-Fe plating. Naturally, heat treatment may be performed by combining these base plating and alloy plating. The heat treatment temperature is preferably 100 ° C. or higher and 180 ° C. or lower. If the temperature is 100 ° C. or lower, diffusion does not occur sufficiently. If the temperature exceeds 180 ° C., an alloy element diffusion barrier layer is formed at the interface as in the case of Cu.

  These alloy phases are removed from the plating cross-section when the Ga + ion beam is applied to the film thickness direction from the Sn or Sn alloy plating surface by the Focused ion beam (FIB) device to form the plating cross-section. The presence or absence of the secondary electron image can be examined by taking a secondary electron image. In other words, when Ga + is irradiated, the amount of secondary electrons emitted differs depending on the crystal orientation and crystal structure of the crystal grains appearing on the plating cross section, so that there is a contrast for each alloy phase present in the crystal grains and crystal grain boundaries. Since different images are obtained, the presence or absence of the alloy phase can be confirmed.

  Specifically, in order to protect the surface of Sn or Sn plating, a carbon vapor deposition film was formed on the surface about 2 μm thick, and then the sample was placed in the chamber of the FIB apparatus and evacuated. Then, gallium ions with an acceleration voltage of 30 kV, a beam diameter of 320 nm, and a beam current of about 3700 pA are irradiated perpendicularly to the sample surface (deposition surface), and the Sn plating or Sn alloy plating layer is cut in the sample film thickness direction to obtain a cross section of the plating. put out. Furthermore, after finishing the cross section by irradiating gallium ions with an acceleration voltage of 30 kV, a beam diameter of 92 nm, and a beam current of about 1400 pA in parallel to the cut surface, an acceleration voltage of 30 kV, a beam diameter of 7 nm, and a beam current of about 2 pA Whether or not an alloy phase is formed at the grain boundary can be seen by taking a secondary electron image (SIM image) of secondary electrons emitted from the cross section when the cross section is irradiated with gallium ions. The SIM image was taken with the sample tilted 60 ° with respect to the normal of the sample surface.

  When the presence or absence of the alloy phase is observed in this way, for example, if the proportion of the formation length of the alloy phase in the total length of the grain boundary that can be confirmed in the cross section of the 30 μm width region is 50% or more, the whisker Generation suppression effect is obtained. The proportion of the formation length of the alloy phase is preferably 65% or more, and most preferably 80% or more.

  Here, the length of the grain boundary, the length of the alloy phase precipitated at the grain boundary, and the ratio of the alloy phase can be specifically obtained as follows.

  FIG. 1 shows an example of a cross-sectional photograph of a Sn-plated copper plate formed of FIB. As shown in the photograph of FIG. 1, it can be seen that Sn crystal grains are visible in the cross section of Sn plating due to the difference in contrast, and an alloy phase that appears white at the crystal grain boundary is also observed. In order to obtain the length of the crystal grain boundary and the length of the alloy phase by image analysis, first, the Sn plating layer portion of FIG. 1 is cut out as shown in FIG. By drawing a line on the alloy phase and adjusting the brightness, contrast, and gamma value, the photographic image is erased so that only the line drawn on the alloy phase remains in the image. This is shown in FIG. Similarly, a line having the same thickness as that drawn on the alloy phase is drawn on the crystal grain boundary of the photograph of FIG. 2 so that only the drawn line remains by erasing the image of the photograph. This is shown in FIG. These figures are image-analyzed to determine the number of pixels of the line, and the ratio of the length of the alloy phase to the grain boundary length is determined by dividing the number of pixels in FIG. 3 by the number of pixels in FIG. In the case of FIG. 3, the number of pixels is 2907, and FIG. 4 has the number of pixels 3922. Therefore, the ratio of the alloy phase in the example of the Sn-plated copper plate is calculated as 74%.

  When the substrate has a copper plate or a copper base plating, Sn plating and a copper plate, and Cu6Sn5 that is an alloy phase of Sn and Cu are formed between the Sn plating and the copper base plating. The grain boundary between this alloy phase and Sn plating is considered to be equivalent to the interface between the substrate and Sn plating, and no line is drawn at this boundary.

  In order to form an alloy phase at such a crystal grain boundary, it is desirable that Sn or Sn alloy plating is first oriented in the (220) plane and the (321) plane. That is, among the peaks of the crystal plane of Sn or Sn alloy plating when the range of 2θ is measured from 20 ° to 80 ° by X-ray diffraction of the θ-2θ method using a Cu X-ray source, (220) It is desirable that the peak intensity of the plane and the (321) plane satisfy the formula (1). Eleven peaks appear on the crystal plane of Sn from 20 ° to 80 °. That is, the surfaces are (200), (101), (220), (211), (301), (112), (400), (321), (420), (411), and (312). Of these, since the (200) plane and the (400) plane are the same plane, if the (400) plane is omitted, basically 10 different plane peaks appear. Here, the crystal plane is represented by (hkl), the peak intensity of Sn (hkl) plane described in the JCPDS diffraction data card is I0 (hkl), and the peak intensity (peak) of the (hkl) plane obtained by measurement When the height is I (hkl), I (hkl) / I0 (hkl) / ΣI (hkl) / I0 (hkl) represents the orientation of the (hkl) plane. Here, Σ represents the sum of 10 crystal planes excluding (400) appearing from 20 ° to 80 °. I (hkl) / I0 (hkl) / ΣI (hkl) / I0 (hkl) is 10 if the measured peak intensity is exactly the same as the JCPDS diffraction data card, that is, no orientation. Since we are thinking about the peak of, it becomes 0.1. Therefore, if the peak of a certain (hkl) plane is strong and oriented in that plane, it will exceed 0.1, and if the peak intensity of that plane is weak, it will be less than 0.1. In other words, equation (1) represents the degree of orientation of the (220) plane and the (321) plane. When this value is 0.5 or more, an alloy phase is formed at the grain boundary of Sn or Sn plating. It becomes easier. Preferably, it is 0.65 or more, and most preferably 0.8 or more.

Examples of the present invention and comparative examples will be described below. The present invention is not limited to this embodiment, and can be implemented with appropriate modifications within a range that can be adapted to the gist of the present invention, all of which are within the technical scope of the present invention. include.
(Example 1)
The copper plate was immersed in an Sn plating bath using alkanol sulfonic acid to produce a 10 μm thick Sn plating at a current density of 15 A / dm 2 and a plating temperature of 30 ° C. In addition, the copper plate was immersed in a sulfuric acid Sn plating bath to produce a 10 μm thick Sn plating at a current density of 2 A / dm 2 and a plating temperature of 15 ° C.

  These Sn platings were prepared by using FIB (SII Nano Technology Co., Ltd .: SMI9200 high-performance ion microscope) to produce plated sections by Ga + ion irradiation, SIM images of the sections were taken, and Sn plating grain boundaries were observed. The SIM image was taken over a width of 30 μm of the Sn plating layer at a magnification of 4500 times. Calculate the total length of the grain boundaries observed from this SIM image, then calculate the total length of the grain boundaries where the alloy phase occupies the total, and calculate the total length of the entire grain boundaries. The ratio was calculated. This cross-sectional observation was performed at three arbitrary locations, and the average value of the ratio with the total length of the entire grain boundary obtained at each location was calculated, and this was calculated as the total length of the entire grain boundary of the main plating. And the ratio. In addition, the alloy phase crystals were processed into thin pieces with a thickness of about 100 nm using FIB, and the diffraction image obtained as a result of electron beam diffraction using a transmission electron microscope (TEM) was analyzed. As a result, Cu6Sn5 was obtained. . This shows that Cu diffused from the Cu substrate to the grain boundary of Sn plating to form an alloy phase.

  The ratio of the alloy phase of Sn plating prepared from the alkanol sulfonic acid Sn plating bath to the crystal grain boundary was 90%. On the other hand, the ratio of the Sn plating alloy phase produced from the sulfuric acid Sn plating bath to the crystal grain boundary was 37%.

  Further, Sn plating was performed by X-ray diffraction from 20 ° to 80 ° by a θ-2θ method using a Cu X-ray source, the height of the Sn peak was measured, and the calculation of equation (1) was performed. At this time, the Sn plating formed from the alkanol sulfonic acid Sn plating bath had a value of 0.99 in the formula (1), whereas the Sn plating formed from the sulfuric acid Sn bath had the formula (1). The value was 0.1.

  These Sn platings were placed in a constant temperature and humidity test apparatus having a temperature of 85 ° C. and a relative humidity of 85 RH%, and held for 500 hours. Thereafter, the surface of the Sn plating was observed with a scanning electron microscope (SEM) at a magnification of 100 times, and the number of whiskers generated in an area of 0.5 mm × 1 mm at any five locations on the plating surface was measured, and the average value Asked. As a result, no whiskers were observed in the Sn plating produced from the organic acid Sn plating bath in which many alloy phases at the grain boundaries were formed. On the other hand, ten whiskers were observed on the Sn plating surface prepared from the sulfuric acid Sn plating bath in which the alloy phase was not formed so much.

From the above results, when the Sn plating crystal is oriented in the (220) plane or the (321) plane, many Sn and Cu alloy phases are formed at the grain boundary of the Sn plating, and the generation of whiskers is effective. It turns out that it is suppressed.
(Example 2)
By adding alkanol sulfonic acid copper to the plating bath of alkanol sulfonic acid Sn and changing the addition amount, Sn-Cu alloy plating having a different Cu composition was formed on a 42 alloy substrate to a thickness of 10 μm. At this time, plating was performed at current densities of 2.5 A / dm 2 and 5 A / dm 2.

  After plating, the composition of copper in Sn-Cu alloy plating was analyzed by EDX (energy dispersive X-ray fluorescence spectrometer). Further, similarly to Example 1, the Sn—Cu plating cross section was observed by FIB, and the ratio of the alloy phase in the crystal grain boundary was measured. Furthermore, the orientation of the Sn—Cu alloy plating was also determined by X-ray diffraction using the formula (1).

  Further, as in Example 1, it was left in a constant temperature and humidity tester at 85 ° C. and 85 RH% for 500 hours, and the number of whiskers generated was observed by SEM (observation area was 0.5 mm × 1 mm).

  The results are shown in Table 1. No generation of whiskers was observed in the Sn—Cu alloy plating No. 3 to 6 in the preferred range of the present invention. In No. 1 and 2 with Cu compositions of 1 wt% and 2 wt%, several bump-shaped protrusions were generated. No. 7 has a sufficient Cu composition, but it is not oriented to (220) and (321) of Sn-Cu plating, so the alloy phase of Cu and Sn is not sufficiently formed at the grain boundary and some whiskers are generated did. In addition, No. 8 was oriented, but because the amount of Cu was small, the formation of an alloy phase at the crystal grain boundary was not sufficient, and some whiskers were generated.

Example 3
After depositing Cu plating in a copper sulfate plating bath on the surface of a 42 alloy of 2cm x 10cm x 0.3mm thickness, the Sn plating was 8μm thick at a current density of 3A / dm2 in an alkanesulfonic acid Sn plating solution. The film was formed in such a manner that a three-layer plating of 42 alloy, Cu plating, and Sn plating was produced. The thickness of the Cu plating was 4 types: 0 μm, 0.05 μm, 0.1 μm, 0.25 μm, and 0.6 μm.

  Similarly, after depositing Cu plating on the surface of 42 alloy in a copper sulfate plating bath, plating film with a current density of 3A / dm2 in a bath in which copper alkanesulfonate was added to an alkanesulfonic acid Sn plating bath By plating to a thickness of 8 μm, a three-layer plating of 42 alloy, Cu plating, and Sn—Cu alloy plating was produced. The film thickness of the Cu plating was 0.25 μm.

  Similar to Example 1, the cross sections of these plating materials were prepared by FIB and the cross sections were observed, whereby the ratio of the Sn—Cu alloy phase generated at the grain boundaries was determined. Furthermore, the orientation of the plating was also investigated by X-ray diffraction.

  These plating materials were bent into an L shape at 90 ° C., and a constant temperature and humidity test was conducted in the same manner as in Example 1 under the conditions of 85 ° C., 85 RH%, and 500 hours. Thereafter, an inner 1 mm × 0.5 mm region bent into an L shape was observed with SEM (magnification 100 times).

  The results are shown in Table 2. In the case where there was no Cu plating layer, since there was no supply of Cu, many whiskers were observed. When the thickness of the Cu plating layer was 0.05 μm, the supply of Cu was insufficient, so the formation of Sn—Cu alloy phase at the grain boundary was not sufficient, and whiskers were slightly generated. When the Cu plating thickness was 0.1 μm or more, nodules were generated in the range of 0.1 to 0.25, but no whiskers were observed.

Example 4
After copper plating, Fe plating, Co plating, and Ni-P plating were 0.2μm thick, Sn plating with a current density of 2A / dm2 and a thickness of 4μm was prepared in a Sn plating bath containing brightener. .

  Next, these plated materials were put in a heat treatment furnace at a temperature of 120 ° C. and subjected to heat treatment for 24 hours.

  Then, in the same manner as in Example 1, cross sections of these plated materials were prepared by FIB and the cross section was observed, whereby the ratio of the alloy phase in the grain boundary was determined. Further, when X-ray diffraction was performed, the plating was all oriented in the (220) and (321) planes, and the value calculated by the equation (1) was between 0.8 and 0.88.

  Bending these plating materials to 90 ° C L-shaped in the same manner as in Example 3, 85 ° C, 85RH%, 500 hours constant temperature and humidity test, SEM (100 times magnification) inside bent to L-shaped The degree of whisker generation was observed by observing with.

  The results are shown in Table 3. No whisker was observed in any of the platings.

(Example 5)
A 42 alloy plate is immersed in a plating bath in which ferrous sulfate, nickel sulfate, and cobalt sulfate are added to a methanesulfonic acid Sn bath, respectively, at a current density of 8 A / dm 2, and Sn—Fe, Sn—Ni, Sn, respectively. -Co alloy plating was performed so that the plating film thickness was 10 μm. Thereafter, X-ray diffraction was performed on these platings.

  Then, it heat-processed for 16 hours in the 130 degreeC heat processing furnace.

  Further, in the same manner as in Example 1, a cross section of plating was prepared by FIB, and the cross section was observed. In addition, these platings were bent into a 90 ° L-shape, subjected to a constant temperature and humidity test for 85 hours at 85 ° C., 85RH%, and then 0.5 mm × 1 mm inside the portion bent into an L shape by SEM. This region was observed by SEM (magnification 100 times) to observe the state of whisker generation.

  The results are shown in Table 4. No whisker was observed from any of these platings.

(Example 6)
An Sn-Ag plating film having a thickness of 8 μm was formed on a copper substrate in a plating solution obtained by adding alkanol sulfonic acid Ag to an alkanol sulfonic acid Sn plating bath.

  When the composition was analyzed from the surface of this plating with EDX (acceleration voltage: 20 keV, electron gun-sample distance: 15 mm, magnification: 100 times), the Ag content in the Sn-Ag plating was 2.1 wt%. .

  As in Example 1, the ratio of the alloy phase occupying the grain boundary was determined by producing a cross section of this plated material with FIB and observing the cross section, and it was 90%. Further, when the X-ray diffraction of the Sn—Ag alloy plating was performed, the value calculated by the equation (1) was 0.84.

  This plating material was bent to 90 ° C in an L shape in the same manner as in Example 3, and subjected to a constant temperature and humidity test for 85 hours at 85 ° C, 85RH%, and the inside of the bent portion was SEM (magnification 100 times). ), The degree of whisker generation was observed, but no whisker generation was observed.

An example of the cross-sectional photograph of the Sn plating copper plate formed by FIB is shown. The part of Sn plating layer cut out from the photograph of FIG. 1 is shown. The figure obtained by drawing a line on the alloy phase produced | generated in the crystal grain boundary of the photograph of FIG. 2 is shown. The figure obtained by drawing a line on the crystal grain boundary of the photograph of FIG. 2 is shown.

Claims (10)

  Sn plating or Sn alloy plating characterized in that an Sn alloy phase is formed at a grain boundary of Sn plating or Sn alloy plating.   2. The Sn plating or Sn alloy plating according to claim 1, wherein the proportion of the Sn alloy phase formed in the grain boundary of the Sn plating or Sn alloy plating in the length of the crystal grain boundary is 50% or more. .   2. The Sn alloy phase formed at the grain boundary of Sn plating or Sn alloy plating is any one of Sn and Cu, Sn and Fe, Sn and Co, and Sn and Ni. Or Sn plating or Sn alloy plating of 2   4. The Sn alloy plating according to claim 1, wherein an alloy element of the Sn alloy plating is at least one selected from Cu, Co, Fe, and Ni.   On the substrate, there is one layer of Cu, Fe, Co, Ni, Ni-P plating layer as the first layer, and Sn plating or Sn alloy plating layer as the second layer. The Sn plating or Sn alloy plating according to any one of claims 1 to 4. 4. The Sn plating or Sn alloy plating according to claim 3, wherein an Sn alloy phase formed at a grain boundary of Sn plating or Sn alloy plating is an alloy of Sn and Cu. Among the Sn peaks of the X-ray diffraction spectrum obtained by measuring 2θ from 20 ° to 80 ° by the θ-2θ method of the X-ray diffraction method using a Cu X-ray source, the peak on the (220) plane The Sn plating or Sn alloy plating according to any one of claims 1 to 6, wherein the peak intensity I (321) of the strength I (220) and the (321) plane satisfies the formula (1).
[I (220 / I ₀ 220) + I (321 / I ₀ 321)] / [ΣI (hkl) / I ₀ (hkl)] ≧ 0.5 (1)
Here, I ₀ (hkl) represents the peak intensity of the (hkl) plane described in the JCPDS card, and I (hkl) represents the peak height of the measured Sn (hkl) plane.   A copper or copper alloy plated product to which the Sn plating or Sn alloy plating according to any one of claims 1 to 7 is applied.   By performing a Sn plating or Sn alloy plating process on a Cu or Cu alloy substrate and then a heat treatment process at a temperature of 100 ° C. to 180 ° C., Sn— or Sn alloy plating grain boundaries are formed. A method of forming a Cu alloy phase. A step of plating any one of Fe, Co, Ni, Ni-P and Cu plating layers as a first layer on the substrate, a step of performing Sn plating or Sn alloy plating thereon, and then 100 ° C. to 180 ° C. A method of forming an alloy phase of a metal element and Sn contained in a first plating layer at a grain boundary of Sn plating or Sn alloy plating by performing a heat treatment at a temperature of ° C.

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