JP2006307328A - LEADLESS Sn-BASE PLATING FILM, METHOD FOR PRODUCING THE SAME, AND CONTACT STRUCTURE OF CONNECTING PART - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a leadless Sn-base plating film in which the growth of whiskers can be suppressed though being a Pb-free film, to provide a method for producing the same, and to provide a contact structure of connecting parts having the leadless Sn-base plating film. <P>SOLUTION: In the leadless Sn-base plating film obtained by stacking plating layers in which metal is precipitated, and the stacked boundary between the plating layers forms the discontinuous face I of the crystal growth of the above metal, as the plating layers, a plurality of plating layers A with a film thickness of ≤0.5 μm are comprised, and the whole film thickness is 1 to 10 μm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a lead-free Sn-based plating film used for an electrode of an electronic component and the like, and a method for manufacturing the same, and relates to a contact structure of a connecting component having the lead-free Sn-based plating film and fitting a component.

  In recent years, lead-free has been promoted in various parts from the background of environmental considerations. Among these, the development and introduction of lead-free solders that do not contain lead are also in progress for plating and solder materials used for electrodes of electronic components. Specifically, switching from a tin-lead plating (common name, solder plating) film to a lead-free Sn-based plating film and from a lead solder material to a lead-free solder material has been studied.

  However, regarding the plating film of the electrode of the electronic component, there was a time when a tin whisker was generated in a natural standing state when it was an Sn plating film, and this caused a problem of short-circuiting between the electrodes. There was a history of measures to suppress the occurrence of whiskers by using a solder plating composition in which a lead component was added to the tin component of the film. Therefore, the recurrence of the tin whisker problem has been feared by simply removing lead from the electrode plating of electronic parts. In recent years, with the high-density mounting of electronic devices, miniaturization of components has progressed and the distance between electrodes tends to be shortened, so that whisker suppression has been demanded more strictly. In such a background, whiskering occurs particularly in electrode plating of parts subjected to external stress, or electrode plating of fitting parts that are subjected to external stress due to fitting, and it is easy to cause a short circuit between the electrodes. It was.

  By the way, in order to prevent the abnormal precipitation at the time of plating which generate | occur | produces on the surface of a lead-free tin alloy plating film, the plating method which performs electrolytic deposition intermittently, what is called a pulse plating method is proposed (for example, refer patent document 1). .) Here, specifically, the ratio (a / b) of the plating current OFF time (a) to the ON time (b) is preferably 0.2 or more.

JP 2004-204308 A

  However, although abnormal deposition during plating can be prevented by this plating method, the particles constituting the plating film tend to be finer, and whiskers may grow more.

  The present invention has been made in view of the above problems in the prior art, and provides a lead-free Sn-based plating film that can suppress whisker growth while being Pb-free, and a method for producing the same, and the lead-free Sn base. It is an object of the present invention to provide a contact structure for a connecting part having a plating film.

  The present invention provided to solve the above-mentioned problems is a lead-free Sn base in which a plating layer in which a metal is deposited is laminated, and the lamination interface of the plating layer is a discontinuous surface of the crystal growth of the metal. A lead-free Sn-based plating film comprising a plurality of plating layers A having a film thickness of 0.5 μm or less as the plating layer and having a total film thickness of 1 to 10 μm. ).

Here, it is preferable to have a structure in which the plating layer A is continuously laminated.
Alternatively, the plating layer has a plating layer B having a thickness of 0.1 to 5 μm as the plating layer, and the plating layer A has one layer or a laminated structure in which a plurality of the plating layers A are continuously laminated and a plating layer B and B may be laminated alternately.

  Moreover, it is preferable that the said plating layer A is Sn single-piece | unit, or consists of a plating material which has Sn as a main component and contains 1 type, or 2 or more types chosen from Bi, Cu, and Ag.

  Further, the plating layer B is made of any one of Sn, Bi, and Ag, or is made of a plating material containing Sn as a main component and including one or more selected from Bi, Cu, and Ag. Preferably there is.

In addition, the present invention provided to solve the above-mentioned problems is that a plating layer formed by depositing a metal is laminated on the surface of the base material by immersing the base material in a plating solution and applying a current. A method for producing a lead-free Sn-based plating film, comprising producing a lead-free Sn-based plating film in which a laminated interface of the plating layer is a discontinuous surface of the crystal growth of the metal,
In a current application pattern in which energization and stop of plating current during current application are repeated as one cycle, the energization time per cycle is a second, the stop time is b seconds, and D = a / (a + b ) Is a method for producing a lead-free Sn-based plating film, characterized in that it includes a cycle A in which D = 0.1 to 0.9 and Ls1 = a + b = 0.2 to 60 seconds. Claim 6).

Here, the cycle A is preferably repeated continuously.
Alternatively, the current application pattern includes a cycle B in which both the energization time a and the stop time b are 300 seconds or less, and the cycle A is repeated once or continuously several times in the current application pattern. The pattern and the cycle B may be alternately repeated.

  Further, the present invention provided to solve the above-mentioned problems is a contact structure of a connecting part that forms an electric circuit by contacting a pair of detachable contact portions, wherein at least one of the contact portion surfaces is defined in claims 1 to 5. A contact structure for a connecting part, comprising the lead-free Sn-based plating film according to claim 1.

According to the lead-free Sn-based plating film of the present invention, whisker growth can be suppressed by the crystal structure of the plating film while being Pb-free. Moreover, the expensive gold plating currently used as a countermeasure against a whisker can be avoided.
Moreover, according to the method for producing a lead-free Sn-based plating film of the present invention, a plating film capable of suppressing the growth of whiskers can be formed by a simple plating method.
Furthermore, according to the contact structure of the connection component of the present invention, the problem of short-circuiting between the contact electrodes can be solved by the lead-free Sn-based plating film capable of suppressing the growth of whiskers.

Below, the structure of the lead-free Sn base plating film which concerns on this invention is demonstrated.
The lead-free Sn-based plating film according to the present invention is formed by laminating a plating layer in which a metal is deposited, and a lamination interface of the plating layer is a discontinuous surface of the crystal growth of the metal. A plurality of plating layers A having a film thickness of 0.5 μm or less are included, and the total film thickness is 1 to 10 μm.

FIG. 1 is a cross-sectional view showing a configuration of a first embodiment of a lead-free Sn-based plating film according to the present invention.
The lead-free Sn base plating film 10 has a laminated structure in which a plating layer A having a periodic thickness d of 0.5 μm or less, which is a repetition of the same thickness, is continuously laminated on the base material 11. The laminated interface is a discontinuous surface I for crystal growth.

  Here, the plating layer A is preferably composed of Sn alone or made of a plating material containing Sn as a main component and including one or more selected from Bi, Cu, and Ag.

  The discontinuous surface I is a boundary surface of crystal growth formed by energizing and stopping the plating current in the electroplating method described later, and the crystal orientation is discontinuous at the interface between crystal grains or within the crystal grains. It is a formed surface (surface defect or the like). In the present invention, the discontinuous surface I for crystal growth has a morphologically clear structure, thereby providing a barrier surface that further suppresses whisker growth. The discontinuous surface I incorporates inorganic and organic substances other than the elements constituting the main plating composition remaining in the plating solution by interrupting the plating current, so that the movement of Sn atoms related to the growth of tin whiskers Suppress. The interval between the discontinuous surfaces I for crystal growth is the periodic film thickness d of the plating layer A.

  FIG. 2A is a bright-field image obtained by observing a cross section of the lead-free Sn-based plating film of the first embodiment with a high-resolution ion microscope (SIM). FIG. FIG. 4 is a schematic diagram of a cross-sectional structure of the lead-free Sn-based plating film. The cross section of the sample was prepared by ion irradiation using gallium ions, that is, FIB (Focused Ion Beam). Moreover, the schematic diagram of FIG.2 (b) is created surrounding each area | region observed as a difference of the brightness in the cross-sectional structure of the lead-free Sn base plating film of Fig.2 (a). FIG. 2 shows a lead-free Sn-based plating film made of Sn alone.

  As shown in FIG. 2, the lead-free Sn base plating film 10 is a plating layer made of a lead-free solder material formed by electroplating, and a plurality of crystal grains 10p are laminated in the thickness direction and periodically in the film surface direction. It has a columnar crystal structure in which a discontinuous surface (barrier surface) I is formed. Further, the periodic film thickness d formed by the period is 15 to 500 nm, and the total film thickness is 1 to 10 μm. This crystal structure also looks like a columnar joint structure in which the columnar structure is divided in the plane direction.

FIG. 3 shows a configuration of a conventional lead-free Sn-based plating film as a comparison.
FIG. 3A is a bright field image of a cross-section of the lead-free Sn base plating film when observed by TEM, and FIG. 3B is a schematic diagram of the cross-sectional structure of the lead-free Sn base plating film.
As can be seen from FIG. 3, unlike the present invention, the lead-free Sn base plating film 90 has a columnar crystal structure composed of crystal grains 90p that are long in the film thickness direction.

Whisker is easy to grow in the conventional lead-free Sn-based plating film 90, but in the lead-free Sn-based plating film 10 of the present invention, the discontinuous surface I (the barrier surface in the layer structure) stops the movement of Sn atoms so that the growth of whiskers is achieved. Can be suppressed. This difference in whisker growth is due to the difference in crystal structure between the present invention and the conventional lead-free Sn-based plating film, and further stems from the difference in plating method.
Hereinafter, the manufacturing method of the lead-free Sn base plating film of 1st Embodiment is demonstrated.

  The method for producing a lead-free Sn-based plating film of the present invention includes a lead-free Sn-based plating having a crystal structure as shown in FIG. 1 on the surface of the substrate by immersing the substrate in a plating solution and applying a current. A film is manufactured. Here, the plating solution, the substrate, the counter electrode (anode), and the connection configuration thereof used in the present invention are the same as those of a conventionally known lead-free Sn-based plating technique, but are characterized by a current application method.

  That is, in the method for producing a lead-free Sn-based plating film of the present invention, a plating layer formed by depositing a metal is laminated on the surface of the substrate by immersing the substrate in a plating solution and applying a current. A lead-free Sn base plating film manufacturing method comprising: manufacturing a lead-free Sn base plating film in which a laminated interface of the plating layer is a discontinuous surface of the crystal growth of the metal, and plating at the time of current application In a current application pattern in which energization and stop of current are repeated as one cycle, when energization time per cycle is a second, stop time is b seconds, and D = a / (a + b) , D = 0.1 to 0.9, and Ls1 = a + b = 0.2 to 60 seconds.

  Here, in order to form a discontinuous surface of crystal growth in the crystal grains in the lead-free Sn-based plating film and / or the boundary thereof, a rectangular wave in which the plating current waveform is alternately turned on and off is applied. Based on. At this time, unlike the conventional pulse plating, it is important to lengthen the time of one cycle of energizing / stopping the plating current and lengthen the time of stopping the plating current.

FIG. 4 shows a current application method when forming a lead-free Sn base plating film in the present embodiment.
In a current application pattern in which energization and stopping of the plating current during current application are repeated as one cycle, the energization time per cycle is a second, the stop time is b seconds, and the cycle is a + b seconds. When the ratio of energization time per cycle is Duty ratio: D = a / (a + b), D = 0.1 to 0.9, and Ls1 = a + b = 0.2 to 60 seconds Including times. Here, the current application pattern is such that the cycle A is continuously repeated. More preferably, D = 0.2 to 0.7 and a + b = 1 to 30 seconds. Such a plating method is referred to as chop plating. A similar plating method is pulse plating in which periodic plating is intermittently performed, but the crystal grains of the plating film formed according to the present invention are characterized by being larger than the crystal grains formed by pulse plating (grain size 1 to several μm).

Next, a second embodiment of the lead-free Sn-based plating film of the present invention will be described.
FIG. 5 is a cross-sectional view showing a configuration of a second embodiment of the lead-free Sn-based plating film according to the present invention.

  In FIG. 5A, a lead-free Sn-based plating film 20A includes a laminated structure 21 in which a plurality of plating layers A are continuously laminated on a substrate 11, and a plating layer B having a thickness of 0.1 to 5 μm. Are laminated in this order, and the laminated interface between the plated layers A and the laminated interface between the laminated structure 21 and the plated layer B are discontinuous surfaces I for crystal growth. Here, the plating layer A and the discontinuous surface I are the same as those shown in the first embodiment. FIG. 5A shows a laminated structure 21 in which four plating layers A are continuously laminated.

  The plating layer B is preferably composed of Sn alone or a plating material containing Sn as a main component and including one or more selected from Bi, Cu, and Ag. Alternatively, any one of Bi and Ag may be used.

  FIG. 5B shows a cross-sectional configuration of a lead-free Sn-based plating film 20B, which is a variation of the second embodiment, and a plating layer B having a thickness of 0.1 to 5 μm on the substrate 11. And a laminated structure 21 in which a plurality of plating layers A are continuously laminated are laminated in this order, and a lamination interface between the plating layer B and the lamination structure 21 and a lamination interface between the plating layers A are provided. It is a discontinuous surface I for crystal growth.

Next, a third embodiment of the lead-free Sn-based plating film of the present invention will be described.
FIG. 6 is a cross-sectional view showing the configuration of the third embodiment of the lead-free Sn-based plating film according to the present invention. In the lead-free Sn-based plating film of the third embodiment, the plating layer A or a laminated structure 31 in which a plurality of the plating layers A are continuously laminated on the substrate 11 and the plating layer B are alternately arranged. The laminated interface between the plated layers A and the laminated interface between the plated layer A or the laminated structure 31 and the plated layer B are discontinuous surfaces I for crystal growth. Here, the plating layer A and the discontinuous surface I are the same as those shown in the first embodiment, and the plating layer B is the same as that shown in the second embodiment.

  Specifically, in the lead-free Sn-based plating film 30A of FIG. 6A, the laminated structure 31 in which three plating layers A are continuously laminated on the substrate 11 and the plating layers B are alternately 4 It is formed by stacking times.

  Further, in the lead-free Sn-based plating film 30B of FIG. 6B, a laminated structure 31 in which two plating layers A are continuously laminated on the substrate 11 and a plating layer B are alternately laminated twice. It will be.

  In addition, in the lead-free Sn base plating film 30C of FIG. 6C, the plating layer A and the plating layer B are alternately stacked four times on the base material 11 respectively.

  The film thickness of the plating layer A in the second embodiment and the third embodiment may be 0.015 to 0.5 μm as in the first embodiment. In the embodiment, the plating layer B is superimposed on a plating layer A or a laminated structure in which a plurality of plating layers A are continuously laminated, thereby further suppressing whisker growth. Therefore, the film thickness is 0.015 μm. It may be less.

  In the present invention, the effect of suppressing whisker growth can be obtained by forming a discontinuous surface for crystal growth at the laminated interface of the plating layers. Therefore, a dissimilar metal plating layer may be provided between the two Sn-based plating layers as long as a discontinuous surface for crystal growth can be formed. An example thereof is shown in FIG. 7 as a fourth embodiment.

  In the lead-free Sn-based plating film 40 of the fourth embodiment, a plating layer C and a laminated structure 41 in which a plurality of the plating layers A are continuously laminated are alternately laminated on the substrate 11. The laminated interface between the plated layers A and the laminated interface between the laminated structure 41 and the plated layer C are discontinuous surfaces I for crystal growth. Here, the plating layer A and the discontinuous surface I are the same as those shown in the first embodiment.

  The plating layer C is a plating layer made of either Bi or Ag having a thickness of 0.5 μm or less. In metal plating, since a specific deposition potential is determined for each plating metal, when forming the plating layer C, the magnitude of the plating current corresponding to that (either Bi or Ag alone) is controlled. What should I do?

The lead-free Sn base plating films of the second embodiment and the third embodiment are manufactured as follows.
That is, in the method for producing these lead-free Sn-based plating films, the metal is deposited on the surface of the base material by immersing the base material in a plating solution and applying an electric current, as in the first embodiment. A method for producing a lead-free Sn-based plating film comprising: producing a lead-free Sn-based plating film in which the plating layer is laminated, and the lamination interface of the plating layer is a discontinuous surface for crystal growth of the metal. However, in a current application pattern in which energization and stop of the plating current at the time of current application are repeated as one cycle, the energization time per cycle is a second, the stop time is b seconds, and D = Cycle A in which D = 0.1 to 0.9, Ls1 = a + b = 0.2 to 60 seconds, and both energization time a and stop time b are 300 seconds or less when a / (a + b) B and the current Among the pressure pattern, the cycle A are those, wherein the one or continuously repeated a plurality of times patterns, that is a cycle B is alternately carried out or repeated once performed.

FIG. 8 shows an example of a current application method when forming a lead-free Sn-based plating film in the second and third embodiments.
FIG. 8A shows a current application pattern for producing a lead-free Sn-based plating film having the structure shown in FIG. 5A. The cycle A of energization a ₁ second and stop b ₁ second is performed four times. After repeating, the cycle B of stop b ₂ seconds and energization a ₂ seconds is performed.

FIG. 8B shows a current application pattern for producing a lead-free Sn-based plating film having the structure shown in FIG. 6B. The cycle A of energization a ₁ second and stop b ₁ second is performed twice. After the repetition, the cycle B of stop b ₂ seconds and energization a ₂ seconds is performed, and cycle A2 times and cycle B1 times are performed again. Note that after the first cycle B, a stop time b ₃ seconds is provided before cycle A. The stop time _{b 3} may be any 300 seconds or less, may be the same as the example _{b 2.} Or it may stop time b ₃ are not. In FIG. 8B, the current values corresponding to the energization times a ₁ and a ₂ are shown to have the same magnitude, but when the composition of the plating layer formed in cycle A and cycle B is different, What is necessary is just to set to the magnitude | size of the precipitation current which suited the plating layer composition.

(Concept of manufacturing method of lead-free Sn-based plating film in the present invention)
The detailed mechanism of whisker growth is currently unknown, but it seems that residual or external stress present in the plating film is the driving energy for whisker whisker crystal growth. In particular, tin whiskers, which are a problem in the present invention, are generated when pressure is applied at normal temperature and pressure, and thus external pressure is considered to be the driving force for whisker crystal growth. Tin whiskers are caused by Sn atoms moving, rearranging and recrystallization. In the present invention, lead-free Sn-based plating is not continuously plated as in the prior art, but plating and stopping of plating are alternately repeated in the process of forming a plating film, and plating is stacked in a stacked manner. By providing a discontinuous surface of crystal growth (periodically divided crystal grain structure, surface defects of the periodically formed crystal, etc.) formed by this, the movement of Sn atoms is suppressed using this as a barrier surface. The goal is to reduce whisker growth. Here, there is already a technique called pulse plating as a method of plating with the on / off of the plating current, but the size of crystal grains formed by general pulse plating is 1 μm or less, that is, submicron level fine crystal grains are formed. is doing. In the plating method of the present invention, in order to clearly form a discontinuous surface (barrier surface) periodically formed from the guideline of forming crystal grains large and further suppressing the movement of Sn atoms, the plating period It is characterized in that the (cycle) time is increased in units of seconds of 0.1 seconds or more and the plating current stop time is increased as much as possible to sufficiently form discontinuous surfaces of crystal growth.

  Further, in the technique of plating on and off the plating current of the present invention periodically and intermittently, plating is performed using an element other than the main element constituting the plating solution or an organic group as an impurity. The method of incorporating into the film also leads to generation of Sn-based crystal grain boundaries and crystal defects in the crystal grains, and serves to stop the movement of Sn atoms contributing to whisker growth, and is effective in suppressing whisker growth. is there.

  Thereby, a plurality of crystal grains are stacked in the thickness direction, and discontinuous surfaces (barrier surfaces) for crystal growth are periodically formed in the film surface direction. At this time, the energization time of the plating current controls the film thickness of the plating layer such as the periodic film thickness d, and the stop time contributes to the formation of a discontinuous surface of crystal growth. Here, it is sufficient that the energization time is long enough to secure a predetermined film thickness. If it is too long, the crystal grains are likely to form a column (columnar shape) in the film thickness direction of the plating film, and that part when fitted as a part. When external force is applied to the whisker, it becomes easy to grow. Therefore, the energization time for forming the plating layer A is preferably 0.1 to 40 seconds. More preferably, it is 0.1 to 20 seconds. Further, the longer the stop time, the clearer the crystal growth discontinuity can be formed. However, when the length is too long, the residual stress in the lead-free Sn-based plating film increases and adversely affects the whisker growth. Therefore, the stop time when forming the plating layer is preferably 0.1 to 20 seconds. More preferably, it is 0.1 to 10 seconds.

  Further, regarding the plating layer B, if the energization time is long, the above-described growth of crystal grains tends to grow in a column shape. An aspect ratio of 1 or more is not preferable because the aspect ratio is z / x, where x and z are the crystal plane film thickness direction and the film thickness direction size, respectively. The plating thickness of the parts to which the present invention is applied is usually around 5 μm. Assuming this thickness, the thickness of the plating layer B is preferably around 5 μm at the maximum. Further, the film formation rate of the conventional constant current plating is about 1 μm / min, and if this good film formation rate is increased, the columnar structure is promoted in terms of crystal growth. The film forming speed is 1 μm / min at the maximum. Accordingly, the energization time a when forming the plating layer B is preferably 300 seconds or less.

  In FIG. 9, the film thickness range of the plating layer A and the film thickness range of the plating layer B of the lead-free Sn base plating film of the present invention are shown. The hatched area is the film thickness range of the plating layer A and the plating layer B required in the present invention, the film thickness of the plating layer A is 0.5 μm or less (not including 0 μm), and the film thickness of the plating layer B is 0 ~ 5 μm.

  Further, the residual stress of the lead-free Sn-based plating film of the present invention is preferably −5 MPa or more and 5 MPa or less in order to suppress whisker growth.

  The base material is an electrode of an electronic component, and examples thereof include a Cu frame, a Ni frame plated with the Cu frame, and a 42 alloy type iron-based metal.

  The lead-free Sn-based plating film 10 of the present invention produced as described above can be applied to an electrode of an electronic component. For example, in a contact structure of a connecting part that forms an electric circuit by contacting a pair of detachable contact portions, at least one of the contact portion surfaces may be composed of the lead-free Sn base plating film 10 of the present invention.

An example is shown in FIG.
In FIG. 10, a contact structure 100 of a connecting part in which any one of the lead-free Sn-based plating films 10, 20, 30, and 40 of the present invention is formed on a base material, and a spring contact structure 200 having a hairpin shape in cross section. Show. Here, the contact structure 100 is inserted into the spring contact structure 200 so as to be sandwiched between the hairpin shapes. At this time, the surface of the contact structure 100, that is, any one of the lead-free Sn base plating films 10, 20, 30, and 40 and the spring contact structure 200 are held in pressure contact with each other by the spring action of the spring contact structure 200. An electrical connection is obtained. Further, the contact structure 100 can be detached by being extracted from the spring contact structure 200.

FIG. 11 shows a surface state of the lead-free Sn base plating film 10 in the contact structure 100 after the contact structure 100 of the connection component of the present invention is inserted into and removed from the spring contact structure 200. In the contact portion, traces of external stress acting on the surface of the lead-free Sn base plating film 10 were observed.
According to the present invention, it is possible to suppress whisker growth in a portion where the external stress is applied.

Examples of the present invention will be described below.
<Example 1>
(Example 1-1)
The lead-free Sn plating film (lead-free Sn base plating film 10) of the present invention was formed under the following conditions.
-Base material: Connector board made of phosphor bronze (Plating object area: 578 mm ² )
・ With Ni pre-plating ・ Plating solution: Sulfuric acid bath Sn plating solution (LPW-Chemie, product name Tinto)
・ Plating bath temperature: Room temperature ・ Plating bath stirring: Stirrer stirring ・ Anode: High purity tin ・ Distance between electrodes: 37 mm
・ Target film thickness: 3μm
・ Plating current condition ・ ・ Applied current: 175 mA
· · Energization time a: 14 seconds · · Stop time b: 5 seconds · · 1 cycle (a + b): 19 seconds · · Duty ratio D: 0.74
..Plating time: 2.5 minutes (8 cycles)

  The Ni plating film thickness of the sample prepared as described above was 1.8 μm, and the film thickness of the lead-free Sn plating film was 3.1 μm.

(Example 1-2)
In Example 1-1, a plating current condition was changed as follows, and a sample was manufactured in the same manner as in Example 1-1 except that.
・ Plating current condition ・ ・ Applied current: 175 mA
· · Energization time a: 23 seconds · · Stop time b: 5 seconds · · 1 cycle (a + b): 28 seconds · · Duty ratio D: 0.82
..Plating time: 2.3 minutes (5 cycles)

  The Ni plating film thickness of the sample prepared as described above was 1.6 μm, and the lead-free Sn plating film film thickness was 2.9 μm.

(Example 1-3)
In Example 1-1, a plating current condition was changed as follows, and a sample was manufactured in the same manner as in Example 1-1 except that.
・ Plating current condition ・ ・ Applied current: 175 mA
· · Energizing time a: 36 seconds · · Stop time b: 5 seconds · · 1 cycle (a + b): 41 seconds · · Duty ratio D: 0.88
..Plating time: 2 minutes (3 cycles)

  The Ni plating film thickness of the sample prepared as described above was 1.4 μm, and the lead-free Sn plating film film thickness was 2.9 μm.

(Comparative Example 1)
In Example 1-1, the plating current condition was changed to the constant current plating condition as follows, and a sample was prepared in the same manner as in Example 1-1 except that.
・ Plating current condition ・ ・ Applied current: 175 mA
..Plating time: 1.9 minutes

  The Ni plating film thickness of the sample prepared as described above was 1.8 μm, and the film thickness of the lead-free Sn plating film was 2.6 μm.

  The obtained sample was sandwiched between two acrylic plates having a diameter of 30 mm and a thickness of 5 mm, and held for 72 hours in a room temperature environment with a torque pressure of 0.5 Nm applied. Then, the sample was taken out, the whisker in the pressurization part was observed, and the longest one was measured as the maximum whisker length.

The result is shown in FIG. Here, a value obtained by dividing the total film thickness of the lead-free Sn plating film by the number of cycles at the time of each plating is defined as the periodic film thickness.
As a result, whisker growth was suppressed in all Examples as compared with Comparative Example 1. Moreover, in Examples 1-1 to 1-3, the growth of whiskers was suppressed as the periodic film thickness was reduced.

<Example 2>
(Example 2-1)
The lead-free Sn plating film (lead-free Sn base plating film 10) of the present invention was formed under the following conditions.
・ Base material: Connector board made of phosphor bronze ・ With Ni pre-plating (film thickness 1μm)
・ Plating solution: Sulfuric acid bath Sn plating solution (LPW-Chemie, trade name Tinto)
・ Plating bath temperature: 20 ℃
・ Plating bath agitation: Stirrer agitation ・ Anode: High purity tin ・ Plating current condition ・ ・ Applied current: 2 A / dm ²
.. Energization time a: 0.2 sec. Stop time b: 0.2 sec. 1 cycle (a + b): 0.4 sec. Duty ratio D: 0.5
..Periodic film thickness: 15 nm
..Total film thickness: 5 μm

(Example 2-2)
In Example 2-1, the plating current conditions were changed as follows, and the other samples were prepared as in Example 2-1.
・ Plating current condition ・ ・ Applied current: 2 A / dm ²
· · Energization time a: 0.7 seconds · · Stop time b: 0.7 seconds · · 1 cycle (a + b): 1.4 seconds · · Duty ratio D: 0.5
..Periodic film thickness: 50 nm
..Total film thickness: 5 μm

(Example 2-3)
In Example 2-1, the plating current conditions were changed as follows, and the other samples were prepared as in Example 2-1.
・ Plating current condition ・ ・ Applied current: 2 A / dm ²
· · Energizing time a: 1.3 seconds · · Stop time b: 1.3 seconds · · 1 cycle (a + b): 2.6 seconds · · Duty ratio D: 0.5
..Periodic film thickness: 100 nm
..Total film thickness: 5 μm

(Example 2-4)
In Example 2-1, the plating current conditions were changed as follows, and the other samples were prepared as in Example 2-1.
・ Plating current condition ・ ・ Applied current: 2 A / dm ²
.. Energization time a: 2.6 seconds. Stop time b: 2.6 seconds. 1 cycle (a + b): 5.2 seconds. Duty ratio D: 0.5.
..Periodic film thickness: 200 nm
..Total film thickness: 5 μm

(Comparative Example 2)
In Example 2-1, the plating current condition was changed to the constant current plating condition as follows, and a sample was prepared in the same manner as in Example 2-1, except that.
・ Plating current condition ・ ・ Applied current: 2 A / dm ²
・ ・ Plating time: 66 seconds ・ ・ Total film thickness: 5μm

  About the obtained sample, the whisker test was done on the same conditions as Example 1 except having made the test time into 500 hours, and the time-dependent change of the maximum whisker length was measured.

The result is shown in FIG.
As a result, in all the examples, the growth of whiskers was suppressed as compared with Comparative Example 2. Moreover, in Examples 2-1 to 2-4, the growth of whiskers tended to be suppressed as the periodic film thickness decreased.

<Example 3>
The lead-free Sn-1% Cu plating film (lead-free Sn base plating film 10) of the present invention was formed under the following conditions.
・ Base material: Connector board made of phosphor bronze ・ With Ni pre-plating (film thickness 1μm)
-Plating solution: Sn-Cu plating solution (manufactured by Nihon MacDermid, trade name NF-111 (Sn / Cu = 99/1))
・ Plating bath temperature: 18 ℃
・ Anode: Insoluble electrode ・ Plating current condition ・ ・ Applied current: 2 A / dm ²
· · Energization time a: 6 seconds · · Stop time b: 20 seconds · · 1 cycle (a + b): 26 seconds · · Duty ratio D: 0.23
..Periodic film thickness: 100 nm
..Total film thickness: 5 μm

(Comparative Example 3)
In Example 3, the plating current condition was changed to the constant current plating condition as follows, and a sample was prepared in the same manner as in Example 3 except that.
・ Plating current condition ・ ・ Applied current: 2 A / dm ²
・ ・ Plating time: 300 seconds ・ ・ Total film thickness: 5μm

The obtained sample was subjected to a whisker test under the same conditions as in Example 1 except that the test time was 1100 hours, and the change over time in the maximum whisker length was measured.
The result is shown in FIG. As a result, whisker growth was suppressed in Example 3 as compared with Comparative Example 3.

<Example 4>
The residual stress of the lead-free Sn plating film was measured using a strip electrodeposition stress measuring instrument manufactured by Specialty Testing Development. In this measuring instrument, a thin sheet made of C194 copper alloy with a notch in the fork is used as the measuring element, and when this measuring element is plated, the residual stress is obtained from the distance where the forked part is warped and separated. It has become.

In Example 1-1, the base material is the above-mentioned measuring element, the periodic film thickness, the total film thickness, and the plating current conditions are the conditions shown in Table 1 below, the applied current is 2 A / dm ² , and the others are the examples. A lead-free Sn plating film (lead-free Sn base plating film 10) was formed under the same conditions as 1-1, and the residual stress of the lead-free Sn plating film was measured.

The above results are shown in FIG.
All samples were in the range of residual stress -10 to 10 MPa.

<Example 5>
Using the strip electrodeposition stress measuring instrument, the relationship between the periodic film thickness of the lead-free Sn plating film and the residual stress was investigated.
(Example 5-1)
The lead-free Sn plating film (lead-free Sn base plating film 10) of the present invention was formed under the following conditions.
・ Substrate: Measuring element of strip electrodeposition stress measuring instrument ・ Plating solution: Sulfuric acid bath Sn plating solution (LPW-Chemie, trade name: Tinto)
・ Plating bath temperature: 20 ℃
・ Plating bath agitation: Stirrer agitation ・ Anode: High purity tin ・ Plating current condition ・ ・ Applied current: 2 A / dm ²
· · Energization time a: 1 second · · Stop time b: 1 second · · 1 cycle (a + b): 2 seconds · · Duty ratio D: 0.5
..Periodic film thickness: 15 nm
..Total film thickness: 5 μm

(Example 5-2)
In Example 5-1, the plating current conditions were changed as follows, and a sample was prepared in the same manner as in Example 5-1.
・ Plating current condition ・ ・ Applied current: 2 A / dm ²
· · Energizing time a: 2 seconds · · Stop time b: 2 seconds · · 1 cycle (a + b): 4 seconds · · Duty ratio D: 0.5
..Periodic film thickness: 30 nm
..Total film thickness: 5 μm

(Example 5-3)
In Example 5-1, the plating current conditions were changed as follows, and a sample was prepared in the same manner as in Example 5-1.
・ Plating current condition ・ ・ Applied current: 2 A / dm ²
· · Energizing time a: 7 seconds · · Stop time b: 3 seconds · · 1 cycle (a + b): 10 seconds · · Duty ratio D: 0.7
..Periodic film thickness: 105 nm
..Total film thickness: 5 μm

(Example 5-4)
In Example 5-1, the plating current conditions were changed as follows, and a sample was prepared in the same manner as in Example 5-1.
・ Plating current condition ・ ・ Applied current: 2 A / dm ²
· · Energization time a: 20 seconds · · Stop time b: 20 seconds · · 1 cycle (a + b): 40 seconds · · Duty ratio D: 0.5
..Periodic film thickness: 300 nm
..Total film thickness: 5 μm

(Comparative Example 5)
In Example 5-1, the plating current condition was changed to the constant current plating condition as follows, and a sample was prepared in the same manner as in Example 5-1, except that.
・ Plating current condition ・ ・ Applied current: 2 A / dm ²
・ ・ Plating time: 66 seconds ・ ・ Total film thickness: 5μm

The above results are shown in FIG.
When the periodic film thickness was 105 nm or less, the residual stress was −5 MPa or more. When the relationship between the periodic film thickness of the lead-free Sn plating film and the maximum whisker length in the result of Example 2 (FIG. 13) is combined with the result of this example, the residual stress of the lead-free Sn plating film is set to −5 MPa or more. This shows that whisker growth can be suppressed.

<Example 6>
(Example 6-1)
The lead-free Sn plating film (lead-free Sn base plating film 10) of the present invention was formed under the following conditions.
-Base material: FPC (Flexible Printed Circuit) flexible substrate made of copper as an electrode (plating target area: 578 mm ² )
・ No pre-plating ・ Plating solution: Sulfuric acid bath Sn plating solution (LPW-Chemie, trade name: Tinto)
・ Plating bath temperature: Room temperature ・ Plating bath stirring: Stirrer stirring ・ Anode: High purity tin ・ Distance between electrodes: 37 mm
・ Target film thickness: 5μm
(Step 11) Plating current condition of plating layer A: Applied current: 175 mA
· · Energization time a: 0.5 seconds · · Stop time b: 0.5 seconds · · 1 cycle (a + b): 1.0 seconds · · Duty ratio D: 0.5
..Plating time: 1 minute 40 seconds (100 cycles)
-The step S11 was performed.

  The thickness of the lead-free Sn plating film of the sample prepared as described above was 5 μm.

(Example 6-2)
In Example 6-1, the plating current conditions were changed as follows, and the lead-free Sn plating film (lead-free Sn base plating film 20A) of the present invention was produced in the same manner as in Example 6-1 except that.
(Step 21) Plating current condition of plating layer A: Applied current: 175 mA
· · Energization time a: 0.5 seconds · · Stop time b: 0.5 seconds · · 1 cycle (a + b): 1.0 seconds · · Duty ratio D: 0.5
..Plating time: 25 seconds (25 cycles)
(Step 22) Plating current condition of plating layer B: Applied current: 175 mA
-Energizing time a: 2 minutes 30 seconds-Stop time b: 2 minutes 30 seconds-Steps S21 and S22 were performed in this order. The total plating time was 5 minutes 25 seconds.

  The thickness of the lead-free Sn plating film of the sample prepared as described above was 5 μm. Moreover, the sample cross section was observed with the electron microscope (SEM). FIG. 17 shows the result. A boundary surface between the laminated structure in which the plating layer A was continuously laminated and the plating layer B was observed, and fine periodic streaks indicating the laminated state of the plating layer A were observed in the laminated structure.

(Example 6-3)
In Example 6-1, the plating current conditions were changed as follows, and the lead-free Sn plating film (lead-free Sn base plating film 20B) of the present invention was manufactured in the same manner as in Example 6-1 except that.
(Step 31) Plating current condition of plating layer B: Applied current: 175 mA
· · Energization time a: 2 minutes and 30 seconds · · Stop time b: 2 minutes and 30 seconds (step 32) Plating current condition of plating layer A · · Applied current: 175 mA
· · Energization time a: 0.5 seconds · · Stop time b: 0.5 seconds · · 1 cycle (a + b): 1.0 seconds · · Duty ratio D: 0.5
..Plating time: 25 seconds (25 cycles)
The steps S31 and S32 were performed in order. The total plating time was 5 minutes 25 seconds.

  The thickness of the lead-free Sn plating film of the sample prepared as described above was 5 μm.

(Example 6-4)
In Example 6-1, the plating current conditions were changed as follows, and a lead-free Sn plating film (lead-free Sn base plating film 30B) of the present invention was manufactured in the same manner as Example 6-1 except that.
(Step 41) Plating current condition of plating layer A: Applied current: 175 mA
· · Energization time a: 0.5 seconds · · Stop time b: 0.5 seconds · · 1 cycle (a + b): 1.0 seconds · · Duty ratio D: 0.5
..Plating time: 7 seconds (7 cycles)
(Step 42) Plating current condition of plating layer B: Applied current: 175 mA
-Energizing time a: 1 minute 10 seconds-Stop time b: 1 minute 10 seconds-The above steps S41 and S42 were repeated twice. The total plating time was 4 minutes 54 seconds.

  The thickness of the lead-free Sn plating film of the sample prepared as described above was 5 μm.

(Example 6-5)
In Example 6-1, the plating current conditions were changed as follows, and the lead-free Sn plating film (lead-free Sn base plating film 30A) of the present invention was manufactured in the same manner as in Example 6-1 except that.
(Step 51) Plating current condition of plating layer A: Applied current: 175 mA
· · Energization time a: 0.5 seconds · · Stop time b: 0.5 seconds · · 1 cycle (a + b): 1.0 seconds · · Duty ratio D: 0.5
..Plating time: 6 seconds (6 cycles)
(Step 52) Plating current condition of plating layer B: Applied current: 175 mA
-Energizing time a: 39 seconds-Stop time b: 39 seconds-The above steps S51 and S52 were repeated four times. The total plating time was 5 minutes and 36 seconds.

  The thickness of the lead-free Sn plating film of the sample prepared as described above was 5 μm.

(Comparative Example 6)
In Example 6-1, the plating current condition was changed to the constant current plating condition as follows, and a sample was prepared in the same manner as in Example 6-1 except that.
・ Plating current condition ・ ・ Plating time: 5 minutes

  The thickness of the lead-free Sn plating film of the sample prepared as described above was 5 μm.

  About the obtained sample, the whisker test was done on the same conditions as Example 1 except having set the test time to 1000 hours, and the time-dependent change of the maximum whisker length was measured.

The results are shown in FIGS. FIG. 18 shows the results of all of Examples 6-1 to 6-5 and Comparative Example 6, and FIG. 19 is an enlarged view of Examples 6-1 to 6-5.
As a result, Example 6-1 (symbol ◯), Example 6-2 (symbol Δ), Example 6-3 (symbol □), Example 6-4 (symbol ◇), Example 6-5 (symbol) In all cases (1), whisker growth was suppressed as compared with Comparative Example 6 (symbol ●). Examples 6-2 to 6-5 are a combination of chop plating and constant current plating, that is, a combination of plating layer A and plating layer B. The number of repetitions of chop plating and constant current plating is as follows. The more whisker, the more whisker growth was suppressed.

It is a schematic diagram which shows the structure of 1st Embodiment of the lead-free Sn base plating film which concerns on this invention. It is a figure which shows the result of having observed the cross section of the lead-free Sn base plating film of 1st Embodiment. It is a figure which shows the result of having observed the cross section of the conventional lead-free Sn base plating film. It is a figure which shows the electric current application method (1) at the time of lead-free Sn base plating film formation in this invention. It is a schematic diagram which shows the structure of 2nd Embodiment of the lead-free Sn base plating film which concerns on this invention. It is a schematic diagram which shows the structure of 3rd Embodiment of the lead-free Sn base plating film which concerns on this invention. It is a schematic diagram which shows the structure of 4th Embodiment of the lead-free Sn base plating film which concerns on this invention. It is a figure which shows the electric current application method (2) at the time of lead-free Sn base plating film formation in this invention. It is a figure which shows the film thickness range of the plating layer A and the plating layer B of the lead-free Sn base plating film of this invention. It is sectional drawing which shows the structure of the contact structure of the connection component which concerns on this invention. It is a figure which shows the surface state of the lead-free Sn base plating film after use in the contact structure of the connection component of this invention. It is a figure which shows the relationship between the periodic film thickness and the maximum whisker length in Example 1. It is a figure which shows the whisker test result in Example 2. FIG. It is a figure which shows the whisker test result in Example 3. FIG. It is a figure which shows the residual stress result of the lead-free Sn plating film in Example 4. It is a figure which shows the relationship between the periodic film thickness of the lead-free Sn plating film in Example 5, and a residual stress. It is a figure which shows the result of having observed the cross section of the lead-free Sn base plating film of Example 6-2. It is a figure which shows the whisker test result in Example 6. FIG. It is an enlarged view of the whisker test result of FIG.

Explanation of symbols

10, 20A, 20B, 30A, 30B, 30C, 40, 90 ... lead-free Sn base plating film, 10p, 90p ... crystal grains, 11 ... base material, 21, 31 ... laminated structure, 100 ... contact structure of connecting parts, 200 ... Spring contact structure, A, B ... Plating layer, d ... Periodic film thickness, I ... Discontinuous surface of crystal growth

Claims (9)

  A lead-free Sn-based plating film in which a plating layer formed by depositing a metal is laminated, and a lamination interface of the plating layer is a discontinuous surface of the metal crystal growth, and the film thickness of the plating layer is A lead-free Sn-based plating film comprising a plurality of plating layers A of 0.5 μm or less and having a total film thickness of 1 to 10 μm.   The lead-free Sn-based plating film according to claim 1, wherein the plating layer A has a structure in which the plating layer A is continuously laminated.   The plating layer has a plating layer B having a thickness of 0.1 to 5 μm as the plating layer, and the plating layer A has one layer or a laminated structure in which a plurality of the plating layers A are continuously laminated, and the plating layer B The lead-free Sn-based plating film according to claim 1, wherein the layers are alternately stacked.   The said plating layer A is Sn single-piece | unit, or consists of a plating material which has Sn as a main component and contains 1 type, or 2 or more types chosen from Bi, Cu, and Ag. The lead-free Sn base plating film of description.   The plating layer B is either a single substance of Sn, Bi, or Ag, or is made of a plating material containing Sn as a main component and including one or more selected from Bi, Cu, and Ag. The lead-free Sn-based plating film according to claim 3. By immersing the substrate in a plating solution and applying an electric current, a plating layer on which the metal is deposited is laminated on the surface of the substrate, and the lamination interface of the plating layer is the crystal growth of the metal. A method for producing a lead-free Sn-based plating film comprising producing a lead-free Sn-based plating film which is a discontinuous surface,
In a current application pattern in which energization and stop of plating current during current application are repeated as one cycle, the energization time per cycle is a second, the stop time is b seconds, and D = a / (a + b ), A method for producing a lead-free Sn-based plating film, comprising a cycle A in which D = 0.1 to 0.9 and Ls1 = a + b = 0.2 to 60 seconds.   The said cycle A is repeated continuously, The manufacturing method of the lead-free Sn base plating film of Claim 6 characterized by the above-mentioned.   The current application pattern includes a cycle B in which the energization time a and the stop time b are both 300 seconds or less, and in the current application pattern, the cycle A is repeated once or continuously several times. And the cycle B are alternately repeated, The method for producing a lead-free Sn-based plating film according to claim 6. In the contact structure of a connecting part that forms an electric circuit by contacting a pair of detachable contact portions,
At least one of the said contact part surface is comprised with the lead-free Sn base plating film as described in any one of Claims 1-5, The contact structure of the connection components characterized by the above-mentioned.