JP4280917B2 - Evaluation method and evaluation tool of contact pressure whisker generation state - Google Patents

Description

  The present invention relates to a method for evaluating a contact pressure whisker generation state for preliminarily evaluating whether or not a contact pressure whisker is generated from a tin or tin alloy film, and an evaluation tool used therefor.

  It is known that tin and tin alloy plating films generate whiskers when the film has internal stress, and this whisker causes problems such as short circuit.

  For this reason, various methods for reducing the internal stress of tin and tin alloy plating films have been proposed, such as improving the plating solution. However, even if the internal stress is reduced and the member itself is difficult to generate a whisker, a contact pressure whisker is generated when stress is applied to the member from the outside. Here, the contact pressure refers to, for example, an external load applied to a contacted tin or tin alloy film in an electronic component such as a connector when a flexible board is fitted to a contact insertion portion, such as tin or tin. It is an external load applied to tin or tin alloy film when other members are pressure-fixed to the alloy film, and Sn, Sn-Cu, Sn-Ag are applied as surface treatments to fitting parts and contact parts of electronic parts. , Sn-Bi and the like have been plated, but contact pressure whiskers are generated at the pressure contact portions such as the fitting portion and the contact portion.

FIG. 1 shows an example of a fitting state between one member a and another member b, and a portion c in the figure is a contact pressure portion.
Specifically, the connector 1 shown in FIG. 2 is subjected to tin or tin alloy plating on the connector pin 2. In this case, in the state where the lead 3 is not inserted as shown in FIG. 2, the connector pin 2 has been subjected to heat treatment or improvement of the plating solution so as to relieve internal stress. Whisker does not occur. However, when the lead 3 having the pattern 5 insulated and separated so as not to contact each other by the polyimide 4 is inserted into the connector 1, an external load is applied to the connector pin 2. If it does so, it will be in the same state as the internal stress in the tin or tin alloy plating film of the connector pin 2, and a whisker (contact pressure whisker) will generate | occur | produce. Thereby, the insulation of the lead 3 by the polyimide 4 is inhibited, and there is a possibility that the pattern 5 is short-circuited.

  In the crystal oscillator shown in FIG. 3, tin or tin alloy plating is applied to the inner and outer surfaces of the container 6, and the crystal oscillator 7 is press-fitted into the container 6. Here, 8 is a crystalline lens, 9 is a lead terminal, and 10 is a lead terminal cover made of silicone resin for covering and protecting the lead terminal. By the above press-fitting, an external load is applied to the container 6 plating film in the portion X in FIG. As described above, the oscillator is provided with the lead terminal cover for the purpose of preventing the lead from being short-circuited, but the contact pressure whisker W grows in the lead terminal cover 10 from the tin or tin alloy plating film of the container 6. There is a risk of short circuit by contact with the lead terminal 9.

  Conventionally, there is no known method for simply evaluating whether or not such contact pressure whiskers are generated or how much they are generated. There was no other way than checking the presence or absence of pressure whiskers, and it took time and time to check whiskers.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a contact pressure whisker occurrence state evaluation method and an evaluation tool that can easily and in a short period evaluate whether or not contact pressure whiskers are generated. And

In order to achieve the above object, the present invention provides an evaluation method and an evaluation tool for the following contact pressure whisker generation state.
(1) A method for evaluating the state of occurrence of contact pressure whiskers generated when an external load is applied from another member to the tin or tin alloy film of the sample on which the tin or tin alloy film is formed. The tip of the press-contact portion projecting from the holding member that holds the tin or tin alloy film of the sample on which the tin or tin alloy film is formed on the sample on which the alloy film is formed is the tin or tin alloy film on the sample. By applying a load by contact, the pressure contact portion is brought into contact with an area smaller than the area of the tin or tin alloy film, and a load is applied. A method for evaluating a contact pressure whisker generation state, characterized by observing the presence or absence and the degree of generation.
(2) A method for evaluating the state of occurrence of contact pressure whiskers generated when an external load is applied from another member to the tin or tin alloy film of the sample on which the tin or tin alloy film is formed. For the sample on which the alloy film is formed, the tip of the pressure contact portion having a spherical or hemispherical tip shape is brought into contact with the tin or tin alloy film of the sample, and a load is applied to the sample. The contact pressure whisker generation is characterized by observing the occurrence of whisker and the degree of the occurrence of whisker after the load is applied in an area smaller than the area of the alloy film and the load is applied for a predetermined period. State evaluation method.
(3) The evaluation method according to (1) or (2), wherein at least the contact portion of the pressure contact portion that contacts the tin or tin alloy film is a metal made of the same material as the pressure contact portion of the other member.
(4) An evaluation tool for evaluating the state of contact whisker generated when an external load is applied from another member to the tin or tin alloy film of the sample on which the tin or tin alloy film is formed, A holding body for holding tin or a tin alloy film of a sample on which a tin alloy film is formed, and the tip or the tin alloy film protruding from the holding body and contacting the tin or the tin alloy film, A contact pressure whisker evaluation tool comprising: a pressure contact portion that is pressure-contacted with an area smaller than the area of the tin alloy film.
(5) An evaluation tool for evaluating the state of contact whisker generated when an external load is applied from another member to the tin or tin alloy film of the sample on which the tin or tin alloy film is formed, A holding body that holds tin or a tin alloy film of a sample on which a tin alloy film is formed, and an area that is smaller than the area of the tin or tin alloy film when the tip contacts the tin or tin alloy film held on the holding body A contact pressure whisker evaluation tool comprising: a pressure contact portion having a spherical shape or a hemispherical tip shape, which is pressure-contacted at a pressure.
(6) The contact pressure whisker according to (4) or (5), wherein at least the contact portion of the pressure contact portion that contacts the tin or tin alloy film is a metal of the same material as the pressure contact portion of the other member. Evaluation tool.

  According to the present invention, the presence or absence and occurrence frequency of whisker (contact pressure whisker) generated at the contact point of the tin or tin alloy film can be easily realized as an accelerated test by creating a contact pressure simulated situation. Whisker characteristics can be quickly evaluated in a short period of time. For this reason, whiskering occurs in the tin or tin alloy plating film that does not occur in the normal state if there is a pressure contact point, but it is possible to evaluate in advance the state of occurrence of such pressure whisker in various electronic components, and tin plating It is easy to systematically investigate the contact pressure whisker generation tendency of tin and tin alloy plating film affected by the liquid composition of tin and tin alloy plating, plating conditions, etc. It can be effectively used for structural improvement of electronic components that are less likely to generate rust, tin, tin alloy plating solution, and verification, improvement, and development of plating conditions.

  The method of evaluating the state of contact pressure whisker generated when an external load is applied to the tin or tin alloy film of the present invention has a smaller area than that of the sample on which the tin or tin alloy film is formed. Then, after leaving for a predetermined period in a state where a load is applied, the presence or absence and the degree of occurrence of whiskers are observed.

  In this case, the tin or tin alloy film is usually formed by a plating method. The plating may be an electroplating method or an electroless plating method, and a vapor phase plating method such as vacuum deposition may be employed. The film thickness is appropriately selected depending on the type of member, purpose of use, etc., but is usually 0.5 to 15 μm, preferably 1.5 to 6 μm. Examples of the tin alloy film include Sn—Cu, Sn—Ag, and Sn—Bi. The tin content in the tin alloy is preferably 50% by mass or more.

  The load applied to the sample on which the tin or tin alloy film is formed is determined by the pressure fixing from other members applied to this member for members for which knowledge of the state of contact pressure whisker generation is required by evaluation and verification of this sample. It is preferable that the load is greater than or equal to the load. If the applied load is smaller than this, even if the contact pressure whisker is not generated in the evaluation and verification of the sample, the contact pressure whisker is generated in actual use of the member. There is a fear.

The pressure contact force of the other member applied to the member is usually 3 to 5 kg / mm ² at the fitting position when the connector is used, but is not limited thereto. Moreover, although the upper limit of the load more than this press-contact force (load) is possible as long as one member is not destroyed mechanically, in the eyeball clip system mentioned later, it can be set as load 400-1300g, At this time, a pressure contact force of about 22 to 26 kg / mm ² can be applied to the sample.

  Furthermore, when a load is applied to the sample, the area to which the load is applied needs to be smaller than the area of this sample (tin or tin alloy film that this sample has), and line contact or Although the reason for applying a load by the pressure contact portion so as to make point contact is unknown, it is advantageous for promoting the generation of the pressure whisker. For this reason, a spherical or hemispherical shape is optimal as the tip shape of the pressure contact portion for applying a load to the sample. When the tip of the pressure contact part is formed in a cone shape even in point contact, there is a possibility that the direction of the force applied by the load may occur, and in order to stably promote the generation of whiskers, as described above, spherical or hemispherical Is more preferable.

  In addition, as for the pressure contact portion for applying a load to the sample, at least the contact portion in contact with the sample is preferably a metal, particularly stainless steel or aluminum, and particularly aluminum which is difficult to cause metal diffusion is preferable. The generation factor can be substantially limited to the pressing force by the pressing portion. However, when investigating the situation of contact pressure whiskers in actual use, it is recommended to use the same material as the pressure contact portion of the other member, that is, in the case of a connector, gold which is the same metal material as the lead. .

  The period in which the sample is allowed to stand in a state where a load is applied is not particularly limited and is appropriately selected, but it is preferably 1 to 10 days, particularly about 1 to 3 days. The leaving condition may be left at room temperature and atmospheric pressure.

  The contact pressure whisker evaluation tool used for carrying out the evaluation method as described above is an evaluation tool for evaluating the occurrence state of contact pressure whisker generated when an external load is applied to the tin or tin alloy film. Or it can be set as the structure provided with the holding body holding the sample in which the tin alloy membrane | film | coat was formed, and the press-contact part which press-contacts the sample held by this holding body in an area smaller than this sample area.

  FIG. 4 is an example in which a commercially available eyeball clip is used as such an evaluation tool, and the sphere 13 is bonded to the inner surface of the pinch 12 of the holding body 11 made of this eyeball clip using a double-sided adhesive tape or the like. Fixed (in the figure, three spheres 13 having a diameter of 1 mm are juxtaposed in a state of being spaced apart from each other at approximately equal intervals), and the sample 14 is placed on the sphere 13 (only the central sphere in the case of three spheres). The sample 14 may be sandwiched by the pin 12 being disposed on the other side of the inner surface of the pin 12 so that the tin or tin alloy film is in contact therewith.

FIG. 5 shows another example of an evaluation tool. A sample 35 is placed on the inner surface of one plate body 32 of a holding body 31 formed by connecting two plate bodies 32 and 33 so that they can be opened and closed by a hinge 34. A pressure contact portion 37 is provided on the inner surface of the other plate 33 so as to fix the sample holding portion 36 to be held and face the sample 35, and when the plates 32 and 33 are closed, the sample is placed on the pressure contact 37. 35, and when one plate body 32 is fixed by the stoppers 38, 38 provided at the tip (opening side) of the other plate body 33, the opening side of one plate body 32 is the other side. The plate 33 is pressed against the pressure, so that the pressure contact portion 37 is pressed against the sample 35 with a required load. A plurality of pressure contact portions 37 (three in the drawing) can be provided as shown in the figure, but the pressure contact portion 37 contacting the sample 35 is preferably only one in the center.

FIG. 6 shows another example of the evaluation tool. In this example, a pressure contact portion 42 is provided on the inner lower surface of the box body 41 whose front surface is open, and the pressure contact portion 42 is at least as thick as the sample 43. A partition plate portion 44 is provided, and a rotary plate 45 having a screw hole in the center is rotatably supported on the box body 41 above the partition plate portion 44, and a screw rod is mounted on the screw hole of the rotary body 45. 46 is screwed so that the tip of the screw rod 46 penetrates the partition plate portion 44, and the rotating body 45 is rotated left and right so that the screw rod 46 moves up and down. The sample 43 is disposed between the pressure contact portion 42 and the partition plate portion 44, operates the rotating body 45 to lower the screw rod 46, and presses the sample 43 against the pressure contact portion 42 at the lower end surface of the screw rod 46. Thus, the sample 43 is brought into pressure contact with the pressure contact portion 42 with a desired pressure contact force. In this case, the box 41, the rotating body 45, and the screw rod 46 constitute a holding body.

Incidentally, as an aspect of the pressure contact portion 37, 42 in FIG. 5 and 6, it can be given 7-12. Example of FIG. 7 that contact portion 52 is spherical and an adhesive fixing the contact portion 52 via the adhesive tape 53 to the member 51 which is disposed, hemispherical protrusion or a pressing portion 52 in Figures 8-10 member 51 example previously projecting conical projections or truncated pyramid-shaped projections, 11 form examples which projects a triangular cross-section ridges on member 51 as the pressure contact portion 52, 12 is a pressure contact portion 52 of the spherical member 51 However, the present invention is not limited to these examples.
In addition, when the substrate (plate) for forming the Sn—Cu alloy plating is Cu or Cu alloy (brass or phosphor bronze), there is a possibility that trace elements may diffuse from the substrate to the Sn—Cu alloy plating film. From the viewpoint of suppressing the generation of whiskers, it is preferable to use a 42 alloy plate for the substrate.

EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not restrict | limited to the following Example.
In the following examples, the following contact pressure clip method was used as a method for measuring the generation of contact pressure whiskers.

Pressure-contacting clip method A double-sided adhesive tape is applied to one side of the pinch 12 of the holding body 11 made of the eyeball clip 11 (65 mm width) shown in FIG. 4, and a stainless steel ball (SUS ball) 13 having a diameter of 1 mm is placed thereon. Adhere in parallel with each other at approximately equal intervals, and Sn-Cu alloy electroplating film on one side of Ni-Fe (42 alloy) alloy plate of 0.3 mm thickness x 15 mm width x 20 mm length A sample 14 (Cu content 2.0 wt%) formed with a film thickness of 5.7 μm is sandwiched so that the plating film is in contact with the center SUS sphere 13, and a certain period (1 to 10 days) has elapsed in this loaded state. Then, the sample was removed, whiskers were observed with a scanning electron microscope (SEM), the contact pressure whiskers were counted from the SEM image, and the results of the number of whisker generation were quantitatively converted into data. In addition, according to this eyeball clip system, it is possible to examine the occurrence state of the contact pressure whisker in a short period (1 to 3 days).

In the above-mentioned contact pressure clipping method, the contact pressure (pressure contact force) applied to the sample when the sample is sandwiched is a load of 750 g (about 24 kg / mm ² ), and after heat treatment at 150 ° C. for a predetermined time in the sample pressure contact state, 3 days We left it at room temperature and examined the situation of whiskers. FIG. 13 shows the results showing the relationship between the heat treatment time and the number of whiskers generated.

It is the figure which showed an example of the fitting state of one member and other members in this invention. It is the figure which showed one specific example of one member in this invention, and another member. It is the figure which showed the other specific example of the one member and other member in this invention, Comprising: (B) is an enlarged view of the X section of (A). It is the figure which showed the example using a commercially available eyeball clip as a contact pressure whisker evaluation tool in this invention. It is the figure which showed an example of the contact pressure whisker evaluation tool in this invention. It is the figure which showed the other example of the contact pressure whisker evaluation tool in this invention. It is the figure which showed the 1st example of the specific form of the press-contact part in this invention. It is the figure which showed the 2nd example of the specific form of the press-contact part in this invention. It is the figure which showed the 3rd example of the specific form of the press-contact part in this invention. It is the figure which showed the 4th example of the specific form of the press-contact part in this invention. It is the figure which showed the 5th example of the specific form of the press-contact part in this invention. It is the figure which showed the 6th example of the specific form of the press-contact part in this invention. It is the figure which showed the relationship between the heat processing time and the number of whisker generation | occurrence | production in the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Connector 2 Connector pin 3 Lead 4 Polyimide 5 Pattern a, b Member c Contact pressure location W Contact pressure whisker 11 , 3 1 Holding body 14, 35, 43 Sample 37, 42, 52 Pressure contact part

Claims (6)

A method for evaluating the state of occurrence of contact pressure whiskers generated when an external load is applied from another member to the tin or tin alloy film of the sample on which the tin or tin alloy film is formed. With respect to the formed sample, the tip of the press-contact portion protruding from the holding body that holds the tin or tin alloy film of the sample on which the tin or tin alloy film is formed is brought into contact with the tin or tin alloy film of the sample. By applying a load, the pressure contact part is brought into contact with an area smaller than the area of the tin or tin alloy film, and the load is applied. A method for evaluating a contact pressure whisker generation state characterized by observing the degree of the above.   A method for evaluating the state of occurrence of contact pressure whiskers generated when an external load is applied from another member to the tin or tin alloy film of the sample on which the tin or tin alloy film is formed. By applying a load to the formed sample by bringing the tip of the pressure contact portion having a spherical or hemispherical tip shape into contact with the tin or tin alloy film of the sample, the pressure contact portion is made of the tin or tin alloy film. The contact pressure whisker generation state is characterized by observing whether or not the whisker has been generated and the degree of the occurrence of the whisker after the contact is applied in an area smaller than the area and the load is applied for a predetermined period. Method.   3. The evaluation method according to claim 1, wherein at least the contact portion of the pressure contact portion that contacts the tin or tin alloy film is a metal made of the same material as the pressure contact portion of the other member. An evaluation tool for evaluating the state of occurrence of contact pressure whiskers generated when an external load is applied from another member to the tin or tin alloy film of the sample on which the tin or tin alloy film is formed, the tin or tin alloy film A holding body for holding the tin or tin alloy film of the sample on which the film is formed, and the above-mentioned tin or tin alloy film protruding from the holding body and contacting the tin or tin alloy film held on the holding body A contact pressure whisker evaluation tool, comprising: a pressure contact portion that is pressure-contacted with an area smaller than the area.   An evaluation tool for evaluating the state of occurrence of contact pressure whiskers generated when an external load is applied from another member to the tin or tin alloy film of the sample on which the tin or tin alloy film is formed, the tin or tin alloy film A holding body holding the tin or tin alloy film of the sample on which the metal is formed, and the tip is brought into contact with the tin or tin alloy film held on the holding body and pressed in an area smaller than the area of the tin or tin alloy film. And a pressure contact whisker evaluation tool comprising a pressure contact portion whose tip shape is spherical or hemispherical.   The contact pressure whisker evaluation tool according to claim 4 or 5, wherein at least the contact portion of the pressure contact portion that comes into contact with the tin or tin alloy film is a metal made of the same material as the pressure contact portion of the other member.

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