JP2005330577A - Method for evaluating whisker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for evaluating whisker acceleratingly in such a condition as the generation and growth of whisker is not inhibited. <P>SOLUTION: This evaluation method includes leaving electronic parts having a connecting terminal 4 provided with an Sn-plated film of a lead-free plated film, in an inert atmosphere for three hours or longer. The inert atmosphere inhibits an oxide film 14 from forming on the surface of the plated film. The method evaluates the degree of the generation and growth of the whisker 18, by observing it after the whisker 18 has been formed and grown on the Sn-plated film 12 of the connecting terminal 4. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a whisker evaluation method, and more particularly, to a method for evaluating the generation and growth of whisker generated in an electrode or the like of an electronic component on which tin or tin alloy plating is applied.

  Electronic components mounted on a mounting substrate or the like are generally subjected to solder plating. In consideration of environmental problems, lead-free solder has been used in recent years. Since lead-free solder does not contain lead, environmental pollution due to lead can be reduced. However, lead contained in conventional solder plating has the effect of suppressing the growth of soot-like crystals called whiskers. When plating is performed using lead-free solder that does not contain lead, whisker is generated. It has been found that there are many problems caused by.

  In addition, whisker generation increases due to lead-free solder plating, but the degree of whisker generation varies depending on the material and shape of a portion to be plated (such as an electrode portion of an electronic component). That is, it is known that whisker generation depends on the stress acting on the plating film. This stress is a stress generated by internal stress of plating, diffusion of underlayer atoms, and recovery / recrystallization of the plated metal structure. Therefore, it is a general practice to evaluate the occurrence and growth of whiskers on solder-plated electronic components and mounting boards on which such electronic components are mounted to ensure product reliability. Yes.

  Conventional whisker evaluation methods include standing at room temperature, standing at constant temperature, standing at high temperature and high humidity, temperature cycle test, pressure cooker test (HAST) with unsaturated steam, and the like. These are used when evaluating the connection reliability of electronic components and the like. In addition, these whisker evaluation methods are described in the “Report on Achievement of Lead-Free Solder in 2003” published by JEITA.

As described above, in the conventional whisker evaluation method, whisker growth is evaluated / observed by the environmental test in which temperature and humidity are applied as described above. For example, according to a conventional whisker evaluation method, it takes 1000 hours at room temperature. Since the evaluation time affects the product development time, an evaluation method for accelerating the generation and growth of whiskers has been proposed in order to evaluate in as short a period as possible. The above-mentioned constant temperature, high temperature and high humidity, temperature cycle test, and pressure cooker test using unsaturated steam are methods for accelerating whisker generation and growth.
JP 2002-167300 A (page 4-6, FIG. 5) JP 2003-193287 A (page 2-3) JP 2003-193289 A (page 2-3)

  First, the process of whisker generation and growth will be briefly described with reference to FIGS.

  1 and 2 are views showing a semiconductor package as an example of an electronic component, FIG. 1 is a plan view thereof, and FIG. 2 is a side view thereof.

The semiconductor package shown in FIG. 1 is a packaged integrated circuit called TSOP (Thin Small Outline Package), and a plurality of connection terminals 4 extend from the resin package part 2 to the left and right. The connection terminal 4 is bent as shown in FIG. 2 and joined to the electrode 6a of the mounting substrate 6 such as a printed circuit board by the solder 8. At this time, the surface of the connection terminal 4 of the semiconductor package is preliminarily plated with tin (Sn) as lead-free plating so that the solder adheres to the connection terminal 4.
As shown in FIG. 3A, the case where the Sn plating film 12 is formed on the base material 10 such as a copper (Cu) alloy will be described. When a certain amount of time elapses after the Sn plating film 12 is formed, the surface of the Sn plating film 12 is oxidized and a surface oxide film 14 is also formed. In addition, the Sn plating film 12 is recrystallized and the crystal grains become coarse. Further, the base material 10 which is the base material diffuses into the Sn plating film 12 to form the base diffusion layer 16.

  Here, the whisker 18 is generated in the surface layer of the Sn plating film 12, and the above-described base diffusion layer 16 grows thickly under the whisker 18. This is because the thickly grown base diffusion layer 16 locally pushes up the Sn plating film 12, and as a result, stress acts on the surface layer of the Sn plating film 12, and the recovery / recrystallization of the Sn metal structure is promoted. This indicates that it leads to the generation / growth of whiskers. A whisker is formed by growing a tin (Sn) crystal into a long and narrow shape, and is also called a solitary crystal. Depending on the environmental conditions, the whisker grows outward through the surface oxide film 14. The longer one grows to a length of about 400 μm to 1 mm.

  When whiskers are generated at the connection terminals 4 of the semiconductor package shown in FIG. 1, the whiskers may be very close or in contact with each other as shown in FIG. FIG. 4 is an enlarged plan view showing the connection terminal 4 shown in FIG. Since the whisker is a crystal of Sn and has high conductivity, a short circuit may occur at this portion when the whiskers of adjacent connection terminals come close to each other or come into contact with each other. If a short circuit occurs between the connection terminals, the semiconductor package may malfunction or the semiconductor package may be damaged.

  The above-mentioned problems caused by whisker generation are examined in advance, and tests conducted to select conditions (whether the material of the base material, the shape, the material of the plating material, etc.) where there is little or no whisker is This test is called an evaluation test. When a test piece or an electronic component is left at room temperature as an evaluation object and the occurrence of whiskers is examined, it is necessary to leave it for a long time, for example, 1000 hours, which is not practical. Therefore, an accelerated evaluation test is used in which whisker generation and growth are promoted to generate whisker in a short time.

  In the accelerated evaluation test, the generation of whiskers is basically promoted by applying heat to the test piece or the electronic component. In addition to heat, humidity and pressure may be applied.

Here, the present inventor investigated whether the accelerated evaluation test actually promotes the generation and growth of whiskers. On the contrary, in the conventional accelerated evaluation test in which heat and humidity are applied, the whisker generation and growth is reversed. I found that it was suppressed. That is, as shown in FIG. 5, in the method of applying heat for acceleration as in the conventional accelerated evaluation test, the surface oxide film 14 grows thick before the whisker grows and reaches the surface oxide film 14. Therefore, it is considered that the whisker 18 cannot break through the surface oxide film 14 and grow. Therefore, it is considered that the surface oxide film 14 suppresses whisker growth.
The surface oxide film 14 is an oxide film formed by the action of oxygen O ₂ in the atmosphere on the surface of the Sn plating film, and such oxidation is accelerated under heating conditions. Therefore, in order to suppress the formation of the surface oxide film 14, it is appropriate not to perform heating. However, heating is an important condition for promoting whisker growth. There is a problem that the time is long. The above example is a case where an oxide film is formed on the surface of the Sn plating film. However, depending on the material of the plating film and the atmospheric conditions, a hydroxide film may be formed instead of the oxide film. Similar to the oxide film, the presence of oxygen in the atmosphere becomes a generation factor in the hydroxide film.

  Thus, in the accelerated test for the purpose of accelerating the generation and growth of whiskers and shortening the evaluation time, it is counterproductive to suppress the generation and growth of whiskers, not only the evaluation time becomes long, There is a problem that accurate evaluation cannot be performed.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a whisker evaluation method capable of accelerating a whisker evaluation test under conditions where generation and growth of whiskers are not suppressed.

  In order to achieve the above object, according to the present invention, a whisker evaluation method for evaluating the degree of whisker generation and growth occurring on a lead-free plating film to be evaluated subjected to lead-free plating, There is provided a whisker evaluation method characterized in that an evaluation object is left in an inert atmosphere for 3 hours or more, and whisker generated on the surface of the evaluation object is observed to evaluate the degree of generation and growth.

  In the above whisker evaluation method, the oxygen concentration in the inert atmosphere is preferably 1000 ppm or less.

  Further, according to the present invention, there is provided a whisker evaluation method for evaluating the degree of whisker generation and growth occurring on a lead-free plated film to be evaluated subjected to lead-free plating, which is generated on the surface of the evaluation target. The evaluation target is left in an inert atmosphere for a predetermined time or longer while removing the oxidized film, and whisker generated on the surface of the evaluation target is observed to evaluate the degree of generation and growth. A whisker evaluation method is provided.

  In the above whisker evaluation method, the removal of the oxide film is preferably achieved by introducing a reducing gas into the inert atmosphere.

  Moreover, it is preferable to heat the evaluation object to a temperature below the melting point of the lead-free plating film in an inert atmosphere.

  As described above, according to the present invention, since the generation and growth of whisker is accelerated in an inert atmosphere, the formation of an oxide film or a hydroxide film that suppresses the growth of whisker is suppressed. Generation and growth can be accelerated. Furthermore, whisker generation and growth are accelerated while introducing a reducing gas into the inert atmosphere and removing the oxide film, so that whisker generation and growth can be accelerated. Therefore, it is possible to evaluate the original whisker generation characteristics of the plating film, and to perform appropriate and accurate whisker evaluation.

  Next, embodiments of the present invention will be described with reference to the drawings.

The present inventor has considered removing oxygen in the atmosphere, which is a cause of formation of an oxide film or a hydroxide film that suppresses the growth of whiskers. For this purpose, as shown in FIG. 6, a test piece or electronic component is subjected to a whisker evaluation test in an inert atmosphere. Here, the inert atmosphere is an atmosphere that does not contain oxygen or has a very low oxygen concentration. Examples of the medium constituting the inert atmosphere include an inert gas such as helium (He), nitrogen (N ₂ ), and argon (Ar), or an inert organic solvent vapor. In addition, as described below, when the oxygen concentration is 1000 ppm or less, generation of a surface oxide film or a hydroxide film can be effectively suppressed.

  In addition, the following solvents are mentioned as an example of an inert organic solvent.

* Glycol diethylene glycol, triethylene glycol, tetraethylene glycol,
Pentaethylene glycol, hexylene glycol * Ether series Ethylene glycol monomethyl ether, Diethylene glycol monomethyl ether * Perfluorocarbon series Fluorinate, Galden The above-mentioned inert atmosphere is introduced to suppress oxidation, but more aggressive oxidation The generation of whiskers can be accelerated by removing the film. That is, it is inevitable that an extremely thin surface oxide film (natural oxide film) is generated on the surface of the lead-free plating film before being subjected to the whisker evaluation test. It is considered that this surface oxide film hinders whisker growth in the whisker evaluation test. Therefore, by introducing a reducing gas such as hydrogen gas into the above inert atmosphere, whisker growth can be further promoted by conducting a whisker evaluation test while removing the oxide film that has already been generated. .

  The whisker evaluation test performed using the whisker evaluation method according to the present invention will be described below.

Experimental Example 1): Whisker growth in an inert atmosphere An Sn plating film is formed to a thickness of 10 μm by electroplating on a 40 mm × 5 mm × 0.3 mm copper (Cu) plate (Cu: 99, 99%) Prepared samples. This sample was made an inert atmosphere with an oxygen concentration of 200 ppm by blowing nitrogen in an inert oven, heated to 150 ° C., subjected to a constant temperature test, and a whisker evaluation was performed. As a comparative sample, even in a thermostatic chamber in an air atmosphere, the sample was left to be tested at 150 ° C. in the same manner. For the whisker evaluation, the number of whiskers having a length of 50 μm or more that occurred after 100 hours of standing on the entire surface of one sample was examined.

  As a result, the number of whiskers generated in the sample left in the inert oven in the inert atmosphere was 35, and the number of whiskers generated in the sample left in the thermostat in the atmospheric atmosphere was 18. Therefore, it was confirmed that whisker generation was nearly twice as much in the test conducted in an inert atmosphere than in the test conducted in an air atmosphere. That is, it was confirmed that the heating in the inert atmosphere promotes the generation of whiskers more than the heating in the air atmosphere.

  The whisker evaluation method according to the present invention is particularly suitable for the evaluation of whiskers generated in the Sn-plated portion in the connection terminal of the electronic component as shown in FIG. 1, but Sn plating or solder plating is performed. The present invention can also be applied to other components and mounting boards.

Experimental Example 2): Whisker growth in an inert atmosphere An Sn plating film is formed to a thickness of 10 μm by electrolytic plating on a 40 mm × 5 mm × 0.3 mm copper (Cu) plate (Cu: 99.99%). Prepared samples. This sample was heated to 155 ° C. in a fluorocarbon vapor atmosphere generated by a VPS (Vapor Phase Soldering) apparatus, and subjected to a constant temperature test, and a whisker evaluation was performed. As a comparative sample, even in a thermostatic chamber in an air atmosphere, the sample was left to be tested by being heated to 155 ° C. For the whisker evaluation, the number of whiskers having a length of 50 μm or more that occurred after 100 hours of standing on the entire surface of one sample was examined. The VPS device is a reflow soldering device using saturated steam used for high-density mounting boards, etc., and the product is immersed in a saturated steam atmosphere obtained by heating a fluorine-based inert chemical liquid (Galden, etc.). This is a device capable of giving uniform heat energy to the entire product by condensing the vapor touching the product by releasing vaporization latent heat and condensing. VPS is a kind of low oxygen reflow similar to N ₂ reflow, and reflow can be performed with lower oxygen (almost oxygen-free) than N ₂ .

  As a result of the above experiment, the number of whiskers generated in the sample left in the fluorocarbon vapor atmosphere was 27, and the number of whiskers generated in the sample left in the thermostat in the atmospheric atmosphere was 8. Therefore, it was confirmed that whisker generation was more than three times higher in the test conducted in the inert atmosphere than in the test conducted in the air atmosphere. That is, it was confirmed that the heating in the inert atmosphere promotes the generation of whiskers more than the heating in the air atmosphere.

  In the above experimental examples 1) and 2), the sample was allowed to stand in an inert atmosphere and heated to promote whisker growth. However, it was only allowed to stand in an inert atmosphere at room temperature without heating. However, it was found that the whisker evaluation test can be accelerated because the formation of an oxide film or a hydroxide film is suppressed.

  In the above experimental example, the sample was allowed to stand in an inert atmosphere for 100 hours. However, it was found that if whisker generation and growth are fast, a difference appears in whisker growth even if left for about 3 hours.

  Furthermore, even if it is an inert atmosphere, if it contains some residual oxygen and the oxygen concentration is 1000 ppm or less, the generation of whisker can be accelerated by suppressing the formation of a surface oxide film or a hydroxide film. I understood.

  In addition, if the heating temperature of the sample is not lower than room temperature, the effect of acceleration can be obtained, but it is necessary to make the temperature below the melting point of the plating film. This is because if the plating film is heated to a temperature higher than the melting point, the plating film is melted and whiskers are not generated.

Experimental Example 3): Whisker growth in inert atmosphere + reducing gas On a copper (Cu) plate (Cu: 99, 99%) of 40 mm × 5 mm × 0.3 mm, an Sn plating film having a thickness of 10 μm is formed by electroplating. A sample formed in this way was prepared. This sample was heated to 150 ° C. in an inert oven into which hydrogen gas and nitrogen gas were introduced at an oxygen concentration of 270 ppm and subjected to a constant temperature test for 100 hours, and a whisker evaluation was performed. As a comparative sample, the sample was left to stand in a case where the sample was heated to 150 ° C. in an inert atmosphere containing only nitrogen gas without introducing hydrogen gas, and the case where the sample was similarly heated to 150 ° C. in a constant temperature bath in an air atmosphere. It was. For the whisker evaluation, the number of whiskers having a length of 50 μm or more that occurred after 100 hours of standing on the entire surface of one sample was examined.

  As a result, the number of whiskers generated in samples left in an inert oven into which hydrogen gas and nitrogen gas were introduced was 51, and the number of whiskers generated in samples left in an inert atmosphere containing only nitrogen gas was 32. Yes, the number of whiskers generated in the sample left in the thermostat in the atmospheric atmosphere was 15. Therefore, the number of whisker generations was highest in the test conducted in an inert atmosphere into which hydrogen gas was introduced, and 1.5 times or more of the number of whisker generations in an inert atmosphere test using nitrogen was conducted in an air atmosphere. It was confirmed that the number of whiskers generated in the test was three times or more. That is, it was confirmed that the introduction of hydrogen gas as a reducing gas into the inert atmosphere promotes the generation of whiskers as compared with the case of only the inert atmosphere.

Experimental Example 4): Whisker growth in inert atmosphere + reducing gas On a copper (Cu) plate (Cu: 99, 99%) of 40 mm × 5 mm × 0.3 mm, an Sn plating film having a thickness of 10 μm is formed by electroplating. A sample formed in this way was prepared. This sample was heated to 150 ° C. while introducing hydrogen gas in a fluorocarbon (Galden 155) vapor atmosphere generated by a VPS apparatus, and subjected to a 50-hour constant temperature test to perform whisker evaluation. As a comparative sample, the sample was left to stand in a case where the sample was heated to 150 ° C. in an inert atmosphere containing only fluorocarbon vapor without introducing hydrogen gas, and the case where the sample was similarly heated to 150 ° C. in a thermostatic chamber in an air atmosphere. It was. As the whisker evaluation, the number of whiskers having a length of 50 μm or more generated after 50 hours of standing on the entire surface of one sample was examined.

  As a result of the above experiment, the number of whiskers generated in the sample left in the atmosphere in which hydrogen gas was introduced into the fluorocarbon vapor was 41, and the number of whiskers generated in the sample left in the inert atmosphere containing only the fluorocarbon vapor. Was 16, and the number of whiskers generated in the sample left in the thermostatic chamber in the air atmosphere was 7. Therefore, the number of whisker generations was highest in the test conducted in an inert atmosphere into which hydrogen gas was introduced, and the whisker generation number was about 2.5 times the number of whisker generations in the test in an inert atmosphere containing only fluorocarbon vapor. It was confirmed that the number of whisker generation in the test was nearly six times as many. That is, it was confirmed that the introduction of hydrogen gas as a reducing gas into the inert atmosphere promotes the generation of whiskers as compared with the case of only the inert atmosphere.

Experimental Example 5): Whisker Growth in Inert Atmosphere + Reducing Gas The number of whiskers having a length of 50 μm or more generated under the same conditions as in the above Experimental Example 3) with a standing time of 3 hours was examined.

  As a result, the number of whiskers generated in the sample left in the inert oven introduced with hydrogen gas and nitrogen gas is 5, and the number of whiskers generated in the sample left in the inert atmosphere of only nitrogen gas is 2. There was no whisker generation in the samples left in a constant temperature bath. Therefore, according to the test conducted in an inert atmosphere into which hydrogen gas was introduced, it was confirmed that the whisker evaluation test could be performed in a short time of 3 hours.

  In the above experimental examples 3), 4) and 5), the sample was left in an inert atmosphere and heated while removing the oxide film by introducing a reducing gas to promote whisker growth. Even if it is not, the oxide film is removed and the formation of the oxide film or the hydroxide film is suppressed only by leaving it in an inert atmosphere where reducing gas is introduced at room temperature, so that the whisker evaluation test can be accelerated. I knew it was possible.

  It was also found that by introducing hydrogen gas, the generation of whiskers can be accelerated by suppressing the formation of surface oxide films and hydroxide films when the oxygen concentration in the inert atmosphere is less than 20%.

  In addition, if the heating temperature of the sample is not lower than room temperature, the effect of acceleration can be obtained, but it is necessary to make the temperature below the melting point of the plating film. This is because if the plating film is heated to a temperature higher than the melting point, the plating film is melted and whiskers are not generated.

  The above-described whisker evaluation test according to the present invention is applied to an electronic component or a mounting substrate subjected to lead-free plating. For example, when an electronic component and a mounting substrate are purchased and assembled into a product, whisker evaluation is performed before using the purchased electronic component or mounting substrate to determine whether or not the electronic component can be used. FIG. 7 is a flowchart of the process from whisker evaluation to product shipment.

  First, in step S1, a sample for conducting a whisker evaluation test is prepared from the purchased electronic component and the mounting substrate. The electronic component and the mounting substrate are not limited to those purchased, but may be manufactured in-house.

  Next, in step S2, the electronic component or the mounting substrate is evaluated by the above-described whisker evaluation method according to the present invention. Specifically, the electronic component or the mounting substrate is left for a predetermined time while being heated in an inert atmosphere, and the occurrence of whiskers is examined. In step S2, if the whisker evaluation is NG, that is, if it is determined in the whisker evaluation test that the generation of whiskers is not less than the specified value, the electronic component or the mounting board is not adopted in step S3.

  If the whisker evaluation is OK in step S2, the electronic component and the mounting board are sent to the assembly process and assembled as a product. An operation test is performed on the assembled product in step S5. When it becomes NG in the operation test, the NG product is repaired in S6 and sent again to the assembly process in step 4.

  If it is determined to be OK in step S5, the product is sent to the product shipping process and shipped.

  In the process up to the shipment of the product as described above, the step 2 in which the whisker evaluation test is performed requires a relatively long time, and if this step is completed in a short time, the parts can be quickly assembled. It can be sent and there is no stagnation of parts inventory. Therefore, by performing whisker evaluation of electronic components and mounting boards using the whisker evaluation method according to the present invention, the whisker evaluation time can be shortened, and the retention of parts inventory can be reduced. Further, according to the whisker evaluation method of the present invention, since the growth of whisker is not suppressed, an accurate evaluation result can be obtained and the reliability of the product is improved.

  As described above, this specification discloses the following invention.

(Appendix 1)
A whisker evaluation method for evaluating the degree of whisker generation and growth occurring on a lead-free plating film to be evaluated subjected to lead-free plating,
A whisker evaluation method, wherein the evaluation object is left in an inert atmosphere for 3 hours or more, and whisker generated on the surface of the evaluation object is observed to evaluate the degree of generation and growth.

(Appendix 2)
A whisker evaluation method according to appendix 1,
A whisker evaluation method, wherein the oxygen concentration in the inert atmosphere is 1000 ppm or less.

(Appendix 3)
A whisker evaluation method for evaluating the degree of whisker generation and growth occurring on a lead-free plating film to be evaluated subjected to lead-free plating, while removing an oxide film generated on the surface of the evaluation object A whisker evaluation method, wherein the evaluation object is left in an inert atmosphere for a predetermined time or more, and whisker generated on the surface of the evaluation object is observed to evaluate the degree of generation and growth.

(Appendix 4)
A whisker evaluation method according to appendix 1,
A whisker evaluation method, wherein the oxygen concentration in the inert atmosphere is less than 20%.

(Appendix 5)
The whisker evaluation method according to attachment 3 or 4,
The whisker evaluation method is characterized in that the removal of the oxide film is achieved by introducing hydrogen gas into the inert atmosphere.

(Appendix 6)
The whisker evaluation method, wherein the reducing gas is hydrogen gas.

(Appendix 7)
The whisker evaluation method according to any one of supplementary notes 1 to 6,
The whisker evaluation method, wherein the evaluation object is heated to a temperature below the melting point of the lead-free plating film in the inert atmosphere.

(Appendix 8)
The whisker evaluation method according to any one of appendices 1 to 7,
A whisker evaluation method, wherein the inert atmosphere is generated by at least one of an inert gas and an inert organic solvent vapor.

(Appendix 9)
The whisker evaluation method according to appendix 8,
The whisker evaluation method, wherein the inert gas includes any of nitrogen, argon, and helium.

It is a top view which shows the semiconductor package as an example of an electronic component. FIG. 2 is a side view of the semiconductor package shown in FIG. 1 mounted on a mounting substrate. It is a figure for demonstrating generation | occurrence | production of a whisker. It is a figure which shows the whisker which generate | occur | produced in the connection terminal of an electronic component. It is a figure which shows the example by which the growth of a whisker is suppressed by a surface oxide film It is a figure which shows the growth of the whisker in the whisker evaluation method by this invention. It is a flowchart of the process from whisker evaluation to product shipment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 Package part 4 Connection terminal 6 Mounting board 6a Electrode 8 Solder 10 Base material 12 Sn plating film 14 Surface oxide film 16 Underlayer diffusion layer 18 Whisker

Claims (5)

A whisker evaluation method for evaluating the degree of whisker generation and growth occurring on a lead-free plated film to be evaluated subjected to lead-free plating,
A whisker evaluation method, wherein the evaluation object is left in an inert atmosphere for 3 hours or more, and whisker generated on the surface of the evaluation object is observed to evaluate the degree of generation and growth. The whisker evaluation method according to claim 1,
A whisker evaluation method, wherein the oxygen concentration in the inert atmosphere is 1000 ppm or less. A whisker evaluation method for evaluating the degree of whisker generation and growth occurring on a lead-free plating film to be evaluated subjected to lead-free plating,
While removing the oxide film generated on the surface of the evaluation object, the evaluation object is left in an inert atmosphere for a predetermined time or more, and whisker generated on the surface of the evaluation object is observed to determine the degree of generation and growth. The whisker evaluation method characterized by evaluating. A whisker evaluation method according to claim 3,
The whisker evaluation method according to claim 1, wherein the removal of the oxide film is achieved by introducing a reducing gas into the inert atmosphere. A whisker evaluation method according to any one of claims 1 to 4,
The whisker evaluation method, wherein the evaluation object is heated to a temperature below the melting point of the lead-free plating film in the inert atmosphere.

Images