JP4552468B2 - Whisker inspection method for tin plating film - Google Patents

Description

  The present invention relates to a whisker inspection method for a tin plating film, which can perform tin whisker that requires a long time for inspection in a short period of time.

  Tin plating is generally used as a metal surface treatment method for decorative articles, electronic parts, structural parts, etc. because of its low cost and excellent corrosion resistance, appearance, and solderability. However, it is known that needle-like crystals made of a single crystal of tin called whiskers are generated on the surface of tin plating. This whisker usually has a diameter of 1 to 2 μm and a length of several μm to several mm, and is particularly likely to occur in a bright tin plating film to which a brightening agent has been added. In the circuit and between the terminals, a short circuit occurred, causing noise. Moreover, recent electronic components tend to be smaller, higher density, and weaker current, and when a whisker is generated, a failure is likely to occur.

The problem to be solved is that, in order to inspect the occurrence and growth state of whiskers in order to ensure the reliability of tin-plated electronic parts, etc., it is conventionally a very long time of 2 years from 6 months This is the point. There have been various reports on methods for preventing whiskers, but no reports have been made on methods for efficient research and inspection by growing whiskers quickly.
JP 57-126992 A Japanese Patent Laid-Open No. 62-020895 JP-A-01-259195 Japanese Patent Application Laid-Open No. 07-300696 JP 2003-163135 A

The present invention relates to a whisker inspection method for a tin-plated film. After ultrasonic vibration is applied to a copper or copper alloy substrate on which a tin-plated film is formed, the storage temperature is 30 to 60 ° C. and the storage humidity is 90% RH. The main feature is to provide a whisker inspection method that significantly shortens the time for whisker growth by placing the substrate in a high humidity environment .

  The whisker inspection method of the present invention has an advantage that a highly reliable plating film can be obtained in a short time by repeating the inspection many times because whisker growth of the plating film can be performed in a short period of time.

The tin plating film was formed on a copper or copper alloy substrate promptly tin plating film was immersed in an aqueous solution containing a surfactant, after applying ultrasonic vibration at ultrasonic cleaner, a tin plating film By storing in a constant temperature and humidity chamber at 50 ° C. and 90% RH for 168 hours, whisker having a length corresponding to 2600 hours (15 weeks) when stored at 30 ° C. can be grown and inspected.

  In addition, regarding a whisker inspection method for a tin plating film, after forming a tin plating film having a thickness of 0.5 to 3 μm on a substrate, the storage environment is stored in a constant temperature and humidity chamber at 85 ° C. and 90% RH for 168 hours. By doing so, it is possible to grow and inspect about twice the density whisker when stored at 30 ° C.

  A lead frame for electronic parts used in a PPF (PrePlated Frame) method will be described as an example. 2 and 3 are a plan view and a cross-sectional view of the lead frame for an electronic component used in the present invention. As the base material used for the lead frame for electronic parts, low tin phosphor bronze, precipitation hardened copper or copper alloy, or iron / nickel alloy containing about 42 wt% nickel in iron is used. In this example, alloy 194, which is a copper alloy, was used as the fabric. First, a thin plate of the alloy 194 is processed into a lead frame shape. As a processing method, a die for punching the shape of the lead frame is manufactured, a punching process is performed using a press device using this die, a photosensitive resist is applied on the surface, a pattern is baked, and then developed and photosensitive. There is a method in which a resist is left as a positive pattern of a lead frame and processed with an etching solution such as ferric chloride or cupric chloride. In the present invention, the pressing method and the etching method can be arbitrarily selected. In the first embodiment, a plate of alloy 194 is processed into a lead frame shape by a pressing method, and then a cleaning process is performed, and a heat treatment process is performed as necessary to remove the stress remaining on the base material when punched with a press. . Thereafter, the plating process is started.

  Details of the plating process of the present invention will be described below.

  After removing the oil component of the press process and heat treatment process adhering to the fabric by the washing process by using an alkaline degreasing agent or the like by using a dipping method or an electrical method in combination or using alone, a copper base plating is formed to 0.2 μm or more. A copper cyanide solution was used as a copper base plating solution. Thereafter, the inner lead portion 2 is subjected to silver plating by a silver partial plating step.

  After the silver partial plating 5 is performed, the tin plating layer of the outer lead portion 3 is treated with a treatment agent selected from one or more of hydrochloric acid, nitric acid and sulfuric acid in order to improve the adhesion between the fabric and the tin plating layer. 6 is processed. In Example 1, 5% sulfuric acid was used.

After this pretreatment, the outer lead part 3 was partially plated with tin at a current density of 40 A / dm ² . MST-400 (manufactured by Reybold) is used as the plating solution, MST-tin is used as metal tin, 50 g / L as metal tin, MST-acid as acid is 75 mL / L, and MST-400 is prepared as additive at a concentration of 60 mL / L. did. A tin plating film was formed under conditions of a bath temperature of 50 ° C. and a flow rate of 5 L / min. The anode electrode can be arbitrarily selected from insoluble electrodes containing one or more of platinum, iridium, tantalum, rhodium, ruthenium metal or oxides thereof.
In Example 1, an insoluble electrode in which a titanium fabric was coated with a mixture of iridium oxide and tantalum oxide was used. When a soluble electrode using a normal tin plate or the like is used, electrode replacement becomes frequent, and it is necessary to stop the production line each time, so that mass productivity is extremely lowered, which is not preferable. Of course, when a high-speed plating method is not used, a soluble anode can also be used.

The plating thickness can be arbitrarily selected within a range of 3 to 15 μm. When the plating thickness is less than 3 μm, the solder wettability deteriorates due to the influence of the base. A thickness of 15 μm or more is not preferable because problems such as resin leakage from the gaps in the mold occur in the molding resin sealing step. In Example 1, tin plating of 9 μm was performed. After the tin plating, the plating solution is sufficiently removed by washing with water, and then the surface of the tin plating is etched by dipping the trisodium phosphate 12 hydrate at a concentration of 50 g / L at 60 ° C. for 20 seconds. Processed. Next, in order to remove silver leaked to the side surface of the lead, silver on the surface of the lead frame was electrically removed, followed by an anti-discoloration treatment with an organic film, and then washed with water and dried.
Next, the lead frame on which the tin plating film is formed is promptly subjected to ultrasonic vibration by an ultrasonic cleaner, and stored in a constant temperature and humidity chamber at 30 ° C. and 90% RH, and is stored for 168 hours, 504 hours, 864 hours, 1512. When the time of 2,616 hours passed, the sample was taken out each time, and the occurrence of whiskers was observed using a scanning electron microscope (SEM). The average whisker length was selected from 20 long whisker lengths. The ultrasonic washer was 8510J-DTH (manufactured by Brandonic), and was subjected to ultrasonic vibration at 40,000 Hz and 50 ° C. for 30 minutes.

  The method was the same as in Example 1 except that the constant temperature and humidity storage condition was 40 ° C. and 90% RH.

  The method was the same as in Example 1 except that the constant temperature and humidity storage condition was 50 ° C. and 90% RH.

  The method was the same as in Example 1 except that the constant temperature and humidity storage conditions were 60 ° C. and 90% RH.

  This was performed in the same manner as in Example 1 except that a surfactant was used when applying ultrasonic vibration and the constant temperature and humidity storage condition was 30 ° C. and 90% RH. As the surfactant, Neoperex G-15 (manufactured by Kao) was used at 1 mL / L.

  A surfactant was used when applying ultrasonic vibration, and the same method as in Example 1 was performed except that the constant temperature and humidity storage condition was 40 ° C. and 90% RH. As the surfactant, Neoperex G-15 (manufactured by Kao) was used at 1 mL / L.

  A surface active agent was used when applying ultrasonic vibration, and the method was the same as in Example 1 except that the constant temperature and humidity storage condition was 50 ° C. and 90% RH. As the surfactant, Neoperex G-15 (manufactured by Kao) was used at 1 mL / L.

This was performed in the same manner as in Example 1 except that a surfactant was used when applying ultrasonic vibration and the constant temperature and humidity storage condition was 60 ° C. and 90% RH. Surfactant is Neoperex G-15
(Kao) was used at 1 mL / L.
(Comparative Example 1)

It was carried out in the same manner as in Example 1 except that ultrasonic vibration by an ultrasonic cleaner was not applied and the constant temperature and humidity storage condition was 30 ° C. and 60% RH.
(Comparative Example 2)

  The method was the same as in Example 1 except that the constant temperature and humidity storage condition was 50 ° C. and 60% RH.

  The inspection conditions of the tin plating film and the progress of whisker growth up to 2616 hours (Table 1) are shown in FIG.

（表１）、図４に示す様に、実施例１〜４では錫めっき皮膜が形成された銅または銅合金基材に超音波振動を与えた後、３０℃９０％ＲＨ〜６０℃９０％ＲＨの環境下に１６８時間保存することで、比較例１の３０℃６０％ＲＨ保存時の４００時間〜１７００時間に相当する長さのウイスカを得た。特に、５０℃９０％ＲＨに１６８時間保存することで、３０℃６０％ＲＨ保存時の１７００時間に相当する長さのウイスカを得た。

(Table 1), as shown in FIG. 4, in Examples 1-4, after giving an ultrasonic vibration to the copper or copper alloy base material in which the tin plating film was formed , 30 degreeC90% RH-60 degreeC90% By storing in an RH environment for 168 hours, whisker having a length corresponding to 400 hours to 1700 hours in Comparative Example 1 when stored at 30 ° C. and 60% RH was obtained. In particular, whisker having a length corresponding to 1700 hours when stored at 30 ° C. and 60% RH was obtained by storing at 50 ° C. and 90% RH for 168 hours.

Further, in Examples 5 to 8, ultrasonic vibration was applied to a copper or copper alloy substrate on which a tin plating film was formed in an aqueous solution containing a surfactant , and then 30 ° C. and 90% RH to 60 ° C. and 90%. By storing in an RH environment for 168 hours, whiskers having a length corresponding to 600 to 2600 hours when stored at 30 ° C. and 60% RH were obtained. In particular, whisker having a length corresponding to 2600 hours or more when stored at 30 ° C. and 60% RH was obtained by storing at 50 ° C. and 90% RH for 168 hours.

  FIG. 1 shows whiskers after 168 hours grown in Example 8. The whisker grown by the method of the present invention has a tendency that the root portion becomes thin, and there is a gap between the whisker and the root portion.

Although the whisker growth mechanism according to the method of the present invention is not clear, it is a tin-copper alloy of a copper or copper alloy base material and a tin plating film, and Cu ₆ Sn ₅ that increases the internal stress easily grows. In the temperature range (30-60 ° C) where Cu ₃ Sn is difficult to grow, there is a slight gap between the particles of the plating film crystals due to the energy supply by ultrasonic vibration and the improvement of water permeability by the surfactant. By making it easier, the stress inherent in the plating film is easily released, and it is thought that whiskers grew in a short period of time.

Next, after forming a tin plating film on a copper or copper alloy substrate, it can be inspected by increasing the whisker generation density by quickly storing it in a constant temperature and humidity chamber at 85 ° C. and 90% RH for 168 hours. .

Except that the thickness of the tin plating film was 1 μm, no ultrasonic vibration was applied by an ultrasonic cleaner, and the constant temperature and humidity storage condition was 85 ° C. and 90% RH for 168 hours, the same method as in Example 1 was performed. The production density of whiskers generated in an area of 100 μm × 100 μm was observed.
(Comparative Example 3)

The whisker production density was observed in the same manner as in Example 1 except that the ultrasonic cleaning by the ultrasonic cleaner was not applied and the constant temperature and constant humidity storage condition was stored at 85 ° C. and 90% RH for 168 hours.
(Comparative Example 4)

Except that the thickness of the tin plating film was 1 μm, no ultrasonic vibration was applied by an ultrasonic cleaner, and the constant temperature and humidity storage conditions were 30 ° C. and 60% RH for 168 hours, the same method as in Example 1 was performed. The whisker formation density was observed.
(Comparative Example 5)

  Except that the thickness of the tin plating film was 1 μm, no ultrasonic vibration was applied by an ultrasonic cleaner, and the constant temperature and humidity storage condition was 60 ° C. and 90% RH for 168 hours, the same method as in Example 1 was performed. The whisker formation density was observed.

  The relationship between the inspection conditions of the tin plating film and the whisker generation density is shown in (Table 2). As shown in (Table 2), when the tin plating film thickness is 1 μm, the whisker generation density is remarkably larger than the tin plating film thickness of 9 μm by storing it in an environment of 85 ° C. and 90% RH after forming the tin plating film. It was observed that whisker production density was larger even at the same film thickness of 1 μm than when stored at 30 ° C. and 60% RH and 60 ° C. and 90% RH.

次に、錫めっき皮膜の厚さを０．２から９μｍまで変化させた時のウイスカの成長状況を３０℃６０ＲＨ％に５００時間、１０００時間、２０００時間で観察した結果を図５に示す。

Next, FIG. 5 shows the results of observation of the whisker growth state at 30 ° C. and 60 RH% over 500 hours, 1000 hours, and 2000 hours when the thickness of the tin plating film was changed from 0.2 to 9 μm.

  The thickness of the tin plating film was changed from 0.2 to 9 μm, and the whisker growth progress was observed at 500 h, 1000 h, and 2000 h when stored at 30 ° C. and 60% RH for each.

  As shown in FIG. 5, when the tin plating film thickness is less than 0.6 μm, almost no whisker is generated, and when the tin plating film thickness is more than 3 μm, whisker growth is reduced. For this reason, in the environment of 30 ° C. and 60% RH, there was a range in which whiskers were likely to grow in the range of 0.6 to 3 μm.

Next, after forming a tin plating film having a thickness of 0.5 to 3 μm on a copper or copper alloy base material and quickly applying ultrasonic vibration in an aqueous solution containing a surfactant , the plating film is By placing in an environment of 20 to 40 ° C. while maintaining deformation due to arc-shaped bending with a radius of 60 to 90 mm, the growth of whiskers can be increased and inspected.

  The same procedure as in Example 1 was performed except that the thickness of the tin plating film was 1 μm, the ultrasonic vibration was not applied by an ultrasonic cleaner, and the constant temperature and humidity storage condition was 30 ° C. and 60% RH for 168 hours. It was.

  When the tin plating film has a thickness of 1 μm, a surfactant is used when applying ultrasonic vibration, and the lead frame with the plating film formed on the outside of a 500 mL glass beaker is wound to form an arc with a radius of 88 mm. This was performed in the same manner as in Example 1 except that the constant temperature and humidity storage conditions were stored at 30 ° C. and 60% RH for 168 hours in a state where the deformation due to bending was maintained.

  When the tin plating film has a thickness of 1 μm, a surfactant is used to apply ultrasonic vibration, and a lead frame having a plating film formed on the outside of a 300 mL glass beaker is wound to form an arc with a radius of 76 mm. This was performed in the same manner as in Example 1 except that the constant temperature and humidity storage conditions were stored at 30 ° C. and 60% RH for 168 hours in a state where the deformation due to bending was maintained.

When the tin plating film has a thickness of 1 μm, a surfactant is used to apply ultrasonic vibration, and a lead frame having a plating film formed on the outside of a 200 mL glass beaker is wound to form an arc shape with a radius of 66 mm. This was performed in the same manner as in Example 1 except that the constant temperature and humidity storage conditions were stored at 30 ° C. and 60% RH for 168 hours in a state where the deformation due to bending was maintained.
(Comparative Example 6)

It was carried out in the same manner as in Example 1 except that the ultrasonic vibration by the ultrasonic cleaner was not applied and the constant temperature and humidity storage conditions were stored at 30 ° C. and 60% RH for 168 hours.
(Comparative Example 7)

The thickness of the tin plating film is 1 μm, the ultrasonic wave is not applied by an ultrasonic cleaner, and the lead frame having the plating film formed on the outside of a 200 mL glass beaker is wound to form an arc-shaped plating film having a radius of 66 mm. It was carried out in the same manner as in Example 1 except that the constant temperature and humidity storage conditions were stored at 30 ° C. and 60% RH for 168 hours in a state in which deformation due to bending was maintained.
(Comparative Example 8)

The thickness of the tin plating film is 1 μm, the ultrasonic wave is not applied by an ultrasonic cleaner, and the lead frame having the plating film formed on the outside of a 200 mL glass beaker is wound to form an arc-shaped plating film having a radius of 66 mm. It was performed in the same manner as in Example 1 except that the constant temperature and humidity storage condition was stored at 60 ° C. and 90% RH for 168 hours in a state where deformation due to bending was maintained.
(Comparative Example 9)

The same method as in Example 1 except that the thickness of the tin plating film was 1 μm, a surfactant was used when applying ultrasonic vibration, and the constant temperature and humidity storage condition was 30 ° C. and 60% RH for 168 hours. went.
(Comparative Example 10)

  When the tin plating film has a thickness of 1 μm, a surfactant is used when applying ultrasonic vibration, and a lead frame having a plating film formed on the outside of a 100 mL glass beaker is wound to form an arc-shaped plating film with a radius of 54 mm This was performed in the same manner as in Example 1 except that the constant temperature and humidity storage conditions were stored at 30 ° C. and 60% RH for 168 hours in a state where the deformation due to bending was maintained.

  The relationship between the inspection conditions of the tin plating film and the whisker growth after 168 hours is shown in (Table 3). As shown in (Table 3), when the tin plating film thickness is 1 μm, it is more prominent than when the tin plating film thickness is 9 μm by storing in a 30 ° C. and 60% RH environment after forming the tin plating film for 168 hours. Whisker growth was observed. Further, whisker growth became more remarkable as the stress due to bending was increased in the plating film after ultrasonic vibration was applied in an aqueous solution containing a surfactant even with the same film thickness of 1 μm. At this time, if too much stress due to bending was applied, the effect was not obtained.

以上、本実施例で示した様に、錫めっき皮膜を３〜１５μｍ形成後、超音波振動、界面活性剤存在下での超音波振動を与え、温度が３０〜６０℃、湿度が８０〜９５％ＲＨで保存することにより、ウイスカ成長を大きくして検査することが出来る。

As described above, after forming a tin plating film of 3 to 15 μm as shown in this example, ultrasonic vibration and ultrasonic vibration in the presence of a surfactant are applied, and the temperature is 30 to 60 ° C. and the humidity is 80 to 95. By storing at% RH, whisker growth can be increased and inspected.

  In addition, after forming a tin plating film of 0.5 to 3 μm, the whisker production density can be increased by storing at a temperature of 80 to 100 ° C. and a humidity of 80 to 95% RH. Furthermore, it is possible to inspect the whisker growth by applying ultrasonic vibration in the presence of a surfactant and maintaining the temperature at 20 to 40 ° C. while the tin plating film retains deformation due to bending. I can do it.

  Although the tin plating film on the lead frame for electronic parts has been described in the above embodiment, the present invention is not limited to this application.

  By increasing whisker growth, whisker inspection that required a long period of time can be completed in a short period of time, so it is possible to develop and produce highly reliable products that do not generate whiskers in all products that use tin plating. .

Whisker diagram grown in the present invention The top view of the lead frame for electronic components used by this invention Sectional view of the lead frame for electronic components used in the present invention Relationship diagram of whisker growth process according to tin plating film inspection conditions Relationship between tin plating film thickness and grown whisker length

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Chip mounting part 2 Inner lead part 3 Outer lead part 4 Tie bar part 5 Silver or silver alloy plating part 6 Tin plating part

Claims (1)

After ultrasonic vibration is applied to a copper or copper alloy substrate on which a tin plating film is formed, the substrate is stored in a high humidity environment where the storage temperature is 30 to 60 ° C. and the storage humidity is 90% RH. Whisker inspection method for tin plating film .

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