JPS63317654A - Method for inhibiting development of whisker in filament body of tinned or tin alloy-plated copper alloy - Google Patents

Abstract

PURPOSE:To inhibit the development of whiskers at the surface and also to improve reliability as material for electronic parts, by passing a filament body of thinned or tin alloy-plated copper alloy through a >=three-high roller leveler and applying the prescribed tension, etc., to the filament body. CONSTITUTION:A filament body of tinned or tin alloy-plated copper alloy is passed through a >=three-high roller leveler. Tension is applied to the above filament body to provide 0.2-5% elongation percentage, and further, repeated bending stress is also applied to inhibit the development of whiskers at the surface.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for suppressing whiskers generated on the surface of a copper alloy wire body plated with tin or a tin alloy.

[Prior Art] Generally, electronic components such as terminals and connectors are coated with matte tin plating or bright tin plating for the purpose of maintaining the corrosion resistance and solderability of the electronic components for a long period of time.

Further, such tin plating has been carried out by a so-called post-muffing method in which plating is performed after processing into electronic parts.

However, in recent years, for the purpose of streamlining the manufacturing process of electronic components and reducing costs, the so-called tin plating method, in which the material before processing is pre-plated with tin, has been increasing.

The tin-plated material plated by the above-mentioned tin plating method is processed to become an electronic component, but it goes without saying that the processability, as well as the corrosion resistance and solderability after processing, are affected by the above-mentioned boss. The product must not be inferior to electronic components obtained by the meshing method.

The processability, corrosion resistance, and solderability of the above products are compared to electronic parts plated using the Bost plating method.
Although not inferior, it is generally known that needle-shaped crystals made of tin single crystals called whiskers occur on tin-plated surfaces.

This whisker usually has a thickness of 1 to 5 μm and a maximum length of several mm.
This phenomenon is particularly likely to occur in bright tin plating to which brighteners have been added.

Therefore, when whiskers occur and grow on electronic components with matte tin plating or especially bright tin plating, it can cause short-circuits between electronic components used in electronic circuits, such as terminals, or short circuits within the circuit. There were problems such as poor insulation.

Furthermore, recent electronic circuits are trending toward smaller size, higher density, and weaker current, and the occurrence of whiskers in electronic components used in such circuits is increasingly leading to short-circuit failures in electronic circuits. It is increasing.

The cause of the whiskers is that tin, like zinc and cadmium, is a low melting point metal whose atoms move at relatively low temperatures (20 to 100° C.) and are easily recrystallized. Another possible cause of the occurrence is that tin plating tends to occur in parts of the tin-plated material that contain fine particles of impurities, such as in high-pressure hydrogen parts that are occluded during tin plating. Furthermore, whiskers are particularly likely to occur in bright tin plating with a brightening agent added, because internal stress increases due to the coexistence of tin plating and brightening agent, or due to the density of lattice defects in the plating film due to small crystal grains. is extremely high, the internal strain energy is large, and since there are many grain boundaries, there are many so-called short-circuit diffusion paths in which tin atoms diffuse and move along the grain boundaries.

Although the above is thought to be the cause of whisker generation, the actual situation is that the exact cause of whisker generation has not been investigated.

On the other hand, as a method for preventing whisker generation in tin plating, the following method has been proposed.

That is, (1) a method of heat-treating at a temperature of 150 to 180° C. for 1 to 3 hours after tin plating, and (2) a method of irradiating electron beam in vacuum after tin plating. (Tokuko Showa 55-0
31196). (3) A method of forming an anodic oxide film after tin plating (Japanese Patent Publication No. 52-053735).

(4) Method of alloy-plating tin with lead, nickel, etc.; (5)
) Methods have been proposed to reduce hydrogen absorption in plating by applying ultrasonic energy.

However, the method described above has various problems when continuously processing long lines and stripes.

In other words, method (1) requires a long time for heat treatment, making continuous processing difficult, and furthermore, bright plating with brighteners added may cause plating defects such as discoloration, blisters, and cracks. may occur. Method (2) is not suitable for continuous processing because it must be maintained in a vacuum.
Furthermore, the irradiation equipment and vacuum processing equipment are expensive, increasing the processing cost. Method (3) is suitable for continuous processing, but if processing is performed after plating, such as in tin plating, the oxide film may be destroyed during processing.

There are doubts about the plating performance, such as the corrosion resistance, solderability, and electrical properties of the plating. Method (5) is effective if the generation, growth, and growth of whiskers is caused only by hydrogen absorption during plating. It is not possible to be sure, as many other factors are thought to be involved.

[Problems to be Solved by the Invention] The present invention has been made for the purpose of providing a method for suppressing tin or tin alloy whiskers, which solves all the problems of the prior art described above.

[Means for Solving the Problems] The present invention is characterized by applying a tension that gives an elongation rate of 0.2 to 5% to a tin or tin alloy plated copper alloy wire body, and repeatedly applying bending stress. The gist of the present invention is to provide a method for suppressing whiskers in tin or tin-plated copper alloy wire bodies.

[Function] The method for plating tin or tin alloy of the present invention will be described below.

Normally, copper alloy wires may or may not be plated with a Cu base plating, but if we explain the case where a Cu base plating is applied, for example, a zinc-containing copper alloy wire has copper Plating is applied, and it is necessary to suppress the diffusion of zinc from the copper alloy in order to maintain the corrosion resistance and solderability of electronic components for a long time, and to prevent discoloration and whisker formation over time. This is because it is essential to apply a copper plating layer as a base for the tin plating layer.

The above copper plating is a bright copper base plating, and if it is a bright copper base plating, fine microcrystals can be obtained.
This can be applied to the actual situation where the thickness of the plating layer has become extremely thin, around 1 μm, as electronic components have become lighter, thinner, and shorter in recent years. The method for treating the bright copper plating layer is to perform alkaline degreasing, water washing, cathodic electrolytic degreasing, water washing, and acid activation of the copper alloy filament by conventional methods, and after washing with water, bright copper plating is performed.

In the above bright copper plating method, for example, thiocarbonyl (
Brighteners such as C=S), dextrin (C6H2゜0
．． )・. Electroplating is carried out in a bath suitably mixed with a leveling agent such as, and a dispersant such as a nonionic or anionic activator. Note that the plating method is not limited.

After the above-mentioned bright copper plating, tin plating is performed. When bright tin plating is applied, the bright tin plating layer is usually zero in order to increase the corrosion resistance of electronic components and maintain solderability for a long period of time. It is applied to a thickness of .5 to 5 μm, but recently,
As electronic parts become lighter, thinner, shorter and smaller, thin plating of around 1 μm has become the most common. The method for forming this bright tin plating layer is to use an electroplating bath in which a tin sulfuric acid bath, a tin fluoride bath, a phenolsulfonic acid bath, an alkaline bath, etc. are appropriately mixed with additives as a brightening agent, a smoothing agent, and a dispersing agent. to give

Note that the present invention does not limit the plating method, and general bright tin plating methods other than the above methods,
A matte plating method or a semi-bright tin plating method may be used.

In the present invention, processing stress is applied after applying the tin plating or tin alloy plating layer, but the method of applying processing stress is not particularly limited, but usually the elongation rate is 0°2 to 5. The plate is passed through a leveler as shown in Fig. 1 while applying a tension of %. In FIG. 1, 1 is a copper alloy wire body, and 2 is a roll. Note that the number of rolls of the leveler shall be three or more stages.

The reasons for limiting the elongation rate and the number of rolls mentioned above are explained below. The stress dispersion within is small, and the whisker suppression effect is small. Moreover, if the elongation rate exceeds 5%, the copper alloy filament will undergo large plastic deformation and the gloss of the tin or tin alloy wipe will decrease, which is not preferable. Therefore, the elongation rate is 0
．． The tension was set to be 2 to 5%.

Next, the reason why the number of rolls of the leveler is set to three or more is that if the number of rolls is less than three, the load of repeated bending stress becomes insufficient and the effect of suppressing whiskers cannot be obtained.

As described above, the present invention suppresses the growth of tin or tin alloy plating whiskers by applying tensile stress and repeated bending stress to a copper alloy wire body coated with tin or tin alloy plating. The suppression mechanism is assumed to be that the growth of whiskers is suppressed by dispersion of plating stress due to crystal deformation of tin plating or tin alloy plating, and changes in stress balance between each layer of the material, tin plating, and tin alloy plating. Thus, the present invention was completed.

[Example] The method for suppressing whiskers in a tin or tin alloy plated copper alloy wire body according to the present invention will be described below with reference to Examples.

JISC-2600 ()OCu-30Zn) Plate thickness: 0.
A strip with a width of 25 mm and a width of 150 mm was pretreated using a conventional method, and then treated in a copper sulfate plating bath (CuSO4).
'5H20: 190g/1. H2SO2: 50g/u.

After performing copper base plating with a plating thickness of 0.8 μm using CJl: 50 mg/j2, brightener: 10 g/j2), current density: 3 A/drn', temperature: 20 ° C.
It is washed with water and then activated with a 10% H2So4 aqueous solution.

After the above, wash with water, tin sulfate plating bath (SnSO4: 60g/J2.H2SO4: to o
g7x, cresol sulfonic acid: 30 g/J2,
Formalin: 5mj2/J! , brightener: 10m1/11
, current density: 3A/dt using dispersant 20g/J2)
Bright tin plating was performed at a plating thickness of 1.2 μm under conditions of 20° C. and temperature: 20° C.

Next, while applying tension to the bright tin-plated copper alloy strip, it is passed through a leveler, and the leveler rolls are 3 on the upper side and 4 on the lower side, and 11 on the upper side and 12 on the lower side, Elongation rate 0.1%.

Tensions were applied to give 0.2%, 1%, 5%, and 10%.

In addition, as a comparison, a tin-plated strip was prepared under tension to give an elongation rate of 0.1%.

A length of 100 mm from each of the above tensioned strips,
A test piece for whisker investigation with a width of 50 mm was prepared.

The whisker test method was performed as follows.

That is, compressive stress was applied to the test piece 22 in a jig 21 having a concave cross section with an inner width of 94 mm as shown in FIG. 2, and the test piece 22 was placed indoors.

For whisker measurement, whiskers generated within compressive stress surface B: 20 mm x 50 mm were observed using a stereoscopic microscope.

Table 1 shows the change in reflectance of the strips that were passed through a leveler under tension to achieve the elongation rate of 0.1 to 10% as explained above, and the whisker test of test pieces made from these strips over a period of 3 months. This shows the whisker generation status after one year.

No. 1 to No. 4 are Examples of the present invention, in which the elongation rate was within the range of 0.2 to 5%, there was no significant change in reflectance, and there was no visible change in appearance. Furthermore, N
For 091 to NO63, the number of rolls of the leveler is set to 1 on the upper side.
There are 1 tree and 12 trees on the lower side, and for No. 4, there are 3 trees on the upper side,
There are 4 on the lower side, which meet the essential requirements of the present invention, and 3
Even after one month and one year, no whiskers or nodules were generated.

No. 005 to No. 8 are comparative examples to the examples of the present invention, and No. 5 is a comparative example in which no tension was applied and the plate was not passed through the leveler, and nodules were observed to occur after 3 months. After one year, whiskers with a length of 100 μm were observed.

In N006, since the elongation rate was set to 0.1%, nodules were observed to appear after 3 months, and whiskers with a length of 100 μm were observed to occur after 1 year.

For No. 7, the number of rolls of the leveler is one on the upper side,
Since there was only one on the lower side, repeated bending stress did not work, and nodules and whiskers were observed to occur after 3 months.

For NO38, the elongation rate was 10%, and the change in reflectance was as high as 11%, visible changes in appearance were observed, and nodules and whiskers were observed to occur after 3 months.

[Effects of the Invention] As explained above, the present invention provides a highly reliable tin or tin alloy plated copper alloy wire body that suppresses the generation of whiskers and is used as a material for electronic components such as terminals and connectors. Furthermore, it is possible to provide a simpler whisker suppression method than ever before.

[Brief explanation of drawings]

FIG. 1 is an explanatory sectional view of a leveler, and FIG. 2 is an explanatory diagram of a whisker test method. 1... Tin or tin alloy plated copper alloy wire body, 2...
Roll, 21... Test piece, 22... Metal jig, A.
... Compressive stress surface, B... Whisker measurement part.

Claims (2)

[Claims] (1) Tin or tin alloy plated copper alloy wire with an elongation rate of 0.
A method for suppressing whiskers in a tin or tin-plated copper alloy wire, the method comprising applying a tension of 2 to 5% and repeatedly applying bending stress. (2) The tin or tin alloy plated copper according to claim 1, wherein the tin or tin alloy plated copper alloy wire is passed through a leveler having three or more rolls in order to apply repeated bending stress. A method for suppressing whiskers in alloy striata.