JP2587258B2 - Method for producing reflow tin or tin alloy plated material using copper or copper alloy as base material - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a reflow plating material of tin or tin alloy of copper and copper alloy having excellent appearance and solderability.

2. Description of the Related Art Conventionally, after a tin or a tin alloy is electroplated on a surface using copper or a copper alloy as a base material, the plating layer is heated and melted at a temperature higher than the melting point of the tin or the tin alloy. The so-called reflow plating material is generally used for leads of connectors, switches and other electronic components.

In both cases of reflow tin plating and reflow tin alloy plating, depending on the type of base material and the application of the plating material, there are cases where it is directly plated on the base material and cases where copper or nickel is applied as a base plating. is there.

However, when the undercoating is omitted or the tin or tin alloy electroplated coating is extremely thin, such as when the thickness of the base coating is 0.2 mm or less, the molten metal gathers and the coating thickness becomes uneven. A defect called "dewetting" or "wetting defect" occurs. The resulting material due to poor wetting not only has poor appearance, but also poor solderability, and has a problem of adversely affecting the manufacturing conditions and quality of parts using the material.

Thus, despite the fact that the wetting failure is a serious industrial defect, there is no established mechanism for its occurrence, and the conventional measures have not been satisfactory.

Conventionally, the mechanism of occurrence is that it is a phenomenon of repelling phenomenon, that it can be reduced by chemically polishing the base material by pretreatment or by thickly applying a base material, and that organic matter ( (Additive) is known to easily occur when the amount of eutectoid is large.

In particular, those requiring chemical polishing in the plating pretreatment step have been strongly required to take an alternative measure from the viewpoint of productivity and economy.

Problems to be Solved by the Invention The present invention has been made in view of the situation as described above, and is a copper or copper alloy reflowed tin or tin alloy plated material which does not cause poor wetting and has both excellent appearance and solderability. By improving the copper or copper alloy base material used for the above-mentioned plating material, in particular, in the case of a reflow plating material in which the base plating is omitted, the base material is chemically polished in the plating step. An object of the present invention is to provide a method for producing the above-mentioned reflow tin or tin alloy-coated material which is excellent in both appearance and solderability without any problem.

 Hereinafter, the present invention will be described in detail.

Configuration features of the present invention, without mechanical polishing the surface after the final annealing, copper or copper alloy base material obtained by performing the final rolling, tin or tin alloy electroplating, In addition, the reflow process is performed.

Here, the final annealing does not include the strain relief annealing after the final rolling. Therefore, it is possible to appropriately perform strain relief annealing or the like after the final annealing in order to improve spring characteristics and the like.

Means for solving the problem Copper or copper alloy material is generally subjected to mechanical polishing by a buff or the like for removal of surface oxides and surface defects generated in the annealing step, and then to finish rolling. . However,
When the material is mechanically polished with a buff or the like, minute streaks, so-called polished lines, are formed in the polishing direction.The cross-sectional profile perpendicular to the polished direction of the polished line is extremely obtuse. Alternatively, a scab-like defect occurs. The existence of this warp-like defect has been known in the past, and furthermore, it has been known that when it is used for a base material for precious metals such as gold and silver for electronic components, the heat resistance thereof is reduced. However, the heat resistance of precious metal plating for electronic components is much lower than the melting point of the plating metal (for example, at most about 500 ° C for gold and silver plating). Correlation with poor wetting that occurred in the above was not expected from the viewpoint of the mechanism of occurrence and the phenomenon.

Although the details of the above mechanism are not clear, the return defects on the material surface are not sufficiently activated in the pretreatment of the plating step, and when the electroplated tin or tin alloy is reflowed thereon, the mother board becomes defective. It is estimated that the interaction with the inactive point remaining at the interface with the material induces poor wetting.

In the present invention, in order to prevent the occurrence of the above-described wetting failure, mechanical polishing is omitted in a step of final annealing or the like. To that end, the atmosphere of the final annealing is made non-oxidizing to oxidize the material surface or other Prevent or minimize reaction with the atmosphere, and clean the surface only by pickling.

Non-oxidizing atmospheres include hydrogen (H ₂ ), carbon monoxide (CO),
Ammonia decomposition gas (N ₂ + 3H ₂ ), charcoal gas (CO + CO ₂ )
In the case of a reducing gas atmosphere such as that described above, the surfaces of copper and copper alloy are not oxidized. As the non-oxidizing conditions in the present invention,
In the final annealing treatment in which oxidation of the material surface or other reaction with the atmosphere is prevented or slightly suppressed, for example, in the case of a combustion furnace for petroleum fuel such as butane, the concentration of oxygen in the atmosphere is adjusted to 0.1 by adjusting the air-fuel ratio. %, The degree of oxidation of copper and copper alloy is slight, which is an acceptable condition. With an oxide film of this degree, it can be removed by light pickling for several seconds using a mixed acid of pickling 10% sulfuric acid + 1% hydrogen peroxide or the like, so that the material surface is not mechanically polished with a buff or the like. A clean copper or copper alloy surface is obtained.

However, in the present invention, the conditions for the subsequent finish rolling are not limited at all.

After performing the above treatment, as a tin alloy used in the plating step, an alloy with lead, so-called solder plating can be exemplified as a typical one, but in addition, bismuth, antimony and the like can be reflowed at a low melting point. Tin alloy films can also be used effectively.

 Hereinafter, the present invention will be described specifically with reference to examples.

In the present invention, the final annealing is performed in a non-oxidizing atmosphere, and since the heat treatment step can be completed without causing a streak due to mechanical polishing on the material, the surface of the tin-plated material has a uniform glossy surface over the entire surface, No poor wetting is observed, and a uniform plating film having excellent solderability is obtained.

On the other hand, when the final annealing is performed in an oxidizing atmosphere, a non-uniform oxide film is formed. Therefore, surface removal by a buff is indispensable to remove the film, and therefore, the surface of the tin-plated material is The entire surface exhibited poor wetting, and solder repelling was partially observed.

Example Cold-rolled 0.3 mm-thick phosphor bronze consisting of 0.8 wt% tin, 0.1 wt% phosphorus, and the balance copper was 650 ° C x 2 hours in a non-oxidizing atmosphere.
Heat treatment of r was performed.

Next, the heat-treated one was subjected to cold rolling by 0.2 mm.
A thick phosphor bronze plate was made. The phosphor bronze plate was degreased and pickled under general conditions, and then subjected to a 1 μm thick matte tin plating using a sulfuric acid bath. Then, it was kept in an electric furnace at a temperature of 700 ° C., and after the tin-plated layer had been fused, it was taken out of the furnace and quenched.

The surface of the tin-plated material thus prepared had a uniform glossy surface, and no poor wetting was observed. Also, MI
When subjected to a soldering test under the conditions of L-STD-202E-208C, the entire surface immersed in the solder showed good wetting.

Comparative Example The same phosphor bronze plate having a thickness of 0.3 mm as used in the example was subjected to a heat treatment at 650 ° C. for 2 hours in an air atmosphere, and the surface was polished with a # 3000 Scotch buff to remove oxide scale. Thereafter, a phosphor bronze plate having a thickness of 0.2 mm was formed by cold rolling. The phosphor bronze plate thus prepared was electroplated with tin under the same conditions as described in the examples, and then subjected to a reflow treatment.

The surface of the tin-plated material thus produced exhibited poor wetting over the entire surface. Further, the sample was subjected to a soldering test under the same conditions as in Example 1, but solder repelling was partially observed.

Claims (1)

(57) [Claims] In a method for producing a reflow tin or tin alloy plating material using copper or a copper alloy as a base material, the atmosphere of the copper or copper alloy is made non-oxidizing so that the surface of the material is oxidized or is exposed to another atmosphere. The final annealing treatment is performed under the condition that the reaction is prevented or slightly suppressed, and the surface is not mechanically polished in the subsequent steps, and the copper or copper alloy base material obtained after rolling is electroplated and then reflowed A method for producing a reflow tin or tin alloy plated material, characterized by treating.