JPS5887275A - Stripping method for sn layer on cu and cu alloy - Google Patents

Abstract

PURPOSE:To easily strip and remove Sn layers in a short time by immersing Cu and a Cu alloy each plated with Sn in dil. sulfuric acid or dil. nitric acid contg. some Cu ions and having a restricted Cl ion content. CONSTITUTION:Cu and Cu alloy scraps plated with Sn, etc. are immersed in 2-40% aqueous soln. of sulfuric acid and/or nitric acid contg. 0.1-10% Cu ions and having a Cl ion content restricted to <=50ppm to dissolve and remove only the Sn layers in a short time and to recover the Cu and Cu alloy base metal while almost preventing the carrosion. Since Cu is nobler than Sn in potential, Sn is dissolved by a reaction represented by Cu<++>+Sn Sn<++>+Cu, and after removing the Sn layers, Cu is hardly carroded by the dil. acid soln. contg. no oxidizing agent.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the exfoliation of Sn layers on Cu and Cu alloys.

Conventional? ), 8N plating materials based on Cu and Cu alloys are widely used in the field of electronic equipment as terminals or connectors. These 8N plating materials are usually plated in a pool shape to save labor and reduce costs, and then the connectors and terminals are punched out. However, since the scrap generated by this punching process contains 0.5 to 3 wt$g of 8N, it is difficult to handle it as general Cu scrap, and its uses are limited. In order to effectively utilize such scraps as resources, it is necessary to remove the middle layer of 811 metals.

Up to now, methods for stripping 8N plating on Cu and Cu alloys have been proposed, such as hot concentrated ')/ml, immersion in concentrated hydrochloric acid, or electrolysis in sodium hydroxide. ing. However, the method of using a high-temperature strong ammonium solution has serious problems in terms of equipment maintenance and hygiene, and is also extremely poor in workability.

In addition, in any conventional method, if immersion is continued until after the Sn plating layer has been dissolved and removed, the Cu and Cu alloy base materials will be eroded, resulting in poor recovery efficiency as scrap.

In addition, since materials with different thicknesses of Sn plating on general KCu and CO alloys are mixed, when these scraps are immersed in the above stripping mt, the processing time is controlled by the scrap with the thickest plating layer. Inevitably, scraps with thin plating layers will undergo erosive bath decomposition of the Cu and Cu alloy substrate during processing time. Therefore, the properties required of the stripping solution are such that it only dissolves the Sn plating layer and does not corrode the Cu and Cu alloy base materials even if they are exposed during the process.

The present invention is similar to the prior art described above, and it is possible to dissolve and remove only the Sn plating layer in a short time using a dilute acid solution, and it is possible to dissolve and remove only the Sn plating layer in a short time using a dilute acid solution. provides a method for stripping 5nN1 on CU and Cu alloys that is almost non-erosive.

The 5n7i1 peeling method on Cu and Cu alloys according to the present invention is characterized by the use of sulfuric acid containing 0.1 to 10% of Cu ions and suppressing Ct ions to 50 ppm or less;
2 to 40 g of nitric acid units or both 6 water 11i [
The method involves immersing Sn-plated CU and Cu alloys.

A method for peeling off Sn layers on Cu and Cu alloys according to the present invention will be described in detail below.

In the method for peeling off Sn layers on Cu and Cu alloys according to the present invention (hereinafter sometimes referred to as the method according to the present invention),
Considering Sn that is peeled off or removed by dissolution,
Sn is an amphoteric metal and is stable in a neutral range, but is said to be soluble in acids and alkalis. However, this dissolution rate in a dilute acid bath is extremely slow at 1 to 10μ7/24 hours.

In the method according to the present invention, Cu and Cu
The inventors of the present invention have diligently studied that a certain amount of dissolution driving force is required in order to peel off or dissolve the Sn layer on the alloy in a short time, for example, 1 to 5 minutes. This is what I found as a result.

The basic principle of this dissolution driving force is to utilize the difference in electrochemical order between sn and Cu.

That is, Cu and 8n (Dllllllll electric electrode potential u=C
u +2e...(1) go=0.3378
n=Sn+2m-<2)Eo=-[1,137.

Therefore, when sn is immersed in an acidic solution containing Cu ions, Sn preferentially elutes and Cu precipitates on the surface.
−es +Cu ”° (31.

From this, it can be seen that 900 deposited on the Sn surface has a smaller hydrogen overvoltage of /J· compared to 8n, so it forms an effective cathode point and further promotes the dissolution of an, which is an anode reaction.

This reaction progresses in the area where the Sn plating layer remains, and the P
M6 The part where the base material of Cu and Cu alloy is partially exposed is S.
Since it has a higher potential than n, its dissolution is completely suppressed.

In this way, the Sn plating layer is t
i! When dissolved and removed from the surface, the base material of Cu and Cu alloy i/j will be eroded by the dilute acid solution, but 4III! Since the corrosion rate of Cu and Cu alloys in acid #i solution is minute, even if they are immersed for the required time, it will not result in a planer.

Further, the present inventors have found that in order for the reaction of the above formula (3) to proceed smoothly, it is necessary to suppress Ct ions in the acidic water bath solution to 50 ppm or less. The acids used are Htomi 804, HNOs Hireka 181 [ka,
Alternatively, a mixture may be used.

In the method related to this patent, II! ! 1 degree to 2
~10%, but if it is less than 2%, the dissolution rate is very low, and even if it exceeds 40%, the dissolution rate does not increase much, and on the contrary, the generation of harmful gas becomes significant, and This is because the workability is poor and the process is undesirable.

In addition, the action and/or effect of Cu ions in the acid solution is as described in the above device, but the effect is small if the Cu ion is less than 0.1%, and there is no effect even if it is present for more than 10 ts. It is almost saturated.

Therefore, it is preferable that the Cu ion content be 1 to 10%.

Furthermore, Ct ions have a significant effect on the dissolution rate of Sn, and if it exceeds 50 ppm, uniform dissolution is suppressed and at the same time the dissolution rate is significantly reduced, making it difficult to peel off the Sn plating layer industrially. To do this, be sure to use 50 ppm.
It is necessary to suppress it to the following.

Examples of the method for peeling off Sn layers on Cu and Cu alloys according to the present invention will be described together with comparative examples.

EXAMPLE This is an example of the peeling state of the AN plating layer on Cu and Cu alloy and the corrosion state of the Cu and Cu alloy base material between the solution used in the method according to the present invention and each AF6 solution for comparison.

(1) Metal material to be treated: A round material group made of a Cu alloy (01167-70%, residual Zn) as a base material and plated with 1-2 μm of Sn.

(21Sn plating peeling test The test method for the peeling state of the Sn plating and the corrosion state of the Cu alloy base material is as follows.

■ Peeling status of Sn Analyze the amount of Sn remaining in the test material after being eroded by each solution.
I rated the 61st floor.

○・・・・・・Sn peeling $ 90% or more △・・・
・・・・・・ ＃50− or more×・・・・・・・・・
, 50- or less Note that those marked with ◯ and above are targets of the method according to the present invention.

Erosion state of the Cu alloy base material The corrosion of the Cu alloy base material was observed with the naked eye and evaluated on a four-level scale.

○・・・・・・No corrosion of Cu alloy base material @...
・・・・・・ is slightly eroded Δ・・・・・・
・・・ is eroded×・・・・・・・・・
is severely eroded.

These results are shown in Table 1.

As detailed above, Cu and C related to the present invention
Since the peeling method for the BN layer on the U alloy has the above-mentioned advantages, most of the 8N plating layer on the Cu and Cu alloys can be peeled off or dissolved and removed in a very short time. Moreover, the corrosion of the Cu and Cu alloy substrates is extremely small, which is an excellent effect.

Claims (1)

[Claims] Contains 0.1-10% of Cu ions and 50% of Ct ions.
A method for peeling off an 8N layer on Cu and Cu alloys, which comprises immersing 8N plated Cu and CU gold alloys in a 2 to 4096 aqueous solution of sulfuric acid, nitric acid, or both, suppressed to ppm or less.