Method for recovering solder containing Sn

Abstract

To provide a method for recovering Sn-containing solder which can recover inexpensively and efficiently Sn-containing solder from a substrate having a component soldered by the Sn-containing solder.SOLUTION: From a substrate having a component soldered by Sn-containing solder, the component is removed; after that, the substrate is immersed in molten metal (at 190-320°C) of a Pb-Sn alloy with the ratio between the contents of Pb and Sn (mass%) of Pb: Sn=10-90: 90-10; so that the Sn-containing solder is recovered in the molten metal of Pb-Sn alloy.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for recovering solder containing Sn, and more particularly to a method for recovering solder containing Sn from a substrate such as an electronic substrate to which components such as electronic parts are soldered with solder containing Sn. [Background technology]

[0002] Traditionally, in electronic boards where electronic components are mounted, the electronic components are fixed to the board using solder. In recent years, there has been a shift from conventional lead-containing solder (such as eutectic solder made from Pb-Sn alloys) to lead-free solder (which does not contain lead) in order to reduce the burden on the human body and the environment.

[0003] Such lead-free solders include Sn-Ag-Cu, Sn-Zn-Bi, Sn-Cu, Sn-Ag-In-Bi, and Sn-Zn-Al systems, and the Sn content in electronic substrates is on the rise.

[0004] Therefore, in order to efficiently recover various metals such as precious metals from waste electronic substrates, it is desirable to recover solder containing Sn in advance before processing the waste electronic substrates in a refining furnace such as a copper refining furnace.As a method for recovering solder from waste electronic substrates, a method of chemically dissolving the solder from the waste electronic substrates using a solvent (see, for example, Patent Document 1) is known. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-508658 A (paragraph number 0032) Summary of the Invention [Problem to be solved by the invention]

[0006] However, when recovering solder using the method of Patent Document 1, it takes a long time to chemically dissolve the solder using a solvent, and recovery costs increase due to waste liquid treatment, making it impossible to recover the solder efficiently. Furthermore, during leaching with the solvent, oxides are formed on the surface of the Sn phase of the solder, reducing the leaching rate and the recovery rate of the solder.

[0007] Therefore, in view of the above-mentioned conventional problems, the present invention aims to provide a method for recovering solder containing Sn, which can recover solder containing Sn inexpensively and efficiently from a substrate to which components are soldered with solder containing Sn. [Means for solving the problem]

[0008] As a result of intensive research to solve the above problems, the inventors have found that solder containing Sn can be recovered inexpensively and efficiently from a substrate to which components have been soldered with solder containing Sn by removing the components from the substrate and then immersing the substrate in molten Pb-Sn alloy, thereby recovering the solder containing Sn in the molten Pb-Sn alloy, and have completed the present invention.

[0009] That is, the method for recovering solder containing Sn according to the present invention is characterized in that after removing components from a substrate to which the components have been soldered with solder containing Sn, the substrate is immersed in a molten Pb-Sn alloy, thereby recovering the solder containing Sn in the molten Pb-Sn alloy.

[0010] In this method for recovering solder containing Sn, the ratio of the Pb and Sn contents (mass%) in the Pb-Sn alloy is preferably Pb:Sn=10-90:90-10, and the temperature of the molten Pb-Sn alloy is preferably 190-320°C. [Effects of the Invention]

[0011] According to the present invention, solder containing Sn can be recovered inexpensively and efficiently from a substrate on which components have been soldered with the solder containing Sn. DETAILED DESCRIPTION OF THE INVENTION

[0012] In an embodiment of the method for recovering Sn-containing solder according to the present invention, after components soldered with Sn-containing solder are removed from a substrate, the substrate is immersed in a molten Pb-Sn alloy to recover the Sn-containing solder in the molten Pb-Sn alloy. By immersing the substrate in the molten Pb-Sn alloy in this manner, the Sn in the substrate is absorbed into the molten Pb-Sn alloy in a short time, thereby dramatically improving the recovery rate of the Sn-containing solder.

[0013] In this method for recovering Sn-containing solder, the ratio of Pb to Sn (mass%) in the Pb-Sn alloy is preferably Pb:Sn = 10-90:90-10, more preferably Pb:Sn = 30-70:70-30, and most preferably Pb:Sn = 40-60:60-40. The temperature of the molten Pb-Sn alloy is preferably 190-320°C, more preferably 200-300°C, and most preferably 230-270°C. Because such low-temperature molten metal can be used, a metal pump can also be used. While it is theoretically possible to use molten Pb (molten metal containing 100% Pb by mass) instead of molten Pb-Sn alloy, using molten Pb is not recommended when the substrate is a glass epoxy substrate because a thermal decomposition reaction occurs at the melting point of Pb and may result in combustion in the air.

[0014] Immersion in a molten Pb-Sn alloy can be achieved by repeatedly immersing a basket (such as a stainless steel mesh) containing a substrate in the molten Pb-Sn alloy, which is heated to 190-320°C in a graphite crucible, for 10-60 minutes, preferably 15-30 minutes. The molten Pb-Sn alloy after this immersion can be used as a raw material for lead refining. Alternatively, the molten Pb-Sn alloy after this immersion can be circulated and used again for immersion to increase the Sn content, after which the Sn can be recovered and purified.

[0015] In the method for recovering solder containing Sn, after removing components from the substrate, the substrate is preferably heated and vibrated before being immersed in molten Pb-Sn alloy. The heating temperature is preferably 250 to 300°C, and the vibration is preferably 30 to 100 Hz. Furthermore, when the soldered surface of the substrate extends horizontally and faces downward vertically, the tilt angle of the substrate is 0°, and when the substrate extends vertically, the tilt angle of the substrate is 90°. When the substrate is heated and vibrated, the substrate is preferably positioned so that the angle is 0 to 90°. [Example]

[0016] Hereinafter, examples of the method for recovering solder containing Sn according to the present invention will be described in detail.

[0017] [Example 1] First, a glass epoxy substrate with electronic components soldered using solder containing Sn was prepared, and then the electronic components were removed from the substrate. The weight of the glass epoxy substrate from which the electronic components had been removed was measured, and composition analysis by X-ray fluorescence analysis revealed that the weight was 404.03 g and contained 86 g (21 mass%) of Sn and 81 g (20 mass%) of Cu.

[0018] Furthermore, a Pb-Sn alloy was prepared, its weight was measured, and its composition was analyzed by X-ray fluorescence analysis. The weight was 2630 g and it contained 1311 g (49.84 mass%) of Sn and 1282 g (48.745 mass%) of Pb.

[0019] This Pb-Sn alloy was placed in a graphite crucible and heated to 250°C. The stainless steel mesh basket containing the glass epoxy substrate from which the electronic components had been removed was immersed in the resulting molten metal for 20 minutes.

[0020] The weight of this Pb—Sn alloy after immersion was measured and its composition was analyzed by fluorescent X-ray analysis. The weight was 2530 g and it contained 1397 g (55.20 mass%) of Sn and 6 g (0.25 mass%) of Cu.

[0021] From this result, it can be seen that the Sn content in the Pb—Sn alloy after immersion increases by 5.36 mass % (= 55.20 mass % − 49.84 mass %).

[0022] [Example 2] First, a glass epoxy substrate with electronic components soldered using solder containing Sn was prepared, and then the electronic components were removed from the substrate. The weight of the glass epoxy substrate from which the electronic components had been removed was measured, and composition analysis by X-ray fluorescence analysis revealed that the weight was 406.72 g and contained 43 g (11 mass%) of Sn and 81 g (20 mass%) of Cu.

[0023] Furthermore, a Pb-Sn alloy was prepared, its weight was measured, and its composition was analyzed by X-ray fluorescence analysis. The weight was 2630 g and it contained 1379 g (52.43 mass%) of Sn and 1165 g (44.29 mass%) of Pb.

[0024] This Pb-Sn alloy was placed in a graphite crucible and heated to 250°C. The molten metal obtained was immersed for 20 minutes in the basket containing the glass epoxy substrate from which the electronic components had been removed.

[0025] The weight of this Pb-Sn alloy after immersion was measured and its composition was analyzed by fluorescent X-ray analysis. The weight was 2530 g and it contained 1422 g (56.21 mass%) of Sn and 5 g (0.21 mass%) of Cu.

[0026] From this result, it can be seen that the Sn content in the Pb—Sn alloy after immersion increases by 3.78 mass % (= 56.21 mass % − 52.43 mass %).

[0027] [Example 3] The same Pb-Sn alloy as in Example 1 was placed in a graphite crucible and heated to 250°C. A basket containing a glass epoxy substrate from which the same electronic components as in Example 1 had been removed was immersed in the molten metal for 1 minute, then for 3 minutes, and then for 5 minutes after leaching. The number of solder particles removed from the substrate (the number of holes in the substrate) was counted, and the solder recovery rate (%) (= (number of solder particles removed from the substrate) x 100 / (number of solder particles on the substrate before leaching) was calculated. After 1 minute of immersion, For the board immersed in 1 minute, the number of solder pieces on the board before leaching was 90, the number of solder pieces that had come off the board was 78, and the solder recovery rate was 86.7%.For the board immersed in 3 minutes, the number of solder pieces on the board before leaching was 101, the number of solder pieces that had come off the board was 81, and the solder recovery rate was 80.2%.For the board immersed in 5 minutes, the number of solder pieces on the board before leaching was 180, the number of solder pieces that had come off the board was 157, and the solder recovery rate was 87.2%.

[0028] These results show that even with a very short leaching time (1 to 5 minutes), solder can be recovered with a very high recovery rate (80% or more). [Industrial Applicability]

[0029] The method for recovering solder containing Sn according to the present invention can be used as a method for recovering solder containing Sn from a substrate such as an electronic substrate to which components such as electronic parts are soldered with solder containing Sn.

Claims

1. A method for recovering solder containing Sn, comprising removing components from a substrate to which the components have been soldered with solder containing Sn, and then immersing the substrate in molten Pb-Sn alloy, thereby recovering the solder containing Sn in the molten Pb-Sn alloy.

2. 2. The method for recovering solder containing Sn according to claim 1, wherein the ratio of the Pb and Sn contents (mass%) in the Pb-Sn alloy is Pb:Sn=10-90:90-10.

3. 3. The method for recovering solder containing Sn according to claim 1, wherein the temperature of the molten Pb-Sn alloy is 190 to 320°C.