JP3978673B2 - Solder plating method and solder plating equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solder plating technique, and more particularly to a solder plating method and a solder plating apparatus capable of separating an intermetallic compound produced in molten solder in a bath.
[0002]
[Prior art]
A solder dipping method is known in which when a lead terminal of a semiconductor device is coated with solder and a solder plating film is formed on the lead terminal, the lead terminal is dipped into the molten solder for a short time as a material to be plated. It is. As the solder to be melted in the bath, tin silver (SnAg) eutectic solder containing 96.5% by weight of tin and 3.5% by weight of silver for improving solder wettability is used. The eutectic solder may be tin copper solder in which copper (Cu) and zinc (Zn) are mixed or copper is mixed with tin instead of silver. The melting point of the solder of 96.5% by weight of tin and 3.5% by weight of silver is 221 ° C., and the solder in the bath is heated to a temperature higher by 30 to 50 ° C. than the melting point of the solder. The lead terminal is immersed in solder that melts in the bath, and solder plating of the lead terminal is performed.
[0003]
For example, as shown in FIG. 3, a conventional solder plating apparatus includes a metal bathtub (1) for storing molten solder (2) and a bathtub (1) disposed in the center of the bathtub (1). And a heating device (3) for heating. After energizing the heating device (3) provided with the heater of the electrical heating resistance element and heating the solder (2) in the bathtub (1) to a molten state, the resin sealing body of the electronic component (20) ( The metal lead terminal (22) derived from 21) is immersed in the molten solder (2) to form a solder plating film on the lead terminal (22). After the solder plating film is formed on the lead terminal (22), the lead terminal (22) is familiar to the solder when the lead terminal (22) is mounted on the board, and the lead terminal (22) is securely attached to the board. Can be attached.
[0004]
[Problems to be solved by the invention]
By the way, when solder plating is performed by repeatedly immersing a large number of lead terminals (22) in the solder (2) in the bathtub (1), the solder (2 that tin or silver contained in the lead terminals (22) melts) ) And the metal composition ratio in the solder (2) changes. For example, when silver elutes from the lead terminal (22) into the solder (2) and the silver capacity increases, the melting point of the solder (2) increases. For example, when the silver capacity increases from 3.5 wt% to 5 wt% and 10 wt%, the melting temperature of the solder (2) increases from 221 ° C. to 250 ° C. and 295 ° C., respectively. When the melting point of the solder (2) increases, a silver tin intermetallic compound is formed in the melting solder (2), the viscosity of the solder (2) increases, and the lead terminal (22) solderability deteriorates. Will occur.
Then, an object of this invention is to provide the solder plating method and solder plating apparatus which can reduce the density | concentration of the intermetallic compound contained in the center part of the solder which is a molten state within a bathtub.
[0005]
[Means for Solving the Problems]
The solder plating method according to the present invention includes a step of heating the solder (2) accommodated in the bathtub (1) to a molten state, and a plated material (22) in the solder (2) accommodated in the bathtub (1). A step of performing solder plating on the plated material (22), and a step of rotating the bathtub (1) together with the solder (2) after immersing the plated material (22) in the solder (2) The step of moving the intermetallic compound (13) formed in the bathtub (1) to the bottom of the outer peripheral side in the bathtub (1) by the rotation of the bathtub (1) and the amount of the intermetallic compound (13) are reduced. Immersing the plated material (22) in the central portion of the molten solder (2) accommodated in the bathtub (1). When the intermetallic compound (13) is formed in the molten solder (2) during the solder plating operation, if the solder (2) in the bathtub (1) is rotated by the rotating device (4), the specific gravity is large. The intermetallic compound (13) moves to the bottom on the outer peripheral side in the bathtub (1) by the centrifugal force in the molten solder (2) and precipitates. Therefore, since the central portion of the molten solder (2) accommodated in the bathtub (1) in which the amount of the intermetallic compound (13) is reduced is maintained at a predetermined melting temperature, the center of the solder (2) A good solder film can be formed on the plated material (22) by immersing the plated material (22) in the portion.
A solder plating apparatus according to the present invention includes a bathtub (1) for containing solder (2) in which a plated material (22) is immersed, and a heating apparatus (3) for heating the solder (2) in the bathtub (1) to a molten state. ), A support device (5) that rotatably supports the bathtub (1) including the heating device (3), and a rotation device (4) that rotates the bathtub (1) on the support device (5), The intermetallic compound formed in the bathtub (1) is moved to the bottom on the outer peripheral side in the bathtub (1) by the rotation of the bathtub (1).
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a solder plating method and a solder plating apparatus according to the present invention will be described with reference to FIGS. 1 and 2, the same parts as those shown in FIG.
[0007]
As shown in the figure, the solder plating apparatus according to the present invention is disposed, for example, in a bathtub (1) for containing solder (2) made of lead-free (lead-free) tin-silver, and a central portion in the bathtub (1). A heating device (3), a supporting device (5) for rotatably supporting the bathtub (1), a rotating device (4) for rotating the bathtub (1), and a plating disposed above the bathtub (1). And a solder supply device (8) for replenishing the bathtub (1) with the solder (2) reduced by the above. The bathtub (1) is formed in a circular shape from a metal such as stainless steel, which has a melting point sufficiently higher than that of the solder and hardly dissolves in the solder in which the metal component melts. The heating device (3) for heating the solder (2) in the bathtub (1) includes a heater arranged on the center side of the bathtub (1). In the embodiment shown in FIG. 1, the rotating device (4) includes a rotating shaft (7) connected to the bottom surface of the bathtub (1) and a rotating shaft (7) via a power transmission device such as a gear device or a pulley. And a driving device (6) such as a motor which is operatively connected to the rotating shaft and rotates the rotating shaft. The support device (5) has a thrust bearing that is disposed at the bottom of the bathtub (1) and rotatably supports the bathtub (1). A harness (9) for supplying electric power to the heating device (3) is disposed in the rotating shaft (7). The harness (9) is connected to a power source through a connector (not shown) that can supply power even when the bathtub (1) is rotated. The solder (2) is a solder containing silver, which is at least part of a metal constituting the external lead (22), and tin.
[0008]
When performing plating, after supplying solder into the bathtub (1), the heating device (3) is operated to heat the bathtub (1) to a predetermined temperature and melt the solder in the bathtub (1). . Since the heating device (3) is disposed on the center side of the bathtub (1), the temperature of the solder (2) accommodated on the center side of the bathtub (1) is the solder accommodated on the outer periphery side of the bathtub (1). It becomes higher than the temperature of (2). In this state, the lead terminal (22) of the semiconductor device is immersed in the solder (2) to be melted as the plated material (22), and the lead terminal (22) is solder plated. When the plating is repeated, the copper and silver constituting the lead terminal (22) melt into the solder (2), increasing the composition ratio of copper and silver in the solder (2). ) Forms an intermetallic compound (13) such as silver tin. In this case, the temperature of the solder (2) close to the heating device (3) arranged at the center of the bathtub (1) is higher than the temperature of the solder (2) arranged outside the bathtub (1). In addition, the intermetallic compound (13) is easily formed on the solder (2) at the center.
[0009]
Therefore, after performing solder plating a predetermined number of times or while performing solder plating, the rotating shaft (7) is rotated by the rotating device (4) and the bathtub (1) is rotated. However, the intermetallic compound (13) having a large specific gravity tends to move to the bottom of the outer peripheral side in the bathtub (1) due to centrifugal force and precipitate. In this case, the number of rotations of the bathtub (1) depends on the size of the bathtub (1), but is 10 to 120 rpm, preferably 30 to 80 rpm. Therefore, since the concentration of the intermetallic compound (13) in the solder (2) in the central part of the bathtub (1) is reduced, the composition change of the solder (2) in the central part of the bathtub (1) and accompanying this An increase in viscosity can be prevented and good solderability can be maintained.
[0010]
In the embodiment of the present invention, a removing means (10) for removing the intermetallic compound (13) in the solder (2) is provided. In the embodiment shown in FIG. 1, the removing means (10) is connected to the lower part of the bathtub (1), for example, the outlet (11) provided in the bottom wall (5), and the outlet (11). A drain pipe (15) and an on-off valve (12) attached to a part of the drain pipe (15) and controlling the discharge port (11) to be openable and closable are provided. When the bathtub (1) is rotated and the intermetallic compound (13) is allowed to settle on the bottom of the outer periphery of the bathtub (1), when the on-off valve (12) is opened, the discharge port (11), on-off valve ( The solder (2) containing a large amount of the intermetallic compound (13) can be discharged out of the bathtub (1) through 12) and the drain pipe (15).
[0011]
FIG. 2 shows another embodiment of the removing means (10) in which a substantially cylindrical collector (14) for collecting the intermetallic compound (13) is arranged on the outer peripheral side of the bathtub (1). The collector (14) is provided at the lower end of the cylindrical portion, and a cylindrical portion that is detachable along the entire circumference of the inner wall (1a) of the bathtub (1) and is in close contact with the side surface of the bathtub (1). It has a substantially L-shaped cross section consisting of an inner flange. Although not shown, a circulation path for circulating cooling water is formed in the collector (14), and the solder (2) on the outer peripheral side in the bathtub (1) is lower than the temperature of the solder (2) on the center side. To promote adhesion of the intermetallic compound to the collector (14). When the bathtub (1) is rotated, the intermetallic compound (13) moves to the outside of the bathtub (1) in the molten solder (2) and adheres to the inner surface of the collector (14). 13) can be collected. Thereafter, the rotating bathtub (1) is stopped at a predetermined position, and when the collector (14) is taken out from the bathtub (1), the intermetallic compound (13) adhering to the collector (14) is removed from the solder (2). be able to. In addition, the bathtub (1) can be cleaned after the on-off valve (12) is released and the solder (2) is discharged from the drain pipe (15) to the outside after use for a predetermined time.
[0012]
The embodiment of the present invention can be modified. The product for solder plating may be a metal product other than the semiconductor device.
[0013]
【The invention's effect】
As described above, in the present invention, the concentration of the intermetallic compound contained in the solder is reduced at the center of the bathtub, and the intermetallic compound can be removed from the solder in the bathtub as necessary. It can be performed continuously, and productivity can be improved and uniform and good solder plating can be performed. Further, it is possible to regenerate the solder, and resource saving can be achieved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a solder plating apparatus showing a first embodiment of the present invention. FIG. 2 is a cross-sectional view of a solder plating apparatus showing a second embodiment of the present invention. Sectional view of the device [Explanation of symbols]
(1) ・ ・ Bathtub, (2) ・ ・ Solder, (3) ・ ・ Heating device, (4) ・ ・ Rotating device, (5) ・ Support device, (10) ・ ・ Removing means, (11) ・・ Exhaust port, (14) ・ ・ Collector, (20) ・ ・ Electronic parts, (22) ・ ・ Lead terminal (plated metal),

Claims (5)

A solder plating method comprising: heating the solder accommodated in the bath to a molten state; and immersing a plating material in the solder accommodated in the bath and performing solder plating on the plating material. In
A step of rotating the bathtub together with the solder after immersing the plated material in the solder;
Moving the intermetallic compound formed in the bathtub by rotation of the bathtub to the bottom on the outer peripheral side in the bathtub;
Immersing the plated material in a central portion of the molten solder accommodated in the bath in which the amount of the intermetallic compound is reduced. A removal step of removing the solder on the outer peripheral side in a molten state with a high content of the intermetallic compound from the bath,
The removing step includes a step of discharging the solder from an openable and closable discharge port provided in a lower portion of the bathtub, or arranging a collector along the inner wall of the bathtub before rotating the bathtub, and by rotating the bathtub. 2. The method according to claim 1, further comprising: collecting the intermetallic compound moving outward in the molten solder by the collector, and then taking out the collector to which the intermetallic compound is attached to the outside of the bath. Solder plating method. In a solder plating apparatus provided with a bathtub for containing solder for dipping the plated material, and a heating device for heating the solder in the bathtub to a molten state,
A support device that rotatably supports the bathtub including the heating device;
A rotating device for rotating the bathtub on the support device,
A solder plating apparatus, wherein the intermetallic compound formed in the bathtub is moved to the bottom on the outer peripheral side in the bathtub by the rotation of the bathtub. A removing means for removing the intermetallic compound in the solder;
The removing means is disposed in a detachable manner along an openable / closable discharge port provided in a lower portion of the bathtub or an inner wall of the bathtub, and moves outward in the molten solder by the rotation of the bathtub. The solder plating apparatus according to claim 3, further comprising a collector that collects intermetallic compounds.   5. The solder plating apparatus according to claim 3, wherein the solder is a solder containing at least a part of the same metal as the metal constituting the plated material and tin.

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