JPH06212487A - Partially plating device - Google Patents

Abstract

PURPOSE:To prevent the deposition of a plating soln. even if the soln. is wetted by applying the same or baser potential to the region except a specified region to be plated. CONSTITUTION:A plating soln. is ejected from an election port 5 to plate a specified region of a lead frame 1. An electrical conductive wire 7 such as a copper wire is tied on a top plate 2 to allow the wire 7 and frame 1 to have the same potential or the wire 7 to have a lower potential than the frame 1. A voltage follower circuit is formed between a plating power source and the wire 7, and a current value between an opening 6 for ejecting a liq. as an anode and the frame 1 as a cathode is kept constant even if the plating soln. is leaked or not.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a partial plating apparatus for semiconductor device lead frames and the like, and particularly to prevent plating on rail portions and outer lead portions other than predetermined plating regions.

[0002]

2. Description of the Related Art Conventionally, in the case of silver plating of a semiconductor element lead frame, only a predetermined lead tip portion is partially plated in order to connect the inner lead tip and the element terminal portion by wire bonding. As shown in FIG. 1, the partial plating apparatus used for this silver plating or the like supports the lead frame 1 and a press section 4 that presses the entire lead frame 1 from the back side against the pressure of the plating solution, While having a top plate portion 2 made of a non-conductive material that forms a mask for partial plating covering a portion of the lead frame 1 other than a predetermined area to be plated, the plating solution 5 is sprayed from the tip of the opening portion 6. It is common that silver plating is applied only to a predetermined area such as the tip of the inner lead of the lead frame 1. Figure 1
Then, since the vicinity of the opening is connected to (+) and the opening is made of a conductive material, the opening is substantially the anode (+), and the lead frame portion other than the predetermined area to be plated is masked, Only the portion to be plated, such as the inner lead portion, is exposed to the plating solution, and an electric current is passed from the opening portion serving as the anode (+) to the lead frame 1 serving as the cathode (-). However, for various reasons, the plating solution ejected from the openings also flows onto the surface of the top plate in FIG. 1, and the frame portion of the lead frame other than the predetermined area to be plated is also immersed in the flowing plating solution. , The flowing out plating solution may reach the plating solution drain hole. In this case, electricity flows from the anode (+) to the rail portion of the lead frame other than the opening and the predetermined area to be plated, and silver is deposited. Such deposition of silver plating on a region other than the predetermined region not only wastes silver, but also affects the amount of current flowing to the predetermined region, which may cause uneven plating on the predetermined region. . In recent years, even in the field of lead frames, finer, higher quality, diversification,
Mass production and cost reduction are becoming more and more demanded, and leakage of the plating solution to a portion other than a predetermined area due to the leakage of the plating solution has become a big problem.

[0003]

Conventionally, in the silver plating on the inner lead portion of the lead frame for a semiconductor element, as a measure for preventing the plating adhesion to the frame portion other than such a predetermined area, (1) the predetermined area Removal of plating adhered to other parts by peeling process (2) Eliminate the outflow of plating solution on the top plate part consisting of a non-conductor supporting the lead frame part and the mask for partial plating, (3) Masking the entire lead frame (4) When plating, shield with a fence to prevent the formation of an electrically closed circuit in the openings that will become the anode (+), which ejects the liquid, and the frame part other than the prescribed area to be plated. Have been considered.
Although (1) is the simplest method, it is difficult to use a Cu material and the chemicals for peeling are expensive. 42 material also damages the silver-plated surface, leading to defects such as black spots (2)
Is difficult to do completely, and if it is not done completely, leakage cannot be prevented for a long time, (3) takes a long time to adjust, (4) requires a major modification of the device, etc. there were. With regard to (2), it is not possible to completely prevent the leakage of the plating solution for various reasons. In fact, it is very difficult to completely prevent leakage for a long time. As described above, preventing the plating from adhering to the rail portion or the like other than the predetermined area can be prevented by the above (1)
According to the method (4), it is difficult to perform plating without being attached to the frame portion other than the predetermined area stably for a long period of time, and there has been a demand for a corresponding method instead of (1) to (4). . Under the circumstances as described above, the present invention, by a relatively simple method, stably stabilizes for a long period of time, prevents the adhesion of plating to areas other than the predetermined area, and has no uneven plating amount in the predetermined area. A partial plating method is provided.

[0004]

DISCLOSURE OF THE INVENTION The present invention is intended to provide a method capable of solving the above problems relatively easily and effectively, in which a conductor is arranged in advance so as to enclose an object to be plated. When the plating liquid flows out onto the top plate and the portion other than the predetermined region to be covered and the anode are electrically connected by the plating liquid, the object to be plated and the conductor are at the same potential, or By setting the electric potential of the conductor to be low with respect to the object to be plated, plating in a region other than a predetermined region to be plated is prevented. As shown in FIG. 1, an electrically conductive wire such as a copper wire is attached to the top plate portion and the wire and the lead frame are connected so as to have the same potential, or the wire portion is connected to the lead frame. By providing a circuit so as to have a low potential and connecting the circuit, it is possible to prevent the plating solution from adhering to the rail portion or the like other than the predetermined area of the lead frame to be plated by the plating solution that has flowed out.

This prevents the adhesion of plating in areas other than the predetermined area. However, when the conductor and the lead frame are directly connected so as to have the same potential, the current from the anode (+) is the same as the current to the lead frame section. The current to the top plate portion is separated, and the current value to the predetermined area of the lead frame to be plated is reduced. In order to prevent this, in addition to the above configuration, the plating power source and the wire power source are different power sources. That is, a voltage follower circuit was inserted between the plating power source and the wire as shown in FIG. 1 to make the current value between the anode (+) and the lead frame (−) constant. As the voltage follower circuit, a circuit having an input resistance 100 times or more the bath resistance between the anode and the lead and an output resistance of 1 ohm or less is suitable. Needless to say, the above means is not limited to the partial plating apparatus as shown in FIG.

[0006]

As described above, in the partial plating such as silver plating of the lead frame for a semiconductor device of the present invention, the following effects are exhibited. (1) A circuit in which an object to be plated is surrounded by an electric conductor such as a copper wire, and the electric conductor has the same potential as the object to be plated or the electric conductor has a lower potential than the object to be plated. With this structure, even if the plating liquid leaks and the portion other than the area to be plated is immersed in the plating liquid and the plating liquid electrically connects the object to be plated and the anode, the conductor is covered. Since the same potential or base potential is applied to the plated object, it is possible to electrically prevent the plated object from being attached to a portion other than the predetermined region to be plated. (2) By inserting a voltage follower circuit between the plating power source and the wire, the current value between the object to be plated such as the lead frame etc., which becomes the cathode (-) and the opening (where the anode (+) is ejected) It can be kept constant regardless of whether or not the plating solution leaks.

[0008]

EXAMPLE An example relates to silver plating on the tip of the inner lead for wire bonding the element terminal of the lead frame for a semiconductor element and the tip of the inner lead of the lead frame, which will be described with reference to FIG. FIG. 1 shows an apparatus for performing a partial plating of silver only on a predetermined area of a lead frame 1, 1 is a lead frame that is an object to be plated, 2 is a lead frame portion, and constitutes a mask for partial plating. Top plate parts 3 and 4 are press parts for suppressing the lead frame against the plating liquid pressure, 3 is a press rubber made of an elastic material such as silicon rubber, and 4 is a press block for applying pressure. is there. 5
Is injected into the lead frame 1 which is the object to be plated by the plating solution through the opening portion 6 and is discharged. The opening portion 6 is a jet of the plating solution and is an anode portion (+) of the plating, and the top plate portion 2 is mounted with a lead frame 1 serving as a cathode of the plating, and only a predetermined area of the lead frame 1 is plated. It is for exposing to the liquid and covering the entire plating liquid. As shown in FIG. 1, the copper wire portion 7 is attached to the entire circumference of the side surface of the top plate 2 so that the copper wire portion 7 and the lead frame portion 1 are connected so as to have the same potential, and a voltage follower circuit is formed. However, the amount of current to the predetermined area of the lead frame to be plated is constant (about 1%).
The following fluctuation). As a result, the plating adhesion to the frame and the like other than the predetermined region of the lead frame was eliminated, and the plating adhesion amount to the predetermined region was stabilized, and the plating could be performed for a long time.

[0009]

With the above-described structure, silver is prevented from being deposited on unnecessary portions other than the predetermined area to be plated on the object to be plated, and the current amount to the predetermined area to be plated is increased. This makes it possible to provide a device that can perform stable partial plating in terms of quality and productivity.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a conventional partial plating apparatus.

[Explanation of symbols]

 1 Lead frame 2 Top plate 3 Plate rubber 4 Press part 5 Plating liquid 6 Opening part (plating liquid injection part) 7 Copper wire 8 Constant current source for plating 9 Voltage follower circuit 10 Power supply for voltage follower circuit

Claims (3)

[Claims] 1. A circuit in which an object to be plated is surrounded by a conductor such as a wire, and the conductor has the same potential as the object to be plated or the conductor has a lower potential than the object to be plated. Partial plating device characterized by having 2. The jig for partial plating according to claim 1, wherein a voltage follower circuit is provided between a plating power source and a conductor such as a wire, and the anode (+) and the object to be plated (-) are placed.
Partial plating device characterized in that the current between the electrodes is constant regardless of whether or not the plating solution leaks. 3. The apparatus for partial plating according to claim 1 or 2, which supports a press section for pressing the entire lead frame as the object to be plated from the back side against the pressure of the plating solution and a lead frame section. However, it is a jig for partial plating for a lead frame, which has a top plate portion made of a non-conductive material that constitutes a mask for partial plating, and is plated through the mask for partial plating, such as a wire. Device for partial plating of lead frame for semiconductor element, characterized in that the electric conductor is attached to the entire circumference of the side surface of the top plate portion.