JPH05259363A - Treatment of copper-made lead frame - Google Patents

Abstract

PURPOSE:To securely adhere a lead frame to a synthetic resin which is the base material of a molding by forcedly oxidizing a copper-made frame and then by roughening the surface through plasma cleaning. CONSTITUTION:A lead frame 20 is forcedly oxidized in a heating furnace and roughened are made fragile in the surface. Next, the lead frame 20 is transported into a plasma cleaning casing 1. The interior of the casing 1 is depressurized and supplied with Ar gas, and a high-frequency AC voltage is impressed on an electrode 3 to develop plasma. Inside the casing 1, a part of the Ar gas is ionized with the result that Ar gas molecules and ionized Ar<+> minus electrons make high-speed movement to cut and roughen the surface of the lead frame 20. Impurities deposited on the surface are filtered out and sucked by a vacuum pump. This process strengthens adhesion to the synthetic resin by roughening the surface of the lead frame 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating a copper lead frame, and more specifically, it can improve the adhesiveness with a synthetic resin, which is a material of a mold body, by roughening the surface of the copper lead frame. The present invention relates to a method for processing a copper lead frame.

[0002]

2. Description of the Related Art FIG. 10 is a sectional view of a conventional electronic component 50 known as QFP, SOP or the like. 51 in the figure
Is a lead, 52 is a semiconductor chip bonded to the land 53, 54 is an electrode of the semiconductor chip 52 and the lead 51.
, 55 is a semiconductor chip 52 or a wire 5.
4 is a mold body for protecting 4. The electronic component 50 is manufactured as follows. First, after bonding a semiconductor chip (generally referred to as a die or a pellet) 52 cut out from a wafer to a land 53 of a lead frame, an electrode of the semiconductor chip 52 and a lead frame lead 51 are connected by a wire 54. Then, a mold body 55 that protects the semiconductor chip 52 and the wires 54 is molded from a synthetic resin, and the leads 51 of the lead frame are punched out by a punch to complete the electronic component 50.

Conventionally, alloys such as 42 alloy have been generally used as the material of the lead frame, but in recent years, copper lead frames have been gradually popularized because they are inexpensive and have good electrical conductivity.

[0004]

However, since the copper lead frame has a smooth surface, it has a weak adhesion to the synthetic resin, which is the material of the mold body 55. For this reason, the joint surface between the lead 51 or the land 53 and the mold body 55 is easily peeled off to form a minute gap, and moisture in the air enters from this gap (see a broken line arrow), and the metal portion inside the mold body 55 is separated. There are problems such as being easily corroded and cracks in the mold body 55.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method of treating a copper lead frame capable of solving the above conventional problems.

[0006]

To this end, the present invention roughens the surface of a copper lead frame by forcibly oxidizing it and then plasma-cleaning the lead frame.

[0007]

According to the above construction, since the surface of the lead frame is a rough surface, the mold body adheres strongly to the lead frame, and moisture does not penetrate from the joint surface with the leads.
Particularly, by forcibly oxidizing the lead frame in advance, it is possible to effectively roughen the surface by plasma cleaning. Further, the plasma cleaning also removes impurities adhering to the surface of the lead frame, so that the wire bondability is also significantly improved.

[0008]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is an internal side view of a heating furnace for oxidizing a copper lead frame. In the figure, 31 is a heating furnace, which is provided with a heater 32. Reference numeral 20 denotes a copper lead frame placed on the shelf 33 in the heating furnace 31. The lead frame 20 is forcibly oxidized in the heating furnace 31. The internal temperature of the heating furnace 31 is 300 ° C, and the oxidation time is 5
It's a minute.

FIG. 5 is a photograph of the lead frame 20 before forced oxidation taken with an electron microscope at a magnification of 50,000. The surface composition of the lead frame 20 before the forced oxidation is in a natural oxidation state (Cu2O), and the surface is smooth. With such a smooth surface, a strong adhesive force with the synthetic resin, which is the material of the molded body, cannot be obtained. Further, FIG. 6 is a photograph of the lead frame 20 after forced oxidation taken at the same magnification. The surface of the lead frame 20 is a fragile and rough surface due to the forced oxidation. Further, due to being oxidized, the surface composition is CuO.

Next, after taking out the lead frame 20 from the heating furnace 31, plasma cleaning is performed. 2, FIG. 3, and FIG. 4 are a plan view, a side view, and a sectional view of the plasma cleaning device. This plasma cleaning device
What the applicant has previously proposed (Japanese Patent Laid-Open No. 15914/1993)
(See Japanese Patent Publication No. 3), and the structure thereof will be briefly described below. In FIG. 2, reference numeral 1 is a cylindrical glass casing, and an opening 2 is opened in the front end surface thereof. An electrode portion 3 made of an aluminum plate is arranged on the peripheral surface of the casing 1. In FIG. 4, reference numeral 4 is a power source for applying a high frequency AC voltage to the electrode portion 3. A pipe 5 is connected to the upper part of the casing 1, and the plasma discharge gas is supplied from the pipe 5 into the casing 1. A rotary vacuum pump 6 for sucking gas in the casing 1 is connected to the lower portion of the casing 1, and a valve 7 is connected to the rear end surface of the rotary vacuum pump 6. 9
Is a valve of the vacuum pump 6.

In FIG. 3, reference numeral 10 denotes a mounting portion made of an aluminum plate arranged in the front portion of the opening portion 2, and a lid member 11 for the opening portion 2 is attached to the rear portion thereof. The lid member 11 is supported by a bracket 14 provided upright on the nut portion 12. Reference numeral 13 is a feed screw with which the nut portion 12 is screwed, and 15 is a driving motor thereof. When the motor 15 is driven, the nut portion 12 moves in the Y direction along the feed screw 13, and the mounting portion 10 is opened. It goes in and out of the casing 1 from the portion 2. Further, the lid member 11 moves integrally with the mounting portion 10 to open and close the opening 2.

In FIG. 2, reference numerals 17 and 18 denote a mounting portion 10.
The lead frame 20 is a conveyor that is arranged in a direction intersecting with the placing portion 10 with the lead frame 20 interposed therebetween.
It is conveyed in the X direction that intersects the Y direction, which is the moving direction of 0. Reference numeral 19 is a stopper for stopping the lead frame 20. In FIG. 3, reference numeral 21 denotes a transfer means for the lead frame 20, which is provided between the conveyor 17 and the mounting portion 10.
Also, the lead frame 20 is reciprocated between the mounting portion 10 and the conveyor 18 in the X direction, and the lead frame 20 is adsorbed to the adsorption pad 22 and transferred. Next, the operation will be described.

In FIG. 2, the lead frame 20 conveyed by the conveyor 17 hits the stopper 19 and stops. Then, the delivery means 21 adsorbs the lead frame 20 and takes it up (see FIG. 3), and transfers it to the mounting portion 10. At this time, the mounting unit 10 is connected to the motor 15
Is driven to feed the pitch toward the casing 1. The delivery means 21 reciprocates between the conveyor 17 and the mounting portion 10 in synchronism with the pitch feeding to move the lead frame 20 to the mounting portion 10. The lead frames 20 are sequentially arranged and mounted one by one on the mounting portion 10 by being transferred.

In this way, a large number of lead frames 2 are formed.
When 0 is mounted, the mounting portion 10 completely enters the casing 1, and the lid member 11 closes the opening 2 (see the chain line in FIG. 2).

Next, the vacuum pump 6 is actuated, the interior of the casing 1 is decompressed (about 0.5 Torr), Ar gas is supplied into the casing 1, and then a high frequency AC voltage is applied to the electrode portion 3. , Plasma is generated. At this time, part of the Ar gas is ionized, and Ar gas molecules and ionized Ar + and minus electrons move violently and rapidly in the casing 1, collide with the surface of the lead frame 20, and scrape the surface of the lead frame 20. The surface is roughened and impurities adhering to the surface are removed, and the removed impurities are sucked by the vacuum pump 6.

When the plasma cleaning is completed in this way, the valve 9 of the vacuum pump 6 is closed and the valve 7 is opened to return the inside of the casing 1 to normal pressure.
Next, the mounting portion 10 is pitch-fed in the opposite direction to the previous direction and pulled out from the casing 1. At this time, in synchronization with the pitch feed, the delivery means 21 causes the placing portion 10 and the conveyor 18 to move.
The lead frame 20 is passed back and forth between the conveyors 18 and conveyed to the next step.

FIG. 7 shows the surface of the lead frame 20 after plasma cleaning. By performing the plasma cleaning as described above, the surface thereof is scraped and becomes more rough. The surface composition is Cu2
It is O + CuO. By making the surface of the lead frame 20 rough as described above, the synthetic resin, which is the material of the molded body, is firmly bonded with a strong adhesive force. In particular, in this method, prior to the plasma cleaning, the lead frame 20 is forcibly oxidized as described above to make the surface fragile and rough, so that the surface thereof is collided by Ar gas molecules, Ar +, and minus electrons. Is effectively shaved, and can be processed into a surface having high roughness as shown in FIG.

In FIG. 8, Ar gas and H 2 are used instead of Ar gas.
The mixed gas of the gas is supplied to the casing 1, and 0.5 To
The surface of the lead frame 20 when plasma cleaning is performed at about rr is shown. Its surface composition is Cu
2O + CuO, and as is clear from the photograph, the roughness is higher than that in the case of FIG.

FIG. 9 shows an ultimate pressure atmosphere (0.05 Tor).
The surface of the lead frame 20 when the plasma cleaning is performed under reduced pressure is shown in r). The surface composition is Cu2O + CuO, the roughness is further increased, and the adhesive force with the synthetic resin mold body is further improved. The plasma cleaning time is 10 minutes in any case. Figure 7
The magnification of each of the photographs in FIG. 9 is 50,000 times.

The forced oxidation conditions are not limited to those in the above-mentioned embodiment, and the point is that the surface of the lead frame 20 should be sufficiently oxidized to make it brittle. Further, the type of plasma discharge gas, the magnitude of the applied voltage, the plasma cleaning conditions such as the application time is not limited to the above examples, the point is to scrape off the surface components of the lead frame that became brittle even after forced oxidation, The surface may be roughened.

[0021]

As described above, according to the present invention, after the copper lead frame is forcibly oxidized, the surface of the lead frame is roughened by plasma cleaning, so that the material of the mold body is made. The adhesive strength with the synthetic resin is extremely strong, and therefore, a gap is not formed in the joint surface with the mold body and moisture does not enter.

[Brief description of drawings]

FIG. 1 is a sectional view of a heating furnace according to the present invention.

FIG. 2 is a plan view of a plasma cleaning device according to the present invention.

FIG. 3 is a side view of a plasma cleaning device according to the present invention.

FIG. 4 is a sectional view of a plasma cleaning device according to the present invention.

FIG. 5 is an enlarged view of the lead frame according to the present invention before forced oxidation.

FIG. 6 is an enlarged view of the lead frame according to the present invention after forced oxidation.

FIG. 7 is an enlarged view of the lead frame according to the present invention after plasma cleaning.

FIG. 8 is an enlarged view of a lead frame according to the present invention after plasma cleaning.

FIG. 9 is an enlarged view of a lead frame according to the present invention after plasma cleaning.

FIG. 10 is a sectional view of a conventional electronic component.

[Explanation of symbols]

 20 Lead frame 31 Heating furnace

Claims (1)

[Claims] 1. A method of treating a copper lead frame, which comprises roughening the surface of the lead frame by plasma-cleaning the lead frame after forced oxidation.