JPH05129507A - Composite lead frame - Google Patents

Abstract

PURPOSE:To reduce the defect of a pattern by a method wherein, out of conductor layers on an insulating film layer, the conductor layers to be used as inside wiring layers are formed by sputtering or vapor-depositing copper or a copper alloy. CONSTITUTION:A lead frame 11 is provided with an outer frame 13. Outside wiring layers (outer leads) 15 (15a, 15b) are extended and installed toward parts near the center of the outer frame 13 from the outer frame 13. A flexible multilayer wiring board (FPC) 17 is arranged in the central part of the outer frame 13 of the lead frame 11. The FPC 17 is provided with inner wiring layers (inner leads) 27 on the upper side of an insulating film layer 19. The inner leads 27 are formed of a thin film by sputtering or vapor-depositing copper or a copper alloy. The inner leads 27 may be formed on both faces of the upper side and the lower side of the insulating film layer 19. Thereby, a defect such as a rolling flaw, a hole or the like is eliminated, and the defect of a pattern can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin-encapsulated composite lead frame for semiconductor devices.

[0002]

2. Description of the Related Art A flexible wiring board (hereinafter referred to as FPC), which is an inner wiring layer of a composite lead frame, is conventionally a casting material obtained by coating a copper foil with polyimide and baking it, or a copper foil is bonded to a polyimide film with an adhesive. The pasted material is used. The former is called a two-layer material because of its structure, and the latter is called a three-layer material because it has an adhesive layer.

In each of the above materials, the limit of the thickness of the copper foil is the limit of each pattern dimension at the time of forming a fine pattern in the subsequent process, and it becomes impossible to cope with the composite lead frame which is required to be further miniaturized. Is coming.

That is, the limit thickness of copper foil that can be manufactured is currently 18
As is clear from the graph shown in FIG. 1, the fine circuit forming pitch A at this time has a required conductor width C of 90 μm.
The limit is 120 μm in terms of μm. This is because in the photoresist coating chemical etching, the space that can be dissolved and removed between the patterns is limited to about twice the thickness of the copper foil.

The reason for this is that no matter how narrow the photoresist width is, if the copper foil is thick, the etching time becomes long and the side etching proceeds. In addition, B in FIG. 1 indicates a pattern width.

[0006]

For this reason, a copper foil having a thickness of less than 18 μm is required, but in reality, it cannot be manufactured by a continuous rolling method on a mass production basis.

Although a method of directly forming a plating film on polyimide by an electroless copper plating method has been studied, a plating technique with good adhesion has not been established yet.

An object of the present invention is to solve the above problems and provide a composite lead frame having a finer pattern and high reliability.

[0009]

According to a first aspect of the present invention to achieve the above object, a flexible wiring board having a conductor layer on at least one side of an insulating film, and an outer wiring layer are provided. In the composite lead frame formed of the metal conductor, the composite lead frame is characterized in that, among the conductor layers, the conductor layer serving as an inner wiring layer is formed by sputtering or vapor deposition of copper or a copper alloy. Provided.

According to a second aspect of the present invention, there is provided a composite lead frame characterized by further comprising a copper or copper alloy plating layer on a conductor layer which is an inner wiring layer of the composite lead frame. To be done.

The present invention will be described in more detail below. According to the present invention, when the conductor layer serving as the inner wiring layer is formed by sputtering or vapor deposition, it is easy to form a 1 μm thick layer. In this case, a theoretically 2 μm space can be formed if the resolution of the photoresist ink is increased. It was made based on the knowledge that

FIG. 2 is a partial cross sectional view showing an embodiment of the present invention. By the way, it should be noted that the drawings are partially omitted or simplified for the sake of explanation, and are different from actual ones.

The lead frame 11 is provided with an outer frame 13, and from this outer frame 13, an outer lead 15 which is an outer wiring layer.
(15a, 15b) are extended toward the vicinity of the center of the outer frame 13. An EPC 17 is arranged in the center of the outer frame 13 of the lead frame 11. The FPC 17 has a conductor layer 27 serving as an inner wiring layer above the insulating film layer 19 made of, for example, polyimide. The conductor layer 27 is formed into a thin film by sputtering or vapor deposition of copper or a copper alloy.

The thin-film conductor layer 27 is not limited to one surface, but may be formed on both upper and lower surfaces of the insulating film layer 19.

In this case, by cutting the pattern on the back side and connecting the through holes, it is possible to fabricate a composite frame of three-layer wiring including the ground layer (the lowest bonding layer).

This thin-film conductor layer 27 will later become an inner lead which is an inner wiring layer on which, for example, a signal layer pattern is formed. The insulating film layer 19 has holes 23 for grounding and power supply and a lock hole 25 opened by press punching or the like, and notches 29 are provided at four corners of the FPC 17. A conductor layer 21 is attached to the insulating film layer 19 with an adhesive or the like. This FPC
The inner lead 27 is formed by etching or vapor-depositing a thin-film conductor layer formed on at least one surface of the insulating film layer 19 of 17. At the inner tip of the inner lead 27, a good conductor such as gold is plated on the base of Sn-Ni, for example, in order to make a good wire bonding connection. The hole 23 of the FPC 17 is also plated with a good conductor such as gold on the base of Sn-Ni. The lead frame 1
1 outer wiring layer (outer lead 15) and the FPC 17
The electrical connection with the inner wiring layer (inner lead 27) is performed by solder-plating the tips of the outer leads 15 and then appropriately arranging the outer leads 15 and the inner leads 27 so that they are connected by the infrared beam heating method. It is achieved by thermocompression bonding.

In the figure, the outer leads 15 of the lead frame 11 are ground and power supply leads 15a extending from the outer frame 13 near, for example, four corners, and the other leads are signal leads 15b. .. The signal lead 15b is connected to the inner lead 27 as described above, but the ground and power supply lead 15a is directly grounded to the conductor layer 21. For this grounding, first, bumps 31 are formed by solder plating on the corners of the conductor layer 21 exposed from the notches 29 of the insulating film layer 19, and the tips of the grounding and power supply leads 15a are applied to the bumps 31. The conductor layer 21 is electrically connected to the ground and power supply lead 15a by thermocompression bonding.

The semiconductor element 33 is mounted on the composite lead frame 11, and the signal terminal of the semiconductor element 33 and the plating terminal of the inner lead 27 are connected by bonding wire 35, and the ground terminal of the semiconductor element 33 is further connected. The grounding of the FPC 17 of the conductor layer 21 and a portion exposed from the power supply hole 23 are connected by bonding with a bonding wire 35. Finally, a semiconductor device can be manufactured by resin-sealing so as to wrap the inner lead 27.

The inner leads 27 are required to have particularly fine wiring. For example, when the semiconductor element 33 is 15 mm square, the limit of increasing the number of pins is determined by the limit of miniaturization of the inner lead, and therefore the technique development of fine etching (composition of etching solution etc.) is underway.

However, in reality, the limit of increasing the number of pins is determined by the thickness of the conductor layer material which is the source of the pattern. Normally, if the copper foil is 18 μm thick, it is 15 ÷ from Fig. 1.
0.12 × 4 sides = 500 pin arrangement is the limit,
For example, in the case of a 3 μm-thick sputter or vapor-deposited film, up to 15 / 0.1 × 4 = 600 pins are possible. Also,
When the required conductor width C is changed from 90 μm to, for example, 70 μm, the number of pins can be further increased.

For example, in the case of producing a polyimide film coated with a conductor thin film of pure copper having a thickness of 3 μm, a polyimide coil is put in a continuous vapor deposition facility and pure copper thin film of 3 μm is formed on the entire film coil by using pure copper as an evaporation source. Can be made In this case, in order to improve the adhesion between the copper thin film and the polyimide, the polyimide film may be roughened in plasma in advance. The plasma treatment was performed with argon ion plasma in the range of 0.01 to 0.
A roughening of about 2 μm is preferable.

The formation of the copper thin film is not limited to vapor deposition, but sputtering may be used.

This film for holding a copper thin film having a thickness of 3 μm can be cut into multiple strips and used for the production of a composite lead frame. After forming predetermined holes 23, 25, etc. in this material, the conductor layer 21 is attached by, for example, an adhesive. After that, the inner leads 27 can be formed by the photoetching method, and the outer leads 15 can be further connected to form a composite lead frame.

The present invention has also developed a composite lead frame in which a thin conductor layer formed by sputtering or vapor deposition is further thickened by a copper or copper alloy plating method. This is because an LSI having a high current capacity requires a copper thickness of about 3 μm. As the plating method, either electroplating or electroless plating can be used.

Although the conductor layer is made of copper or a copper alloy, the copper alloy may be brass such as Cu--Zn or Cu--Sn.
Bronze can be mentioned.

[0026]

EXAMPLES The present invention will be specifically described below based on examples. (Example 1) First, the inner lead 27 is formed with a thickness of 3 μm.
A polyimide film coated with a conductor thin film of pure copper was used. Put a coil of polyimide of 500mm in width and 200m in continuous vapor deposition equipment and use pure copper as an evaporation source to 3μm
Of pure copper thin film was formed on the entire film coil.

In this case, in order to improve the adhesion between the copper thin film and the polyimide, the polyimide film was preliminarily roughened in plasma. The plasma treatment was roughened to about 0.07 μm with argon ion plasma.

The film having a copper thin film of 3 μm is 70
It was cut into multiple strips with a width of mm and used for manufacturing a composite lead frame. After forming predetermined holes 23, 25, etc. in this material, the conductor layer 21 was bonded with an adhesive, and then the inner lead 27 was formed by the photoetching method. Further, the outer leads 15 were connected to form a composite lead frame.

(Example 2) As a method of forming a thin-film conductor layer in Example 1, first, a vapor-deposited film of copper having a thickness of 0.5 μm was prepared, and then copper was plated with a thickness of 2.5 μm by electroplating. The entire size was 3 μm. In this case, since the vapor-deposited film may have a minimum thickness through which electricity can pass, high-speed roll-up vapor deposition is possible and productivity is improved.

In both the first and second embodiments, the number of pins is 600. As for the method of connecting the outer leads 15, first, 0.5 to 1.0 .mu.m of gold plating is applied to the entire inner leads, the bonding hole, and the lower portion of the notch 29 where the ground layer is exposed. This gold plating is excellent in the bonding performance of the bonding wire 35 and is Au-Sn.
Was used as the gold plating seed with excellent eutectic bondability.

Next, 8 to 10 μm is attached to the tip of the outer lead.
m of pure tin plating 31 was applied. In the figure, the bump 31 is used, but in actuality, it is not necessary to use thick plating such as a bump.
10 μm tip plating is optimal. FPC in this state
Then, the outer lead and the outer lead were aligned at a stretch, and they were heat-pressed at 350 to 400 ° C. for 5 seconds by the heat contact tool method to join them to obtain a composite lead frame.

In each of the composite lead frames of Examples 1 and 2, the inner lead pitch could be miniaturized, and the miniaturization rate was 1.5 to 2.0 times that of the conventional one.

[0033]

Since the present invention is constructed as described above, the inner lead pitch can be greatly reduced. Further, there were no defects such as rolling flaws and perforations, and pattern defects could be reduced. In addition, since there are few defects, defect-free plating could be formed on the pattern.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the thickness of a copper foil and the pitch and width of an FPC pattern.

FIG. 2 is a partial cross-sectional explanatory view for explaining one embodiment of the composite lead frame of the present invention.

FIG. 3 is a sectional view illustrating another embodiment of the present invention.

FIG. 4 is a plan view illustrating another embodiment of the present invention.

[Explanation of symbols]

 11 Lead Frame 13 Outer Frame 15 Outer Wiring Layer (Outer Lead) 17 Flexible Multilayer Wiring Board 19 Insulating Film Layer 21 Grounding and Power Supply Conductor Layer 23 Grounding and Power Supply Hole 25 Lock Hole 27 Inner Wiring Layer (Inner Lead) 29 Notch 31 Bump 33 Semiconductor element 35 Bonding wire 37 Solder joint layer 15a Grounding and power supply lead 15b Signal lead

Claims (2)

[Claims] 1. A composite lead frame comprising a flexible wiring board having a conductor layer on at least one surface of an insulating film and a metal conductor serving as an outer wiring layer, wherein inner wiring of the conductor layer is included. A composite lead frame, wherein a conductor layer to be a layer is formed by sputtering or vapor deposition of copper or a copper alloy. 2. A composite lead frame according to claim 1, further comprising a copper or copper alloy plating layer on the conductor layer serving as an inner wiring layer of the composite lead frame.