JPH09237865A - Material for manufacturing lead frame - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a material for manufacturing inner leads which are high in accuracy and very fine in pitch. SOLUTION: An etching stop layer 2, a high-melting metal diffusion preventing layer 3, and a second thin metal layer 4 are successively formed on a first metal layer 1 for the formation of a lead frame manufacturing material. The first metal layer 1 and the second metal layer 4 are formed of copper or copper alloy, the etching stop layer 2 is formed of aluminum or aluminum alloy, and the diffusion preventing layer 3 is formed of one or two metals selected out of chromium, nickel, molybdenum, tantalum, and titanium. The diffusion preventing layer 3 is as thick as 0.01 to 1.0μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lead frame manufacturing material capable of forming inner leads at a fine pitch.

[0002]

2. Description of the Related Art Conventionally, a lead frame for semiconductor elements such as LSI has been manufactured mainly by a method of punching a metal plate using a press die. However, recently, as semiconductor elements have become highly integrated and the number of pins has increased, and the inner leads bonded to semiconductor chips have tended to have a high density, it has become impossible to cope with the punching method, which has a limit to fine processing. There is. Further, in the conventional processing method using the etching method, since the pitch of the inner leads is determined by the thickness of the metal plate, there is a limit to the reduction of the thickness of the metal plate that corresponds to the fine pitch.

Therefore, a method for manufacturing a lead frame having a high arrangement density of inner leads has been proposed, for example, in Japanese Patent Laid-Open No. 148856/1993. According to the method of this document, a three-layer structure in which a thick copper layer, an aluminum layer, and a thin copper layer are laminated in this order is used as a material for manufacturing a lead frame, and a photoresist is formed on both surfaces thereof, and then only copper is etched. Etch the copper layers on both sides. As a result, the inner lead is formed of the thin copper layer, while the outer lead is formed of the thick copper layer (and the thin copper layer). Next, the exposed portion of the aluminum layer is etched under the condition that only aluminum is etched to manufacture a lead frame having thin inner leads and thick outer leads.

According to the above method, it is possible to perform etching with high accuracy by making the inner lead thin while ensuring the mechanical strength of the outer lead sufficiently.
It becomes possible to form the inner leads with a finer pitch than the conventional method.

[0005]

By the way, in order to manufacture a three-layer structure used as a raw material by the above method, a method in which a thick copper plate, an aluminum foil and a thin copper foil are sequentially stacked and clad bonded is easy to carry out. However, this method has a limit in thinning the thin copper layer. Therefore, the present inventors have tried to further thin the inner lead by forming the thin copper layer by a film forming method such as vacuum deposition or sputtering. However, in the lead frame that was actually created, the thin copper layer formed by vapor deposition was separated from the aluminum layer, the aluminum layer was dissolved during the selective etching of copper, or the aluminum layer was sufficiently dissolved during the selective etching of aluminum. It was difficult to manufacture the lead frame with high accuracy.

The present inventors have conducted a detailed study on the above phenomenon, and as a result, heating the material during the formation of the thin copper layer causes mutual diffusion of atoms between the aluminum layer and the thin copper layer. It has been found that this is caused by the mutual alloying in the vicinity of the interface between these layers.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a material for manufacturing a lead frame capable of forming inner leads of a fine pitch with high accuracy.

[0008]

In order to solve the above-mentioned problems, a material for manufacturing a lead frame according to the present invention comprises a metal plate to be a first metal layer, and an etching stopper formed on the first metal layer. A layer, a diffusion barrier layer made of a refractory metal formed on the etching stopper layer, and a second metal layer thinner than the first metal layer formed on the diffusion barrier layer. And

[0009]

FIG. 1 is an enlarged cross-sectional view of an embodiment of a material for manufacturing a lead frame according to the present invention. This material for manufacturing a lead frame is on a metal plate 1 which is a first metal layer 1. The etching stop layer 2, the diffusion preventing layer 3 made of a refractory metal, and the second metal layer 4 thinner than the first metal layer.
Are sequentially formed by a vacuum vapor deposition method, a DC or RF sputtering method, or the like. The film forming conditions may be conventionally known conditions depending on the film forming substance.

The material of the first metal layer 1 is preferably copper or a copper-based alloy such as a Cu-Cr alloy, a Cu-Fe-P alloy, or a Cu-Ni-Si alloy because of its high heat dissipation property. However, other materials such as 42 alloy and Kovar alloy can also be used. On the other hand, as the material of the second metal layer 4, since it is important that the electric resistance is small, copper is preferable. From the viewpoint of the balance between strength and processing accuracy, the thickness of the first metal layer 1 is about 0.10 to 0.30 mm, and the thickness of the second metal layer 4 is about 0.5 to 10 μm. Is not limited to only these ranges.

When the material of the first metal layer 1 is copper or copper alloy, the material of the etching stop layer 2 is preferably aluminum or aluminum alloy. The thickness of the etching stop layer 2 is not limited, but is preferably 1 to 10 μm. Within this range, the effect of preventing etching can be reliably obtained and the film can be formed at a relatively low cost.

The diffusion preventing layer 3, which is a feature of the present invention, is made of a high melting point metal having a melting point of 1400 ° C. or higher. 1 selected
It is desirable in terms of characteristics and cost that it is formed of one kind or two kinds of metals. When it is composed of two or more kinds of substances, it may have a multi-layered structure or an alloy layer. The thickness of the diffusion prevention layer 3 is preferably 0.01 to 1.0 μm, more preferably 0.05 to 0.5 μm.
m. If the diffusion prevention layer 3 is thinner than 0.01 μm, the diffusion prevention effect cannot be obtained, and it is not necessary to be thicker than 1.0 μm.

Next, an example of a method for manufacturing a lead frame using the above-mentioned material for manufacturing a lead frame will be described.
In this method, first, as shown in FIG. 2, masking layers 5 and 6 are formed on both surfaces of a lead frame manufacturing material, respectively. It is advantageous to use a photoresist as the masking layers 5 and 6 because a highly precise pattern can be formed.
Other types of masking materials known in the art may be used. The masking layer 5 formed on the first metal layer 1 is formed in a pattern corresponding to a portion of the lead frame to be manufactured which is to be thickened, that is, an outer lead portion. On the other hand, the masking layer 6 formed on the second metal layer 4 is formed in a pattern corresponding to the portion of the lead frame to be manufactured which is to be thinned, that is, the inner lead.

Next, as shown in FIG. 3, the regions where the masking layers 5 and 6 are not formed in the first metal layer 1 and the second metal layer 4 are partially formed under the condition that the etching stopper layer 2 is not etched. To etch. As a result, the inner leads are formed by the second metal layer 4, while the first metal layer 1 is formed.
Outer leads are formed of (and the second metal layer 4).
The inner lead and the outer lead may have any shape.

The conditions under which the etching stop layer 2 is not etched are, for example, when the first metal layer 1 and the second metal layer 4 are made of copper or a copper alloy, and the etching stop layer 2 is made of aluminum or an aluminum alloy. Examples of the method include chemical etching using a hydrogen peroxide / sulfuric acid-based etching solution or a ferric chloride-based etching solution. In order to perform etching, the lead frame manufacturing material may be dipped in an etching solution, but in order to improve the etching uniformity, it is preferable to spray the etching solution evenly on the mask surface of the lead frame manufacturing material. To be taken. However, the present invention is not limited to the above etching method and conditions,
Of course, other etching methods and conditions may be adopted.

After the etching of the first metal layer 1 and the second metal layer 4 is completed, the masking layers 5 and 6 are then dissolved and removed by a known removing solution as shown in FIG. However, the removal of the masking layers 5 and 6 may be performed simultaneously with or after the etching step of the etching stop layer described later.

Next, as shown in FIG. 5, under the condition that the first metal layer 1 and the second metal layer 4 are not etched, the first metal layer 1 and the second metal layer 4 are exposed at the removed traces. The etching stop layer 2 and the diffusion preventive layer 3 are etched. As an etching method in this case, for example, if the first metal layer 1 and the second metal layer 4 are formed of copper or a copper alloy and the etching stop layer 2 is formed of aluminum or an aluminum alloy, a strong alkaline substance is used. An example is a method of chemically etching with an etching solution containing (for example, an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide). When the material of each layer is different, etching conditions suitable for the material may be used.

Further, as shown in FIG. 6, the second metal layer 4
Bumps 8 for connecting a semiconductor chip are formed at the tip of each inner lead 7 formed by. As a means for forming the bumps 8, it is preferable to use a film forming method such as a vacuum vapor deposition method or a sputtering method to collectively form the bumps 8 on the tips of the inner leads. The material of the bump 8 is aluminum, Sn-P
Examples include b alloy and Pd. The thickness of the bump 8 is 0.
1 to 5.0 μm is suitable, and more preferably 1.0 to
It is set to 3.0.

According to the material for manufacturing a lead frame having the above-mentioned structure, even if each of the layers 1 to 4 is heated in the process of forming the layers 2 to 4 on the first metal layer 1, the material is used as the etching stop layer 2. Since the diffusion prevention layer 3 made of a refractory metal is formed between the second metal layer 4 and the second metal layer 4, mutual diffusion of atoms between the etching stop layer 2 and the second metal layer 4 is prevented. Therefore, since a brittle alloy layer is not formed at the interface, the second
Not only the peeling of the metal layer 4 can be prevented, but also the second metal layer 4
Of the etching stopper layer 2 during the etching of the
There is no phenomenon such as that does not dissolve. Therefore, the second
Since it becomes possible to form the metal layer 4 by a vapor deposition method or the like, the second metal layer 4 can be made sufficiently thin with a uniform thickness, as compared with a manufacturing method in which a metal foil is clad bonded. Accordingly, the inner leads can be made thinner, and the pitch thereof can be made more precise and finer.

[0020]

EXAMPLES Next, the effects of the present invention will be demonstrated with reference to examples. [Experiment 1] Whether a lead frame manufacturing material having various thicknesses of the diffusion prevention layer and a lead frame manufacturing material not having the diffusion prevention layer are respectively formed, and whether the copper layer peels off after heat treatment It was confirmed.

On a copper plate having a thickness of 150 μm, a thickness of 3.0 μm
An aluminum layer having a thickness of m, a diffusion preventing layer made of Ni or Cr, and a copper layer having a thickness of 2.0 μm were sequentially formed by a DC magnetron sputtering method. In any film formation, after evacuation to 1 × 10 ⁻³ Pa, argon gas was introduced and the sputtering was performed at 3 × 10 ⁻¹ Pa.
On the other hand, a comparative product was prepared under the same conditions except that the diffusion prevention layer was not formed. All of these lead frame manufacturing materials were heated by a hot plate at 430 ° C. for 3 minutes, and it was examined whether or not the copper layer was peeled off after cooling. Table 1 shows the results.

[0022]

[Table 1]

As is clear from Table 1, in the lead frame manufacturing material having no diffusion preventing layer and the lead frame manufacturing material having the diffusion preventing layer having a thickness of 0.005 μm, the thin second copper layer is peeled off. However, peeling did not occur in the lead frame manufacturing material in which the diffusion prevention layer was formed with a thickness of 0.01 μm or more.

[Experiment 2] 0.2 μm thick using chromium
Of the lead frame manufacturing material having the diffusion prevention layer formed thereon, which has been subjected to the heat treatment, and the lead frame manufacturing material having no diffusion prevention layer formed, which has been subjected to the heat treatment. The depth distribution of the elements was examined by Auger electron spectroscopy while the surface was scraped from the layer side by argon sputtering. Figure 7
8 shows the results obtained by forming a diffusion preventing layer of chromium having a thickness of 0.2 μm, and FIG. 8 shows the results obtained by not forming the diffusion preventing layer. As is clear from these graphs, the diffusion prevention layer made of chromium suppressed the mutual diffusion of copper atoms and aluminum atoms.

[0025]

As described above, in the lead frame manufacturing material according to the present invention, the process of forming the etching stop layer, the diffusion prevention layer and the second metal layer on the first metal layer and the subsequent annealing process. Even if each layer is heated by the above, since the diffusion prevention layer made of a refractory metal is formed between the etching stop layer and the second metal layer, the atoms between the etching stop layer and the second metal layer are not formed. Mutual diffusion is hindered. Therefore, since a brittle alloy layer is not formed at the boundary surface, not only can the peeling of the second metal layer be prevented, but
The phenomenon that the etching stopper layer is not dissolved when the second metal layer is etched and the etching stopper layer is not dissolved when the etching stopper layer is etched does not occur.

With this, since the second metal layer can be formed by the vapor deposition method or the like, the second metal layer can be made sufficiently thin with a uniform thickness, and the inner lead can be thinned accordingly. It is possible to obtain the excellent effect that the pitch can be made highly precise and fine.

[Brief description of drawings]

FIG. 1 is an enlarged cross-sectional view of an embodiment of a lead frame manufacturing material according to the present invention.

FIG. 2 is an enlarged cross-sectional view of a state where a masking layer is formed on the same lead frame manufacturing material.

FIG. 3 is an enlarged cross-sectional view showing a state in which a first metal layer and a second metal layer of the same lead frame manufacturing material are etched.

FIG. 4 is an enlarged cross-sectional view showing a state in which a masking layer is removed from the lead frame manufacturing material.

FIG. 5 is an enlarged cross-sectional view showing a state where the etching stop layer and the diffusion prevention layer of the same lead frame manufacturing material are etched.

FIG. 6 is an enlarged cross-sectional view showing a lead frame obtained by forming bumps on the same lead frame manufacturing material.

FIG. 7 is a graph showing the atomic concentration distribution in the thickness direction after heat treatment of the example according to the present invention.

FIG. 8 is a graph showing the atomic concentration distribution in the thickness direction after heat treatment of a comparative example.

[Explanation of symbols]

 1 First Metal Layer 2 Etch Stop Layer 3 Diffusion Prevention Layer 4 Second Metal Layer 5, 6 Masking Layer 7 Inner Lead 8 Bump

Claims (3)

[Claims] 1. A metal plate to be a first metal layer, an etching stopper layer formed on the first metal layer, a diffusion preventing layer made of a refractory metal formed on the etching stopper layer, and A material for manufacturing a lead frame, comprising a second metal layer formed on the diffusion prevention layer and thinner than the first metal layer. 2. The first metal layer and the second metal layer are formed of copper or a copper-based alloy, the etching stop layer is formed of aluminum or an aluminum alloy, and the diffusion prevention layer is chromium, nickel, molybdenum, The lead frame manufacturing material according to claim 1, which is formed of one or two kinds of metals selected from tungsten, tantalum, and titanium. 3. The thickness of the diffusion barrier layer is 0.01-1.
The lead frame manufacturing material according to claim 1 or 2, wherein the material is 0 μm.