JPH07147363A - Manufacture of lead frame - Google Patents

Abstract

PURPOSE:To make inner leads finer without hindrance and to intensify the adhesibility of the inner leads to an etching stopper in a lead frame forming method in which a lead frame is formed by using a lead frame forming material having a three-layer structure composed of a thick Cu layer for forming outer leads and thin Cu layer for forming inner leads respectively formed on both surfaces of an Al layer which becomes the etching stopper. CONSTITUTION:A lead frame material comprises a copper base 1, which is coated by physical vapor deposition with an Al layer 2 on one side and a Cu layer 3 on the other side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a lead frame, and more particularly, to a second metal layer serving as an etching stopper on one surface of a first metal layer serving as an outer lead. An outer lead is formed by patterning the metal layer to be the outer lead, using a lead frame material having a third metal layer to be the inner lead on the surface opposite to the first metal layer of the layer. The present invention relates to a method for manufacturing a lead frame, in which an inner lead is formed by patterning a metal layer to be formed, and an unnecessary portion of the second metal layer is removed by etching using the outer lead and the inner lead as a mask.

[0002]

2. Description of the Related Art As a method of manufacturing a lead frame, a second frame made of, for example, aluminum to be an etching stopper is used.
A lead frame material having a three-layer structure sandwiched between a first metal layer made of, for example, copper and serving as outer leads and a third metal layer made of, for example, copper, serving as inner leads on both sides of the metal layer of There is a method of patterning the third metal layer by selective etching to form an outer lead and an inner lead, and removing an unnecessary portion of the second metal layer using the outer lead and the inner lead as a mask.

FIGS. 3A to 3E show an example of a method of manufacturing a lead frame using such a three-layer lead frame material as a base material in the order of steps. (A) First, as shown in FIG. 3A, a lead frame member 4 having a three-layer structure in which a thick metal layer 1 made of copper, a metal layer 2 made of aluminum and a thin metal layer 3 made of copper are laminated is prepared. To do. (B) Next, as shown in FIG. 3B, resist films 5 and 6 for forming a lead frame are formed on both surfaces of the lead frame material 4.

(C) Next, the metal layers 1 and 3 are etched by using the resist films 5 and 6 as masks to form outer leads and inner leads, and then the resist films 5 and 6 are removed. . During the etching, the metal layer 2 plays a role as an etching stopper, and the metal layer 1 and the metal layer 3 are formed in the same pattern as the resist films 5 and 6 formed on the surfaces thereof, respectively. To be done. FIG. 3C shows a state after removing the resist films 5 and 6. (D) Next, the electrodeposition resist film 7 is applied to the surface of the lead frame 4 on the outer lead side, and is patterned by exposure and development. As a result, as shown in FIG. The bumps are left only on the portions to be formed.

(E) Thereafter, the metal layer 2 is etched by using the outer lead 1, the inner lead 3 and the electrodeposition resist film 7 made of copper as a mask.
The unnecessary portions are removed to eliminate the state where the leads are electrically short-circuited by the metal layer 2 and the bumps 8 made of the metal layer 2 are formed near the tips of the inner leads 3. FIG. 3E shows a state after the bump 8 is formed.

By the way, a lead frame member 4 having a three-layer structure
Conventionally, a has often been formed by a cold rolling method. However, according to the cold rolling method, it is becoming difficult to cope with the miniaturization of the inner leads. This is because ICs, LSIs, VLSIs, and other semiconductor integrated circuits are becoming more and more pinned, and as a result, there is a strong demand for finer inner leads, which are used as inner leads and etching stoppers. It is essential to thin the metal layer. However, according to the cold rolling method, it is very difficult to set the inner leads and the etching stopper to 5 μm or less. This is because pinholes frequently occur in the metal layer, and the metal layers 2 and 3 may be corroded by chemicals during the formation of inner leads and etching for removing unnecessary portions of the etching stopper.
Then, it is becoming necessary to reduce the thickness of the metal layer used as the inner leads and the etching stopper to 5 μm or less, for example, 3 to 1 μm or less.

Therefore, recently, based on a two-layer structure as shown in FIG. 4 (A) consisting of a metal layer 1 made of copper and a metal layer 2 made of aluminum, as shown in FIG. 4 (B),
After the surface of the metal layer 2 is treated with zinc zincate, as shown in FIG. 4 (C), the metal layer 3 for inner leads made of copper is formed on the surface of the zinc coating 9 formed by the zinc zincate treatment. A technique has been developed in which the lead frame material 4b is formed by a method of forming by plating. According to this, there is an advantage that pinholes are hard to be formed even if the metal layers 2 and 3 are thin, and further, the metal layers 2 and 3 are made thinner than before so that the inner leads are made finer and the number of pins is increased to some extent. Can respond.

[0008]

However, the method of forming the lead frame material 4b as shown in FIG. 4 has two problems. The first problem is that it is difficult to sufficiently increase the adhesive strength between the metal layer 2 and the metal layer 3. The zinc zincate treatment contributes to improving the adhesion between the surface of the metal layer 2 made of aluminum and copper, but in order to sufficiently enhance the adhesion of the metal layer 3 formed by plating to the metal layer 2 made of aluminum. It does not happen, and peeling defects are likely to occur.

The second problem is that there is a great variation in the film thickness of the metal layer 3 due to plating. For example, even if an attempt is made to form a metal layer 3 having a film thickness of 8 μm, the film thickness will be 8 ± 2 μm. In this case, it is difficult to control the etching time for patterning the inner leads, and disadvantages such as insufficient etching and excessive etching are likely to occur. Therefore, it is difficult to form fine inner leads. Therefore, there is a limitation in meeting the demand for miniaturization of the inner leads and the increase in the number of pins, and it is difficult to meet the demand for making the number of pins of the IC several hundred.

The present invention has been made to solve such a problem, and an object thereof is to respond to miniaturization of the inner lead without any trouble and to enhance the adhesion of the inner lead to the etching stopper.

[0011]

According to a first aspect of the present invention, there is provided a method for manufacturing a lead frame, wherein a lead frame material is formed from a first metal layer as a base material and a second metal layer is formed on one surface thereof by a physical vapor deposition method. It is characterized in that it is formed and then formed by forming a third metal layer on the surface of the second metal layer opposite to the first metal layer by a physical vapor deposition method. A method of manufacturing a lead frame according to claim 2 is the method of manufacturing a lead frame according to claim 1, wherein the first metal layer is reverse-sputtered before the formation of the second metal layer.

[0012]

According to the method of manufacturing a lead frame of claim 1, the second metal layer on the first metal layer and the third metal layer on the second metal layer are formed by physical vapor deposition (for example, sputtering, Since it is formed by the vacuum vapor deposition method, it is possible to obtain the second and third metal layers having a dense film quality. Therefore, even if the second metal layer and the third metal layer are made thin, pinholes can be eliminated, and moreover, the adhesive force with the base can be strengthened. Moreover, the thickness of the second and third metal layers can be controlled with high accuracy by controlling the physical vapor deposition time (plus or minus 10% of the thickness).
It is possible to suppress the variation within the above range), and etching for inner lead patterning can be performed without any trouble. Therefore, the second metal layer and the third metal layer can be thinned without any trouble, and the peeling strength can be increased. Therefore, the inner leads can be miniaturized to meet the demand for a large number of pins. You can

According to the lead frame manufacturing method of the second aspect, since the surface is reverse-sputtered after the first metal layer is formed, this surface is cleaned. Therefore,
The adhesion of the second metal layer formed thereafter with the first metal layer can be enhanced.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method of manufacturing a lead frame of the present invention will be described in detail below with reference to the illustrated embodiments. 1A to 1C are cross-sectional views showing a main part of one embodiment of a method for manufacturing a lead frame according to the present invention in the order of steps. (A) For example, a metal layer 1 made of copper having a thickness of 100 to 150 μm is prepared, and this is reverse-sputtered by a sputtering device (not shown) as shown in FIG. Specifically, the pressure inside the sputtering apparatus is set to 1 × 10 ⁻³ Pa by evacuation, and then the pressure is 0.8 [Pa],
RF power 200 [W], argon Ar gas supply amount 58
[SCCM], etching rate 58 [/ min],
Reverse sputtering is performed under the condition that the etching time is 5 [min]. As a result, one surface of the metal layer 1 is cleaned.

(B) Next, as shown in FIG. 1B, a metal layer 2 made of aluminum is formed by sputtering. Specifically, the metal layer 2 made of aluminum containing 1% silicon and 2% copper is formed subsequent to the above reverse sputtering. The sputtering conditions at this time are DC power of 1000 [W] and argon Ar.
Gas supply rate 58 [SCCM], film formation rate 447 [/ m
in], and the film thickness of the metal layer 2 is 1 to 10 (for example, 3) [μm] or less.

(C) Next, as shown in FIG. 1C, a third metal layer 3 made of copper is formed on the surface of the second metal layer 2 by sputtering, followed by formation of the second metal layer 2. To form. The purity of copper of this metal layer 3 is, for example, 99.99%.
That is all. The sputtering conditions at this time were as follows: DC power 1000 [W], argon Ar gas supply amount 58 [SC
CM], the film formation rate is 745 [/ min], and the film thickness is 1 to 10 (for example, 2) [μm] or less.
With this, the lead frame material 4 is completed. Based on this lead frame material 4, for example, FIGS.
A lead frame is formed by the process shown in FIG.

When the lead frame material 4 is formed by the method shown in FIGS. 1A to 1C, the metal layer 2 and the metal layer 3 are formed.
Since it is formed by sputtering, the film quality can be made extremely dense, pinholes cannot be formed even if the film thickness is as thin as 1 to 10 μm, and peeling is less likely to occur because the adhesion to the base is good. . In particular, the adhesiveness between the metal layer 1 and the metal layer 2 is not a problem because the surface of the metal layer 1 is cleaned by reverse sputtering and then the metal layer 2 is formed there by sputtering. That is, when aluminum is formed on the surface of copper without cleaning it, the adhesion may be reduced. However, in the present embodiment, since reverse sputtering is performed on copper, aluminum is sputtered. Adhesion does not decrease. When copper is sputtered on the sputtered aluminum film, the adhesion between the aluminum film and copper can be easily and sufficiently strengthened from the beginning.
Moreover, by controlling the physical vapor deposition time, the second,
The thickness of the third metal layer can be controlled with high accuracy, and etching for inner lead patterning can be performed without any problems. Specifically, it is possible to suppress the variation within the range of plus or minus 10% with respect to the film thickness, and the disadvantages of insufficient etching or excessive etching are less likely to occur. Therefore, the second metal layer, the third
Since the metal layer can be thinned without any trouble and the peeling strength can be increased, it is possible to miniaturize the inner leads and meet the demand for increased pin count.

In the method of manufacturing the lead frame shown in FIG. 3, the bumps 8 are masked with the electrodeposition resist 7 during the etching of the second metal layer 2 which functions as an etching stopper. However, when it is difficult to form the electrodeposition resist 7 at each place where the bump 8 is to be formed and the position shift easily occurs, the case shown in FIG.
As shown in FIG. 3, when the metal layer 2 was etched, the portions where the bumps 8 were to be formed were removed without being covered with the electrodeposition resist, and the portions other than the tip of the inner lead were masked by, for example, the mask jig 10 or a mask film made of polyimide or the like. The bumps 8 may be formed by sputtering aluminum Al in this state. 2A shows a state before etching the metal layer 2 which is an etching stopper in such a bump forming method, FIG. 2B shows a state after etching, and FIG. The state when the sputtering for forming is shown is shown.

In the above embodiment, the metal layer 2,
3 (and bumps 8) were formed by sputtering, but need not necessarily be formed by sputtering, and needless to say, may be formed by vacuum vapor deposition. In addition, the second metal layer 2 and the third metal layer 3 are not entirely formed on the first metal layer 1, but selected in a region (for example, a rectangular region) where a large number of inner leads are formed. The second metal layer 2 and the third metal layer 3 may not be formed by masking the portions where the outer leads are formed with a jig. As described above, the present invention can be implemented in various modes.

[0020]

According to the first aspect of the present invention, there is provided a method for manufacturing a lead frame, the first metal layer being a base material, the second metal layer being formed on one surface of the lead frame by physical vapor deposition, and thereafter The second metal layer is formed by forming a third metal layer on the surface of the second metal layer opposite to the first metal layer by a physical vapor deposition method. Therefore, according to the method of manufacturing a lead frame of claim 1, the second metal layer on the first metal layer and the third metal layer on the second metal layer are formed by physical vapor deposition (eg, sputtering, vacuum). Since it is formed by the vapor deposition method), the second and third metal layers having a dense film quality can be obtained. Therefore, the second metal layer, the third
Even if you thin the metal layer of, you can eliminate pinholes,
Moreover, it is possible to strengthen the adhesive force with the base. Moreover, by controlling the physical vapor deposition time, the second and third
The thickness of the metal layer can be controlled with high accuracy, and etching for inner lead patterning can be performed without any problems. Therefore, the second metal layer and the third metal layer can be thinned without any trouble, and the peeling strength can be increased. Therefore, it is possible to miniaturize the inner leads and meet the demand for a large number of pins. it can.

A method of manufacturing a lead frame according to claim 2 is
The first metal layer is reverse-sputtered before the formation of the second metal layer. Therefore, claim 2
According to the method for manufacturing a lead frame described above, since the surface is reverse-sputtered after the first metal layer is formed, this surface is cleaned. Therefore, the adhesion of the second metal layer formed thereafter with the first metal layer can be enhanced.

[Brief description of drawings]

1A to 1C are cross-sectional views showing a main part of one embodiment of a method for manufacturing a lead frame according to the present invention in the order of steps.

2A to 2C are cross-sectional views showing an example of a bump forming method in the order of steps.

3A to 3E are cross-sectional views showing an example of a method of manufacturing a lead frame in process order.

4A to 4C are cross-sectional views showing a conventional example of a method for forming a lead frame material in the order of steps.

[Explanation of symbols]

 1 1st metal layer (Cu) 2 2nd metal layer (Al) 3 3rd metal layer (Cu) 4 Etching stopper

Claims (2)

[Claims] 1. A second metal layer serving as an etching stopper is provided on one surface of a first metal layer that serves as an outer lead, and a second metal layer that serves as an etching stopper is provided on a surface of the second metal layer opposite to the first metal layer. An outer lead is formed by patterning the metal layer to be the outer lead, and an inner lead is formed by patterning the metal layer to be the inner lead, using a lead frame material having a third metal layer to be the inner lead. In the method of manufacturing a lead frame, wherein an unnecessary portion of the second metal layer is removed by etching using the outer lead and the inner lead as a mask, the lead frame is physically formed on one surface of the first metal layer as a base material. The second metal layer is formed by the physical vapor deposition method, and then the third metal layer is formed on the surface opposite to the second first metal layer by the physical vapor deposition method. Method for fabricating a lead frame, characterized in that to make by 2. The method of manufacturing a lead frame according to claim 1, further comprising a step of reverse-sputtering the surface of the first metal layer on the side where the second metal layer is formed before forming the second metal layer. Method