JP2867903B2 - Lead frame manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates mainly to a method for manufacturing a lead frame in which an inner lead is connected to an end of the outer lead via an etching stop made of another metal material.

[0002]

2. Description of the Related Art As a lead frame, for example, as shown in FIG. 2, an outer lead 1 made of copper, an etching stop portion 2 made of aluminum formed on a base surface thereof, and a copper connected to the etching stop portion 2 are formed. And a thin inner lead 3 made of aluminum and a bump 4 made of aluminum or the like formed at the tip of the inner lead 3 are known. This lead frame is usually used by bonding to the electrode pads 6 of the semiconductor chip 5 via the bumps 4 and sealing the semiconductor chip 5 with a sealing resin 7.

In manufacturing such a lead frame, conventionally, as shown in FIG. 3, a thick outer lead copper layer 8 and an etching stop aluminum layer 9 are formed.
A method is known in which a three-layered clad material 11 in which a thin copper layer 10 for an inner lead is laminated with a thin layer is used and etched. That is, the lead frame is manufactured by selectively etching the outer lead copper layer 8 and then selectively etching the inner lead copper layer 10 with respect to the clad material 11. By providing the etching stop aluminum layer 9 in this manufacturing, the erosion of the outer leads due to the etching for the inner leads and the erosion of the inner leads due to the etching for the outer leads are respectively prevented.

However, in such a conventional lead frame, the patterning of the outer lead 1 has to be formed by one-sided etching in manufacturing, so that an increase in the amount of side etching cannot be avoided. Therefore, there is a problem that the fine pitch of each lead is limited, and the demand for ultra-high integration cannot be sufficiently satisfied. In recent years, in order to solve such a problem, the inner lead copper layer 10 of the clad material 11 is not etched to directly form the inner leads 3. There is provided a method of forming an inner lead by plating copper on the inner lead.

[0005]

However, in the method of forming an inner lead by further plating copper on the inner lead copper layer 10 as described above, the copper layer 10 is formed after the inner lead is formed by plating. In this case, it is necessary to etch only the copper layer 10 while leaving the inner lead made of the same copper. In order to perform such delicate etching, an expensive expensive dedicated etching agent (for example, a mixed solution of hydrogen peroxide, sulfuric acid, and hydrofluoric acid) is used.
Is required, which results in an increase in cost. Moreover, even if such a soft etching agent is used, it is difficult to control the conditions of the etching process, for example, the etching rate, and if the control is insufficient, even the inner leads may be etched, so that the quality stability may be reduced. At present, this is not a sufficient method.

Further, since such a soft etching process is difficult to control, a sufficient precision is required for the thickness of the copper layer 10 which greatly affects the process, and as a result, the production of a lead frame is required. The whole method is quite difficult. The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a method for manufacturing a lead frame which is easy in process control, and is therefore excellent in quality stability, cost reduction, and the like. .

[0007]

According to the method for manufacturing a lead frame of the present invention, a plate-shaped metal base, an etching stop layer formed on one surface of the metal base from a metal material different from the metal base, A method for manufacturing a lead frame using a three-layer metal material comprising a chromium layer formed on the etching stop layer, wherein a negative electrode is formed on the chromium layer of the three-layer metal material with respect to a lead to be formed. A step of forming a plating resist layer having a pattern, a step of forming leads by plating copper on the chromium layer of the three-layer metal material using the plating resist layer as a mask, and a step of forming the leads of the metal base. A step of etching the back side of the provided region by etching, a step of etching the etching stop layer, and a step of removing the chromium layer. It was solutions of the object to. Preferably, the step of forming a lead by plating is performed such that the base end of the lead is connected to the surface of the metal base.

[0008]

According to the lead frame manufacturing method of the present invention,
Using a three-layer metal material consisting of a metal base, an etching stop layer, and a chromium layer, plating the copper on the metal base using the plating resist layer as a mask to form the lead on the etching stop layer. When the chromium layer is removed, since the material of the chromium layer is different from that of the copper forming the leads, the management becomes easier as compared with the case where these are made of the same material, and there is no possibility that the leads are removed at the same time.

Further, when forming a lead, the base end of the lead is connected to the surface of the metal base, and this connecting portion is formed as a part of another lead, so that another lead is formed. For example, since the other lead and the lead are directly connected to each other, the bonding strength between them is increased, and no potential difference is generated between them. Therefore, when a semiconductor chip is mounted on this lead frame, sealed with a resin, and used as an IC, even if moisture infiltrates into the sealing resin due to aging, etching stops with the lead or another lead. A local cell is formed between the etching stop portion and the portion, thereby preventing inconvenience such as accelerated corrosion of the etching stop portion.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a lead frame according to the present invention will be described below in detail with reference to the drawings. First, prior to manufacturing,
As shown in the partial cross-sectional view of FIG. 1A, a three-layer clad material 20 which is a three-layer metal material in the present invention is prepared. The three-layer clad material 20 includes a plate-shaped metal base 21 made of a copper alloy or a 42 alloy, an etching stop layer 22 formed on one surface of the metal base 21, and formed on the etching stop layer 22. And a metal base 2 formed by dry plating.
1 is vapor-deposited on aluminum (Al) to form an etching stop layer 22, on which chromium (C) is further deposited.
r) is obtained by vapor deposition to form the chromium layer 23.

Here, the metal base 21 is 150 μm.
An alloy material having a thickness of about m and a predetermined dimension is used. Also,
The etching stop layer 22 has a thickness of 1.0 to 3.0.
μm, and the chrome layer 23 has a thickness of 0.0
The thickness is about 5 to 0.2 μm. The etching stop layer 22 and the chromium layer 23 are formed only in a predetermined region on the metal base 21, that is, in a portion corresponding to a region where the inner lead is formed. Is composed of only the metal base 21.

When such a three-layer clad material 20 is prepared, a plating resist layer (not shown) having a negative pattern with respect to the inner lead to be formed is formed on the inner lead forming portion on the chromium layer 23. For the formation of the resist pattern, for example, an electrodeposition resist (oligo EC-UV manufactured by Nippon Chemical Oil Co., Ltd.) is used as the resist material, and the coating thickness is set to about 10 to 30 μm. Further, the amount of exposure at the time of exposure in patterning is about 150 to 400 mj / cm ^2, and the spraying method using, for example, a 1% Na ₂ CO ₃ solution (45 ° C.) is used for development.

After completion of the development, the surface of the chromium layer 23 is subjected to acidic degreasing, activated with sulfuric acid or the like, if necessary, and then plated with copper sulfate as shown in FIG.
Are formed on the chromium layer 23 on the surface of the etching stop layer 22 as shown in FIG. For copper sulfate plating, specifically, CuSO ₄
0 g / l, 200 g / l of H ₂ SO _4, 50 ppm of Cl ⁻ ion, and a current density of 1.0 to 4.0 A
/ Dm ² for electroplating. The inner leads 24 formed in this manner have a line width of about 30 μm and an interval between the leads of about 30 μm. Here, each inner lead 24 is shown in FIG.
As shown in FIG. 3B, the base end protrudes outward from the chromium layer 23 (that is, the etching stop layer 22) and is directly bonded to the metal base 21.

After forming the inner leads 24 in this manner, the plating resist layer is removed, and a reinforcing tape (not shown) is adhered to the surface of the inner leads 24 in a direction intersecting with the inner leads 24 if necessary. Then, the inner leads 24 are reinforced.

Next, a resist pattern (not shown) is formed on the back surface of the metal base 21, that is, on the surface opposite to the side on which the inner leads 24 are formed, and the metal base 21 is etched using the resist pattern as a mask. Thus, the outer leads 25 are formed as shown in FIG. At the same time, the metal base 21 is also etched away on the back side A where the inner leads 24 have been previously formed. At this time, the inner leads 24 ...
Are formed on the back side of the chrome layer 23 and the etching stop layer 22 made of aluminum, so that the inner leads 24 are protected without being damaged by the etching process.

As for the etching at the portion A on the back side of the inner leads 24..., Not all the portions corresponding to the etching stop layer 22 formed thereon are removed, but the outer peripheral portion of the etching stop layer 22. Is performed so as to leave a portion corresponding to the predetermined width as it is. Therefore, the patterns of the outer leads 25 are formed such that the portions corresponding to the remaining portions of the etching stop layer 22 are part of the outer leads 25.

Next, after the metal base 21 is removed by etching in this manner, the etching stop layer 22 exposed on the back side A of the location where the inner lead is formed is removed by etching. This etching must naturally be performed so as to erode aluminum and not erode the outer lead 25 and the inner lead 24. For example, when performing wet etching, a phosphoric acid-based etchant is used. When dry etching is performed, BCl ₃ (40 SCCM) + Cl ₂ is used as an etching gas.
(100 SCCM) + He or N ₂ (1500 SCC
M), RF power is 220W, pressure is 1340P
a, table temperature 5 ° C., etching rate 7 μm / 240
This is performed by reactive ion etching under conditions such as sec. When the etching stop layer 22 is etched in this manner, the metal base 21 remains without being removed at a predetermined portion of the outer peripheral portion corresponding to a portion where the metal base 21 remains without being removed as described above. The remaining portion becomes the etching stop portion 2 shown in FIG.

Thereafter, the chromium layer 23 exposed on the side opposite to the inner leads 24... Due to the removal of the etching stop layer 22 is removed by treatment with an appropriate concentration of hydrochloric acid. 24, 24 are completely separated. (Of course, after resin sealing, the diver portion 25a of the outer lead 25 is short-circuited until the unnecessary portion of the outer lead is cut.) Then, each inner lead 24 is formed by aluminum sputtering, photoetching or the like. A bump (not shown) is formed on the surface of the front end of the lead frame to obtain a lead frame having a configuration as shown in FIG.

In such a method of manufacturing a lead frame, a three-layer clad material 20 composed of a metal base 21, an etching stop layer 22, and a chromium layer 23 is used, and a plating resist layer is used as a mask on the metal base 21. Since the inner leads 24 are formed on the etching stop layer 22 by plating copper, when the chromium layer 23 is removed after the inner leads are formed, the chromium layer 23 is made of the same material as copper forming the inner leads 24. The difference makes the management easier. That is, for example, when these are made of the same material as in the related art, it is necessary to use a special soap etching agent, and it is necessary to sufficiently control the etching rate. The chromium layer 23 can be removed only by treatment with hydrochloric acid, as compared with the case where sufficient control of the film thickness of the copper layer 10 shown is required, and the inner leads 24 made of copper are used in this hydrochloric acid treatment. Is not removed, so that process control becomes extremely easy.

Since the inner leads 24 are formed so that the base ends of the inner leads 24 are in contact with the metal base 21, the obtained lead frame is made of the outer leads 2.
5 and the inner leads 24 are directly connected. Accordingly, in this lead frame, the bonding strength between the outer leads 25 and the inner leads 24 is increased, and a potential difference is not generated between them. Therefore, a semiconductor chip is mounted on the lead frame. When used as an IC after being sealed with a resin, even if moisture penetrates into the sealing resin due to aging, even if moisture enters the sealing resin, the inner leads 24 and the outer leads 25 and the etching stop portion (etching stop layer 22) may not be connected. A local battery is formed in between, thereby preventing the disadvantage that corrosion of the etching stop portion is promoted.

[0021]

As described above, the method for manufacturing a lead frame according to the present invention uses a three-layer metal material consisting of a metal base, an etching stop layer and a chromium layer, and forms a copper layer on the metal base by using a plating resist layer as a mask. Since the lead is formed on the etching stop layer by plating, when the chromium layer is removed after the lead is formed, the chromium layer is made of the same material as that of the copper forming the lead. In this case, the management is easier than in the case of (1), and there is no danger of removing the leads at the same time.

That is, since it is not necessary to use a dedicated and expensive soft etching agent, the manufacturing cost can be reduced. Further, since the control of the etching rate and the control of the thickness of the chromium layer are almost unnecessary, the manufacturing cost is reduced. The process control becomes extremely easy, thereby increasing the yield of the obtained product and improving its reliability. Furthermore, the thickness of the chromium layer is made smaller than that of the conventional copper layer by using a three-layer metal material having a chromium layer formed of a different material from the lead, as compared with the conventional case using a copper layer. This makes it possible to reduce the film forming time when manufacturing a three-layer metal material.

Further, when forming the lead, the base end of the lead is connected to the surface of the metal base, and this connection part is formed as a part of another lead, so that another lead is formed. For example, since the other lead and the lead are directly connected to each other, the bonding strength between them is increased, and no potential difference is generated between them. Therefore, when a semiconductor chip is mounted on this lead frame and used as an IC after sealing with a resin, even if moisture enters the sealing resin due to aging, the lead or another lead and the etching stop portion may be used. A local battery is formed during the process, thereby preventing the disadvantage that corrosion of the etching stop portion is promoted.

[Brief description of the drawings]

FIGS. 1A to 1C are manufacturing process diagrams for explaining an embodiment of a manufacturing method of the present invention.

FIG. 2 is a side sectional view showing an example of a lead frame.

FIG. 3 is a side sectional view showing an example of a conventional three-layer clad.

[Explanation of symbols]

 Reference Signs List 20 three-layer clad material 21 metal base 22 etching stop layer 23 chromium layer 24 inner lead 25 outer lead

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 23/50

Claims (2)

(57) [Claims] 1. A plate-shaped metal base, an etching stop layer formed on one surface of the metal base from a metal material different from the metal base, and a chromium layer formed on the etching stop layer. A method for manufacturing a lead frame using a three-layer metal material, comprising: forming a plating resist layer having a negative pattern on a lead to be formed on the chromium layer of the three-layer metal material; A step of forming leads by plating copper on the chromium layer of the three-layer metal material using the plating resist layer as a mask, and a step of etching away the back side of a region where the leads of the metal base are provided. A step of etching the etching stop layer; and a step of removing the chromium layer. 2. The method of manufacturing a lead frame according to claim 1, wherein the step of forming a lead by plating is performed such that a base end of the lead is connected to the surface of the metal base. Lead frame manufacturing method.