JP5787319B2 - Lead frame manufacturing mask and lead frame manufacturing method using the same - Google Patents

Description

  The present invention relates to a method of manufacturing a lead frame that supports and fixes a semiconductor element and enables electrical connection with external wiring in a semiconductor package.

  One of semiconductor component mounting parts is a lead frame. The lead frame mainly includes a die portion for mounting a semiconductor element, an inner lead portion for enabling electrical connection between an electrode portion provided on the surface of the semiconductor element and an external wiring, and the lead frame as a circuit board. It is comprised from the outer lead part for joining.

  As electronic devices become smaller, a lead frame having a high density in which the width of the inner lead with respect to the lead frame and the interval between adjacent inner leads is extremely narrow has been demanded. An etching method is frequently used as a processing method for obtaining such a high-density lead frame.

  For example, a photosensitive resist layer is provided on the surface of the lead frame material, a mask having a desired pattern is closely contacted with the resist layer, exposed, developed to obtain an etching mask, and then the exposed material portion is removed. Etching is then performed, the remaining etching mask is removed, and plating is performed on the necessary portions to obtain a lead frame. The plating applied at this time is performed in order of nickel plating, palladium plating, and gold plating when the material is copper in consideration of obtaining good wire bonding properties.

  Incidentally, one of such lead frames is a BCC lead frame. In this lead frame for BCC, a recess for forming the electrode part and the die part is provided in the lead frame material by the etching method as described above, and then the lead is provided at a necessary part including the concave electrode part and the concave die part. A plating layer having a melting property different from that of the frame material is provided.

  When using this lead frame, a semiconductor element is mounted in the concave die part, the electrode part on the surface of the semiconductor element and the concave inner surface of the concave electrode part of the lead frame are wire-bonded, and then resin-sealed, and then for the lead frame Dissolve and remove the material. Therefore, a package using a BCC lead frame can be made smaller in package size than other packages.

  In such a BCC lead frame, when both the concave portion and the flat portion are provided in the die portion, the flat portion other than the concave portion may be plated. In such a case, the resist layer used as the etching mask cannot be used as it is as the plating mask. After removing the resist layer once, the resist layer is provided again, and exposure and development are performed using a desired mask. It is necessary to obtain a plating mask, apply plating using this plating mask, and then remove the plating mask. For this reason, the lead frame for BCC is inevitably more expensive than other packages, and is difficult to be used in a wide range while having an advantage in package size.

  On the other hand, Japanese Patent No. 4457532 discloses a technique for solving the above problem by dividing the degree of exposure in stages. Specifically, when a positive resist is used as the resist layer, light is transmitted through the portion corresponding to the etched portion, light is transmitted through the portion corresponding to the plated portion other than the etched portion, and the other portions. Then, when using an exposure mask formed so that light is shielded, or when using a negative photoresist as a resist layer, light is shielded at a portion corresponding to the etched portion, and other than the etched portion. A manufacturing method is described in which plating is partially performed using an exposure mask formed so that light is partially transmitted through a portion corresponding to the plating portion and light is transmitted through other portions.

  Specifically, using such an exposure mask, the resist layer is exposed and developed for the first time, thereby opening a portion corresponding to the etched portion of the resist layer, and using the etching mask. Form and etch the material to form the required shape (lead frame contour). Next, a second development is performed on the etching mask, and a portion corresponding to the plating portion of the etching mask is opened to form a plating mask, thereby plating a desired portion of the material. It is possible to apply.

  However, in this technique, when a lead frame is manufactured by etching a metal plate, if an attempt is made to plate a necessary portion, it is formed on the surface of the lead frame material (1) as shown in FIG. An overhang portion (8) occurs in the etching resist layer (2). For this reason, the resist layer (2) is peeled off from the overhang portion (8) as a starting point, or the peeled resist layer falls in the plating solution. Problems such as adhesion of foreign matter to the surface occur (see FIGS. 4D and 4E), and there is a problem that the yield or operating rate is reduced.

Japanese Patent No. 4457532

  The present invention solves the above problems by eliminating the state of the overhang portion of the resist layer for etching, and provides a high quality partial plating at a desired position on a lead frame formed by penetrating a metal plate. Another object of the present invention is to provide a lead frame manufacturing mask that can be formed at low cost, and a lead frame manufacturing method using the same.

The mask for manufacturing a lead frame according to the present invention is composed of an exposed resist layer formed on the surface of a lead frame material, dissolved and removed by the first development, and a second development. by comprising a second removal portion has dissolved, and the first and the second remaining portion which is not dissolved and removed by development, a.

The first removal portion is formed in a portion corresponding to the etching portion of the lead frame material, and an etching mask is formed by dissolving and removing the first removal portion.

The second removal portion is formed in a portion corresponding to a portion where the lead frame material is plated, and the plating mask is formed by dissolving and removing the second removal portion.

The second removal unit is formed along the contour of the lead frame formed by etching the etched portion. For this reason, of the remaining portion, the overhang portion protruding from the contour loses its support and is separated and removed when the second removal portion is dissolved and removed by the second development.

The method for manufacturing a lead frame according to the present invention includes a step of forming the lead frame manufacturing mask on the surface of the lead frame material, a first development, and an etching process by dissolving and removing the first removal portion. Forming a lead mask, etching the lead frame material to form the lead frame, performing a second development, dissolving and removing the second removal portion, and overhanging the portion. And a step of forming a plating mask by separating and removing.

  It is preferable that the method further includes a step of plating the surface of the lead frame material corresponding to the opening of the resist layer after the second development.

  According to the present invention, plating leakage due to chipping of the overhang portion of the plating mask (resist chipping) that occurs when plating is performed (plating formation on unnecessary portions) and chipped resist pieces adhere to the portions where plating is formed. It is possible to eliminate the defect of lack of plating due to the above and to manufacture a lead frame with a high yield.

These are the figure which represented typically the (a) top view which shows the state which formed the mask for lead frame manufacture based on this invention in the raw material for lead frames, and the AA cross section of (b) (a). . FIG. 2 schematically shows a state of the lead frame and the etching mask after etching in the manufacturing method of the present invention, (a) a plan view, and (b) a cross section along BB in (a). It is an enlarged view of the C part of a figure and (c) (b). FIG. 3 is a diagram schematically showing a cross section of a lead frame material (lead frame) and a lead frame manufacturing mask (etching mask, plating mask) in each step of the lead frame manufacturing method of the present invention. It is. FIG. 4 is a diagram schematically showing a cross section of a lead frame material (lead frame) and a lead frame manufacturing mask (etching mask, plating mask) in each step of a conventional lead frame manufacturing method. It is.

  Hereinafter, the lead frame manufacturing mask of the present invention and a method of manufacturing a lead frame using the mask will be described in detail.

(1) Leadframe Manufacturing Mask The leadframe manufacturing mask of the present invention comprises a resist layer (2) formed on the surface of a leadframe material (1) as shown in FIG. a first removing unit that is by the development dissolved away (3), and the second removal unit that is dissolved and removed by development for the second time (4, 4a), is not dissolved and removed by development of the first round and second round And a remaining portion (5).

Since the first removal portion (3) is formed in the portion corresponding to the etching portion of the lead frame material, the first removal portion (3) is dissolved and removed by the first development, so that the etching is performed. A mask is formed.

Since the second removal portion (4, 4a) is formed in the portion (4) corresponding to the portion where the lead frame material is plated, the second removal portion (4, 4a) is formed in the second development . By dissolving and removing 4a), a plating mask constituted by the remaining portion (5) is formed.

In particular, as shown in FIG. 2, in the present invention, the second removal portion (4, 4a) includes not only the portion (4) corresponding to the portion where the lead frame material is plated, but also the etching portion. It is also formed on the portion (4a) along the outline (1b ) of the lead frame (1a) formed by etching. For this reason, by dissolving and removing the second removal portion (4, 4a) in the second development, the overhang portion (8) can be separated and removed together. It is effective that the overhang part (8) peels off, or the peeled overhang part (8) becomes a resist piece and adheres to the surface to be plated, thereby causing a problem. Can be prevented. The overhang portion (8) is the portion of the resist layer (2) after etching that protrudes (overhangs) from the contour (1b) of the lead frame and the correction portion (7). 2 means a portion excluding the removal portion (4a) (see FIG. 2C).

The width of the second removal portion (4a) corresponding to the portion along the outline (1b) of the lead frame (1a) is not particularly limited, but is preferably 5 μm or more. If the width of the second removal portion (4a) is smaller than this, there is a possibility that it cannot be completely dissolved and removed during development. Further, it may be difficult to form such a pattern on the resist layer (2) in an industrial mass production process.

Moreover, in FIG. 1 and FIG. 2, although the 2nd removal part (4) is formed with respect to the whole part to plate, it is not necessary to form the 2nd removal part (4) with respect to the said part whole. Instead, for example, the remaining portion (5) may be formed in a slit shape having a width of about 5 μm in a portion excluding the outer peripheral portion of the second removal portion (4). In this case, the remaining part (5) formed in the part loses the support by the second removal part (4) by the second development, and the second removal part (4) is dissolved and removed. It will be removed.

  Further, as the photoresist for forming such a lead frame manufacturing mask, either a positive type or a negative type can be used. When a positive photoresist is used, light is transmitted through the first removal unit (3), light is transmitted through the second removal unit (4, 4a), and other portions (5, 8) are used. By exposing the resist layer (2) using an exposure mask configured to shield light, a lead frame manufacturing mask can be formed.

  On the other hand, when a negative photoresist is used as the resist layer (2), the first removal unit (3) shields light, and the second removal unit (4, 4a) transmits light semi-transparently. A lead frame manufacturing mask can be formed by exposing the resist layer (2) using an exposure mask configured to transmit light in the other portions (5, 8).

  As the exposure mask, for example, any material can be adopted as long as it has a structure capable of controlling the light transmittance to the resist layer (2) on the surface of the resist layer (2). For example, when the light is ultraviolet rays, the second removal portion (the property of making the color different and absorbing or reflecting the ultraviolet rays to the portion corresponding to the first removal portion (3) and not reaching the resist layer (2)). 4, 4a) has a property of transmitting ultraviolet light by half or a predetermined ratio with respect to the resist layer (2), and other portions (5, 8) correspond to the resist layer (2). On the other hand, a property of transmitting ultraviolet rays may be given. In general, a glass mask on which a necessary pattern is drawn with dedicated ink is used.

  In addition, as a form of the resist layer (photoresist), an alkali development type dry film mainly using an acrylic polymer can be preferably used. However, if such an alkali development type material is used, a film shape Alternatively, any liquid form can be used.

(2) Lead Frame Manufacturing Method Next, a lead frame manufacturing method using the lead frame manufacturing mask (2) will be described in detail with reference to FIG.

First, a resist layer (2) is formed on the surface of the lead frame material (1) using the positive type or negative type photoresist, and the first removal unit (3), the second removal unit (4, 4a) Using the exposure mask depicting the remaining portion (5), the resist layer (2) is exposed (see FIG. 3A). Thereafter, the exposure mask is removed, and a first development is performed on the resist layer (2) using a developing solution to dissolve and remove the first removal portion (3) of the resist layer (2). Thus, this portion is opened to form an etching mask (see FIG. 3B). Then, the etched portion (6) of the lead frame material (1) exposed by the first development is etched to form the shape of the lead frame (1a) (see FIG. 3C).

Next, a second development is performed on the resist layer (2) in the state of the etching mask, and the second removal portion (4) is dissolved and removed from the etching mask. Opening is performed to form a plating mask (see FIG. 3D). At this time, since the second removal portion (4a) formed along the contour (1b) of the lead frame (1a) whose surface is not plated is also dissolved and removed, the contour (1b) of the lead frame (1a) is removed. The overhang portion (8) along) is also separated and removed at the same time. Thereafter, using this plating mask, plating (9) is applied to the exposed surface of the lead frame material (1) (see FIG. 3E).

As described above, in the present invention, the overhang portion (8) is separated and removed during the second development, and therefore, in the subsequent steps, plating leakage caused by the overhang portion (8), mask, It is possible to solve the problem of lack of plating due to the lack of resist (resist lack) as a resist piece. In particular, according to the method of the present invention, compared with the method described in Japanese Patent No. 4457532, these problems can be effectively solved without increasing the number of steps, so that the industrial Significance is enormous. Note that unnecessary portions of the plating (9) formed on the side surface of the lead frame (1a) can be removed by performing a peeling process.

(Example)
An example of manufacturing a lead frame using a negative photoresist will be described below. When a positive type photoresist is used, a lead frame can be manufactured in the same manner except that the black and white of the exposure mask is reversed.

  As the lead frame material (1), a strip-shaped copper material having a thickness of 0.15 mm and a width of 180 mm (manufactured by Kobe Steel, Ltd .: KLF-194) was used, and a resist layer having a thickness of 25 μm was formed on both surfaces of the copper material. (Asahi Kasei E-Materials Co., Ltd. product: AQ-2558) was formed.

Next, in the exposure mask of the product pattern, as a part corresponding to the remaining part (5), a white part through which ultraviolet rays are transmitted and a part corresponding to the second removal part (4) are applied to the part to be plated with ultraviolet rays. Is provided with a gray portion that transmits 10%, and a black portion is provided as a portion corresponding to the first removal portion (3). In addition, in order to cut off the overhang portion (8) of the resist layer formed along the contour (1b) of the lead frame, a portion corresponding to the contour (1b) and a continuous portion of the overhang portion (8) As the second removal portion (4a), a black cutting line having a width of 8 μm was provided. The exposure mask was brought into close contact with the resist layer (2) formed on the surface of the lead frame material (1) and patterned by irradiating with 80 mJ / cm ² of ultraviolet rays.

Next, the resist layer (2) is immersed in a 1% sodium carbonate solution for 40 seconds, the first development is performed, the first removal portion (3) is dissolved and removed, and this portion is opened. Then, an etching mask was formed. Thereafter, the exposed copper material was etched, and the shape of the lead frame (1a) was produced. Incidentally, the development of the first round, the second removal unit set by the width of 8μm Some (4a) is to be dissolved and removed, opened by it have na (FIG. 3 (c) see ).

Furthermore, it was immersed in a 0.5% sodium hydroxide solution for 80 seconds, the second development was performed, and the portion (4) to be plated was opened. At the same time, the second removal portion (4a) functioning as a cutting line formed along the contour (1b) of the lead frame (1a) after being etched is dissolved and removed, and the etching mask overhangs. The part (8) which is present was separated and removed to form a plating mask. The second removal portion (4a) is formed at a position where the remaining portion (5) does not expose the surface of the lead frame in consideration of etching variations, etching conditions, and the etching process capability of the owned equipment. Although the length of the correction portion (7) shown in (c) is overhanging, the length is very short, so that there is no resist chipping or peeling between the second development and plating. .

  Thereafter, nickel plating having a thickness of about 1 μm is applied using this plating mask, and then a palladium plating layer having a thickness of about 0.1 μm is formed thereon, and then gold plating having a thickness of about 0.003 μm is formed. A layer was formed.

  Finally, the plating mask was removed, the plating formed on the unnecessary portion was peeled off, and cut into a predetermined length to obtain a sheet-like lead frame (1a). The lead frame thus obtained had very few defects such as lack of plating, and the yield was 90% or more.

(Comparative example)
The lead frame is the same as the embodiment except that the second removal portion (4a) along the outline (1b) of the lead frame (1a) functioning as a cutting line is not formed. A resist layer was formed on the material for use and patterned. Thereafter, in the same manner as in the example, after the first development, etching, second development, and plating treatment, the plating mask was removed, and the sheet was cut into a predetermined length. Got the lead frame. In the lead frame obtained in this manner, plating leakage due to lack of resist in the overhang portion and adhesion of foreign matters to the plated surface were observed, and the yield was about 70%.

DESCRIPTION OF SYMBOLS 1 Lead frame material 1a Lead frame 1b Lead frame outline 2 Resist layer 3 First removal part 4, 4a Second removal part 5 Remaining part 6 Etching part 7 Correction part 8 Overhang part 9 Plating

Claims (3)

A first removal portion formed of an exposed resist layer formed on the surface of the lead frame material and dissolved and removed by the first development; and a second removal portion dissolved and removed by the second development. A remaining portion that is not dissolved and removed by the first and second development,
The first removal portion is formed in a portion corresponding to the etching portion of the lead frame material,
Second removal unit, the portion corresponding to the portion where plating material for the lead frame is, and is formed along the contour of the lead frame formed by etching the etched portion,
Of the remaining portion, the overhang portion protruding from the contour is configured to be separated and removed when the second removal portion is dissolved and removed by the second development .
Mask for lead frame manufacturing. Forming a lead frame manufacturing mask according to claim 1 on a surface of the lead frame material;
Performing the first development and dissolving and removing the first removal portion to form an etching mask;
Etching the lead frame material to form the lead frame;
Performing a second development, dissolving and removing the second removal portion, and separating and removing the overhang portion , thereby forming a plating mask;
A method for manufacturing a lead frame.   The lead frame manufacturing method according to claim 2, further comprising a step of plating the surface of the lead frame material corresponding to the opening of the resist layer after the second development.