HK1069010B

HK1069010B - Lead frame and its manufacturing method

Info

Publication number: HK1069010B
Application number: HK04110373.2A
Authority: HK
Inventors: 饭谷一则; 滨田阳一郎
Original assignee: 住友金属矿山株式会社
Priority date: 2001-07-09
Filing date: 2002-07-09
Publication date: 2007-12-07

Description

Lead frame and method of manufacturing the same

Technical Field

The present invention relates to a lead frame used in a semiconductor device and a method of manufacturing the same.

Background

Conventionally, a lead frame is formed into a predetermined shape from a metal sheet by etching or press working, after the entire surface is plated with palladium, a semiconductor element is mounted at a predetermined position, and after the semiconductor element is sealed with a resin, the semiconductor element is cut into individual pieces by a die or the like, and is put into practical use as an electronic element such as an IC chip.

In recent years, the specifications of lead frames have been limited to the use of lead-containing external tin plating in consideration of the influence on the environment, and a method of plating the entire surface of the lead frame with palladium has been adopted. However, since palladium is an expensive metal material, there is a problem that the product cost is increased by plating the entire surface with palladium.

Accordingly, a main object of the present invention is to provide an inexpensive lead frame while minimizing the amount of palladium used.

Another object of the present invention is to provide a method of manufacturing a lead frame in which malfunction is eliminated.

Disclosure of Invention

In order to achieve the above object, the present invention provides a lead frame molded from a metal sheet, characterized in that: only the minimum required portions of the semiconductor element mounting portion, the gold wire bonding portion, and the soldering portion on the substrate mounting surface side are subjected to plating including nickel plating, palladium plating, and gold plating in this order.

Further, the present invention provides a lead frame molded from a metal sheet, characterized in that: only the surface on the side where the semiconductor element is mounted and the surface on the side where the substrate is mounted are plated in this order by nickel plating, palladium plating, and gold plating, and the molded lead portion, the pad portion, and other portions and side surfaces which do not need to be mounted are not plated.

Further, the present invention provides a lead frame molded from a metal sheet, characterized in that: plating including nickel plating, palladium plating, and gold plating is performed in this order only on the surface on the semiconductor element mounting side and the surface on the substrate mounting side, and plating is not performed on the molded lead portion, the pad portion, and other portions and side surfaces that do not need to be mounted.

With this, since the area to be plated with palladium is minimized, a lead frame can be provided at a lower cost than a conventional lead frame plated with palladium on the entire surface.

Further, the present invention provides a method of manufacturing a lead frame, characterized in that: a lead frame blank is prepared by molding a metal sheet, plating including nickel plating, palladium plating, and gold plating is performed partially on the minimum required portion of a semiconductor element mounting portion of the lead frame blank, and then plating including nickel plating, palladium plating, and gold plating is performed partially on the minimum required portion of a gold wire bonding portion and a soldering portion on a substrate mounting surface side of the lead frame blank.

Further, the present invention provides a method of manufacturing a lead frame, characterized in that: a lead frame blank is prepared by molding a metal sheet, plating including nickel plating, palladium plating, and gold plating is performed in this order only on the semiconductor element mounting side surface of the lead frame blank, plating including nickel plating, palladium plating, and gold plating is performed in this order only on the substrate mounting side surface of the lead frame blank, and plating is not performed on the lead portion, the pad portion, and other portions not required to be mounted and the side surfaces of the lead frame blank.

The lead frame of the present invention is produced by preparing a metal sheet on which a lead frame is to be formed, providing photoresist layers on the front and back surfaces of the metal sheet, bringing a mask having a desired lead frame shape, for example, into close contact with the surface of the photoresist layer, exposing and developing the mask to produce a mask for plating, then plating the exposed surface of the metal sheet to provide a plating layer containing at least a palladium layer, then stripping the mask, providing photoresist layers on both front surfaces again, exposing and developing the mask with a predetermined pattern to obtain an etching mask, and then etching the etching mask to form a guide portion, a pad portion, and other shapes.

In addition, the lead frame of the present invention is manufactured by preparing a metal sheet to be formed into a lead frame, a photoresist layer is provided on the front and back surfaces of the metal sheet, a mask having a desired lead frame shape is brought into close contact with the front surface of the photoresist layer, for example, and is exposed to light and developed to produce a mask for plating, plating the exposed surface of the metal sheet to form a plating layer containing at least a palladium layer, removing the photoresist layer, etching the metal sheet using the plating layer as an etching photoresist, the etching process is stopped before the portion of the metal sheet to be etched penetrates through the etching process, the back surface of the metal sheet is protected by an adhesive tape, the etching process is performed again, the portion of the metal sheet to be etched penetrates through the etching process, and the plurality of guide portions and the like are held in independent positional relation by the adhesive tape.

In the lead frame manufacturing method of the present invention, a metal sheet for forming a lead frame is prepared, a photoresist layer is provided on the front and back surfaces of the metal sheet, a mask having a desired lead frame shape is brought into close contact with the front surface of the photoresist layer, for example, and exposed to light and developed to form an etching mask, and then the exposed portion of the metal sheet is etched away to form a lead frame shape, and then the front and back surfaces are plated to provide a plating layer containing at least a palladium layer.

In the lead frame manufacturing method of the present invention, a metal sheet for forming a lead frame is prepared, a photoresist layer is provided on the front and back surfaces of the metal sheet, a mask having a desired lead frame shape is brought into close contact with the surface of the photoresist layer, for example, and exposed to light and developed to prepare a mask for plating, and then the surface of the exposed metal sheet is plated, and the plated layer is used to etch the photoresist-etched metal sheet to form a plurality of lead portions, pad portions, and other shapes.

With the above method, not only can a lead frame which is less expensive than the conventional lead frame plated with palladium over the entire surface be provided, but also a lead frame which is: when a semiconductor element is mounted on a predetermined position of a lead frame and resin-sealed, and then cut into individual pieces by dicing technology, the metal portion to be cut is dissolved by etching treatment, and therefore, only the resin is cut, and thus, failures such as shortage of leads and breakage of the resin do not occur as in the conventional lead frame.

Other objects, features and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.

Drawings

Fig. 1 is a process diagram showing an embodiment of a method for manufacturing a lead frame according to the present invention.

Fig. 2 is a process diagram showing another embodiment of the method for manufacturing a lead frame according to the present invention.

Fig. 3 is a process diagram showing still another embodiment of the method for manufacturing a lead frame according to the present invention.

Fig. 4 is a process diagram showing still another embodiment of the method for manufacturing a lead frame according to the present invention.

Detailed Description

(example 1)

Fig. 1 is a process diagram showing an embodiment of a method for manufacturing a lead frame according to the present invention. In the figure, 1 is a metal sheet such as a copper sheet used to form a lead frame; 2 is a dry film provided on the front and back surfaces of the metal sheet 1; 3 is a glass mask formed by covering the dry film 2 provided on the surface of the metal sheet 1 and forming a lead frame pattern 3a with a light-shielding agent; 4 is a glass mask formed by covering the dry film 2 provided on the back surface of the metal sheet 1, sandwiching the metal sheet 1, and forming lead frame patterns 4a with a light-shading agent symmetrically to the lead frame patterns 3 a; 5. 6 is a glass mask formed with a desired light-shielding pattern; reference numeral 7 denotes a plurality of etching liquid ejecting nozzles which are provided to face each other with the metal sheet 1 interposed therebetween.

Next, the lead frame manufacturing process will be described in order. First, as shown in fig. 1(a), a dry film 2 functioning as a photoresist is provided on the entire surface of the front and back surfaces of a metal sheet 1, and then, in a state where patterns are aligned, glass masks 3 and 4 having lead frame patterns 3a and 4a are covered on the front and back surfaces, and both surfaces are exposed to ultraviolet light through the glass masks 3 and 4.

After exposure, the glass masks 3 and 4 are removed and the metal sheet 1 with the dry film is immersed in a developing solution to be developed, so that only the dry film 2 of the portion to be plated with palladium, such as the gold wire bonding portion or the semiconductor element mounting portion, which is the portion irradiated with ultraviolet light, can be removed as shown in fig. 1 (b).

Next, the resultant is placed in a plating bath, and as shown in fig. 1(c) in an enlarged manner, plating of nickel (Ni), palladium (Pd), gold (Au), and the like is performed on necessary portions in this order. By peeling off the dry film 2 in this manner, the metal piece 1 with the plated layer 1a having the cross-sectional shape shown in fig. 1(d) can be obtained.

The metal sheet 1 with the plating layer 1a thus obtained was provided with a dry film 2 again on the entire surface and back surface thereof, and as shown in fig. 1(e), patterned glass masks 5 and 6 were covered thereon so that only the portions having been subjected to plating were shielded from light, and both surfaces thereof were exposed again with ultraviolet light. Then, development was performed in the same manner as in the case illustrated in fig. 1(b), to obtain a metal sheet 1 with a plated layer 1a having a cross-sectional shape as illustrated in fig. 1 (f).

As shown in fig. 1(g), an etching solution is sprayed on both surfaces of the metal sheet 1 having the plating layer 1a by means of a spray nozzle 7 to perform an etching process. By removing the metal of the non-plated portion by dissolution by this etching treatment and finally peeling off the dry film 2, a lead frame having a cross-sectional shape as shown in fig. 1(h), that is, a frame having only a minimum necessary portion plated can be obtained.

The steps of fig. 1(a) to 1(h) are continuously performed by conveying a metal sheet having a length corresponding to the number of frames including the lead frame by an appropriate conveyor belt, and the lead frame is cut at the end of the step to complete each lead frame. As a result, it was found that each lead frame was plated with palladium only at necessary portions on the front and back surfaces.

(example 2)

Fig. 2 is a process diagram showing another embodiment of the method for manufacturing a lead frame according to the present invention. In this figure, substantially the same members and portions as those used in fig. 1 are given the same reference numerals, and the description thereof is omitted. As is clear from comparison with fig. 1, the respective steps shown in fig. 2(a), (b), (c), and (d) are the same as those in fig. 1, and therefore, the description thereof will be omitted, and the steps shown in fig. 2(e) and thereafter will be described.

As shown in fig. 2(e), etching is performed by spraying an etching solution to both surfaces of the metal sheet 1 having the plating layer 1a through a nozzle 7. The etching treatment is performed until the metal in the non-plated portion is almost completely dissolved and removed to make the metal extremely thin.

After the tape 8 is attached to the entire surface of the metal piece 1 with the plating layer 1a obtained as described above as shown in fig. 2(f), the etching treatment is performed by spraying the etching solution again through the nozzle 7 from the side to which the tape 8 is not attached as shown in fig. 2(g), and the metal portion which is extremely thin and is not subjected to the plating (unnecessary portion to be cut after the assembly, such as a tie bar or a flying lead portion of a connecting lead portion) is completely dissolved and removed. In this case, the remaining metal portion to be plated, that is, the necessary portion such as a pad portion or a lead portion to which the semiconductor element is to be mounted, is reliably held by the tape 8 as shown in fig. 2(h) without destroying the relative positional relationship thereof.

(example 3)

Fig. 3 is a process diagram showing still another embodiment of the method for manufacturing a lead frame according to the present invention. In this figure, substantially the same members or portions as those used in fig. 1 are given the same reference numerals, and the description thereof is omitted. As is clear from comparison with fig. 1, the respective steps shown in fig. 3(a) and 3(b) are the same as those related to fig. 1, and therefore, the steps shown in fig. 3(c) and thereafter will be described.

As shown in fig. 3(c), etching is performed by spraying an etching solution through the spray nozzle 7 onto both surfaces of the metal sheet 1 on which the dry film 2 remains corresponding to the lead frame pattern. The etching process is performed to dissolve and remove the metal in the portion where the dry film 2 is not present, until the metal sheet 1 is opened as shown in fig. 3 (d). The dry film 2 is peeled from both surfaces of the metal sheet 1 thus opened, and a lead frame blank having a cross section as shown in fig. 3(d) can be manufactured.

The necessary portions of the front and back surfaces of the thus obtained lead frame blank (metal sheet 1) are plated with nickel (Ni), palladium (Pd), and gold (Au), respectively, as shown in fig. 3(e) in an enlarged manner, thereby completing the lead frame. That is, as shown in fig. 3(f), nickel (Ni) plating is first applied as a primer to the entire front and back surfaces of the lead frame, then, as shown in fig. 3(g), palladium (Pd) plating is applied only to the minimum necessary positions of the semiconductor mounting portion, the gold wire bonding portion, and the soldering portion on the substrate mounting surface side, and finally, as shown in fig. 3(h), gold (Au) plating is applied to the entire front and back surfaces of the lead frame, thereby completing the lead frame. As described above, the lead frame can be manufactured at a low cost compared to the conventional lead frame by minimizing the use amount of expensive palladium.

(example 4)

Fig. 4 is a process diagram showing still another embodiment of the method for manufacturing a lead frame according to the present invention. In this figure, substantially the same members or portions as those used in fig. 1 are given the same reference numerals, and the description thereof is omitted. As is clear from comparison with fig. 1, the respective steps shown in fig. 4(a) to (d) are the same as those related to fig. 1, and therefore, the steps shown in fig. 4(e) and thereafter will be described.

In this example, as shown in fig. 4(e), the etching solution was sprayed from the spray nozzle 7 to both sides of the metal piece 1 after the plating treatment obtained in fig. 4(d) to obtain a product without performing the exposure and development of the 2 nd time, which is different from example 1. According to the present embodiment, a more inexpensive product can be provided.

As described above, according to the present invention, it is possible to provide a lead frame which is much less expensive than the case of using the conventional method, and which does not cause problems such as lead detachment and resin breakage.

Claims

1. A lead frame formed from sheet metal, characterized by: only the minimum required portions of the semiconductor element mounting portion, the gold wire bonding portion, and the soldering portion on the substrate mounting surface side are subjected to plating including nickel plating, palladium plating, and gold plating in this order.

2. A lead frame formed from sheet metal, characterized by: only the surface on the side where the semiconductor element is mounted and the surface on the side where the substrate is mounted are plated in this order by nickel plating, palladium plating, and gold plating, and the molded lead portion, the pad portion, and other portions and side surfaces which do not need to be mounted are not plated.

3. A lead frame formed from sheet metal, characterized by: plating including nickel plating, palladium plating, and gold plating is performed in this order only on the surface on the semiconductor element mounting side and the surface on the substrate mounting side, and plating is not performed on the molded lead portion, the pad portion, and other portions and side surfaces that do not need to be mounted.

4. A manufacturing method of a lead frame is characterized in that: a lead frame blank is prepared by molding a metal sheet, plating including nickel plating, palladium plating, and gold plating is performed partially on the minimum required portion of a semiconductor element mounting portion of the lead frame blank, and then plating including nickel plating, palladium plating, and gold plating is performed partially on the minimum required portion of a gold wire bonding portion and a soldering portion on a substrate mounting surface side of the lead frame blank.

5. A manufacturing method of a lead frame is characterized in that: a lead frame blank is prepared by molding a metal sheet, plating including nickel plating, palladium plating, and gold plating is performed in this order only on the semiconductor element mounting side surface of the lead frame blank, plating including nickel plating, palladium plating, and gold plating is performed in this order only on the substrate mounting side surface of the lead frame blank, and plating is not performed on the lead portion, the pad portion, and other portions not required to be mounted and the side surfaces of the lead frame blank.

6. A manufacturing method of a lead frame is characterized in that: a lead frame blank is prepared by molding a metal sheet, plating including nickel plating, palladium plating, and gold plating is performed in this order only on the minimum necessary portion of the surface of the lead frame blank on the semiconductor element mounting side, plating including nickel plating, palladium plating, and gold plating is performed in this order only on the minimum necessary portion of the surface of the lead frame blank on the substrate mounting side, and plating is not performed on the lead portion, the pad portion, and other portions not required to be mounted and the side surfaces of the lead frame blank.