Lead frame, method for manufacturing the same and semiconductor device

A lead frame includes a lead frame body 21 having a die pad 24 to which a semiconductor chip 12 is bonded and a plurality of leads 25 arranged around the die pad 24 and made of Cu or an alloy containing Cu, and a metallic film formed on the lead frame body 21 and to connected to a metallic wire 15 connected to the electrode pad 36 of the semiconductor chip 12. The metallic film is an Ag-plated film 22 with nanoparticles 34 arranged in gaps 33 among Ag crystal grains 31.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims priority under U.S.C. §119 from Japanese Patent Application No. 2008-301976 filed on Nov. 27, 2008.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates to a lead frame, a method for manufacturing the same and a semiconductor device, and more particularly to a lead frame having an Ag film (including an Ag-plated film) formed on a lead frame body and to be connected to a metallic wire connected to an electrode pad of a semiconductor chip, a method for manufacturing the same and a semiconductor device having the same.

2. Related Art

There are some conventional semiconductor devices including a semiconductor chip, a lead frame electrically connected to the semiconductor chip through a metallic wire and a mold resin sealing the semiconductor chip (seeFIG. 1).

FIG. 1is a sectional view of a conventional semiconductor device.

Referring toFIG. 1, a conventional semiconductor device200includes a lead frame201, a semiconductor chip203and a mold resin206.

The lead frame201includes a lead frame body211and an Ag film212. The lead frame body211has a die pad214and a plurality of leads215arranged around the die pad214. The lead frame body211may be made of Cu, an alloy containing Cu or an 42 alloy. Where the lead frame body211is made of the 42 alloy, a Cu film (not shown) serving as a contact layer is formed between the Ag film212and the lead frame body211. The Cu film serves to improve the contact between the Ag film212and the lead frame body211.

The Ag film212is formed on an upper surface217A of an inner lead segment217of each the leads215. The upper surface212A of the Ag film212is connected to a metallic wire204(e.g. an Au wire) connected to the electrode pad221of the semiconductor chip203. Thus, the Ag film212is electrically connected to the semiconductor chip203. The Ag film212has high purity of Ag (99.9%). The Ag film212serves to prevent Cu contained in the lead frame body211(where the 42 alloy is used, Cu contained in the Cu film formed between the Ag film212and the lead frame body211) from being deposited onto the upper surface212A of the Ag film212. To this end, the Ag film212must be so thick that Cu is not deposited onto the upper surface212A of the Ag film212. Concretely, the thickness of the Ag film212may be e.g. 4 μm to 5 μm.

The semiconductor chip203is bonded to the upper surface214A of a die pad214using an adhesive205(e.g. Ag paste). In bonding the semiconductor chip203to the upper surface214A of the die pad214, the lead frame body211is heated (e.g. at the temperature of 175° C. to 200° C. for one hour so that the adhesive205is hardened). The semiconductor chip203has a plurality of electrode pads221. The electrode pads221each is connected to the metallic wire204. The metallic wire204is formed with the lead frame body211being heated (e.g. for 1 to 5 minutes at the temperature of 200° C. to 250° C.).

The mold resin206seals the semiconductor chip203, the metallic wire204, the die pad214, a portion of the lead215and the Ag film212. The mold resin206is hardened by heating (for 1 to 2 minutes at the temperature of 175° C. to 200° C.) (see, e.g. Patent Reference 1).[Patent Reference 1] WO00/62341

FIG. 2is a view for explaining the problem involved with the semiconductor device. Arrows inFIG. 2indicate a moving path of Cu contained in the lead215.

However, where the thickness of the Ag film212using expensive Ag is decreased (4 μm or less) in order to reduce the cost of the lead frame201, owing to the heating while the semiconductor device200is manufactured (e.g. heating in hardening the adhesive205, heating in forming the metallic wire204, and heating in hardening the mold resin206), as shown inFIG. 2, Cu contained in the lead215moves through the gaps226among Ag crystal grains225(in other words, Cu is diffused into the gap226among the Ag crystal grains225) so that it will be deposited onto the upper surface212A of the Ag film212; thus, copper oxide227will be formed on the supper surface212A of the Ag film212to deteriorate the contact with the metallic wire204. This gives rise to a problem that the metallic wire204cannot be connected to the upper surface212A of the Ag film212.

SUMMARY OF THE INVENTION

This invention has been accomplished in order to solve the problem described above. An object of this invention is to provide a lead frame capable of decreasing the thickness of an Ag film, thereby reducing the cost and surely connecting a metallic wire to the upper surface of the Ag film, a method for manufacturing the same and a semiconductor device having the same.

According to a first aspect of this invention, there is provided a lead frame including:

a lead frame body having a die pad to which a semiconductor chip is bonded and a plurality of leads arranged around the die pad and made of Cu or an alloy containing Cu, and

a metallic film formed on the lead frame body and to be connected to a metallic wire connected to the electrode pad of the semiconductor chip, wherein

the metallic film is an Ag-plated film with nanoparticles arranged in gaps among Ag crystal grains.

Besides, nanoparticles mean grains having diameter of less or equal to 5 μm.

In accordance with this invention, by employing the Ag-plated film with the carbon grains arranged in the gaps among the Ag crystal grains as the metallic film to be connected to the metallic wire connected to the electrode pad of the semiconductor chip, the carbon grains block the diffusion paths (gaps among the Ag crystal grains) of Cu. Thus, it is possible to prevent Cu contained in the lead frame body from being deposited onto the upper surface of the Ag-plated film. Accordingly, the thickness of the Ag-plated film can be decreased (e.g. 0.3 μm to 3 μm) so that the lead frame can be reduced in cost and the metallic wire can be surely connected to the upper surface of the Ag-plated film. Further, by decreasing the thickness the Ag-plated film, the Ag-plated film can be formed in a short time so that productivity of the lead frame can be improved.

According to a second aspect of this invention, there is provided a lead frame including:

a lead frame body having a die pad to which a semiconductor chip is bonded and a plurality of leads arranged around the die pad,

a Cu film formed on the lead frame body, and

a metallic film formed on the Cu film and to be connected to a metallic wire connected to the electrode pad of the semiconductor chip, wherein

the metallic film is an Ag-plated film with nanoparticles arranged in gaps among Ag crystal grains.

In accordance with this invention, by employing the Ag-plated film with the carbon grains arranged in the gaps among the Ag crystal grains as the metallic film to be connected to the metallic wire connected to the electrode pad of the semiconductor chip, the carbon grains block the diffusion paths (gaps among the Ag crystal grains) of Cu. Thus, it is possible to prevent Cu contained in the Cu film from being deposited onto the upper surface of the Ag-plated film. Accordingly, the thickness of the Ag-plated film can be decreased (e.g. 0.3 μm to 3 μm) so that the lead frame can be reduced in cost and the metallic wire can be surely connected to the upper surface of the Ag-plated film. Further, by decreasing the thickness the Ag-plated film, the Ag-plated film can be formed in a short time so that productivity of the lead frame can be improved.

According to a third aspect of this invention, there is provided the lead frame according to the first or second aspect, wherein

the diameter of each the nanoparticles is within a range from 0.01 μm to 0.5 μm.

According to a fourth aspect of this invention, there is provided a semiconductor device including:

a lead frame according to any one of the first to third aspects,

the semiconductor chip bonded to the die pad,

the metallic wire of electrically connecting the metallic film and the electrode pad, and

a mold resin of sealing a part of the leads, the semiconductor chip, the metallic wire and the Ag-plated film.

In accordance with such a configuration, the semiconductor device can be reduced in cost and improved in productivity.

According to a fifth aspect of this invention, there is provided a method for manufacturing a lead frame including: a lead frame body having a die pad to which a semiconductor chip is bonded and a plurality of leads arranged around the die pad and made of Cu or an alloy containing Cu, and a metallic film formed on the lead frame body and to be connected to a metallic wire connected to the electrode pad of the semiconductor chip,

the method including a step of:

preparing an Ag plating solution dispersed with nanoparticles each having a grain diameter of 0.01 μm to 0.5 μm

by electrolytic plating using the Ag plating solution, forming an Ag-plated film containing the carbon grains, as the metallic film, on the lead frame body of the portion corresponding to the region of forming the metallic film.

In accordance with this invention, by electrolytic plating using an Ag plating solution dispersed with carbon grains each having a grain diameter of 0.01 μm to 0.5 μm, an Ag-plated film containing the carbon grains is formed, as the metallic film, on the lead frame body of the portion corresponding to the region of forming the metallic film. Thus, the carbon grains contained in the Ag-plated film block the gaps among the Ag crystal grains which are the diffusion paths of Cu (Cu contained in the lead frame body) so that the thickness of the Ag-plated film can be decreased (e.g. 0.3 μm to 3 μm). For this reason, the lead frame can be reduced in cost and the metallic wire can be surely connected to the upper surface of the Ag-plated film. Further, by decreasing the thickness the Ag-plated film, the Ag-plated film can be formed in a short time so that productivity of the lead frame can be improved.

According to a sixth aspect of this invention, there is provided a method for manufacturing a lead frame including: a lead frame body having a die pad to which a semiconductor chip is bonded and a plurality of leads arranged around the die pad, a Cu film formed on the lead frame body, and a metallic film formed on the Cu film and to be connected to a metallic wire connected to the electrode pad of the semiconductor chip,

the method including the steps of:

by plating, forming the Cu film on the lead frame body of the portion corresponding to the region of forming the metallic film, and

by electrolytic plating using an Ag plating solution dispersed with nanoparticles each having a diameter of 0.01 μm to 0.5 μm, forming an Ag-plated film containing the nanoparticles, as the metallic film, on the Cu film.

According to a seventh aspect of this invention, there is provided the method for manufacturing a lead frame according to the fifth aspect, wherein

the Ag plating solution contains the nanoparticles by 0.1 wt % to 20 wt %.

In accordance with this invention, by electrolytic plating using an Ag plating solution dispersed with carbon grains each having a grain diameter of 0.01 μm to 0.5 μm, an Ag-plated film containing the carbon grains is formed, as the metallic film, on the Cu film. Thus, the carbon grains contained in the Ag-plated film block the gaps among the Ag crystal grains which are the diffusion paths of Cu (Cu contained in the Cu film) so that the thickness of the Ag-plated film can be decreased (e.g. 0.3 μm to 3 μm). For this reason, the lead frame can be reduced in cost and the metallic wire can be surely connected to the upper surface of the Ag-plated film. Further, by decreasing the thickness the Ag-plated film, the Ag-plated film can be formed in a short time so that productivity of the lead frame can be improved.

In accordance with this invention, by providing an Ag-plated film containing carbon grains blocking the gaps among Ag crystal grains and also decreasing the thickness of the Ag-plated film, the lead frame and semiconductor device can be reduced in cost and a metallic wire can be surely connected the upper surface of the Ag-plated film.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, referring to the drawings, an explanation will be given of an embodiment of this invention.

FIG. 3is a sectional view of a semiconductor device according to the first embodiment of this invention.

Referring toFIG. 3, a semiconductor device10according to the first embodiment includes a lead frame11, a semiconductor chip12and a mold resin13.

The lead frame11includes a lead frame body21, an Ag-plated film22containing carbon grains (hereinafter referred to as an Ag-plated film22). The lead frame body21includes a die pad24and a plurality of leads25arranged around the die pad24.

The die pad24serves to bond the semiconductor chip12and has a chip bonding surface24A to which the semiconductor chip12is bonded. The die pad24is separated from the plurality of leads25. The die pad24is square when viewed from above. The die pad24is arranged at a position lower than an inner lead segment27on the die pad24side.

The leads25each has the inner lead segment27sealed by the mold resin13and an outer lead segment28exposed from the mold resin13and formed integrally to the inner lead segment27and bended.

The lead frame21having the above configuration may be made of Cu or an alloy containing Cu.

FIG. 4is a schematic view of the Ag-plated film containing carbon grains formed on the lead frame body. InFIG. 4, like reference numerals refer to like portions in the semiconductor device10according to the first embodiment shown inFIG. 3.FIG. 4is a view schematically illustrating the observation result of the Ag-plated film22by a scanning electron microscope.

Referring toFIGS. 3 and 4, the Ag-plated film22is formed on the upper surface27A of the inner lead segment27of the portion corresponding to the region to which a metallic wire15(e.g. Au wire) is connected. The metallic wire15electrically connected to an electrode pad36of the semiconductor chip12is connected onto the upper surface22A of the Ag-plated film22. The Ag-plated film22contains carbon grains34arranged so as to the gaps33among the Ag crystal grains31(paths of diffusing Cu contained in the lead frame body21. The carbon grains34each has a diameter enough to be arranged among the crystal grains33. Concretely, the gain diameter of each the carbon grains34may be 0.01 μm to 5 μm, preferably 0.01 μm to 0.5 μm. The content of the carbon grains34contained in the Ag-plated film22can be appropriately selected within the range of 0.1 wt % to 10 wt %, preferably 1 wt % to 3 wt %. The carbon grain34may be e.g. carbon black. The thickness A of the Ag-plated film22may be e.g. 0.3 μm to 3 μm.

In this way, by employing the Ag-plated film22with the carbon grains34arranged in the gaps33among the Ag crystal grains31as the metallic film to be connected to the metallic wire15(e.g. Au wire) connected to the electrode pad36of the semiconductor chip12, the carbon grains34block the diffusion paths (gaps33among the Ag crystal grains31) of Cu (Cu contained in the lead frame body21). Thus, in heating the lead frame body21while the semiconductor device10is manufactured, it is possible to prevent Cu contained in the lead frame body21from being deposited onto the upper surface22A of the Ag-plated film22. Accordingly, the thickness A of the Ag-plated film22can be decreased (e.g. 0.3 μm to 3 μm) so that the lead frame11can be reduced in cost and the metallic wire15can be surely connected to the upper surface22A of the Ag-plated film22.

Further, by decreasing the thickness the Ag-plated film22, this Ag-plated film22can be formed in a short time so that productivity of the lead frame11can be improved.

The mold resin13seals the semiconductor chip12, metallic wire15, Ag-plated film22and inner lead segment27. The material of the mold resin13may be e.g. thermosetting epoxy resin.

In accordance with the lead frame according to this embodiment, by employing the Ag-plated film22with the carbon grains34arranged in the gaps33among the Ag crystal grains31as the metallic film to be connected to the metallic wire15(e.g. Au wire) connected to the electrode pad36of the semiconductor chip12, the carbon grains34block the diffusion paths (gaps33among the Ag crystal grains31) of Cu (Cu contained in the lead frame body21). Thus, in heating the lead frame body21while the semiconductor device10is manufactured, it is possible to prevent Cu contained in the lead frame body21from being deposited onto the upper surface22A of the Ag-plated film22. Accordingly, the thickness A of the Ag-plated film22can be decreased (e.g. 0.3 μm to 3 μm) so that the lead frame11can be reduced in cost and the metallic wire15can be surely connected to the upper surface22A of the Ag-plated film22.

Further, in accordance with the semiconductor device according to this embodiment, by providing the lead frame11with reduced cost and improved in productivity, the semiconductor device10can be reduced in cost and improved in productivity.

FIGS. 5 to 15are views showing the manufacturing process of the semiconductor device according to the first embodiment. InFIGS. 5 to 15, like reference symbols refer to like elements in the semiconductor device10according to the first embodiment.

Reference toFIGS. 5 to 15while explaining the method for manufacturing the semiconductor device10according to the first embodiment, the method for manufacturing the lead frame11according to this embodiment will be explained.

First, in the step shown inFIG. 5, a plate45constituting a motherboard of the lead frame body21is prepared. The material of the plate45may be e.g. Cu or an alloy containing Cu. The thickness of the plate45may be e.g. 125 μm to 150 μm.

Next, in the step shown inFIG. 6, the plate45shown inFIG. 5is stamped to form the lead frame body21having a die pad24and a plurality of leads25. In this stage, the outer lead segment28of the lead frame body21is not still bended. Further, at this stage, the die pad24is not still depressed more downward than the plurality of leads25.

Next, in the step shown inFIG. 7, the lead frame body21shown inFIG. 6is arranged within a plating device47. More specifically, with the upper surface27A of the inner lead segment27of the portion corresponding to the region of forming the Ag-plated film22being exposed, the lead frame body21as shown inFIG. 6is arranged between a plating solution supplying case51and a stage section48described later.

Now, the structure of the plating device47will be explained. The plating device47includes the stage section48and a plating solution supplying section49. The surface48A of the stage section48is a portion in contact with the lower surface of the lead frame body21shown inFIG. 6. The plating solution supplying section49includes the plating solution supplying case51, a first plating mask53, a second plating mask54and a plating solution accommodating section56.

The plating solution supplying case51has a supplying mouth (not shown) for supplying a plating solution to the plating solution accommodating section56. The first plating mask53is formed integrally to the plating solution supplying case51. The first plating mask53serves to prevent the Ag-plated film22from being formed on the plurality of leads25of the portion corresponding to the region other than the region of forming the Ag-plated film22. The lower surface53A of the first plating mask53is in contact with the upper surface of each the plurality of leads25of the portion corresponding to the region other than the region of forming the Ag-plated film22.

The second plating mask54is formed integrally to the plating solution supplying case51. The second plating mask54serves to prevent the Ag-plated film22from being formed on the chip bonding surface24A. The second plating mask54is in contact with the entire chip bonding surface24A.

Between the first plating mask53and the second plating mask54, an opening58is made to expose the upper surface27A of each the plurality of inner lead segments27of the portion corresponding to the region of forming the Ag-plated film22.

The plating solution section56serves as a space for accommodating a plating solution for forming an Ag-plated film plating solution62described later) which is supplied to the upper surface27A of each the plurality of inner lead segments27of the portion corresponding to the region of forming the Ag-plated film22via the opening58.

Next, in the step shown inFIG. 8, by electrolytic plating using the Ag plating solution62dispersed with carbon grains34each having a grain diameter of 0.01 μm to 0.5 μm in the plating solution accommodating section56, the Ag-plated film22containing the carbon grains34is formed on the upper surface27A of each the plurality of inner lead segments27of the portion corresponding to the region of forming the Ag-plated film22(In this case, minus electricity is applied to the lead frame body21).

In this way, the configuration shown inFIG. 4as described above, more specifically the Ag-plated film22with the carbon grains34arranged in the gaps33among the Ag crystal grains31is formed. Further, by executing the step shown inFIG. 8, the lead frame11with the outer lead segment28still not being bended is formed. The thickness A of the Ag-plated film22may be e.g. 0.3 μm to 3 μm.

Thus, by electrolytic plating using the Ag plating solution62dispersed with carbon grains34each having a grain diameter of 0.01 μm to 0.5 μm, the Ag-plated film22containing the carbon grains34is formed on the upper surface27A of each the plurality of inner lead segments27of the portion corresponding to the region of forming the Ag-plated film22. Thus, the carbon grains34of preventing Cu from being diffused are arranged so as to block the gaps33among the Ag crystal grains31so that the thickness of the Ag-plated film22can be decreased (e.g. 0.3 μm to 3 μm). Accordingly, the lead frame11can be reduced in cost and the metallic wire15(e.g. Au wire) can be surely connected to the upper surface22A of the Ag-plated film22. Further, by decreasing the thickness of the Ag-plated film22, this Ag-plated film22can be formed in a short time so that productivity of the lead frame11can be improved.

The Ag plating solution62is preferably an Ag plating solution dispersed with carbon black of the carbon grains34by 0.1 wt % to 20 wt % (plating solution containing silver potassium cyanide, conductive salt, silver cyanide solution). If the carbon grains34are dispersed in the Ag plating solution62by 0.1 wt % or less, the number of the carbon grains34existing in the gaps33among the Ag grains31is not enough so that Cu contained in the lead frame body21will be diffused into the gaps33among the Ag crystal grains31thereby to form copper oxide on the upper surface22A of the Ag-plated film22. On the other hand, if the carbon grains34are dispersed in the Ag plating solution62by 20 wt % or more, carbon (carbon grains34) will be deposited onto the upper surface22A of the Ag-plated film22so that its connection with the metallic wire (e.g. Au wire)15will be deteriorated.

Further, where carbon black is dispersed in the Ag plating solution62as the carbon grains34, the carbon black with high hydration not requiring a dispersing agent is preferably employed.

Additionally, in the step shown inFIG. 8, in order that the carbon grains34contained in the Ag plating solution62are distributed at a greater rate on the side of the lead frame body21, after the Ag plating solution62is prepared, the Ag-plated film22containing the carbon grains34may be formed on the upper surface27A of each the plurality of inner lead segments27of the portion corresponding to the region of forming the Ag-plated film22. More specifically, for example, in the early stage of electrolysis, with the current density being low (e.g. 10 A/dm2) the Ag-plated film containing a large amount of the carbon particles34is formed, and thereafter with the current density being high (e.g. 40 A/dm2), on the Ag-plated film containing a large amount of the carbon grains34, the Ag-plated film containing a very small amount of the carbon grains34as formed, thereby forming the Ag-plated film22including the two Ag-plated films having different contents (densities) of the carbon grains34.

Next, in the step shown inFIG. 9, the lead frame11shown inFIG. 8is taken out from the plating device47. In the step shown inFIG. 10, by stamping, the die pad24is depressed so that the die pad24is located at a lower position than the plurality of leads25.

In this way, the die pad24is located at a lower position than the plurality of leads25so that the size of the semiconductor device10can be reduced in its thickness direction.

Next, in the step shown inFIG. 11, using the adhesive16(e.g. Ag paste), the semiconductor chip12having the plurality of electrode pads36is bonded to the chip bonding surface24A of the die pad24. Where the Ag paste is employed as the adhesive16, in order to harden the resin (e.g. epoxy resin) contained in the Ag paste, the lead frame body21is heated (under the heating condition of e.g. the heating temperature of 175° C. to 200° C. and the heating time of one hour). As described above, the Ag-plated film22has a configuration in which the carbon grains34preventing Cu from being diffused are arranged in the gaps33among the Ag crystal grains31so that Cu contained in the lead frame body21will not be deposited onto the upper surface22A of the Ag-plated film22by the heating processing in the step shown inFIG. 11.

Next, in the step shown inFIG. 12, the structure shown inFIG. 11(specifically, the lead frame11with the semiconductor chip12bonded) is arranged on a heater block65. In this state, the lead frame11is heated by the heater block65(under the heating condition of e.g. the heating temperature of 200° C. to 300° C. and the heating time of 30 sec to 60 sec).

Further, by wire bonding, the metallic wire15(e.g. Au wire) to be connected to the upper surface22A of the Ag-plated film22and the electrode pad36is made. As described above, the Ag-plated film22has a configuration in which the carbon grains34preventing Cu from being diffused are arranged in the gaps33among the Ag crystal grains31so that Cu contained in the lead frame body21will not be deposited onto the upper surface22A of the Ag-plated film22by the heating processing in the step shown inFIG. 12.

Next, in the step shown inFIG. 13, after the metallic wire15is formed, the lead frame11wire-bonding connected to the semiconductor chip12is dismantled from the heater block65shown inFIG. 12.

Next, in the step shown inFIG. 14, the mold resin13is formed to seal the semiconductor chip12, metallic wire15, Ag-plated film22and inner lead segment27provided in the structure shown inFIG. 13(specifically, the lead frame11wire-bonding connected to the semiconductor chip12). The mold resin13can be formed using e.g. transfer molding. The material of the mold resin13may be e.g. thermosetting epoxy resin.

Where the material of the mold resin13is the thermosetting epoxy resin, by heating the structure shown inFIG. 14(under the heating condition of e.g. the heating temperature of 175° C. to 200° C. and the heating time of 1 to 2 minutes), the mold resin13is hardened. As described above, the Ag-plated film22has a configuration in which the carbon grains34preventing Cu from being diffused are arranged in the gaps33among the Ag crystal grains31so that Cu contained in the lead frame body21will not be deposited onto the upper surface22A of the Ag-plated film22by the heating processing in the step shown inFIG. 14.

Next, in the step shown inFIG. 15, by bending the outer lead segment28of the structure shown inFIG. 14, the semiconductor device10according to the first embodiment is manufactured.

In accordance with the method for manufacturing the lead frame according to this embodiment, by electrolytic plating using the Ag plating solution62dispersed with carbon grains34each having a grain diameter of 0.01 μm to 0.5 μm, the Ag-plated film22containing the carbon grains34is formed on the upper surface27A of each the plurality of inner lead segments27of the portion corresponding to the region of forming the Ag-plated film22. Thus, the carbon grains34of preventing Cu from being diffused are arranged to block the gaps33among the Ag crystal grains31so that the thickness A of the Ag-plated film22can be decreased (e.g. 0.3 μm to 3 μm). Accordingly, the lead frame11can be reduced in cost and the metallic wire15(e.g. Au wire) can be surely connected to the upper surface22A of the Ag-plated film22. Further, by decreasing the thickness A of the Ag-plated film22, this Ag-plated film22can be formed in a short time so that productivity of the lead frame11can be improved.

In this embodiment, the die pad24is located at a lower position than the plurality of leads25. However, also in the lead frame having the configuration in which the die pad24and plurality of leads25(plurality of leads25before bended) are flush with each other, the same advantage as in this embodiment can be obtained.

Now, an explanation will be given of an experimental result of verifying the advantage of this invention. In this experiment, the following samples 1 to 4 (samples 1 and 2 are conventional products (comparative examples) and samples 3 and 4 are samples manufactured by the manufacturing method according to this invention) are prepared. Thereafter, the detected amount of Cu in the upper surface of the Ag-plated film formed in each of these samples is evaluated by the AES (Auger Electron Spectroscopy) qualitative/quantitative analysis (under the analysis condition of the probe diameter of φ50 μm, accelerating voltage of 10 KeV and probe current of 1×10−8A) (The experimental result is shown inFIG. 16).

As the sample 1, using the Ag plating solution not containing the carbon grains34, the Ag-plated film not containing the carbon grains34and having a thickness of 1 μm is formed on the lead frame body21.

In the sample 2, using the Ag plating solution not containing the carbon grains34, the Ag-plated film not containing the carbon grains34and having a thickness of 1 μm is formed on the lead frame body21, and thereafter heated under the condition of the heating temperature of 400° C. and the heating time of one minute.

In the sample 3, using the Ag plating solution dispersed with the carbon grains34in the Ag plating solution by 1 wt %, the Ag-plated film with the carbon grains34(Ag-plated film22with the carbon grains34of preventing Cu from being diffused, arranged in the gaps33among the Ag crystal grains31) and having a thickness of 1 μm is formed on the lead frame body21is formed and thereafter heated under the condition of the heating temperature of 400° C. and the heating time of one minute.

In the sample 4, using the Ag plating solution dispersed with the carbon grains34in the Ag plating solution by 5 wt %, the Ag-plated film containing the carbon grains34(Ag-plated film22with the carbon grains34of preventing Cu from being diffused, arranged in the gaps33among the Ag crystal grains31) and having a thickness of 1 μm is formed on the lead frame body21and thereafter heated under the condition of the heating temperature of 400° C. and the heating time of one minute.

FIG. 16is a graph showing the experimental result of verifying the advantage of this invention.

From the detected amount of Cu in the samples 1 and 2 shown inFIG. 16, it can be seen that Cu is deposited onto the upper surface of the Ag-plated film not containing the carbon grains34by executing the heating processing (in this case, at 400° C. and for one minute).

From the detected amount of Cu in the samples 2 to 4 shown inFIG. 16, it can be seen that Cu is not almost deposited onto the upper surface of the Ag-plated film containing the carbon grains34(Ag-plated film22with the carbon grains34of preventing Cu from being diffused, arranged in the gaps33among the Ag crystal grains31) after the heating processing (in this case, at 400° C. and for one minute). Further, from the detected amount of Cu in the sample 3 and 4 shown inFIG. 16, it can be seen that there is no difference in the effect of preventing Cu from being diffused between the Ag-plated film formed using the Ag plating solution dispersed with the carbon grains34in the Ag plating solution by 1 wt % and the Ag-plated film formed using the Ag plating solution dispersed with the carbon grains34in the Ag plating solution by 5 wt %.

From the above experimental result, it could be confirmed that it is possible to prevent Cu contained in the lead frame body21from being deposited onto the upper surface22A of the Ag-plated film22by forming the Ag-plated film22with the carton grains34(Ag-plated film with the carbon grains34of presenting Cu from being diffused, arranged in the gaps33among the Ag crystal grains31) on the lead frame body21, using the Ag plating solution62dispersed with the carbon grains34in the Ag plating solution.

FIG. 17is a sectional view of a semiconductor device according to the second embodiment of this invention. InFIG. 17, like reference symbols refer to like parts in the semiconductor device10according to the first embodiment.

Referring toFIG. 17, a semiconductor device80according to the second embodiment is structured in the same fashion as the semiconductor10except that a lead frame81is provided in place of the lead frame11provided in the semiconductor device10according to the first embodiment.

The lead frame81is structured in the same fashion as the lead frame11except that a lead frame body83is provided in place of the lead frame body21provided in the lead frame11explained in this first embodiment and a further a Cu film84is formed.

The lead frame body83includes a die pad86having a chip bonding surface86A and a plurality of leads87arranged to surround the die pad86and each having an inner lead segment91and an outer lead segment92formed integrally thereto. The die pad86is formed in the same shape as the die pad24explained in the first embodiment. Using the adhesive16, the semiconductor chip12is bonded onto the chip bonding surface86A. The lead87is formed in the same shape as the lead25explained in the first embodiment.

The lead frame body83is made of a material different from that of the lead frame body21(specifically, Cu or Cu alloy). The material of the lead frame83may be e.g. an alloy containing very little Cu (e.g. 42 alloy).

The Cu film84is formed on the upper surface91A of the inner lead segment91at the portion corresponding to the region of forming the Ag-plated film22with the carbon grains34arranged in the gaps33among the Ag crystal grains31. On the upper surface84A of the Cu film84, the Ag-plated film22is formed. The Cu film84serves to improve the contact between the Ag-plated film22and inner lead segment91. The Cu film84may be e.g. a Cu-plated film. The Cu film84can be formed by e.g. electrolytic plating. The thickness of the Cu film84may be 0.1 μm to 0.3 μm.

In accordance with the lead frame according to this embodiment, by employing the Ag-plated film22with the carbon grains34arranged in the gaps33among the Ag crystal grains31as the metallic film to be connected to the metallic wire15connected to the electrode pad36of the semiconductor chip12, the carbon grains34block the diffusion paths (gaps33among the Ag crystal grains31) of Cu. Thus, in heating the lead frame body83while the semiconductor device80is manufactured, it is possible to prevent Cu contained in the Cu film84from being deposited onto the upper surface22A of the Ag-plated film22. Accordingly, the thickness A of the Ag-plated film22can be decreased (e.g. 0.3 μm to 3 μm) so that the lead frame81can be reduced in cost and the metallic wire15can be surely connected to the upper surface22A of the Ag-plated film22.

Further, in accordance with the semiconductor device according to this embodiment, by providing the lead frame81reduced in cost and improved in productivity, the semiconductor device80can be reduced in cost and improved in productivity.

The semiconductor device80according to this embodiment can be manufactured in the same process as in the semiconductor device10according to the first embodiment except that the step of forming the Cu film84(step of forming the Cu film84by e.g. electrolytic plating) is added between the step shown inFIG. 6and the steps of forming the Ag-plated film22, explained in the first embodiment. The Cu film84can be formed by the same technique as the steps of forming the Ag-plated film22(steps shown inFIGS. 7 to 9) explained in the first embodiment.

FIG. 18is a sectional view of a semiconductor device according to the third embodiment of this invention. In FIG.18, like reference symbols refer to like parts in the semiconductor device10according to the first embodiment.

Referring toFIG. 18, a semiconductor device100according to the third embodiment is structured in the same fashion as the semiconductor device10according to the first embodiment except that a lead frame101and a semiconductor chip103are provided in place of the lead frame11and semiconductor chip12provided in the semiconductor device10according to the first embodiment.

The lead frame101is structured in the same fashion as the lead frame11except that in the structure of the lead frame11, the Ag-plated film22(Ag-plated film with the carbon grains34arranged in the gaps33among the Ag crystal grains31) is formed to cover the upper surface of the die pad24(specifically, the chip bonding surface24A and the surface24B of the die pad24corresponding to a wire connecting region provided around the chip bonding surface24A). The upper surface22A of the Ag-plated film22at the portion provided on the surface24B of the die pad24is connected to a metallic wire105(e.g. Au wire) connected to each of electrode pads107of the semiconductor chip103.

The semiconductor chip103is structured in the same fashion as the semiconductor chip12except that the plurality of electrode pads107are further provided in the structure of the semiconductor chip12explained in the first embodiment. The electrode pads107each is connected to the metallic wire105. The electrode pads107each is electrically connected to the lead25though the metallic wire105. The semiconductor chip103having the above structure is bonded onto the Ag-plated film22formed on the chip bonding surface24A by the adhesive16.

In accordance with the lead frame according to this embodiment, by employing the Ag-plated film22with the carbon grains34arranged in the gaps33among the Ag crystal grains31as the metallic film to be connected to the metallic wire15,105(e.g. Au wire) connected to the electrode pad36of the semiconductor chip103,107of the semiconductor chip12, the carbon grains34block the diffusion paths (gaps33among the Ag crystal grains31) of Cu (Cu contained in the lead frame body21). Thus, in heating the lead frame body21while the semiconductor device100is manufactured, it is possible to prevent Cu contained in the lead frame body21from being deposited onto the upper surface22A of the Ag-plated film22. Accordingly, the thickness A of the Ag-plated film22can be decreased (e.g. 0.3 μm to 3 μm) so that the lead frame101can be reduced in cost and the metallic wire15,105can be surely connected to the upper surface22A of the Ag-plated film22.

Further, in accordance with the semiconductor device according to this embodiment, by providing the lead frame101reduced in cost and improved in productivity, the semiconductor device100can be reduced in cost and improved in productivity.

The Ag-plated film22formed in the semiconductor device100according to this embodiment can be formed by executing the same processing as the steps shown inFIGS. 7 to 9using the plating device in which the second plating mask54is excluded from the configuration of the plating device47shown inFIG. 7explained in the first embodiment.

In the semiconductor device100according to this embodiment, although the Ag-plated film22is also formed on the chip bonding surface24A, the Ag-plated film22has only to be formed in the lead frame body21at the portion corresponding to the region of forming the metallic wire15,105and the Ag-plated film22may not be formed on the chip bonding surface24A.

FIG. 19is a sectional view of a semiconductor device according to a modification of the third embodiment of this invention. InFIG. 19, like reference symbols refer to like parts in the semiconductor device100according to the third embodiment and the semiconductor device80according to the second embodiment.

Referring toFIG. 19, a semiconductor device110according to the modification of the third embodiment is structured in the same fashion as the semiconductor device100except that a lead frame111is provided in place of the lead frame101provided in the semiconductor device100according to the third embodiment.

The lead frame111is structured in the same fashion as the lead frame101except that the lead frame body83explained in the second embodiment (lead frame body made of the material containing very little Cu (e.g. 42 alloy)) is provided in place of the Lead frame body21(the lead frame body made of Cu or Cu alloy) provided in the lead frame101, and the Cu plated film84explained in the second embodiment is formed between the Ag-plated film22and the lead frame body83so as to be in contact with the Ag-plated film22and lead frame body83.

The lead frame111and semiconductor device110having the above structure can provide the same advantage as the lead frame101and semiconductor device100according to the third embodiment.

Besides, in the present invention, nanoparticles may be nanocarbon substances, carbon nanoparticles, carbon nanotube or almuna et al. in addition to carbon grains.

The detailed explanation has been hitherto made of the preferred embodiments of this invention. However, this invention should not be limited to these specific embodiments but may be modified or changed in various manners within the scope of this invention described in claims.

This invention can be applied to the lead frame provided in a lead frame body and having an Ag film (including the Ag-plated film) connected to the metallic wire connected to the electrode pad of the semiconductor chip, a method for manufacturing the same and the semiconductor device having the same.