JPH05117898A - Lead frame for mounting semiconductor chip and production thereof - Google Patents

Abstract

PURPOSE:To produce a lead frame excellent in wire bonding properties at a low cost by successively forming a primary coat of Zn and Sn, etc., an intermediate layer of Ni and the uppermost layer of Pd and Au, etc., on the lead frame main body. CONSTITUTION:A lead frame main body A is obtained by pressing Cu-Cr-Sn-Zn alloy and forming a pad part 1, inner leads 2, a dibber part 3 and outer leads 4, etc. This main body A is coated with Zn, Sn, Pb, In, Co, Cr or alloy thereof or alloy of these and Cu to form a primary coat having 0.01-0.2mum thickness. This primary coat is coated with an intermediate Ni layer having 0.05-2.0mum thickness. Furthermore this intermediate layer is coated with the uppermost layer of Pd, Au, Ag, Pt or alloy thereof having 0.01-0.2mum thickness. The coating is preferably performed by an electroplating method. Thereby the lead frame for mounting semiconductor chips is obtained which is excellent in wire bonding properties, solderability, adhesive properties of resin, corrosion resistance, adhesive properties of plating and bending properties.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor chip mounting lead frame and its manufacturing method.

[0002]

2. Description of the Related Art A lead frame used for mounting electronic parts such as transistors and ICs usually has a structure as shown in the plan view of FIG. That is, the entirety is made of metal, and a plurality of inner leads 2 are arranged around the pad portion 1 on which the semiconductor chip is mounted so as to be spaced apart from the pad portion 1.
It is connected to the outer lead 4 via.

This lead frame is usually made of Fe--Ni.
A plate material made of an alloy or Cu alloy is pressed or etched to form a lead frame main body having the shape shown in FIG. 1, and then a noble metal such as Ag is applied to the pad portion 1 and the inner lead 2 in a thickness of 3 to 5 μm. Spot plating is performed to some extent to prevent oxidation at that location.
Mounting of a semiconductor chip on this lead frame is generally
This is done as follows.

That is, as shown in FIG. 2, first, the semiconductor chip 6 is die-bonded onto the pad portion 1 using the adhesive 5. Then, the electrode pad 7 preloaded on the semiconductor chip 6 and the inner lead 2 are wire-bonded with a wire 8 made of Au, Al or Cu to electrically connect them. Then, the entire bonded portion is sealed with a sealing resin 9 such as an epoxy resin.

Then, for example, Sn-
After the Pb alloy plating is applied to improve the solderability, the diver portion 3 is cut, deburred, and the outer lead 4 is bent. The component manufactured in this manner is mounted on the printed wiring board, and the required wiring and the outer lead 4 are soldered to form a desired electronic component.

By the way, the plating treatment on the outer leads 4 is usually performed by applying hot dipping or electroplating. However, in hot-dip plating, the bath temperature is as high as 240 to 300 ° C., so when the components after mounting the semiconductor chips are immersed in the plating bath, they are subjected to a large thermal shock and the sealing resin and the lead frame body are There is a problem that a minute gap is generated between

Further, in the case of electroplating, since the plating bath used is generally alkaline or acidic, the sealing resin is partially eroded and the ions of the plating bath penetrate into the sealing resin, resulting in Corrosion of wires and electrode pads may occur. For this reason, in both the hot dipping and electroplating processes, the reliability of the obtained electronic component is likely to deteriorate.

For this reason, recently, a method has been performed in which an outer lead is electroplated with a Sn--Pb alloy in advance and a semiconductor chip is mounted on the lead frame. However, in the case of this method, Sn-Pb plated by the heat at the time of bonding which is a later step is used.
Alloy melts or leadframe body is Cu
When it is, the Sn-Pb alloy and C which are plating layers
This causes a problem that u and interdiffuse to form a compound of Sn and Cu, and as a result, the solderability of the outer leads is deteriorated.

In order to solve these problems, a lead frame in which outer leads are electroplated with Pd has been proposed (Japanese Patent Laid-Open Nos. 59-168659 and 6-59).
(See Japanese Patent Application Laid-Open No. 3-2358, Japanese Patent Application Laid-Open No. 2-42753, etc.). Since Pd is stable in the air, it is difficult to oxidize, and it hardly causes thermal diffusion with the lead frame body. Therefore, the lead frame has good wire bondability, solderability and resin adhesion. Is also good. Therefore, Ag on the pad and inner leads
Spot plating is also unnecessary, and it is also unnecessary to plate the outer lead with a Sn-Pb alloy or the like.

However, Pd is very expensive.
Therefore, from the industrial point of view, it is preferable to make the thickness of Pd plated on the lead frame body as thin as possible. Therefore, recently, a Ni plating layer is interposed between the lead frame body and the Pd plating layer as an underlayer, and the Ni plating layer prevents corrosion of the lead frame body, thereby reducing the thickness of the Pd plating layer. It is being thinned.

[0011]

By the way, in the case of the Ni plating layer, when the thickness thereof is 2 μm or more, when the bending process is performed, cracks remarkably occur in the processed portion. This is an inconvenient problem when the outer lead is bent. Therefore, the above inconvenience can be solved by thinning the Ni plating layer. However, as the thickness of the Ni plating layer becomes thinner, pinholes frequently occur in the plating layer, and the lead frame body The function of preventing the corrosion of is deteriorated. In order to completely prevent the corrosion of the lead frame body, it is necessary that the thickness of the Ni plating layer be 5 μm or more.

Therefore, it is extremely difficult to obtain a lead frame having a thin Pd plating layer and having both corrosion resistance and bending workability by simply interposing the Ni plating layer. It was The present invention solves the above-mentioned problems in conventional lead frames, has excellent bonding properties with wires, good solderability, and resin adhesion, and is a semiconductor in which cracks hardly occur during bending of outer leads. An object of the present invention is to provide a chip mounting lead frame and a manufacturing method thereof.

[0013]

In order to solve the above problems, in the present invention, a lead frame body and Zn, S formed on the lead frame body are formed.
at least one metal selected from the group consisting of n, Pb, In, Co and Cd, an alloy thereof, or the above metal and C
At least one selected from the group consisting of an underlayer of an alloy of u, an intermediate layer of Ni formed on the underlayer, and an intermediate layer of Pd, Au, Ag, Pt formed on the intermediate layer. Provided is a lead frame for mounting a semiconductor chip, which is provided with a top layer of one kind of metal or an alloy thereof, and the entire surface of the lead frame body is
An underlayer is formed by coating with at least one metal selected from the group consisting of n, Sn, Pb, In, Co, and Cd or an alloy thereof or an alloy of the above metal and Cu, and then,
The surface of the underlayer is coated with Ni to form an intermediate layer, and finally, the surface of the intermediate layer is coated with at least one metal selected from the group of Pd, Au, Ag, and Pt or alloys thereof. A method of manufacturing a lead frame for mounting a semiconductor chip is provided, which comprises forming the uppermost layer.

In the lead frame of the present invention, a base layer, an intermediate layer, and an uppermost layer, which will be described later, are sequentially formed on the entire surface of the lead frame body. The lead frame body may be made of any material that has been conventionally used, for example, Fe-42% Ni alloy or Cu-0.
3% Cr-0.25% Sn-0.2% Zn alloy etc. can be mentioned. If the surface of the lead frame body is further subjected to Cu strike plating with a thickness of about 0.02 to 0.2 μm, the adhesion with the above-mentioned underlayer can be improved.

The underlayer formed on the entire surface of the lead frame body is a metal selected from the group consisting of Zn, Sn, Pb, In, Co and Cd, an alloy thereof, or an alloy of these and Cu. Is a layer that is provided to prevent corrosion of the lead frame body,
Its thickness is preferably in the range of 0.01 to 0.2 μm.

If the thickness is less than 0.01 μm, sufficient corrosion resistance to the lead frame body cannot be ensured due to frequent occurrence of pinholes, and if it is thicker than 0.2 μm,
This is because there is no problem in terms of ensuring corrosion resistance, but the adhesiveness between the lead frame body and the intermediate layer formed on the underlayer becomes poor, and a peeling tendency tends to occur. A particularly preferred thickness is 0.05 to 0.1 μm.

The intermediate layer formed on this underlayer is Ni.
The lead frame body, together with the underlayer, prevents corrosion of the lead frame body, and the metal of the lead frame body diffuses to the uppermost layer formed on this intermediate layer due to, for example, heat during bonding. This is a layer provided to prevent This function of the intermediate layer allows the thickness of the uppermost layer to be set to 0.2 μm or less.

The thickness of the intermediate layer is preferably set in the range of 0.05 to 2.0 μm. If the thickness is thinner than 0.05 μm, sufficient corrosion resistance to the lead frame body cannot be secured, and if it is thicker than 2.0 μm, cracks will occur during bending of the outer leads. A particularly preferable thickness is 0.2 to 1.0 μm.

The uppermost layer is made of any one of Pd, Au, Ag, and Pt or alloys thereof, and suppresses oxidation of the lead frame body during storage or heating of the lead frame and bondability with wires. , A layer provided to enhance solderability and adhesion to the sealing resin. The thickness of this uppermost layer is 0.01-0.2 μm
It is preferable to set within the range. This thickness is 0.01
This is because if the thickness is less than μm, the above-mentioned function is not fully exhibited, and if the thickness is more than 0.2 μm, the overall price becomes higher than that of the conventional Ag spot plating. Particularly preferred thickness is 0.02 to 0.15μ
m.

The lead frame of the present invention can be manufactured by sequentially covering the surface of the lead frame body with an underlayer, an intermediate layer and an uppermost layer. In this case, each layer is formed by electroplating, electroless plating, or PVD.
Method, a dry plating method such as a CVD method can be applied. Among these methods, the electroplating method is suitable because it is excellent in mass productivity.

When each layer is formed of an alloy, a conventional alloy plating method may be applied, but the following thermal diffusion treatment method can also be applied. That is, a layer of each elemental metal is formed by, for example, electroplating so as to have a desired alloy composition, and then the whole is heat-treated under predetermined conditions to diffuse each elemental metal into each other. The heat treatment conditions in this case change depending on the alloy composition, but the temperature is generally 2
The temperature is from 00 to 500 ° C. and the time is from several seconds to one hour.

The thermal diffusion treatment may be performed in a predetermined heat treatment furnace after forming each single metal layer, or may be performed by heat of wire bonding when mounting a semiconductor chip.

[0023]

【Example】

Example 1 A Cu-0.3% Cr-0.25% Sn-0.2% Zn alloy strip was pressed to obtain a DIP (dual inline package) type leadframe body having the shape shown in FIG.

In this lead frame body, a bath composition: 200 g / l of first tin borofluoride, 81 g / first tin concentration
1, free boric acid 25 g / l, gelatin 6 g / l, β-naphthol 1 g / l, bath temperature: 20 ° C., current density: 1 A / dm
Electroplating was performed under the conditions of ² to form a Sn plating layer (base layer) having a thickness of 0.07 μm. Then, bath composition: nickel sulfamate 600 g / l, nickel chloride: 10 g
/ L, boric acid 40g / l, bath temperature: 60 ° C, current density: 1
A Ni plating layer (intermediate layer) having a thickness of 0.2 μm was formed on the Sn plating layer under the condition of 0 A / dm ² .

Finally, bath composition: palladium chloride 15 g /
1, ammonium chloride 30 g / l, ammonia (pH 9
Under the conditions of bath temperature: 60 ° C. and current density: 2 A / dm ^2. Pd with a thickness of 0.1 μm is formed on the Ni plating layer.
A plating layer was formed. About the obtained lead frame,
The following specifications were examined for bondability, resin adhesion, presence of cracks during bending, solderability, corrosion resistance, and plating adhesion.

Bondability: A semiconductor chip is mounted on the pad portion, and the wire diameter is 25 μm under the conditions of 280 ° C. and load of 50 g.
m Au wire was bonded, and the Au wire was subjected to a pull strength test and evaluated by the wire breakage rate (%). Resin adhesion: Shear strength was measured by thermocompression bonding with epoxy resin, and when the strength was higher than that of conventional Ag spot plating, it was evaluated as ◯.

Solderability: 3 for eutectic solder at 230 ° C
It is soaked for a second and the solder wet area at that time is measured. When this area is 95% or more, it is judged as ◯, and when it is less than 95%, it is judged as ×. Whether or not cracks occur during bending:
R: Bent to 90 ° with 0.4 mm, observe the processed part with a scanning electron microscope, and ○ when no cracks are generated.
When there is a crack, it is judged as ×.

Corrosion resistance: A 5% sodium chloride aqueous solution was sprayed on the lead frame for 24 hours, and when the rust did not occur on the lead frame body, ○, when rust occurred ×
Determined as. Plating Adhesion: When the outer lead is bent 180 ° and bent and then bent back, the case where the plating is not peeled is judged as ◯, and the case where the peeling is recognized is judged as ×. The above results are shown in Table 1.

EXAMPLE 2 An Fe-42% Ni alloy strip was subjected to an etching process, and FIG.
A DIP (dual in-line package) type lead frame body having the shape shown in FIG. In this lead frame body, bath composition: copper sulfate 210 g / l, sulfuric acid 52 g /
1, bath temperature: 30 ° C., current density: 3 A / dm ² , electroplating was performed to form a Cu plating layer (base layer) having a thickness of 0.2 μm.

Then, a zincate bath having a Zn concentration of 8 g / l and a sodium hydroxide concentration of 80 g / l (bath temperature 30 ° C.)
Was used to form a Zn plating layer (base layer) having a thickness of 0.05 μm on the Cu plating layer at a current density of 0.5 A / dm ² . Then, in the same manner as in Example 1, a Ni plating layer having a thickness of 0.2 μm and a thickness of 0.1 μm was formed on the Zn plating layer.
m Pd plating layer is sequentially formed, and finally, the whole is heat-treated at a temperature of 300 ° C. for 30 seconds in the atmosphere to obtain the C
The u-plated layer and the Zn-plated layer are subjected to thermal diffusion treatment, and then Cu-
A Zn alloy layer was formed.

With respect to the obtained lead frame, Example 1
Each property was measured in the same manner as in, and the results are shown in Table 1. Example 3 In the lead frame body used in Example 2, bath composition: sodium tin oxide 67 g / l, zinc cyanide: 10 g / l
1, sodium cyanide 25 g / l, sodium hydroxide 6 g / l, bath temperature: 65 ° C., current density: 2 A / dm ² under the condition of 0.1 μm thick Sn—Zn alloy plating layer (underlayer) did.

Then, in the same manner as in Example 1, the S
A 0.7 μm thick Ni plating layer (intermediate layer) and a 0.05 μm thick Pd plating layer (uppermost layer) were sequentially formed on the n-Zn alloy plating layer. About the obtained lead frame,
Each property was measured in the same manner as in the method of Example 1. The results are shown in Table 1.

Example 4 An Fe-42% Ni alloy strip was pressed to obtain a lead frame body having the shape shown in FIG. The thickness of the lead frame body was set to 0.
A Cu plating layer (underlayer) of 1 μm is formed, and then bath composition: cadmium oxide 25 g / l, sodium cyanide 100 g / l, bath temperature: 30 ° C., current density: 0.5 A / d
m ² above the Cu plating layer with a thickness of 0.1 μm of Cd
A plating layer (base layer) was formed.

Then, in the same manner as in Example 1, the C
A 0.3 μm-thick Ni plating layer (intermediate layer) is formed on the d plating layer, and the bath composition: potassium gold cyanide 20
g / l, potassium cyanide 10 g / l, potassium cyanide 50 g / l, titanium compound 2 g / l, bath temperature: 6
Under the condition of 0 ° C. and current density: 2 A / dm ² , an Au—Ag alloy plating layer (uppermost layer) having a thickness of 0.05 μm was formed on the Ni plating layer.

With respect to the obtained lead frame, Example 1
Each property was measured in the same manner as in, and the results are shown in Table 1. Example 5 In the lead frame body used in Example 2, bath composition: indium chloride 35 g / l, potassium cyanide: 150 g /
1, potassium hydroxide 35g / l, dextrin 35g /
1, a bath temperature: 20 ° C., and a current density: 2 A / dm ² , an In plating layer (base layer) having a thickness of 0.15 μm was formed.

Then, in the same manner as in Example 1, the I
A 0.2 μm thick Ni plating layer (intermediate layer) and a 0.1 μm thick Pd plating layer (uppermost layer) were sequentially formed on the n plating layer. Each property of the obtained lead frame was measured in the same manner as in the method of Example 1. The results are shown in Table 1.

Example 6 A Cu-0.3% Cr-0.25% Sn-0.2% Zn alloy strip was etched to obtain a leadframe body having the shape shown in FIG. In this lead frame body,
In the same manner as in, 0.05 μm thick Sn plating layer (base layer), 1.2 μm thick Ni plating layer (intermediate layer), thickness 0.1 μm.
A 1 μm Pd plating layer (uppermost layer) was sequentially formed, and then bath composition: potassium gold cyanide 10 g / l, potassium cyanide 30 g / l, potassium carbonate 30 g / l, dibasic potassium phosphate 30 g / l, bath temperature: 55 ℃, current density: 0.
An Au plating layer having a thickness of 0.02 μm was formed on the Pd plating layer under the condition of 5 A / dm ² .

Si is formed on the pad portion of the obtained lead frame.
The chip was die-bonded, and the inner lead was wire-bonded with an Au wire. After that, when the cross section of the lead frame was examined, the surface of the lead frame body was a Cu—Sn alloy layer, a Ni layer was formed thereon, and an Au—Pd alloy layer was further formed thereon.

The characteristics of this lead frame were examined in the same manner as in Example 1. The results are shown in Table 1. Example 7 In the lead frame body used in Example 2, the bath composition: basic lead carbonate 150 g / l, hydrofluoric acid 240 g / l, boric acid 105 g / l, glue 0.2 g / l, bath temperature: 20 ℃,
Current density: P of 0.15 μm thickness under the condition of ² A / dm ^2.
A b-plated layer (base layer) was formed.

Then, in the same manner as in Example 1, the P
A 0.1 μm thick Ni plating layer (intermediate layer) is formed on the b plating layer, and the bath composition: ammonium chloroplatinate 15 g / l, sodium hydroxide 20 g / l, ammonium chloride 5 g / l, quench Acid 90g / l, bath temperature: 80 ° C,
Under the condition of current density: 0.2 A / dm ² , a Pt plating layer (uppermost layer) having a thickness of 0.15 μm was formed on the Ni plating layer.

With respect to the obtained lead frame, Example 1
Each property was measured in the same manner as the method of. The results are shown in Table 1. Example 8 In the lead frame body used in Example 1, bath composition: cobalt sulfate 504 g / l, sodium chloride 17 g / l, boric acid 45 g / l, bath temperature: 20 ° C., current density: 4 A / dm.
Under the conditions of ² , a Co plating layer (underlayer) having a thickness of 0.1 μm was formed.

Then, in the same manner as in Example 1, the C
On the o plating layer, a 0.5 μm thick Ni plating layer (intermediate layer) and a 0.1 μm thick Pd plating layer (uppermost layer) were sequentially formed. Each characteristic of the obtained lead frame was measured in the same manner as in the method of Example 1. The results are shown in Table 1.

Comparative Example 1 The lead frame body of Example 1 was directly coated with a Ni plating layer having a thickness of 0.2 μm and a Pd plating layer having a thickness of 0.1 μm by the method of Example 1 without forming an Sn plating layer. It was sequentially formed into a lead frame. Each characteristic of this lead frame was measured in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 2 In the same manner as in Example 1, the lead frame main body of Example 1 was coated with a Sn plating layer having a thickness of 0.5 μm and a thickness of 0.2 μm.
After the Ni plating layer and the Pd plating layer having a thickness of 0.1 μm were sequentially formed, the whole was heat-treated at a temperature of 300 ° C. for 30 seconds in the atmosphere.

With respect to the obtained lead frame, Example 1
Each property was measured by the same method as in. The results are shown in Table 1. Comparative Example 3 On the lead frame body of Example 2, a Cu plating layer having a thickness of 0.1 μm was formed in the same manner as in Example 2, and then, in the same manner as in Example 1, the Cu plating layer was formed on the Cu plating layer. Then, a Ni plating layer having a thickness of 5 μm and a Pd plating layer having a thickness of 0.1 μm were sequentially formed.

With respect to the obtained lead frame, Example 1
Each property was measured in the same manner as in. The results are shown in Table 1. Comparative Example 4 On the lead frame body of Example 2, a Cu plating layer having a thickness of 0.1 μm was formed in the same manner as in Example 2, and then on the Cu plating layer in the same manner as in Example 1. Ni plating layer with a thickness of 0.03 μm and a thickness of 0.005 μm
Pd plating layers of were sequentially formed.

With respect to the obtained lead frame, Example 1
Each property was measured in the same manner as in. The results are shown in Table 1.

[0048]

[Table 1]

[0049]

As is clear from the above description, the lead frame of the present invention is excellent in wire bonding property, soldering property, adhesion with sealing resin, corrosion resistance, and plating adhesion. In addition, even when the outer leads are bent, cracks do not occur.

Moreover, since the thickness of the uppermost layer made of a noble metal such as Pd may be thinner than 0.2 μm, its cost is reduced. Such an excellent effect is that by interposing an underlayer between the lead frame body and the intermediate layer, the corrosion resistance is improved by the joint action of the intermediate layer and the underlayer, and at the same time, the Ni plating layer which is the intermediate layer. This is because it is possible to make the thickness thinner, which also improves the bending workability. Then, the intermediate layer and the underlayer perform the above-mentioned functions, so that the uppermost noble metal layer can be thinned.

[Brief description of drawings]

FIG. 1 is a plan view of a lead frame body.

FIG. 2 is a sectional view showing a state in which a semiconductor chip is mounted on a lead frame body.

[Explanation of symbols]

 1 Pad Part 2 Inner Lead 3 Diver Part 4 Outer Lead 5 Adhesive 6 Semiconductor Chip 7 Electrode Pad 8 Wire 9 Sealing Resin

Claims (8)

[Claims] 1. A lead frame body and Zn, Sn, Pb, I formed on the lead frame body.
an underlayer of at least one metal selected from the group consisting of n, Co, and Cd or an alloy thereof or an alloy of the above metal and Cu; and a Ni intermediate layer formed on the underlayer; Pd, A formed on the intermediate layer
A lead frame for mounting a semiconductor chip, comprising a top layer of at least one metal selected from the group of u, Ag, and Pt or an alloy thereof. 2. The thickness of the underlayer is 0.01 to 0.2 μm,
2. The lead frame for mounting a semiconductor chip according to claim 1, wherein the intermediate layer has a thickness of 0.05 to 2.0 [mu] m and the uppermost layer has a thickness of 0.01 to 0.2 [mu] m. 3. The entire surface of the lead frame body is coated with Zn, S.
at least one metal selected from the group consisting of n, Pb, In, Co and Cd, an alloy thereof, or the above metal and C
to form an underlayer by coating with an alloy with u, and then to coat the surface of the underlayer with Ni to form an intermediate layer, and finally,
Manufacturing of a lead frame for mounting a semiconductor chip, characterized in that the uppermost layer is formed by coating the surface of the intermediate layer with at least one metal selected from the group of Pd, Au, Ag and Pt or alloys thereof. Method. 4. The method for manufacturing a lead frame for mounting a semiconductor chip according to claim 3, wherein the coating of each layer is formed by an electroplating method. 5. The method of manufacturing a lead frame for mounting a semiconductor chip according to claim 3, wherein the underlayer and / or the uppermost layer is an alloy layer. 6. The method for manufacturing a lead frame for mounting a semiconductor chip according to claim 5, wherein the alloy layer is formed by an alloy plating method. 7. The method for manufacturing a lead frame for mounting a semiconductor chip according to claim 5, wherein the alloy layer is formed by thermal diffusion treatment. 8. The method of manufacturing a lead frame for semiconductor mounting according to claim 7, wherein the thermal diffusion treatment is performed by heat of a bonding process when mounting a semiconductor chip.