JPH04174546A - Manufacture of semiconductor lead frame - Google Patents

Abstract

PURPOSE:To prevent diffusion of substratum metal, by forming a substratum layer of 0.05-2.0mum in thickness in a specified region of a metal lead frame main body, by Ni-plating process using sulfamic acid Ni plating bath, and forming a noble metal layer on the substratum layer. CONSTITUTION:In a specified region of a metal lead frame main body having leads and pad parts, an Ni substratum layer of 0.05-2.0mum in thickness is formed by Ni-plating process using sulfamic acid Ni plating bath. In the case where the substratum layer is thinner than 0.05mum, the number of pin holes increases, and corrosion and diffusion of substratum metal can not be restrained. In the case where the thickness exceeds 2.0mum, cracks are generated in the substratum layer at the time of bending process. The thickness is desirable to be 0.2-1.0mum. After that, by Pd-plating process on the Ni substratum layer, a noble metal layer is formed of 0.2mum in thickness, and a lead frame is formed. Thereby excellent bondability and soldeability can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing a semiconductor lead frame for mounting electronic components.

[Prior Art] Generally, a metal lead frame is used as a base on which electronic components such as transistors and ICs are mounted. This lead frame is constructed as shown in FIG. In the figure, 1 indicates a lead frame. The lead frame 1 includes a separate part 10, a plurality of inner leads 11, a plurality of outer leads 12, and a tie bar portion 1 that connects and supports the inner leads 11 and the outer leads 12.
It consists of 3. The plurality of inner leads 11 are arranged around the pad part 10 at a distance from each other, and are connected by wire bonding to electrode pads (not shown) of a semiconductor chip 14 such as a Si chip die-bonded onto the pad part 10. electrically connected. Outer lead 1
2 is electrically connected to the conductive portion of the base on which the element is mounted by soldering. This kind of lead frame is
A lead frame main body (hereinafter referred to as a base body) having a predetermined shape is produced by press working or etching a metal plate material usually made of Fe-Ni alloy or Cu alloy, and a pad portion 10 to which a semiconductor chip 14 is die-bonded. It is manufactured by partially plating the inner leads 11 to be wire-bonded to the electrode pads of the semiconductor chip 14 with a noble metal such as Ag to a thickness of 3 to 5 μm to prevent oxidation.

When assembling an electronic component as shown in FIG. 2 using a lead frame, it is performed as follows.

First, the semiconductor chip 14 is die-bonded onto the pad section 10 using the adhesive 20. Next, the electrode pads 21 previously formed on the semiconductor chip 14 and the inner leads 11 are wire-bonded using wires 22 made of A u SA 1 and Cu. Next, the bonding portion is sealed with a sealing resin 23 such as epoxy resin. Next, in order to improve the soldering properties of the outer leads 12, the outer leads 12 are plated with 5n-Pb. Thereafter, the tie bar part 13 is cut, the edges are removed, and the outer lead 12 is bent.

The electronic components manufactured in this way are mounted on a printed wiring board by soldering.

In this assembly, the outer leads 12 are usually plated by hot-dip plating or electroplating. When hot-dip plating is used, the bath temperature is very high at 240 to 300° C., so heat shock occurs during plating, resulting in small gaps between the sealing resin and the lead frame. Furthermore, when using electric metal, ions enter the sealing resin because they are immersed in an alkaline or acidic solution, and these ions corrode the wires and electrode pads. Therefore, no matter which plating method is used, there is a problem in that the reliability of the parts decreases.

In order to solve this problem, first Aratari-F 1
21: There is a method of applying Sn-Pb electroplating. However, in this case, the Sn or 5n-Pb plating layer may melt due to heating in the bonding process, which is a subsequent process, or the lead frame material (substrate) EC may melt.
When U is used, 5n-Pb and Cu in the metal layer diffuse into each other to form a compound of Sn and Cu, resulting in poor soldering properties.

Therefore, Japanese Patent Application Laid-open No. 59-168659, Japanese Patent Application Laid-open No. 63
In JP-A-2358 and JP-A-2-42753, a lead frame is proposed in which Pd is coated as a noble metal by plating or the like. Since Pd is stable in air, it is difficult to oxidize and also hardly causes thermal diffusion. Therefore, by applying Pd to the lead frame body, it is possible to achieve the excellent bonding properties, soldering properties, resin adhesion, etc. required for the lead frame. As a result, there is no need to perform Ag spot plating (partial plating), etc., which requires conventional advanced technology. Furthermore, it is no longer necessary to apply 5N-PB plating to the outer leads to improve solderability.

However, since Pd is very expensive, it is desired to reduce the thickness of the Pd layer as much as possible. For this purpose, a base layer is required to prevent corrosion of the base metal. Therefore, a Ni underlayer is provided under the Pd layer to reduce the thickness of the Pd layer and to prevent corrosion of the base metal. Conventionally, a Watts bath has been used when providing this Ni underlayer.

[Problems to be Solved by the Invention] However, the Ni underlayer formed using a Watts bath has many pinholes and cannot sufficiently prevent corrosion of the base metal. In particular, when Cu or Cu alloy is used as the base metal, Cu corrodes and dissolves in the Pd plating bath through pinholes in the Ni plating film, and the C
U ions are attracted to Pd due to the local battery action, producing corrosion products of Cu within the Pd layer. This Cu corrosion product deteriorates soldering and bonding properties.

If the thickness of the Ni underlayer is increased to prevent the formation of pinholes, there is a problem in that cracks occur when the outer lead is bent. - The present invention has been made in view of these points, and can sufficiently prevent corrosion of the base metal and diffusion of base metal ions, prevent the occurrence of cracks when bending the outer lead,
Moreover, it is an object of the present invention to provide a method for manufacturing a semiconductor lead frame that can produce a lead frame that exhibits excellent bonding properties, soldering properties, and resin adhesion.

[Means for Solving the Problems] The present invention provides Ni plating treatment using a Ni sulfamate bath on a predetermined region of a metal lead frame body having leads and pad portions to a thickness of 0.05 to 2.0 μm.
Provided is a method for manufacturing a semiconductor lead frame, characterized in that a Ni underlayer is provided, and then a noble metal layer is provided on the Ni underlayer.

Here, the thickness of the Ni underlayer is set to 0.05 to 2.0 μm. This is because if the thickness of the Ni base layer is less than 0.05 μm, there will be many pinholes in the Ni base layer, and corrosion and diffusion of the base metal cannot be sufficiently suppressed. This is because if it exceeds this, cracks will occur in the Ni underlayer when bending is performed. Particularly preferably, N
The thickness of the i-base layer is 0.2 to 1.0 μm.

The noble metal of the noble metal layer includes Au in addition to Pd.

Noble metals such as Ag and Pt can be used. As a method for depositing this noble metal on the Ni underlayer, a commonly used electroplating method, electroless plating method, etc. can be used.

The liquid composition of the Ni sulfamate bath is, for example, 200 to 700 g/i of Ni sulfamate! .

Ni chloride is 5 to 60 g/it, and boric acid is 30 to 50 g/g. In addition, sodium laurate may be added as a bit inhibitor.

The conditions for Ni plating using a Ni sulfamate bath are preferably a liquid temperature of 25 to 70°C, a pH of 2.5 to 4.5, and a current density of 2 to 2 OA/dm2. This is because even if plating is performed under conditions outside this range, a Ni underlayer with sufficient properties cannot be obtained. Note that these plating processing conditions are appropriately set according to the liquid composition of the Ni sulfamate bath.

[Function] According to the method for manufacturing a semiconductor lead frame of the present invention, a Ni base layer is provided on a metal lead frame body by Ni plating using a Ni sulfamate bath, and then,
A noble metal layer is provided on the Ni underlayer.

The Ni coating obtained by Ni plating using a Ni sulfamate bath is more ductile than the Ni coating obtained by Ni plating using a Watts bath, and the stress remaining on the surface is also smaller. Therefore, it is possible to prevent cracks from occurring due to bending of the outer lead. Further, the Ni film obtained by Ni plating using a Ni sulfamate bath has very few pinholes because the crystal grains are dense. Therefore, corrosion of the base metal and diffusion into the noble metal layer can be sufficiently prevented.

[Example code] Examples of the present invention will be specifically described below.

Example 1 First, Cu-0,3Cr-0,25Sn-0,2Zn
The alloy strip is pressed to form a DIP with the shape shown in Figure 1.
(Dual inline package) type lead frame body was obtained. Next, the liquid composition was 600g/# of Ni sulfamate and 10g/# of Ni chloride on the entire surface of this lead frame main body.
/it, boric acid 40 g/l)
Ni plating treatment was performed using an i-bath to form an N1 base layer with a thickness of 0.2 μm. At this time, the conditions for Ni plating treatment were: liquid temperature 60°C, pH 3, current density 10A/d112
And so. After that, Pd plating treatment (using Varadex 110 manufactured by Nichiki Kikinzoku Co., Ltd.) was applied to the Ni base layer to a thickness of 0.
A 2 μm noble metal layer was formed.

At this time, the conditions for Pd plating treatment were: liquid temperature: 60°C, pH:
8,5, and the current density was set to 3 A/dg+2. In this way, a lead frame (Example 1) was produced.

Thereafter, the bonding properties of the lead frame, resin adhesion, the occurrence of cracks in the Ni underlayer during bending, and soldering properties were examined. The results are shown in Table 1 below.

Note that the bonding property was determined by a wire tensile test, and the case where the wire broke was rated O, and the case where the wire peeled off at the interface of the substrate was rated X. Resin adhesion was judged by shear strength, and when compared with Cu material only, cases where it was equivalent or higher were rated 0, and cases where it was equivalent or lower were rated X. The quality of soldering is judged by the wetted area of the solder, and if it is 95% or more, it is 019.
The case where it was less than 5% was designated as X. The presence or absence of cracks during bending was determined by SEM observation after bending.

Examples 2 to 4 Lead frames of Examples 2 to 4 were produced in the same manner as in Example 1, except that the thickness of the Ni underlayer was set to the value shown in Table 1 below.

The lead frames of Examples 2 to 4 obtained were examined in the same manner as in Example 1 for bonding properties, resin adhesion, occurrence of cracks during bending, and soldering properties. The results are also listed in Table 1 below.

Comparative Example 1.2 A lead frame of Comparative Example 1.2 was produced in the same manner as in Example 1 except that the thickness of the Ni underlayer was set to the value shown in Table 1 below.

The resulting lead frames of Comparative Examples 1 and 2 were examined in the same manner as in Example 1 for bonding properties, resin adhesion, occurrence of cracks during bending, and soldering properties. The results are also listed in Table 1 below.

Comparative Example 3 A Cu-0,3Cr-0,25Sn-0,2Zn alloy strip was pressed to obtain a DIP type lead frame body having the shape shown in FIG. Next, the entire surface of this lead frame body was coated with a liquid composition of Ni sulfate (250 g/l) and Ni chloride (50 g/l).
g/#, N using a Watts bath with boric acid 40 g/fl.
An i-plating process was performed to form a Ni underlayer with a thickness of 0.2 μm. At this time, the conditions for Ni plating treatment are as follows: liquid temperature: 10
°C, pH 4, and current density 3 A/di2.

Thereafter, Pd plating treatment (using Varadex 110 manufactured by Nichi-Kizoku Kogyo Co., Ltd.) was performed on the Ni base layer to form a noble metal layer with a thickness of 0.2 μm. At this time, the conditions for the Pd plating treatment were a liquid temperature of 60° C., a pH of 8.5, and a current density of 3 A/da2. In this way, a lead frame (Comparative Example 3) was produced.

The resulting lead frame of Comparative Example 3 was examined in the same manner as in Example 1 for bonding properties, resin adhesion, occurrence of cracks during bending, and soldering properties. The results are also listed in Table 1 below.

Comparative Examples 4 to 6 Lead frames of Comparative Examples 4 to 6 were produced in the same manner as Comparative Example 3 except that the thickness of the Ni underlayer was set to the value shown in Table 1 below.

The lead frames of Comparative Examples 4 to 6 obtained were examined in the same manner as in Example 1 for bonding properties, resin adhesion, occurrence of cracks during bending, and soldering properties. The results are also listed in Table 1 below.

As is clear from Table 1, the lead frames obtained according to the present invention (Examples 1 to 4) exhibit excellent bonding properties, resin adhesion properties, and soldering properties, and also exhibit excellent bending properties of the outer leads. No cracks occurred in the Ni underlayer. On the other hand, lead frames having a Ni underlayer thickness outside the range of the present invention (Comparative Example 1.2) and lead frames obtained by a method using a Watts bath (Comparative Examples 3 to 6) have a base metal Bonding and soldering properties were poor due to corrosion and diffusion of base metal ions, and cracks occurred in the Ni underlayer during bending of the outer leads.

[Effects of the Invention] As explained above, according to the method of the present invention, it is possible to sufficiently prevent the diffusion of the base metal, prevent the occurrence of cracks when bending the outer lead, and achieve excellent bonding. It is possible to obtain a lead frame that exhibits good solderability, good solderability, and resin adhesion.

Further, by providing the Ni underlayer, the thickness of the noble metal layer can be reduced and economical efficiency can be improved.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a semiconductor lead frame, and FIG. 2 is a sectional view showing an example of an electronic component. DESCRIPTION OF SYMBOLS 1... Lead frame, 10... Pad part, 11.
...Inner lead, 12...Outer lead, 13
...Part of tie bar, 14...Semiconductor chip, 20...
・Adhesive, 21... Electrode pad, 22... Wire,
23... Sealing resin. Applicant's agent Patent attorney Takehiko Suzue

Claims (1)

[Claims] A Ni sulfamate bath was used to inject Ni into a predetermined area of a metal lead frame body having leads and pads.
A method for manufacturing a semiconductor lead frame, which comprises providing a Ni base layer with a thickness of 0.05 to 2.0 μm by plating, and then providing a noble metal layer on the Ni base layer.