JPH04255259A - Lead frame of semiconductor device - Google Patents

Abstract

PURPOSE:To provide a semiconductor device lead frame which is plated with Ni-P and excellent in adhesion to a plating coat and bendability. CONSTITUTION:In a semiconductor lead frame whose die bonding part is coated with an Ni-P plating layer through the intermediary of an Ni plating layer, the Ni-P plating layer concerned is possessed of a structure composed of two or more layers where a layer becomes higher in P concentration as it is located at a higher level, the Ni-P plating layers are so set as to be less than 5% by weight in P content difference, the uppermost layer is set to 9-15% by weight in P concentration, and the total thickness of the Ni-P plating layers is set half or below as large as that of the Ni plating layer.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lead frame for a semiconductor device, and more particularly to a lead frame for a semiconductor device in which Ni--P plating has improved plating adhesion and bending workability.

0002

2. Description of the Related Art A lead frame for a semiconductor device such as a power transistor uses a copper alloy material plated with Ni or a Ni alloy.

[0003] Semiconductor devices are manufactured through the following steps: a step of soldering (die bonding) a semiconductor element to the lead frame using high-temperature solder, a step of wiring the wiring part of the element and a lead part with a wire such as an aluminum wire (wire bonding);
The device is manufactured through a process of sealing the semiconductor element portion with resin and pre-soldering the lead portion.

Semiconductor devices are products that require high reliability, and in particular, the characteristics of solder die bonding (die bonding properties) that join semiconductor elements and lead frames have a large effect on the reliability of semiconductor devices. Therefore, it is required to improve the stability of die bonding properties.

Conventionally, in order to improve and stabilize die bonding properties, P, which has a higher affinity for oxygen than Ni, has been used.
Ni-P plating containing is used. but,
In these platings, as the P content increases, the hardness of the plating film increases, and significant cracks occur during stamping or bending of the lead after semiconductor device assembly, leading to lead breakage and electrical damage. This may cause problems such as poor conduction.

On the other hand, as a measure to improve bending workability, two-layer plating is used in which a Ni plating layer that does not contain P is formed as the lower layer, and a plating layer that contains P is formed on top of it (Japanese Patent Publication No. 1983- 33312). In this case, the lower N
Although it is possible to improve the bending workability of the plating by increasing the thickness of the plating layer, there is a problem of poor adhesion such as the plating peeling off between the two plating layers.
It is difficult to effectively use Ni-P plating, which has excellent die bonding properties.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a lead frame for a semiconductor device which is plated with Ni--P and has excellent adhesion and bending workability of the plated film.

[0008]

[Means for Solving the Problems] The present invention attempts to solve the above problems by the following means.

That is, the gist of the present invention is to provide a lead frame for a semiconductor device in which a Ni--P plating layer is formed at least in the die bonding portion with a Ni-plated layer interposed therebetween, in which the Ni--P plating layer is formed on the upper layer. It has a multilayer structure of two or more layers in which the P concentration increases as the layer increases, and the difference in P content between adjacent Ni-P plating layers is within 5% by weight, and the P concentration in the upper layer is 9 to 15% by weight. and the total thickness of the Ni--P plating layer is 1/2 or less of the thickness of the Ni plating layer.The lead frame for a semiconductor device has excellent plating adhesion and bending workability.

0010

[Operation] The present inventor has conducted intensive research and testing on a lead frame for semiconductor devices that satisfies both the bending workability and adhesion of the plating film while taking advantage of the characteristics of Ni-P plating, which has excellent solder die bonding properties. .

As a result, unlike the conventional improvement method, Ni
With the technology of layering plating and plating film with high P content,
From the formation process of the first layer of Ni plating layer to the second layer of Ni-P
It was found that the surface of the first layer was oxidized during the step of forming the plating layer, and therefore it was difficult to practically stabilize the adhesion between the two layers.

[0012] Therefore, we earnestly searched for a technology to eliminate the influence of oxides, and found that the Ni-P plating layer had a multilayer structure.
In addition, by setting the P content and thickness of the Ni-P plating layer within a predetermined range, the influence of oxides can be eliminated, and a lead frame for semiconductor devices with excellent plating film adhesion and bending workability can be obtained. We have found that this can be obtained, and have come up with the present invention.

[0013] The Ni plating layer and each Ni-P plating layer are formed by lining up three or more types of plating baths with different P concentrations in the same plating line and plating continuously to prevent the formation of oxides. This is preferable from the viewpoint of further improving the adhesion of the plating film.

The reasons for limiting the numerical values will be explained below.

1) First, the P concentration in the upper layer of the Ni-P plating is set to 9 to 15% (weight %, the same applies hereinafter) because the lower limit for obtaining good solderability is 9%. The reason why the upper limit is set to 15% is that if P exceeds 15%, oxidation of P tends to proceed, and oxides on the Ni plating surface increase, reducing solder jointability and adhesion.

The reason why the difference in P concentration between adjacent Ni--P plating layers is set to be 5% or less is because if the P concentration exceeds 5%, the adhesion of the plating layers decreases.

The reason why the total thickness of the Ni--P plating layer is set to 1/2 or less of the thickness of the Ni plating layer is to prevent the occurrence of cracks during bending. This is because cracks that reach the base material are likely to occur.

2) As a means of obtaining the plating described in item 1) above, a film with good adhesion can be obtained by plating by successively passing through plating tanks with different plating solution compositions provided in the same line. .

The Ni plating bath used in the present invention is not particularly limited, and any plating bath such as a sulfuric acid bath or a sulfamic acid bath may be used as long as it meets the requirements of the present invention.

[0020] In this specification, the term "Ni plating" includes alloy plating of Ni and components other than P.

[0021]

[Example] (Example 1) Using a material made of copper alloy wire (plate thickness 0.5 mm), after performing the usual plating pretreatment of alkaline immersion degreasing → electrolytic degreasing → pickling, the following steps were carried out. Under the plating conditions shown, a Ni plating layer and three Ni--P plating layers with different P concentrations were formed on the Ni plating layer, and bending workability and adhesion tests were conducted.

[0022] The P concentration in the plating film was determined by analyzing the P concentration in each plating bath composition in advance, and based on the results, multilayer plating was performed by combining plating films with different P concentrations.

(Plating conditions) 1st layer NiSO4 6H2 O 24
0g/1NiCl2 ・6H2O 45g
/1H3 BO3
35g/1 bath temperature: 55°C Current density: 3A/dm2 2nd layer NiSO4 ・6H2 O 15
0g/1NiCl2 ・6H2O 150g/
Primary hypophosphorous acid 10-30g/1 bath temperature: 60℃ Current density: 3A/dm2 3rd layer NiSO4 ・6H2 O 15
0g/1NiCl2 ・6H2O 150g/
Primary hypophosphorous acid 30-50g/1 bath temperature: 60℃ Current density: 3A/dm2 4th layer NiSO4 ・6H2 O 15
0g/1NiCl2 ・6H2O 150g/
Primary hypophosphorous acid 50 to 100 g/1 bath temperature: 60°C Current density: 3 A/dm2 (Plating adhesion test conditions) Plating adhesion was determined by cutting out a 10 mm x 50 mm test piece from the plated material as a test material, and exposing it to air. The sample was heated at 400° C. for 5 minutes in a vacuum chamber, followed by 180° close bending with a bending radius of OR, and the presence or absence of peeling of the plating film at the bent portion was observed using a stereomicroscope (×40). Note that the number n was set to 100.

(Bending workability test conditions) A test piece having the same dimensions as the adhesion test piece was bent at 90° with a bending radius of 1 mmR, and the maximum crack width at the bent portion was measured using an optical microscope (×100).

The above results are shown in Table 1.

[0026] In Table 1, "thickness" is the thickness of the plating (unit: μm) P
Concentration unit is wt% *1 Adhesion evaluation (n=100) Evaluation by number of film peeling ○: 0 to 1/100 △: 2 to 5/100 ×
: 6 or more / 100 *2 Bending workability evaluation Evaluated by maximum crack width ○:
2 μm or less △: 3 to 5 μm ×: 6 μm or more

0
[027] In Table 1, No. 1~No. No. 5 is an example of the present invention. 6~No. 9 is a comparative example, No. 1
0~No. 11 shows a conventional example.

First, conventional example No. No. 10 is a single layer of Ni-P plating, and has poor bending workability and adhesion.

Conventional example No. 11 is Ni that does not contain P
This is a plating in which a Ni--P plating layer containing 12% P is formed on the plating, and the bending workability of the plating is good, but the adhesion is poor.

Comparative example No. 6~No. In No. 7, the total plating thickness including P is 1/2 or more of the Ni plating thickness not including P, and the bending workability is poor.

Comparative example No. 8~No. In No. 9, the difference in P concentration between the plating layers containing P was 0.5% or more, and the adhesion was poor.

[0032]No. 1 to No. In Example 5, the difference in the P concentration of the plating layer containing P is 0.5% or less, and the plating thickness is 1
/2 or less, and both bending workability and adhesion are good.

(Example 2) In order to form a multilayer plating film of a Ni plating layer and a Ni--P plating layer with different P concentrations, plating was performed according to the continuous plating process shown in FIG.
Two-layer plating performed in combination on different lines was used as a comparative example, and the adhesion and bending workability of both were investigated.

The investigation results are shown in Table 2.

*1 Adhesion evaluation (n=100) Evaluation based on the number of peeled films ◎: 0/100 △: 1 to 5/100 ×: 6
Over/100 *2 Bending workability evaluation Evaluated by maximum crack width ○:
2 μm or less △: 3 to 5 μm ×: 6 μm or more

0
[036] In Table 2, No. 21~No. No. 23 is an example of the present invention. 24~No. 25 shows a conventional example.

First, No. 24 and No. In the conventional example No. 25, the first layer of Ni plating and the second layer of Ni--P plating are plated in separate processes, resulting in poor adhesion between the layers. No. 21
~No. In Example No. 23, each layer was plated continuously in the same process, and the adhesion between the layers was good.

[0038]

Effects of the Invention The present invention is constructed as described above, and improves the plating adhesion and bending workability of Ni-P plating that has excellent solder die bonding properties, and provides an economical and highly productive semiconductor. We were able to provide lead frames.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the plating process of Example 2.

Claims (2)

[Claims] Claim 1: At least in the die bonding part, N
In a lead frame for a semiconductor device in which a Ni-P plating layer is formed through an i-plating layer, the Ni-P plating layer has a multilayer structure of two or more layers in which the P concentration increases as the upper layer increases, P of each adjacent Ni-P plating layer
The difference in content is within 5% by weight, the P concentration in the upper layer is 9 to 15% by weight, and the total thickness of the Ni-P plating layer is 1/2 or less of the thickness of the Ni plating layer. A lead frame for semiconductor devices that features excellent plating adhesion and bending workability. 2. The Ni plating layer and each Ni-P plating layer are plating layers formed by successively passing through three or more types of plating baths having different P concentrations. 1. The lead frame for a semiconductor device according to 1.