JPH07109869B2 - Lead frame material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a lead frame member used for an electronic component such as an IC package.

[Conventional technology]

Conventionally, as a material for lead frames of integrated circuits (ICs)
Ni-Fe alloys such as 42% Ni-Fe alloy (commonly known as 42Ni alloy), 50% Ni-Fe alloy (commonly known as 50Ni alloy), 29% Ni-17Co-Fe alloy (commonly known as Kovar alloy) (hereinafter generically In the present invention, a Ni-Fe based alloy) or various Cu alloys were used.

The lead frame material is required to have (1) thermal expansion matching with the Si chip, (2) good mechanical strength, (3) good electrical conductivity, and (4) good thermal conductivity. However, conventional Ni-Fe-based alloys have low electrical conductivity, and Cu alloys have advantages and disadvantages, such as thermal expansion matching with Si chips and problems with mechanical properties. The development of lead frame members that meet the required characteristics has been awaited.

Furthermore, in recent years, lead frames have been increased in number with increasing integration of ICs.

Along with this, the spacing between the inner leads has become very narrow, and etching workability has become extremely important. However, the following problems have been pointed out regarding the etching processability of conventional Ni-Fe-based alloys and Cu-based alloys.

Generally, etching is performed simultaneously from both side surfaces of the material to be etched on which the resist has been applied. FIG. 2 shows the etching progress process at that time (cross-sectional view). From the initial stage of etching, as shown in FIGS. 2 (a) → (b) → (c), the etching progresses mainly in the plate thickness direction, but due to the difference in etching time, the central part of the plate thickness has a convex sectional shape. . This protrusion is
It may lead to defective lead size or lead short circuit and should be eliminated. In order to eliminate this convex portion, it is sufficient to lengthen the etching time, but this is not desirable from the viewpoint of production efficiency, and the etching is not limited to the plate thickness direction as it goes from the surface portion where the resist is applied to the inside. , 2nd because it also progresses in the width direction (side etching)
As shown in FIG. 6D, the etching proceeds excessively in the plate width direction, which is not desirable.

[Problems to be Solved by the Invention]

In view of the above, the purpose of the present invention is to improve the conventional Ni-Fe-based alloy and Si.
A new lead that combines thermal compatibility with the chip, good electrical and thermal conductivity of a Cu alloy or Cu-based alloy with mechanical strength, and further satisfies the requirements for ultra-high pin count with improved etching processability. It is to provide a frame member.

[Means for Solving the Problems]

The present inventor has conventionally been used for lead frames.
Ni-Fe-based alloy, and Cu, when the etching processability of the Cu-based alloy was evaluated, as described above, the Ni-Fe-based alloy,
Although both Cu and Cu-based alloys have an etched cross-section with a convex center of thickness, Cu and cu-based alloys have a higher etching rate than Ni-Fe-based alloys, and as a result, occur in the center of thickness. It was found that the degree of convexity was small.

Therefore, the present inventor has used Cu or Cu-based alloy having excellent etching workability in the central portion of the plate thickness where a projection is generated by etching, and using a material of a composite structure in which Ni-Fe-based alloys are arranged on both sides thereof, the etching workability is obtained. As a result of the evaluation, it was confirmed that it is possible to obtain an extremely excellent etching cross section as compared with a lead frame member made of a conventional Ni—Fe based alloy or a simple substance such as Cu.

The present invention has been made based on the above findings, the lead frame is characterized in that both layers in the plate thickness direction are Ni-Fe based alloys, and the intermediate layer sandwiched between the two layers is Cu or a Cu based alloy. The both side layers are disposed on the entire front and back surfaces of the intermediate layer, and suppress the convexity of the central portion of the plate thickness of the etched surface.

[Action]

FIG. 1 is a cross-sectional view showing an etching progress process when the lead member of the present invention is etched.

Etching progresses in the same manner as the conventional material shown in FIG. 2 up to FIGS. 1 (a) and 1 (b), but thereafter, in the intermediate layer made of Cu or the like, the etching easily progresses in the thickness direction. During this time, since the sand etching of both side layers is smaller than the etching amount of the intermediate layer in the plate thickness direction, the etching cross-sectional shape as shown in FIG. 1C can be obtained.

That is, in the case of a single material, an etching cross section as shown in FIG. 2 (c) (or (d)) is obtained no matter how excellent the etching property is, but a material having good etching property as in the present invention is used. By adopting a composite structure having an intermediate layer, a near-ideal etching cross section as shown in FIG. 1 (c) can be achieved.

In the present invention, arranging the Ni-Fe based alloys on both layers is
This is because the lead frame is provided with the required mechanical strength and compatibility with the Si chip.

The Ni-Fe-based alloy that can be used in the present invention is a 42% Ni-Fe alloy that is conventionally used as a lead frame,
It is a concept that broadly includes 50% Ni-Fe alloy, 29% Ni-17% Co-Fe alloy or improved alloys of these alloys, and it is natural that they are appropriately selected according to the specific application and requirements of the lead frame. However, it is not particularly limited from the viewpoint of achieving the object of the present invention.

Further, it is desirable that the plate thicknesses of both side layers are uniform from the viewpoint of etching processability.

In the present invention, the presence of the intermediate layer made of Cu or a Cu-based alloy serves not only to improve the etching processability but also to satisfy the electrical conductivity and thermal conductivity required for the lead frame.

The Cu-based alloy is not limited as well as the Ni-Fe-based alloy as long as the object of the present invention is achieved, and well-known Cu-based alloys for lead frames can be widely applied.

The plate thickness ratio of both side layers (Ni-Fe based alloy) and intermediate layer (Cu, etc.) can be appropriately selected according to the specific application and requirements of the lead frame, but if the intermediate layer is too thin, the Ni-Fe based alloy alone Therefore, the effect of improving the etching processability cannot be expected, and sufficient electrical conductivity cannot be ensured. Therefore, it is desirable that the thickness ratio of the intermediate layer be 20% or more. On the other hand, if the intermediate layer becomes too thick, Cu or Cu
It is desirable to set the upper limit of the plate thickness ratio of the intermediate layer to 70%, because there is no difference from the base alloy alone, the improvement effect of etching workability cannot be expected, and sufficient mechanical strength cannot be secured. . The plate thickness ratio is defined as follows.

TR ₁ = (T ₁ / (T ₁ + T ₂₁ + T ₂₂ )) × 100 (%) TR ₂ = (T ₂ / (T ₁ + T ₂₁ + T ₂₂ )) × 100 (%) TR ₁ : The thickness of the intermediate layer Ratio TR ₂ : Plate thickness ratio of both layers (one side only) T ₁ : Plate thickness of intermediate layer T ₂₁ , T ₂₂ : Plate thickness of both layers Next, the lead frame member of the present invention is manufactured by well-known cold clad rolling. can do.

〔Example〕

 Hereinafter, the present invention will be described based on examples.

As Ni-Fe alloy of both layers, 42% Ni-Fe, 50% Ni-Fe,
29% Ni-17% Co-Fe (Kovar), oxygen-free copper as an intermediate layer, Cu-2.3% Fe-0.03% P were prepared, and each had the combination of the sample contents and the plate thickness ratio in Table 1. , These materials are pressure-bonded by cold rolling to obtain a plate thickness of 0.15 mm and a plate width of 45.
A clad material of mm was obtained.

The samples, 42% Ni-Fe alloy, and oxygen-free copper were evaluated for etching workability, mechanical strength, and electrical conductivity. The results are shown in Table 1.

The etching workability is 0.8m in width as shown in Fig. 3.
The rectangular hole of m was made 5 with ferric chloride solution (FeCl ₃ + 6H ₂ O).
It was evaluated by the open area ratio after performing the etching for a minute. The porosity means W ₂ / W ₁ × 100 (%), where W _{1 is} the maximum width and W ₂ is the minimum width of the etched cross section after etching.

It can be seen from Table 1 that the lead frame member of the present invention is excellent in etching workability and has the mechanical strength and electrical conductivity required for the lead frame.

〔The invention's effect〕

As described above, according to the present invention, the etching workability is improved, and the mechanical strength and electrical conductivity are good, and the present invention is effective as a lead frame member for ultra-multi pins.

[Brief description of drawings]

FIG. 1 is a diagram showing an etching progress process of a lead frame member of the present invention, FIG. 2 is a diagram showing a progress process of a conventional lead frame member, and FIG. 3 is a diagram explaining an etching test.

Claims (2)

[Claims] 1. Both side layers in the plate thickness direction are Ni-Fe based alloys, an intermediate layer sandwiched by the both side layers is Cu or Cu based alloy, and the both side layers are arranged on the entire front and back surfaces of the intermediate layer. The lead frame member is characterized in that the central portion of the plate thickness on the etched surface is suppressed from being convex. 2. The plate thickness ratio of the Cu plate or Cu-based alloy in the intermediate layer is 20.
The lead frame member according to claim 1, wherein the lead frame member is about 70%.