JPH03179768A - Lead frame member - Google Patents

Abstract

PURPOSE:To obtain a lead frame member which is excellent in thermal conformity to an Si chip, mechanical strength, electrical conductivity, thermal conductivity, and etching processability by a method wherein both the side layers of a lead frame member in a thicknesswise direction are formed of Ni-Fe base alloy and an intermediate layer sandwiched between the side layers is formed of Cu or Cu base alloy. CONSTITUTION:Both the side layers of a lead frame in a thicknesswise direction are formed of Ni-Fe base alloy, and an intermediate layer sandwiched between the side layers is formed of Cu or Cu base alloy. The Ni-Fe base alloy is one of those alloies usually used for a lead frame such as 42% Ni-Fe alloy, 50% Ni-Fe alloy, 29% Ni-17% Co-Fe alloy, and improved alloies of the above alloies. It is preferable that the side layers are equal to each other in thickness from the standpoint of an etching processability. Well known lead frame Cu base alloies can be widely applied to Cu base alloy the same as Ni-Fe base alloy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a lead frame member used for electronic components such as IC packages.

[Conventional technology]

Conventionally, materials for lead frames of integrated circuits (IC) include 42% Ni-Fe alloy (commonly known as 42Ni alloy) and 50% Ni-Fe alloy (commonly known as 42Ni alloy).
%Ni-Fe alloy (commonly known as 5ONi alloy), 29%N 1
-17 N such as Go-F e alloy (commonly known as Kovar alloy)
i-Fe alloy (hereinafter, these are collectively referred to as N in the present invention)
i-Fe-based alloys) 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 problems with thermal expansion matching with Si chips and mechanical properties. The development of a lead frame member that satisfies the required characteristics has been awaited.

Furthermore, in recent years, as ICs have become highly integrated, lead frames have also become multi-bin.

As a result, the spacing between inner leads has become extremely 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.

-a Etching is performed simultaneously from both sides of the material to be etched, which is coated with resist. The etching progress process at that time is shown in FIG. 2 (cross-sectional view).

From the beginning of etching, etching progresses mainly in the thickness direction as shown in Figure 2 (a) - (b) → (C), but due to the difference in etching time, the cross-sectional shape becomes convex at the center of the thickness. . These protrusions cause dimensional defects in the leads and lead short circuits, and must be eliminated. In order to eliminate these protrusions, it is possible to lengthen the etching time, but this is undesirable from the point of view of production efficiency, and etching occurs not only in the thickness direction, but also as you go from the surface where the resist is applied to the inside. Since etching also progresses in the board width direction (side etching), etching progresses excessively in the board width direction, as shown in FIG. 2(d), which is undesirable.

[Problems to be Solved by the Invention] In view of the above, an object of the present invention is to improve the thermal compatibility and mechanical strength of the conventional Ni-Fe-based alloy and Si chip, and the good electrical properties of the Cu alloy or the Cu-based alloy. It is an object of the present invention to provide a new lead frame member that has both conductivity and thermal conductivity, and also has improved etching processability and satisfies the demands for ultra-high number of bins.

[Means to solve the problem]

The present inventor evaluated the etching processability of Ni-Fe-based alloys, Cu, and Cu-based alloys that have been conventionally used for lead frames, and found that Ni-Fe-based alloys, as described above,
Although both Fe-based alloys and Cu and Cu-based alloys have an etched cross section with a convex central part of the plate thickness, the etching speed of Cu and Cu-based alloys is faster than that of Ni-Fe-based alloys, and as a result, the plate thickness increases. It was found that the degree of convexity occurring in the central part was small.

Therefore, the present inventor used a material with a composite structure in which Cu or Cu-based alloy, which has excellent etching workability, was used in the central part of the sheet thickness where a convexity occurs due to etching, and Ni-Fe-based alloy was arranged on both sides. As a result of evaluation, it was confirmed that an extremely superior etched cross section could be obtained compared to conventional lead frame members made of Ni--Fe based alloys or single elements such as Cu.

The present invention has been made based on the above findings, and provides a lead frame characterized in that the layers on both sides in the plate thickness direction are made of a Ni-Fe-based alloy, and the intermediate layer sandwiched between the layers on both sides is made of Cu or a Cu-based alloy. It is a member for use.

[Effect]

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

Up to Fig. 1(a) and (b), etching progresses in the same way as the conventional material shown in Fig. 2, but after that, etching progresses easily in the thickness direction in the intermediate layer made of Cu etc. During this time, the amount of side etching on both phases is small compared to the amount of etching in the thickness direction of the intermediate layer, so as shown in Fig. 1(c).
It is possible to have an etched cross-sectional shape as shown in FIG.

In other words, in the case of a single material, no matter how good the etching property of the material is, the etched cross section will be as shown in FIG. 2 (C) (or (d)). By forming a composite structure in which the intermediate layer is formed, an etched cross section close to the ideal as shown in FIG. 1(e) can be achieved.

In the present invention, the reason why Ni-Fe-based alloy is disposed on both sides is to meet the mechanical strength required for the lead frame and the Si-Fe base alloy.
This is to ensure consistency with the chip.

Note that the Ni-Fe-based alloy with which the present invention can be implemented is 42% Ni-Fe, which has been conventionally used for lead frames.
Fe alloy, 50%Ni-Fe alloy, 29%Ni-17%
The concept broadly includes Co-Fe alloys and improved alloys of these alloys, and it goes without saying that they can be selected as appropriate depending on the specific use and requirements of the lead frame, but from the perspective of achieving the purpose of the present invention, there are no particular limitations. It is not something that can be done.

In addition, it is desirable that the thicknesses of both layers be equal from the viewpoint of etching processability.

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

Note that, like the Ni-Fe-based alloy, the Cu-based alloy is not limited 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 selected as appropriate depending on the specific use and requirements of the lead frame, but if the intermediate layer is too thin, the Ni-Fe-based alloy alone It is desirable that the plate thickness ratio of the intermediate layer is 20% or more, since there is no difference between the two and the effect of improving etching processability cannot be expected, and sufficient electrical conductivity cannot be ensured.

On the other hand, if the intermediate layer becomes too thick, there will be no difference from Cu or Cu-based alloy alone, and no improvement in etching processability can be expected, and sufficient mechanical strength cannot be ensured. It is desirable that the upper limit of the plate thickness ratio be 70%. Note that the plate thickness ratio is defined as follows.

TR, = (T, /(T, 10T,, 10T.))
X 100(%)TR, = (T, /(T, 10T,
, 10T,,)) Plate Thickness Next, the lead frame member of the present invention can be manufactured by the well-known cold clad rolling method.

〔Example〕

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

As the Ni-Fe alloy on both sides, 42% Ni-Fe,
50%Ni-Fe, 29%N 1-17%Go-Fe(
= r bar), oxygen-free copper as the intermediate layer, Cu-23%F
e-0.03% P was prepared, and these materials were crimped by cold rolling so that the combination of sample contents and plate thickness ratio were as shown in Table 1, and the plate thickness was 0.15 mm and the plate width was 45 mm. Obtained the Marshal's Clad Lumber.

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

Note that the etching processability is as shown in Fig. 3 when the width is 0.
A 5 mm rectangular hole was filled with ferric chloride solution (FeC1, +68,
Evaluation was made based on the porosity after etching for 5 minutes using O). Note that the porosity is W when the maximum width of the etched cross section after etching is W3 and the minimum width is W2.
, /W, means X100 (%).

From Table 1, it can be seen that the lead frame member of the present invention has excellent etching processability and has the mechanical strength and electrical conductivity required for a lead frame.

〔Effect of the invention〕

As described above, the present invention improves etching processability, has good mechanical strength and electrical conductivity, and is effective as a lead frame member for a very large number of bins.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the progress of etching of a lead frame member of the present invention, FIG. 2 is a diagram showing the progress of a conventional lead frame member, and FIG. 3 is a diagram illustrating an etching test. ] Figure (a) (b) (c) r 1C7l)?ノ1cti＊Go=Z≧Dzuto>□Diagram procedural amendment (voluntary) 1st February 1998 Nikko, Incident indication 1999 patent application No. 312683 2゜Name of invention Lead frame member 3. Detailed explanation of the invention of the person making the amendment Attachment 1. The Detailed Description of the Invention column in the specification is corrected as follows. (1) Replace Table 1 on page 9 of the specification with the attached Table 1. (2) ro, 5mmJ in the same book, page 10, line 5 is rO, 8
m+1". (3) Change rW, /W, and J on page 10, line 9 of the same book to “W2/
Corrected to "W1". that's all

Claims (1)

[Scope of Claims] 1. A member for a lead frame, characterized in that both layers in the plate thickness direction are made of a Ni-Fe-based alloy, and an intermediate layer sandwiched between the both-side layers is made of Cu or a Cu-based alloy. 2 The plate thickness ratio of the intermediate layer Cu plate or Cu-based alloy is 20~
70%.