JPS63304654A - Lead frame - Google Patents

Abstract

PURPOSE:To simplify the manufacturing process, improve the productivity, and reduce the cost, by providing the outer lead tip part of at least each lead part with a specified plated layer. CONSTITUTION:The outer lead 5 tip part of at least each lead part 3 is provided with a plated layer 7 of Ag-Pd alloy or Ag-Sb alloy. Ag-Pd or Sb alloy plated layer 7 has an effect to improve the solder wettability of the outer lead 5. Therefore, electroplating of solder or plating of molten solder which are usually performed for the outer lead part 5 after a semiconductor device (IC package) is completed can be omitted. Thereby, the number of processes is decreased, the productivity is improved, and the cost is reduced.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is directed to IC, LS 1. [Related to lead frames for semiconductor integrated circuits (hereinafter collectively referred to as ICs) such as LSI.

<Prior art> A lead frame has a mounting base (tab) on which an IC element is mounted in the center, and a plurality of lead parts around the tab that extend toward the mounting base. It consists of an inner lead that is wire-bonded to a corresponding electrode on an IC element mounted on the IC, and an outer lead that becomes an external terminal of the semiconductor device (IC package).

This lead frame is made of plate materials such as iron, iron-based alloys (e.g., 42 aronincovar, stainless steel, etc.), copper, copper-based alloys (e.g., phosphor bronze, CA194, C505, etc.), and is photo-etched into this material. Alternatively, press punching is performed and unnecessary parts are cut out to produce the desired 7□ shape. Because the adhesion to the tip of the inner lead of a wire or single wire is poor, the mounting base and the tip of the inner lead are plated with a precious metal such as gold or silver.

In addition, IC elements are mounted on such lead frames,
After performing predetermined wire bonding, the semiconductor device (IC package) is formed by resin molding with epoxy resin, etc., cutting the connecting portions, and bending the outer leads. In order to improve the solder connectivity of the outer leads during attachment, the tips of the outer leads are sometimes plated with semi-Ill plating or tin plating. This plating is performed after the semiconductor device is completed, and can be either electroplating or hot-dip plating. However, since the plating on the tips of the outer leads is done after the semiconductor device is completed, the semiconductor device must be placed in a plating environment.
Causes adverse effects on equipment. In other words, plating solution or gas generated from plating solution (acidic or alkaline atmosphere)
There is a problem in that the semiconductor devices are exposed to air, which penetrates into the resin mold through the outer leads, reducing the reliability of the semiconductor device. In addition, especially when hot-dip plating is used, the lead frame is subjected to a thermal history of about 250°C, which causes internal thermal stress, which can cause cracks in the molding resin or in the IC element itself due to stiffness. This significantly reduces the reliability of semiconductor devices.
Furthermore, after the semiconductor device is completed, a step of solder plating or tin plating must be provided to the outer leads, resulting in a decrease in productivity.

Therefore, a lead frame in which the outer sword portion of the lead frame is pre-plated with solder or tin has been proposed (Utility Model Application No. 55-141956, Japanese Patent Application Publication No. 58-1989).
No. 123744).

However, in addition to soldering or tin plating on the outer leads, these lead frames require
The inner lead part and the IC element mounting part are plated with gold or silver, and during manufacturing, different types of plating must be applied to each part of the lead frame.
The manufacturing process becomes complicated, leading to a decrease in lead frame productivity and an increase in manufacturing costs.

In addition, solder plating and tin plating have the disadvantage that, not only in the case of hot-dip plating but also in the case of electroplating, it is not possible to speed up plating by adopting a plating solution injection method, which takes time to manufacture and leads to a decrease in productivity. .

<Problems to be Solved by the Invention> The purpose of the present invention is to - eliminate the drawbacks of the prior art mentioned above;
An object of the present invention is to provide a lead frame that can improve the reliability of a semiconductor device, simplify the manufacturing process, improve productivity, and reduce costs.

<Means for Solving the Problems> In order to achieve these objectives, the inventors of the present invention have conducted intensive research and have developed an Ag-Pd system that has excellent solderability and is capable of spouting out plating solution at high speed. The present invention was achieved by discovering that alloy plating should be applied in advance to at least the tips of the outer leads.

That is, the present invention provides a lead frame having a mounting base on which a semiconductor integrated circuit element is mounted in the center and a plurality of lead parts extending toward the mounting base around the mounting base, at least the outer leads of each of the lead parts. Ag-P at the tip
The present invention provides a lead frame characterized by having a plating layer of a d-based alloy or an Ag-Sb-based alloy.

Further, the content of Pd or Sb in the Ag-Pd alloy or Ag-Sb alloy is preferably 2 to 40 wt%.

Hereinafter, preferred embodiments of the lead frame of the present invention shown in the accompanying drawings will be described in detail.

FIG. 1 is a plan view showing a preferred example of the lead frame of the present invention.

The lead frame 1 has a semiconductor integrated circuit (I
C) It has a mounting stand 2 for mounting the element. This mounting base 2 has a size corresponding to the size of the intended IC element.

A plurality of bottle-shaped lead portions 3 are formed around the mounting base 2 and extending toward the mounting base 2.

The lead portion 3 is composed of an inner lead 4 located within the mold resin when resin molded in a later mounting process, and an outer lead 5 protruding outside the mold resin as an external terminal of the semiconductor device. Each of these lead portions 3 is connected by a pair of tie bars 9.9 which are cut and removed in a later process.

The tip portion 41 of each inner lead 4 is located near the mounting base 2, and is electrically connected to the corresponding electrode on the IC element by wire bonding.

FIG. 2 is a sectional view taken along line A-A in FIG. 1. As shown in the figure, in the lead frame 1, a base plating layer 6 is first formed on a lead frame base, and a plating layer 7 (hereinafter referred to as An Ag--Pd or sb gold alloy plating layer 7) is coated thereon, and furthermore, an Ag or Au plating layer 8 is formed on the tower mount 2 and the inner lead tip 41.

The constituent material of the lead frame base material is not particularly limited, and may include iron, iron-based alloys (for example, Fe-42% Ni alloy [42 alloy], Fe-36,5% Ni alloy [Invar), Fe-
32%Ni-5%Co (Kovar), various stainless steels, etc.), copper, copper-based alloys (e.g., phosphor bronze, tinned copper, Fe
(containing copper (CA194), low silver phosphor bronze (C505), etc.)
Materials commonly used for lead frames are possible.

The base plating layer 6 can be plated with various metals depending on the purpose, but in the embodiment shown in FIG. 2, Ni or Ni-based alloy plating is preferable. Also, Ni
Co or CO-based alloy plating having similar properties may also be used.

This base plating layer made of Ni or Ni-based alloy plating plays the following role depending on the metal of the lead frame base. When the lead frame base material is copper or a copper-based alloy, the surface is prevented from oxidation and discoloration [[-], and the Ag-Pd or sb gold alloy plating layer 7 on the - layer is
Prevent the spread of u. When the lead frame base is made of iron or iron-based alloy, the formation of rust on its surface is suppressed.

As the Ni-based alloy suitable for the base plating layer 6, N 1-
Co alloy, Ni-P alloy, Ni-5n alloy, N1-
Examples include Pd alloy and N1-Fe alloy.

In addition, the composition of the Ni-based alloy is determined by the formation of the base plating layer [1]
It will be determined as appropriate depending on the situation.

The preferred thickness of the base plating layer 6 made of Ni or Ni alloy is 0.1 to 4 μm. The reason is that the thickness is 0.1μ
This is because if the thickness is less than 4 μm, the corrosion resistance will be poor, and if the thickness exceeds 4 μm, it will be expensive in terms of workability.

Note that in the lead frame of the present invention, it goes without saying that the formation of the base plating layer 6 as described above is not essential.

The Ag-Pd or sb gold alloy plating layer 7 has a function of improving the solder wettability (solderability) of the outer lead 5. Therefore, unlike the embodiment shown in FIG. 2, the entire lead frame is not coated with the Ag-Pd or sb gold alloy plating layer 7, and as shown in FIG. Only the Ag-Pd or sb gold alloy plating layer 7 may be formed.

Formation of such an Ag-Pd or sb gold alloy plating layer can be performed by a plating solution injection method similar to Ag plating, so that plating can be performed at high speed.

Note that pure A is used instead of the Ag-Pd or sb gold alloy plating layer.
It is not difficult to use a plating layer. That is, pure Ag causes migration and causes a short circuit accident.

P in such Ag-Pd or sb gold alloy plating layer 7
The content of d or Sb is preferably 2 to 40 wt%. The reason for this is that if the content is less than 2wt%, the migration resistance will deteriorate, and if the content is less than 2wt%,
This is because if it exceeds wt%, it becomes hard and brittle.

Moreover, the suitable thickness of the Ag-Pd or sb gold alloy plating layer 7 is 0.1 to 3 μm. The reason is that the thickness is 0.1
This is because if the thickness is less than μm, the solder wettability will be poor, and if the thickness exceeds 3 μm, it will become brittle. Note that if the Ag-Pd or sb gold alloy coating layer is not formed on the portion of the outer lead to be bent, the thickness may exceed 3 μm.

As shown in FIGS. 1 and 2, the Ag or Au plating layer 8 on the mounting base 2 and the inner lead tips 41 improves adhesiveness when fixing the IC element to the mounting base 2, and improves the adhesiveness of the inner lead tips 41. It is formed for the purpose of improving the adhesion of the bonding wire (Au thin wire, A1 thin wire, etc.) to 41.

The preferred thickness of this Ag or Au plating layer 8 is 2 to 10
It is μm. The reason for this is that if the thickness is less than 2 μm, the heat resistance will be poor, and if the thickness exceeds 110 At, it will be expensive.

Note that in the lead frame of the present invention, it goes without saying that the formation of such Ag or Au plating layer 8 is not essential.

In particular, as shown in FIG.
If the layer 7 is also formed, the layer 7 containing Ag contributes to improving the adhesion and wire bonding properties of the IC element, so the Ag or Au plating layer 8 may not be provided. In this case, the outer lead tip 51
Since the Ag-Pd or sb gold alloy plating layer 7 is simultaneously formed on the mounting base 2 and the inner lead tip 41 in one process, the number of processes is reduced and productivity can be improved.

<Example> (Example 1) A lead frame having the shape shown in FIG. 1 was produced by press punching a phosphor bronze plate material (thickness: 0.25 mm). The entire lead frame was coated with 1 μm thick bright Ni plating, and then variously modified Ag-5% Pd alloy plating was applied in the range of 0 to 5 μm using electroplating. The tip of each inner word was partially plated with 5 μm Ag to complete the lead frame.

The IC element 10 is fixed on the mounting base of this lead frame with Ag paste, each electrode on the IC element and the corresponding inner lead tip are wire-bonded with Au wire 11, and resin molded with epoxy resin 12. Then, unnecessary parts were cut and an IC package was assembled (see Figure 5).

On the other hand, for comparison, as a conventional lead frame, a 1 μm thick bright Ni plating was applied to the entire phosphor bronze lead frame similar to the above, and then the top of the IC element mounting table and the tip 41 of each inner lead were plated with 1 μm thick. A copper base plating layer 13 with a thickness of 0.2 μm is formed, and a 5 μm thick Ag partial plating is further applied on the copper base plating layer 13 to complete a lead frame. Using this lead frame, an IC is manufactured in the same manner as described above. The package was assembled (see FIG. 6), and then solder plating 14 with a thickness of about 10 μm was applied to the surfaces of the outer leads exposed from the mold resin by hot-dip plating.

For these IC packages, we examined the solder wettability of the outer leads using the MIL-3TD-202D-208B method, and also bent the outer leads and observed the plating layer on the surface of the bent portion to determine whether cracks occurred. The presence or absence of was investigated. The results are shown in Table 1 below.

The same test as above was also conducted for Ag-5% sb alloy, but the same results as for the Ag-5% Pd alloy were not obtained in this case as well, so the description thereof will be omitted.

The evaluation methods for solder wettability and bending tests are as follows.

i) Solder wettability O: Wetting 95% or more △: Wetting 80-94% ×: Wetting less than 80% ii) Bending test O: Good (no cracks) △: Minute clicks ×: Cracks Table 1 (Example 2) A phosphor bronze lead frame similar to Example 1 was produced,
The same bright Ni plating as described above was applied, and then 0.5 μm thick Ag-Pd alloy plating or Ag-Sb alloy plating with various Pd or sb content in the range of θ ~ 100 wL% by electroplating method. Then, the same Ag partial plating as above was applied to complete the lead frame.

Using this lead frame, an IC was manufactured in the same manner as in Example 1.
The package was assembled, and the solder wettability of the actor lead and the occurrence of cracks at the bent portion of the outer lead were examined by a bending test using the same method. The results are shown in Table 2 below.
Shown below.

Table 2 From the results shown in Tables 1 and 2, the lead frame of the present invention has good solder wettability of the outer leads, especially Ag.
- The thickness of Pd alloy (or Ag-Sb alloy) plating is 0.
It was found that no cracking occurred in the plating layer due to bending of the outer lead in the range of 1 to 3.0 μm or in the range of Pd or sb content in the alloy plating of 2 to 40 wt%.

<Effects of the Invention> According to the lead frame of the present invention, a plating layer of Ag-Pd alloy or Ag-Sb alloy is formed on the tip of the outer lead, which makes it possible to complete a semiconductor device (IC package) Later, it became possible to omit the electro-solder plating or hot-dip semi-F(l) plating that had been applied to the outer leads. As a result, ■ the number of steps was reduced, improving productivity and reducing costs; The completed semiconductor device is placed in a solder plating environment and does not come into contact with the solder plating solution or its gas or undergo thermal history due to molten solder plating, improving the reliability of the semiconductor device.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an example of the structure of a lead frame of the present invention. FIG. 2 is a sectional view taken along line A-A in FIG. 1. 3 and 4 are cross-sectional side views each showing an example of the structure of the lead frame of the present invention. FIG. 5 and FIG. 6 each show an IC in an example.
FIG. 3 is a partially sectional side view showing the structure of the package. Explanation of symbols 1...Lead frame, 2...Mounting base, 3...Lead portion, 4...Inner lead, 41-...Inner lead tip, 5...Outer lead, 51-...・Outer lead tip, 6... Base plating layer, 7-A g -P d or sb gold alloy plating layer, 8-A
g or Au plating layer, 9-... tie bar dam), 10- IC element, 11... bonding wire, 12... epoxy resin, 13... copper base plating layer, 14... solder plating FIG, 2 FIG, 5 FIG, 6 ``0°' and ゛21222

Claims (2)

[Claims] (1) In a lead frame having a mounting base on which a semiconductor integrated circuit element is mounted in the center and a plurality of lead parts extending toward the mounting base around the mounting base, at least the outer lead tip of each of the lead parts A lead frame characterized by having a plating layer of an Ag-Pd alloy or an Ag-Sb alloy. (2) The lead frame according to claim 1, wherein the content of Pd or Sb in the Ag-Pd alloy or Ag-Sb alloy is 2 to 40 wt%.