JPS63169056A - Lead frame material - Google Patents

Abstract

PURPOSE:To stabilize weldability on wire-bonding of a gold wire, by disposing a high-purity copper layer of 0.5mum or more in thickness on a surface of an iron-nickel group alloy. CONSTITUTION:A high-purity copper layer of 0.5mum or more in thickness is disposed on a surface of an iron-nickel group alloy. This copper layer is formed into a soft metal copper material to have internal porosity smaller than a plating material. Therefore, oxidation-proof and corrosion-proof properties in this copper layer are made approximately identical with those in pure copper, and wire-bonding performance of this copper layer is stabilized when a gold wire is pressed thereon by heating under a reducing atmosphere. Further, when the copper layer on the surface of the iron-nickel group alloy is thereafter annealed at a specific temperature, H2 gases and impurities and the like contained on plating are removed and diffused together with reduction of voids, so that surface quality of the layer can be stabilized.

Description

[Detailed Description of the Invention] [Industrial Application 9g/month] The present invention relates to a lead frame material, and more particularly,
The present invention relates to semiconductors such as transistors or RC and lead frame materials, particularly to semiconductor lead frame materials to which gold wires or copper wires of bonding wires can be directly bonded.

[Prior art] In general, Fe-Ni alloy (42 alloy) and copper alloy are used as lead frame materials for semiconductors. It consists of three parts: an inner lead part that is sealed and an external lead part that serves as a lead wire and is usually soldered.

The silicon element in the Guibat part is Au-9i, A
It is attached by bonding with G-8i, etc., by bonding with conductive paste, or by soldering, and the electrodes and inner leads of this element are bonded by thermocompression bonding or ultrasonic thermocompression bonding with Au wire or Cu wire. However, it is difficult to directly bond Au or Cu wires in 4270I, and it has been common knowledge that the inner lead portions are plated with Au or Ag.

However, it is generally known that Au wire can be thermally welded to pure copper in a reducing atmosphere;
It is possible to use Cu plating instead of G plating, but it is possible to heat pressure weld Au wire to Cu plating immediately after plating, but Cu plating has high porosity and surface roughness of 0.8~ Because the roughness is 1.0 μm, it oxidizes at room temperature in a short time, and is easily oxidized during heat bonding with Au wire, causing alloy components in the base material, especially Fe, to diffuse to the surface layer and cause I
A problem with multi-pin leads such as C leads is that the bonding strength of all the pins becomes unstable.

In addition, by plating the external leads with Cu, it becomes easier to perform exterior plating (tin or solder) or solder dipping, or by plating copper with a thickness of 0.5 μm or more on 42 alloy and then applying tin on top of it. Alternatively, if solder plating or solder dipping is performed, 15
After being held at a temperature of 0° C. for 1000 hours, it becomes difficult for the tin or solder to remain in close contact without peeling off. That is, η phase (Cua
It has been found that an ε phase (CuiSn) is generated under the ε phase (CuiSn), voids are generated at the interface between the ε phase and the copper plating layer, and these voids are connected to cause peeling.

From the above explanation, it is conceivable to perform Cu plating only on the Guibat part and the finger lead part, but since the surface roughness is as rough as 0.8 to 1.0 μm and the porosity is high, Cu plating may be applied to the base material during wire bonding. There is a problem that the alloy components diffuse to the surface and deteriorate bonding properties, and eventually local plating of Ag has to be performed.

[Problems to be Solved by the Invention] As explained above, the present invention is based on various problems of conventional semiconductor glue frame materials, and the present invention has been made through intensive research and repeated consideration. As a result, it is possible to reliably and reliably join the Au wire directly to the lead frame without applying Ag plating only to the die pad and finger leads, and the leads provide good external lead parts. They developed the Flay 14 material.

[Means for Solving the Problems] The lead frame material according to the present invention is characterized by having a highly pure copper layer with a thickness of 0.5 μm or more on the surface of an iron-nickel alloy. It's in being.

The lead frame material according to the present invention will be explained in detail below.

The lead frame material according to the present invention has a copper layer of 0.5 μm or more on the surface of an iron-nickel alloy, and has a maximum roughness of 0.4 μm or less, which is 0.8 μm or less than that of the plating material. ,
Because it is a soft metallic copper that is finer than 0 μm and has smaller internal porosity than plating materials, its oxidation resistance and corrosion resistance are almost the same as pure copper, and as a result, it is difficult to heat gold wire in a reducing atmosphere. Wire bonding properties by pressure welding are also stable.

Furthermore, by cold rolling the copper layer on the surface of the iron-nickel alloy with an area reduction of at least 10%, the voids that existed during bonding can be changed and at the same time the maximum roughness can be reduced. was adjusted to 0.4 μm or less, and then 40
By performing annealing at a temperature of 0 to 600° C. for at least 1 second, voids are reduced, and at the same time, IE2 gas and impurities contained during plating are removed and diffused to stabilize the surface quality.

In addition, the lead frame material according to the present invention can be produced by providing a copper layer of 0.5 μm or more on the surface of an iron-nickel alloy, and by annealing it at a temperature of 400 to 600°C for at least 1 second to remove the alloy components in the base material. In particular, it is possible to prevent Fe from appearing on the surface layer.

Since stress is locally applied to the base material during cold working, the annealing conditions for softening the Cu surface layer and simultaneously removing residual stress in the base material are: at a temperature of 400 to 600°C for at least 1 second; Furthermore, from the viewpoint of productivity, it is preferable to set the time to a maximum of 30 seconds.

In addition, the external lead material with solder 1 does not peel off even after being held at a temperature of 150°C for 1000 hours. This means that the copper layer becomes soft metallic copper, reducing voids during plating. This is because.

[Example] Examples of lead frame materials according to the present invention will be described.

Example Fe-42 wt% N1 (42 alloy) H/2 material, plate thickness 0.15 mm, was plated with copper, copper plating thickness, area reduction after skin pass rolling, annealing conditions, and wire made of Au wire Bonding property, corrosion resistance by moisture test (temperature 40℃, humidity 95% or more, time 4 hours), soldering (Pb-9n solder, flux is Alpha 1)
00, temperature 230°C, immersion time 5 seconds) and then too at a temperature of 150°C.

A constant temperature holding test was conducted to examine the solder adhesion.

In addition, all materials were subjected to surface analysis based on varnish force in advance.

Table 1 shows the results.

Wire bonding test The lead frame material was mounted on the holder of a thermocompression wire bonder, shielded with 1100 pp of H, N containing gas, and gas, the stage temperature was set to 250°C, and the contact pressure load was 100.
Wedge bonding was performed using an Au wire with a diameter of 30 μl under the conditions of 30 g, and the breakage point and breakage load were measured using a pull tester.

In Table 1, No. 1 to No. 5 are lead frame materials according to the present invention, and the surface roughness after copper plating is 0.
The plating layer thickness is 1.0 to 5.0 μm, and the surface roughness is 0.3 to 0.4 μm by skin pass processing to a thickness of 0.55 to 4.0 μm.
m, and further heat treatment at a temperature of 400 to 600°C for 1 second or more improves corrosion resistance and improves the corrosion resistance by half a day.
It is clear that the adhesion after 1000 hours is improved at a temperature of 0°C.

The bonding strength shows a value of 10 g or more even in the plated material as it is and in the subsequently rolled and annealed material, and there is no peeling at the fractured part and it is on the acceptable line.

However, considering corrosion resistance, if copper plating is used as it is, the surface remains activated and discolors very easily, resulting in unstable surface properties and poor bonding properties, as shown in comparative materials No. 6 to No. 8. This indicates that deterioration over time cannot be avoided.

[Effects of the Invention] As explained above, since the lead frame material according to the present invention has a copper layer with a thickness of 0.5 μm or more on the surface of the iron-nickel alloy, it is not necessary to heat-treat the lead frame material. This reduces voids in the copper layer, removes TL gas, and removes local stress caused by the skin pass of the base metal, resulting in finer surface roughness of the copper layer and improved bonding properties during wire bonding of gold wires. It is stable, there is no peeling of the solder on the external lead part, and the copper layer improves electrical and thermal conductivity.Especially compared to silver, copper can reduce porosity through rolling and annealing. It has the excellent effect of making a large contribution to the semiconductor industry because the layer can be made thinner and productivity and quality can be improved by shortening the plating time.

Claims (1)

[Claims] A lead frame material characterized by having a highly pure copper layer with a thickness of 0.5 μm or more on the surface of an iron-nickel alloy.