JPS61183425A - Precipitation type copper alloy material for lead frame - Google Patents

Abstract

PURPOSE:To obtain the titled material superior in conductivity, strength and electrical plating property, by adding, incorporating specified quantities of Cr, Zr to Cu. CONSTITUTION:As for lead frame material in semiconductor electron inductry, Cu alloy contg. 0.2-1.5% Cr, <0.5% Zr is melted to prepare ingot. This ingot is scalping treated, then held at 950-1,000 deg.C for 2-3hr, then hot rolled to plate material. Next, said plate is cold rolled including intermediate annealing at <=570 deg.C, then annealed finally to prepare annealed sheet having about 0.25mm thickness. Heterogemous phases of Cr, Zr ppt.s having <=0.5mum size are dispersed finely and uniformly in lead frame sheet made of ppt. type Cu alloy, and lead frame superior in conductivity, strength and also in Ag plating adhesive property is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION A) Industrial application field The present invention is applied to transistors and I/O in the semiconductor electronic industry.
This invention relates to improving the plating adhesion of lead frame materials made of precipitated copper alloys used in the assembly of C and other materials.

(b) Conventional technology When assembling transistors and ICs, so-called die bonding is performed to fix, for example, a Si chip to a part of the surface of a lead frame material, and a so-called die bonding process is performed to bond a thin wire bond wire (for example, Au wire) to another part. Wire bonding is carried out, but in order to carry out these bondings industrially, one of the factors that increases reliability is to apply plating with high adhesion to the small areas on the surface of the lead frame material. It is said to be one.

Currently, precipitated copper alloys are often used as lead frame materials in the assembly of transistors, ICs, and the like. This is because some of these alloy materials share high strength and high conductivity. Ag is normally used for plating, and electroplating is commonly used as the plating method. This is because it is suitable for industrially applying adhesive plating.

ρ→Problem to be Solved by the Invention For lead frame materials, ease of plating and excellent adhesion are important characteristics for obtaining reliability of transistors, ICs, etc. Therefore, in order to obtain these characteristics, cleaning, activating, and smoothing the surface of the lead frame, which is the base metal for plating, is an important pretreatment. It is said that reducing the presence of as much as possible improves the adhesion of plating.

Lead frame materials, on the other hand, are often required to have high strength and high conductivity. In such a case, it is known to use a precipitation type alloy as the material of the lead frame, and to precipitate a different phase consisting of the added elements through heat treatment. In other words, in order to share high strength and high conductivity with the lead frame material, a precipitated copper alloy containing precipitates is used, and in order to obtain the above-mentioned bonding reliability, a non-conductive copper alloy is used, which avoids the presence of precipitates. The problem of the present invention is to resolve the contradiction between the two by deliberately adopting a plating method.

(2) Means for solving the problem Even in precipitation type alloys, depending on the added elements, the different phases that precipitate are finely dispersed, which improves the adhesion of Ag plating, and also provides suitable strength and conductivity for the lead frame. Maintains high performance. Attempts should be made to find such additive elements and to find means to finely disperse the precipitates.

The present invention was made for the purpose of narrowing down the
A precipitated copper alloy material with high conductivity, high strength, and good electroplating properties has been obtained. That is, Cr and Zr are added to Cu, and the content (weight %) of Cr is 0.2 to 1.
5%, Zr is less than 0.5 inch during plastic working of alloy material,
Appropriate heat treatment, i.e. intermediate annealing temperature during cold working, is 570℃.
If the temperature at the start of hot working is set at 950°C or higher and the end temperature at 700°C or higher, the precipitates become fine particles with a size of 0.5 μm or less and are dispersed in the Cu. I found out that.

When melting and casting the above-mentioned alloy of the present invention, it is preferable to use a vacuum melting and casting method so that the amount of oxygen in the molten metal is 50 ppm or less, since Zr is easily oxidized and may be lost during melting. be.

(e) Effect The alloy to which Cu1CCr is added exhibits significantly greater precipitation hardening due to solubility change than other precipitation type copper alloys. Further, an alloy in which Zr is added to Cu is a precipitation type copper alloy with high strength and high conductivity. The present invention uses Cr, which is highly effective as such an additive element.
They have found that by simultaneously containing Cu and Zr within the range according to the present invention and subjecting them to appropriate heat treatment, the plating adhesion improves as the precipitate foreign phase becomes finer in size.

As the above-mentioned appropriate heat treatment, the heating temperature of hot rolling is 95%.
It is preferable to maintain the temperature at 0 to 1000°C for 2 to 3 hours.

In this way, the precipitates generated during casting of Zr and Cr will dissolve into solid solution, and the remaining precipitates will become smaller. Further, if the temperature during rolling falls below 700°C, precipitation will occur, so it is preferable to roll for a short period of time and to rapidly cool the rolling after finishing. Further, it is necessary that the intermediate annealing temperature during cold rolling is 570°C or lower.

If this is done, the precipitates will not become large, and the shorter the temperature holding time is, the better the conductivity and strength will be at appropriate values.

The reason why Cr is limited to 0.2 to 1.5 inches and Zr is limited to 0.5 inches or less is that within these ranges, both properties of strength improvement and electrical conductivity are satisfied as a lead frame.

If the Cr content exceeds 1.5%, the strength is higher than practical. If the Cr content is less than 0.21, the conductivity is good, but the strength is low (not practical. Also, if the Zr content exceeds 0.5%, the strength is higher than practical.) However, it is difficult to melt and cast, making it impractical.

(to) Example 1'1&Ll trVkL2 tNa3 of the example table,
Copper alloy according to the present invention having four types of chemical compositions I'&4 and N11 having a chemical composition outside the scope of the present invention as a comparative example
15. Melt the copper alloy of 6゜l'V&L7 in vacuum,
The ingot was cast and hot rolled at 950'C to a plate thickness of 7mm, with an intermediate annealing temperature of 5mm during cold rolling.
Two types of heat treatment annealing were performed at 50°C for 2 hours and at 650°C for 2 hours to adjust the size of the different precipitated phases, followed by bearing pressure cold rolling and final annealing to obtain an annealed plate with a thickness of 0.25 mm. Ta.

A sample of 20 mm in length and width was taken from the obtained plate material, the plate surface was etched with a mixed solution of H2SO, -H20□, and observed with a scanning electron microscope at 1000 to 5000 times magnification to determine the size of the precipitated foreign phase. Examined. Tensile strength, elongation, and electrical conductivity were measured as strength, and adhesion of Ag plating was measured at a thickness of 0.
5μ on a sample plate with a width of 25mm and a length of 30m + n and a length of 80mm.
After silver plating and heating in the air for 450'CXS minutes, the swelling on the surface was observed visually or using a stereomicroscope.

The evaluation was ``○'' for 5 or less bulges, and ``X'' for 5 or more bulges.

The results are also listed in the table. According to public knowledge, 41. according to the present invention. The size of the precipitate is 0 for both *Na3 and 4.
．． All those with a diameter of 5 μm or less had high strength and conductivity, and good adhesion to the plating. The intermediate annealing temperature during these heat treatments was 550°C for 2 hours. However, N[L2 and Arashi 4
Samples with precipitate sizes of 0.5 μm or more had high strength, but conductivity was slightly lower than those with precipitate sizes of 0.5 μm or less, and plating adhesion was poor. The intermediate annealing temperature of the heat treatment was 650° C. for 2 hours.

Comparative example N[15, lV! Regarding L6 and depression 7, the size of the precipitates was 0 when the intermediate annealing was performed at 550°C for 2 hours.
．． They were small, less than 5 μm, but those heated at 650°C for 2 hours were thicker, more than 0.5 μm. However, regardless of whether the precipitates were large or small, the plating adhesion was poor in all cases except Slow 5 (unsuitable as a lead frame material. In addition, 5 had good plating adhesion but lacked strength. Therefore, it was unsuitable for lead frames.

(g) Effects of the invention As mentioned above, Cr is an added element of the precipitation type copper alloy.

If Zr is selected and the composition is within the range according to the present invention, the foreign phase of the precipitate will be fine-grained and dispersed through appropriate heat treatment, the plating adhesion will be good, and the strength and conductivity will be sufficient for a lead frame. to hold.

Therefore, the lead frame material according to the present invention contains Ag.
Even after plating, die bonding, and wire bonding, the bond maintains its high strength, allowing reliable ICs and transistors to be obtained.

Claims (1)

[Claims] Contains 0.2 to 1.5% of Cr and 0.5% or less of Zr, and the size of both Cr and Zr precipitates is 0.5 μm
A precipitated copper alloy material for lead frames characterized by the following: