JPH0674463B2 - Copper alloy for lead frame - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a copper alloy for a lead frame of a device such as an IC and an LSI having a semiconductor as an element, particularly a copper alloy excellent in electric (thermal) conductivity, heat resistance, bending workability and mating adhesion. It is about.

Generally, devices such as ICs and LSIs, which are semiconductors, are all composed of semiconductor pellets, leads, bonding wires and sealed with hermetic seal, ceramic seal or plastic seal technology. Are used.

Thus, as lead frame materials for these devices, Kovar (Fe-29wt% Ni-17wt% Co alloy), Fe-42Ni alloy, Fe, Kovar's clad material, Fe-Ni alloy have been used as lead frame materials for these devices. A cladding material coated with Al, phosphor bronze as a copper alloy, Alloy 194 (Cu-Fe-Zn-P alloy),
Alloy 195 (Cu-Fe-Co-Sn-P alloy), Cu-Sn-P alloy, etc. are used. However, the above iron-based materials are excellent in heat resistance and strength, but cost is high and conductivity is poor and workability is poor.
Copper-based alloys, which have good adhesion and solderability, are becoming the mainstream. However, the above-mentioned copper alloy is inferior in heat resistance and bending workability, so that it cannot exhibit sufficient characteristics as a lead frame material. Especially since high density and high degree of integration have been strongly demanded recently, a material having high conductivity, strength, bending workability and heat resistance and having a surface quality which is easily processed by plating has been required.

The surface quality that is easy to be plated is silver used to improve the connectivity between the semiconductor pellet and the lead frame and the bonding wire and the lead frame, and to improve the oxidation resistance, corrosion resistance and solderability of the lead frame. ,
Due to the excellent coating coverage of gold, nickel, tin, etc., such plating processing occupies a large proportion in the processing cost of the lead frame and greatly affects the quality reliability.

Iron-based materials such as Kovar and Fe-42Ni alloys are not only inferior in electrical conductivity and thermal conductivity, but also difficult to be plated and require special measures. For example, a nickel layer and Sn-
After sequentially depositing a Ni alloy layer, a silver layer is deposited on the Sn-Ni alloy layer, or the surface of the substrate is plated with a cyan alkaline plating solution containing silver and copper, and the surface thereof is coated. Is making a purchase. In general, there is a strong demand for materials satisfying the following seven items as copper alloys for lead frame materials.

(1) Good electrical and thermal conductivity (2) Good heat resistance (3) Good bending workability (4) Great strength (5) Good adhesion to solder (6) Soldering (7) The coefficient of thermal expansion is close to the coefficient of thermal expansion of the molding material. As a result of various studies in view of this, the present invention is superior in heat resistance and bending workability to conventional lead frame copper alloys and has sufficient strength. We have developed a copper alloy for lead frames of semiconductor devices that has electrical (heat) conductivity and adhesiveness of Cr 0.03 ~
0.40 wt% (hereinafter wt% is simply abbreviated to%), Ni 0.03 to 0.
It relates to an alloy containing 40% and P0.005 to 0.03% and the balance Cu.

That is, the alloy of the present invention has Cu as a base material and Cr, Ni, and P added thereto, and the intermetallic compounds such as CrNi ₃ and NixPy and C
Precipitating r and Ni as fine precipitates in the Cu base, and the deoxidizing effect of P have strength, heat resistance and conductivity that exceed conventional wisdom as a copper alloy, and have good plating adhesion and solder. It has adhesiveness.

However, in the alloy of the present invention, Cr 0.03 to 0.40%, Ni 0.03 to
The reason for limiting to 0.40%, P0.005-0.03% is Cr0.03%, Ni
If it is less than 0.03% and P0.005%, the required strength and heat resistance cannot be obtained, and if it exceeds Cr0.40%, Ni0.40% and P0.03%, excellent performance in strength and heat resistance is obtained. This is because electrical and thermal conductivity is reduced, and bending workability, plating adhesion and solderability are also deteriorated.

Examples of the alloy of the present invention will be described below.

Cu was melted using a graphite crucible, the hot water surface was covered with charcoal powder and sufficiently melted, and then Cu-Cr mother alloy, Ni, and P were added in this order, and this was cast to give the composition width shown in Table 1. 150mm, length 2
An ingot having a thickness of 00 mm and a thickness of 25 mm was obtained.

Next, after the surface of this ingot is chamfered by 2.5 mm per side, hot rolling is performed to obtain a plate with a width of 150 mm and a thickness of 8 mm, and then cold rolling and annealing are repeatedly applied to this plate and the final rolling rate is 40%. A cold rolled rolled material having a thickness of 0.45 mm was obtained.

Bendability, conductivity, tensile strength,
The heat resistance, adhesiveness to solder, solderability and coefficient of thermal expansion were measured. The results are shown in Table 1. For comparison, the same measurement was performed for the conventional copper alloy for lead frames shown in Table 1, and the results are also shown in Table 1.

Bending workability is 5 mm wide and 50 mm long from the plate material and cut out a rectangular test piece, and perform 180 ° close contact bending at the center part, observing the surface state of the bending part, cracking, smoothness without wrinkles Bending workability is good, and ○ indicates that cracking is apparent, and bending workability is bad.
A mark and a slight wrinkle in the middle are indicated by a mark.

Conductivity and tensile strength are measured according to JIS-H0505 and JIS-Z22
Based on 41.

The adhesion of the matting is the same as in the mating process of the lead frame for the blunted material. Alkali degreasing (1 minute) -20% nitric acid etching (30 seconds) -Washing-Cyanide strike plating (10
A / dm ² , for 10 seconds) -silver cyanide plating (1 A / dm ² ) gives a 7 μm thick silver plating. This is heated in the atmosphere and the swelling that occurs in the silver plating layer is observed.
○: No swelling after heating for 5 minutes
No swelling is observed after heating at 5 ° C. for 5 minutes, but swelling occurs at 550 ° C. for 5 minutes, and Δ indicates swelling at 450 ° C. for 5 minutes.

Solderability is measured by vertical dipping method at 230 ℃ Sn-40% Pb
Observe the surface of the product immersed in the eutectic solder bath for 10 seconds, and as a result, the one with a smooth surface is marked with a circle, and the one with a slight unevenness on the surface is marked with a triangle, and the unevenness is generated on the surface. What is shown is indicated by X.

Heat resistance is cut out from the tensile test specimen specified in JIS-Z2201 from the rolled material, and this is 350
After annealing at 5 ° C for 5 minutes, a tensile test is performed, and the tensile strength is 30% or less compared to that before annealing. Poorness is indicated by a cross.

The thermal expansion coefficient was measured using the compressive load method and tested. The non-equilibrium of the balance was used for the load on the material, and the displacement of the sample was detected.

As is apparent from Table 1, the alloy of the present invention has an electric conductivity of 90 to 93% IA.
CS and tensile strength of 39 to 42 kg / mm ² and excellent bending workability and heat resistance. Tensile strength comparable to Cu-Fe-Zn-P alloy and much better heat resistance and electrical resistance. It can be seen that it has conductivity (heat conductivity). Further, it can be seen that the plating adhesion and solderability are sufficiently superior to the Cu-Fe-Zn-P alloy. The coefficient of thermal expansion is Cu-Fe-Zn-
The values are almost the same as those of the P alloy and Cu-Sn-P alloy, and there is no problem.

On the other hand, in Comparative Alloys Nos. 7, 8 and 9 in which the contents of Cr, Ni and P are less than the composition range of the alloy of the present invention, the heat resistance was not improved and the contents of Cr and Ni of the alloy of the present invention were not improved. Comparative alloys Nos. 10, 12, and 13 in which the contents of comparative alloys No. 10 Cr, Ni, and P, which are higher than the composition range, are higher than the compositional range of the alloy of the present invention, tensile strength,
It can be seen that although the heat resistance is sufficient, the conductivity is remarkably lowered, and the bending workability, the plating adhesion, and the solderability are poor.

As described in detail above, the alloy of the present invention is a copper alloy having both excellent strength, heat resistance and sufficient conductivity, bending workability, mating adhesion, and solderability, and has a thermal expansion coefficient of the conventional level. It exhibits almost the same value as copper alloy, and has a remarkable effect as a lead frame material for semiconductor devices.

Claims (1)

[Claims] 1. Cr0.03-0.40 wt%, Ni0.03-0.40 wt%, P
A copper alloy for a lead frame, characterized by containing 0.005 to 0.03 wt% and the balance being Cu.