JPH08319528A - Copper alloy for semiconductor lead frame excellent in silver plating suitability - Google Patents

Abstract

PURPOSE: To prevent the occurrence of projection of Ag plating at the time of applying Ag plating to a copper alloy for a Cu-Ni-Si type semiconductor lead frame. CONSTITUTION: This alloy is a copper alloy for semiconductor lead frame, excellent in Ag plating suitability, which has a composition consisting of, by weight, 0.4-4.0% Ni, 0.1-1.0% Si, 0.05-2.0% Zn, 0.02-1.0% Mn, 0.00001-0.001% (not including 0.001%) Mg, <=0.003% S, further 0.001-0.01%, in total, of one or >=2 kinds selected from 0.001-0.01% B, 0.001-0.01% Cr, 0.001-0.01% Ti, and 0.001-0.01% Z, and the balance copper with inevitable impurities. By limiting Mg content to <0.001%, the occurrence of projection of Ag plating can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copper alloy for a semiconductor lead frame having excellent Ag plating property, and more specifically, to A
The present invention relates to a copper alloy for semiconductor lead frames capable of preventing the occurrence of g-plated protrusions.

[0002]

2. Description of the Related Art Semiconductors such as ICs and transistors are excellent in strength and heat dissipation and have a low manufacturing cost.
(See Japanese Patent No. 8541 and Japanese Patent Publication No. 62-31059)
Copper alloy lead frames such as are often used.
In the manufacturing process of a lead frame, a copper alloy material is processed into a lead frame shape by etching or pressing, and then Cu or Ni or Ag is entirely or partially formed.
Single or multilayer plating such as. In a semiconductor assembly process, a lead frame undergoes a die bonding process for bonding a semiconductor element to a lead frame and a wire bonding process for bonding a semiconductor element and a lead frame with an Au wire. Ag plating is applied on top of Cu plating.

[0003]

The Ag plating is required to be smooth in order to prevent defective bonding between the semiconductor element and Au wire and the lead frame, but in the past, the Ag deposition state was non-uniform. Surface defects such as Ag-plated protrusions having a diameter of 20 to 100 μm and a height of several μm often occur. Since the Ag plating protrusions may be a factor that lowers the reliability of the joint between the semiconductor element and the Au wire and the lead frame, the plating pretreatment conditions and Ag plating conditions have been widely studied to prevent this. However, there is still no effective solution, and the current situation is to cope with the sacrifice of productivity by reducing the current density of Ag plating.

The present invention has been made in view of the above problems of the prior art. By improving the copper alloy material itself, Ag is improved.
It is an object of the present invention to prevent the occurrence of plating protrusions, thereby improving the reliability of the joint portion of a semiconductor device, and to prevent the productivity of lead frames from decreasing.

[0005]

The present inventors have found that Cu-Ni-Si known as a copper alloy for semiconductor lead frames.
As a result of detailed investigation of the cause of the Ag-plated protrusions in the alloys based on alloys, it was found that the generation state of the Ag-plated protrusions depends on the Mg content added to the copper alloy. The invention was completed.

That is, the copper alloy for a semiconductor lead frame excellent in Ag plating property according to the present invention is Ni: 0.4.
~ 4.0 wt%, Si: 0.1-1.0 wt%, Zn:
0.05-2.0 wt%, Mn: 0.02-1.0 wt
%, Mg: 0.00001 to 0.001 wt% (however,
0.001 wt% is not included), S: 0.003 wt% or less, and B: 0.001-0.01 wt%,
Cr 0.001-0.01 wt%, Ti: 0.001-
0.01 wt%, Zr: 0.001 to 0.01 wt% One or more selected from 0.001 in total
A copper alloy containing 0.01 wt% and the balance copper and unavoidable impurities, or Sn: 0.1 to 0.1 in addition to the above alloy elements.
It is a copper alloy containing 2.0 wt%.

[0007]

The function and content of the copper alloy according to the present invention will be described below.

Mg When the Mg content is 0.001 wt% or more in the copper alloy, Ag plating protrusions start to be generated, and the number thereof increases as the Mg content increases. On the other hand, Mg is an essential element that fixes S mixed in from the raw material, the furnace material and the atmosphere in the matrix in the form of a stable compound with Mg to improve the hot workability. As described later, Mn has a similar effect, but the fixing force of the compound is weak, and Mg is a necessary element to complement the effect of Mn. When Mg is not contained, free S moves along the grain boundaries during heating during hot working or during hot working to cause intergranular cracking. Although the effect of adding Mg is exhibited at 0.00001 wt% or more,
Its content is 0.001 to suppress Ag plating protrusions.
Limited to less than wt%. The Mg content is 0.0
001 to 0.001 wt% (however, 0.001 wt% is not included) is desirable because the above effect is stabilized,
More preferably, it is 0.0001 to 0.0008 wt%.

Ni Ni is an element that improves the strength of the copper alloy. If the content is less than 0.4 wt%, the strength is not improved even if Si is contained in an amount of 0.1 to 1.0 wt%. If it is contained in an amount of more than 0.0 wt%, the electrical conductivity is lowered, the workability is lowered, and the improvement in strength is reduced. Therefore, the Ni content is 0.4 to 4.0 wt%.

Si Si is also an element for improving the strength of the copper alloy. If the content is less than 0.1 wt%, Ni is 0.4 to 4.0 wt.
% Does not improve the strength, and 1.0 wt%
If it is contained in excess of%, the workability and the electrical conductivity decrease, and the solder adhesion also decreases. Therefore, the Si content is set to 0.1 to 1.0 wt%.

Zn Zn is an element having an effect of suppressing peeling of plated tin and solder, and if the content is less than 0.05 wt%, such an effect is small, and if it exceeds 2.0 wt%. If so, the solder wettability decreases. Therefore, the Zn content is 0.05 to 2.0 wt%.

Mn Mn is an element that easily bonds with S, fixes S as MnS and improves hot workability, and its content is 0.02 w.
If it is less than t%, this effect is small, and if it is contained in excess of 1.0 wt%, this effect is not only saturated, but also the flowability of molten metal at the time of the ingot is deteriorated and the ingot yield is lowered, resulting in a poor conductivity. The rate also decreases. Therefore, the Mn content is 0.02 to 1.0.
wt%.

S S is an impurity which is mixed from a raw material, a refractory material such as a furnace or a gutter, a fuel, an atmosphere, etc., exists as a compound with a metal or as free S, and is a main cause of cracking during heating or hot working. It is an element. If S is contained in an amount of more than 0.003 wt%, even if Mg is contained in an amount of nearly 0.001%, a compound with Mg cannot be formed completely, and free S moves through the grain boundaries and grain boundary cracking easily occurs. . Therefore, it is desirable that S is not present, and if S is present, the content must be limited to 0.003 wt% or less.

Sn Sn is an element that contributes to the improvement of strength, stiffness strength and repetitive bendability. If the content is less than 0.1 wt%, these effects are small, and if it exceeds 2.0 wt%. And reduces the conductivity and hot workability. Therefore, the Sn content is set to 0.1 to 2.0 wt%.

B, Cr, Ti, Zr B, Cr, Ti, Zr are all elements that improve the hot workability, and even if each element described above is contained in a specific range, hot working is performed. It is possible to solve the problem that time cracking cannot be completely prevented. If the content is less than 0.001 wt%, cracking during hot working cannot be suppressed, and 0.01 wt% If it is contained in excess of%, the molten metal is likely to be oxidized and a sound ingot cannot be obtained. Therefore, the contents of B, Cr, Ti, and Zr are each 0.001 to 0.01 wt%. In addition, B, C
Even when two or more of r, Ti and Zr are contained, the total content is 0.0 due to the same reason as described above.
It is set to 01 to 0.01 wt%.

In addition to the elements described above, F
0.2 wt% of one or more of e, Co and Al elements
% Or less, the properties necessary for the copper alloy of the present invention, that is, high conductivity, high strength, heat resistance, solderability, heat-resistant peelability of solder, hot workability, etc. are practically maintained without problems. It

[0017]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples.

(Example 1) Cu-having the composition shown in Table 1 below
The Ni-Si based copper alloy was melted in the atmosphere under the coating of charcoal using an electric furnace.

[0019]

[Table 1]

After that, the molten copper alloy is cast into a cast iron book mold to have a thickness of 50 mm and a width of 70 m.
An ingot having a length of m and a length of 180 mm was produced. After each of these ingots was ground by 2.5 mm on both sides, 900
It was hot-rolled at a temperature of ℃ to a thickness of 15 mm, and then rapidly cooled in water from a temperature of 700 ℃. After removing the scale on the surface of this hot rolled material by a grinder, cold rolling was performed until the thickness became 0.5 mm. This cold rolled material was heated at a temperature of 500 ° C. for 2 hours, pickled, and then cold rolled to obtain a plate having a thickness of 0.25 mm.

Test pieces each having a thickness of 0.25 mm, a width of 25 mm and a length of 60 mm were cut out from these plates and subjected to Cu undercoating and Ag plating under the conditions shown in Table 2 below.
The surface was observed with a 40 × stereoscopic microscope to measure the amount of Ag-plated protrusions having a diameter of 20 μm or more. The result is shown in Figure 1.
Shown in

[0022]

[Table 2]

As shown in FIG. 1, when the Mg content corresponding to the embodiment of the present invention is less than 0.001 wt%, no Ag plating protrusions are generated, and when the Mg content is 0.001 wt% or more, the Mg content is increased. The number of Ag-plated protrusions increases with the increase of

(Example 2) A Cu-Ni-Si alloy was melted in the atmosphere using an induction furnace and a width of 5 was obtained by a semi-continuous casting method.
An ingot having a length of 00 mm, a length of 4000 mm and a thickness of 150 mm was produced. The composition of the ingot is shown in Table 3 below.

[0025]

[Table 3]

The ingot was heated to 880 ° C. and hot-rolled to a thickness of 15 mm. The surface after hot rolling was observed and the hot workability was evaluated from the occurrence of cracks.

[0027]

[Table 4]

As shown in Table 4, No. 1 corresponding to the embodiment of the present invention. 9 and No. 10 is 0.00 for each Mg
Since it contains 03 wt% and 0.0007 wt%, it has excellent hot workability and no cracking occurs. On the other hand, N which is a comparative example
o. No. 11 had a Mg content of less than 0.00001 wt% and thus was inferior in hot workability and cracked.

[0029]

According to the present invention, in the Ag plating of the Cu-Ni-Si-based semiconductor lead frame copper alloy, Ag is used.
It is possible to prevent the generation of plating protrusions, improve the reliability of the joint portion of the semiconductor device, and greatly contribute to the improvement of the productivity of the lead frame.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the Mg content in a Cu—Ni—Si-based copper alloy material and the number of Ag plated protrusions generated.

Claims (2)

[Claims] 1. Ni: 0.4 to 4.0 wt%, Si:
0.1-1.0 wt%, Zn: 0.05-2.0 wt
%, Mn: 0.02-1.0 wt%, Mg: 0.000
01 to 0.001 wt% (excluding 0.001 wt%), S: 0.003 wt% or less, and
B: 0.001-0.01 wt%, Cr 0.001-
0.01 wt%, Ti: 0.001-0.01 wt%,
Zr: Ag plating property characterized by containing 0.001 to 0.01 wt% in total of one or more selected from 0.001 to 0.01 wt% and the balance copper and unavoidable impurities An excellent copper alloy for semiconductor lead frames. 2. Ni: 0.4 to 4.0 wt%, Si:
0.1-1.0 wt%, Zn: 0.05-2.0 wt
%, Mn: 0.02 to 1.0 wt%, Sn: 0.1
2.0 wt%, Mg: 0.00001 to 0.001 wt
% (However, not including 0.001 wt%), S: 0.00
Contains 3 wt% or less, and further B: 0.001 to 0.0
1 wt%, Cr 0.001-0.01 wt%, Ti:
0.001 to 0.01 wt%, Zr: 0.001 to 0.
Copper for semiconductor lead frames with excellent Ag plating properties, characterized by containing 0.001 to 0.01 wt% in total of one or more selected from 01 wt% and the balance copper and unavoidable impurities alloy.