GB2158095A - Copper alloys for integrated circuit leads - Google Patents

Abstract

The invention provides copper-nickel alloy having high strength and high conductivity for lead conductor materials and/or lead frames for transistors, integrated circuits, and the like. The alloy comprises copper and from 0.05 to 3.0% by weight nickel; from 0.01 to 1.0% by weight silicon; and from 0.01 to 0.1% by weight phosphorus. In a preferred embodiment 0.01 to 3% by weight % of iron is also added. An improved method is provided for fabricating the alloy according to a specific series and sequence of steps, including steps at specific conditions and for specific times, for providing precipitation hardening.

Description

SPECIFICATION Copper alloys This invention relates to copper alloys, and especially to a novel series of copper alloys, and methods for their production, which are useful for making electrical and electronic parts.

Background of the invention In the field of metallurgy, it is advantageous to provide high strength, high conductivity, copper-base alloys. it is also advantageous to provide a method for producing copper-base alloys, and copper alloy plate having high tensile strength and high electrical conductivity, in an economical manner and with desirable fabrication characteristics for making electrical or electronic parts.

To this end, copper by itself has excellent electrical conductivity and other characteristics. However, copper by itself is deficient in tensile strength for many applications. Thus, extensive research has long been undertaken to increase the tensile strength of copper by adding thereto alloying elements, such as tin, manganese, silver, zinc, cobalt, titanium, chromium and zirconium. In particular, the tensile strength of copper has been increased by adding tin as an alloying element, as described in Japanese Patent Applications 52-78621 and 53-89662, as well as U.S. Patent 4,337,089. However, the electrical conductivity of the resulting alloys has been so reduced that these alloys have not been suitable for the lead frames of transistors or integrated circuits, which require a high tensile strength and a high electrical conductivity respectively.Such tensile strengths are in the range of greater than about 40 dg/mm2. Such electrical conductivities have been in the range of about 60% or more of the conductivity of pure copper, which is referred to as a conductivity percent IACS, as referred to in the above-mentioned U.S. Patent 4,337,089.

It is also advantageous to improve the fabrication characteristics and the method for making copper nickel alloys by reducing the brittleness and the hot working steps known heretofore, and/or by reducing the poor workability in the heretofore known reduction ratios of the cold working, which resulted from adding such alloying elements as tin, or too much of some other elements, such as the above-mentioned elements.

It is further advantageous to reduce the cost of copper- nickel alloys by eliminating expensive alloying elements, such as tin and/or manganese, by reducing the amounts of the additives, and/or by finding cheaper additives.

Still further, it is advantageous to improve the elongation characteristics of copper-nickel alloys known heretofore for the above-mentioned applications, including the mentioned lead frames for transistors and/or integrated circuits.

Accordingly, it is an object of this invention to provide and to fabricate improve copper-nickel alloys having the required high tensile strength, high electrical conductivity, and other characteristics.

It is a further object of the invention to produce economical copper-nickel alloys with excellent properties by using easily obtainable and inexpensive elements.

It is another object to provide a copper-nickel alloy with high electrical conductivity and also high tensile strength for lead frames for transistors, integrated circuits and the like.

It is another object to provide alloying additives that can be easily utilized industrially without difficulty.

It is another object to provide an improved precipitation hardening method.

It is another object to provide ways of increasing the tensile strength of copper-nickel alloys.

It is another object to provide precipitation hardening type alloys.

It is a still further object to provide a copper-nickel alloy by a precipitation method of fabrication that increases the strength and does not decrease the electrical conductivity and elongation of the alloy by adding specific weight percents of nickel, phosphorus and silicon to the copper, and/or by adding specific weight percents of iron, nickel, phosphorus and silicon to the copper.

Summary of the invention In accordance with this invention, it has been discovered that certain additives may be eliminated from the heretofore known alloys. These additives are tin, manganese, silver zinc, cobalt, titanium, chromium and zirconium.

This invention accordingly provides an economic copper- nickel alloy containing the following components: from about 0.05 to about 3.0% by weight nickel, from about 0.01 to about 1.0% by weight silicon; from about 0.01 to about 0.1% by weight phosphorus, and optionally from about 0.01 to about 3.0% iron, the balance being copper.

The invention also involves a novel method of producing copper-nickel alloys economically for electrical or electronic parts requiring high tensile strength and high electrical conductivity, such as the abovementioned strengths and conductivities.

To this end, the process comprises the steps of economically casting these elements into a copperbase alloy, hot rolling the alloy at a temperature between about 750 and about 950 C, rapidly cooling the hot rolled alloy; cold rolling the resultant alloy with a size reduction of between about 60% and 80%, annealing the resultant product at a temperature between about 40000 and 5200C for about two hours; rapidly cooling the resultant product; cold rolling the resultant product with a size reduction of between about 50% and about 70%; and low temperature annealing the resultant product at a temperature between about 25000 and about 40000.

In another aspect, the invention provides a novel precipitation-hardened alloy and a method for producing a product with improved elongation characteristics.

With the proper selection of elements and their amounts, as well as the proper selection of steps and their sequence during fabrication, as described in more detail hereinafter, the desired high tensile strength, high electrical conductivity, copper-nickel alloy is achieved with the desired elongation and other fabrication characteristics.

The above and further novel features and objects of this invention will become apparent from the following detailed description of preferred embodiments when read in connection with the accompanying drawings, and the novel features will be particularly pointed out in the appended claims. It is to be expressly understood, however, that the drawings are not intended as a definition of the invention, but are for the purposes of illustration only.

Brief description of the drawings In the drawings; Figure 1 is a graphic representation of the variation of the physical properties as a function of the annealing temperatures and times of one embodiment of the copper- nickel alloys of this invention (A) and conventional copper alloys (B) having added elements that are eliminated by this invention; Figure 2 is a graphic representation of the variation of the physical properties as a function of the annealing temperatures and times of the copper alloy (A') of another embodiment of the present invention and the conventional alloys (B) of Fig. 1.

Detailed description of the preferred embodiment This invention is useful for lead frames and conductors for transistors and integrated circuits requiring high tensile strength and high electrical conductivity. The required tensile strength is in the range of at least 40 kg/mm2 and the required conductivities are in the range of at least about 60% of the electrical conductivity of pure copper. However, this invention is also useful in any application where such tensile strengths and electrical conductivites, or even higher or selected of these characteristics, are required.

In one preferred embodiment, this invention provides copper-nickel alloys for electrical lead conductor materials for integrated circuits consisting essentially of copper and from about 0.05 to about 3.0% by weight nickel, from about 0.01 to about 1.0% by weight silicon, and from about 0.01 to about 0.1% by weight phosphorus.

In another preferred embodiment this invention also provides copper-nickel alloys for electrical lead conductor materials for integrated circuits consisting essentially of the additives specified above, and wherein about 0.01 to about 3.0% by weight iron is also added and is alloyed therewith.

In the preferred embodiment of the method of this invention, this invention comprises the following steps and sequence of melting, hot working and cold working stages; first, in the melting stage, a pure copper ingot without additives is charged into a crucible in a furnace and the copper is melted completely. Thereafter, the copper melt is heated to approximately 130000.

Nickel or iron are then added to the melt. The melt is then deoxidized with phosphorus and silicon, which are enveloped with copper foil, which is added into the melt and melted therewith. The final step in this stage is a rapid cooling step to form a casting.

The hot working stage includes a hot working step at a temperature of between about 75000 and about 95000. This step includes hot rolling the casting into a size reduced element in order to accomplish the solution treatment of the rapidly cooled melt from the first melting stage. Subsequently to this hot working step, the resulting solution treated and size reduced element is rapidly cooled.

In the following cold working stage, cyclic cold working is performed with a size reduction of between about 60 and 80%. After each cold working cycle, the resulting cold worked element is annealed in a cycle at a temperature of between about 40000 and about 52000 for ageing treatment and recrystallization. The cycle of these respective sequential cold working and annealing steps is performed three times altogether.

By the foregoing process the material of the present invention can be shown to have more than about 60% (IACS) of the electrical conductivity of pure copper without any additives, a tensile strength of from about 40 to about 62.7 kg/mm2 and greater than about 3% elongation, which properties are quite suitable for the requirements of the lead frames for electronic circuit elements, such as semiconductors, transistors and integrated circuits. However, as will be understood in more detail hereinafter, this invention and the process for making the material of the present invention can be shown to have a wide application due to a desirable range of properties.

Moreover, the described invention has the advantage that its manufacturing cost is low. To this end, the material of the present contains relatively small amounts of expensive alloying elements, and has additives that are relatively inexpensive. Also, the workability of the material of this invention is good.

Still further, the high tensile strength, high electrical conductivity and high elongation nickel-copper alloy obtained may be used for many applications requiring severe bending.

The present invention will be more readily understood from a consideration of the following illustrative examples.

Example 1 Using a medium frequency inducation furnace in air, alloys having the compositions shown in Table 1 are melted at about 120000 and then cast by rapid cooling. In this melting step, high purity copper without additives is charged into the furnace first, and after melt- down the melt is covered with charcoal.

Subsequently to this described heating and melting, which is approximately 1200 C, the charcoal is removed, and the melt is heated to about 132000 in order to add nickel, or nickel-iron, which may be in an alloy form, and, after putting the nickel or the nickel- iron in, all these elements are melted and mixed thoroughly together.

Then after deoxidizing with phosphorus, silicon is added and the melt is brought to the pouring temperature. The melt is then poured and made into an ingot.

The ingot is hot rolled at a temperature of between about 75000 and about 95000 so that it has a thickness of between about 7 and about 9mm, and then the material is rapidly cooled.

The hot rolled and rapidly cooled material is cold rolled with a reduction in size of about 70%, which is controlled as to gauge to be about 2 to about 2.5mm thick. The material is then brought to an annealing temperature of about 45000 to about 480 C, and is again cold rolled with a size reduction of about 65%, which is controlled to a desired gauge in a final cold rolling step, wherein the thickness is made to approximate a 0.25mm thickness. Then it is low temperature annealed at a temperature of about 2500 to about 40000.

The results are shown in Table 2, and curves of the physical properties versus the temperatures and times of the final low temperature annealing are given in Fig. 1.

Example 2 Using a medium frequency induction furnace, alloys having the compositions shown in Table 1 are melted at about 1200#0 for casting by a rapid cooling step, as described in Example 1. In this melting step high purity copper without any additives is charged into the furnace first, at about 1200 C, and after melt- down the melt is covered with charcoal, also as described in Example 1.

Subsequently to the described heating and melting step at approximately 1200 C, the charcoal is removed, the melt is heated to about 1320 C, and then nickel is put into the melt After complete melting, the melt is deoxidized with phosphorus and then brought to a lower temperature.

Thereafter, a silicon ingot, which is enveloped by a high purity copper foil without any additives, is added into the melt. After complete melting, the melt is cast into an ingot.

The ingot is hot rolled at a temperature between about 750 C and about 95000 to a thickness of about 7 to 9mm., and then the material is rapidly cooled.

The hot rolled material is cold rolled with a reduction of about 70% in size, which is controlled to a gauge of about 2 to about 2.5mm.

The material is then brought to an annealing temperature of about 47000 to about 52000 and is again cold rolled to bring about a 65% size reduction, which is controlled as to gauge to about 0.8mm. Then the resulting material is annealed at a temperature of about 47000 to about 520 C, cold rolled to approximately 0.33mm in thickness, annealed at a temperature of about 3500 to about 450 C, which is controlled as to gauge in a final cold rolling to about 0.254mm, and then annealed at a low temperature.

The results are shown in Table 3. The changes of the physical properties versus the temperatures and the times of the final low temperature annealing are shown in Fig. 2.

Example 3 In this Example the steps and procedures of the preceding Examples were followed. The additives were selected to produce a composite having the following weight %; nickel = 1%, phosphorus = 0.03%, silicon = 0.2%, and the balance copper.

Example 4 In this Example, the steps and procedures of Examples 1 and 2 were followed. The additives were selected to produce an alloy having the following weight percents: iron = 0.7%, nickel =0.5%, phosphorus = 0.03%, silicon = 0.1% and the balance copper.

This invention has the advantage of providing an economic new high tensile strength, high conductivity copper alloy for electrical and electronic equipment, such as leads and lead frames for transistors and integrated circuits. To this end, this invention has the advantage of using specific amounts of the inexpensive elements nickel, silicon, phosphorus, iron and copper. Also this invention has the advantage of providing an improved method of making such an alloy, including a specific sequence of specific steps.

The specific steps produce precipitation hardening, as will be understood from the above description by one skilled in the art. Also the alloys and method of this invention have other desirable characteristics, including the production of economic elongations at which bending can advantageously take place.

In one embodiment, this invention has the advantage of providing the following weight percent of inexpensive elements: 0.05 to 3.0% by weight nickel, 0.01 to 1.0% by weight silicon, and from 0.01 to 0.1% by weight phosphorus.

In another preferred embodiment this invention has the advantage of adding the inexpensive iron in a specific weight percent, of achieving precipitation hardening, and of eliminating the elements used heretofore in copper alloys, specifically tin, manganese, silver, zinc, cobalt, titanium, choromium and zirconium.

TABLE 1 (in weight %'s) Ni Si P Fe Cu {%) (%) (%) (%) {%J Al 0.1 0.1 0.03 - Balance A2 1.0 0.1 0.03 A3 1.0 0.2 0.03 - A4 0.5 0.1 0.03 0.7 AS 0.5 0.1 0.03 TABLE 2 Tensile Elongation Hardness Electrical Strength (%) Hv Conductivity (Kglmm2) {/ACS) (% of the conductivity of pure copper) Al 48.3 3.2 135 63 A2 58.5 4.9 165 62 A3 64.2 6.1 175 64 A4 54.4 4.0 143 60 AS 54.7 5.1 151 67 TABLE 3 Tensile Elongation Hardness Electrical Strength (%) Hv Conductivity (Kg/mm2) IACS (%) Al 40.1 13.5# 116 65 A2 52.4 7.2 149 64 A3 62.7 6.7 175 68 A4 53.3 6.7 140 62 AS 53.1 6.1 144 67

Claims (18)

1. A copper-nickel alloy for electrical lead conductor materials for integrated circuits consisting essentially of copper and from about 0.05 to about 3.0% by weight nickel, from about 0.01 to about 1.0% by weight silicon, and from about 0.01 to about 0.1% by weight phosphorus.

2. A copper-nickel alloy according to claim 1, containing also from about 0.01 to about 3.0% by weight iron.

3. A copper-nickel alloy as claimed in claim 1 comprising, by weight: 1% nickel, 0.03% phosphorus, 0.2% silicon, and the balance copper.

4. A copper-nickel alloy as claimed in claim 2 comprising, by weight: 0.7% iron, 0.5% nickel, 0.03% phosphorus, 0.1% silicon, and the balance copper.

5. A method for producing a copper-nickel alloy as claimed in any of claims 1 to 4, for electrical lead conductor materials for integrated circuits, comprising the following sequential steps: (a) casting the composition specified in any of claims 1 to 4; (b) hot rolling the obtained casting at a temperature between about 750dg and 950 C; (c) rapidly cooling the rolled casting; (d) cold rolling the casting with a reduction in size of about 60 to 80%; (e) annealing the casting at a temperature between about 400 C and 520 C for about two hours; (f) rapidly cooling the resulting product; (g) again cold rolling the resulting product with a reduction in size of about 50 to 70%; (h) annealing the resulting product at a temperature between about 40000 and 520 C for about two hours;; (i) rapidly cooling the resulting product; (j) cold rolling the casting with a size reduction of about 50 to 70%; (k) low temperature annealing the resulting product at a temperature between about 25000 and 40000.

6. A method for producing a copper-nickel alloy as claimed in any of claims 1 to 4, for electrical lead conductor materials for integrated circuits, comprising the following sequential steps: (a) casting the composition specified in any of claims 1 to 4; (b) hot rolling the casting at a temperature between 75000 and 950"C and then rapidly cooling it; (c) cold rolling the casting with a size reduction of about 60 to 80%; (d) annealing the casting at a temperature between about 400 C and 52000 for about two hours and rapidly cooling it; (e) cold rolling the casting with a size reduction of about 50 to 70%; (f) annealing the casting at a temperature between 40000 and 52000 for about two hours and rapidly cooling it;; (g) cold rolling the casting with a size reduction of about 30 to 50%; (h) annealing the casting at a temperature between about 35000 and 50000 for about two hours; (i) rolling the casting with a reduction in size of between about 10 to 25%; (j) low temperature annealing the casting at a temperature between about 25000 and 40000.

7. A copper-nickel alloy as claimed in any of claims 1 to 4, having a tensile strength of greater than about 40 kg/mm2.

8. A copper-nickel alloy according to claim 7 in which the tensile strength is between about 40.1 and 62.7 kg/mm2.

9. A copper-nickel alloy according to any of claims 1 to 4, 7 and 8, having a conductivity of at least about 60% of the conductivity of pure copper.

10. A copper-nickel alloy according to claim 9 in which the conductivity is between about 60% and 70% of the conductivity of pure copper.

11. A copper-nickel alloy according to any of claims 1 to 4 and 7 to 10, in which the alloy has an elongation of between about 3.2% and 13.5%.

12. A copper-nickel alloy according to any of claims 1 to 4 and 7 to 11, in which the alloy has a hardness of between about 16 to 175 HV.

13. A copper-nickel alloy according to any of claims 7 to 12 in which the alloy consists essentially of copper and from about 0.05 to about 3.0% by weight nickel, from about 0.1 to about 1.0% by weight silicon, and from about 0.01 to 0.1% by weight phosphorus.

14. A copper-nickel alloy according to claim 13 in which about 0.01 to about 3.0% by weight iron is added to the alloy and alloyed therewith.

15. A copper-nickel alloy according to claim 14 consisting essentially of about 0.5% by weight nickel, about 0.1% by weight silicon, about 0.03% by weight phosphorus, about 0.7% by weight iron, and the balance copper.

16. A copper-nickel alloy according to claim 15, having an elongation of at least about 4.0%.

17. A copper-nickel alloy according to any of claims 13 to 16, having a hardness of 143 HV.

18. A copper-nickel alloy according to claim 1, substantially as described.