JP4750602B2 - Copper alloy with excellent hot workability - Google Patents

Description

  The present invention relates to a copper alloy excellent in hot workability for high-strength, high-conductivity electronic device parts, and particularly in a small and highly integrated copper alloy for semiconductor device leads and terminal connectors. The present invention relates to a copper alloy for electronic parts that is particularly excellent in strength and conductivity without deteriorating bending workability and excellent in hot workability.

Copper and copper alloys are materials that are widely used for electronic parts such as connectors and lead terminals and flexible circuit boards, and are highly functional and miniaturized due to the rapid development of IT.・ Further improvements in properties (strength, bending workability, conductivity) are required in response to thinning.
In addition, with the high integration of ICs, many semiconductor elements with high power consumption are used, and the lead frame material of semiconductor devices has a good heat dissipation (conductivity) such as Cu-Ni-Si or Cu. Precipitation alloys such as -Fe-P, Cu-Cr-Sn, and Cu-Ni-P have come to be used. The Cu—Ni—P alloy is strengthened by the fine precipitation of the Ni—P compound, but in Patent Document 1, the amount of Ni, P, and Mg components in the alloy is adjusted to reduce the strength, conductivity, and stress resistance. It has been reported that an alloy with properties is obtained.

JP 2000-273562 A

In general, in the casting of a copper alloy, for example, continuous or semi-continuous casting, the ingot is heat-extracted by a mold, and the inside solidifies with some time except for a few mm of the surface layer of the ingot. At this time, alloy elements contained exceeding the limit during the solidification and after the solidification cooling process are crystallized or precipitated in the crystal grain boundaries and in the crystal grains. A copper alloy containing 1.0% or more of Ni and 0.2% or more of P has the advantage of high strength and high conductivity, but at room temperature, it has a Ni-P component exceeding the solid solubility limit in the Cu matrix. Since it is contained in a large amount, when an ingot is produced, a Ni-P compound is usually crystallized or precipitated at the crystal grain boundary. And since the melting point of the Ni-P compound compound crystallized or precipitated at the grain boundary of the Cu-Ni-P alloy is lower than that of the parent phase Cu, the solidification of these copper alloys becomes uneven and internal strain occurs. However, due to the stress and external force, fracture occurs in the Ni-P-based compound portion, causing cracks in the casting and cooling stages. Moreover, since the Ni-P compound softens or becomes a liquid phase prior to the parent phase during the hot rolling, cracks are similarly generated.
However, since the composition of the Cu-Ni-P alloy of Patent Document 1 is 0.01 to 1.0% for Ni and 0.01 to 0.2% for P, the above problem was not particularly conscious.
An object of the present invention is to provide a Cu-Ni-P alloy that prevents cracking during casting, cooling, hot working heating or hot working, has excellent high temperature ductility and good hot workability. It is what.

As a result of repeated research to achieve the above object, the present inventors have identified a Cu-Ni-P alloy having excellent hot workability, excellent strength and conductivity by specifying the following configuration. It was found that it can be obtained.
In the present invention, the copper alloy contains Ni: 1.0% or more and 2.0% or less (in the present specification,% representing the component ratio is mass%), P: 0.10% or more and 0.50% or less And the content ratio of Ni and P Ni / P: 4.0 to 6.5 and Cr: 0.03% to 0.45%, with the balance being Cu and inevitable impurities Copper alloy excellent in hot workability, preferably exhibiting a characteristic value of tensile strength: 700 MPa or more and electrical conductivity: 40% IACS or more, high strength and high conductivity copper for high-conductivity electronic equipment Regarding alloys. When one or more of Sn and In are contained in the above component composition in an amount of 0.01% or more and 1.0% or less, preferably the tensile strength is 750 MPa or more and the electrical conductivity is 40% IACS or more.

In the present invention, by adding a specific amount of Cr to the Cu—Ni—P alloy, crystallization or precipitation of the Ni—P compound at the grain boundary is suppressed, thereby improving the high temperature brittleness of the grain boundary. Thus, the hot workability is improved.
The copper alloy excellent in hot workability of the present invention has an excellent effect for high-strength and high-conductivity electronic equipment.

Next, the reason for limiting the numerical range of the component composition of the copper alloy in the present invention will be described together with its action.
[Ni content]
Ni has the effect of ensuring the strength and heat resistance of the alloy and precipitates a Ni—P compound with P, which will be described later, thereby contributing to an increase in the strength of the alloy. However, if the content is less than 1.0%, the desired strength cannot be obtained. On the other hand, if Ni exceeds 2.0%, the hot workability decreases and the bending workability of the product and The decrease in conductivity becomes remarkable. Furthermore, the area ratio of Ni—P-based precipitates having a large major axis is increased, which is not preferable. Therefore, the Ni content of the alloy of the present invention is 1.0% to 2.0%, preferably 1.1 to 1.8%.

[P amount]
P precipitates a compound with Ni to improve the strength and heat resistance of the alloy. If the P content is less than 0.10%, precipitation of the compound is insufficient, so that the desired strength cannot be obtained. On the other hand, when the P content exceeds 0.50%, hot workability is lowered and the conductivity is significantly lowered. Furthermore, the area ratio of Ni—P-based precipitates having a large major axis is increased, which is not preferable. Therefore, the P content of the alloy of the present invention is 0.1% to 0.5%, preferably 0.2 to 0.4%.

[Ni / P ratio]
If the Ni / P content ratio Ni / P deviates from the appropriate stoichiometric composition ratio of the Ni-P compound even if the Ni and P contents are within the above-mentioned limited range, that is, less than 4.0 In this case, when P exceeds 6.5, the amount of Ni dissolved increases, which is not preferable because the decrease in conductivity is remarkable. Therefore, the Ni / P ratio of the alloy of the present invention is 4.0 or more and 6.5 or less, preferably 4.5 to 6.0.

[Size and area ratio of Ni-P-based precipitates]
When the major axis of the Ni-P-based precipitate is a (nm) and the minor axis is b (nm), the precipitate with a before the final cold rolling of less than 20 nm undergoes rolling with a work strain η = 2 or more. Then, the precipitate is re-dissolved in copper, which lowers the conductivity, which is not preferable. On the other hand, a precipitate having a of 20 nm or more before the final cold rolling is not easily re-dissolved even in a rolling process having a working strain η = 2 or more, and exists as a precipitate having a thickness of 10 nm or more. Precipitates of 20 nm or more have little change in size before and after rolling. Particularly, precipitates with a major axis a before rolling exceeding 50 nm maintain a major axis exceeding 50 nm after rolling, but the dispersion interval of the precipitates in the alloy is large. Since it becomes too large, precipitation strengthening and work strengthening cannot be obtained.
The major axis a and the minor axis b are obtained by cutting the alloy strip before the final cold rolling in a direction perpendicular to the thickness parallel to the rolling direction, and measuring all the precipitates having a major axis a of 5 nm or more using an image analyzer. It is the average value of each major axis and minor axis of all the precipitates. Further, the processing strain eta, the plate thickness before rolling t _0, when the plate thickness after rolling was t, is expressed by _{η = ln (t 0 / t} ).
From the above, the major axis “a” of the Ni—P-based precipitate before the final cold rolling of the alloy of the present invention is preferably 20 nm to 50 nm.
Moreover, when the aspect ratio of the precipitate is expressed by a / b, when a / b exceeds 5, when the rolling process is performed with η = 2 or more, the precipitate is re-dissolved in the copper, and the conductivity is reduced. It will decrease. Therefore, the aspect ratio a / b of the precipitate is preferably 1 to 5, more preferably 1 to 3.
In order to prevent a decrease in strength and electrical conductivity, a after the final cold rolling is preferably 10 nm to 50 nm and a / b is 1 to 5.

However, since it is difficult to make all the precipitates within the preferable ranges of a and a / b, the ratio of the precipitates within the ranges of a and a / b to the total precipitates is important. Therefore, when the ratio of the total area of precipitates in the preferable range of a and a / b to the total area of all precipitates in the alloy is defined as area ratio C, the area ratio C of the present invention is preferably 80% or more. It is.
The case where the area ratio C is less than 80% is a case where there are many precipitates in which a exceeds 50 nm or precipitates less than 20 nm. For example, precipitates in which a exceeds 50 nm and crystallized products generated during melt casting remain 1000-nm or more Ni-P particles (crystallized products) that remain without being dissolved in the heating or solution treatment before hot rolling. When there are many, the dispersion interval of fine precipitates having a size of 20 to 50 nm that contributes to the strength improvement is large, so that the desired strength by work hardening in the rolling process cannot be obtained. On the other hand, since the precipitate with a of less than 20 nm is re-dissolved by rolling, the decrease in conductivity becomes remarkable.

[Cr content]
In general, when the cooling rate during solidification of a Cu—Ni—P alloy is slow, for example, when the cooling rate from 1100 ° C. to 950 ° C. is less than 30 ° C./min, the Ni—P compound is aggregated and coarsened at the grain boundaries. It is not preferable because it crystallizes with crystallization.
Cr suppresses crystallization or precipitation of the Ni-P compound at the grain boundary during the solidification of the Cu-Ni-P alloy, during the cooling process after solidification, and during the hot working heating, and hot working of the alloy Improve sexiness. However, if the content is less than 0.03%, the effect of improving hot workability cannot be obtained. On the other hand, if the Cr content exceeds 0.45%, Ni—P—Cr, Cr—P, etc. This compound is generated during dissolution or solidification, and a crystallized product of Cr is generated. These Cr-containing compounds and crystallized substances are not solid-dissolved in the Cu matrix by the solution treatment, so that the Ni—P-based compounds precipitated by the aging treatment are reduced, and the strength of the alloy is reduced. Further, compounds such as Ni—P—Cr and Cr—P remain in the product as inclusions having a major axis of 5 μm or more, and surface defects of the product, starting points of cracks during bending, and defects during plating processing. Since it becomes a starting point, it is not preferable. Therefore, the Cr content of the alloy of the present invention is 0.03% to 0.45% or less, preferably 0.05% to 0.30%.
It is not preferable that inclusions such as Ni—P—Cr compounds and Cr—P compounds having a major axis of 5 μm or more are present, preferably the number of inclusions exceeding 50 μm of major axis is 0 per 1 mm ² and the major axis is 5 to 50 μm. The number of inclusions is 100 or less per 1 mm ^2, more preferably, the number of inclusions having a major axis of 5 to 50 μm is 50 or less per 1 mm ² . The major axis of the Ni—P—Cr compound and Cr—P compound precipitate is measured in the same manner as the major axis of the Ni—P-based precipitate.

[Sn, In amount]
Both the Sn and In contents have the effect of improving the strength mainly by solid solution strengthening without greatly reducing the conductivity of the alloy. Accordingly, if necessary, one or more of these metals are added. If the total content is less than 0.01%, the effect of improving the strength by solid solution strengthening cannot be obtained, while the total amount is 1.0. When adding more than%, the electrical conductivity and bending workability of the alloy are significantly reduced. For this reason, the amount of Sn and In added individually or in combination of two or more types is 0.01% to 1.0%, preferably 0.05% to 0.8% in total. In the present invention, these elements are intentionally added elements and are not regarded as inevitable impurities.
[O amount]
O easily reacts with Cr in the alloy, and if O exists in an oxide state in the alloy, the effect of adding Cr cannot be obtained. Therefore, the O content of the alloy of the present invention is 0.0050% or less, preferably 0.0030% or less.

[Tensile strength and conductivity]
The copper alloy of the present invention is excellent in hot workability and further has excellent conductivity, tensile strength and bending workability. The tensile strength of the copper alloy of the present invention is preferably 700 MPa or more, more preferably 750 MPa or more, and the upper limit is usually about 950 MPa. The conductivity is preferably 40% IACS or more, more preferably 45% IACS or more, and the upper limit is usually about 65% IACS.

  The Cu—Ni—P alloy satisfying the above-mentioned requirements of the present invention is generally used by those skilled in the art for ingot casting, hot rolling, solution treatment, intermediate cold rolling, aging treatment, final cold rolling, strain. In the annealing and the like, it can be manufactured by appropriately selecting the heating temperature, time, cooling rate, rolling degree, and the like.

Sample manufacture:
Electrical copper or oxygen-free copper as the main raw material, nickel (Ni), 15% P-Cu master alloy (P), 10% Cr-Cu master alloy (Cr), tin (Sn), indium (In) as auxiliary raw materials And melted in a high-frequency melting furnace in a vacuum or in an argon atmosphere, and cast into a 45 × 45 × 90 mm ingot using a cast iron mold. Ingots were subjected to a hot rolling test, and ingots that were not cracked by hot rolling were subjected to hot rolling and solution treatment, aging treatment, intermediate cold rolling, aging treatment, final cold rolling, and strain relief annealing. It implemented in order and was set as the flat plate of thickness 0.15mm. Various test pieces of the obtained plate material were collected and tested, and “strength” and “conductivity” were evaluated.

Ingot hot workability evaluation:
“Hot workability” was evaluated by hot rolling. That is, the ingot was cut into 45 × 45 × 25 mm, heated to 850 ° C. for 1 hour, and then subjected to a hot rolling test in three passes from a thickness of 25 mm to 5 mm. The case where cracks were visually observed on the surface and edge of the sample after hot rolling was defined as “cracked”, and the case where the surface and edge were not cracked and smooth was defined as “no crack”.

Physical property evaluation of test piece:
About "strength", it carried out using the No. 13 B test piece by the tension test prescribed | regulated to JISZ2241, and measured the tensile strength.
“Conductivity” was measured by measuring the electrical resistance of a test piece using a four-terminal method and expressed in% IACS.
“Bending workability” was evaluated by a 90 ° W bending test. The test was performed in accordance with CES-M0002-6, and bending was performed 90 degrees with a load of 50 kN using an R-0.1 mm jig. In the evaluation of the bent portion, the state of the surface of the central mountain was observed with an optical microscope. The bending axis was set at right angles to the rolling direction (Good way).

Evaluation of Ni-P-based precipitates:
The alloy strips before the final cold rolling were cut parallel to the rolling direction at a right angle to the thickness, and using a scanning electron microscope and a transmission electron microscope, 10 precipitates of the cross section were observed. When the size of the precipitate is 5 to 50 nm, the field of view is about 500,000 to 700,000 times (about 1.4 × 10 ^{10 to} 2.0 × 10 ¹⁰ nm ² ), and when the size is 100 to 2000 nm, the field is 50,000 times to Photographing was performed with a 100,000 × field of view (approximately 1.0 × 10 ^{13 to} 2.0 × 10 ¹³ nm ² ). Using the image of the photographed photograph, the major axis a, the minor axis b, and the area of each of the precipitates having a major axis a of 5 nm or more were measured using an image analyzer (manufactured by Nireco Corporation, trade name Luzex). Select 100 randomly from these deposits, with the average of the aspect ratio a _ta / b _ta the major axis determined from the mean a _ta and and average b _ta of minor all these precipitates, respectively major axis a, the minor axis b and aspect ratio a / b. The total area of all precipitates having a major axis a of 5 μm or more was taken as the total area of all precipitates. The ratio of the total area of the precipitates having a major axis a of 10 nm to 50 nm and an aspect ratio a / b of 1 to 5 was defined as an area ratio C (%) with respect to the total area of all the precipitates.
In addition, by the final cold rolling (usually processing strain η = 2 or more), Ni—P-based precipitates having a major axis of 20 nm or less or precipitates having a major axis exceeding 20 nm but having an aspect ratio exceeding 3 are dissolved. However, it was confirmed that a precipitate having an aspect ratio of 1 to 3 at 20 nm or more maintained its major axis, minor axis and aspect ratio even after the final cold rolling. Also, the area ratio C of the precipitates hardly changed even after the final cold rolling because the precipitates exceeding 200 nm were not dissolved.

  Examples of the high-strength, high-conductivity copper alloy excellent in hot workability according to the present invention will be described with reference to the copper alloys having the component compositions shown in Table 1 together with comparative examples. Alloy Examples 1 to 9 of the present invention had excellent strength and electrical conductivity without cracking during hot rolling. On the other hand, when the results up to Comparative Examples 10 to 22 were examined, in Comparative Examples 10 to 13 there was no addition of Cr or less than the specified amount, so cracking occurred during hot rolling. Since Comparative Example 14 has an addition amount of P exceeding 0.50%, Comparative Example 15 has a total addition amount of Sn and In exceeding 1.0%. Since the total exceeded 1.0%, cracks occurred during hot rolling. Comparative Example 17 has a low strength because Ni addition amount and Comparative Example 18 has a low addition amount of P from the range defined by the present invention. In Comparative Example 19, since the Ni / P ratio deviates high, the amount of Ni dissolved increases and the conductivity decreases, and the amount of precipitates is small, so the strength is low. In Comparative Example 20, since the Ni / P ratio deviated from an appropriate composition ratio, the amount of dissolved P increased and the conductivity decreased. In Comparative Example 21, since the addition amount of Ni exceeded 2.0% and the addition amount of P exceeded 0.50%, cracks occurred during hot rolling. In Comparative Example 22, since the Cr addition amount exceeds 0.45%, a compound such as Ni-P-Cr, Cr-P, or Cr crystallizes or precipitates during solidification, so that the amount of Ni-P-based precipitate is increased. Decrease, strength and conductivity are low, bending workability is poor.

Claims (1)

Ni: 1.0% to 2.0%, P: 0.10% to 0.50% in terms of mass ratio, Ni / P content ratio Ni / P: 4.0 to 6.5 And Cr: 0.03% to 0.45%, the balance being made of Cu and inevitable impurities, a copper alloy having excellent hot workability .