JP2016180131A - Cu-Ni-Si-BASED COPPER ALLOY SHEET MATERIAL AND METHOD FOR PRODUCING THE SAME, AND LEAD FRAME - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Cu-Ni-Si-based copper alloy having a high strength and a good conductivity, in which the thermal shrinkage, which becomes a problem during the heat treatment of a parts fabrication step, is reduced.SOLUTION: Provided is a copper alloy sheet material having a composition of, in mass%, Ni: 1.0 to 4.5%, Si: 0.1 to 1.2%, Mg: 0 to 0.3%, Cr: 0 to 0.2%, Co: 0 to 2.0%, P: 0 to 0.1%, B: 0 to 0.05%, Mn: 0 to 0.2%, Sn: 0 to 0.5%, Ti: 0 to 0.5%, Zr: 0 to 0.2%, Al: 0 to 0.2%, Fe: 0 to 0.3%, Zn: 0 to 1.0%, and the balance being Cu and unavoidable impurities, having a 0.2% yield strength in rolling direction of 800 MPa or more and a conductivity of 35% IACS or more, and having a thermal shrinkage λ represented by λ=(L-L)/L×100 when subjected to a heating test of holding at 500°C for 10 min, of 0.020% or less (here, Land Lare each a length of a test piece in direction parallel to the rolling direction before and after the heating test).SELECTED DRAWING: None

Description

  The present invention relates to a Cu—Ni—Si based copper alloy sheet having high strength, high conductivity, and low heat shrinkability, and a method for producing the same. The present invention also relates to a lead frame using the copper alloy sheet.

  A material (plate material) used for an energized component constituting an electric / electronic component is required to have excellent “strength” and “conductivity” as basic characteristics. Furthermore, a material to be processed into a precision part such as a lead frame is required to have a property that a good shape (that is, high dimensional accuracy) can be obtained when processed into the part.

  However, in general, when trying to increase the strength of a copper alloy sheet, it is difficult to maintain good dimensional accuracy when processing into a precision part. Recently, semiconductor packages have become smaller and thinner, and a package called QFN (Quad Flat Non-Leaded Package) in which the outer peripheral lead portion (outer lead) of the lead frame has been removed has been used frequently. Needs are growing. In order to cope with the increase in the number of pins of the QFN type, a material capable of realizing higher strength and improved dimensional accuracy at a higher level than before is required.

  As a copper alloy having an excellent balance between strength and conductivity, there is a Cu—Ni—Si based copper alloy (so-called Corson alloy). This alloy system can be adjusted to a high strength of 0.2% proof stress of 800 MPa or more while maintaining a relatively high conductivity (35 to 50% IACS). Patent Document 1 describes a high-strength Cu—Ni—Si based copper alloy with improved thermal shrinkage. Patent Documents 2 to 5 describe high-strength Cu—Ni—Si based copper alloys with reduced internal residual stress. Improvement of heat shrinkage and reduction of internal residual stress are effective in improving the dimensional accuracy of parts.

  However, according to the study by the inventors, the copper alloys disclosed in these documents are subject to thermal shrinkage in order to be applied to precision-shaped high-strength current-carrying parts such as lead frames of QFN packages that are becoming increasingly multi-pinned. The level is not satisfactory. In order to improve the dimensional accuracy of parts, further improvements on the material side are desired.

JP 2008-115465 A JP 2011-38126 A JP 2010-7174 A JP 2005-48262 A JP 2004-131829 A

  In the conventional technology, considering the processing into parts that require high dimensional accuracy, such as QFN package multi-pin lead frames, a level that can satisfy the heat shrinkage of high strength Cu-Ni-Si copper alloy sheet Can not be reduced. The present invention is to provide a copper alloy sheet material in which the heat shrinkage, which is a problem in the heat treatment of the component processing process, is reduced compared to the conventional Cu-Ni-Si copper alloy having high strength and good conductivity. .

  As a result of research, the inventors have determined that (i) a work roll for finish cold rolling performed after aging treatment is thickened in order to stably and significantly reduce the thermal shrinkage of a high-strength Cu—Ni—Si based copper alloy sheet. Limit the rolling reduction in the final pass, and (ii) strictly control the tension applied to the plate in the final low-temperature annealing within a certain range and make sure that the cooling rate does not become excessive. It has been found that strictly controlling the cooling rate is extremely effective. The present invention has been completed based on such findings.

That is, in the present invention, in mass%, Ni: 1.0 to 4.5%, Si: 0.1 to 1.2%, Mg: 0 to 0.3%, Cr: 0 to 0.2%, Co : 0 to 2.0%, P: 0 to 0.1%, B: 0 to 0.05%, Mn: 0 to 0.2%, Sn: 0 to 0.5%, Ti: 0 to 0.0. 5%, Zr: 0 to 0.2%, Al: 0 to 0.2%, Fe: 0 to 0.3%, Zn: 0 to 1.0%, balance Cu and inevitable impurities. A rectangular test piece having a 0.2% proof stress in the rolling parallel direction of 800 MPa or more and an electrical conductivity of 35% IACS or more, and having a 180 mm parallel to the rolling direction and a 50 mm perpendicular to the rolling direction is collected from the plate. A copper alloy sheet material having a property that the thermal shrinkage ratio λ in the rolling parallel direction defined by the following formula (1) is 0.020% or less when subjected to a heating test for 10 minutes at That.
λ (%) = (L ₀ −L ₁ ) / L ₀ × 100 (1)
Here, L ₀ is the length (mm) in the rolling parallel direction at 20 ° C. of the test piece before the heating test, and L ₁ is the length (mm) in the rolling parallel direction at 20 ° C. of the test piece after the heating test.

  Among the above alloy elements, Mg, Cr, Co, P, B, Mn, Sn, Ti, Zr, Al, Fe, and Zn are optional additional elements. The said copper alloy board | plate material makes object the board width | variety of a rolling right-angle direction 50 mm or more. Such a plate product may be subjected to a press punching process as it is, or may be further slit to form a narrow strip and then used for part processing. The 0.2% yield strength in the rolling parallel direction is a 0.2% yield strength by an offset method measured according to JIS Z2241: 2011 using a tensile test piece whose longitudinal direction is parallel to the rolling direction.

  The average crystal grain size by the cutting method measured in the direction perpendicular to the rolling direction with respect to the plate surface (rolled surface) is, for example, 3 to 50 μm. The plate thickness can be in the range of, for example, 0.03 to 0.5 mm, but as a QFN type multi-pin lead frame application, a plate thickness of 0.08 to 0.2 mm tends to be frequently used. The copper alloy sheet of the present invention can meet such needs.

Further, as a method for producing the copper alloy sheet, the intermediate product sheet having the above chemical composition is subjected to a work roll having a roll diameter (diameter) of 70 mm or more, and the rolling reduction of the final pass is set to 4 to 15%. A step of performing cold rolling at a rolling rate of 20 to 80% (finish cold rolling step),
The plate after the finish cold rolling step, after heating while applying 5N / mm ² or more 30 N / mm ² under tension 250 to 550 ° C. preferably at a temperature range of three hundred thirty to five hundred and thirty ° C., the maximum cooling rate 100 ° C. / Cooling process to room temperature at / sec or less (low temperature annealing process),
The manufacturing method of the copper alloy board | plate material which has this is provided.

In addition, the rolling rate from a certain plate thickness t ₀ (mm) to a certain plate thickness t ₁ (mm) is obtained by the following equation (2).
Rolling ratio (%) = (t ₀ −t ₁ ) / t ₀ × 100 (2)
In this specification, a rolling rate in one pass in a certain rolling pass is particularly referred to as a “rolling rate”.

  The present invention also provides a lead frame using the above copper alloy sheet as a material.

  The Cu—Ni—Si based copper alloy sheet according to the present invention has high strength and good electrical conductivity, and has very little “heat shrinkage” when heat treatment is performed in the part processing stage. This plate material is suitable for a current-carrying component that requires high dimensional accuracy, such as a multi-pin lead frame for a QFN package.

<Alloy composition>
In the present invention, a Cu—Ni—Si based copper alloy is employed. Hereinafter, “%” regarding alloy components means “% by mass” unless otherwise specified.

Ni forms Ni-Si based precipitates. When Co is contained as an additive element, a Ni—Co—Si based precipitate is formed. These precipitates improve the strength and conductivity of the copper alloy sheet. The Ni—Si based precipitate is considered to be a compound mainly composed of Ni ₂ Si, and the Ni—Co—Si based precipitate is considered to be a compound mainly composed of (Ni, Co) ₂ Si. These compounds are sometimes referred to herein as “second phase”. In order to sufficiently disperse fine precipitate particles effective for improving the strength, the Ni content needs to be 1.0% or more, and more preferably 1.3% or more. You may manage to the quantity exceeding 2.0%. On the other hand, if Ni is excessive, coarse precipitates are likely to be generated, and are easily cracked during hot rolling. The Ni content is limited to 4.5% or less. More preferably, the content is less than 4.0%, and may be controlled to 3.5% or less.

  Si produces Ni—Si based precipitates. When Co is contained as an additive element, a Ni—Co—Si based precipitate is formed. In order to sufficiently disperse fine precipitate particles effective for improving the strength, the Si content needs to be 0.1% or more, and more preferably 0.4% or more. On the other hand, if Si is excessive, coarse precipitates are likely to be generated, and are easily cracked during hot rolling. The Si content is limited to 1.2% or less. You may manage to less than 1.0%.

  Co forms Ni—Co—Si-based precipitates to improve the strength and conductivity of the copper alloy sheet, and can be added as necessary. In order to sufficiently disperse fine precipitates effective for improving the strength, it is more effective to set the Co content to 0.1% or more. However, when the Co content increases, coarse precipitates are likely to be generated. Therefore, when Co is added, it is performed within a range of 2.0% or less. You may manage to less than 1.5%.

  As other elements, Mg, Cr, P, B, Mn, Sn, Ti, Zr, Al, Fe, Zn, and the like can be contained as necessary. The content ranges of these elements are Mg: 0 to 0.3%, Cr: 0 to 0.2%, P: 0 to 0.1%, B: 0 to 0.05%, Mn: 0 to 0 0.2%, Sn: 0 to 0.5%, Ti: 0 to 0.5%, Zr: 0 to 0.2%, Al: 0 to 0.2%, Fe: 0 to 0.3%, Zn : 0 to 1.0% is preferable.

  Cr, P, B, Mn, Ti, Zr, and Al have a function of further increasing the alloy strength and reducing stress relaxation. Sn and Mg are effective in improving the stress relaxation resistance. Zn improves the solderability and castability of the copper alloy sheet. Fe, Cr, Zr, Ti, and Mn are easy to form a high melting point compound with S, Pb, etc. present as inevitable impurities, and B, P, Zr, and Ti have a refinement effect on the cast structure, It can contribute to the improvement of inter-workability.

  When including one or more of Mg, Cr, P, B, Mn, Sn, Ti, Zr, Al, Fe, and Zn, the total content thereof should be 0.01% or more. It is effective. However, if it is contained in a large amount, it adversely affects hot or cold workability and is disadvantageous in terms of cost. The total amount of these optional added elements is preferably 1.2% or less, and more preferably 1.0% or less.

"Characteristic"
[Heat shrinkage]
Many dislocations are introduced into the metal matrix of the Cu-Ni-Si-based copper alloy sheet that has been strengthened. When lattice defects such as dislocations are introduced, the volume of the crystal lattice expands slightly. Lead frame members formed by processing plate materials, which are processed materials, can be moved until the semiconductor parts are completed by undergoing strain relief annealing after the forming process or by being heated during packaging. It is often heated to a temperature range where dislocations can move. When the movable dislocations move by heating and the internal strain of the metal matrix is released, the density of lattice defects is reduced and the volume of the crystal lattice contracts. This type of shrinkage phenomenon is referred to herein as “thermal shrinkage”. Thermal shrinkage is a factor that reduces the dimensional accuracy of the part. Therefore, in applications that require particularly high dimensional accuracy, such as QFN type multi-pin lead frames, a plate-like material with smaller thermal shrinkage than conventional ones is required.

The high-strength Cu—Ni—Si copper alloy sheet according to the present invention is intended to reduce thermal shrinkage in order to meet such demands. Specifically, when a rectangular test piece having a rolling parallel direction of 180 mm and a rolling perpendicular direction of 50 mm is collected from the plate material and subjected to a heating test held at 500 ° C. for 10 minutes, the rolling parallel direction defined by the following formula (1) Has a property that the thermal shrinkage ratio λ is 0.020% or less.
λ (%) = (L ₀ −L ₁ ) / L ₀ × 100 (1)
Here, L ₀ is the length (mm) in the rolling parallel direction at 20 ° C. of the test piece before the heating test, and L ₁ is the length (mm) in the rolling parallel direction at 20 ° C. of the test piece after the heating test.

  In a high-strength Cu—Ni—Si-based copper alloy sheet (sheet thickness is, for example, 0.03 to 0.5 mm) adjusted to a 0.2% proof stress of 800 MPa or more in the rolling parallel direction, the thermal shrinkage ratio λ is 0.0. What is suppressed to 020% or less has remarkable thermal shrinkage reduction performance as compared with a conventional material having an equivalent strength level. It is more effective that the thermal shrinkage ratio λ is 0.010% or less. As will be described later, the remarkable reduction in heat shrinkage can be realized by strictly managing the conditions of finish cold rolling and the conditions of low temperature annealing.

  According to the study by the inventors, it is difficult to stably and significantly reduce the thermal shrinkage simply by reducing the internal residual stress of the metal matrix. The reason why “reduced residual stress” and “reduced thermal shrinkage” do not correspond straight is not necessarily clear, but materials with actually small thermal shrinkage are particularly “among other factors that increase residual stress. It is inferred that the “residual amount of movable dislocations” is decreasing.

[Average crystal grain size]
The smaller the average crystal grain size is, the more advantageous it is for improving the strength. However, if the average crystal grain size is too small, precipitates are not dispersed and the strength tends to decrease. As a result of various studies, in the final plate product, it is more desirable that the average crystal grain size by the cutting method measured in the direction perpendicular to the rolling direction on the plate surface (rolled surface) is 3 to 50 μm, and 5 to 30 μm. More preferably it is.

[Strength / Conductivity]
In order to use a Cu—Ni—Si based copper alloy sheet as a material for a current-carrying part such as a lead frame, a strength level of 0.2 MPa in the rolling parallel direction (LD) of 800 MPa or more is desired. On the other hand, in order to reduce the thickness of the current-carrying parts, it is an important requirement even though the conductivity is good. Specifically, the electrical conductivity is desirably 35% IACS or more, and more preferably 40% IACS or more.

"Production method"
The copper alloy sheet material described above can be produced by the following manufacturing process, for example.
“Melting / Casting → Hot Rolling → Cold Rolling → Solution Treatment → Aging Treatment → Finish Cold Rolling → (Shape Correction) → Low Temperature Annealing”
Not only this but heat processing and cold rolling can be added in the process as needed.
In the present invention, in order to obtain a plate product having a small thermal shrinkage, it is particularly important to make it in the final two steps of “finish cold rolling” and “low temperature annealing”. There is no need to pay particular attention to the steps up to the aging treatment, and general production conditions for a Cu—Ni—Si based copper alloy may be adopted.
Although not described in the above steps, chamfering is performed as necessary after hot rolling, and pickling, polishing, or further degreasing is performed as necessary after each heat treatment. Further, after finish cold rolling, shape correction by a tension leveler is performed as necessary. Hereinafter, each step will be described.

[Melting / Casting]
The slab may be manufactured by continuous casting, semi-continuous casting, or the like. In order to prevent oxidation of Si or the like, it is preferable to carry out in an inert gas atmosphere or a vacuum melting furnace.

(Hot rolling)
Hot rolling may follow a normal method. The slab heating before hot rolling can be 1 to 5 hours at 900 to 1020 ° C., for example. The total hot rolling rate may be, for example, 70 to 97%. The rolling temperature in the final pass is preferably 700 ° C. or higher. After the hot rolling is finished, it is preferable to quench by water cooling or the like.

(Cold rolling)
By cold rolling before the solution treatment, reduction of the plate thickness and introduction of strain energy (dislocation) are attempted. The strain energy effectively acts on the solution of the second phase in the solution treatment. If necessary, cold rolling can be performed a plurality of times with intermediate annealing. It is effective to set the cold rolling rate before the solution treatment (the cold rolling rate after the final intermediate annealing when performing cold rolling with the intermediate annealing interposed therebetween) to, for example, 70% or more. The rolling tolerance range of 99% or less is usually used in the facility tolerance range such as mill power.

[Solution treatment]
A solution treatment is performed to sufficiently dissolve the second phase. What is necessary is just to set the heat treatment temperature in the range of 850-1020 degreeC as solution treatment conditions. The range of 850-980 degreeC is more preferable. What is necessary is just to set the time hold | maintained in the said temperature range in the range of 10 sec-10min. In the plate material after solution treatment, the heating temperature and the heating time can be adjusted so that the average crystal grain size determined by the above-mentioned method is 3 to 25 μm, more preferably 5 to 20 μm, and still more preferably 5 to 17 μm. desirable. The optimal solution conditions for ensuring re-solution and recrystallization and adjusting the average crystal grain size to the above range will vary depending on the composition and manufacturing conditions before solution treatment, In addition, by grasping the optimum solution treatment heat pattern condition according to the cold rolling rate, it becomes easy to set the appropriate condition range. The average cooling rate from 530 ° C. to 300 ° C. is preferably 100 ° C./sec or more.

[Aging treatment]
Next, an aging treatment is performed to precipitate fine precipitate particles that contribute to the strength. The conditions are preferably determined by adjusting in advance the temperature and time at which the hardness reaches its peak due to aging according to the alloy composition. Specifically, the aging temperature is preferably 400 to 550 ° C, and more preferably 425 to 525 ° C. Good results are obtained when the aging treatment time is in the range of 3 to 12 hours. In order to suppress the surface oxidation during the aging treatment as much as possible, a hydrogen, nitrogen or argon atmosphere can be used.

[Finish cold rolling]
Finish cold rolling is effective in improving the strength level (particularly 0.2% yield strength). The finish cold rolling rate (total rolling rate) is effectively 20% or more, and more preferably 25% or more. When the finish cold rolling rate increases, the strength tends to decrease during low-temperature annealing, so the rolling rate is preferably 80% or less, and more preferably 70% or less. You may manage in the range of 65% or less. The final plate thickness can be set, for example, in the range of about 0.03 to 0.50 mm, and may be controlled to 0.08 to 0.20 mm.

  Usually, it is advantageous to use a work roll having a small diameter in order to increase the rolling reduction in cold rolling. However, according to the study by the inventors, it has been found that it is extremely effective to use a work roll having a large diameter in finish cold rolling in order to produce a plate product having a small thermal shrinkage. By using a large-diameter work roll, it is presumed that the introduction amount of movable dislocations may be reduced as compared with the case where the same rolling rate is performed with a conventional small-diameter work roll. As a result of various studies, it is possible to obtain a plate material having a thermal shrinkage ratio λ of 0.020% or less by using a large-diameter work roll having a diameter of 70 mm or more. In particular, when a work roll having a diameter of 80 mm or more is used, a plate material having a thermal shrinkage ratio λ of 0.010% or less can be created by strictly managing the restriction of low-temperature annealing conditions described later. On the other hand, if the work roll diameter is excessively large, the mill power necessary to sufficiently secure the rolling reduction increases as the plate thickness decreases, which is disadvantageous in finishing to a predetermined plate thickness. The upper limit of the large-diameter work roll to be used can be determined according to the mill power and the target plate thickness of the cold rolling mill. For example, when obtaining a plate material in the above plate thickness range with a total rolling rate of 20% or more, it is preferable to use a work roll having a diameter of 100 mm or less.

  In order to reduce thermal shrinkage, it is extremely effective to set the rolling reduction in the final pass of finish cold rolling to 15% or less. More preferably, it is 12% or less or less than 10%. However, if the rolling reduction rate in the final pass is too low, productivity will be reduced, so a rolling reduction rate of 4% or more is secured.

[Shape correction]
The plate material that has undergone finish cold rolling may be subjected to shape correction by a tension leveler before final low temperature annealing. A tension leveler is a device that bends and stretches a plate material with a plurality of shape correction rolls while applying tension in the rolling direction. In the case of passing a tension leveler, it is desirable that the elongation is 1.5% or less.

[Low temperature annealing]
After finish cold rolling, low temperature annealing is usually performed for the purpose of reducing the residual stress of the strip material, improving the bending workability, and improving the stress relaxation resistance by reducing the dislocations on the pores and the sliding surface. However, in the present invention, in order to obtain a plate product having a small heat shrinkage, it is necessary to strictly limit the conditions for low-temperature annealing, which is the final heat treatment.

  1stly, the heating temperature of low-temperature annealing shall be 250-550 degreeC. At a temperature lower than 250 ° C., it is difficult to sufficiently reduce the remaining amount of movable dislocations, and the effect of reducing thermal shrinkage becomes insufficient. When the temperature is higher than 550 ° C., the material becomes soft and it is difficult to sufficiently secure a predetermined high strength. It is more preferable to set it as the range of 330-530 degreeC. The holding time at the above temperature may be set in the range of 5 to 600 seconds.

Second, to control the tension applied to the sheet material during heating in the temperature range below 5N / mm ² or more 30 N / mm ^2. In a continuous line, the direction of tension is the rolling parallel direction. When the tension is less than 5 N / mm ² , particularly in a high-strength material, the effect of reducing movable dislocation is insufficient, and it becomes difficult to stably realize a remarkable reduction in heat shrinkage. If it is 30 N / mm ² or more, the residual stress tends to increase particularly in the case of a high-strength material, which becomes a negative factor in reducing thermal shrinkage. More preferably, it is 25 N / mm ² or less. Incidentally, by strict control tension 5N / mm ² or more 25 N / mm ² or less in the range in the use of the above work roll diameter 80mm at the aforementioned finish cold rolling, and the low-temperature annealing, thermal shrinkage λ Of 0.010%, which can make a plate material product with extremely small heat shrinkage.

  Third, it is cooled to room temperature at a maximum cooling rate of 100 ° C./sec or less. That is, the temperature is lowered to room temperature (5 to 35 ° C.) so that the cooling rate does not exceed 100 ° C./sec after the heating. When the maximum cooling rate exceeds 100 ° C./sec, a large number of movable dislocations remain due to rapid cooling, resulting in insufficient reduction of heat shrinkage. The temperature distribution in the direction perpendicular to the plate surface (in the direction perpendicular to rolling) with respect to the sheet passing direction during cooling becomes non-uniform, and sufficient flatness cannot be obtained. Cooling after heating can be forced cooling using a cooling gas, for example. In that case, the maximum cooling rate can be kept within a range of 100 ° C./sec or less by controlling the number of rotations of the cooling fan, the ambient temperature of the cooling zone, and the type of the cooling gas. As the cooling gas, hydrogen, nitrogen, air, or the like can be used.

A copper alloy having the composition shown in Table 1 was melted and cast using a vertical semi-continuous casting machine. The obtained slab was heated at 1000 ° C. for 3 hours, extracted, hot-rolled to a thickness of 10 mm, and then water-cooled. The total hot rolling rate is 90 to 95%, and the hot rolling finish temperature is 700 to 750 ° C. After hot rolling, the surface oxide layer was removed (faced) by mechanical polishing. Subsequently, cold rolling was performed at a rolling rate of 90 to 99%. Thereafter, solution treatment, aging treatment, finish cold rolling, and low-temperature annealing were performed under the conditions shown in Table 2, and a plate product having a plate thickness of 0.15 mm and a plate width W _{0 in the} direction perpendicular to the roll of 510 mm (test material) Got.

  The low-temperature annealing was performed by air cooling after continuously passing through a catenary furnace. The heating time is 10 to 90 sec. The tension during heating was calculated from the catenary curve of the material in the plate passing through the furnace (the height position of the plate at both ends and the center of the plate passing through the furnace and the length in the furnace). By measuring the temperature of the plate surface during cooling at various positions in the plate direction, a cooling temperature curve was obtained with time on the horizontal axis and temperature on the vertical axis. Since one test material was cooled under the same conditions over the entire length of the plate in the plate, the maximum gradient of this cooling curve was adopted as the maximum cooling rate of the test material. The cooling rate for each specimen was changed by controlling the cooling atmosphere and fan rotation speed, and by lowering the cooling temperature in multiple stages.

〔conductivity〕
The electrical conductivity of each test material was measured according to JIS H0505.
[0.2% proof stress in the rolling direction]
A tensile test piece (JIS No. 5) in the rolling direction (LD) was taken from each test material, and a tensile test based on JIS Z2241 was performed with the number of tests n = 3, and a 0.2% yield strength was measured. The average value of n = 3 was defined as the result value of the test material.

[Heat shrinkage]
A rectangular test piece having a length of 180 mm in the rolling parallel direction and a length of 50 mm in the direction perpendicular to the rolling was cut out from each sample material and subjected to a heating test that was held at 500 ° C. for 10 minutes in a nitrogen atmosphere. The heating time from room temperature to 500 ° C. is about 30 seconds. For cooling after heating, the test piece was taken out of the furnace at room temperature and left on a horizontal table to cool. The heat shrinkage ratio λ is obtained by the above equation (1) from the length L ₀ in the rolling parallel direction at 20 ° C. of the test piece before the heating test and the length L ₁ in the rolling parallel direction at 20 ° C. of the test piece after the heating test. It was. L ₀ and L ₁ are obtained by a method in which the test piece is placed on a horizontal plate and the length in the rolling parallel direction of the test piece at the center position in the width direction of the test piece (that is, the central position in the direction perpendicular to the rolling direction) is measured with a laser displacement meter. It was. Among the measured values of the number of tests n = 3, the largest λ value was adopted as the result value of the test material.

[Residual stress]
A test piece having a width of 10 mm and a length of 200 mm was cut out from each specimen (however, the longitudinal direction coincides with the rolling direction), and the Truting-Read method (reference: Shigeru Yoneya, “Generation and countermeasures of residual stress”, Co., Ltd. Residual stress was determined by Yokendo, p.54-56, 1975). Specifically, the method disclosed in paragraphs 0029 and 0030 of Patent Document 2 was followed. The average value of the number of tests n = 3 was defined as the result value of the test material.

[Average crystal grain size]
By observing the surface of the specimen (rolled surface) polished and etched with an optical microscope, a line segment of a known length in a direction parallel to the rolled surface and perpendicular to the rolled direction by the cutting method of JIS H0501. The average crystal grain size was determined by counting the number of crystal grains that were completely cut. However, the total number of crystal grains to be measured is 100 or more. Twin boundaries are not considered grain boundaries. In the optical microscope observation for measuring the average crystal grain size, the observation area was a rectangular area of 300 μm × 300 μm.
These results are shown in Table 2.

As can be seen from Table 2, each of the copper alloy sheet materials of the present invention has a high strength with a 0.2% proof stress of LD of 800 MPa or more and a thermal shrinkage rate reduced to 0.020% or less. The residual stress is 100 MPa or less, which is a low value as a Cu—Ni—Si based copper alloy sheet having a strength level of 0.2% proof stress of 800 MPa or more. The conductivity is also good. These plate materials are extremely useful as materials for precision energized parts such as QFN type multi-pin lead frames that require high dimensional accuracy. In addition, it turns out that heat shrinkage rate 0.010% or less can be stably implement | achieved by making the work roll diameter in finish cold rolling into 80 mm or more and the tension | tensile_strength in low temperature annealing to 25 N / mm < ² > or less.

  On the other hand, Comparative Example No. 31 had a low strength level because the total rolling ratio in the finish cold rolling was too low. In No. 32, the strength decreased because the heating temperature for low-temperature annealing was too high. In Nos. 33 and 34, the reduction ratio in the final pass of the finish cold rolling was excessive, so the thermal contraction of the plate material was large. In Nos. 35 and 36, the diameter of the work roll used for the finish cold rolling was too small, so the heat shrinkage was large. Since No. 37 has an excessive Ni content, and No. 39 has an excessive Si content, these were inferior in conductivity. No. 38 had a low Ni content, and No. 40 had a low Si content, so these were low in strength. No. 41 had a large thermal shrinkage due to excessive tension during heating in low-temperature annealing. In Nos. 42 and 43, since the maximum cooling rate in the low-temperature annealing was excessive, the thermal contraction of the plate material was large. No. 44 had a large thermal shrinkage because the heating temperature of the low-temperature annealing was too low. In No. 45, since the finish cold rolling rate was too high, the strength decreased during low temperature annealing. No. 46 had a large thermal shrinkage because the tension during low-temperature annealing was too low.

Claims (5)

In mass%, Ni: 1.0 to 4.5%, Si: 0.1 to 1.2%, Mg: 0 to 0.3%, Cr: 0 to 0.2%, Co: 0 to 2. 0%, P: 0 to 0.1%, B: 0 to 0.05%, Mn: 0 to 0.2%, Sn: 0 to 0.5%, Ti: 0 to 0.5%, Zr: A plate material having a composition comprising 0 to 0.2%, Al: 0 to 0.2%, Fe: 0 to 0.3%, Zn: 0 to 1.0%, the balance Cu and unavoidable impurities, Heating of 0.2% proof stress in the rolling parallel direction of 800 MPa or more, electrical conductivity of 35% IACS or more, taking a rectangular test piece of 180 mm in the rolling parallel direction and 50 mm in the rolling perpendicular direction from the plate material, and holding at 500 ° C. for 10 minutes A copper alloy sheet having a property that when subjected to the test, the heat shrinkage ratio λ in the rolling parallel direction defined by the following formula (1) is 0.020% or less.
λ (%) = (L ₀ −L ₁ ) / L ₀ × 100 (1)
Here, L ₀ is the length (mm) in the rolling parallel direction at 20 ° C. of the test piece before the heating test, and L ₁ is the length (mm) in the rolling parallel direction at 20 ° C. of the test piece after the heating test.   2. The copper alloy sheet according to claim 1, wherein an average crystal grain size by a cutting method measured in a direction perpendicular to the rolling direction with respect to the sheet surface (rolled surface) is 3 to 50 μm. In mass%, Ni: 1.0 to 4.5%, Si: 0.1 to 1.2%, Mg: 0 to 0.3%, Cr: 0 to 0.2%, Co: 0 to 2. 0%, P: 0 to 0.1%, B: 0 to 0.05%, Mn: 0 to 0.2%, Sn: 0 to 0.5%, Ti: 0 to 0.5%, Zr: Intermediate after aging treatment having a composition consisting of 0 to 0.2%, Al: 0 to 0.2%, Fe: 0 to 0.3%, Zn: 0 to 1.0%, the balance Cu and unavoidable impurities The product plate material is subjected to cold rolling with a work roll having a roll diameter of 70 mm or more and a final rolling reduction ratio of 4 to 15%, and a total rolling ratio of 20 to 80% (finishing cold rolling process),
The plate after the finish cold rolling step, after heating at 5N / mm ² or more 30 N / mm ² lower than the temperature range of 250 to 550 ° C. while applying tension to room temperature at less than the maximum cooling rate 100 ° C. / sec Cooling process (low temperature annealing process),
The manufacturing method of the copper alloy board | plate material which has this.   The method for producing a copper alloy sheet according to claim 3, wherein the temperature range of heating is 330 to 530 ° C in the low-temperature annealing step.   A lead frame using the copper alloy sheet according to claim 1 as a material.