JP4020881B2 - Cu-Ni-Si-Mg copper alloy strip - Google Patents

Description

  The present invention relates to a copper alloy strip, and more particularly to a copper alloy strip used for a conductive spring material such as a lead frame material of a semiconductor device such as an integrated circuit (IC), a connector, a terminal, a relay, or a switch.

  Copper alloy strips for electronic materials used for lead frames, terminals, connectors, and the like are required to have both high strength and high electrical conductivity (thermal conductivity) as basic characteristics of the alloy. In addition to these characteristics, bending workability, stress relaxation resistance, heat resistance, adhesion to plating, solder wettability, etching workability, press punchability, corrosion resistance, and the like are required.

  On the other hand, in response to the recent miniaturization and high integration of electronic components, lead frames, terminals, and connectors have been increased in the number of leads and narrow pitch, and the shape of the components has become complicated. At the same time, there is an increasing demand for improved reliability during assembly and after mounting. Against this background, the required level for the properties of the copper alloy material described above is becoming increasingly sophisticated.

  From the viewpoint of high strength and high conductivity, in recent years, the amount of age-hardening type copper alloys has increased as a copper alloy for electronic materials, replacing conventional solid solution-strengthened copper alloys such as phosphor bronze and brass. is doing. In an age-hardening type copper alloy, by aging the solution-treated supersaturated solid solution, fine precipitates are uniformly dispersed, the strength of the alloy is increased, and at the same time, the amount of solid solution elements in copper is reduced. Electrical conductivity is improved. For this reason, a material excellent in mechanical properties such as strength and spring property and having good electrical conductivity and thermal conductivity can be obtained.

  Of the age-hardening type copper alloys, Cu—Ni—Si based copper alloys are representative copper alloys having both high strength and high electrical conductivity, and have been put into practical use as materials for electronic devices. In this copper alloy, the strength and electrical conductivity are increased by the precipitation of fine Ni—Si intermetallic particles in the copper matrix.

In order to improve mechanical characteristics and the like, elements other than Ni and Si are often added to the Cu—Ni—Si based copper alloy in many cases. In particular, Mg is a typical element added to a Cu—Ni—Si based copper alloy. As an effect of Mg addition,
(1) Strength and stress relaxation resistance are improved (Japanese Patent Laid-Open No. 61-250134).
(2) Hot workability is improved (Japanese Patent Laid-Open No. 05-345941).
(3) By forming Mg as an oxide and trapping oxygen, generation or coarsening of Si oxide during heat treatment can be prevented (Japanese Patent Laid-Open No. 09-209062).
Etc. have been reported.

  However, when Mg is added to the Cu-Ni-Si alloy, the strength and stress relaxation resistance are improved, but coarse inclusions are easily generated in the alloy, and bending workability, etching property, plating property, etc. are improved. There was a problem of lowering. It is known that the presence of inclusions in the alloy adversely affects bending workability, etching properties, plating properties, and the like.

  There are two types of inclusions of Cu—Ni—Si based copper alloys: nonmetallic inclusions such as oxides and sulfides and coarse Ni—Si based compounds. In the case of a Cu—Ni—Si—Mg based copper alloy, Mg is more easily oxidized than Si, so that the oxide composition is MgO, and the sulfide is MgS. However, it has been clarified in JP-A-05-059468 that the generation of MgO and MgS can be suppressed if the O and S concentrations are reduced to 15 ppm or less.

  On the other hand, according to Mizuno et al., When Mg is added to a Cu—Ni—Si based copper alloy, coarse Ni—Si based precipitates containing about 15 at% Mg at the grain boundaries grow coarsely (Masataka Mizuno, Yoshio Izumi) , Tetsuzo Ogura, Takashi Hamamoto: Journal of Copper Technology Research, vol.38 (1999), p291-297.). That is, when Mg is added to a Cu—Ni—Si based copper alloy, coarse Ni—Si based compounds are remarkably increased.

When the coarse Ni-Si compound increases, the amount of smut generated during etching increases, and the plating property and bending workability decrease. Therefore, Japanese Patent Laid-Open No. 2001-49369 discloses a Cu-Ni-Si compound. Inclusion of Ni-Si compound or the like is 10 μm or less with respect to the copper alloy, and further, the number of inclusions of 5 to 10 μm is adjusted to less than 50 / mm ^{2 in the} cross section parallel to the rolling direction. The influence of inclusions can be suppressed.

JP-A-61-250134 JP 05-345941 A Japanese Patent Application Laid-Open No. 09-209062 JP 05-059468 A JP 2001-49369 A Masataka Mizuno, Yoshio Iemi, Tetsuzo Ogura, Takashi Hamamoto: Journal of Copper and Copper Technology, vol. 38 (1999), p291-297.

  Here, Japanese Patent Laid-Open No. 2001-49369 includes a Cu—Ni—Si—Mg based copper alloy, but includes a Cu—Ni—Si based alloy containing other metal components such as Zn, Sn, and Fe. This is only a comprehensive case that can be applied to Cu-Ni-Si-Mg alloys, and does not disclose specific case conditions for each Cu-Ni-Si-Mg alloy. Further, the focus on Ni-Si coarse particles was only the size and average number of individual particles. Furthermore, in order to produce an alloy having the size and number of inclusions within the range required by the present invention, it is necessary to perform hot rolling and solution treatment for a long time at a high temperature, and a Cu—Ni—Si—Mg system. There was a problem of raising the manufacturing cost of the copper alloy strip. In addition, high temperature and long time hot rolling and solution treatment may lead to coarsening of the crystal grains of the Cu-Ni-Si-Mg-based copper alloy strips, and the desired properties (strength, bending processing) In other words, there was a problem that a product having the property could not be obtained.

  Therefore, an object of the present invention is to solve the above problems. More specifically, it can be manufactured without the need for high-temperature and long-time hot rolling and solution treatment, which will increase the manufacturing cost, and has excellent strength, conductivity, stress relaxation resistance, bending workability, and etching properties. It is an object of the present invention to provide a Cu—Ni—Si—Mg based copper alloy strip that has wettability and plating properties and can be stably manufactured.

  In order to achieve the above-mentioned problems, the present inventors first conducted extensive research to capture Ni-Si coarse particles from a different viewpoint, and as a result, the focus on conventional Ni-Si coarse particles is: Focusing on the fact that it is only the size and average number of individual particles, and considering the distribution state of Ni-Si coarse particles by newly devising the concept of “particle group” described below, Ni The influence of the Si-based coarse particles on the characteristics was investigated.

  Referring now to FIG. 1, FIG. 1 shows a representative form of an aggregate of Ni—Si coarse particles that can be observed at a magnification of 1000 times using an FE-SEM (electrolytic emission scanning electron microscope: manufactured by PHILIPS). ing. When a cross section parallel to the rolling direction or a cross section perpendicular to the rolling direction is observed, it is observed as an aggregate of Ni—Si based coarse particles arranged in a direction orthogonal to the thickness direction. Hereinafter, this aggregate can form a Ni-Si-based particle group defined later.

The Ni—Si-based particle group caused the following adverse effects on the characteristics.
(1) When soldering, the solder repelled on the particle group.
(2) During etching, particles remained undissolved and the smoothness of the etched surface was lost.
(3) When plating with Ag, Ni or the like, plating pinholes were formed on the particles. Further, sufficient plating adhesion strength was not obtained on the particle group, and peeling of plating and plating swelling occurred at this portion.
(4) During bending, the particle group became the starting point of cracking, and bending workability deteriorated.
(5) The surface appearance was damaged due to the generation of scratches during cold rolling.

On the other hand, the present inventors also obtained the following knowledge.
(1) Even if the particles having a particle size of 10 μm or more and 20 μm or less are dispersed and distributed, the properties are adversely affected, but if they are 2 particles / mm ² or less, the adverse effects can be ignored.
(2) For particles having a particle size of 2 μm or more and less than 10 μm, the effect on the properties is small if they are dispersed and distributed, but if they are aggregated and present as a particle group, the properties are adversely affected.
(3) For particles having a particle size of less than 2 μm, the influence on the characteristics is small even if they aggregate and exist as a particle group,
I found.

The present invention has been completed on the basis of the above knowledge, contains 1.0 to 4.0% by mass of Ni, and contains Si at a concentration of 1/6 to 1/4 with respect to the mass% concentration of Ni. And a copper-based alloy containing 0.05% to 0.3% by mass of Mg, the balance being Cu and inevitable impurities, and in a cross section parallel to the rolling direction, The Cu—Ni—Si—Mg based copper alloy strips having the distribution states of (1) and (2).
(1) The number of Ni—Si compound particles having a particle size of 10 μm or more and 20 μm or less is 2 / mm ² or less.
(2) The number of Ni—Si based particles having a length of 0.05 mm or more and 1.0 mm or less among the Ni—Si based particles composed of Ni—Si based particles having a particle size of 2 μm to 20 μm Is 2 pieces / mm ² or less.

  The present invention further provides a Cu-Ni-Si-Mg based copper alloy strip characterized by containing one or more of Sn, Zn, and Ag in a total amount of 0.01 to 2.0 mass%.

  In another embodiment, the present invention is an electronic device component such as a lead frame of a semiconductor device obtained by processing the alloy strip or a conductive spring such as a connector, a terminal, a relay, or a switch.

  The Cu-Ni-Si-Mg-based copper alloy strip of the present invention does not require high-temperature / long-time hot rolling, which increases the manufacturing cost, and has good strength, conductivity, stress relaxation resistance, bending work Therefore, it has higher technical value and practicality than conventional techniques, and is suitable as a copper alloy used for lead frames, terminals, connectors and the like.

(1) Ni and Si
Ni and Si form fine particles of an intermetallic compound mainly composed of Ni ₂ Si by performing an aging treatment. As a result, the strength of the alloy is significantly increased and at the same time the electrical conductivity is increased. The addition concentration (mass%) of Si is in the range of 1/6 to 1/4 of the addition concentration (mass%) of Ni. If the Si addition amount is out of this range, the electrical conductivity is lowered. Ni is added in the range of 1.0 to 4.0% by mass. If Ni is less than 1.0% by mass, sufficient strength cannot be obtained. When Ni exceeds 4.0 mass%, a crack generate | occur | produces by hot rolling.

(2) Mg
When 0.05 mass% or more of Mg is added to the Cu—Ni—Si alloy, the tensile strength and the proof stress are increased, and the heat resistance and the stress relaxation characteristics are also improved. On the other hand, if the amount of Mg added exceeds 0.3% by mass, the manufacturability deteriorates and the conductivity decreases greatly.

(3) Ni-Si-based particles having a particle size of 10 μm or more and 20 μm or less Particles having a particle size of 10 μm or more may adversely affect solder wettability, plating properties, bending workability, etc. even if dispersed and distributed. It has been found that if the number of particles having a particle size of 10 μm or more is 2 particles / mm ² or less in a cross section parallel to the rolling direction, adverse effects on characteristics can be ignored. Here, the Ni—Si-based particles are defined as particles containing Ni at 50 at% or more and containing Si at 20 at% or more. Further, the particle diameter of the Ni—Si-based particles is defined as the diameter of the smallest circle surrounding the particles (the same applies hereinafter). Note that particles having a particle size exceeding 20 μm adversely affect the characteristics regardless of the number of particles, but there are no particles exceeding 20 μm in a normal Cu—Ni—Si alloy.

(4) Ni—Si-based particle group When Ni—Si-based particles having a particle diameter of 2 μm or more are aggregated to form a particle group, it adversely affects solder wettability, plating property, bending workability and the like. FIG. 2 shows a typical form of the Ni—Si-based particle group observed in the rolling parallel section (FE-SEM [electrolytic emission scanning electron microscope: manufactured by PHILIPS) can be observed at a magnification of 1000 times]. Here, an aggregate of Ni—Si particles having a particle diameter of 2 μm or more and 20 μm or less having a distance (d) of 10 μm or less between adjacent Ni—Si particles having a particle diameter of 2 μm or more and 20 μm or less is obtained as Ni-Si particles. Define as a group. If Ni—Si-based particles are dispersed at intervals exceeding 10 μm, the adverse effect on the characteristics can be ignored if the particle size is 10 μm or less, but if they are aggregated at a distance of 10 μm or less, the particle size is 10 μm. Even if the particle size is less than 2 μm, it adversely affects the properties as a particle group unless the particle size is less than 2 μm. Here, the “particle group length (L)” is defined as the diameter of the smallest circle surrounding one particle group. However, the larger the particle group and the larger the number of particle groups, the more adverse the influence on the characteristics. large. However, according to the experimental results by the present inventor, even when Ni—Si-based particles having a size of 2 μm or more gather to form a particle group, the length (L) of the particle group in the cross section parallel to the rolling direction is 0. When the length is shorter than 05 mm, regardless of the number, the solder wettability, plating property, bending workability, etc. are not adversely affected, and the particle group length (L) is 0.05 mm or more and 1.0 mm or less. It was found that when the number of particle groups was 2 / mm ² or less, the properties were not adversely affected. Note that a particle group having a length (L) exceeding 1.0 mm adversely affects the characteristics regardless of the number of particles, but a normal Cu—Ni—Si alloy does not have a particle group exceeding 1.0 mm.

(5) Additive elements other than Mg When an element that chemically reacts with Ni or Si is added to the Cu—Ni—Si—Mg based copper alloy strip, the form and distribution of the Ni—Si based particles change. The effect of the invention cannot be obtained. On the other hand, when adding an element that does not chemically react with Ni and Si, such as Sn, Zn, and Ag, for the purpose of increasing the strength or the like, the effect of the present invention can be obtained in the same manner as when these elements are not added. However, since the conductivity decreases, the total amount of addition is desirably 2.0% by mass or less, but in order to obtain a desired effect, it is preferably 0.01% by mass or more.

In a general manufacturing process of a Cu-Ni-Si-Mg-based copper alloy strip, first, an atmospheric melting furnace is used to melt raw materials such as electrolytic copper, Ni, Si, Mg under a charcoal coating, and a desired composition. Get molten metal. Then, this molten metal is cast into an ingot. Thereafter, hot rolling is performed, and cold rolling and heat treatment are repeated to finish a strip or foil having a desired thickness and characteristics. Heat treatment includes solution treatment and aging treatment. In the solution treatment, heating is performed at a high temperature of 700 to 1000 ° C., so that the Ni—Si-based compound is dissolved in the Cu matrix, and at the same time, the Cu matrix is recrystallized. The solution treatment may be combined with hot rolling. In the aging treatment, Ni and Si heated in a temperature range of 350 to 550 ° C. for 1 h or more and solid-dissolved by the solution treatment are precipitated as fine particles mainly composed of Ni ₂ Si. This aging treatment increases strength and conductivity. In order to obtain higher strength, cold rolling may be performed before aging and / or after aging. In addition, when cold rolling is performed after aging, strain relief annealing (low temperature annealing) may be performed after cold rolling.

  In the above process, the most important process for the production of Ni—Si coarse particles is casting. The generation site of Ni—Si coarse particles during casting is a grain boundary of a solidified structure, and Si and Mg are concentrated (segregated) at the grain boundary. During the solidification process of the molten metal, Ni—Si coarse particles are generated (crystallized) at the grain boundaries. In the cooling process after solidification, coarse Ni—Si grains grow and become larger, and generation (precipitation) of new Ni—Si coarse particles occurs. Due to the presence of Mg, the generation and growth of Ni—Si coarse particles at the grain boundaries are significantly promoted. Since Ni—Si coarse particles are generated at the grain boundaries, the distribution of Ni—Si coarse particles becomes sparse when the cast structure is refined to increase the grain interface area. Conversely, when the cast structure is coarsened, the grain boundary area is reduced, the distribution of Ni—Si based coarse particles becomes dense, and the occurrence frequency of Ni—Si based particles as shown in FIG. 1 increases. .

  The Cu—Ni—Si—Mg based copper alloy strip of the present invention has a cooling rate at the time of casting without increasing the temperature of hot rolling and / or solution treatment and dissolving the coarse Ni—Si based particles. It is a copper alloy strip that can obtain desired properties by simply controlling the cast structure such as raising.

  Hereinafter, in order to clarify the features of the present invention and the best mode for carrying out the present invention, the present invention will be specifically described with reference to examples.

Using a high-frequency induction furnace, 3 kg of electrolytic copper is melted in a graphite crucible having an inner diameter of 60 mm, Ni, Si and Mg are added, and the molten metal component is 2.5 mass% Ni-0.5 mass% Si (Ni (Concentration of 1/5 with respect to mass%)-0.15 mass% Mg. After the molten metal was adjusted to a predetermined temperature, it was cast into a mold having the shape shown in FIG. In order to change the size of the cast structure, the casting temperature and the mold material were changed as follows.
(1) Casting temperature: It was performed under two conditions of 1150 ° C and 1250 ° C. By lowering the casting temperature, it was expected that the cast structure became fine and Ni—Si based particles were dispersed.
(2) Mold material: Performed under four types of conditions: refractory brick, graphite, cast iron, and pure copper. The cooling rate increases in the order of refractory brick, graphite, cast iron, and pure copper. By increasing the cooling rate, it was expected that the cast structure became fine and Ni—Si-based particles were dispersed.

  For comparison, an alloy not containing Mg was also produced, and the influence of Mg on the formation of Ni-Si inclusions was investigated.

Next, this ingot was processed and heat-treated in the following order to obtain a sample having a thickness of 0.15 mm.
(1) The ingot was heated at 780 ° C. for 3 hours and then hot rolled to a thickness of 8 mm. The hot rolling end temperature was 620 ° C.
(2) The oxidized scale on the surface of the hot rolled material was removed with a grinder.
(3) Cold rolled to a thickness of 2 mm.
(4) As a solution treatment, it was heated at 780 ° C. for 20 seconds and quenched in water.
(5) The surface oxide film was removed by chemical polishing.
(6) Cold rolled to a plate thickness of 0.5 mm.
(7) Heated at 430 ° C. for 3 hours in hydrogen as an aging treatment.
(8) The surface oxide film was removed by chemical polishing.
(9) Cold rolled to a plate thickness of 0.15 mm.
(10) As strain relief annealing (low temperature annealing), it heated at 400 degreeC in hydrogen for 1 minute.

  The following evaluation was performed about the sample produced in this way. In any sample, the O concentration was in the range of 5 to 10 ppm by mass, and the S concentration was in the range of 10 to 15 ppm by mass.

(1) Number of Ni—Si-based particles and particle groups After a cross section parallel to the rolling direction is mirror-finished by mechanical polishing using diamond abrasive grains having a diameter of 1 μm, chlorination at 20 ° C. and 47 ° Be (Baume) is performed. It was immersed in the ferric aqueous solution for 2 minutes with stirring. By this etching process, the base of Cu was dissolved, and Ni—Si based particles remained undissolved and appeared. This cross section was observed at a magnification of 1000 times using an FE-SEM (electrolytic emission scanning electron microscope: manufactured by PHILIPS), and the number of particles of 10 μm or more and the number of particle groups were measured. Here, the number of particles and particle groups was measured by randomly selecting and observing a plurality of observation fields so that the observation area was 2 mm ² from a cross section parallel to the rolling direction of the sample. In addition, the particle | grains exceeding 20 micrometers were not observed. Moreover, the particle group whose length exceeds 1.0 mm was not observed. It was confirmed by analyzing EDS [energy dispersive X-ray analysis] of FE-SEM that the typical form was that the component of particle | grains and particle group was a Ni-Si type particle.

(2) Bending workability As shown in FIG. 4, repetitive bending is performed at 90 ° on one side with a bending radius of 0.15 mm in the direction (Bad Way) so that the bending axis is parallel to the rolling direction. The number of times until breakage was counted by the method of counting as times. The test was performed 5 times and the average of 5 times was calculated | required.

(3) Solder wettability A strip-shaped test piece having a width of 10 mm was collected, the surface was degreased with acetone, and pickled with a 10 vol% sulfuric acid aqueous solution. Thereafter, the sample was immersed in 25% rosin-ethanol for 5 seconds and then immersed in a solder bath for 10 seconds. The solder composition was 60 mass% Sn-40 mass% Pb, the solder temperature was 230 ° C., and the immersion depth of the sample was 10 mm. When the surface of the sample after the solder immersion was observed with a stereomicroscope, depending on the sample, a spot-like portion repelling the solder was observed. For the area of 1000 mm ² (the front and back portions of 5 test pieces), the number of solder repelling portions was determined.

(4) Stress relaxation properties As shown in FIG. 5, a test piece having a thickness t = 0.15 mm processed to a width of 10 mm × a length of 100 mm was loaded with a bending stress of a target distance l = 50 mm and a height y ₀ = 20 mm. The amount of permanent deformation (height) y shown in FIG. 6 after heating at 150 ° C. for 1000 hours was measured, and the stress relaxation rate {[(y−y ₁ ) (mm) / (y ₀ −y ₁ ) (mm)] × 100 (%)} was calculated. Y ₁ is the initial warp height before stress is applied.

  As can be seen from Table 1, according to the present invention, the comparative example No. Cu-Ni-Si-Mg-based copper alloy strips having good bending workability and solder wettability equivalent to or higher than 9 and 10 were obtained [Example No. 1-5].

On the other hand, no. 6 to 8 are alloys of the same composition as the present invention, but the ingot structure is not sufficiently reduced due to the influence of the casting material and casting temperature, and the number of particles having a particle size of 10 μm or more and Ni-Si-based particle groups is 2 / Exceeding mm ² , solder wettability and bending workability deteriorated.

Comparative Example No. 9 and no. 10 is a Cu—Ni—Si alloy to which no Mg is added. 5 and no. 7 that the number of particles having a particle size of 10 μm or more and the number of Ni—Si-based particle groups was increased by adding Mg that produced an ingot under the same conditions as in FIG. Comparative Example No. 9 and no. The bending workability and solder wettability of No. 10 were good because Mg was not added and the number of particles having a particle diameter of 10 μm or more and the number of Ni—Si based particles were suppressed to ² / mm ² or less. Therefore, it was inferior to the examples in terms of stress relaxation resistance.
In the JP 200 1 -49369 discloses and defines the size of all the particles and 10μm or less, and the size of inclusions number of 5~10μm below 50 / mm ^2. In order to obtain this state, the hot rolling heating temperature is defined as 800 ° C. or higher, the end temperature is defined as 650 ° C. or higher, and the solution treatment temperature is preferably 800 ° C. or higher. Here, no. As for No. 5, the number of Ni—Si particles having a particle diameter of 10 μm or more was 1.0 / mm ² , and when the number of particles of 5 to 10 μm was separately measured, it was 60 / mm ² . This is because the hot rolling temperature and the solution treatment temperature are low. However, by optimizing the casting conditions and adjusting the distribution of Ni—Si particles, good solder wettability and repeated bending workability are obtained despite the large number of Ni—Si particles.

It is the schematic diagram which showed the typical form of the aggregate | assembly of Ni-Si type coarse particle. It is the schematic diagram which showed the typical form of the Ni-Si type particle group observed in a rolling parallel cross section. It is the figure which showed the mold shape. It is explanatory drawing of a repeated bending test method. It is explanatory drawing of a stress relaxation test method. It is explanatory drawing regarding the amount of permanent deformation of a stress relaxation test method.

Claims (2)

1.0 to 4.0 mass% Ni is contained, Si is contained at a concentration of 1/6 to 1/4 with respect to the mass% concentration of Ni, and 0.05% to 0.3 mass% of Mg is contained. A copper-based alloy containing Cu and unavoidable impurities in the balance, and in a cross section parallel to the rolling direction, the Ni-Si compound particles have the following distribution states (1) and (2): A Cu-Ni-Si-Mg-based copper alloy strip characterized.
(1) The number of Ni—Si compound particles having a particle size of 10 μm or more and 20 μm or less is 2 / mm ² or less (the number of inclusions having a size of 5 to 10 μm is 50 / mm in a cross section parallel to the rolling direction) Except when less than ² ).
(2) The number of Ni—Si based particles having a length of 0.05 mm or more and 1.0 mm or less among the Ni—Si based particles composed of Ni—Si based particles having a particle size of 2 μm to 20 μm Is 2 pieces / mm ² or less. The component for electronic devices obtained by processing the alloy strip of Claim 1 .

Images