JP2006104495A - Copper alloy, manufacturing method therefor, and heat sink - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a copper alloy which is suitable for the heat sink of a semiconductor module, and has particularly a high effect of inhibiting the heat sink from deforming when the heat sink is jointed with a substrate through Pb-free solder. <P>SOLUTION: The copper alloy has a composition comprising, by mass, 3-15% Ni, 3% or less B, while controlling the ratio Ni/B to 7 or less, 3% or less of elments other than Cu, Ni and B in total, and the balance Cu; has a Cu matrix in which the concentration of Ni is controlled to 2.5 mass% or lower; and has properties including a heat conductivity of 260 W/m×K or higher, a thermal expansion coefficient of 16.6×10<SP>-6</SP>/K or lower, a 0.2% yield strength of 270 N/mm<SP>2</SP>or higher, and a heat resisting temperature of 270°C or higher. The method for manufacturing the alloy comprises the steps of: cold-rolling the alloy with a reduction rate of 10% or higher; annealing the cold-rolled material in a temperature range of 400 to 900°C, so that the material can cause age precipitation and have the concentration of Ni in the Cu matrix to 2.5 mass% or lower; and subsequently finish-rolling it with a reduction rate of 5 to 40%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a Cu-Ni-B-based copper alloy, a method for manufacturing the same, and a heat radiating plate joined to a substrate on which a semiconductor element is mounted, and relates to a heat radiating plate using the Cu-Ni-B-based copper alloy. It is.

  As a means for efficiently dissipating heat generated from a semiconductor element, there is a wide variety of means for joining a "heat sink" made of a material having good thermal conductivity to a substrate on which the semiconductor element is mounted (hereinafter referred to as "semiconductor element substrate"). It has been adopted.

  FIG. 1 schematically shows a configuration example of a semiconductor module in which a heat sink is bonded to a semiconductor element substrate. A copper pattern 4 is formed on the surface of a substrate 5 made of a ceramic such as alumina or aluminum nitride, and a conductor layer 6 made of a copper plate or the like is formed on the opposite surface. The substrate 5, the copper pattern 4, and the conductor layer 6 are integrated to constitute the semiconductor element substrate 3. A semiconductor element 7 is mounted on the surface of the semiconductor element substrate 3 on which the copper pattern 4 is formed, for example, via a solder layer 2. A lead wire 8 made of a conductive material such as Al is attached between the copper pattern 4 and the semiconductor element 7 as necessary to constitute a circuit. On the other hand, the heat sink 1 is attached to the surface of the semiconductor element substrate 3 on which the conductor layer 6 is formed via the solder layer 2.

  Since the substrate 5 requires a coefficient of thermal expansion as small as that of a semiconductor element, it is generally made of ceramics. On the other hand, since the heat sink 1 is not directly joined to the semiconductor element, it is not required to have a small thermal expansion coefficient equivalent to that of the semiconductor element. Rather, thermal conductivity has been prioritized. For this reason, conventionally, a copper plate having good thermal conductivity has been mainly used as the heat radiating plate.

The heat sink also has a role as a reinforcing member for the semiconductor module. Also, it is often used by attaching to a heat sink. For this reason, it is desirable that the heat sink is not deformed as much as possible during the assembly process of the semiconductor module or during use as an electric / electronic device. As an index of “strength” that does not deform, 0.2% proof stress can be adopted. Although the copper sheet shows a 0.2% proof stress of around 300 N / mm ^{2 in} the state after rolling, it is softened by the temperature rise at the time of soldering, and the 0.2% proof stress tends to decrease. For this reason, a heat sink made of a copper plate is likely to be “warped” due to a difference in thermal expansion from the semiconductor element substrate. Usually, as a countermeasure against this warp, a measure is taken in which a so-called “reverse warp” is formed in advance on the heat radiating plate part by pressing so that the warp generated during soldering is offset as much as possible. However, even with this measure, there is a so-called compatibility problem such as the amount of warp that can be reduced depending on the type and arrangement of the semiconductor element, and it is not a complete measure for stably eliminating the warp.

  Therefore, the present applicant has proposed a Cu-Fe-P system and a Cu-Co-P system as alloys that have improved 0.2% yield strength and improved heat resistance (resistance that does not soften due to an increase in temperature during soldering). , Cu-Fe-Co-P-based and Cu-Fe-Ni-P-based copper alloys have been developed and disclosed in Patent Document 1.

JP 2003-68949 A Japanese Patent Laid-Open No. 11-307701 Japanese Patent Laid-Open No. 10-8166

  In the heat sink using the copper alloy of Patent Document 1, warpage immediately after soldering is reduced, and an excellent shape recovery effect is obtained in the subsequent aging process. That is, the warp once generated by soldering is naturally recovered by being left at room temperature, and finally a fairly high flatness is obtained.

  This shape recovery is largely affected by the normal temperature creep phenomenon that occurs in the solder layer after solidification. That is, stress is applied to the solder layer due to the difference in thermal expansion between the semiconductor element substrate and the heat radiating plate during the process of solidifying the solder and lowering the temperature to room temperature. When the heat radiating plate is a copper plate, the heat radiating plate is softened by heating at the time of soldering, and the restraining force between the solder layer and the heat radiating plate generated during the temperature lowering process is relaxed. For this reason, the normal temperature creep of the solder layer does not proceed so much, and as a result, there is little recovery of warpage. On the other hand, in the case of the alloy of Patent Document 1, the solder layer is hardly softened by heating at the time of soldering, and when the temperature is lowered to room temperature, a large stress is applied to the solder layer. For this reason, the room temperature creep of the solder layer proceeds, and the “warping shape” of the heat sink is greatly recovered.

  On the other hand, when looking at solder materials, in recent years, due to environmental problems, there is an increasing need for using “Pb-free solder” that does not contain Pb. As the Pb-free solder, Sn-Cu system, Sn-Ag system, Sn-Ag-Cu system and the like are known. However, when these Pb-free solders are used, there is a problem that even the alloy of Patent Document 1 has difficulty in sufficiently recovering the warp of the heat sink. The main cause is that in the case of Pb-free solder, deformation of the solder layer due to room temperature creep hardly occurs.

  For this reason, in order to cope with joining using Pb-free solder, it is necessary to increase the initial amount of reverse warpage as the amount of warpage recovery decreases. In this case, since the absolute amount of warpage becomes large, the flatness of the solder layer after soldering may not be obtained, or the soldering operation may be difficult.

  In addition, in electronic devices used in automobiles (especially those installed in an engine room), the temperature is frequently raised and lowered, and the temperature during use tends to increase. For this reason, stress may be applied between the solder layer and the substrate due to a difference in thermal expansion between the heat sink and the substrate when the temperature is raised or lowered, and the solder layer or the substrate may crack. Therefore, it is important that the heat sink is not easily deformed by a temperature change during use. The alloy of Patent Document 1 is desired to be further improved in this respect.

  The present invention is intended to develop and provide a copper alloy that is highly effective in reducing warpage of the heat sink even when Pb-free solder is used, and that is highly effective in reducing deformation due to temperature changes when used as a heat sink. Is.

As a result of various studies, the inventors have been able to reduce the warpage of the heat sink even when Pb-free solder that hardly causes room temperature creep is used when an alloy having a lower thermal expansion coefficient than the alloy of Patent Document 1 is used for the heat sink. I found. In this case, it was also found that deformation due to temperature change when used as a heat sink is also reduced. Various alloys and composite materials having a low coefficient of thermal expansion are known. For example, Patent Document 2 discloses a Cu-Mo composite substrate manufactured by molding and infiltration of a green compact, and its thermal expansion coefficient is 7 to 8.5 × 10 ⁻⁶ / K, which is extremely low. However, this is very expensive and is not suitable for a heat sink of a semiconductor module. Patent Document 3 discloses a Cu—Cr-based alloy, which exhibits a thermal expansion coefficient of 11.5 to 12.8 × 10 ⁻⁶ / K, which is comparable to that of a semiconductor element. However, this is not manufacturable, and contains a large amount of Cr, so that the solderability is not good. These are materials with a very low coefficient of thermal expansion, but in order to reduce the warpage when using Pb-free solder in the heat sink of the semiconductor module, the effect can be obtained without using such low thermal expansion characteristics. It has been found that the thermal expansion coefficient should be approximately 16.6 × 10 ⁻⁶ / K or less. However, it is necessary that the alloy has good heat conductivity and good heat resistance (resistance to softening) at the time of increasing the temperature of the solder joint.

As a result of detailed studies, the inventors have developed a Cu—Ni—B based copper alloy as such an alloy.
That is, in the present invention, the composition of Ni: 3-15%, B: 3% or less, the total of elements excluding Cu, Ni, and B: 3% or less, the balance Cu, and Ni / B ≦ 7, or In particular, in terms of mass%, Ni: 3 to 15%, B: 3% or less, the balance being Cu and inevitable impurities, and having a composition of Ni / B ≦ 7. Focusing on the metal structure of 260 W / m · K or more, a copper alloy having a Ni concentration in the Cu matrix of 2.5% by mass or less is provided.
Among them, the average particle diameter of the second phase is 25 μm or less, the 0.2% proof stress is 270 N / mm ² or more, “cold rolling → heat treatment → 5 to 40% finish cold rolling” One having a structure obtained in the process, one having thermal conductivity (W / m · K) and Ni content (% by mass) satisfying the following formula (1), and an average coefficient of thermal expansion of 25 to 300 ° C. of 16.6 Those having ^{x10 −6} / K or less are preferable targets.
Thermal conductivity ≧ -13.5Ni + 357 (1)
Moreover, the copper alloy material which has a Ni plating layer on the surface of these copper alloys is provided.

  The element content expressed in mass% is substituted for Ni and B in “Ni / B ≦ 7” and Ni in the formula (1), respectively. The “Ni concentration in the Cu matrix” is the Ni concentration (% by mass) in the portion where only the Cu matrix portion excluding the second phase or the like is targeted. The Ni concentration in the Cu matrix can be known from the elemental analysis value obtained by focusing the beam only on the portion of the Cu matrix not containing the second phase, such as EPMA.

  As a method for producing such a copper alloy, a cold rolled material having the above-described chemical composition and subjected to cold rolling of 10% or more, preferably 30% or more, is 400 to 900 ° C, preferably 500 to 750 ° C. The Ni concentration in the Cu matrix is set to 2.5% by mass or less, preferably 2.0% by mass, and then finish rolling is performed at 5 to 40% to improve conductivity. A method for producing a Cu-Ni-B based copper alloy is provided.

  The present invention also provides a heat dissipation plate made of such a copper alloy and bonded to a semiconductor element substrate using solder. As the “solder”, “Pb-free solder”, in particular, solder including Sn—Ag, Sn—Cu, and pure Sn is suitable. This heat sink can be used as a member of a power semiconductor module.

  According to the Cu-Ni-B-based copper alloy of the present invention, deformation at the time of joining with Pb-free solder in a semiconductor module heat sink using the Cu-Ni-B-based copper alloy is greatly reduced, and the heat sink is used for an electronic device. When mounted and used, deformation of the heat sink due to temperature change is suppressed. Furthermore, this copper alloy does not require special processes such as green compact molding, infiltration and melting in vacuum, and can be manufactured in manufacturing processes such as melting / casting and hot rolling. Since the molding can be performed by pressing, the copper alloy and the heat sink of the present invention can be mass-produced at a relatively low cost. Therefore, the present invention promotes the promotion of Pb-free soldering in the semiconductor module and contributes to the improvement of environmental problems, and also increases the degree of design freedom of the semiconductor module and the usage environment.

In the present invention, a Cu—Ni—B alloy composition is employed. As described above, when the heat sink is bonded to the semiconductor element substrate with Pb-free solder, and when the semiconductor module thus configured is used in a high temperature environment such as an engine room of an automobile, the heat sink is deformed. In order to suppress effectively, it is very effective to comprise a heat sink with the raw material whose average thermal expansion coefficient of 25-300 degreeC is about 16.6 * 10 < ^-6 > / K or less. In addition, the heat conductivity at 25 ° C. is required to be 260 W / m · K or more for the heat sink application of the semiconductor module. Moreover, in order not to soften by the temperature rise at the time of soldering using Pb-free solder, a heat resistant temperature of 270 ° C. or higher is necessary. In particular, having a heat-resistant temperature of 300 ° C. or more is advantageous in supporting a wide variety of Pb-free solders. Furthermore, to exhibit a sufficient strength as a heat sink, it is desirable 0.2% proof stress at room temperature is 270N / mm ^2, hopefully 300N / mm ² or more, or is more 330N / mm ² or more Is preferred.

When a Cu—Ni—B alloy is used, a thermal expansion coefficient of 16.6 × 10 ⁻⁶ / K or less can be obtained, and a thermal conductivity of 260 W / m · K or more can be obtained by controlling the composition and structure. , 270 ° C. or higher, or 300 ° C. or more refractory temperature, further 270N / mm ² or more, or 330N / mm ² or more 0.2% proof stress can be realized.

  Ni combines with B to form a second phase mainly composed of Ni and B (hereinafter referred to as “Ni-B second phase”), which improves heat resistance and heat conductivity. Bring. Further, the coefficient of thermal expansion tends to decrease as the Ni amount increases. In order to sufficiently bring out these effects of Ni, it is necessary to contain 3% by mass or more of Ni. It is preferable to set it as 4 mass% or more. On the other hand, when the Ni content increases, the thermal conductivity and cold workability tend to decrease. For this reason, the upper limit of Ni content shall be 15 mass%. Usually, good characteristics as a heat sink can be secured in a Ni content range of approximately 10% by mass or less. A particularly preferable range of the Ni content is 4 to 10% by mass, and a more preferable range is 4.5 to 8% by mass.

  B is necessary for the formation of the Ni—B system second phase, and also has the effect of precipitating as B alone and reducing the thermal expansion coefficient. The action of these Bs is exhibited when the content of B is approximately 0.4% by mass or more. However, in the present invention, control of the Ni / B ratio is important in order to obtain predetermined material characteristics, and Ni / B ≦ described later. The lower limit is limited by the limitation of 7. When the B content is lower than this lower limit, it becomes difficult to precipitate a Ni-B second phase by heat treatment, and a predetermined thermal conductivity cannot be obtained. If the B content is too large, the above action is saturated, and since B is expensive, it causes an increase in the cost of the entire material and causes a decrease in cold workability. For this reason, B content shall be the range of 3 mass% or less. A particularly preferable range of the B content is 0.5 to 2.0% by mass, and a more preferable range is 0.75 to 1.8% by mass.

  In the present invention, the Ni / B content ratio in the alloy is set to 7 or less. If this value exceeds 7, it tends to cause an increase in thermal expansion coefficient and a rapid decrease in thermal conductivity. A particularly preferable range of the Ni / B ratio is 2.5 to 7, and a more preferable range is 3 to 6.5.

  In addition to Ni, B, and Cu, various elements may be contained as long as the object of the present invention is not impaired. For example, Sn having an effect of improving heat resistance and 0.2% proof stress, Zn having an effect of improving adhesion to solder, and the like can be added. However, the total content of other elements (including impurities) excluding Ni, B, and Cu is 3% by mass or less. It is preferable to set it as 1 mass% or less. Moreover, the composition which consists of Ni: 3-15%, B: 3% or less, remainder Cu, and an unavoidable impurity by mass% is employable.

  As the metal structure, it is preferable that the Ni concentration in the Cu matrix is adjusted to 2.5% by mass or less in order to improve thermal conductivity and plating adhesion. It is still more preferable that it is 2.0 mass% or less. Ni dissolved in a large amount in the matrix not only lowers the thermal conductivity, but also lowers the pretreatment property at the time of plating and lowers the plating property, particularly the Ni plating property. The Ni concentration in the Cu matrix can be reduced by sufficiently causing aging precipitation as will be described later.

The second phase desirably has an average particle size of 25 μm or less. When the second phase is coarse, edge cracking is likely to occur during the cold rolling process, and not only the yield is lowered, but also the quality of the copper alloy product may be deteriorated. Further, when the average particle size of the second phase exceeds 25 μm, mechanical properties and heat resistance are liable to be lowered, which is disadvantageous in stably realizing a heat resistant temperature of 270 ° C. or higher and a 0.2% proof stress of 270 N / mm ² or higher. It becomes. More preferably, the average particle size of the second phase is 5 μm or less.

  An ideal metal structure of the alloy of the present invention can be obtained, for example, by a process of “hot rolling → cold rolling → heat treatment with aging precipitation → finish cold rolling of 5 to 40%” described later. That is, the thermal expansion coefficient, the thermal conductivity, the heat resistance temperature, and the 0.2% proof stress are all brought to the above desired values by the cold-worked structure in which the second phase is dispersed in the matrix obtained through such steps. It becomes possible to improve.

Further, since the thermal conductivity tends to increase as the Ni content decreases, the thermal conductivity can be controlled by the Ni and B contents. However, even at the same Ni content level, there is a difference in thermal conductivity between the metal structure optimized as described above and the non-metal structure. When the metal structure is optimized, depending on the Ni content, even if the Ni content is the same, it exhibits a high level of thermal conductivity as shown in the following formula (1). Can be used for
Thermal conductivity ≧ -13.5Ni + 357 (1)
Here, the unit of thermal conductivity is W / m · K, and the Ni content is mass%.
Such a copper alloy takes advantage of its excellent thermal conductivity, low thermal expansion coefficient, electrical conductivity, 0.2% proof stress, heat resistance, etc., and the bonded substrate and chip are small in size and do not warp. It can also be used effectively in applications such as plates and lead frames.

The copper alloy of the present invention can be produced, for example, as follows.
First, at the time of melting, it is desirable to use a Ni-B master alloy as the B raw material because single B is expensive. However, the Ni-B master alloy has a melting point higher than Cu, and when the molten metal temperature is low, B rises and the yield deteriorates. In melting in a general air atmosphere, the temperature is raised to 1150 ° C. or higher, preferably about 1200 to 1280 ° C., and then the Ni—B master alloy is added. Casting can be carried out by an ingot-making method, but it is desirable to use a general continuous casting machine for copper alloys in actual operation. Both horizontal continuous casters and vertical continuous casters can be used. However, cooling from the solidus temperature to 400 ° C. is preferably performed within 10 minutes. More desirably, it is preferably within 5 minutes. If the cooling rate is slow, the second phase in the slab becomes coarse, and edge cracking is likely to occur during cold rolling in the subsequent process. Further, it is disadvantageous in obtaining the desired characteristics.

The obtained slab is reduced in thickness by hot rolling. The heating temperature during hot rolling is desirably 900 ° C. or lower, and more preferably 875 ° C. or lower.
The obtained hot-rolled sheet is subjected to chamfering as necessary, and then the process of “cold rolling → heat treatment” is performed once or more. Among the steps of “cold rolling → heat treatment”, it is necessary to secure a cold rolling rate of 10% or more by cold rolling at least once. For example, a cold rolling rate of 30 to 95% is preferable. Precipitation can be efficiently advanced by combining this cold rolling and heat treatment. That is, precipitation of Ni-B second phase and B simple substance is promoted, thermal conductivity and plating properties are improved by reducing Ni concentration in Cu matrix, and thermal expansion coefficient is reduced by precipitation of B simple substance. It is.

  The heat treatment performed after the cold rolling (heat treatment before finish cold rolling) is performed at a temperature of 400 to 900 ° C., preferably 500 to 750 ° C. In this heat treatment, it is important to promote aging precipitation together with recrystallization. By advancing aging precipitation by this heat treatment, the Ni concentration in the Cu matrix is controlled to 2.5% by mass or less, or even 2.0% by mass or less. As described above, this effectively functions to improve the thermal conductivity. Control of the Ni concentration in the Cu matrix can be realized by optimizing the combination of heat treatment temperature and time according to the Ni content. Actually, an appropriate condition range may be obtained in advance for alloys having various Ni contents, and the heat treatment temperature and time may be set based on the data during operation. The heat treatment time varies somewhat depending on the Ni content level and the heating temperature, but may be set in the range of about 0.2 to 100 hours, preferably 1 to 20 hours.

As for the above heat treatment (recrystallization-aging heat treatment), the desired characteristics can be obtained if it is carried out under the above-mentioned conditions. However, when the emphasis is on improving the thermal conductivity, a very fine second phase is precipitated. In order to improve the heat resistance, “two-stage aging” in which aging is performed at a low temperature of 400 to 500 ° C. after aging heat treatment at a high temperature of about 600 to 800 ° C. may be employed.
About repetition of said rolling-heat processing, it is possible to perform rolling-heat processing several times according to final board thickness.

  Next, finish cold rolling is performed. As a result, the 0.2% proof stress can be remarkably improved while maintaining the heat resistance. It is necessary to secure a finish cold rolling rate of at least 5%. However, if the finish rolling rate is too high, the heat-resistant temperature decreases. According to the study by the inventors, it is effective to perform finish rolling in a rolling rate range of approximately 40% or less. More preferably, it is about 8 to 30%.

  Thereafter, low-temperature annealing can be performed in a range of approximately 300 ° C. or less as necessary. For example, what is necessary is just to hold | maintain at 200-300 degreeC for about 5-300 minutes. By this low-temperature annealing, the residual stress due to rolling is released, and the amount of change in warpage during soldering of the heat sink can be kept small.

  Thus, for example, the copper alloy of the present invention finished to a thickness of, for example, about 0.5 to 5 mm is formed into a heat radiating plate of a semiconductor module by a pressing process. At this time, it is desirable to give the above-mentioned “reverse warp”. Further, after pressing, Ni plating is performed as necessary. Ni plating is effective in improving corrosion resistance, solderability, solder weather resistance, and the like. Next, if this is joined to the semiconductor element substrate by Pb-free solder, the warp after solder joining can be reduced as compared with a conventional heat sink using copper or copper alloy. In addition, when the semiconductor module is mounted and used in an electronic device, deformation due to repeated temperature changes is reduced compared to the prior art, leading to improved reliability. In particular, a power semiconductor module having a large amount of heat generated from a semiconductor element is a suitable application target of a heat sink using the copper alloy of the present invention.

  A Cu—Ni—B based copper alloy having various compositions shown in Table 1 and a part of the Cu—Cr based copper alloy and a Cu—Fe—P based copper alloy were melted. Elements other than those listed in the table are inevitable impurities. In the case of a Cu—Ni—B alloy, Ni-18B master alloy, Cu-2B master alloy, and oxygen-free copper scrap were used as raw materials. A plate material having a plate thickness of 3 mm was finished by the following step A.

[Process A]
(A) Melting / Casting: Using a high-frequency induction furnace, casting in a mold at 1220 ° C. in an air atmosphere. However, Cu-Cr alloy is cast at 1350 ° C. The cooling time from the solidus temperature to 400 ° C is within 5 minutes. The ingot size is 35t x 50w x 200L (mm).
(B) Hot rolling: Rolling from an extraction temperature of 875 ° C. and a plate thickness of 35 mm to 9 mm.
(C) Chamfering: The surface oxide scale is removed, and the plate thickness is about 8.8 mm.
(D) Cold rolling: Rolled to a thickness of 3.4 mm, cold rolling rate of about 61%.
(E) Annealing: Nitrogen atmosphere, 700 ° C. × 4 hours holding, furnace cooling (cooling to 300 ° C. is about 1 hour). However, the Cu-Fe-P alloy is held at 550 ° C for 1 hour.
(F) Pickling (g) Finish cold rolling: Rolled to a plate thickness of 3.0 mm, finish cold rolling rate of 12%.

  Using the obtained plate material having a thickness of 3.0 mm, the thermal conductivity at 25 ° C. and the average thermal expansion coefficient at 25 to 300 ° C. were measured. Further, castability, cold workability, solderability, and average particle size of the second phase were examined. However, in the solderability test, a plate material having a plate thickness of 3.0 mm was further cold-rolled to 0.9 mm. Test materials Test methods and evaluation criteria are as follows.

Thermal conductivity: The thermal conductivity at 25 ° C. was measured by a laser flash method, and 260 W / m · K or more was determined to be good.
Thermal expansion coefficient: An average thermal expansion coefficient of 25 to 300 ° C. in a temperature rising process at a temperature rising rate of 5 ° C./min was determined by a thermal expansion coefficient measuring device (Rigaku TMA8310). A value of 16.6 × 10 ⁻⁶ / K or less was judged good.
Castability: The ingot was cut at three locations from the bottom of the bath at 10 mm, 20 mm, and 30 mm, and ○ (good) when the blowhole was not observed by visual observation of the polished cut surface. X (defect) was determined.
Cold workability: Using a part of the chamfered hot-rolled sheet obtained in the step A (c), a cold rolling experiment with a rolling rate of 50% was performed, and the obtained cold-rolled sheet was applied to the edge of the cold-rolled sheet. A crack was not recognized or the crack length was slightly less than 5 mm, and it was judged that there was no problem in the process, ○ (good), and one with an edge crack of 5 mm or more in length was judged as x (bad). .

  Solderability: A test material having a thickness of 3.0 mm was further cold-rolled to a thickness of 0.9 mm, and a test piece having a thickness of 0.9 mm, a width of 16 mm, and a length of 60 mm was collected. The test piece was degreased with acetone and pickled, and then subjected to a soldering test. The soldering test conforms to JIS C0053, and a rosin-based weakly active flux (RM5004 manufactured by Alpha Metals Co., Ltd.) is used as a flux in a solder bath maintained at 260 ° C. (Sn-3.5Ag-0.8Cu solder alloy). Soaked in. During the immersion, the test piece was suspended through the load cell, and the load applied to the load cell during the immersion was recorded. The immersion depth was 8 mm, the immersion speed was 25 mm / second, and the holding time was 10 seconds. After the start of immersion, the load decreases due to the buoyancy of the test piece, but the load starts to increase as wetting progresses over time. The elapsed time from the start of immersion until the load becomes equal to the load at the start of immersion is called zero cross time. Solderability was judged by the zero cross time, and those having a zero cross time of 5 seconds or less were judged as ◯ (good) and those over 5 seconds were judged as x (bad).

Average particle diameter of the second phase: The sample was buried in a resin, a 400-fold optical micrograph was taken of a cross section parallel to the rolling direction and the plate thickness direction, the maximum length a in the rolling direction for each second phase, and The maximum length b in the thickness direction was measured, and the value obtained by (3/4) × a × b was taken as the second phase particle size, and the average was obtained. Here, the second phase includes a Ni-B system second phase and a B simple substance precipitate. Those having an average particle size of 25 μm or less in the second phase were judged as “good” and those exceeding 25 μm were judged as “poor”.
The results are shown in Table 1.

As can be seen from Table 1, the alloy of the invention clears a thermal conductivity of 260 W / m · K or more and a thermal expansion coefficient of 16.6 × 10 ⁻⁶ / K or less, castability, cold workability, solderability and The average particle size of the second phase was also good.

  On the other hand, comparative alloys No. 6 and 7 had high Ni / B ratios exceeding 7, low thermal conductivity, and high thermal expansion coefficient. In No. 8, since the Ni content was too low, the thermal expansion coefficient was high. In No. 9, the Ni and B contents were too high, and the average particle size of the second phase was large, so the thermal conductivity was poor and the cold workability was also poor. Since No. 10 contained a large amount of Cr, its castability and solderability were poor. No. 11 is a Cu—Fe—P alloy disclosed in Patent Document 1, and has a high thermal expansion coefficient.

  About the invention subject alloy shown in Table 1 and some comparative alloys, a copper alloy plate having a plate thickness of 3.0 mm was manufactured by a manufacturing method in which the process A (b) and subsequent steps were partially changed. The newly adopted processes are as follows. In each process, the parts other than those shown below are the same conditions as in process A.

[Process B]
Cold rolling to 3.7 mm in step A (d), cold rolling rate of about 56%. In (g), cold rolling to a sheet thickness of 3.0 mm, finish cold rolling rate 19%.
[Process C]
Hot rolling to plate thickness of 3.5 mm in step A (b). (D) is omitted.
[Process D]
Cold rolling to plate thickness of 3.0 mm in step A (d). (E) Subsequent steps are omitted.
[Process E]
In step A (d), cold rolling to a sheet thickness of 6.0 mm, cold rolling rate of about 32%. In (g), cold rolling to a sheet thickness of 3.0 mm, finish cold rolling rate of 50%.
[Process F]
Cold rolling to 3.1 mm in step A (d), cold rolling rate of about 64%. In (g), cold rolling to a sheet thickness of 3.0 mm, finish cold rolling rate of 3%.

  For the obtained copper alloy plate having a thickness of 3.0 mm, the Ni concentration in the Cu matrix, the thermal conductivity, the thermal expansion coefficient, the 0.2% proof stress at normal temperature, and the heat resistance temperature were determined. The test and evaluation methods are as follows. The test and evaluation methods for the thermal conductivity and the thermal expansion coefficient are the same as in Example 1.

Ni concentration in the Cu matrix: Using EPMA (JEOL wavelength dispersion type EPMA JXA-8200), the Cu matrix portion of the sample was selectively irradiated with an electron beam at a magnification of 3000 times. Considering not to collect information, quantitative analysis was performed by the ZAF method. In the analysis, the acceleration voltage was 20 kV and the irradiation current was 3.0 × 10 ⁻⁸ A. A Ni concentration (mass%) of 2.5% or less was judged good.
0.2% yield strength at normal temperature: A JIS No. 5 tensile test piece parallel to the rolling direction was prepared, and a tensile test based on JIS Z2241 was performed to obtain a 0.2% yield strength from a stress-strain curve. A value of 270 N / mm ² or more was judged good.
Heat-resistant temperature: The copper alloy plate samples were heated and held at various temperatures in a nitrogen atmosphere for 0.5 hours, then allowed to cool outside the furnace, and the Vickers hardness of the heated samples was measured. The highest heating temperature at which the value maintains 80% or more of the initial (before heating) Vickers hardness was defined as the heat resistant temperature. A heat-resistant temperature of 270 ° C. or higher was judged as good.
The results are shown in Table 2. In Table 2, the result of the copper alloy plate obtained in Example 1 is displayed for the process A. When the structure was observed by the method described above, the average particle size of the second phase of any copper alloy plate was 25 μm or less.

  As can be seen from Table 2, in the example of the present invention produced by the process A or B, the Ni concentration in the Cu matrix is reduced to 2% by mass or less, the thermal conductivity, the thermal expansion coefficient, and the 0.2% proof stress. Good results were obtained at both heat resistant temperatures.

  On the other hand, Comparative Example No. 7-1 had a high Ni / B ratio of 10, and even if it was produced in Step A, the Ni concentration in the Cu matrix was not less than 2.5% by mass. As shown in Example 1, the thermal conductivity and thermal expansion coefficient were inferior. In Nos. 3-3 and 4-2, the intermediate cold rolling was omitted, so the Ni concentration in the Cu matrix was not less than 2.5% by mass and the thermal conductivity was low. No. 2-2 had a low 0.2% proof stress because the finish cold rolling rate was too low. In No. 3-4, since the rolling-annealing in the intermediate process was omitted, the Ni concentration in the matrix was high and the thermal conductivity was low. Moreover, since the cold rolling rate was too high, the heat resistant temperature was low, and a large edge crack occurred. In addition, since annealing after cold rolling and finish cold rolling were omitted, the Ni concentration in the Cu matrix was not less than 2.5% by mass, the thermal conductivity was low, and the heat resistant temperature was low. In No. 3-5, since the finish cold rolling rate was too high, the heat resistant temperature was lowered.

The plating adhesion test was performed on the subject alloy of Table 1 and some comparative alloys of Tables 1 and 2 as follows.
Similar to the soldering test of Example 1, a test piece having a thickness of 0.9 mm, a width of 16 mm, and a length of 70 mm was taken from a plate material cold-rolled to a thickness of 0.9 mm, and near one end in the longitudinal direction. An electric wire (lead wire) was attached to the end, and the end portion 10 mm on the side where the electric wire was attached was masked to obtain a test material. As a pretreatment, this test material was subjected to electrolytic degreasing for 2 A × 30 seconds, washed with pure water, then pickled for 10 seconds using 10% sulfuric acid, and washed with pure water. Thereafter, Ni plating was performed by energization of 2 A × 120 seconds. The plating bath was a sulfamic acid Ni bath, and a pure Ni plate was placed so as to face the surface of the test material. The whole of the test material that was not masked was immersed in the plating bath.

After subjecting the plated test piece to heat treatment at 300 ° C. for 5 minutes in the atmosphere, cutting and resin filling were performed at a position 10 mm from the end on the bottom side (opposite the masked side) of the test material. Observation (optical microscope 300 times) was performed. As a result, the plating adhesion was evaluated with ○ (good) indicating that no voids were observed between the base material and the plating layer, and X (defective) being observed.
The results are shown in Table 3. In addition, the manufacturing process to the board thickness of 3 mm of each material shown in Table 3 is the same as the manufacturing process of the board | plate material of Table 1 and Table 2.

As can be seen from Table 3, the Ni concentration in the Cu matrix of the example of the present invention produced in Step A or B was reduced to 2% by mass or less and exhibited excellent plating adhesion.
On the other hand, Comparative Example 7-1, which has a high Ni concentration and the Ni / B ratio is also outside the scope of the present invention, and Comparative Example No. 3-3 in which the manufacturing process is not appropriate, have a high Ni concentration in the matrix and are closely adhered to the plating. Inferior. This is thought to be due to a decrease in pretreatment. Further, in the alloy of Comparative Example No. 10 containing a large amount of Cr, a second phase, which is considered to be the precipitation of the Cr phase, is observed from the cross-sectional observation, and all the voids are recognized at the interface between the second phase and the Ni plating layer. It was. That is, it was confirmed that the plating adhesion was very poor.

Sectional drawing which illustrated typically the structure of the semiconductor module which joined the heat sink with the solder.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heat sink 2 Solder layer 3 Semiconductor element board | substrate 4 Copper pattern 5 Board | substrate 6 Conductor layer 7 Semiconductor element 8 Lead wire

Claims (15)

  In mass%, Ni: 3 to 15%, B: 3% or less, total of elements excluding Cu, Ni, and B: 3% or less, balance Cu, and Ni / B ≦ 7 at 25 ° C. Copper alloy with a thermal conductivity of 260 W / m · K or higher.   Ni: 3 to 15%, B: 3% or less, total of elements excluding Cu, Ni, and B: 3% or less, balance Cu, and Ni / B ≦ 7. A copper alloy having a Ni concentration of 2.5% by mass or less.   In mass%, Ni: 3-15%, B: 3% or less, balance Cu and inevitable impurities, Ni / B ≦ 7, and thermal conductivity at 25 ° C. of 260 W / m · K More copper alloy.   In mass%, Ni: 3-15%, B: 3% or less, balance Cu and inevitable impurities, Ni / B ≦ 7, Ni concentration in Cu matrix is 2.5 mass% or less Copper alloy.   The average particle diameter of a 2nd phase is 25 micrometers or less, The copper alloy of Claims 1-4. The copper alloy according to any one of claims 1 to 4, which has a 0.2% proof stress of 270 N / mm ² or more.   The copper alloy according to claim 1, which has a structure obtained by a process of “cold rolling → heat treatment → finish cold rolling of 5 to 40%”. The copper alloy according to claim 1, wherein the thermal conductivity (W / m · K) and the Ni content (mass%) satisfy the following formula (1).
Thermal conductivity ≧ -13.5Ni + 357 (1) The copper alloy according to claim 1, wherein an average coefficient of thermal expansion at 25 to 300 ° C. is 16.6 × 10 ⁻⁶ / K or less.   The copper alloy according to claim 1, which has a Ni plating layer on the surface.   In mass%, Ni: 3 to 15%, B: 3% or less, total of elements excluding Cu, Ni, and B: 3% or less, balance Cu, and composition of Ni / B ≦ 7, 10% or more The cold-rolled material subjected to cold rolling is annealed with aging precipitation in the temperature range of 400 to 900 ° C. to make the Ni concentration in the Cu matrix not more than 2.5% by mass, and then 5 to 40%. A method for producing a Cu—Ni—B based copper alloy with improved conductivity, which is finish-rolled.   Ni: 3 to 15%, B: 3% or less, total of elements excluding Cu, Ni, and B: 3% or less, balance Cu, and composition of Ni / B ≦ 7, 30% or more The cold-rolled material subjected to the cold rolling is annealed with aging precipitation in the temperature range of 500 to 750 ° C. so that the Ni concentration in the Cu matrix is 2.0 mass% or less, and then 5 to 40%. A method for producing a Cu—Ni—B based copper alloy with improved conductivity, which is finish-rolled.   A heat sink made of the copper alloy according to any one of claims 1 to 10 and bonded to a substrate on which a semiconductor element is mounted using solder.   The heat sink according to claim 13, wherein the solder is Pb-free solder.   The heat sink according to claim 13 or 14, wherein the heat sink is a member of a power semiconductor module.

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