JP2003277853A - Copper alloy for heat spreader - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost Cu alloy for a heat spreader, which has excellent thermal conductivity and also has excellent reliability in a jointed part during an assembly step or during use because of relatively high semi-softening temperature and can be used for IC package. <P>SOLUTION: The Cu alloy for the heat spreader has (100 to 200) N/mm<SP>2</SP>0.2% proof stress, ≥350 W/m.K thermal conductivity, 0.14 to 0.18 work hardening index and ≤25 μm grain size in a width direction of a rolled surface sheet. The Cu alloy consists of 0.05 to 0.3 wt.%, in total, of P and at least one or more elements among Fe, Ni and Co and the balance Cu with inevitable components. Further, grain size after heat treatment at 600°C for 30 min after cold forging at ≤40% reduction of area is ≤25 μm; and Vickers hardness after heat treatment at 600°C for 30 min after cold forging at ≤40% reduction of area is HV 60 to 170. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copper alloy used for a heat spreader or the like for heat dissipation in an IC package or the like.

[0002]

2. Description of the Related Art In recent years, semiconductor integrated circuits for PCs (I
C) is required to be personalized, highly functionalized, and have a large capacity, and the packaging technology for ICs is also becoming higher in density.
Countermeasures against heat generated from ICs have become an important issue.

The densification of IC mounting technology began in the 1970s, and the mounting technology is the terminal insertion mounting technology DI.
It has evolved from P (dual inline package) to peripheral terminal mounting technology QFP (quad inline package). However, in the peripheral terminal mounting technology, it is difficult to handle around the terminals during mounting, because the external terminals project to the periphery. Then, in the 1990s, BGA (Ball Grid Array) appeared, which accelerated the densification. In this mounting method, the size is small, the number of pins is easy to be increased, and solder balls are used. Therefore, surface mounting is facilitated, and low-cost, high-density mounting that dramatically reduces the defect rate is made possible. Currently, a PBGA having a laminated substrate structure and a TBGA combining a TAB tape and a heat spreader, which realizes higher density, are used.

As the density is increased, it is an important problem to dissipate the heat generated from the IC in order to operate the IC normally, which leads to BGA and a Cu heat dissipation plate directly on the semiconductor chip. The heat dissipation was improved by packaging a so-called heat spreader.

As described above, the heat spreader is required to have excellent heat dissipation, but it is necessary that the heat spreader is not softened and the hardness is not reduced by the heat treatment applied at the time of assembly process and mounting, and the joint portion with the semiconductor chip is required. Credibility is also necessary. Furthermore, it is also desired that the price of the PC is low as the price of the PC is reduced. As described above, since the heat spreader that is responsible for heat dissipation of the high density IC needs to have excellent heat dissipation and heat resistance and be inexpensive, the heat spreader should be an inexpensive oxygen-free copper having excellent thermal conductivity. Cu-based alloys are used.

[0006]

The heat spreader is
Since it is formed by cold forging, residual stress is generated, and heat treatment may be performed to remove this residual stress. Further, when mounting PBGA or TBGA, there is a solder reflow process, and the heat spreader is heated in this process. At this time, oxygen-free copper has a semi-softening temperature of 200 ° C.
Depending on the degree, the crystal grains coarsen unevenly, the hardness changes, and it becomes difficult to maintain flatness and strength. for that reason,
The reliability of the joint between the semiconductor chip and the heat spreader is impaired, and the operational reliability of the PC is reduced.

As high conductivity Cu or Cu-based alloys used in heat spreaders, in addition to oxygen-free copper, Cu-
Zr-based Cu-based alloy (C151, C15150) and Cu-
Fe-Zn-P-based Cu-based alloys (such as C19400) are available. The Cu-Zr-based alloy has high electrical conductivity, is excellent in heat dissipation, and has a semi-softening temperature of 400 ° C or higher, but it is not inexpensive due to the contained components. The Cu-Fe-Zn-P-based alloy has a semi-softening temperature of 400 [deg.] C. or higher, but has a conductivity of about 45% to 65% IACS, which is a substitute characteristic of thermal conductivity, and lacks thermal conductivity. .

Therefore, in view of such conventional problems, the present invention is inexpensive, has excellent thermal conductivity, and has a semi-softening temperature of a relatively high temperature, so that it is joined in the assembly process and during use. It is an object of the present invention to provide a Cu-based alloy for a heat spreader used for an IC package or the like, which is excellent in part reliability.

[0009]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have set the 0.2% proof stress of a copper alloy for a heat spreader to 100 to 200 N / mm ² and the thermal conductivity. By setting it to 350 W / mK or more, the price is low, the thermal conductivity is excellent, and the semi-softening temperature is relatively high, so the reliability of the joint portion during the assembly process and during use is excellent. The inventors have found that a Cu-based alloy for heat spreaders used for IC packages and the like can be provided, and have completed the present invention.

That is, the copper alloy for a heat spreader excellent in heat dissipation and heat resistance according to the present invention has a 0.2% proof stress of 100 to 200 N / mm ² and a thermal conductivity of 350.
It is characterized in that it is W / m · K or more. In this copper alloy for heat spreaders, the work hardening index is 0.14 to
It is preferably 0.18. Further, the crystal grain size in the width direction of the rolled surface plate is preferably 25 μm or less. In addition, at least one kind of Fe, Ni, and Co and P
Is contained in a total amount of 0.05 to 0.3 wt%, and the balance is composed of Cu and inevitable components. Furthermore, the crystal grain size after the heat treatment at 600 ° C. for 30 minutes after cold forging with the cross-section reduction rate of 40% or less is 25 μm or less, and the cross-section reduction rate of 40% or less.
% Or less, the Vickers hardness after heat treatment at 600 ° C. for 30 minutes is preferably HV60 to 170.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the copper alloy for a heat spreader excellent in heat dissipation and heat resistance according to the present invention will be described below.

The heat spreader plays a role of radiating heat from the semiconductor chip, but for that purpose, the semiconductor chip and the heat spreader must be surely in contact with each other. However, if the strength of the heat spreader is not sufficient, the heat spreader may be deformed during the assembly process, the contact surface with the semiconductor chip or the package resin may not be flat, and heat dissipation may be impaired. Here, Cu used for the heat spreader
The 0.2% proof stress is an index of the deformation of the base alloy. In order to maintain heat dissipation by contacting the semiconductor chip without deformation of the heat spreader, the 0.2% proof stress should be 100 N / mm ² or more.

The main role of the heat spreader is to absorb the heat generated from the semiconductor chip and dissipate it to the outside. However, in recent years, the PC package has high functionality and high density, and the amount of heat generated is increasing. Therefore, there is a demand for a heat spreader using a Cu-based alloy having excellent thermal conductivity, and the material used for the heat spreader needs to have a thermal conductivity of 350 W / m · K or more.
This is because if the thermal conductivity is less than 350 W / m · K, the heat generated from the semiconductor chip cannot be sufficiently released to the heat sink when the IC is used, and the operational reliability of the IC package is impaired.

In order to mold the heat spreader, progressive cold forging is performed in terms of cost. Ease of molding and molding accuracy are required for the material characteristics in this cold forging. The 0.2% proof stress is an index showing the ease of molding, and the work hardening index is an index for maintaining the molding accuracy of the heat spreader after forging. The balance of the two indices is important for the material to have good cold forgeability. The 0.2% proof stress needs to be 100 N / mm ² or more so that the heat spreader does not deform during the assembly process or during cold forging, in order to facilitate the forming of the heat spreader by cold forging and to suppress the forging pressure. 200N
/ Mm ² or less is desirable. Further, a material having a work hardening index of 0.14 to 0.18 has ease of forming by cold forging and excellent forming accuracy.

Since the heat spreader is mounted on an IC package or the like and directly contacts the semiconductor chip to radiate heat, variations in characteristics such as flatness, hardness and softening characteristics of the heat spreader among products are caused by the IC package. Operation reliability is impaired. The crystal grain size of the material is one of the material characteristics that cause the variation. If this variation in crystal grain size is large, the local mechanical properties and softening properties will differ, and the formability after cold forging will be impaired. Further, flatness is also impaired due to the difference in softening behavior due to heat treatment during the assembly process. Therefore, a material having a uniform crystal grain size is suitable as a material for the heat spreader.
Further, if the crystal grain size is uniform but coarse, the surface of the heat spreader becomes rough after cold forging, a sufficient contact with the semiconductor chip cannot be obtained during mounting, and the operation reliability of the IC package is impaired. Further, the press punching property is deteriorated, which is not preferable in appearance. Therefore, the heat spreader material preferably has a uniform and fine crystal grain size, and the crystal grain size in the width direction of the rolled surface plate needs to be 25 μm or less.

Further, the heat spreader is formed by cold forging, and the cross section of the material is reduced. At this time, the metal structure changes and residual stress is accumulated. The change in the metal structure and the accumulation of residual stress may cause deformation of the heat spreader in the heat treatment process at the time of mounting the heat spreader, which may reduce the reliability of the package. Generally, oxygen-free copper used as a material for heat spreaders has a possibility that the residual stress is released by heat treatment during mounting of the heat spreaders, the metal structure is unevenly coarsened and softened, and the heat spreaders may be deformed. is there. Further, in order to remove the residual stress, the heat spreader may be subjected to heat treatment before mounting, but similarly, the crystal grains are nonuniformly coarsened, and the strength of the heat spreader may vary and the flatness may be impaired. Therefore, it is desirable that the crystal grains do not coarsen unevenly in order to maintain the hardness and flatness of the heat spreader even after the heat treatment process.

Further, the heat spreader is required to secure hardness in order to prevent deformation during processing, and it is desirable that the crystal grain size is fine.

After the heat treatment at 200 to 600 ° C. for 10 to 30 minutes, which is considered as the heat treatment condition to which most heat is applied in practice, the crystal grains are not unevenly coarsened and the crystal grain size is fine. Since the crystal grain size of the material is 25
It is desirable that the hardness is not more than μm and the hardness is secured to HV60 to 120.

In order for the heat spreader to have the above characteristics and be inexpensive, (Fe, Co, Ni) -P
It is preferable to use a Cu-based alloy that utilizes a system precipitate. Generally, precipitation strengthening and solid solution strengthening are used as means for improving the 0.2% proof stress and heat resistance of Cu-based alloys. The precipitation strengthening can improve the 0.2% proof stress and the heat resistance of the Cu-based alloy without lowering the thermal conductivity, as compared with the solid solution strengthening. This is because the use of (Fe, Co, Ni) -P-based precipitates among such precipitation-strengthened Cu-based alloys is advantageous in terms of raw material cost and equipment in terms of manufacturing.

As described above, in order to utilize the (Fe, Co, Ni) -P based precipitate, at least one or more of Fe, Ni and Co and P are added in a total amount of 0.05 to 0.3 wt.
% Must be included. When it is less than 0.05 wt%, the amount of precipitates is small, and sufficient 0.2% proof stress and heat resistance cannot be obtained. When it is 0.3 wt% or more, the required thermal conductivity cannot be obtained. This is because. However, the thermal conductivity is 3
Within the range of 50 W / mK, Sn,
It is possible to add Ti, Be, Mg, Zr, Cr, Si, and it is expected that the addition of these will improve the strength and heat resistance, but this will lead to cost increase, so the total amount of these additional elements should be It should be 0.3 wt% or less.

[0021]

EXAMPLES Examples of the copper alloy for a heat spreader excellent in heat dissipation and heat resistance according to the present invention will be described in detail below.

[Examples 1 to 5 and Comparative Examples 1 to 4] Cu-based alloys for heat spreaders of various components shown in Table 1 were melted in a high frequency melting furnace to cast ingots of 40 × 40 × 150 (mm). did. After that, 40 × 40 × 30 (mm) test pieces were cut out, homogenized at 900 ° C. for 60 minutes, hot-rolled to a plate thickness of 8 mm, water-cooled and pickled. After that, cold rolling, annealing, cold rolling are repeated,
Cu having a plate thickness of 1.85 mm as the Cu-based alloy material of Example 1
A base alloy material was produced. Moreover, Cu or Cu-based alloy materials of Examples 2 to 5 and Comparative Examples 1 to 4 were produced by the same method.

[0023]

[Table 1]

Next, regarding the obtained Cu or Cu-based alloy materials of Examples 1 to 5 and Comparative Examples 1 to 4, thermal conductivity,
0.2% proof stress, work hardening index and crystal grain size were examined.
The results are shown in Table 2. The thermal conductivity was calculated from the electrical conductivity, and the electrical conductivity, 0.2% proof stress and work hardening index were measured according to JIS H 0505, JIS Z 22441 and JIS Z 2253, respectively. Also,
The crystal grain size was measured by an optical microscope after polishing the material surface with emery paper, buffing and etching. The manufacturing cost was evaluated by considering the raw material cost in the case of manufacturing with an actual machine and also considering the ratio of the cast manufacturing amount and the commercialized amount as a defective loss.

[0025]

[Table 2]

In Table 2, ∘ indicates that the manufacturing cost is low, and Δ indicates the cost of the additive element, the meandering of the surface condition and width of the strip, the lack of required material characteristics as a heat spreader, and the atmosphere control. The one that corresponds to any one of the use of heat treatment such as casting or aging treatment during the manufacturing method, and the one that corresponds to two or more.

[Examples 6 to 10 and Comparative Examples 5 to 8] The Cu-based alloy material of Example 1 was stamped out and cold-forged to produce the Cu-based alloy material of Examples 6 to 10, The quality of them was investigated. Similarly, Cu materials of Comparative Examples 5 and 6 and Comparative Examples 7 and 8 were produced from the Cu materials of Comparative Examples 1 and 2 which are currently general materials for heat spreaders, and their quality was investigated. The results are shown in Table 3. In addition, as shown in FIG. 1, the shape of the heat spreader 10 after cold forging is a shape of a cavity type heat spreader having a cavity 12 and having a large cross-sectional reduction rate,
The cross-section reduction rate was about 30%. Further, the press punching property was evaluated by the unevenness of the sagging portion and the amount of burr, and the cold forgeability was evaluated by the formability after the forging and the rough surface.

[0028]

[Table 3]

In the Cu-based alloy materials of Examples 6 to 10, since the crystal grain size was uniform and fine, both unevenness and burrs in the sagging portion were small due to press punching. Also, in the molding after cold forging, the balance between 0.2% proof stress and work hardening index was good, and the balance between forging pressure and molding precision was excellent. The Cu materials of Comparative Examples 5 and 6 are C of Examples 6 to 10.
Although the crystal grain size is larger than that of the u-based alloy material, both unevenness and burrs in the sagging portion are caused by press punching in Examples 6 to 6.
It was equivalent to the Cu-based alloy material of No. 10. However, 0.2%
The balance between yield strength and work hardening index was poor, and the precision of cold forging was poor. The Cu materials of Comparative Examples 7 and 8 were inferior to the Cu-based alloy materials of Examples 6 to 10 due to the severe unevenness of the sagging portion and the large amount of burrs due to press punching.

[Examples 11 to 14 and Comparative Examples 9 to 16] The Cu-based alloy material of Example 1 was used to produce the heat spreader of Examples 11 to 14 by cold forging, and the hardness and shape of the heat spreader by heat treatment. Was evaluated. Similarly, from the Cu materials of Comparative Examples 1 and 2, Comparative Examples 9, 11, 13, 15 and Comparative Examples 10, 12, 14, respectively.
Sixteen heat spreaders were produced and changes in the heat spreader due to heat treatment were evaluated. The shape of the heat spreader 10 after cold forging is the shape of a cavity heat spreader having a large cross-sectional reduction rate as shown in FIG.
The cross-section reduction rate was about 30%. Further, in the case of Example 11 and Comparative Examples 9 and 10, 250 ° C., in the case of Example 12 and Comparative Examples 11 and 12, 300 ° C., in the case of Example 13 and Comparative Examples 13 and 14, 550 ° C., and Example 14. In Comparative Examples 15 and 16, the crystal grain size and Vickers hardness were measured after annealing for 30 minutes at an annealing temperature of 600 ° C. The results are shown in Tables 4-7. Incidentally, the evaluation of the heat spreader after annealing, the crystal grain size and uniformity,
It was performed by the difference in Vickers hardness depending on the site, the decrease in Vickers hardness, and the deformation of the heat spreader. Moreover, the semi-softening temperature of the heat spreaders of Examples 11 to 14 made from the Cu-based alloy material of Example 1 was 550 to 600 ° C., and Comparative Example 9 made from the Cu materials of Comparative Examples 1 and 2.
11, 13, 15 and Comparative Examples 10, 12, 14, 16
The semi-softening temperature of the heat spreader was 250 to 300 ° C.

[0031]

[Table 4]

[0032]

[Table 5]

[0033]

[Table 6]

[0034]

[Table 7]

From the results of Tables 1-7, C of Examples 1-14
It can be seen that the u-based alloy material and the heat spreader have low manufacturing costs, excellent thermal conductivity, and sufficient mechanical strength. It is also found that the crystal grains before cold forging are uniform and fine. Further, it can be seen that even after the heat treatment after the cold forging, the crystal grains do not become non-uniform due to softening, are uniform and fine, and have sufficient strength as a heat spreader.
Further, in the Cu-based alloy materials of Examples 1 to 5, the heat treatment at the time of mounting the heat spreader is performed at 200 ° C. to 300 ° C., but since it does not soften in the heat treatment in that temperature range, it is necessary to perform annealing in advance before mounting. There is also no cost advantage. Therefore, the Cu-based alloy materials of the examples are excellent as Cu-based alloy materials used for heat spreaders and the like.

On the other hand, Cu materials of Comparative Examples 1 and 2 which are currently used as general materials for heat spreaders (Comparative Examples 9, 11, 13, 15 and Comparative Examples 10, 1).
The heat spreaders (2, 14, 16) have excellent thermal conductivity and are advantageous in terms of cost, but when heat-treated, the material is softened and the crystal grains are uneven and coarse to the extent that the degree of sizing cannot be measured. Therefore, the hardness is different depending on the part, there is a case where minute deformation is accompanied, and there is a possibility that the IC operation reliability is lowered, and it is inferior to the Cu-based alloy materials of Examples 1 to 5. Further, the Cu-based alloy material of Comparative Example 3 has excellent thermal conductivity, has a fine crystal grain size, and satisfies the material properties as a heat spreader, but since Zr is used, the raw material cost is low. Since the Zr-O-based oxide has a bad influence on the quality in the casting and hot rolling processes, it is also inferior in the manufacturing cost.

[0037]

As described above, according to the present invention, it is possible to provide a Cu-based alloy which is excellent in thermal conductivity, is highly reliable in joining with a semiconductor chip in an assembly process and can be manufactured at low cost. Therefore, it is possible to provide the Cu-based alloy as an optimal material for the heat spreader.

[Brief description of drawings]

FIG. 1 is a diagram showing a shape of a heat spreader manufactured in Examples and Comparative Examples, in which (a) is a plan view,
(B) is a sectional view.

[Explanation of symbols]

10 heat spreader 12 cavities

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C22F 1/00 623 C22F 1/00 630A 630 630C 630Z 650F 650 681 681 682 682 683 683 685 685Z 685 686A 686A 686 691C H01L 23/36 M (72) Inventor Kunihiko Chihara 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. F-term (reference) 5F036 BD01

Claims (6)

[Claims] 1. A 0.2% proof stress is 100 to 200 N / mm.
^{2. The} copper alloy for a heat spreader, which has a thermal conductivity of 350 W / m · K or more. 2. The copper alloy for a heat spreader according to claim 1, wherein the work hardening index is 0.14 to 0.18. 3. The grain size in the width direction of the rolled face sheet is 25 μm.
It is m or less, The copper alloy for heat spreaders of Claim 1 or 2 characterized by the above-mentioned. 4. The method according to claim 3, wherein at least one of Fe, Ni and Co and P are contained in a total amount of 0.05 to 0.3 wt%, and the balance is Cu and inevitable components. Copper alloy for the heat spreader described. 5. After cold forging with a reduction in area of 40% or less, 6
The copper alloy for a heat spreader according to claim 3, wherein the crystal grain size after heat treatment at 00 ° C. for 30 minutes is 25 μm or less. 6. After cold forging with a cross-section reduction rate of 40% or less, 6
Vickers hardness after heat treatment at 00 ℃ for 30 minutes is HV
It is 60-170, The copper alloy for heat spreaders of Claim 5 characterized by the above-mentioned.