JPH116002A - Production of thin plate-like sintered body and heat spreader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep a plane precision high by restraining a strain quantity in a produced product, at the time of producing a thin plate formed product, such as a heat spreader constituting a semiconductor. SOLUTION: At the time of obtaining the heat spreader by recompacting a sintered body 1B after sintering a thin plate-like compact body 1b having a thick thickness part 4b and a thin thickness part 5b, the density difference of the thin thickness part 5b to the thick thickness part 4b after recompacting the sintered body 16 is adjusted to within the range of ±1.5% and further, a true density ratio after recompacting the sintered body 1B is adjusted to within the range of 95-99% by adjusting the compacting densities and different size of step between both of the thick thickness part 4b and the thin thickness part 5b at the step of forming the compact body. The plane precision is improved by satisfying these conditions, and since this product is the sintered body, the deformation caused by the inner strain is restrained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of obtaining a thin plate-like sintered body by sintering a thin plate-like compact having a thin portion and a thick portion, and for example, is mounted in an IC package. The present invention relates to a manufacturing method suitable for manufacturing a heat spreader (radiator plate) and the like, and further relates to a heat spreader having a small amount of distortion.

[0002]

2. Description of the Related Art In recent years, semiconductors are required to be sophisticated and diversified.
In the C package, high functionality such as miniaturization, increase in capacity, reduction in thickness, increase in the number of pins, etc. has been remarkably progressing. With such advanced functions, the heat generation of the IC package also tends to increase steadily.
The number of IC packages loaded with a heat spreader for heat dissipation is increasing.

This heat spreader is a heat radiating plate, for example, a square thin plate having a side of 25 to 45 mm and a thickness of about 0.5 to 1.0 mm.
Is generally formed with a concave portion for incorporating the same. Conventionally, such a heat spreader is
A metal plate made of copper, aluminum, or the like having high thermal conductivity, that is, heat radiation, is formed by punching, drawing, rolling, or other plastic working.

[0004]

When a heat spreader is manufactured by performing plastic working in this way, distortion during plastic working is inevitably left as residual stress in a product. If the residual stress remains, the residual stress is released by heat generation when a circuit is manufactured by solder bonding or the like on the substrate on which the heat spreader is mounted, so that the heat spreader is warped or bent. Such deformation reduces the planar accuracy of the substrate mounting surface, deteriorating the degree of adhesion with the substrate, and as a whole IC package,
Various inconveniences such as tearing of the connection wire, peeling of the IC chip, and defective formation of the solder ball are caused.

In order to avoid such a problem, a method has been proposed in which a thin plate having a hole formed by punching is attached to the center of a heat spreader with an adhesive to manufacture the heat spreader.
However, in this manufacturing method, since there are two members, problems such as an increase in the number of steps, separation during heating due to a difference in thermal expansion between the adhesive and the plate material, or insufficient rigidity due to sticking of a thin plate have occurred. Was. Therefore, the present invention provides a method of manufacturing a thin plate-like sintered body capable of holding a thin plate-shaped product such as a heat spreader with a small amount of distortion and high planar accuracy, and provides a heat spreader with a small amount of distortion. It is intended to be.

[0006]

SUMMARY OF THE INVENTION According to a method of manufacturing a thin plate-like sintered body of the present invention, after a thin plate-like compact having a thin portion and a thick portion is sintered, the sintered body is pressed again. In obtaining a thin plate-like sintered body, the density difference between the thin part and the thick part after the re-pressing of the sintered body is set within a range of ± 1.5%, and the true value of the sintered body after the re-pressing is obtained. It is characterized in that the density ratio is in the range of 95 to 99%.

According to the study of the present inventor, it has been found that in order to use the thin plate-shaped sintered body as a heat spreader, it is necessary that the flatness is less than 0.05 mm before being mounted on a semiconductor. . Therefore, as a result of repeated studies to obtain such a thin plate-shaped sintered body, the flatness and the density difference between the thin portion and the thick portion after sintering and re-pressing and the true density ratio were compared. Was found. That is, the density difference between the thin portion and the thick portion expresses the difference between the powder density and the pressure (working degree) at the time of recompression. The degree improves. According to the experiment of the present inventor, in order to reduce the flatness after re-pressing to less than 0.05, sintering is performed by adjusting the pressure distribution at the stage of compacting or at the time of re-pressing. It was found that the density difference between the thin portion and the thick portion after re-pressing had to be within ± 1.5%.

[0008] The true density ratio after re-pressing also expresses the powder density and the pressure at the time of re-pressing. To 8
It must be 7% or more, and must be 93% or less in order to prevent galling of the molding die. When re-compressing a sintered body obtained by sintering a green compact having such a density ratio, when the true density ratio after re-pressing is small, dimensional correction is insufficient and flatness is reduced, and On the other hand, when the true density ratio after re-pressing is large, the flatness is reduced due to large springback. According to the experiment of the present inventor, in order to reduce the flatness after re-pressing to less than 0.05, sintering and re-pressing are performed by adjusting the pressure at the stage of compacting or at the time of re-pressing. It has been found that the true density ratio after the process needs to be in the range of 95 to 99%. In the thin plate-like sintered body obtained by satisfying these conditions, the planar accuracy is remarkably improved, and the amount of distortion remaining inside is reduced due to the fact that the sintered body is formed by sintering. It has been found that the deformation due to the influence of the above is greatly suppressed, and the heat spreader can be sufficiently used.

In the above-mentioned manufacturing method, if a rib is formed on at least one surface of the green compact and the rib is left after the re-pressing step, the rigidity is improved and distortion remains after the re-pressing. This is preferable because the deformation is suppressed.

Further, when the thin plate-like sintered body is made to have a substantially rectangular shape, after re-pressing, in some cases, the sides of the sintered body tend to bulge outward, so that the shape accuracy may be reduced. . For this reason, in the above-mentioned method, when the green compact is formed, a concave portion that curves inward is formed on the side of the green compact. In this case, after re-pressing, the concave portion swells and each side becomes linear,
Shape accuracy is improved and residual stress is suppressed. Furthermore, when incorporating a heat spreader into a semiconductor and molding it with resin, gas is generated from the periphery of the semiconductor due to the heat of the resin, but when re-pressing, if a hole that penetrates in the thickness direction of the sintered body is formed, It is preferable that the gas vent hole can be formed without performing machining.

Further, the heat spreader of the present invention has a thin portion and a thick portion obtained by repressing the sintered body, and has a density difference between the thin portion and the thick portion after repressing the sintered body. Is ± 1.5
%, And the true density ratio of the sintered body after re-pressing is within the range of 95 to 99%.
In such a heat spreader, since the amount of distortion due to a rise in temperature is reduced, there is no problem even after a semiconductor chip producing process that generates heat.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to the above-described method for manufacturing a heat spreader will be described below with reference to the drawings. In FIGS. 1A and 1B, reference numeral 1 denotes a heat spreader to be manufactured.
This heat spreader 1 is a square thin plate-like sintered body. The dimensions are as follows: one side L: 20 to 45 mm, thickness T:
0.3 to 1.0 mm, and has a square recess 2 for incorporating an IC in the center of one side thereof. The dimensions of the recess 2 are 1:10 to 25 mm on a side 1 and a thickness t: 0. 2-0.6
mm. That is, the recess 2 has a thin portion 5 and a thick portion 4 around the thin portion 5. Thick part 4 to thin part 5
Is a slope, and the angle θ is about 30 °. Further, gas vent holes 6 having a diameter of about 0.8 mm are formed at the four corners of the recess 2. The gas vent hole 6 is for releasing gas generated by heat of the resin to the outside when the semiconductor in which the heat spreader 1 is incorporated is molded with the resin. First, a first step of manufacturing a green compact as a material in manufacturing the heat spreader 1 will be described.

(1) First step: molding of green compact Al-Mg-Si alloy powder or Cu powder is used as a raw material powder, and a green compact 1A shown in FIGS. 2 (a) and 2 (b) is used.
Is molded. The green compact 1A has a shape and dimensions substantially similar to those of the heat spreader 1, and a recess 2a corresponding to the recess 2 and a thick portion 4a and a thin portion 5a are formed in the center of one surface. To this end, as shown in FIG. 3, the raw material powder filled inside the die 10 is
Outer lower punch 12a and inner lower punch 12b
And molded. The outer and inner lower punches 12a, 12b of this molding die are for forming the thick portion 4a and the thin portion 5a, respectively. The thick portion 4a is the outer lower punch 12a, and the thin portion is the inner lower punch 12a.
b. Therefore, the powder density of the thick portion 4a and the thin portion 5a and the step size between them are adjusted by the protrusion amounts of the outer and inner lower punches 12a and 12b. As compression conditions, for example, 10 to 70
Mpa is appropriate.

The density of the green compact 1A is 87 to 93%.
Is appropriate. As described above, if the content is less than 87%, there is a possibility that the shape may be lost at the time of handling such as taking out and moving the green compact 1A, and if it exceeds 93%, it is inappropriate. This is because, at the time of compression molding, there is a possibility that the molding die may be seized due to overload.

(2) Second Step: Sintering of Green Compact The green compact 1A formed by the above-mentioned molding die is sintered in a sintering furnace (not shown) under predetermined conditions. Sign 1
A sintered body indicated by B is obtained. The sintered body 1B has a shape and dimensions substantially similar to those of the heat spreader 1, and a concave portion 2b corresponding to the concave portion 2 and a thick portion 4b and a thin portion 5
b remain. The sintering temperature under the sintering conditions is, for example, 500 to 600 ° C. in a non-oxidizing atmosphere for Al—Mg—Si alloy powder, and 80 in a reducing atmosphere for Cu powder.
About 0 to 1000 ° C. is appropriate.

(3) Third Step: Recompression of the Sintered Body The sintered body 1B obtained in the second step is compressed again to form a final product, ie, sizing (dimension correction). For this purpose, a re-pressing die as shown in FIG. 4 is used. The re-pressing die is provided with a die 20 which can be moved in the vertical direction.
The upper punch 21 and the lower punch 22 are respectively disposed above and below. The upper punch 21 is a press ram L
Is slidably supported in the up and down direction via a spring 23 by a guide 24 fixed to the guide 24, and the whole ascends and descends together with the ram L. A lower surface which is a compression surface of the upper punch 21 is flat, and a punch 25 for forming the gas vent hole 6 is slidably inserted in the upper punch 21 in a vertical direction. The upper end of the punch 25 is in contact with the ram L. Next, the lower punch 22
It is fixed to the bed B of the press, and on the upper surface, which is the compression surface, is formed a convex portion 22a which protrudes thinly corresponding to the concave portion 2 of the heat spreader 1 to be manufactured. A punching die 22b through which the punching punch 25 is inserted is formed in the lower punch 22.

To repress the sintered body 1B, first, FIG.
As shown in (a), the green compact 1A is set in a cavity formed by the die 20 and the lower punch 22 so that the concave portion 2b is aligned with the convex portion 22a. Next, the ram L is lowered, and as shown in FIG.
Then, the sintered body 1B is pressed down by four. Then, the ram L is further lowered to form the gas vent hole 6 by penetrating the punch 25 into the sintered body 1B, and press the upper end surface of the upper punch 21 with the ram L to perform re-pressing (FIG. 4
(C)). The pressure of this re-pressing is that the raw material powder is
About 30 to 50 Mpa is suitable for Si alloy powder, and about 30 to 70 Mpa is appropriate for Cu powder. Then
By moving the ram L upward and the die 20 downward, the sintered body 1B mounted on the upper surface of the lower punch 22
To obtain a heat spreader 1 shown in FIG. 1 as a final product.

In the re-pressing step, the thin portion 5b
5 has a thickness that makes it difficult to open the gas vent hole 6, FIG.
As shown in (1), it is preferable to form the depression 30 in advance at the perforation position during the molding of the green compact 1A because the punch 25 can be easily penetrated. Further, after re-pressing, in some cases, each side of the sintered body 1B tends to bulge outward, and the shape accuracy may be reduced. To avoid this,
When the green compact 1A is formed, a concave portion 32 that curves inward is formed in the center of each side portion 31 in advance as shown in FIG. When the pressure is repressed, the concave portion 32 bulges, and each side portion 31 becomes linear, improving the shape accuracy and reducing the residual stress.

Here, in this embodiment, the thick portion 4 and the thin portion 5 of the heat spreader 1 obtained by re-pressing are used.
And the true density ratio of the whole is within a range of 95 to 99%, and by satisfying these conditions, the flatness of the heat spreader 1 is reduced. Secured. The true density ratio here refers to the ratio of pores remaining in the heat spreader 1 after re-pressing, and the smaller the number of pores, the higher the true density ratio. Therefore, in order to satisfy such conditions after the re-compaction, the compact 1
When forming A, the density ratio between the thick portion 4a and the thin portion 5a is adjusted in advance by the vertical position of the outer and inner lower punches 12a, 12b, and the compression allowance of the green compact 1A is adjusted by the upper punch 11. It is necessary to adjust in advance depending on the position of the bottom dead center.

In order to verify the flatness based on the above conditions, the amount of protrusion of the inner lower punch 12b and the position of the lower dead center of the upper punch 11 shown in FIG. By adjusting, a plurality of types of samples were manufactured in which the densities of the thick portion 4a and the thin portion 5a in the green compact 1A were changed. The following Tables 1 and 2 show the density difference between the thin portion 5a and the thick portion 4a after the re-pressing, and the relationship between the true density ratio of the entire heat spreader 1 and the flatness.
FIG. 7 shows a diagram of these.

[0021]

[Table 1]

[0022]

[Table 2]

As shown in FIG. 7, in order to ensure less than 0.05 mm required as a high-precision flatness, the density difference between the thick portion 4 and the thin portion 5 after re-pressing is ± 1.
5%, and the overall true density ratio is 95%.
It must be in the range of ~ 99%. That is,
After the recompression, the density difference of the thin portion 5 with respect to the thick portion 4 is ±
Within 1.5% and the overall true density ratio is 95-9.
By setting it within the range of 9%, the flatness is 0.05 mm.
And a high plane accuracy can be obtained.

In addition to securing such high plane accuracy, since it is manufactured by sintering, the stress remaining inside is reduced as compared with the conventional method of manufacturing by plastic working. Therefore, even if heat is generated when a circuit is manufactured by solder bonding or the like on a substrate on which the heat spreader 1 is mounted in manufacturing an IC package, or heat is generated when the heat spreader 1 is operated as a semiconductor, the heat spreader 1 is deformed due to release of residual stress. Is unlikely to occur. Therefore, the above-described high planar accuracy is maintained and the degree of adhesion to the substrate is maintained for a long period of time. When incorporated as a semiconductor, the performance of the semiconductor is maintained at a high level.

FIGS. 8A to 8H show the heat spreader 1 in which the ribs 3 are formed on the flat surface of the heat spreader 1 where the recess 2 is not formed. By forming such ribs 3 in advance during powder compaction and leaving them after re-pressing, rigidity is improved, and deformation is suppressed even if distortion remains after re-pressing.

The various shapes of the ribs 3 will be described in detail. (A) is a cross-shaped star having a triangular cross-section extending from the central peak to each corner and extending downward with a radiating portion 40, and (b) is a cross-shaped star. (A)
, The height of the radiating part 41 is almost constant,
(C) is a modification of (b) in which the radiation section 42 is orthogonal to each side. (D) is a square-shaped peak 4 at the center.
In this embodiment, a radiating portion 44 having a triangular cross section and a short slope is extended from 3 toward each corner. Further, (e) is formed in a circular shape around the center, and (f) is a deformation of (e) in which the radiating portion 46 of the inclined surface extends downward from the circular rib portion 45 toward each corner. It is a form. Further, (g) is formed parallel to each other across the center of the surface across a pair of parallel sides, and (h) is in a cross-girder form.

In the above embodiment, the lower punch for powder molding is replaced with the outer and inner lower punches 12a and 12a.
The lower punch is used for mass production. The density ratio can also be set by providing a pressure difference of re-pressure between the thin portion and the thick portion. Further, the present invention can be applied to the production of various thin plate-shaped sintered bodies other than the above heat spreader, and is particularly required as a method for producing a product that requires high planar accuracy or suppresses deformation. is there.

[0028]

As described above, in the method for producing a thin plate-like sintered body according to the present invention, the density difference between the thin portion and the thick portion after the re-pressing is set within a range of ± 1.5%, and Since the true density ratio after the re-pressing is in the range of 95 to 99%, there is an effect that the planar accuracy is remarkably improved, and the amount of internal strain is reduced and deformation is largely suppressed. 1).
In addition, a rib is formed on at least one surface of the green compact, and the rib is left after the re-pressing step, so that the rigidity is improved and deformation is suppressed even if distortion remains after the re-pressing. (Claim 2). Further, when the thin plate-shaped sintered body is formed in a substantially rectangular shape, a concave portion that curves inward is formed in a side portion of the green compact when the green compact is formed, so that the concave portion expands after re-pressing. As a result, each side becomes linear, thereby improving the shape accuracy and suppressing the residual stress (claim 3).

[Brief description of the drawings]

FIG. 1A is a plan view and FIG. 1B is a cross-sectional view of a heat spreader that is a thin plate-shaped sintered body to be manufactured by a method according to an embodiment of the present invention.

FIG. 2A is a plan view and FIG. 2B is a cross-sectional view of a green compact manufactured in a first step of the method according to the embodiment of the present invention.

FIG. 3 is a cross-sectional view showing a state in which the green compact is compacted in the first step.

FIG. 4 shows the order of repressing the sintered body in the third step of the method according to one embodiment of the present invention, (a) a cross-sectional view in a set state, (b) a cross-sectional view in an initial pressurized state, and (c). It is sectional drawing of a state after a pressurization.

FIG. 5 is a sectional view showing a method of easily forming a gas vent hole in a sintered body.

FIG. 6 is a plan view showing another form of the green compact.

FIG. 7 is a diagram showing a relationship between a flatness and a density difference and a true density ratio of a thin portion to a thick portion in a sintered body after re-pressing.

FIGS. 8A to 8H are perspective views showing various forms of ribs formed on the heat spreader.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Heat spreader (thin-plate sintered body), 1A ... Green compact, 1B ... Sintered body, 3 ... Rib, 4 ... Thick part, 5 ... Thin part, 31 ... Side part, 32 ... Convex part.

Claims (5)

[Claims] 1. After sintering a thin plate-shaped compact having a thin portion and a thick portion, re-pressing the sintered body to obtain a thin plate-shaped sintered body The difference between the density of the thin portion and the thickness of the thick portion afterward is set within a range of ± 1.5%, and the true density ratio of the sintered body after re-pressing is set within a range of 95 to 99%. A method for producing a thin plate-shaped sintered body. 2. The thin plate-shaped sintered body according to claim 1, wherein a rib is formed on at least one surface of the green compact, and the rib is left after the re-pressing step. Production method. 3. The compact as set forth in claim 3, wherein the thin plate-shaped sintered body has a substantially rectangular shape, and when the compact is formed, a concave portion that curves inward is formed in a side portion of the compact. Item 3. The method for producing a thin plate-shaped sintered body according to Item 1 or 2. 4. The method according to claim 1, wherein a hole penetrating in the thickness direction of the sintered body is formed during the re-pressing.
The method for producing a thin plate-shaped sintered body according to any one of the above. 5. A heat spreader having a thin portion and a thick portion obtained by repressing a sintered body, wherein a density difference between the thin portion and the thick portion after repressing the sintered body. Is ±
A heat spreader characterized by being within a range of 1.5% and a true density ratio after re-pressing of the sintered body is within a range of 95 to 99%.