JP5278011B2 - Semiconductor cooling structure and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cooling structure for a semiconductor that is improved in cooling efficiency with simple constitution, and to provide a method of manufacturing the cooling structure. <P>SOLUTION: The cooling structure 10 for the semiconductor has a heat sink 8 arranged on the semiconductor 2 mounted on a substrate 1. Further, a heat-conductive heat spreader 6 is fitted on an upper surface of the semiconductor 2 through a heat-conductive member 5. Furthermore, the heat sink 8 is fitted to an upper surface 6c of the heat spreader 6 through heat-conductive grease 7. Here, the heat spreader 6 comprises a plurality of plate-like members 6a, which preferably each have a lower surface inclined in conformity with the shape of the upper surface of the semiconductor 2. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a semiconductor cooling structure that dissipates heat generated by an electronic component such as a semiconductor mounted on a substrate and a manufacturing method thereof, and more particularly, to a semiconductor in which a heat sink is disposed on a semiconductor mounted on a substrate. The present invention relates to a cooling structure and a manufacturing method thereof.

  In recent years, with higher performance of computers, higher integration and higher speed of semiconductors such as LSI are progressing, and as a means to transmit LSI electrical signals in a large amount and at high speed, LSI is directly soldered to a printed circuit board, Many flip chip mountings are used. At the same time, the power consumption of an LSI is increasing, and a cooling structure that cools the LSI with high efficiency is always required.

  In general, as a mounting structure of an LSI, a structure in which a QFP (Quad Flatpack Package) or BGA (Ball Grid Array) incorporating a silicon chip is mounted on a printed board, or a structure in which the flip chip is mounted is known. In these structures, a heat sink is mounted on the heat generating LSI.

  By the way, in a structure in which an LSI is flip-chip mounted on a printed circuit board, a convex warp occurs on the back surface (upper surface) side of the LSI due to a difference in thermal expansion coefficient between the LSI and the printed circuit board. On the other hand, in the conventional cooling structure 100, a heat sink 18 having a flat lower surface is attached on the LSI 12 via a thermal conductive grease 17 (FIG. 6). Thereby, since the thickness of the end side D part of the heat conductive grease 17 becomes larger than the thickness of the center side C part, the thermal resistance of the end side D part becomes larger than the thermal resistance of the center side C part. . Therefore, there is a problem that it is difficult to efficiently transfer the heat generated in the LSI 12 to the heat sink 18.

JP 2006-237060 A

  To solve this problem, a structure in which a heat sink is bonded to the LSI using an adhesive having high thermal conductivity instead of the thermal conductive grease is conceivable. However, for example, as the LSI becomes larger, the warpage of the convex shape of the LSI also becomes larger, so that bonding becomes insufficient, and cooling efficiency may be reduced. A method of processing the heat sink into a concave shape in accordance with the warpage of the convex shape of the LSI is also conceivable, but since processing on the order of several tens of μm is required, the processing itself becomes difficult and may lead to an increase in cost. There is also. Furthermore, a heat sink mounting structure is known in which a heat sink placed on a semiconductor is deformed in a shape similar to an LSI shape (see, for example, Patent Document 1). In this mounting structure, it is necessary to process the heat sink.

  The present invention has been made to solve such problems, and a main object of the present invention is to provide a semiconductor cooling structure with improved cooling efficiency with a simple configuration and a method for manufacturing the same.

  One aspect of the present invention for achieving the above object is a semiconductor cooling structure in which a heat sink is disposed on a semiconductor mounted on a substrate, and heat is applied to the upper surface of the semiconductor via a heat conductive member. The semiconductor cooling structure is characterized in that a conductive heat spreader is attached, and the heat sink is attached to the upper surface of the heat spreader via heat conductive grease.

  On the other hand, according to one aspect of the present invention for achieving the above object, a first attachment step of attaching a semiconductor on a substrate, and a first application of applying a heat conductive member to the upper surface of the semiconductor after the first attachment step. A second attachment step of attaching a heat conductive heat spreader on the heat conductive member after the first application step, and a second application of applying heat conductive grease on the upper surface of the heat spreader after the second attachment step. And a third attachment step of attaching a heat sink on the thermally conductive grease after the second application step.

  ADVANTAGE OF THE INVENTION According to this invention, the cooling structure of the semiconductor which improved the cooling efficiency with simple structure, and its manufacturing method can be provided.

It is sectional drawing which shows the outline of the cooling structure of the semiconductor which concerns on one Embodiment of this invention. It is a perspective view showing a schematic structure of a heat spreader concerning one embodiment of the present invention. It is a perspective view showing a schematic structure of a plate-like member of a heat spreader concerning one embodiment of the present invention. It is a figure which shows an example of the state which arrange | positions the inclined surface of each plate-shaped member of a heat spreader along the convex curvature of LSI, and attaches it. It is a figure which shows an example in the state by which the upper surface of a heat spreader becomes substantially planar shape. It is sectional drawing which shows the outline of the cooling structure of the semiconductor which concerns on the past.

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a cross-sectional view schematically showing a semiconductor cooling structure according to an embodiment of the present invention. In the semiconductor cooling structure 10 according to the present embodiment, a flip chip mounting structure in which an LSI (semiconductor integrated circuit) 2 is directly bonded and mounted on a printed board 1 with solder 3 is applied. Further, the joint portion of the solder 3 is filled with an underfill (sealing resin) 4 and hardened and sealed. In the flip chip mounting structure, since the joining portion of the solder 3 is very fine, the underfill 4 is filled and cured to be reinforced, and the reliability of the joining is ensured.

  A heat spreader 6 having high thermal conductivity is attached to the upper surface of the LSI 2 via a heat conductive member 5. The heat conducting member 5 is, for example, a thermosetting heat conductive adhesive, and joins the upper surface of the LSI 2 and the lower surface of the heat spreader 6. Moreover, as the heat conductive member 5, for example, an epoxy-based heat conductive adhesive, a silicone-based adhesive, or a solder material can be used.

  In the case where the heat spreader 6 is bonded to the upper surface of the LSI 2 with the heat conductive adhesive, a treatment for roughening the bonding surface of the heat spreader 6 may be performed in order to improve the adhesion between the heat spreader 6 and the heat conductive adhesive. Good. Further, when the heat spreader 6 is joined to the upper surface of the LSI 2 by the solder 3, it is preferable to perform a surface treatment (for example, Au plating) on the adhesion surface of the LSI 2 and the heat spreader 6 so that the wettability of the solder 3 is good. Thereby, heat conduction efficiency can be improved more. Furthermore, it is preferable to use a material having high thermal conductivity as the material of the heat spreader 6, for example, a metal such as a material based on Cu or CuW, or a ceramic such as AIN (aluminum nitride). it can.

  A heat sink 8 is attached to the upper surface 6 c of the heat spreader 6 via a heat conductive grease 7. The heat conductive grease 7 assists heat conduction between the heat spreader 6 and the heat sink 8. Further, as the thermal conductive grease 7, for example, silicon grease mixed with alumina (aluminum oxide), copper powder, diamond powder, or the like is used, so that highly efficient thermal conduction is possible.

  The heat sink 8 includes, for example, a substantially rectangular base portion 8a and a plurality of rod-shaped fins 8b erected in a lattice shape on the base portion 8a, and highly efficient heat dissipation from each fin 8b. It can be carried out. The heat sink 8 is integrally formed of a material having excellent thermal conductivity such as aluminum or copper. In the semiconductor cooling structure 10 configured as described above, for example, heat generated in the LSI 2 is transmitted with high efficiency in the order of the heat conducting member 5, the heat spreader 6, the heat conducting grease 7, and the heat sink 8. The heat is radiated from each fin 8b.

  FIG. 2 is a perspective view illustrating a schematic configuration of the heat spreader according to the present embodiment. The heat spreader 6 according to the present embodiment is composed of, for example, four substantially square plate-like members 6a. The upper surface (side surface of the heat sink 8) 6c of each plate-like member 6a is formed in a substantially flat shape. Further, the lower surface (side surface of the LSI 2) of each plate-like member 6a is formed with an inclined surface 6b in which a dotted line portion is processed in accordance with the shape of the upper surface of the LSI 2 (FIG. 3). In FIG. 3, the lower surface (inclined surface 6b) of the plate-like member 6a is directed upward so that the inclined surface 6b of the plate-like member 6a can be easily seen.

  The G part (the end side of the heat spreader 6) of each plate-like member 6a is the thickest part, and the E part (the center side of the heat spreader 6) is the thinnest part. Further, the F part and the H part of each plate-like member 6a have substantially the same thickness, and are between the G part and the E part. In addition, each plate-shaped member 6a can be easily processed by forming E part, F part, G part, and H part on the same plane.

  Furthermore, the inclined surface 6b of each plate-like member 6a is preferably formed in accordance with the convex warp of the LSI 2. For example, as shown in FIG. 1, when the convex warp of the LSI 2 is 100 μm along the diagonal line of the LSI 2, the plate-like members 6a are arranged so that the thickness of the E portion is about 100 to 150 μm thinner than the thickness of the G portion. It may be processed.

  As shown in FIG. 2, each plate-like member 6a has a thin E portion on the center side of the heat spreader 6, and each plate-like member 6a has a thick G portion on the corner side (end side) of the heat spreader 6. The shaped member 6a is arranged. As a result, the inclined surface 6b of each plate-like member 6a of the heat spreader 6 is arranged and attached in a state along the convex warp of the LSI 2 (FIG. 4), so that the upper surface 6c of the heat spreader 6 is substantially planar. (FIG. 5). As a result, the heat conduction grease 7 having a substantially uniform thickness can be applied to the upper surface 6c of the substantially planar heat spreader 6, and the heat sink 8 is mounted on the heat conduction grease 7 having a substantially uniform thickness. be able to. Accordingly, since the thermal resistance of the thermal conductive grease 7 can be made substantially uniform from the center side to the end side, the heat generated in the LSI 2 is efficiently transmitted to the heat sink 8 via the thermal conductive grease 7. be able to.

  Next, the manufacturing method of the semiconductor cooling structure according to the present embodiment will be described in detail. For example, the LSI 2 is positioned and placed on the printed circuit board 1 so that the LSI mounting pad on the printed circuit board 1 and the solder 3 of the LSI 2 face each other. Then, the LSI 2 is heated to a temperature at which the solder 3 melts (for example, about 22 ° C. if Sn96.5 / Ag3 / Cu0.5 (wt%)) or higher, and the LSI 2 is soldered (first mounting step). Further, the underfill 4 is supplied and filled into the gap between the printed circuit board 1 and the LSI 2 from the side, and is heated and cured at the curing temperature (for example, 150 ° C.) of the resin.

  At this time, at the temperature (for example, about 150 ° C.) during the resin curing of the underfill 4, the printed circuit board 1 and the LSI 2 are substantially planar (a state in which no warpage occurs). Thereafter, when cooled to room temperature (for example, 25 ° C.) after the resin is cured, a bimetal phenomenon occurs in the printed circuit board 1 and the LSI 2. This bimetal phenomenon is a phenomenon that occurs because the thermal expansion coefficient of the printed circuit board 1 is larger than the thermal expansion coefficient of the LSI 2.

  Due to this bimetal phenomenon, the LSI 2 is warped in a convex shape toward the heat sink 8 side. Note that the warpage of the convex shape generated in the LSI 2 may be estimated based on the thermal expansion coefficients of the printed circuit board 1 and the LSI 2 and the external shape of the LSI 2. For example, the thermal expansion coefficient of LSI 2 is about 3 ppm, the thermal expansion coefficient of printed circuit board 1 (for example, FR4) is about 16 ppm, and if the outer shape of LSI 2 is about 20 mm square, LSI 2 has a convex shape of about 100 μm. Warpage occurs.

  Therefore, as shown in FIG. 3, the plate member 6a of the heat spreader 6 is processed so that the thin E portion of the plate member 6a is thinned by about 100 to 150 μm with respect to the thick G portion of the plate member 6a. . For example, when the thickness of the G portion of the plate-like member 6a is about 3 mm, the thickness of the E portion of the plate-like member 6a is about 2.9 to 2.85 mm, and the thickness of the F portion and the H portion is between Of about 2.95 to 2.92 mm.

  Next, the heat conductive member 5 is applied to the upper surface of the LSI 2 (first application step), and the thin E portion of the plate-like member 6a of the heat spreader 6 becomes the center side of the heat spreader 6 as shown in FIG. Each plate-like member 6 a is arranged so that the thick G portion of 6 a is on the corner side of the heat spreader 6. Then, each of the arranged plate-like members 6a is pressed against the heat conducting member 5 applied on the upper surface of the LSI 2 (second attachment step). Further, a temperature (for example, 150) at which the heat conducting member 5 is cured while pressing the vicinity of the portion A of the heat spreader 6 shown in FIG. C.) and cured.

  When the temperature of the heat conducting member 5 is returned to room temperature after the heat conducting member 5 is cured, a convex warp of about 100 μm is generated in the LSI 2, but the inclined surface 6 b of each plate-like member 6 a of the heat spreader 6 is previously formed in the convex shape of the LSI 2. Processed to warp (machining process). Therefore, the plate-like members 6a of the heat spreader 6 can be bonded in accordance with the convex warpage of the LSI 2 upper surface. Thereby, the upper surface 6c of the heat spreader 6 can be maintained substantially flat. Next, the thermal grease 7 is applied to the upper surface 6c of the heat spreader 6 with a substantially uniform thickness (second application process), and the heat sink 8 is pressed against the applied thermal grease 7 and fixed. Perform (third attachment step).

  Here, when the thickness of the heat conducting member 5 is 10 μm in the A portion, in the B portion, it is about 35 μm, which is obtained by adding 1/4 (25 μm) of the warp 100 μm of the LSI 2 to 10 μm of the A portion. In this case, when the average value of the thickness of the heat conducting member 5 is estimated, (20 + 45) / 2 = about 33 μm. Moreover, since the thickness of the heat conductive grease 7 becomes uniform, it can be set to about 20 μm, for example. As described above, the reason why the heat sink 8 is not directly bonded to the heat spreader 6 is, for example, that the heat sink 8 can be attached and detached.

  On the other hand, as shown in FIG. 6, in a conventional semiconductor cooling structure 100, a thermal conductive grease 17 is applied to the upper surface of the LSI 12, and a heat sink 18 having a flat lower surface is disposed on the applied thermal conductive grease 17. And press-fit. For example, when the warp of the LSI 12 is 100 μm, the thickness of the central portion C of the thermal conductive grease 17 is about 10 μm, but the thickness of the outer peripheral portion D of the thermal conductive grease 17 is about 110 μm. At this time, when the average value of the thickness of the thermal conductive grease 17 is estimated, (110 + 10) / 2 = about 60 μm.

  As described above, for example, the thickness (about 53 μm) obtained by adding the thickness (about 33 μm) of the heat conducting member 5 of the semiconductor cooling structure 10 according to the present embodiment and the thickness (about 20 μm) of the heat conducting grease 7. ) Can be reduced by about 12% compared to the thickness (about 60 μm) of the heat conductive grease 17 of the conventional semiconductor cooling structure 100.

  Thus, in the semiconductor cooling structure 10 according to the present embodiment, the thickness of the heat conducting member 5 and the heat conducting grease 7 can be made thinner than that of the conventional cooling structure 100. For this reason, the thermal resistance between the LSI 2 and the heat sink 8 can be reduced, and the heat generated in the LSI 2 can be transmitted to the heat sink 8 more efficiently. Therefore, the heat dissipation efficiency of the heat sink 8 is improved, and the cooling efficiency in the semiconductor cooling structure 10 can be improved. Furthermore, the cooling efficiency can be improved by simply forming the inclined surface 6 b of each plate-like member 6 a of the heat spreader 6 in accordance with the convex warp of the LSI 2. That is, according to the semiconductor cooling structure 10 according to the present embodiment, the cooling efficiency can be improved with a simple configuration.

  Further, the heat conductive member 5 having a heat transfer coefficient higher than that of the heat conductive grease 7 (better heat conductivity) may be arbitrarily selected. Thereby, the heat dissipation efficiency of the heat sink 8 can be further improved, and the cooling efficiency in the semiconductor cooling structure 10 can be further improved. Further, the heat spreader 6 may be enlarged by making the outer shape of the heat spreader 6 larger than the outer shape of the LSI 2 so that the outer shape of the heat spreader 6 protrudes from the outer shape of the LSI 2. Thereby, the heat dissipation efficiency of the cooling structure 10 can be further improved, and the cooling efficiency can be further improved. Furthermore, by improving the cooling efficiency of the semiconductor cooling structure 10 according to the present embodiment, for example, a higher-performance LSI 2 with higher power consumption can be adopted, or a semiconductor device equipped with the cooling structure 10 Can also contribute to downsizing.

  Although the best mode for carrying out the present invention has been described using the above-described one embodiment, the present invention is not limited to such one embodiment and is within the scope not departing from the gist of the present invention. Various modifications and substitutions can be added to the above-described embodiment.

  For example, in the above-described embodiment, the heat sink 8 has a configuration including the base portion 8a and the plurality of fins 8b. However, the configuration is not limited thereto, and any configuration can be applied. Further, in the above-described embodiment, the heat spreader is configured by the four substantially square plate-like members 6a. However, the heat spreader is not limited to this. For example, the heat spreader is configured by two plate-like members (such as when the LSI 2 is rectangular). And may be configured in any number and shape.

1 Printed circuit board 2 LSI
DESCRIPTION OF SYMBOLS 3 Solder 4 Underfill 5 Thermal conductive member 6 Heat spreader 6a Plate-shaped member 6b Inclined surface 6c Upper surface 7 Thermal conductive grease 8 Heat sink 10 Semiconductor cooling structure

Claims (10)

A semiconductor cooling structure in which a heat sink is disposed on a semiconductor mounted on a substrate,
A heat conductive heat spreader is attached to the upper surface of the semiconductor via a heat conductive member,
The heat sink is attached to the upper surface of the heat spreader via thermal grease ,
The heat spreader includes a plurality of plate-like members, and the lower surface of the plate-like member is inclined in accordance with the shape of the upper surface of the semiconductor. A semiconductor cooling structure according to claim 1 ,
The semiconductor cooling structure, wherein the inclined surface of the plate member of the heat spreader is formed in accordance with the convex warpage of the semiconductor. A semiconductor cooling structure according to claim 1 or 2 ,
The semiconductor cooling structure, wherein the thickness of the heat spreader on the center side is formed to be thinner than the thickness on the end side. A semiconductor cooling structure according to any one of claims 1 to 3 ,
An upper surface of the heat spreader is formed in a substantially planar shape. A semiconductor cooling structure according to any one of claims 1 to 4 ,
2. The semiconductor cooling structure according to claim 1, wherein the heat spreader includes four plate members. A semiconductor cooling structure according to any one of claims 1 to 5 ,
The semiconductor cooling structure according to claim 1, wherein a heat transfer coefficient of the heat conductive member is higher than a heat transfer coefficient of the heat conductive grease. A semiconductor cooling structure according to any one of claims 1 to 6 ,
A semiconductor cooling structure, wherein an outer shape of the heat spreader is formed larger than an outer shape of the semiconductor. A semiconductor cooling structure according to any one of claims 1 to 7 ,
The semiconductor cooling structure, wherein the semiconductor is bonded onto the substrate by solder, and the bonded portion is sealed by underfill. A first mounting step of mounting a semiconductor on a substrate;
After the first attachment step, a first application step of applying a heat conducting member to the upper surface of the semiconductor;
A second attachment step of attaching a heat conductive heat spreader on the heat conductive member after the first application step;
After the second mounting step, a second application step of applying a thermal grease on the upper surface of the heat spreader;
After the second coating step, seen including a third mounting step of mounting the heat sink to the heat conducting on grease,
The heat spreader is composed of a plurality of plate-like members,
The manufacturing method of the semiconductor cooling structure characterized by further including the process process which inclines the lower surface of the said plate-shaped member according to the shape of the upper surface of the said semiconductor . A method for manufacturing a semiconductor cooling structure according to claim 9 ,
In the processing step, the inclined surface of the plate member of the heat spreader is processed in accordance with the convex warpage of the semiconductor.

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