JP5120304B2 - Printed wiring board with stiffener and method for manufacturing semiconductor package with heat sink - Google Patents

Description

  The present invention relates to a printed wiring board with a stiffener and a method for manufacturing a semiconductor package with a heat sink.

  In order to improve the rigidity of semiconductor package substrates and memory module substrates, which are one of the fields of application of printed wiring boards, materials called stiffeners are bonded to the printed wiring board and integrated or printed. In some cases, a heat sink is attached to a semiconductor package in which a semiconductor chip is mounted on a wiring board in order to improve heat dissipation.

  The stiffener is often made of a metal material such as a copper alloy or an aluminum alloy.

  Further, the stiffener has a high need in terms of improving rigidity, particularly in a so-called tape-based printed wiring board, among printed wiring boards.

  As a material for a tape-based printed wiring board, a polyimide system or the like is often used, but since the thickness is thin, it is usually more flexible than a glass epoxy board used for a printed wiring board, It is easy to bend. For this reason, it is sometimes called a flexible substrate.

  Further, in relation to the mounting method of the semiconductor package on the mother board, a semiconductor package substrate using the tape-based printed wiring board is a T-BGA (Tape Ball Grid Array) substrate or a T-LGA (Tape Land Grid). Array) substrate or the like.

  The printed wiring board is used as a generic term for the semiconductor package substrate, the mother board, the module substrate, and the like.

  One of the important roles of the semiconductor package substrate is to bridge the difference in thermal expansion coefficient between the semiconductor chip and the motherboard on which the semiconductor package is mounted, and to improve the connection reliability of mounting as a system. Due to such a role, the semiconductor package substrate is sometimes called an interposer or an interposer substrate.

  A semiconductor package on which a semiconductor chip is mounted is mounted on a motherboard and actually operates. However, in recent years, as the number of pins of high-speed compatible semiconductor packages has increased, it has become a major problem when driving semiconductor chips. This is a problem of heat generation, and a heat sink has been adopted to deal with it.

  The stiffener plays a role for improving the connection reliability of the semiconductor chip mounting, and the heat sink plays a role of improving the heat dissipation and correcting the warp of the semiconductor package to improve the mounting property to the mother board.

  In order to solve the problem of the connection failure, for example, a method is proposed in which four sides of a printed wiring board are bent to cope with external stress without using a stiffener (Patent Document 1). However, this method has a problem that foreign matter is generated from the bent portion, and delamination is likely to occur in the case of a multilayer printed wiring board.

  For this reason, stiffeners may be attached and integrated in order to reduce the amount of warping by giving rigidity to the printed wiring board. However, since the thermal expansion coefficient of the printed wiring board and the thermal expansion coefficient of the stiffener are usually different, warping occurs after a thermal process when integrating the stiffener and the printed wiring board, and therefore in semiconductor chip mounting, In terms of connection reliability, when a conventional stiffener is integrated with a printed wiring board, the flatness may not always be at a sufficient level.

  In addition, since the thermal expansion coefficient of the printed wiring board and the thermal expansion coefficient of the semiconductor chip are usually different, warping occurs when mounting the semiconductor chip, and therefore, in mounting on the motherboard, in terms of connection reliability, In some cases, the flatness is not always at a sufficient level.

Japanese Patent Application No. 7-253629

  The present invention has been made under the above circumstances, and a method of manufacturing a printed wiring board with a stiffener that reduces warping after integrating the stiffener and the printed wiring board, and a method of integrating the heat sink and the semiconductor package. It is an object of the present invention to provide a method for manufacturing a semiconductor package with a heat sink that warps less.

  The present invention solves such a problem, and the invention according to claim 1 for solving the above-mentioned problem is a method for manufacturing a printed wiring board with a stiffener, and is prior to being integrated with the printed wiring board. If the stiffener has a warped shape and the coefficient of thermal expansion of the stiffener is smaller than the coefficient of thermal expansion of the printed wiring board, the surface of the stiffener warped in a mountain and the printed wiring board are attached. In addition, when the thermal expansion coefficient of the stiffener is larger than the thermal expansion coefficient of the printed wiring board, the surface where the warp direction of the stiffener warps and the printed wiring board are bonded together, and further heated and integrated. A method of manufacturing a printed wiring board with a stiffener.

  The invention according to claim 2 is the method for producing a printed wiring board with a stiffener according to claim 1, wherein the shape of the stiffener before being integrated with the printed wiring board is a dome shape. .

  The invention according to claim 3 is characterized in that the shape of the stiffener before being integrated with the printed wiring board has a hollow portion, and the virtual plane of the stiffener including the hollow portion is a dome shape. It is a manufacturing method of the printed wiring board with a stiffener of Claim 1.

  The invention according to claim 4 is characterized in that the stiffener and the printed wiring board are bonded to each other via a material that exhibits adhesiveness by heating. It is a manufacturing method of the printed wiring board with a stiffener of description.

  The invention according to claim 5 is the method for producing a printed wiring board with a stiffener according to any one of claims 1 to 4, wherein the material of the stiffener is a metal.

  The invention according to claim 6 is the method for manufacturing a printed wiring board with stiffener according to any one of claims 1 to 5, wherein the printed wiring board with stiffener is for a semiconductor package. .

  The invention according to claim 7 is a method of manufacturing a semiconductor package with a heat sink, wherein the heat sink before being integrated with the semiconductor package has a warped shape, and the warping direction of the heat sink becomes a mountain. A method of manufacturing a semiconductor package with a heat sink, wherein a surface and the semiconductor package are bonded together.

  The invention according to claim 8 is the method for manufacturing a semiconductor package with a heat sink according to claim 7, wherein the shape of the heat sink before being integrated with the semiconductor package is a dome shape. .

  According to the present invention, in the method for manufacturing a printed wiring board with a stiffener, before the stiffener and the printed wiring board are integrated, the stiffener is preliminarily opposed to the warp caused by the difference in thermal expansion coefficient between the stiffener and the printed wiring board. By providing the warp in the direction, it is possible to provide a method for manufacturing a printed wiring board with a stiffener so that, after the stiffener and the printed wiring board are integrated, the warpage is less than before the integration.

  In addition, in the method of manufacturing a semiconductor package with a heat sink, before the heat sink and the semiconductor package are integrated, the heat sink is warped in advance in the direction opposite to the warpage of the semiconductor package. It is possible to provide a method for manufacturing a semiconductor package with a heat sink, in which warpage is less than that before integration after the plate and the semiconductor package are integrated.

It is the model figure which looked at the printed wiring board which affixed the stiffener from the top. It is a figure which shows the behavior of the curvature at the time of sticking a flat stiffener on a printed wiring board. (A) It is the figure which bonded the stiffener and the printed wiring board before the heating for hardening. (B) It is the figure after integrating a stiffener and a printed wiring board when it returns to normal temperature after heating and hardening. It is the affixing figure of the stiffener to the printed wiring board in a present Example. It is a conceptual diagram of the semiconductor package which affixed the heat sink. It is a figure which shows the behavior of the curvature at the time of mounting a semiconductor chip on the printed wiring board with a stiffener. (A) It is the figure which mounted the semiconductor chip on the printed wiring board with a stiffener. (B) It is a figure when it returns to normal temperature after reflow and mounting. It is a figure before bonding a heat sink and a semiconductor package in a present Example.

  Although the manufacturing method of the printed wiring board with a stiffener by this invention is demonstrated based on the one embodiment below, this invention is not necessarily limited to this.

  FIG. 1 is a conceptual view of a printed wiring board with a stiffener 1 attached as seen from above. The stiffener 1 has a frame shape with a cutout at the center so that the area where the solder bumps 2 are arranged at the center of the printed wiring board 3 is exposed.

  As the printed wiring board, a multilayer printed wiring board in which six wiring layers were formed using polyimide as an insulating layer and copper as a wiring layer was prepared. The total thickness of the printed wiring board was 220 μm, and the thermal expansion coefficient was 20 ppm. The size is 40 mm square.

  The surface of the printed wiring board was covered with a solder resist, and the solder resist was provided with openings at portions where solder bumps for mounting semiconductor chips were formed. Solder bumps were formed in the openings of the solder resist by a solder printing method. The solder bump is for mounting a semiconductor bare chip.

  As the stiffener, a copper material having a thickness of 700 μm was prepared, and nickel was plated on both surfaces by electrolytic nickel plating. The size is 40 mm square, and the opening at the center is 26 mm square.

  In order to integrate the stiffener and the printed wiring board, a stiffener was attached to the printed wiring board using a thermosetting adhesive. Thereafter, heating for curing the adhesive was performed at 150 ° C. for 2 hours.

  FIG. 2 is a diagram showing the behavior of warpage after integration when a flat stiffener is attached to a printed wiring board.

  FIG. 2 (a) is a view immediately after the printed wiring board 4 and the planar stiffener 1 are pasted through the adhesive 3 at room temperature, and there was no warping in this state before heating.

  FIG. 2B is a schematic view of the adhesive 3 after heat curing. The thermal expansion coefficient of the printed wiring board 4 is 20 ppm, which is larger than the thermal expansion coefficient of the stiffener 1 of 17 ppm. When the flatness was measured at room temperature after heating, the flatness was finally -50 μm.

  Here, the flatness was measured by placing the stiffener and the printed wiring board on a flat surface with the printed wiring board facing down. When the printed wiring board side is a mountain side, the height of the apexes of the four corners of the printed wiring board is indicated as plus (+) flatness. In addition, when the printed wiring board side is a valley side, the height from the plane at the intersection of the diagonal lines of the corners of the printed wiring board, that is, the four corners, is shown as minus (−) flatness.

  As a measuring method, using a laser length measuring instrument, in each case, a printed wiring board with a stiffener, which is the object to be measured, is placed on a flat surface, and a hole is formed in the flat portion corresponding to the measuring portion of the printed wiring board with a stiffener. The distance was calculated by irradiating a laser from below.

  The mechanism of the cause of obtaining the warping result after heating as described above is considered as follows. When the temperature is raised, the adhesive 3 has fluidity, so that the expansion difference due to the difference in thermal expansion coefficient between the stiffener 1 and the printed wiring board 4 is reduced. Accordingly, the adhesive 3 is cured at a certain point, and the stiffener 1 and the printed wiring board 4 are fixed. Next, the temperature is lowered. In this case, since the thermal expansion coefficient of the printed wiring board 4 is larger than the thermal expansion coefficient of the stiffener 1, the printed wiring board 4 is contracted at a high rate, and the printed wiring board 4 side is pulled in the contracting direction. Work. For this reason, it is considered that the printed wiring board side is warped in the shrinking direction from the initial state where there is no warping, and such a result is obtained.

  An embodiment of the present invention will be described below, but the present invention is not limited to this.

  As the printed wiring board, a multilayer printed wiring board in which six wiring layers were formed using polyimide as an insulating layer and copper as a wiring layer was prepared. The total thickness of the printed wiring board was 220 μm, and the thermal expansion coefficient was 20 ppm.

  The surface of the printed wiring board was covered with a solder resist, and the solder resist was provided with an opening in a portion where a solder bump for mounting a bare chip was formed. Solder bumps were formed in the openings of the solder resist by a solder printing method. The solder bump is for mounting a semiconductor bare chip.

  As the stiffener, a copper material having a thickness of 700 μm was prepared, and nickel was plated on both surfaces by electrolytic nickel plating.

  The stiffener was bent into a dome shape with a flatness of 50 μm to obtain a sample of this example.

  In order to integrate the stiffener and the printed wiring board, a stiffener was attached to the printed wiring board using a thermosetting adhesive. Thereafter, heating for curing the adhesive was performed at 150 ° C. for 2 hours.

  FIG. 3 is a diagram in which the stiffener and the printed wiring board in this embodiment are attached and integrated. It is the figure which affixed the printed wiring board 4 and the stiffener 1 via the adhesive agent 3, and the mountain side of the curvature direction of the stiffener 1 is affixed. Before the adhesive 3 is cured, the printed wiring board 4 is also warped by the amount of warpage of the stiffener 1. Heating for curing was performed, and the temperature was returned to room temperature.

  As a result, the printed wiring board 4 was further contracted due to the difference in thermal expansion coefficient between the printed wiring board 4 and the stiffener 1, and the amount of warping was finally reduced. At the time of temperature rise, the adhesive 3 has fluidity, and therefore, the adhesive 3 remains almost warped at first, but at a certain point, the adhesive 3 is cured and the stiffener 1 and the print are printed. The wiring board 4 is fixed. Next, in the case of a temperature drop, since the thermal expansion coefficient of the printed wiring board 4 is larger than the thermal expansion coefficient of the stiffener 1, the rate of contraction is higher, and a pulling force acts in the direction opposite to the warp. Therefore, it is thought that it became smaller than the initial warpage.

  The flatness in this case was measured and found to be 30 μm. By reversing the stiffener warp direction and the warp direction due to the difference in thermal expansion coefficient, the final warp was greatly improved and the warp amount could be reduced.

<Comparative example>
Stiffeners and printed wiring boards similar to those in the examples were prepared. The flatness of the stiffener 1 was set to 50 μm.

  Unlike the example, the valley side in the warp direction of the stiffener 1 and the printed wiring board 4 were bonded together with an adhesive 3 and integrated. Thereafter, the flatness was measured by processing in the same manner as in Example, and the flatness was 90 μm.

  This is considered to be because the warp amount was increased because the warp direction of the original stiffener was the same as the warp direction due to the difference in thermal expansion coefficient.

  Next, a method for manufacturing a semiconductor package with a heat sink according to the present invention will be described based on an embodiment thereof, but the present invention is not limited to this.

  FIG. 4 is a conceptual diagram in which a heat sink 6 is attached to a printed wiring board with a stiffener on which a semiconductor chip 5 is mounted via an adhesive 3.

  As the printed wiring board, a multilayer printed wiring board in which six wiring layers were formed using polyimide as an insulating layer and copper as a wiring layer was prepared. The total thickness of the printed wiring board was 220 μm, and the thermal expansion coefficient was 20 ppm. The size is 40 mm square.

  The surface of the printed wiring board was covered with a solder resist, and the solder resist was provided with openings at portions where solder bumps for mounting semiconductor chips were formed. Solder bumps were formed in the openings of the solder resist by a solder printing method. This solder bump is for mounting a semiconductor chip.

  As the stiffener, a copper material having a thickness of 700 μm was prepared, and nickel was plated on both surfaces by electrolytic nickel plating. The size is 40 mm square, and the opening at the center is 26 mm square.

  In order to integrate the stiffener and the printed wiring board, a stiffener was attached to the printed wiring board using a thermosetting adhesive. Thereafter, heating for curing the adhesive was performed at 150 ° C. for 2 hours.

  A printed wiring board with a stiffener was produced as described above, and a semiconductor chip made of Si was mounted on the solder bump portion. The size of the semiconductor chip was 20 mm square, and the thermal expansion coefficient was 4 ppm. Mounting was performed by melting the solder bumps at 260 ° C. for 30 seconds.

  On the printed wiring board with a stiffener on which the semiconductor chip was mounted, a heat radiating plate was attached using a thermosetting adhesive. Thereafter, heating for curing the adhesive was performed at 150 ° C. for 2 hours.

  FIG. 5 is a diagram showing the behavior of warpage after integration when a semiconductor chip is mounted on a printed wiring board with a stiffener.

  FIG. 5A is a view immediately after placing the semiconductor chip 5 on a printed wiring board with a stiffener at room temperature, and there was no warpage in this state before heating.

  FIG. 5B is a schematic view after the semiconductor chip 5 is mounted and reflowed. The thermal expansion coefficient of the printed wiring board 4 is 20 ppm, which is larger than the thermal expansion coefficient of the semiconductor chip 5 of 4 ppm. When the flatness was measured at room temperature after reflow, the flatness was finally -100 μm.

  Here, the flatness was measured by placing the printed wiring board on the lower side and placing the semiconductor chip on the plane. When the printed wiring board side is a mountain side, the height of the apexes of the four corners of the printed wiring board is indicated as plus (+) flatness. In addition, when the printed wiring board side is a valley side, the height from the plane at the intersection of the diagonal lines of the corners of the printed wiring board, that is, the four corners, is shown as minus (−) flatness.

  As a measuring method, using a laser length measuring instrument, in each case, a printed wiring board with a stiffener, which is the object to be measured, is placed on a flat surface, and a hole is formed in the flat portion corresponding to the measuring portion of the printed wiring board with a stiffener. The distance was calculated by irradiating a laser from below.

  The mechanism of the cause of the warping result after reflow as described above is considered as follows. When the temperature rises, the solder bumps 2 are not melted or are melted and have fluidity, so that each expansion difference due to the difference in thermal expansion coefficient between the semiconductor chip 5 and the printed wiring board 4 is alleviated. Let Accordingly, the flat state formed first is maintained, but when the temperature falls, the solder bump 2 becomes solid when the temperature falls below the melting point of the solder, and the semiconductor chip 5 and the printed wiring board 4 are fixed. Is done. The temperature is further lowered. In this case, since the thermal expansion coefficient of the printed wiring board 4 is larger than the thermal expansion coefficient of the semiconductor chip 5, the printed wiring board 4 is contracted at a high rate, and the printed wiring board 4 side is pulled in the contracting direction. Power works. For this reason, it is considered that the printed wiring board side is warped in the shrinking direction from the initial state where there is no warping, and such a result is obtained.

  An embodiment of the present invention will be described below, but the present invention is not limited to this.

  As the printed wiring board, a multilayer printed wiring board in which six wiring layers were formed using polyimide as an insulating layer and copper as a wiring layer was prepared. The total thickness of the printed wiring board was 220 μm, and the thermal expansion coefficient was 20 ppm.

  The surface of the printed wiring board was covered with a solder resist, and the solder resist was provided with an opening in a portion where a solder bump for mounting a bare chip was formed. Solder bumps were formed in the openings of the solder resist by a solder printing method. This solder bump is for mounting a semiconductor chip.

  As the stiffener, a copper material having a thickness of 700 μm was prepared, and nickel was plated on both surfaces by electrolytic nickel plating.

  In order to integrate the stiffener and the printed wiring board, a stiffener was attached to the printed wiring board using a thermosetting adhesive. Thereafter, heating for curing the adhesive was performed at 150 ° C. for 2 hours.

  A printed wiring board with a stiffener was produced as described above, and a semiconductor chip made of Si was mounted on the solder bump portion. The size of the semiconductor chip was 20 mm square, and the thermal expansion coefficient was 4 ppm. Mounting was performed by melting the solder bumps at 260 ° C. for 30 seconds.

  On the printed wiring board with a stiffener on which the semiconductor chip was mounted, a heat radiating plate was attached using a thermosetting adhesive. Thereafter, heating for curing the adhesive was performed at 150 ° C. for 2 hours.

  FIG. 6 is a diagram before the heat sink and the semiconductor package are attached in the present embodiment. It is a figure before a semiconductor package and the heat sink 6 are affixed through the adhesive agent 3, and the mountain side of the curvature direction of the heat sink 6 is affixed.

  The semiconductor package after mounting the semiconductor chip is warped in the mounting direction of the semiconductor chip, and the amount of warping is finally reduced by attaching the heat sink 6 which is warped in the reverse direction.

  The flatness in this case was measured and found to be 30 μm. Since the warpage amount of the semiconductor package before the heat sink was attached was 100 μm, the final warpage was greatly improved and the warpage amount could be reduced.

DESCRIPTION OF SYMBOLS 1 ... Stiffener 2 ... Solder bump 3 ... Adhesion layer 4 ... Printed wiring board 5 ... Semiconductor chip 6 ... Heat sink

Claims (8)

A method of manufacturing a printed wiring board with a stiffener,
The stiffener before being integrated with the printed wiring board has a warped shape,
When the coefficient of thermal expansion of the stiffener is smaller than the coefficient of thermal expansion of the printed wiring board, the surface of the stiffener warped in a mountain and the printed wiring board are bonded together,
When the thermal expansion coefficient of the stiffener is larger than the thermal expansion coefficient of the printed wiring board, the surface of the stiffener warping direction becomes a valley and the printed wiring board are bonded together,
The method of manufacturing a printed wiring board with a stiffener, further comprising: heating and integrating the bonded stiffener and the printed wiring board.   The method for manufacturing a printed wiring board with a stiffener according to claim 1, wherein the shape of the stiffener before being integrated with the printed wiring board is a dome shape.   2. The stiffener according to claim 1, wherein a shape of the stiffener before being integrated with the printed wiring board has a hollow portion, and a virtual plane of the stiffener including the hollow portion is a dome shape. A method for manufacturing a printed wiring board.   The method for manufacturing a printed wiring board with a stiffener according to any one of claims 1 to 3, wherein the stiffener and the printed wiring board are bonded together via a thermosetting adhesive.   The method for manufacturing a printed wiring board with a stiffener according to any one of claims 1 to 4, wherein a material of the stiffener is a metal.   The printed wiring board with a stiffener according to any one of claims 1 to 5, wherein the printed wiring board with a stiffener is for a semiconductor package. A method of manufacturing a semiconductor package with a heat sink,
The heat sink before being integrated with the semiconductor package has a warped shape,
Bonding the semiconductor package with the surface where the warping direction of the heat sink becomes a mountain,
Furthermore, the said heat sink and the said semiconductor package which were bonded together are heated and integrated, The manufacturing method of the semiconductor package with a heat sink characterized by the above-mentioned.   The method of manufacturing a semiconductor package with a heat sink according to claim 7, wherein the shape of the heat sink before being integrated with the semiconductor package is a dome shape.

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