JP5126073B2 - Manufacturing method of semiconductor device - Google Patents

Description

  The present invention relates to a method of manufacturing a semiconductor device in which an insulating substrate is bonded on a heat dissipation base, and more particularly to a method of manufacturing a semiconductor device in which an insulating substrate made of ceramic or the like is soldered to a heat dissipation base using a lead-free solder. .

  In general, an inverter device applied to a variable speed device of a motor includes a power element that performs power conversion, a drive circuit that controls and drives the power element, a protection circuit, and a plurality of semiconductor integrated circuits such as a control circuit that performs overall control thereof It is constituted by. Recently, high power control semiconductor devices such as inverter devices are intelligent power modules (hereinafter referred to as IPMs) that incorporate a power element that converts direct current into alternating current, a drive circuit, and a protection circuit in one package. It has been commercialized as.

FIG. 5 is a schematic cross-sectional view of a main part of a conventional power semiconductor module.
In the insulating substrate 101 of the power semiconductor module 100 shown in FIG. 5, conductor layers 101b and 101c such as copper (Cu) and aluminum (Al) are formed on both surfaces of a ceramic substrate 101a such as aluminum nitride (AlN). A substrate is used, and a semiconductor chip 103 such as a power semiconductor is bonded onto the insulating substrate 101 via a solder layer 102. The insulating substrate 101 to which the semiconductor chip 103 is bonded in this way is formed of a metal such as copper by the solder layer 104 for the purpose of radiating heat generated in the semiconductor chip 103 on the side opposite to the bonding surface side. The heat dissipation base 105 is joined.

  When the power semiconductor module 100 having such a structure is formed, two members having different thermal expansion coefficients, that is, the insulating substrate 101 including the ceramic substrate 101a and the metal heat dissipation base 105 must be joined together by the solder layer 104. . Therefore, the heat dissipation base 105 that was originally flat may be warped after soldering.

FIG. 6 is a schematic cross-sectional view of an essential part showing the heat dissipation base in a warped state. In FIG. 6, the same elements as those shown in FIG. 5 are denoted by the same reference numerals.
For example, when aluminum nitride is used for the ceramic substrate 101a of the insulating substrate 101 and copper is used for the heat dissipation base 105, the thermal expansion coefficient of aluminum nitride is about 4.5 ppm / K, and the thermal expansion coefficient of copper is about 16.5 ppm / K, which produces a relatively large difference. Therefore, in the cooling stage after soldering, the shrinkage of copper is larger than that of aluminum nitride, and the heat dissipation base 105 is warped in a convex shape toward the joint surface with the insulating substrate 101. If such a warp occurs in the heat dissipation base 105, it may hinder the device assembly process after soldering, or may cause the performance of the power semiconductor module 100 to deteriorate depending on the degree of the warp. It was.

  By the way, many solders used for manufacturing semiconductor devices contain lead (Pb) as a component. Electronic devices and electronic parts that use such lead-containing solder, if discarded and left outdoors and exposed to acid rain, etc., lead may elute from the solder and cause environmental pollution. . For this reason, it is desirable to use so-called lead-free solder mainly composed of tin (Sn) containing no lead for various electronic devices and electronic parts. Based on the European Union (EU) RoHS Directive on restrictions on the use of specific hazardous substances in electronic and electrical equipment, solder containing lead in particular is restricted. Instead, silver (Ag), copper, zinc ( Solder joints containing alternative materials such as Zn), bismuth (Bi), and indium (In) have been proposed.

  Such lead-free solder has a property that its hardness is higher than that of solder containing lead. When the insulating substrate 101 of the power semiconductor module 100 shown in FIGS. 5 and 6 is joined to the originally flat heat dissipation base 105 using solder containing lead, the insulating substrate of the heat dissipation base 105 is used when soldering. Even if a convex warp toward the 101 side occurs, the solder itself is soft, so that the solder layer 104 undergoes creep deformation immediately after soldering, and the stress therebetween is relaxed. As a result, the warp of the heat radiating base 105 is eliminated, and the heat radiating base 105 returns to the original flat state or a state close to flat.

  On the other hand, when lead-free solder is used for joining them, since the solder is hard and the creep deformation of the solder layer 104 does not occur, the convex warpage generated in the flat heat radiation base 105 is restored. It will remain without. Further, the amount of warpage is as large as about 200 μm to 500 μm. As a result, as described above, the assembly process after soldering may be hindered or the performance of the power semiconductor module 100 may be degraded.

  FIG. 7 is a schematic cross-sectional view of the relevant part showing the assembly process of the power semiconductor module. In FIG. 7, the same components as those shown in FIGS. 5 and 6 are denoted by the same reference numerals.

  As shown in FIG. 7, the power semiconductor module 100 is usually fixed to the cooling fin 200 by screws or the like after the insulating substrate 101 and the heat dissipation base 105 are soldered. Yes.

  When solder containing lead is used for bonding between the insulating substrate 101 and the heat dissipation base 105, the convex warpage generated in the heat dissipation base 105 during the soldering tends to be eliminated thereafter. Therefore, the contact thermal resistance between the heat dissipation base 105 and the cooling fin 200 is kept relatively small, and the heat generated in the semiconductor chip 103 is efficiently dissipated from the heat dissipation base 105.

  On the other hand, when lead-free solder is used for bonding to the insulating substrate 101 and the heat dissipation base 105 is greatly bent in a convex shape toward the insulating substrate 101, the cooling fin 200 is flat as shown in FIG. A large gap 201 is generated between the surface. When such a gap 201 is generated, the contact thermal resistance is increased, so that the efficiency of dissipation of the heat generated in the semiconductor chip 103 is lowered, and the temperature at the junction of the semiconductor chip 103 is abnormally increased, which may cause thermal destruction. In addition, when the heat dissipation base 105 is greatly warped toward the insulating substrate 101, there is a problem that the ceramic substrate 101a is cracked when the heat dissipation base 105 is screwed to the cooling fin 200. There is also a case.

  Therefore, as a method for manufacturing a semiconductor device using lead-free solder that does not contain lead for joining the insulating substrate and the heat dissipation base and joining the insulating substrate and the semiconductor chip, for example, a technique as described in Patent Document 1 is available. Proposed. In this proposal, when soldering the heat dissipation base and the insulating substrate, the heat dissipation base is preliminarily given a predetermined amount of warpage (recessed) and then insulated using lead-free solder. As a result, the heat dissipation base is soldered to the insulating substrate in a substantially flat state. Therefore, when the heat radiation base is attached to a flat surface such as a cooling fin, a large gap cannot be formed between the heat radiation base and the member, a necessary contact area is ensured, and breakage of the ceramic substrate during attachment is prevented.

JP 2006-202884 A

  FIGS. 8A and 8B are carbon jigs installed on a heat dissipation base when bonding a conventional insulating substrate. FIG. 8A is a plan view thereof, and FIG. 8B is a cross-sectional view taken along line BB. It is. The carbon jig 110 is a jig for positioning the insulating substrate 101, and the insulating substrate 101 has a rectangular shape with a length X in the vertical direction and a length Y in the horizontal direction. The carbon jig 110 has an opening 111 having a size corresponding to the insulating substrate 101. Then, by inserting the insulating substrate 101 into the opening 111, the insulating substrate 101 can be fixed at a bonding position on the heat dissipation base 105.

  However, a gap is generated between the heat dissipating base and the carbon jig in accordance with the amount of warping applied to the heat dissipating base 105 in advance. In addition, since the gap increases as the amount of warping of the heat dissipation base 105 increases, there is a problem in that inadvertent situations such as solder material flowing out or scattering from the gap frequently occur and a large number of defective products occur. Become. In particular, when lead-free solder is used, there is a problem that the affinity with a heat dissipation base such as copper is lowered, and the outflow and scattering are further promoted.

  The present invention has been made in view of these points, and an object thereof is to provide a method of manufacturing a semiconductor device that effectively prevents the outflow of solder material from a gap between a heat dissipation base and a carbon jig. To do.

  In the present invention, in order to solve the above problem, a method of manufacturing a semiconductor device, in which a semiconductor chip is solder-bonded to the wiring layer side of an insulating substrate having conductor layers on both sides and the insulating substrate is solder-bonded to a heat dissipation base. Is provided. In this method of manufacturing a semiconductor device, the heat dissipation base after bonding is insulated from the main surface where the insulating substrate is solder-bonded to the heat dissipation base before bonding so that the heat dissipation base after bonding is in a substantially flat state. A thin film sheet having an opening, comprising: a first step of providing a convex warp to the substrate in advance; a substrate holding frame in which an opening into which the insulating substrate can be inserted is formed; and a heat-resistant organic material. A third step of positioning the insulating substrate on the heat dissipation base by installing the frame on the heat dissipation base via the thin film sheet; and the insulating substrate. And a fourth step of soldering the heat dissipation base.

  According to the present invention, the outflow and scattering of solder in the gap between the heat dissipation base and the frame body are reduced, and the manufacturing efficiency of the power semiconductor module using lead-free solder can be increased.

It is one of the manufacturing processes of the power semiconductor module which concerns on embodiment, Comprising: (A) is a member setting process, (B) is a heating process, (C) is a cross-sectional schematic diagram which shows a pressure reduction process. (A) is a top view of a Kapton sheet, (B) is a sectional view in the state where two Kapton sheets were interposed between a copper base and a carbon jig. It is a top view which shows the opening part shape of a carbon jig. It is a principal part cross-section schematic diagram which shows the power semiconductor module made into normal-pressure normal temperature by the cooling process. It is a principal part cross-sectional schematic diagram of the conventional power semiconductor module. It is a principal part cross-sectional schematic diagram which shows the thermal radiation base of the curved state. It is a principal part cross-sectional schematic diagram which shows the assembly process of a power semiconductor module. It is the carbon jig | tool installed on a thermal radiation base at the time of joining of the conventional insulation board | substrate, Comprising: The figure (A) is the top view, The figure (B) is sectional drawing along the BB line.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is one of manufacturing steps of a power semiconductor module according to an embodiment, where (A) is a member setting step, (B) is a heating step, and (C) is a schematic cross-sectional view showing a decompression step. is there. Here, a solder bonding process for bonding the insulating substrate 1 onto the copper base 2 will be described.

  FIG. 1A shows a state where an insulating substrate 1 is set together with a sheet solder 3 on a copper base 2. The outer periphery of the insulating substrate 1 is held by a carbon jig 4, and a Kapton sheet 5 is disposed between the carbon jig 4 and the copper base 2 around the sheet solder 3 as a means for suppressing solder scattering. The insulating substrate 1 is configured as a substrate in which a copper foil (Cu layer) 1a, a ceramic substrate 1b, and a copper foil (Cu layer) 1c are laminated. Insulating substrate 1 having copper foils 1a and 1c as conductor layers on both sides has copper foil 1a formed as a wiring layer on one main surface, and copper foil 1c on the other main surface is formed by copper base 2 and plate solder 3. Soldered. As the ceramic substrate 1b, a substrate mainly composed of alumina is used.

  The copper base 2 is a heat dissipating base that is fixed to a heat dissipating fin or the like (not shown) in order to release heat from a power semiconductor chip (not shown) disposed on the insulating substrate 1. As shown in FIG. 1, the copper base 2 is processed to have a convex shape on the side opposite to the main surface to which the insulating substrate 1 is soldered and warped in advance. A plurality of protrusions 2a are bossed on the main surface of the copper base 2 facing the substrate. This is for securing the thickness of the solder layer in a melted state at the time of joining to the insulating substrate 1 and improving the reliability of the product.

  The amount of warping of the copper base 2 is, for example, about 100 μm to about 100 μm to about 500 μm when the convex warp toward the insulating substrate 1 generated when the copper base 2 is flat at the time of soldering. The range is about 600 μm. Therefore, considering the actual thickness of the sheet solder 3 (about 0.3 mm), the amount of warping of the copper base 2 is considerably exaggerated in FIG. The amount of warping given in advance is an example, and the thickness and area of the copper base 2, the thickness and area of the insulating substrate 1, and the thicknesses of the copper foil 1 a and the copper foil 1 c bonded to the insulating substrate 1. The value is set appropriately according to the sheath area.

  A solder material (lead-free solder) that does not contain lead is used for the plate solder 3. The component of the plate solder 3 is tin-based solder containing silver, bismuth, copper, indium, antimony (Sb), zinc, aluminum and the like. Also, the lower the melting point of lead-free solder, the lower the heat applied to the copper base 2 during soldering, so the copper expansion and contraction is small, and the warp generated in the copper base 2 is kept small. It becomes possible. In general, the melting point of the sheet solder 3 is preferably 250 ° C. or less.

  The carbon jig 4 has a substantially square shape when seen in a plan view, and is configured as a substrate holding frame in which an opening into which the insulating substrate 1 can be inserted is formed. The opening has a size corresponding to the outer periphery of the insulating substrate 1, and holds the insulating substrate 1 by contacting the inner surface of the opening with the outer periphery of the ceramic substrate 1b. Here, when the insulating substrate 1 is positioned and arranged on the copper base 2 by the carbon jig 4, a Kapton (registered trademark) sheet 5 having an opening having substantially the same shape as the carbon jig 4 is interposed. I am letting.

  The Kapton sheet 5 is a thin film sheet made of an organic material (polyimide resin) degassed by heat treatment, and has a heat resistance of about 450 ° C. Polyimide resin is a kind of organic polymer film, has low affinity with molten solder, and is excellent in chemical resistance and impact resistance. The Kapton sheet 5 used here has a thickness of about 50 μm, but if it is processed to a thickness of 120 μm or less, it has a predetermined flexibility. By installing the Kapton sheet 5 having a low affinity with the molten solder along the curved surface of the copper base 2, the defect rate due to the scattered solder as described later can be improved.

  FIG. 1B shows a molten state of the solder 3 a by the reflow process in the heating furnace 6. When the sheet solder 3 is heated and melted to 280 ° C. to 400 ° C. in the heating furnace 6, a void 7 is generated in the solder 3 a under the insulating substrate 1 by entraining the gas in the melted solder 3 a in the depression on the copper base 2. It's easy to do.

  FIG. 1C shows a void-removed state in which the generated void 7 is removed by suction from the solder 3a by the decompression process in a nitrogen atmosphere. In this decompression process, the void 7 expands and is removed by suction from the solder 3a. At this time, a gap is generated between the copper base 2 and the carbon jig 4. Therefore, from the gap between the copper base 2 and the carbon jig 4, a part of the solder 3a is scattered integrally with the void 7 in the peripheral region. However, since the kapton sheet 5 that repels the splash 3b of the heated solder 3a and has a so-called solder splash suppression effect exists in the gap, even if the splash 3b splashes, it adheres to the periphery of the copper base 2. Can be prevented.

Next, the effect of suppressing solder scattering by the Kapton sheet 5 will be described.
2A is a plan view of the Kapton sheet, and FIG. 2B is a cross-sectional view of a state in which two Kapton sheets are interposed between the copper base and the carbon jig.

  The Kapton sheet 5 is processed into a shape surrounding the opening of the carbon jig 4, and an opening 51 having substantially the same shape as the opening of the jig 4 is formed. The two Kapton sheets 5a and 5b are installed so as to be inserted into the gap with the carbon jig 4 on the copper base 2 as a means for preventing solder scattering, and the insulating substrate 1 is positioned on the copper base 2. In addition, it is preferable that the size of the opening 51 of the Kapton sheet 5 is approximately the same as the outer periphery of the sheet solder so that the molten solder does not adhere to the copper base 2.

  When the copper base 2 used as the heat dissipation base of the insulating substrate 1 has a large area, the amount of warping applied to the copper base 2 in advance is also increased. Therefore, in such a case, it is preferable to interpose two or more Kapton sheets 5 a and 5 b between the copper base 2 and the carbon jig 4. This is because even if the scattered solder remains between the two Kapton sheets 5a and 5b, the subsequent processes are not affected.

  Further, the amount of warping of the insulating substrate 1 as shown in FIG. 2B is determined according to the thickness of the conductor layer copper foils 1a and 1c on both sides (see FIG. 1). Here, the insulating substrate 1 is used in which the copper foil 1a on the front surface and the copper foil 1c on the back surface have the same thickness. In the insulating substrate 1 having the warp shown in FIG. 2, the defect rate due to the scattered solder when the solder is melted in FIG. 1B can be improved.

  Note that when the decompression process shown in FIG. 1C is performed rapidly, gas is generated from the heated Kapton sheet 5. Therefore, if the Kapton sheet 5 is preliminarily degassed, the time required for the decompression process for void treatment during solder heating can be shortened.

FIG. 3 is a plan view showing the opening shape of the carbon jig.
The opening 4a of the carbon jig 4 needs to be large enough to allow the insulating substrate 1 to be inserted. This is because the carbon jig 4 has an original role of holding the insulating substrate 1 on the copper base 2 and performing positioning. The planar shape of the opening 4a may be a rectangle similar to the outer periphery of the insulating substrate. As shown in the drawing, the four protrusions 4b for holding the four corners of the insulating substrate are left at the four corners of the opening 4a, respectively. The positioning may be possible. Note that screw holes 4 c for alignment with the copper base 2 are formed on the left and right sides of the carbon jig 4.

FIG. 4 is a schematic cross-sectional view of an essential part showing a power semiconductor module that is brought to normal pressure and ordinary temperature by a cooling process. On the insulating substrate 1, a semiconductor chip 10 is bonded via a solder layer 9.
Since the above-described Kapton sheet 5 is used to suppress solder scattering, when the copper base 2 returns to a substantially flat state, no solder splashes remain around the upper surface of the copper base 2 to which the insulating substrate 1 is soldered. . Therefore, the resin case 8 can be reliably adhered from above the copper base 2 without performing subsequent correction processing or the like, and the product size can be finished to the standard. Moreover, if there is no gap between the copper base 2 and the resin case 8, when the semiconductor chip is sealed with a gel in a later process, there is no possibility that the gel will flow out without any special treatment. As an example, when the effect was verified, the ratio of correction processing such as solder splash was about 90% when the sheet was not used, but it was greatly improved to about 5% by using two Kapton sheets.

  Further, since the copper base 2 is warped in a concave shape in advance, the copper base 2 becomes almost flat after being cooled and soldered to the insulating substrate 1. Therefore, the copper base 2 can be securely attached to the cooling fin.

DESCRIPTION OF SYMBOLS 1 Insulation board | substrate 2 Copper base 3 Board solder 3a Solder 4 Carbon jig 5 Kapton sheet 6 Heating furnace 7 Void 8 Resin case 9 Solder layer 10 Semiconductor chip

Claims (9)

In a method of manufacturing a semiconductor device, in which a semiconductor chip is soldered to the wiring layer side of an insulating substrate having a conductor layer on both sides and the insulating substrate is soldered to a heat dissipation base.
A convex warp is applied in advance to the side opposite to the main surface to which the insulating substrate is solder-bonded to the heat-dissipating base before bonding so that the heat-dissipating base after the insulating substrate is bonded is substantially flat. A first step;
A second step of preparing a frame for holding a substrate in which an opening into which the insulating substrate can be inserted is formed, and a thin film sheet having an opening made of an organic material having heat resistance;
A third step of installing the frame body on the heat dissipation base via the thin film sheet and positioning the insulating substrate on the heat dissipation base;
A fourth step of solder bonding the insulating substrate and the heat dissipation base;
A method for manufacturing a semiconductor device, comprising:   The method of manufacturing a semiconductor device according to claim 1, wherein the heat dissipation base is made of copper.   The method of manufacturing a semiconductor device according to claim 1, wherein the thin film sheet is made of a polyimide resin and degassed by heat treatment.   The method of manufacturing a semiconductor device according to claim 1, wherein the thin film sheet is processed to have a thickness of 120 μm or less.   2. The method of manufacturing a semiconductor device according to claim 1, wherein the thin film sheet is a flexible Kapton (registered trademark) sheet.   The insulating substrate has conductor layers on both sides of a ceramic substrate, wherein the conductor layer is made of copper foil, and the ceramic substrate is a substrate mainly composed of alumina. A method for manufacturing a semiconductor device according to claim 1.   2. The method of manufacturing a semiconductor device according to claim 1, wherein, in the third step, two or more thin film sheets are interposed between the heat dissipation base and the frame.   2. The method of manufacturing a semiconductor device according to claim 1, wherein the solder bonding in the fourth step uses a plate solder not containing lead having a melting point of 250 [deg.] C. or less.   9. The method of manufacturing a semiconductor device according to claim 8, wherein the plate solder includes at least one of silver, bismuth, indium, antimony, zinc, aluminum, and copper and tin.

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