JP2018018932A - Semiconductor module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor module which has a double-sided cooling structure having a plurality of bonding materials and which can minimize a possible strain amount of all of the boding materials to resolve possible cracks in all of the bonding materials.SOLUTION: In a semiconductor module 10, a first lead frame 1, a bonding material 5, a semiconductor element 3, a bonding material 6, a metallic cooling block 4, a bonding material 7 and a second lead frame 2 are sequentially laminated, and the whole is sealed by an encapsulation resin body 8. The encapsulation resin body 8 is composed of a first encapsulation resin body 8A on the first lead frame 1 side including environment of the semiconductor element 3 and a second encapsulation resin body 8B on the second lead frame 2 side and other than the first encapsulation resin body 8A; and a linear expansion coefficient of the first encapsulation resin body 8A is relatively small compared to a linear expansion coefficient of the second encapsulation resin body 8B.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a semiconductor module having a double-sided cooling structure in which a semiconductor element is disposed between two lead frames.

  A semiconductor module (power module or power card) equipped with semiconductor elements such as IGBT (Insulated Gate Bipolar Transistor) is a case where a laminated body consisting of a lead frame and a semiconductor element joined via a solder layer as a bonding material is a case. A case in which a sealing resin body is formed in the case and a caseless structure in which the laminate is sealed with a relatively hard sealing resin body Various forms exist. It should be noted that a structure in which a heat sink or a cooler that circulates the refrigerant is further arranged to dissipate heat from the semiconductor element to either a caseless structure or a structure having a case is generally applied. ing. There are also two-sided cooling semiconductor modules in which two lead frames exist above and below, a semiconductor element is disposed between them with a bonding material, and these laminates are integrated with a sealing resin body. doing.

  With respect to the semiconductor module having the above-described double-sided cooling structure, one of the purposes of integrating the entire laminate with a sealing resin body is to improve reliability by suppressing distortion that may occur in the bonding material.

  Although the setting of the linear expansion coefficient of the sealing resin body is important for suppressing the distortion of the bonding material, the optimum value of the linear expansion coefficient differs depending on the location of the bonding material.

  More specifically, as the structure of the semiconductor module having a double-sided cooling structure, a first lead frame, a bonding material, a semiconductor element, a bonding material, a metal cooling block, a bonding material, and a second lead frame are sequentially stacked. A semiconductor module having a structure in which the whole is sealed with a sealing resin body can be given.

  In the semiconductor module having such a structure, there are two types of bonding materials sandwiching the semiconductor element, and two types of bonding materials (one type of which is one bonding material sandwiching the semiconductor element). ) And there are a total of three types of bonding materials.

  Since the semiconductor element and a metal cooling block made of copper, for example, have different rigidity from each other, the stress applied to each bonding material and the amount of strain resulting from this differ depending on the bonding material when the semiconductor element generates heat. There is a concern that cracks occur in the bonding material. And the problem of the crack which may arise in a joining material becomes still more remarkable by size reduction of a semiconductor module, and the increase in a heat generation density. To eliminate cracks that can occur in each bonding material, it is necessary to reduce the amount of strain that causes cracking as much as possible. However, the optimal value of the linear expansion coefficient of the sealing resin body is the location of the bonding material. Therefore, it is extremely difficult to uniformly reduce the strain amount of all the bonding materials.

  In currently manufactured semiconductor modules having a double-sided cooling structure, a sealing resin body having a linear expansion coefficient with the best balance among the bonding materials is used. However, it is not always necessary to seal the optimal linear expansion coefficient for each bonding material. Since it is not a stop resin body, the present condition is that the distortion of each joining material is not fully suppressed.

  Here, Patent Document 1 discloses a semiconductor module having a structure in which a semiconductor element and a ceramic column having an approximate linear expansion coefficient are provided between double-sided substrates.

  On the other hand, Patent Document 2 discloses a semiconductor device in which the overall warpage can be suppressed by changing the linear expansion coefficient of the constituent members.

JP 2007-31441 A JP 2007-173680 A

  According to the semiconductor modules and semiconductor devices described in Patent Documents 1 and 2, it is possible to reduce warpage generated in the semiconductor modules and semiconductor devices. However, if a column is provided as in the semiconductor module described in Patent Document 1 to forcibly reduce warpage, stress concentration on the bonding material is likely to occur, and there is a concern about the occurrence of cracks due to this stress concentration. .

  In addition, the stress applied to the bonding interface between the sealing resin body and the substrate is increased, and there is a concern about the problem of peeling of the sealing resin body, and the effect of restraining the bonding material is lost due to peeling of the sealing resin body. The effect of reducing the distortion of the bonding material by the stop resin body cannot be expected.

  On the other hand, the semiconductor device described in Patent Document 2 is also concerned about the same problem as that of Patent Document 1. In addition, as described above, in a semiconductor module having a double-sided cooling structure in which a plurality of bonding materials are present, the linear expansion coefficient of the sealing resin body that is optimal for strain suppression differs for each bonding material. In a resin body, it is extremely difficult to sufficiently reduce the strain amount of all the bonding materials.

  The present invention has been made in view of the problems described above, and relates to a double-sided cooling structure semiconductor module having a plurality of bonding materials, and can reduce the amount of distortion that can occur in all bonding materials as much as possible. An object of the present invention is to provide a semiconductor module capable of eliminating cracks that may occur in all bonding materials.

  In order to achieve the above object, a semiconductor module according to the present invention includes a first lead frame, a bonding material, a semiconductor element, a bonding material, a metal cooling block, a bonding material, and a second lead frame stacked in order. A semiconductor module entirely sealed with a resin body, wherein the sealing resin body includes a first sealing resin body on the first lead frame side including the periphery of the semiconductor element, and a second other than that The second sealing resin body on the lead frame side, and the linear expansion coefficient of the first sealing resin body is relative to the linear expansion coefficient of the second sealing resin body. It is small in size.

  The semiconductor module of the present invention includes two types of sealing resin bodies having different linear expansion coefficients (the first sealing resin body on the first lead frame side including the periphery of the semiconductor element, and the other second lead frame) The second sealing resin body) is applied, and the linear expansion coefficient of the first sealing resin body is made relatively smaller than the linear expansion coefficient of the second sealing resin body, The amount of strain of each bonding material can be reduced as much as possible, and cracks that can occur in all the bonding materials can be eliminated.

  In this specification, the term “lead frame” refers to a literal lead frame, a die pad, a substrate such as a circuit board or a stress relaxation substrate, a substrate made of pure Al and a substrate made of AlN (aluminum nitride). DBA (insulating substrate), heat sinks, etc. are also included, and for example, a lead frame made of Cu material can be applied.

  Examples of the “joining material” include a solder layer made of Pb-based solder, Pb-free solder, or the like.

  Further, examples of the “metal cooling block” include a copper cooling block.

  Furthermore, examples of the “first and second sealing resin bodies” include thermosetting resins such as epoxy resins and thermoplastic resins such as polyamide imide, which are compared with the linear expansion coefficient of the second sealing resin body. Then, both materials are set so that the linear expansion coefficient of the first sealing resin body becomes relatively small.

The linear expansion coefficient of the semiconductor element is, for example, about 3 × 10 ⁻⁶ / K, and the linear expansion coefficient of the copper metal cooling block is, for example, about 16.8 × 10 ⁻⁶ / K. There is a difference of about 6 times.

  Therefore, the sealing resin body around the semiconductor element having a relatively low linear expansion coefficient has a relatively small linear expansion coefficient, so that it can be used for the periphery of the bonding material bonded to the semiconductor element and the metal cooling block. A sealing resin body having a linear expansion coefficient suitable for each bonding material can be disposed around the bonding material being bonded. As a result, the stress applied to each bonding material during heat generation of the semiconductor element can be reduced as much as possible, and this can reduce the amount of strain in each bonding material as much as possible. It is possible to effectively eliminate the occurrence of cracks.

  As can be understood from the above description, in the semiconductor module of the present invention, a semiconductor element and a metal cooling block are disposed between two lead frames, which are joined by a plurality of joining materials, and the whole is a sealing resin. In a semiconductor module having a double-sided cooling structure integrated with a body, the sealing resin body is composed of two types of sealing resin bodies having different linear expansion coefficients, and the first lead frame side including the periphery of the semiconductor element The linear expansion coefficient of one sealing resin body is relatively smaller than that of the second sealing resin body on the other lead frame side. With this configuration, the amount of strain of all the bonding materials can be reduced as much as possible, and cracks that can occur in all the bonding materials can be effectively eliminated.

It is a longitudinal section explaining an embodiment of a semiconductor module of the present invention. It is the flowchart explaining the manufacturing method of the semiconductor module of this invention in order of (a)-(d). It is the figure which showed the experimental result which verified the relationship between the linear expansion coefficient of the 1st sealing resin body, and the inelastic distortion of the joining material between a 1st lead frame and a semiconductor element. It is the figure which showed the experimental result which verified the relationship between the linear expansion coefficient of the 2nd sealing resin body, and the inelastic distortion of the joining material between a 2nd lead frame and metal cooling blocks.

  Hereinafter, embodiments of a semiconductor module of the present invention will be described with reference to the drawings. The semiconductor module is not limited to the illustrated example as long as the semiconductor module has a double-sided cooling structure. In addition to the lead frame of the illustrated form, the substrate includes an insulating substrate, a stress relaxation plate, and the like. The form by which a semiconductor element is mounted in the surface of what laminated | stacked 2 or more types of base materials may be sufficient. In the illustrated example, illustration of a cooler and the like is omitted.

(Embodiment of semiconductor module)
FIG. 1 is a longitudinal sectional view for explaining an embodiment of a semiconductor module of the present invention. In the semiconductor module 10 shown in the figure, a first lead frame 1, a semiconductor element 3, a metal cooling block 4, and a second lead frame 2 are laminated in order, and the first lead frame 1, the semiconductor element 3, and the semiconductor element 3 are stacked. The metal cooling block 4 and the metal cooling block 4 and the second lead frame 2 are joined together by bonding materials 5, 6, and 7 made of solder layers to form a laminate, and sealed around the laminate A resin body 8 is formed to constitute the whole. In the illustrated semiconductor module 10, two semiconductor elements 3 are mounted in parallel.

  The two lead frames 1 and 2 are made of aluminum or an alloy thereof, copper or an alloy thereof, and even if a Ni plating layer is formed on the surface or an Au plating layer is formed on the surface of the Ni plating layer. Good.

The metal cooling block 4 is made of copper, and its linear expansion coefficient is, for example, about 16.8 × 10 ⁻⁶ / K. On the other hand, the linear expansion coefficient of a silicon semiconductor element is, for example, about 3 × 10 ⁻⁶ / K.

  The solder layers constituting the bonding materials 5, 6 and 7 may be either Pb-based solder or Pb-free solder, but in order to reduce the environmental impact load, Sn-Ag solder, Sn-Cu solder, It is preferable to use a Pb-free solder such as Sn—Ag—Cu solder, Sn—Zn solder, Sn—Sb solder.

  The sealing resin body 8 includes a first sealing resin body 8A on the first lead frame 1 side including the periphery of the semiconductor element 3, and a second sealing resin body on the second lead frame 2 side other than that. 8B.

  Further, the materials of both sealing resin bodies are set so that the linear expansion coefficient of the first sealing resin body 8A is relatively smaller than the linear expansion coefficient of the second sealing resin body 8B. ing.

  Here, examples of the material of the first sealing resin body 8A and the second sealing resin body 8B include a thermosetting resin such as an epoxy resin and a thermoplastic resin such as polyamideimide.

  Regarding epoxy resin, it is a thermosetting synthetic resin having a reactive epoxy group at its end, and it is produced by condensation reaction of bisphenol A and epichlorohydrin, novolac epoxy resin, trisphenol. Examples include methane type epoxy resin, bisphenol F type epoxy resin, polyfunctional epoxy resin, flexible epoxy resin, biphenyl type epoxy resin, polymer type epoxy resin and glycidyl ester type epoxy resin. Alternatively, a bisphenol A type epoxy resin and one or more other resins can be mixed and used. Regarding thermosetting resins, in addition to polyamideimide, engineering plastics such as polyphenylene sulfide and polybutylene terephthalate, polyethylene, polypropylene, polystyrene, and polyvinyl chloride are exemplified.

  Thermosetting resins and thermoplastic resins contain inorganic fillers such as silica, alumina, boron nitride, silicon nitride, silicon carbide, and magnesium oxide for the purpose of improving thermal conductivity and thermal expansion. Also good.

As described above, the linear expansion coefficient of the semiconductor element 3 is, for example, about 3 × 10 ⁻⁶ / K, and the linear expansion coefficient of the copper metal cooling block 4 is, for example, about 16.8 × 10 ⁻⁶ / K. There is a difference of about 5 to 6 times in the linear expansion coefficient. Therefore, the first sealing resin body 8A around the semiconductor element 3 having a relatively low linear expansion coefficient has a relatively small linear expansion coefficient, so that the bonding material 5 bonded to the semiconductor element 3 A sealing resin body having a linear expansion coefficient suitable for each of the bonding materials 5 and 7 can be disposed around the bonding material 7 bonded to the metal cooling block 4.

  With this configuration, the stress applied to each bonding material 5, 6, 7 can be reduced as much as possible when the semiconductor element 3 generates heat, and as a result, the amount of strain in each bonding material 5, 6, 7 can be reduced. As a result, the generation of cracks due to strain can be effectively eliminated.

  Next, a method for manufacturing a semiconductor module will be outlined with reference to FIG.

  First, as shown in FIG. 2A, a first intermediate body 10 ′ in which a first lead frame 1, a bonding material 5, a semiconductor element 3, a bonding material 6, and a metal cooling block 4 are stacked is manufactured. .

  Next, as shown in FIG. 2 (b), the first intermediate body 10 'is accommodated in the cavity C of the molding die K composed of the upper die K1 and the lower die K2, and is opened in the upper die K1. By injecting a resin for molding the first sealing resin body from the injection hole K1a (X1 direction) and removing the mold as shown in FIG. 2C, the first intermediate body 10 ′ is surrounded by the first intermediate body 10 ′. A second intermediate body 10 ″ in which one sealing resin body 8A is formed is manufactured.

  Next, as shown in FIG. 2 (d), the second intermediate body 10 ″ is accommodated in the cavity C ′ of a separate molding die K ′ composed of the upper die K1 ′ and the lower die K2 ′, and the upper die. By injecting the resin for molding the second sealing resin body from the injection hole K1′a opened in K1 ′ (X2 direction) and demolding after waiting for curing, the semiconductor module 10 shown in FIG. Manufactured.

(Experiment verifying the relationship between the linear expansion coefficient of the first sealing resin body and the inelastic strain of the bonding material between the first lead frame and the semiconductor element, and the linear expansion coefficient of the second sealing resin body And experiments verifying the inelastic strain relationship of the joint material between the second lead frame and the metal cooling block, and the results)
The inventors have conducted an experiment that verified the relationship between the linear expansion coefficient of the first sealing resin body and the inelastic strain of the bonding material between the first lead frame and the semiconductor element, and the second sealing resin. An experiment was conducted to verify the relationship between the linear expansion coefficient of the body and the inelastic strain of the bonding material between the second lead frame and the metal cooling block.

Specifically, in any experiment, a plurality of semiconductor modules having the configuration shown in FIG. 1 were manufactured by changing the linear expansion coefficients of the first sealing resin body and the second sealing resin body in various ways. And 150 ° C. were subjected to a cooling test to change the temperature condition, and the inelastic strain of the bonding material (bonding materials 5 and 7 in FIG. 1) in each test body was measured. In the manufactured semiconductor module, the linear expansion coefficient of the semiconductor element is 3 × 10 ⁻⁶ / K, the linear expansion coefficient of the metal cooling block is 16.8 × 10 ⁻⁶ / K, and the first and second leads The linear expansion coefficient of the frame is 16 × 10 ⁻⁶ / K, and the linear expansion coefficient of each bonding material is 22 × 10 ⁻⁶ / K.

  FIG. 3 shows the experimental results regarding the relationship of inelastic strain between the first sealing resin body and the surrounding bonding material (bonding material 5 in FIG. 1), and the second sealing resin body and the surrounding bonding material ( FIG. 4 shows the experimental results regarding the relationship of the inelastic strain of the bonding material 7) in FIG.

FIG. 3 shows that the inelastic strain of the bonding material tends to increase as the linear expansion coefficient of the first sealing resin body increases, and the linear expansion coefficient of the first sealing resin body shows the linear expansion coefficient of the semiconductor element. It can be seen that as the expansion coefficient approaches 3 × 10 ⁻⁶ / K, the strain amount of the bonding material decreases. FIG. 3 shows that the linear expansion coefficient of the first sealing resin body is desirably 10 × 10 ⁻⁶ / K or less.

On the other hand, as shown in FIG. 4, the inelastic strain of the bonding material is on a downwardly convex curve showing a minimum value when the linear expansion coefficient of the second sealing resin body is 18 × 10 ⁻⁶ / K. I understand. FIG. 4 shows that the linear expansion coefficient of the second sealing resin body is preferably between the linear expansion coefficient 16 × 10 ⁻⁶ / K of the lead frame and the linear expansion coefficient 22 × 10 ⁻⁶ / K of the bonding material. .

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

  DESCRIPTION OF SYMBOLS 1 ... 1st lead frame, 2 ... 2nd lead frame, 3 ... Semiconductor element, 4 ... Metal cooling block, 5, 6, 7 ... Bonding material (solder layer), 8 ... Sealing resin body, 8A ... 1st sealing resin body, 8B ... 2nd sealing resin body, 10 ... Semiconductor module, 10 '... 1st intermediate body, 10 "... 2nd intermediate body, K, K' ... Mold, K1 , K1 '... upper die, K2, K2' ... lower die, C, C '... cavity

Claims (1)

A semiconductor module in which a first lead frame, a bonding material, a semiconductor element, a bonding material, a metal cooling block, a bonding material, and a second lead frame are laminated in order, and the whole is sealed with a sealing resin body. And
The sealing resin body includes a first sealing resin body on the first lead frame side including the periphery of the semiconductor element, and a second sealing resin body on the second lead frame side other than that. Has been
A semiconductor module in which the linear expansion coefficient of the first sealing resin body is relatively smaller than the linear expansion coefficient of the second sealing resin body.

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