JP5354327B2 - Power module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power module semiconductor device that does not have defects in a silicone gel part or peeling-off of the silicone gel part, while having superior creepage insulation properties. <P>SOLUTION: A power module has a configuration, wherein the creepage of a ceramic insulating substrate is insulated and protected by a silicone gel, in which the weight-average molecular weight of a base polymer, measured by using a GPC (gel permeation chromatograph) method, is 30,000-40,000. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a power module, and more particularly to a power module in which a creeping surface of a ceramic circuit board is insulated and protected with a silicone gel.

  In recent years, power modules have been widely used in power conversion devices centering on IGBTs (Insulated Gate Bipolar Transistors). The power module includes one or more power semiconductor devices to form part or all of the conversion connection, and has a structure in which the power semiconductor and the base plate or the cooling surface are electrically insulated. It is a device.

  A structure of a conventional power module will be described by taking a structure of a general IGBT power module as an example.

  FIG. 1 is a cross-sectional view of a general IGBT power module. In the figure, reference numeral 1 denotes a power chip such as an IGBT or a diode chip. The power chip 1 is mounted on the ceramic insulating substrate 2. The ceramic insulating substrate 2 is soldered to the metal substrate 3. The terminal case 4 is made of thermoplastic resin such as polyphenylene sulfide (PPS), and is insert-molded to fix the external lead metal terminal 5. On the ceramic insulating substrate 2, an external lead terminal 5 fixed by soldering stands. The external extraction terminal 5 and the power chip 1 are electrically connected by a metal wire 6. A terminal case 4 is bonded to the metal substrate 3. The lid 7 is made of the same resin as the terminal case 4. The terminal case 4 is filled with a silicone gel 8 having a low elastic modulus in order to insulate and protect the creeping surface of the ceramic insulating substrate 2 and the chip on the substrate on which the power chip is mounted.

  Patent Document 1 describes an insulating substrate sealed with a sealing resin filled in a case, and a resin-encapsulated power module having a semiconductor element. The sealing resin has a penetration of 25 or more and 35 or less. The use of a silicone elastomer is described.

  Patent Document 2 discloses that a silicon-bonded alkenyl group-containing diorganopolysiloxane and non-functional organopolysiloxane having a viscosity of 50 to 100,000 centipoise at 25 ° C. and a viscosity of 1 to 1,000,000 centipoise at 25 ° C. It comprises a silicon-bonded alkenyl group-containing diorganopolysiloxane and a catalytic amount of a hydrosilylation catalyst, has a JIS A hardness of 0, a penetration of 300 or less, and a tan δ of 0.1 to 10 Hz at a shear frequency of 0.1 to 10 Hz. No. 2 silicone gel composition is proposed, and this composition is said to be excellent in vibration-proof properties and heat resistance.

JP 2008-16564 A JP-A-8-225743

  In the conventional power module semiconductor device, cracks and voids are generated in the silicone gel in an environment where moisture is rapidly absorbed. When such a silicone gel is used for sealing high voltage components, the cracks and voids become an air layer, causing partial discharge and lowering the insulation. Further, there is a problem that the silicone gel peels off from the creeping surface of the ceramic insulating substrate and the creeping insulation is lowered.

  Like the popcorn phenomenon, the main cause of this is that moisture absorbed in the silicone gel interior and the interface with the ceramic insulating substrate is heated rapidly, causing defects in the silicone gel such as cracks, voids, and peeling when scattered. It is. Therefore, in order to improve the creeping insulation in the moisture absorption rapid heating of the power module semiconductor device, it is very effective to prevent the occurrence of structural defects in the silicone gel part.

  When the penetration is 25 to 35 as in Patent Document 1, the P / C (power cycle) life required for the power module cannot be satisfied. Further, it has been confirmed that as the wire diameter becomes thinner, the fracture life is shortened by HC (cooling and heating cycle). The silicone elastomer in the case (Wacker RT745S) is dimethyl silicone rubber, and it is difficult to control the penetration to 7 to 27 as in the case, and the feasibility is poor. Further, since the cold resistance at -40 ° C. or lower is inferior, there is a risk of accelerating wire breakage at HC.

  Patent Document 2 uses a composition containing a polyorganosiloxane having a specific structure, but a penetration of 300 is poor in feasibility. In other words, when the penetration is 110 or more, it is difficult to keep the form in a vertical position, and it is two-component, and it is practically impossible to manage the penetration due to too large variation for blending. is there.

  In addition, in order to prevent exfoliation from the creeping surface of the ceramic insulating substrate, which is a structural defect of the silicone gel, it may be possible to apply and harden an insulating paint such as polyimide or epoxy on the creeping surface of the ceramic insulating substrate. There is a risk of cracking in the more brittle ceramics. In addition, the coating and curing process increases, leading to an increase in material costs and an increase in cost of the final product.

  In order to improve creepage insulation, it is conceivable to apply a silane coupling agent to the creeping surface of the ceramic insulating substrate, but a fatal problem that the silane coupling agent solidifies at the silicone gel interface due to heat deterioration and leads to peeling. Also have.

  In addition, it is conceivable to improve the strength of the silicone gel for defects such as cracks and voids in the silicone gel. However, if the strength of the silicone gel is increased inappropriately, it will peel off at the interface with the ceramic insulating substrate. There was a problem.

  The object of the present invention is to control the strength of the silicone gel in order to suppress cracks, voids and peeling, which are defects of the silicone gel, without significantly changing the existing process or the conventional structure. An object of the present invention is to provide a power module semiconductor device having no creeping or peeling of the silicone gel portion and having excellent creepage insulation characteristics by using the gel.

  As a result of repeated studies to solve the above-mentioned problems, the present inventors have found that the cause of peeling from the cracks, voids and creeping surfaces of the ceramic insulating substrate in the silicone gel generated under the environment of moisture absorption and rapid heating is silicone. It has been found that the weight average molecular weight of the gel base polymer is inappropriately small or large. That is, it has been found that optimizing the weight average molecular weight of the base polymer of the silicone gel is very effective in suppressing defects in the silicone gel portion and peeling.

  In other words, the power module of the present invention is provided to insulate and protect the creeping surface of the ceramic insulating substrate with a silicone gel whose weight average molecular weight of the base polymer measured by GPC (gel permeation chromatography) is 30000-40000. It is characterized by.

  The power module preferably has a measured penetration of 30 to 80 based on ASTM D1403 after curing of the silicone gel that protects the creeping surface of the ceramic insulating substrate, and after curing of the silicone gel The loss coefficient (tan δ) of 0.1 Hz is preferably 0.15 to 0.20.

  Since the power module of the present invention can suppress the peeling of the gel from the insulating substrate and the generation of structural defects in the gel, which cause failure in the moisture absorption rapid heating test of the power semiconductor device, the power module can be operated without changing the current power module structure It becomes possible to improve the reliability of the creeping insulation performance of the ceramic insulating substrate of the module.

  The power module of the present invention is characterized in that the creeping surface of the ceramic circuit board is insulated and protected with a silicone gel whose weight average molecular weight of the base polymer is 30,000 to 40,000. The structure of the power module of the present invention is as follows. It may have a general IGBT power module structure. As an example, in this power module, as shown in FIG. 1, a ceramic insulating substrate 3 is soldered on a metal substrate 4 accommodated in a terminal case 4. The power chip 1 is mounted on the ceramic insulating substrate 3 and has a structure in which the silicone gel 8 insulates and protects the creeping surface of the ceramic insulating substrate 3.

  The silicone gel 8 used in the power module of the present invention has a base polymer weight average molecular weight of 30,000 to 40,000. In addition, the weight average molecular weight of this base polymer is a quantitative value as a polystyrene conversion molecular weight measured using GPC (gel permeation chromatography) method.

  Silicone gel is a cured product by addition reaction of a base polymer having a vinyl group and a crosslinking agent having a hydrogen group with a catalyst such as platinum. The needle is an indicator of the hardness of the gel based on the type and amount of the crosslinking agent. The degree of entry is controlled. On the other hand, control of the strength of the silicone gel itself is important in using the silicone gel of the power module, and the strength of the gel is controlled by controlling the molecular weight of the base polymer. In the present invention, it is preferable to control the weight average molecular weight of the base polymer to 30,000 to 40,000 and to control the penetration to 30 to 80.

  When the weight average molecular weight of the base polymer is less than 30000, the strength is insufficient and voids and cracks are likely to occur. When it exceeds 40,000, the viscosity becomes high and the workability becomes inferior. In addition, the permeability to narrow gaps deteriorates, and in the areas where the penetration has not occurred, poor adhesion occurs, which causes a peeling failure.

  Also, if the penetration is less than 30, due to the cold resistance characteristic unique to dimethyl silicone, the thinner the wire, the easier it is to break during HC (cooling cycle), making it impossible to ensure reliability. On the other hand, when the penetration exceeds 80, the form stability is poor. Moreover, since mechanical strength falls, it will become easy to generate | occur | produce a crack. In addition, tan δ is desirable to have a composition in which the property of the gel that absorbs vibration exhibits a damping property and a large tan δ. However, if tan δ is less than 0.15, cracks are likely to occur. And easy to peel.

  As the weight average molecular weight of the base polymer of the silicone gel 8, a commercially available silicone gel made of a base polymer having a known molecular weight is used, or a plurality of base polymers having a known molecular weight are blended to obtain a weight average molecular weight of a desired base polymer. be able to.

  Examples of the ceramic insulating substrate 3 used in the present invention include those made of silicon nitride, alumina, aluminum nitride or the like.

  In the present invention, the silicone gel 8 insulates and protects the creeping surface of the ceramic insulating substrate 3. That is, the entire surface of the ceramic insulating substrate 3 exposed is covered with the silicone gel 8 for insulation protection. As this coating, all the power module components housed in the terminal case including the ceramic insulating substrate 3 and the power chip 1 (of course, excluding the tip of the external extraction terminal 5 taken out of the terminal case) A method of sealing with the silicone gel 8 can be exemplified. Since the metal substrate 4 also serves as the bottom of the terminal case, only the exposed portion of the upper surface of the metal substrate 4 is covered with the silicone gel 8. Since the metal substrate 4 also serves as a heat sink, a metal having excellent thermal conductivity, such as copper or aluminum, is used.

  Below, it demonstrates that the power module using this silicone gel shows the outstanding performance, when a thing with a weight average molecular weight 30000-40000 is used as a base polymer of a silicone gel using an Example and a comparative example. .

  First, the measuring method of the weight average molecular weight of the base polymer of the silicone gel used in Examples and Comparative Examples is shown below.

  A GPC analysis sample was washed with dichloromethane, and 0.01 g of a silicone gel base polymer was put into a sample bottle consisting of a completely dried 9 cc glass screw tube, and 5.0 g of toluene (manufactured by Wako Pure Chemical Industries, Ltd.). HPLC grade) to obtain a 0.2 wt% analytical sample solution.

  As polystyrene monodisperse standards (TSK standard POLYSTYRENE manufactured by Tosoh Corporation), five types of molecular weights of 355,000, 96,400, 37,900, 19,600, and 5,570 are prepared, and these are prepared in the same manner as described above. It adjusted so that it might become a 0.1 wt% toluene solution.

  The GPC device is a Waters Waters 600E system (detector: Waters 410 differential refractometer), the column is connected in series with two Waters Styragel HR5Es, and a guard column of the same specification is used, and the temperature is kept at 75 ° C. GPC analysis was performed.

  The eluent was toluene (HPLC grade manufactured by Wako Pure Chemical Industries, Ltd.) at a flow rate of 1.0 mL / min, the sample solution injection amount was 100 μL, the detection was RI (refractive index), and the analysis time was 30 minutes. As analysis software, Millennium 32-J manufactured by Waters was used.

  From the chromatogram of the polystyrene standard sample obtained under the above conditions, a calibration curve (cubic curve) of retention time and molecular weight is calculated by the method of least squares, and the following formula is calculated from the calibration curve and the chromatogram of the silicone gel base polymer sample: 1, the polystyrene equivalent weight average molecular weight was calculated.

Weight average molecular weight Mw = Σ (WiMi) / W = Σ (HiMi) / Σ (Hi).
W = total weight of the polymer Wi = weight of the i th polymer Mi = molecular weight at the i th elution time Hi = height at the i th elution time

  The penetration of the silicone gel used in the examples and comparative examples was determined by taking 50 cc of an uncured silicone gel composition in a beaker with a capacity of 50 cc and heating and curing in a hot air dryer at 100 ° C. for 60 minutes. A silicone gel was obtained. After cooling to room temperature, measurements were made using ASTM D1403 using a 1/4 cone.

  In addition, the loss factor (tan δ) of the silicone gel used in Examples and Comparative Examples was measured with a dynamic analyzer manufactured by Rheometric Co., Ltd. on a silicone gel produced on a cone plate.

  Moreover, the cohesive failure rate of the silicone gel used for the Example and the comparative example was measured as follows.

  The uncured silicone gel composition is bonded to two 10 mm × 50 mm × 0.25 mm silicon nitride ceramic substrates as shown in FIG. 2 with an adhesive area of 10 mm × 10 mm and cured by heating at 100 ° C. for 60 minutes. By doing so, a shear adhesion test piece was obtained.

  The shear adhesion test piece was moisture-absorbed at 85 ° C. and 85% for 1000 h, allowed to cool to room temperature, left on a hot plate at 125 ° C. for 8 h, cooled to room temperature, and then cooled to room temperature using an EZ tester manufactured by Shimadzu Corporation. The shear compressive strength was measured at 5 mm / second. Moreover, the fractured surface fractured by the shear compression was observed, and the area of the portion where the gel was adhered to the upper surface of the silicon nitride ceramic substrate was evaluated as the cohesive failure rate.

  Moreover, evaluation of the gel defect of the silicone gel used for the Example and the comparative example was performed as follows.

  As shown in FIG. 3, a metal pattern is applied to both surfaces of a silicon nitride ceramic so that the creepage distance is 2 mm, one side is soldered to a metal plate, and a bar electrode is arranged on the upper surface to place a test piece. Produced.

  This test piece was placed in a petri dish of 140 mmφ, filled with 100 cc of silicone gel from the top, vacuum degassed for 10 minutes at 3 mmHg or less, and heated and cured in a 100 ° C. hot air dryer for 60 minutes. A sample was used.

  Ten samples were hygroscopically treated at 85 ° C. and 85% for 10 hours, cooled to room temperature, allowed to stand on a hot plate at 125 ° C. for 8 hours, and then cooled to room temperature. The number of samples in which gel defects occurred was examined in 10 samples.

  Further, the creeping breakdown voltage of the silicone gel used in Examples and Comparative Examples was measured as follows.

  Using the sample subjected to the hygroscopic rapid heating test used for the observation of the gel defect, the voltage was raised in a normal state with a withstand voltage tester TOSS101 (manufactured by Kikusui Electronics Co., Ltd.) with a cutoff of 2 mA and from AC2 KV to 0.5 KV increments. The breakdown voltage (with back electrode) during application for 60 seconds was measured.

<Examples 1-6, Comparative Examples 1-3>
In Examples 1 to 6 and Comparative Examples 1 to 3, the weight average molecular weight, penetration, and tan δ silicone gel of the base polymer described in Table 1 were used, and these silicone gels were subjected to gel defects according to the evaluation method described above. The creepage breakdown voltage was measured. The results are shown in Table 1.

  The base polymer (weight average molecular weight 31100) used in Examples 1 to 3 was obtained by mixing TSE3051 series base polymer (weight average molecular weight 23800) and weight average molecular weight 38700) manufactured by Momentive Performance Materials.

Base polymers used in Examples 4-6 (weight average molecular weight 38700) was used Momentive Performance Materials Inc. of TSE305 1 series of base polymer (weight average molecular weight 38700).

  The base polymer (weight average molecular weight 23800) used in Comparative Example 1 was a TSE3051 series base polymer (weight average molecular weight 23800) manufactured by Momentive Performance Materials.

  The base polymer (weight average molecular weight 41100) used in Comparative Example 2 was obtained by mixing a base polymer (weight average molecular weight 38700) of TSE3051 series manufactured by Momentive Performance Materials and a silicone base polymer (weight average molecular weight 49700). .

  In Comparative Example 3, a silicone base polymer having a weight average molecular weight of 49,700 was used.

In addition, the adjustment of the needle penetration and tanδ was Tsu line.

  A ceramic substrate made of alumina was used as a substrate, and a circuit pattern was formed on one surface of the ceramic substrate and a solid pattern was formed on the other surface with a copper foil. The circuit pattern is soldered with IGBT and FWD, wire bonded between the circuit pattern and the external lead-out terminal, and between the IGBT (FWD) and the external lead-out terminal, and stored in a resin case, and the surface is made of silicone Sealed with gel to obtain a power module. As a result of examining the module performance of this power module semiconductor device, it was confirmed that it had good performance.

  As shown in the Examples, the power module semiconductor device obtained in the present invention maintained a high creepage breakdown voltage in the moisture absorption rapid heating test, and no gel defects were observed. On the other hand, in Comparative Example 1, the creeping breakdown voltage was lowered and voids and cracks were generated in the silicone gel. In Comparative Examples 2 and 3, no voids or cracks were observed in the silicone gel, but peeling was observed on the surface of the silicon nitride ceramic insulating substrate, and the creeping breakdown voltage increased as the weight average molecular weight increased. It showed an increasing trend.

It is a schematic cross section showing a general IGBT power module. It is a figure which shows the test piece for an adhesion test test. It is a schematic cross section which shows a dielectric breakdown voltage and the sample for gel external appearance evaluation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Power chip 2 Ceramic insulating substrate 3 Metal substrate 4 Terminal case 5 Metal terminal 6 Metal wire 7 Lid 8 Silicone gel 9 Silicon nitride ceramic substrate 10 Silicone gel 11 Silicone gel 12 Ceramic insulating substrate 13 Lead electrode 14 Metal plate 15 Glass petri dish

Claims (3)

A power module, wherein a creeping surface of a ceramic insulating substrate is insulated and protected with a silicone gel having a weight average molecular weight of 30000 or more and 40000 or less of a base polymer measured by a GPC (gel permeation chromatography) method.   The power module according to claim 1, wherein the silicone gel is a silicone gel having a measured penetration of 30 to 80 based on ASTM D1403 after curing.   The power module according to claim 1, wherein the silicone gel is a silicone gel having a loss factor (tan δ) of 0.1 Hz after curing of 0.15 to 0.20.

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