JP2000212518A - Heat bonding sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a heat bonding sheet capable of sufficiently relaxing the thermal stress between a semiconductor element and a wiring circuit board and preventing cracks from occurring and excellent in reliability of electrical connected parts by providing the sheet with respective specific moduli of elasticity at respective prescribed temperatures. SOLUTION: This sheet 3 is provided with characteristics of (i) <=10 MPa modulus of elasticity at 250 deg.C and (ii) <=2,000 MPa modulus of elasticity at -80 deg.C. Furthermore, the heat bonding sheet 3 is preferably composed by forming heat bonding layers 1 formed by using a thermoplastic polyimide such as a silicone-modified polyimide represented by formula I [R1 is represented by formula II or the like; R2 is C3H6, C4H8 or the like; n is 1-100; (a) and b satisfy the relationship of (a+b)=1 and further satisfy the relationship of 0.3<=(a)/(a+b)<=0.99] on at least one surface of a sheetlike porous substrate 2, which is preferably a porous sheet made of polytetrafluoroethylene.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat bonding sheet, and more particularly, to a semiconductor integrated circuit.
The present invention relates to a thermal bonding sheet for fixing a semiconductor chip, which relieves thermal stress between a printed circuit board of a semiconductor package and a semiconductor element.

[0002]

2. Description of the Related Art In a conventional semiconductor device called a semiconductor package, a semiconductor chip is generally attached to a die pad.
It is bonded with a die bonding material such as solder, silver paste, epoxy resin, etc., and sealed with a resin. With the recent miniaturization and high performance of electronic equipment, it has become thinner, smaller, and lighter. It is widely used as a surface mount type semiconductor package.

[0003] However, conventionally used die bonding materials such as epoxy resin, polyimide resin and silicone resin generally have a high elastic modulus and a large thermal stress is generated in the semiconductor chip due to a temperature difference. Poor reliability may cause problems such as breakage of the semiconductor chip or semiconductor package. In this case, it is conceivable to use a silicone resin having a low elastic modulus as the die bonding material.
There is a disadvantage that it is inferior in practicality. In order to improve the productivity, a method such as screen printing has been adopted, but there is a problem that the yield is reduced.

[0004]

In order to solve these problems, as disclosed in Japanese Patent Application Laid-Open No. Hei 8-157621, a porous fluororesin is impregnated with an epoxy resin having a predetermined dielectric constant. And an adhesive sheet in which a porous polytetrafluoroethylene (PTFE) material is impregnated with an epoxy resin, a polyimide resin, or the like as disclosed in Japanese Patent Publication No. 9-500418. I have. However, an adhesive sheet using an epoxy resin cannot easily form a thick adhesive layer because the melt viscosity of the epoxy resin is low at the time of bonding at the B stage (semi-cured), so that the adhesive sheet cannot be formed on a semiconductor element. There is a problem that the epoxy resin sticks out when pasting. On the other hand, an adhesive sheet using a polyimide resin has a high modulus of elasticity, and has a drawback in that it cannot sufficiently reduce the thermal stress between the semiconductor element and the printed circuit board in the application of the semiconductor element.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and in a bonding application of a semiconductor element, the thermal stress between the semiconductor element and the printed circuit board can be sufficiently reduced, and the reliability of the electric connection portion can be improved. It is an object of the present invention to provide a thermal adhesive sheet which is excellent and can prevent cracks in a semiconductor chip or a semiconductor package.

[0006]

Means for Solving the Problems In order to achieve the above-mentioned object, the thermal adhesive sheet of the present invention has a configuration having the following characteristics (A) and (B). (A) The elastic modulus at 250 ° C. is 10 MPa or less. (B) The elastic modulus at -80 ° C is 2000 MPa or less.

That is, the inventor of the present invention can sufficiently alleviate the thermal stress between the semiconductor element and the printed circuit board in the application of the bonding of the semiconductor element, has excellent reliability of the electric connection portion, and has a high reliability. Intensive research was conducted to obtain an adhesive sheet that can prevent the occurrence of cracks. In the course of the series of studies, the inventor focused on the elastic modulus of the adhesive sheet and made various studies on a preferable elastic modulus. As a result, the elastic modulus at 250 ° C. is 10 M
Pa or less (characteristic A) and an elastic modulus at −80 ° C. of 2
The thermal adhesive sheet having a temperature of 000 MPa or less (characteristic B) can sufficiently reduce the thermal stress between the semiconductor element and the printed circuit board, and the semiconductor device using this thermal adhesive sheet has a low reliability of the electrical connection portion. The present invention has been found to be excellent and to be able to prevent the occurrence of cracks in a semiconductor chip or a semiconductor package, and reached the present invention.

In the case where the heat bonding sheet has a single-layer structure composed entirely of a heat bonding layer, the heat bonding sheet is temporarily bonded to a printed circuit board and then permanently bonded to a semiconductor chip irrespective of shell life and pot life. can do. Conversely, the thermal bonding sheet may be temporarily bonded to the semiconductor chip first and then permanently bonded to the printed circuit board.

In the case where the heat bonding sheet has a multilayer structure in which a heat bonding layer is formed on at least one surface of a sheet-like porous substrate, the heat bonding sheet is bonded in two stages (sequential). In addition to the effect that can be done, the sheet-like porous substrate acts as a cushion, reducing distortion,
It has effects such as relaxation of stress and crack prevention.

[0010]

Next, embodiments of the present invention will be described in detail.

The thermal adhesive sheet of the present invention is roughly classified into two modes. The heat-bonding sheet of the first embodiment includes a single-layer structure in which the whole is constituted by a heat-bonding layer. The heat-bonding sheet of the second embodiment includes a sheet-like porous base material having at least one surface. One having a multilayer structure having a heat bonding layer formed thereon is exemplified.

(1) The heat-bonding sheet of the first embodiment having a single-layer structure composed entirely of a heat-bonding layer will be described.
FIG. 1 shows a specific example of the thermal adhesive sheet of the first embodiment.
As shown in FIG. 1, a single-layer structure having only the heat bonding layer 1 can be used.

The material for forming the heat bonding layer 1 is not particularly limited, but is preferably a thermoplastic polyimide, particularly preferably a silicone-modified polyimide. As the above-mentioned silicone-modified polyimide, those having at least one repeating unit selected from the group consisting of the following general formulas (1) to (7) as a main component are preferable. Incidentally, the terminal of the silicone-modified polyimide,
An acid anhydride, a carboxyl group or an amino group.

[0014]

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[0015]

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[0016]

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[0017]

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[0018]

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[0019]

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[0020]

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The silicone-modified polyimide containing, as a main component, at least one repeating unit selected from the group consisting of the general formulas (1) to (7) is, for example, a silicone-modified polyamic acid or a silicone-modified polyamic acid as a precursor thereof. The modified polyamic acid can be produced by imide conversion by heating or the like. The above-mentioned silicone-modified polyamic acid or silicone-unmodified polyamic acid is prepared by reacting the following acid anhydride, silicon-containing diamine and silicon-free diamine in a conventional manner.

Examples of the acid anhydride include, for example, 3,
3 ', 4,4'-biphenyltetracarboxylic dianhydride, 3,3', 4,4'-benzophenonetetracarboxylic dianhydride, pyromellitic dianhydride, 2,2-bis (3,4 -Dicarboxyphenyl) propane dianhydride,
2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride, 2,2-bis (2,3-dicarboxyphenyl) propane dianhydride, bis (3,4
-Dicarboxyphenyl) sulfone dianhydride, bis (3,4-dicarboxyphenyl) ether dianhydride,
1,1'-bis (2,3-dicarboxyphenyl) ethane dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride 1,4,5,8-naphthalenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 2,3,6,8-anthracenetetracarboxylic dianhydride, 1,2,7,8-phenanthrenetetracarboxylic dianhydride and the like can be mentioned.

The silicon-containing diamine, together with the acid anhydride, constitutes the structural unit b of the general formulas (1) to (7). As such a silicon-containing diamine, for example, a diaminosiloxane represented by the following general formula (8) can be given. Specifically, both terminals of bis (3-aminopropyl) tetramethyldisiloxane, bis (3-aminobutyl) tetramethyldisiloxane, α, ω-bis (3-aminopropyl) polydimethylsiloxane, and dimethylsiloxane And those having a primary amino group.

[0024]

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The silicon-free diamine, together with the acid anhydride, constitutes the structural unit a of the general formulas (1) to (7). Examples of such a silicon-free diamine include 2,2-bis [4- (4-aminophenoxy) phenyl] propane and bis [4- (4-aminophenoxy)
Phenyl] ether, bis [4- (3-aminophenoxy) phenyl] ether, 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane,
Bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone, 4,4'-bis (4-aminophenoxy) biphenyl, 4,4'-bis (3 -Aminophenoxy) biphenyl, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene,
4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfide, 3,
3'-Diaminodiphenyl sulfide, 4,4'-diaminobenzanilide, p-phenylenediamine, m-phenylenediamine and the like are used. Of these,
2,2-bis [4- (4-aminophenoxy) phenyl] propane, bis [4- (4-aminophenoxy) phenyl] ether, bis [4- (4-aminophenoxy) phenyl] propane, bis [4- (4-aminophenoxy) phenyl] ether, bis [4- (4-aminophenoxy) phenyl] sulfone, 1,4-bis (4-
It is preferred to use (aminophenoxy) benzene.

Preferred combinations of the above-mentioned acid anhydride, silicon-containing diamine and silicon-free diamine are as follows.

(A) bis (3,4-dicarboxyphenyl) sulfone dianhydride and bis (3-aminopropyl)
Combination of tetramethyldisiloxane and bis [4- (3-aminophenoxy) phenyl] sulfone.

(B) bis (3,4-dicarboxyphenyl) ether dianhydride and bis (3-aminopropyl)
A combination of tetramethyldisiloxane and bis [4- (4-aminophenoxy) phenyl] ether.

(C) 2,2-bis (2,3-dicarboxyphenyl) propane dianhydride, bis (3-aminopropyl) tetramethyldisiloxane, and 2,2-bis [4- (4- Aminophenoxy) phenyl] propane.

(D) 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride, bis (3-aminopropyl) tetramethyldisiloxane,
Combination with 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane.

As the thermoplastic polyimide used as a material for forming the thermal adhesive layer 1, the repeating unit b in the above general formulas (1) to (7) is a heat-resistant acrylic resin other than a silicone resin, a phenoxy resin, an olefin resin. Those composed of a plastic component such as resin and polyamide resin can also be used.

The thermal adhesive sheet of the first embodiment can be manufactured, for example, as follows. First,
A support such as a heat-resistant organic separator or a metal foil is prepared.
Next, a silicone-modified polyamic acid varnish or a silicone-unmodified polyamic acid varnish, which is a precursor of the thermoplastic polyimide, is applied on the support by a casting method or the like. Thereafter, the support is dried and cured to remove the solvent, whereby a single-layer heat-bonding sheet having a heat-bonding layer formed on the support can be obtained. Further, as another method, the heat-bonded sheet of the first aspect can be obtained by extruding the above-mentioned silicone-modified polyamic acid or silicone-unmodified polyamic acid on the support by heating and melting without using a solvent. it can.

The thickness of the heat bonding layer 1 in the heat bonding sheet of the first embodiment thus obtained is appropriately set depending on the use of the heat bonding sheet, but is usually 5 to 500.
μm.

(2) Next, the heat-bonding sheet having a multilayer structure in which a heat-bonding layer is formed on at least one surface of a sheet-like porous substrate according to the second embodiment will be described. As one specific example of the thermal adhesive sheet of the second embodiment, as shown in FIG. 2, a thermal adhesive sheet 3 having a three-layer structure in which a thermal adhesive layer 1 is formed on both surfaces of a sheet-like porous substrate 2. Is raised. In addition,
Although not shown, the pores of the sheet-shaped porous substrate 2 are not impregnated with the material (adhesive) for forming the thermal bonding layer 1.

The material of the sheet-like porous substrate 2 is not particularly limited, but is preferably a fluororesin. Specifically, polytetrafluoroethylene (PTF
E), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyvinyl fluoride, polyvinylidene fluoride and the like, and PTFE is particularly preferred.
These may be used alone or in combination of two or more. The pore size and porosity of the fine pores of the sheet-like porous substrate 2 can be appropriately set, but usually the porosity is 10 to 95% and the pore size of the fine pores is 0.05 to 5 μm.

The material for forming the heat bonding layer 1 formed on at least one surface of the sheet-like porous substrate 2 is as follows.
The same materials as those described for the heat bonding sheet of the first embodiment are used.

The thermal adhesive sheet of the second embodiment is obtained, for example, by applying the thermal adhesive layer 1 obtained in the first aspect to at least one surface of the sheet-like porous substrate 2 at a temperature of 150 to 200 ° C. , At a pressure of 0.1 to 10 kg / cm ² .

The thickness of the sheet-like porous substrate 2 in the thus obtained heat-bonding sheet of the second embodiment is usually 1 to 500 μm, and the thickness of the heat-bonding layer 1 is usually , 5 to 500 μm. The total thickness of the thermal adhesive sheet is usually 6 to 1 in the case of a two-layer structure in which the thermal adhesive layer 1 is formed on one surface of the sheet-like porous substrate 2.
In the case of a three-layer structure in which the heat bonding layer 1 is formed on both sides of the sheet-like porous substrate 2,
1500 μm.

The heat-bonding sheet of the present invention thus obtained is the same as the heat-bonding sheet of any of the above embodiments.
It must have the following characteristics: (A) The elastic modulus at 250 ° C. is 10 MPa or less. (B) The elastic modulus at -80 ° C is 2000 MPa or less.

[0040] More preferably, the thermal adhesive sheet is 2
The elastic modulus at 50 ° C. is set to 8 MPa or less, and the elastic modulus at −80 ° C. is set to 1800 MPa or less. That is, if the elastic modulus at 250 ° C. exceeds 10 MPa, the adhesiveness and adhesion of the heat-adhesive sheet are poor, causing a problem during mounting reflow, and the elastic modulus at −80 ° C. is 2000 MPa.
Is exceeded, the thermal shock test at low temperature (TST
This is because cracks tend to occur in the test. The elastic modulus is a value obtained by measuring dynamic viscoelasticity at -80 ° C and 250 ° C at a frequency of 10 Hz using a dynamic viscoelasticity measuring device.

Although the application of the heat adhesive sheet of the present invention is not particularly limited, it is preferably used for forming a semiconductor device for adhering a semiconductor element to a circuit board. Specifically, as shown in FIG. 3, the semiconductor element 4 is placed on the printed circuit board 7 via an adhesive layer made of the thermal adhesive sheet 1 (or 3), and the semiconductor element 4 is connected to the semiconductor element 4 by wire bonding 5. The present invention can be used for a semiconductor device in which the circuit board 7 is electrically connected. In the drawing, 6 is a sealing resin, and 8 is a solder ball attached to the printed circuit board 7.

The material of the printed circuit board 7 is not particularly limited, and examples thereof include a ceramic substrate and a plastic substrate. Examples of the plastic substrate include an epoxy glass substrate, a bismaleimide triazine substrate, and a polyphenylene ether substrate.

The semiconductor device shown in FIG.
For example, it can be manufactured as follows. That is, first, the adhesive sheet 1 (or 3) is temporarily adhered to the printed circuit board 7, left arbitrarily, and the semiconductor element 4 is placed thereon, and then the adhesive sheet 1 (or 3) is fixed to a predetermined position. The printed circuit board 7 and the semiconductor element 4 are fully bonded by heating under the conditions described above to form an adhesive layer made of the adhesive sheet 1 (or 3). Conversely, first, the adhesive sheet 1 (or 3) may be temporarily bonded to the semiconductor element 4 and left arbitrarily, the printed circuit board 7 may be placed thereon, and then the actual bonding may be performed. Subsequently, after the semiconductor element 4 and the wiring circuit board 7 are electrically connected by wire bonding 5, the resin is sealed by forming a sealing resin 6 using a sealing material. Then, solder balls 8 are provided on the back surface of the printed circuit board 7.
By attaching the semiconductor device, a target semiconductor device can be manufactured.

Next, examples will be described together with comparative examples.

First, prior to Examples and Comparative Examples, a silicone-modified polyimide containing repeating units represented by the following formulas (9) to (17) as main components was prepared.

[0046]

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[0047]

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[0048]

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[0049]

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[0050]

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[0051]

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[0052]

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[0053]

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[0054]

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[0055]

Examples 1 to 7, Comparative Examples 1 and 2 A heat-bonding layer was formed using a silicone-modified polyimide containing repeating units of the type shown in Tables 1 to 3 below as main components. That is, first, an acid anhydride, a silicon-containing diamine, and a silicon-free diamine are reacted in equimolar amounts in N-methyl-2-pyrrolidone to form a repeating unit represented by the above formulas (9) to (17). A silicone-modified polyamic acid varnish or a silicone-unmodified polyamic acid varnish, which is a precursor of a silicone-modified polyimide as a main component, was prepared.
Then, after applying the silicone-modified polyamic acid varnish or the silicone-unmodified polyamic acid varnish on a Kapton film H which has been previously subjected to a release treatment,
By drying at a temperature of 0 ° C. and removing the solvent, a 25 μm-thick thermal adhesive layer was formed on the Kapton film H.
Then, this thermal adhesive layer is prepared to a thickness of 200 μm prepared in advance.
PTFE porous substrate (porosity 80%)
Lamination was performed at a temperature of 0 ° C. under a pressure of ² kg / cm ² to prepare a heat-bonding sheet (thickness: 250 μm) having a three-layer structure in which a heat-bonding layer was formed on both surfaces of a PTFE porous substrate.

[0056]

Example 8 and Comparative Examples 4 and 5 A heat-bonding sheet (thickness: 100 μm) having a single-layer structure consisting of only a heat-bonding layer was prepared without using a porous PTFE substrate.

[0057]

Comparative Example 3 200 μm thick PTFE was used in place of the 150 μm thick PTFE porous substrate (porosity 80%).
Except for using the sheet (porosity: 0%), a three-layer heat-bonding sheet (250 μm in thickness) was produced in the same manner as in Example 1.

[0058]

[Table 1]

[0059]

[Table 2]

[0060]

[Table 3]

Next, a semiconductor device was manufactured according to the above-described manufacturing method using the heat-bonding sheets of the respective Examples and Comparative Examples. That is, as shown in FIG. 3, the above-mentioned heat bonding sheet (size: 10 mm × 10 mm) is placed on a printed circuit board 7 (glass epoxy board having a thickness of 1 mm) at 170 ° C. × 20 seconds ×
Temporarily adhered at a pressure of 5 kgf / cm ² and left for a while,
A semiconductor element 4 (thickness: 350 μm, size: 10 m)
m × 10 mm), then 200 ° C. × 1 minute (pressure 5
The printed circuit board 7 and the semiconductor element 4 were adhered by forming an adhesive layer made of the thermal adhesive sheet 1 (or 3) under the condition of kgf / cm ² ). Subsequently, the semiconductor element 4 and the printed circuit board 7 were electrically connected by wire bonding 5 and then resin-sealed using a sealing resin 6. Then, a solder ball 8 was attached to the printed circuit board 7 to manufacture a semiconductor device.

With respect to the semiconductor devices using the thermal adhesive sheets of the examples and the comparative examples thus obtained, the amount of warpage of the chip, the pressure cooker test (PCT)
The subsequent adhesive strength and chip crack were measured according to the methods described below. Further, the elastic moduli of the thermal adhesive sheets of the above Examples and Comparative Examples were measured according to the method described above. These results are also shown in Tables 4 to 6 below.

[Amount of warpage of chip] 10 mm × 10 m
1 m of each heat-adhesive sheet on a silicone chip
Temporarily fixed under the condition of 70 ° C. × 10 seconds.
And Then, after curing at 200 ° C. for 60 minutes, the difference in height between the center and the end when completely bonded was measured, and this was defined as the amount of warpage of the chip.

[Adhesive strength after PCT] 121 ° C., 100%
The adhesive strength after storing at RH, 2 atm, and high temperature and high humidity for 24 hours was measured according to JIS Z0237.

[Chip Crack] A semiconductor device was manufactured in each of Examples 10
A thermal shock test [TST test (conditions: -50 ° C. × 5 minutes⇔125 ° C. × 5 minutes)] was performed using 500 pieces, and the number of cracks in the semiconductor chip was measured.

[0066]

[Table 4]

[0067]

[Table 5]

[0068]

[Table 6]

From the results shown in Tables 4 to 6, since the elastic modulus at 250 ° C. and the elastic modulus at −80 ° C. are all set to specific values or less, the thermal adhesive sheets of the examples are as follows.
It can be seen that the semiconductor device using this thermal adhesive sheet has a small amount of chip warpage, excellent adhesive strength after PCT, and no chip crack.

On the other hand, the thermal adhesive sheets of Comparative Examples 1 to 3 both have a specific modulus at 250 ° C. and a specific modulus at −80 ° C. It can be seen that the semiconductor device using the semiconductor device has a small amount of chip warpage and a high incidence of chip cracks.
In addition, it can be seen that the semiconductor devices using the thermal adhesive sheets of Comparative Examples 1 and 2 have extremely poor adhesive strength after PCT.
The thermal adhesive sheet of Comparative Example 4 has a modulus of elasticity at −80 ° C. exceeding a specific value. Therefore, a semiconductor device using this thermal adhesive sheet has a small amount of chip warpage deformation,
It can be seen that the incidence of chip cracks is high. Further, since the thermal adhesive sheet of Comparative Example 5 has an elastic modulus at 250 ° C. exceeding a specific value, the semiconductor device using this thermal adhesive sheet has a small amount of chip warpage deformation and a chip crack. It can be seen that the incidence is high.

[0071]

As described above, the thermal adhesive sheet of the present invention has an elastic modulus at 250 ° C. of 10 MPa or less and −
Since the elastic modulus at 80 ° C. is 2000 MPa or less, the thermal stress between the semiconductor element and the printed circuit board can be sufficiently reduced in the bonding application of the semiconductor element. Further, the semiconductor device using the heat bonding sheet has an excellent effect that the reliability of the electrical connection portion is excellent and the occurrence of cracks in the semiconductor chip or the semiconductor package can be prevented.

When the heat bonding sheet has a single-layer structure composed entirely of a heat bonding layer, it is temporarily bonded to a printed circuit board and then permanently bonded to a semiconductor chip regardless of shell life and pot life. It has the effect that it can be done. Conversely, the thermal bonding sheet may be temporarily bonded to the semiconductor chip first and then permanently bonded to the printed circuit board.

In the case where the heat bonding sheet has a multilayer structure in which a heat bonding layer is formed on at least one surface of a sheet-like porous substrate, the heat bonding sheet is bonded in two stages (sequential). In addition to the effect that can be done, the sheet-like porous substrate acts as a cushion, reducing distortion,
It has effects such as relaxation of stress and crack prevention.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of a heat bonding sheet of the present invention.

FIG. 2 is a schematic view showing another example of the thermal adhesive sheet of the present invention.

FIG. 3 is a cross-sectional view illustrating an example of a semiconductor device using the heat bonding sheet of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thermal adhesive layer 2 Sheet-shaped porous base material 3 Thermal adhesive sheet

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // H01L 21/52 H01L 21/52 E

Claims (9)

[Claims] 1. A thermal adhesive sheet having the following characteristics (A) and (B): (A) The elastic modulus at 250 ° C. is 10 MPa or less. (B) The elastic modulus at -80 ° C is 2000 MPa or less. 2. The heat bonding sheet according to claim 1, wherein the heat bonding sheet is for forming a semiconductor device in which a semiconductor element is bonded to a circuit board via itself. 3. The thermal adhesive sheet according to claim 1, wherein the thermal adhesive sheet is entirely composed of a thermal adhesive layer. 4. The thermal adhesive sheet according to claim 1, wherein the thermal adhesive sheet is formed by forming a thermal adhesive layer on at least one surface of a sheet-like porous substrate. 5. The heat bonding sheet according to claim 3, wherein the heat bonding layer is formed using a thermoplastic polyimide. 6. The thermal adhesive sheet according to claim 5, wherein the thermoplastic polyimide is a silicone-modified polyimide. 7. The thermal adhesive sheet according to claim 6, wherein the silicone-modified polyimide has at least one repeating unit selected from the group consisting of the following general formulas (1) to (7) as a main component. . Embedded image Embedded image Embedded image Embedded image Embedded image Embedded image Embedded image 8. The thermal adhesive sheet according to claim 4, wherein the sheet-like porous substrate is a fluorine-based porous sheet. 9. The thermal adhesive sheet according to claim 8, wherein the fluorine-based porous sheet is a polytetrafluoroethylene-made porous sheet.