JPH08311415A - Transfer sheet - Google Patents

Abstract

PURPOSE: To obtain a transfer sheet which prevents the staining on the front side of a semiconductor element and enables the formation of a polyimide film on the back side of the element by forming a specific adhesive layer on the surface of a substrate sheet and sticking a polyimide film to the surface of the adhesive layer under specified conditions. CONSTITUTION: This transfer sheet is produced by forming an adhesive layer 20b contg. a thermal blowing agent on the surface of a substrate sheet 20 and sticking a film 4a formed from at least either a polyimide or a polyimide precursor in the form of scattered spots to the surface of the adhesive layer 20b or is produced by successively forming a rubbery elastic layer 20c, an adhesive layer 20b contg. a thermal blowing agent, and an adhesive layer 20d contg. no thermal blowing agent on the surface of a substrate sheet 20 and sticking film 4a formed from at least either a polyimide or a polyimide precursor in the form of scattered spots on the surface of the adhesive layer 20d contg. no thermal blowing agent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer sheet used for forming a polyimide film distributed in a dotted pattern on a surface of a semiconductor element opposite to a circuit formation surface.

[0002]

2. Description of the Related Art Among semiconductor devices, a surface opposite to a circuit formation surface (hereinafter referred to as "front surface") of a semiconductor element (hereinafter referred to as "rear surface"), such as a lead-on-chip (hereinafter referred to as "LOC") semiconductor device. ")) Is in contact with the sealing resin. Examples of such a semiconductor device include a semiconductor device using a lead frame having a window opening die pad, a semiconductor device using a lead frame having a die pad smaller than a semiconductor element, in addition to the LOC type semiconductor device.

[0003]

In such a type of semiconductor device in which the back surface of the semiconductor element is in contact with the sealing resin, the adhesiveness between the sealing resin and the back surface of the semiconductor element is an important required characteristic. That is, if the adhesive force between the back surface of the semiconductor element and the sealing resin is weak, a gap is formed at the interface between the back surface of the semiconductor element and the sealing resin during heat treatment such as soldering when the semiconductor device is mounted on the circuit board. Occurs, the moisture absorbed by the sealing resin stays in this gap, and vaporizes and expands to generate pressure. As a result, a crack is generated in the sealing resin, a water entry path is formed in the semiconductor device, and the moisture resistance reliability of the semiconductor device is significantly reduced.

In order to solve this problem, various measures have hitherto been taken. For example, there is a method of predrying the semiconductor device to remove moisture absorbed by the sealing resin before heat treatment such as soldering. There is also a method of preventing the moisture absorption of the sealing resin by packaging the semiconductor device in a moisture-proof bag until immediately before heat treatment such as soldering. However, in the above pre-drying method, when the semiconductor device is soldered to the circuit board a plurality of times, the pre-drying process is required each time, which complicates the soldering process. Cause management problems. On the other hand, the method of packing with a moisture-proof bag has a problem that the moisture-proof bag costs a lot and the cost of the semiconductor device is improved. As another method, there is a method for improving the hygroscopicity of the sealing resin itself, but a method for improving the hygroscopicity of the sealing resin that completely prevents cracks in the sealing resin has not been completed. Is the reality.

Such a conventional crack prevention method for a semiconductor device is an ex post facto prevention method, and is not a fundamental solution. That is, the root cause of cracks in the semiconductor device is low adhesion between the back surface of the semiconductor element and the sealing resin. Focusing on this fact, a method of coating the back surface of the semiconductor element with a polyimide film in order to improve the adhesiveness between the back surface of the semiconductor element and the sealing resin has been proposed and partially implemented.

FIG. 9 shows an example in which this technique is applied to a LOC type semiconductor device. As shown in the figure, in this LOC type semiconductor device, one end of a lead frame 3 is located on the semiconductor element 1, and this end and the circuit of the semiconductor element 1 are connected by a metal wire 7. The whole and one end of the lead frame 3 are sealed with a sealing resin 2. In some cases, the entire back surface of the semiconductor element 1 is covered with the polyimide film 12, and the back surface of the semiconductor element 1 and the sealing resin 2 are in contact with each other via the polyimide film 12. In addition, the entire surface of the semiconductor element 1 excluding the connecting portion of the metal wire 7 is covered with the polyimide film 5. Further, one end of the lead frame 3 is fixed to the surface of the semiconductor element 1 with an adhesive 6 via a polyimide film 5.

As described above, when the back surface of the semiconductor element is covered with the polyimide film, the adhesiveness between the sealing resin and the semiconductor element is improved, and the resistance to thermal shock (thermal shock resistance) during solder mounting of the semiconductor device is also improved. It will improve. As a result, in a semiconductor device including such LOC, the moisture resistance reliability becomes excellent.

However, this method has the following problems. That is, in this method, the polyimide film is formed by applying a varnish of polyimide or its precursor to the back surface of the semiconductor element. For example, when the coating is performed by a spin coating method, the varnish is a semiconductor element wafer. There is a problem that it reaches the surface and contaminates it. Such a semiconductor device having the semiconductor element surface contaminated cannot operate correctly. As a method of solving the problem of the contamination of the surface of the semiconductor element, it is conceivable to adopt a method of spraying a gas on the surface of the semiconductor element wafer when the varnish such as polyimide is applied to the back surface of the semiconductor element by the spin coating method. However, this method has problems in terms of equipment cost and production efficiency, such as a special gas spraying device attached to the spinner used in the spin coating method, and gas management is also required. Further, there is a method of spraying pure water onto the surface of the semiconductor element wafer to prevent the varnish such as the polyimide from wrapping around. However, this method does not solve the problems of facility cost and production efficiency.

The present invention has been made in view of such circumstances, and a transfer sheet capable of efficiently forming a polyimide film on the back surface of a semiconductor element at a low cost without contaminating the surface of the semiconductor element. The purpose is to provide.

[0010]

In order to achieve the above object, the present invention provides an adhesive layer containing a heat-foaming agent on the sheet surface of a base material sheet, and polyimide and polyimide on the surface of the adhesive layer. A transfer sheet having a film formed from at least one of the precursors attached in a scattered manner is defined as a first gist, and a rubber elastic layer,
An adhesive layer containing a heating foaming agent, an adhesive layer containing no heating foaming agent, laminated in this order, formed from at least one of polyimide and polyimide precursor on the surface of the adhesive layer containing no heating foaming agent A second aspect is a transfer sheet to which a film is attached in a scattered manner.

[0011]

That is, the present inventors have conducted a series of studies for the purpose of developing a technique for forming a polyimide film on the back surface of a semiconductor element efficiently at low cost without contaminating the surface of the semiconductor element. In the process, the idea of forming a polyimide film on the back surface of the semiconductor element using a transfer sheet was invented. That is, in the conventional method, the contamination of the surface of the semiconductor element occurs because the spraying method or the coating method is adopted. Even if the contamination can be prevented to some extent by the improvement, cost and production efficiency are improved. This is because it is difficult to prevent the occurrence of pollution without the disadvantages such as the above. Then, the present inventors continued research based on this idea, and developed a transfer sheet capable of effectively forming a polyimide film on the back surface of a semiconductor element. As a result, they have invented two types of transfer sheets having the above-mentioned structure.

As described above, the transfer sheet of the present invention is
This is a foam release sheet having a base sheet and an adhesive layer containing a heat-foaming agent as a basic structure, and a film such as polyimide attached thereto. Specifically, a transfer sheet using a foamed release sheet having a relatively weak adhesiveness composed only of the above basic structure, and a rubber sheet having a rubber elastic layer and an adhesive layer containing no heating foaming agent in addition to the above basic structure. There are two types of transfer sheets that use a foamed release sheet with strong adhesiveness. They are,
It is appropriately selected according to various conditions in the step of forming the polyimide film on the back surface of the semiconductor element. Then, when the transfer sheet of the present invention is brought into contact with the back surface of the semiconductor element in a pressurized state and subjected to a heat treatment, the above heating foaming agent foams, and an unevenness is generated on the surface of the adhesive layer, resulting in an abrupt increase in area contributing to adhesion. Decrease, and the adhesive strength is reduced or disappears. Then, the film of polyimide or the like attached to the surface of the adhesive layer is transferred to and transferred to the back surface of the semiconductor element. When the film of the transfer sheet is a polyimide film, the polyimide film is formed on the back surface of the conductor element as it is. Further, when the film of the transfer sheet is a polyimide precursor film, by the imide conversion by the heat treatment at the time of the transfer or the heat treatment after the transfer to the back surface of the semiconductor element,
A polyimide film is formed on the back surface of the semiconductor element. Thus, by using the transfer sheet of the present invention,
Since the polyimide varnish and the like do not wrap around, the surface of the semiconductor element is not contaminated, and complicated operations such as alignment can be simplified. In addition, since the foam release sheet is used, the transfer process can be performed under mild conditions, and the efficiency of the polyimide film forming process can be improved. Since the film such as polyimide of the transfer sheet is in the form of dots, the polyimide film formed on the back surface of the semiconductor element is also distributed in the form of dots.
As described above, the reason why the dot-like pattern is formed is that, according to the research conducted by the present inventors, even if a polyimide film is formed in a dot-like pattern, it is equivalent to forming a polyimide film on the entire back surface of the semiconductor element. This is because it is possible to obtain the effect of preventing the occurrence of cracks, and it is advantageous in terms of material cost.

When a polyimide, a polyamic acid or a partially imidized polyamic acid represented by the general formulas (1) to (14) described later is used, the adhesiveness between the back surface of the semiconductor element and the sealing resin is remarkably high. To improve,
The effect of preventing cracks is further improved.

Next, the present invention will be described in detail.

As described above, the transfer sheet of the present invention is
There are two types: one using a foam release sheet having a relatively weak adhesive force (A type) and one using a foam release sheet having a relatively strong adhesive force (B type).

FIG. 1 shows a sectional view of an example of an A type transfer sheet. As shown in the figure, this transfer sheet comprises a foam release sheet 20A and a film 4a of polyimide or the like. The foam release sheet 20A is a base sheet 20a.
An adhesive layer 20b containing a heat-foaming agent is formed on the sheet surface. Then, the film 4a of polyimide or the like is attached in a scattered manner on the surface of the adhesive layer 20b. As a specific example of this foam release sheet, Japanese Patent Application No.
Those described in Japanese Patent No. 228861 are listed.

Examples of the base sheet include plastic films, paper, woven fabrics, non-woven fabrics, metal foils, and laminates of these. Among these, a plastic film is preferable, and a polyester film is particularly preferable, because it is less likely to be wrinkled. And the thickness of this base material sheet is usually 5 μm to 5 mm.
And preferably 10 μm to 1 mm, particularly preferably 25 μm to 250 μm.

The above-mentioned adhesive layer containing the heat-foaming agent has an adhesive force before heating and adheres a film of polyimide or the like, but when heated, the action of the heat-foaming agent causes the adhesive force to be drastically reduced. It will disappear.

As the base polymer of the adhesive layer, it is preferable to use a high elastic polymer, and it is particularly preferable that the dynamic elastic modulus at room temperature (20 to 30 ° C.) to 150 ° C. is 250,000 to 10 million dyne / cm. ² and optimally 500,000 to 8,000,000 dyne / cm ² . That is, the dynamic elastic modulus is 250,000 dyne /
This is because if it is less than cm ² , the adhesive strength of the adhesive layer at room temperature becomes unnecessarily high, which may cause a problem such as a decrease in adhesive strength during heat treatment. On the contrary, the dynamic elastic modulus is 1
If it exceeds 10 million dyne / cm ² , the adhesive strength at room temperature will be insufficient, the film such as polyimide adhered to the surface of the adhesive layer may fall off, and the foaming of the heating foaming agent may be hindered. Is. Further, the dynamic elastic modulus of the high-elasticity polymer preferably has a small change rate from room temperature to 150 ° C., and a specific preferable range is 5 times or less, and optimally 3 times or less.

No particular limitation is imposed on the monomer component forming the above high-elasticity polymer, and there are known publicly known acrylic pressure-sensitive adhesives, rubber pressure-sensitive adhesives, styrene / conjugated diene block copolymer type pressure-sensitive adhesives, and the like. The monomer component used for the pressure-sensitive adhesive of is mentioned.

Specific examples thereof include methyl group, ethyl group, propyl group, butyl group, 2-ethylhexyl group, isooctyl group, isononyl group, isodecyl group, dodecyl group, lauryl group, tridecyl group, pentadecyl group, hexadecyl group, Acrylic acid-based alkyl ester such as acrylic acid or methacrylic acid having an alkyl group having 20 or less carbon atoms such as heptadecyl group, octadecyl group, nonadecyl group, eicosyl group, acrylic acid, methacrylic acid, itaconic acid, hydroxyethyl acrylate , Hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, N-methylol acrylamide, acrylonitrile, methacrylonitrile, glycidyl acrylate, glycidyl methacrylate,
Examples thereof include vinyl acetate, styrene, isoprene, butadiene, isobutylene, vinyl ether and the like.

The above conditions (conditions such as dynamic elastic modulus)
It is also possible to use a natural rubber or a reclaimed rubber satisfying the requirements as the base polymer.

Next, the above heating foaming agent is not particularly limited, and various inorganic or organic heating foaming agents can be used. As the inorganic type, water,
Examples thereof include ammonium carbonate, ammonium hydrogen carbonate, sodium hydrogen carbonate, ammonium nitrite, sodium borohydride, azides and the like. Further, as the above-mentioned organic type, chlorofluorinated alkanes such as trichloromonofluoromethane and dichloromonofluoromethane, azobisisobutyronitrile, azodicarbonamide, azo compounds such as barium azodicarboxylate, Paratolusulfonylsulfonyl hydrazide, diphenyl sulfone-
Hydrazine compounds such as 3,3′-disulfonyl hydrazide, 4,4 ′ oxybis (benzenesulfonyl hydrazide) and allyl bis (sulfonyl hydrazide), ρ
-Toluylenesulfonyl semicarbazide, semicarbazide compounds such as 4,4'-oxybis (benzenesulfonyl semicarbazide), 5-morpholyl-1,2,
Triazole compounds such as 3,4-thiatriazole, N, N′-dinitrosopentamethylenetetramine,
There are N-nitroso compounds such as N, N'-dimethyl-N, N'-dinitrosoterephthalamide.

Further, it is preferable to use a microencapsulated heat-foaming agent because it can be easily mixed and the like. Specific examples thereof include thermally expandable particles in which gas components such as butane, propane and pentane are microencapsulated. Examples of the capsule-forming material for the microcapsules include vinylidene chloride-acrylonitrile copolymer, polyvinyl alcohol, polyvinyl butyral, polyacrylonitrile copolymer, polyvinylidene chloride, and polysulfone. When the heat-expandable particles are used, it is preferable that the particle size portion is narrow, and the width is usually 1 to 2
5 μm. That is, if the width of the particle size distribution is large, the decrease in adhesive strength may be hindered.

The blending ratio of such a heat-foaming agent is usually 1 to 100 parts, preferably 5 to 50 parts, particularly preferably 10 to 100 parts by weight of the above base polymer (hereinafter abbreviated as "part"). It is 40 copies. The foaming temperature of this heat-foaming agent is usually 100 to 250 ° C, and the treatment time is 1 to 90 seconds.

If desired, various additives such as a foaming aid, a cross-linking agent, a tackifier, a plasticizer, a filler and an antiaging agent can be blended with the heating foaming agent. is there. This mixing ratio is such that the gel content of the base polymer is 4
The range is 0% by weight or more, preferably 50% by weight or more, and particularly preferably 70% by weight or more.

Next, using the above materials, an A type transfer sheet can be produced as follows.

That is, first, in a solvent, the above-mentioned base polymer, the heat-foaming agent, and if necessary various additives are blended in a predetermined ratio and mixed. Examples of the solvent include toluene. Then, the toluene solution is applied to the sheet surface of the base material sheet, and an adhesive layer containing a heating foaming agent by removing the solvent by heating and drying treatment (hereinafter referred to as "heating foaming agent-containing adhesive layer"). To form a foam release sheet. The thickness of the adhesive layer is usually 1 to 500 μm, preferably 5 to 100 μm. The adhesive strength of the above-mentioned heat-foaming agent-containing adhesive layer before heating is usually 100 g / 20 mm or more, preferably 200
It is 2,500 g / 20 mm. The adhesive strength after the heat treatment is 300 g / 20 mm or less, preferably 150
g / 20 mm or less. The rate of decrease in the adhesive strength is usually 50% or more, preferably 65% or more, and most preferably 75% or more.
This decrease in adhesive strength can be appropriately adjusted depending on the types and blending amounts of the base polymer and the heat-foaming agent used.

Next, a film 4a made of at least one of polyimide and a polyimide precursor is attached to the surface of the heat-foaming agent-containing adhesive layer of the foamed release sheet in a scattered manner to form an A type transfer. Sheet is prepared.

The above-mentioned polyimide is not particularly limited, but in order to improve the adhesiveness between the back surface of the semiconductor element and the sealing resin, the following general formulas (1) to (7) are used.
It is preferable to use the one represented by

[0031]

[Chemical 15]

[0032]

Embedded image

[0033]

[Chemical 17]

[0034]

Embedded image

[0035]

[Chemical 19]

[0036]

Embedded image

[0037]

[Chemical 21]

These polyimides can be formed by heating the below-mentioned polyamic acid or partially imidized polyamic acid to convert the imide.

In addition to the above polyimide, a film of a polyimide precursor may be applied to the transfer sheet of the present invention. That is, in the transfer sheet, a polyimide film may be already formed and transferred to the back surface of the semiconductor element, or a polyimide precursor film may be formed and transferred to the back surface of the semiconductor element or after transfer. In, the imide conversion may be performed to form a polyimide film. This can be appropriately determined depending on various circumstances of the manufacturing process of the semiconductor device.

The polyimide precursor is not particularly limited, but the polyamic acids represented by the following general formulas (8) to (14) and these polyamic acids are partially imide-converted. It is preferable to use partially imidized polyamic acid. As described above, these polyamic acids and the like are precursors of the polyimides represented by the general formulas (1) to (7).

[0041]

[Chemical formula 22]

[0042]

[Chemical formula 23]

[0043]

[Chemical formula 24]

[0044]

[Chemical 25]

[0045]

[Chemical formula 26]

[0046]

[Chemical 27]

[0047]

[Chemical 28]

These polyamic acids are prepared by reacting the following acid anhydride, silicon-containing diamine, and silicon-free diamine by a conventional method.

Examples of the acid anhydride include, for example, 3,
3 ', 4,4'-biphenyltetracarboxylic dianhydride, 3,3', 4,4'-benzophenone tetracarboxylic dianhydride, pyromellitic dianhydride, 2,2-bis (3,4) -Dicarboxyphenyl) propane dianhydride,
2,2-bis (3,4dicarboxyphenyl) hexafluoropropane dianhydride, 2,2-bis (2,3-dicarboxyphenyl) propane dianhydride, bis (3,4-
Dicarboxyphenyl) sulfone dianhydride, bis (3,3
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 can be mentioned.

Of these aromatic tetracarboxylic dianhydrides, preferred are 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride and 3,3', 4,4 '.
-Benzophenone tetracarboxylic dianhydride, 2,2-
Bis (3,4-dicarboxyphenyl) propane dianhydride, 2,2-bis (2,3-dicarboxyphenyl) propane dianhydride, bis (3,4-dicarboxyphenyl) sulfone dianhydride, bis (3,4-dicarboxyphenyl) ether dianhydride and the like. By using such an acid dianhydride, it becomes possible to firmly bond the back surface of the semiconductor element and the sealing resin, particularly the epoxy resin. Although other acid anhydrides can be used, in order to obtain the same effect as the above preferable aromatic tetracarboxylic acid dianhydride, the application of the present invention, together with the sealing resin of the semiconductor device, It suffices to take measures such as limiting the water absorption rate or setting the solder mounting temperature lower.

As the above-mentioned diamine, a silicon-containing diamine and a silicon-free diamine are commonly used, and the ratio of the diamine is 1 to 5 for the silicon-containing diamine based on the total amount of the silicon-containing diamine and the silicon-free diamine. 0.0 mol%
Is preferred. That is, if it is less than 1 mol%, the adhesive force between the back surface of the semiconductor element and the sealing resin tends to be weak, and conversely, if it exceeds 5.0 mol%, the strength of the polyimide film at the solder mounting temperature decreases. Because there is a tendency.

As the silicon-containing diamine, diaminosiloxane represented by the following general formula (15) is preferably used. More specifically, for example, bis (3-aminopropyl) tetramethyldisiloxane, bis (3-aminobutyl) tetramethyldisiloxane, α, ω-bis (3-aminopropyl) polydimethyldisiloxane and dimethylpolysiloxane. It has a primary amine at both ends of siloxane.

[0053]

[Chemical 29]

Examples of the silicon-free diamine include 2,2-bis [4- (4-aminophenoxy) phenyl] propane and bis [4- (4-aminophenoxy) diamine.
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,
Examples thereof include 3'-diaminodiphenyl sulfide, 4,4'-diaminobenzanilide, p-phenylenediamine and m-phenylenediamine.

Among these, a preferable silicon-free diamine is 2,2-bis [4- (4-aminophenoxy)
Phenyl] propane, bis [4- (4-aminophenoxy) phenyl] ether, bis [4- (4-aminophenoxy) phenyl] sulfone, 1,4-bis (4-aminophenoxy) benzene. Particularly preferably, 2,
2-bis [4- (4-aminophenoxy) phenyl] propane. As described above, when a suitable silicon-free diamine is used, the adhesiveness between the back surface of the semiconductor element and the sealing resin, especially the epoxy resin becomes extremely excellent.

The preferred combinations of the acid anhydride, silicon-containing diamine, and silicon-free diamine are shown in Tables 1 to 1 below.
It shows in Table 5.

[0057]

[Table 1]

[0058]

[Table 2]

[0059]

[Table 3]

[0060]

[Table 4]

[0061]

[Table 5]

Preferred specific examples of the polyamic acid used in the present invention are represented by the following general formulas (8) to (14):
It is shown below together with the effect of adopting this.

[Specific Example of General Formula (8)]

Embedded image

(Effect of adoption) 85 ° C., 85
The adhesive force (90 ° peel adhesive force) between the silicon wafer and the polyimide film at 260 ° C. after saturated moisture absorption at% RH for 336 hours becomes high (measured value example: 1050 g / c
m).

[Specific Example of General Formula (9)]

[Chemical 31]

(Effect of adoption) 85 ° C., 85
The adhesive force (90 ° peel adhesive force) between the silicon wafer and the polyimide film at 260 ° C. after saturated moisture absorption at% RH for 336 hours becomes high (example of measured value: 1100 g / c
m).

[Specific Example of General Formula (10)]

Embedded image

(Effect of adoption) 85 ° C., 85
The adhesive force (90 ° peel adhesive force) between the silicon wafer and the polyimide film at 260 ° C. after saturated moisture absorption at% RH for 336 hours becomes high (example of measured value: 950 g / c
m).

[Specific Example of General Formula (11)]

[Chemical 33]

(Effect of adoption) 85 ° C., 85
The adhesive force (90 ° peel adhesive force) between the silicon wafer and the polyimide film at 260 ° C. after saturated moisture absorption at% RH for 336 hours becomes high (example of measured value: 600 g / c
m).

[Specific Example of General Formula (12)]

Embedded image

(Effect of adoption) 85 ° C., 85
The adhesive force (90 ° peel adhesive force) between the silicon wafer and the polyimide film at 260 ° C. after saturated moisture absorption at% RH for 336 hours becomes high (example of measured value: 560 g / c
m).

[Specific Example of General Formula (13)]

Embedded image

(Effect of adoption) 85 ° C., 85
The adhesive force (90 ° peel adhesive force) between the silicon wafer and the polyimide film at 260 ° C. after saturated moisture absorption at% RH for 336 hours becomes high (example of measured value: 1200 g / c
m).

[Specific Example of General Formula (14)]

Embedded image

(Effects of adoption) 85 ° C., 85
The adhesive force (90 ° peel adhesive force) between the silicon wafer and the polyimide film at 260 ° C. after saturated moisture absorption at% RH for 336 hours becomes high (example of measured value: 880 g / c
m).

Next, the film 4a formed of at least one of the polyimide and the polyimide precursor can be attached to the surface of the adhesive layer containing a heating foaming agent by using an attachment sheet as shown in FIG. It is preferable from the viewpoint of production efficiency and the like. As shown in the figure, this attachment sheet is one in which a film 4b of polyimide or the like is formed on the sheet surface of the support sheet 30.

The support sheet is not particularly limited as long as the film such as polyimide formed on the sheet surface can be peeled off. Examples of the support sheet include a polymer film separator. Specific examples thereof include a polyester film separator, a polyimide film separator, a polyolefin film separator, an engineering plastic film separator, and a fluororesin film separator. The engineering plastics include polybutylene terephthalate (PBT), polyamide (PA), polyphenylene ether (PPE),
Examples thereof include polyacetal (POM), polyphenylene sulfide (PPS), polyether sulfone (PES) and polycarbonate (PC). The fluororesin film may be, for example, a tetrafluoroethylene resin film. Among these polymer films, it is preferable to use a polyester film separator or a polyolefin film separator because of its heat resistance and low cost, and a polyester film separator is particularly preferable. Further, it is preferable that the support sheet is subjected to a silicone coating treatment in order to facilitate the peeling of the film of polyimide or the like.

Next, the polyimide precursor varnish is applied to the sheet surface of the support sheet in a scattered manner, and then the solvent is removed, or after the solvent is removed, the polyimide precursor is converted into polyimide by heating or the like. By doing so, a film of polyimide or the like can be formed.

As the varnish of the above polyimide precursor,
For example, a varnish prepared by dissolving at least one of the polyamic acids represented by the general formulas (8) to (14) in an amide-based organic solvent can be used.

As the amide-based organic solvent, N-methyl-2-pyrrolidone, N, N-dimethylacetamide,
Highly polar organic solvents such as N, N-dimethylformamide, N, N-dimethylsulfoxide, and hexamethylphosphoramide can be used. Of these, N-methyl-2-pyrrolidone is preferably used because of the high solubility of polyamic acid.

The polyamic acid varnish can be prepared by a conventional method using the acid anhydride, silicon-containing diamine, silicon-free diamine, and amide organic solvent.
For example, in a reaction vessel, in the presence of the above-mentioned highly polar organic solvent, while flowing an inert gas such as nitrogen gas, usually 60
The acid anhydride, the silicon-containing diamine, and the silicon-free diamine are reacted with each other while limiting the temperature to not more than 30 ° C., particularly preferably not more than 30 ° C. This reaction is preferably performed until a high degree of polymerization is obtained. Then, after this polymerization reaction, it is preferable to carry out a heat aging step to reduce the solution viscosity or to adjust the solid content concentration to an optimum state for the spot-like coating described later.

It is possible to add silica powder or the like to the above polyamic acid varnish for the purpose of imparting thixotropic properties, but this is not necessary because the strength of the film of polyimide or the like obtained may decrease. As long as you do not dare to mix.

The viscosity of the above polyamic acid varnish (25 ° C.,
Hereinafter the same) is usually 1 to 1000 dPa · s, preferably 10 to 500 dPa · s, and particularly preferably 20 to 2
It is 00 dPa · s. The solid content is usually 5 to 40% by weight, preferably 10 to 35% by weight, and particularly preferably 15 to 25% by weight in terms of concentration by weight.

Next, this polyamic acid varnish is applied to the sheet surface of the above-mentioned support sheet in a scattered manner, and the solvent is removed by heat treatment. In the heat treatment, the polyamic acid may be partially or completely converted to an imide, or as described below, the transfer sheet of the present invention may be partially or completely converted to an imide. Further, the imide conversion may be completed on the back surface of the semiconductor element.

For coating the polyamic acid varnish, a general coating method such as a dispenser method or a screen printing method can be applied.

In coating the support sheet on the sheet surface by the dispenser method, appropriate needle inner diameter, coating pressure and coating time are set so that coating can be performed with dots having a diameter of about 0.1 mm to 10 mm. Is desirable. The diameter of the dot (point) is preferably 0.5 mm to
It is 5 mm, and particularly preferably 0.3 mm to 3 mm. It is preferable that the dots are distributed at the same pitch as the diameter or at a pitch narrower than this.

After coating by the dispenser method,
Generally, in a temperature range of 120 ° C. or higher, a solvent is volatilized and a polyamic acid (polyimide precursor) film is formed by step curing and drying to a high temperature range (about 180 ° C.) if necessary. . In addition, in this heat treatment, by adjusting the temperature and time, the polyamic acid is converted into polyimide, whereby a polyimide film can be formed. For example, a heat treatment at 180 ° C. or lower forms a polyamic acid-based film, and a heat treatment at 200 ° C. or higher forms a polyimide-based film. The majority of polyamic acid (70%)
Is composed of polyamic acid, but a part of polyimide is formed. Similarly, a polyimide-based material is mainly composed of polyimide (about 70%) but partially composed of polyamic acid. Say. Therefore, in the present invention, there are two types of partially imidized polyamic acid, one mainly containing polyimide and the other mainly containing polyamic acid.

If there is no possibility that defects such as foaming will occur in the film obtained, continuous constant temperature rising may be performed instead of the above step cure. The thickness of the polyamic acid film or the polyimide film is usually 0.
It is 1 to 50 μm, preferably 1 to 25 μm. And when applying this dispenser method, it is preferable to employ the multi-dispenser method using a multi-needle from the viewpoint of production efficiency.

Next, as the screen printing method, a general method can be applied, but a screen suitable for this is selected in order to form a film that is distributed in a scattered spot like the dispenser method. Preferably. Further, as described above, since it is preferable to use a highly polar organic solvent, it is better to avoid using an emulsion type screen that easily dissolves in it, and to use a metal screen with excellent durability. preferable.
The shape of the dots on the screen is not particularly limited,
It may be a circle, triangle, square, etc. Then, after applying the polyamic acid varnish by the screen printing method, heat treatment is performed in the same manner as in the dispenser method, the solvent is removed, and the polyamic acid is converted to polyimide as necessary, and dispersed. It is possible to form a polyamic acid-based film or a polyimide-based film that is distributed in a dot pattern.

Although the dot-like coating of the polyamic acid varnish is described by taking the dispenser method and the screen printing method as examples, the present invention is not limited to this. In addition to this, conventionally, it is possible to apply a transfer method, a brush coating method, a gravure printing method, or the like, which is capable of spot-like coating.

In this way, a film made of at least one of polyimide and a polyimide precursor is formed on the sheet surface of the support sheet, and an adhesion sheet can be prepared.

Next, using this adhesive sheet, a film of polyimide or the like is adhered to the surface of the heat-foaming agent-containing adhesive layer of the foam release sheet. That is, as shown in FIG. 4, the adhesion sheet and the foam release sheet 20 are provided with the coating 4
It is arranged so that b and the heating foaming agent-containing adhesive layer face each other. Then, as shown in the figure, they are pressed against each other. This pressure contact can be performed by, for example, a pressure press or a pressure roll press, and the conditions are usually 1 to 100 kg /
cm ² . After this press-contacting treatment, by separating them from each other, the film 4b of the adhesion sheet moves to and adheres to the surface of the heat-foaming agent-containing adhesive layer of the foam release sheet 30. In this way, an A type transfer sheet is produced.

The attachment of the film of polyimide or the like to the surface of the heat-foaming agent-containing adhesive layer is not limited to the method using the above-mentioned attachment sheet. In addition to this, there is a method of directly forming the above film on the surface of the heat-foaming agent-containing adhesive layer, and this formation can be performed in the same manner as the film formation of the above-mentioned adhesion sheet. As will be described later, since the total coating area of the polyimide coating formed on the back surface of the semiconductor element is preferably 10% or more, the coating such as polyimide of the transfer sheet may adhere according to this proportion. preferable.

Next, the B type transfer sheet of the present invention will be described. FIG. 2 shows a cross-sectional view of an example of this transfer sheet. As shown in the figure, this transfer sheet is composed of a foam release sheet 20B having a relatively strong adhesive force and a film 4a of polyimide or the like. The foam release sheet 20B
Is the rubber elastic layer 20 on the sheet surface of the base material sheet 20a.
c, a heat-foaming agent-containing adhesive layer 20b, and a heat-foaming agent-free adhesive layer 20d (hereinafter referred to as "heat-foaming agent-free adhesive layer") are laminated in this order. in this way,
In addition to the basic structure of the base sheet 20a and the heat-foaming agent-containing adhesive layer 20b, the heat-foaming agent-free adhesive layer is used as the surface layer, whereby the adhesive force of the foam release sheet becomes strong. Further, by interposing the rubber elastic layer 20c between the base material sheet 20a and the heat-foaming agent-containing adhesive layer 20b, the peelability of the film 4a at the time of heat treatment is excellent. That is, this foam release sheet is a high-performance one having improved adhesive strength and releasability at the same time. Then, the coating film 4a of polyimide or the like is attached to the surface of the heating foaming agent-free adhesive layer 20d in a scattered manner. Examples of this foam release sheet include those described in Japanese Patent Application No. 5-226527.

As the above-mentioned substrate sheet, the same ones as described above are used, and the thickness thereof is usually 5 to 250 μm.

As a material for forming the rubber elastic layer, AS is used.
Examples include natural rubber and synthetic rubber having a Shore D type hardness of 50 or less, preferably 40 or less by D type Shore of TM D-2240, or a synthetic resin having rubber elasticity.
Examples of the synthetic rubber or synthetic resin include nitrile-based, diene-based, acrylic-based synthetic rubbers, polyolefin-based or polyester-based thermoplastic elastomers,
Examples thereof include those having rubber elasticity such as ethylene-vinyl acetate copolymer, polyurethane, polybutadiene, and soft polyvinyl chloride. Even an essentially hard polymer such as polyvinyl chloride can be used by adding rubber elasticity by blending a plasticizer or a softening agent.

The rubber elastic layer can be formed, for example, by dissolving the above-mentioned natural rubber, synthetic rubber, synthetic resin or the like in a solvent, applying the solution to the sheet surface of the base material sheet, and drying the solution. it can. Alternatively, a rubber elastic sheet may be formed in advance using the above material, and this may be attached to the base material sheet. The thickness of this rubber elastic layer is usually 1
˜300 μm, preferably 2 to 100 μm, particularly preferably 5 to 50 μm.

The rubber elastic layer improves the releasability of the foamed release sheet by the following mechanism. That is, when the heat-foaming agent-containing adhesive layer is foamed by heating and its shape is deformed, the rubber elastic layer suppresses deformation in the sheet surface direction and promotes deformation in the sheet thickness direction. is there. As a result, the deformation in the sheet thickness direction of the heating foaming agent-free adhesive layer formed on the heating foaming agent-containing adhesive layer also becomes large, and as a result, the contact area contributing to adhesion can be sharply reduced. Therefore, the peeling of the film adhering to this surface is promoted.

Next, the heat-foaming agent-containing adhesive layer is the same as that described above, and the same materials and forming methods are used. The blending ratio of the heat-foaming agent is usually 10% by weight or more, preferably 15 to 95% by weight, based on the whole adhesive layer.
Optimally, it is in the range of 20 to 80% by weight. The thickness of the heat-foaming agent-containing adhesive layer is generally 3 to 70 μm.
Is. The expansion coefficient of foaming of the heat-foaming agent-containing adhesive layer is preferably set to 1.5 to 100 times, which is appropriately selected by selecting the kind and blending ratio of the above heat-foaming agent, and the kind of base polymer. It can be adjusted accordingly.

The heat-foaming agent-free adhesive layer formed on the above-mentioned heat-foaming agent-containing adhesive layer preferably has an adhesive force suitable for the application of the transfer sheet. Therefore,
The adhesive to be used is also not particularly limited, and is appropriately determined depending on the above application. Usually, as the adhesive, a low temperature activation type heat-activatable adhesive, water or organic solvent-activatable adhesive, pressure-sensitive adhesive or the like is used.

Examples of the heat-activatable adhesive and water or organic solvent-activatable adhesive include hot-melt adhesives, silicone adhesives, fluorine-based adhesives, UV-curable adhesives,
A heat-sensitive pressure-sensitive adhesive containing a heat-melting resin having a low melting point and having a low adhesive force at room temperature and exhibiting a strong adhesive force by heating (Japanese Patent Application Laid-Open No. 56-13040, Japanese Patent Publication No. 2-50146), etc. I can give you.

As the pressure-sensitive adhesive, a rubber-based pressure-sensitive adhesive containing natural rubber or various synthetic rubbers as a base polymer, a polymer of an alkyl ester of acrylic acid or methacrylic acid, and other unsaturated compounds. Acrylic pressure-sensitive adhesive using a copolymer with a monomer as a base polymer, a polymer having a weight average molecular weight of about 10,000 to 3,000,000 as a base polymer, and if necessary, a polyisocyanate compound or an alkyl etherified melamine A compound containing an appropriate amount of a cross-linking agent such as a compound, styrene / conjugated diene block copolymer type pressure-sensitive adhesive, silicone pressure-sensitive adhesive, UV-curable pressure-sensitive adhesive, creep-improving pressure-sensitive adhesive Etc. (for example, JP-A-56-
61468, Japanese Patent Laid-Open No. 61-174857,
JP-A-63-17981, JP-B-56-1304
No. 0).

If necessary, various additives such as a cross-linking agent, a plasticizer, an antiaging agent, and a tackifier can be added to such an adhesive.

Then, if necessary, the above-mentioned various additives are mixed with the above-mentioned adhesive, dissolved in a solvent, and this is applied on the layer of the above-mentioned heat-foaming agent-containing adhesive layer and dried to heat it. A foaming agent-free adhesive layer can be formed. The thickness of the heat-foaming agent-free adhesive layer is preferably thin from the viewpoint of improving releasability, but in consideration of workability in forming and adhesive strength, the thickness is usually about 0.1 to 50 μm, preferably 0. It becomes 5 to 30 μm.

As described above, by laminating the rubber elastic layer, the heat-foaming agent-containing adhesive layer, and the heat-foaming agent-free adhesive layer on the sheet surface of the base material sheet in this order, foaming having a relatively strong adhesive force is obtained. A release sheet is produced. In addition, like this,
In addition to sequentially laminating each layer to produce a foam release sheet, a laminated body in which a rubber elastic layer, a heating foaming agent-containing adhesive layer, and a heating foaming agent-free adhesive layer are sequentially laminated is separately prepared, and this is used as a base sheet. It can also be produced by sticking to the surface.

Then, a B-type transfer sheet can be prepared by attaching a film of polyimide or the like to the surface of the heat-foaming agent-free adhesive layer of this foam release sheet. The coating can be attached in the same manner as the above-mentioned method.

Next, a method of manufacturing a semiconductor device using the transfer sheet of the present invention will be described.

In the method for manufacturing a semiconductor device of the present invention, prior to encapsulating a semiconductor element with a cured product (encapsulating resin) of a resin composition, the transfer sheet is used and a dotted polyimide is formed on the back surface of the semiconductor element. It is a manufacturing method characterized by forming a film. There are two types of transfer sheets of the present invention, an A type having a relatively weak adhesive force and a B type having a relatively strong adhesive force, but the manufacturing method of a semiconductor device using these is basically the same, It is used properly according to various conditions for manufacturing semiconductor devices.

That is, first, the surface of the transfer sheet to which the film such as polyimide is attached is brought into contact with the back surface of the semiconductor element. Then, for example, through a cushion material, by thermal transfer by pressure hot press, or by a thermal transfer method using a heating head such as a hot bar or pulse heat, the film such as polyimide of the transfer sheet is coated on the back surface of the semiconductor element. And transfer to.

The above heating conditions are appropriately adjusted depending on the kind of the film, and in the case of a polyimide precursor such as polyamic acid, the heating condition is 2
It is a condition of 00 to 300 ° C. Further, when the polyimide precursor is a partially imidized polyamic acid, 220 to 3
The condition is 00 ° C. The polyimide precursor is
The imide conversion is also caused by the heat treatment at the time of this transfer. When the film is polyimide, the temperature is 300 ° C or higher. In addition, although this heating condition exceeds the peeling temperature (90 to 150 ° C.) of the foam release sheet constituting the transfer sheet, there is no particular problem.

The above-mentioned pressurization is adjusted to such a pressure and time that chip cracks do not occur in the film. In general,
This condition is a pressure of 0.1 to 5 kg / cm ² × 5 to 30 seconds.

After the transfer process (heating and pressing process), the foam release sheet is separated to form a polyimide film distributed in a dotted pattern on the back surface of the semiconductor element. When the polyimide film is not completely imide-converted, it is preferable to carry out post-curing treatment (post-cure) after forming the film. This condition is usually 300 ° C. for 1 minute or longer, preferably 300 ° C. for 2 minutes or longer. The total area covered by this polyimide film is preferably 10% or more of the back surface of the semiconductor element, particularly preferably 15% or more, and most preferably 20% or more.
Practically, it is set to 10 to 80%. That is, when the area covered with the polyimide film on the back surface of the semiconductor element is less than 10%, the adhesive force between the back surface of the semiconductor element and the sealing resin may not be improved. In addition, this transfer process may be performed on a semiconductor element that has been diced from a silicon wafer, or may be performed on a semiconductor element before dicing.

Next, a semiconductor element having a predetermined polyimide film formed on the back surface is mounted on, for example, a lead frame, wire-bonded, and resin-sealed to manufacture a semiconductor device. Conventionally known methods can be applied to mounting the semiconductor element on the lead frame, wire bonding, and resin sealing.

The formation of the polyimide film using the transfer sheet of the present invention is not limited to the back surface of the semiconductor element,
It may be done on the die pad surface of the lead frame. Then, a semiconductor element is mounted on the surface of this die pad and resin-sealed to manufacture a semiconductor device. The semiconductor device thus obtained, by the action of the polyimide film,
Improves thermal shock resistance.

In the present invention, the transfer sheet may be used to form a polyimide film on the back surface of the die pad. That is, the back surface of the die pad also comes into direct contact with the sealing resin, and similarly there is a problem of crack generation.
The polyimide film can be formed on the back surface of the die pad in the same manner as on the back surface of the semiconductor element.

It is also preferable to form a polyimide film on the surface of the semiconductor element. This polyimide film can be formed in the same manner as in the conventional method. That is, as the material used for this formation, a conventionally known polyimide varnish, the above polyimide varnish, or the like can be used. As in the conventional case, the shape of the polyimide film is preferably layered so as to cover the entire surface of the semiconductor element (excluding the connecting portion of the metal wire).

An example of the semiconductor device thus manufactured is shown in FIG. In the figure, an example of a LOC type semiconductor device is shown. As shown in the figure, in this semiconductor device, one end of the lead frame 3 is located on the semiconductor element 1, and this end and the circuit of the semiconductor element 1 are connected by a metal wire 7, and the whole of the semiconductor element 1 is connected. One end of the lead frame 3 is sealed with the sealing resin 2. And
The entire back surface of the semiconductor element 1 is covered with a polyimide film 4 distributed in a scattered manner, and the semiconductor element 1 is covered with the polyimide film 4.
The back surface is in contact with the sealing resin 2. Further, the entire surface of the semiconductor element 1 excluding the connecting portion of the metal wire 7 is covered with the polyimide film 5. Then, one end of the lead frame 3 is fixed to the surface of the semiconductor element 1 via a polyimide film 5 with a polyimide tape 6 or the like.

FIG. 6 shows an example in which the transfer sheet of the present invention is applied to a semiconductor device using a lead frame having a window opening die pad. As shown in the figure, in this semiconductor device, the semiconductor element 1 is mounted on the window opening die pad 8 in a state of being fixed by a silver paste cured body 9. One end of the lead frame 3a is located near the side surface of the semiconductor element 1, and this end and the circuit of the semiconductor element 1 are connected by a metal wire 7. The back surface of the semiconductor element 1 is exposed from the opening of the die pad 8, and the polyimide film 4 is formed on the back surface of the semiconductor element 1 in a dotted pattern, while the front surface of the semiconductor element 1 is a connection portion of the metal wire 7. The entire surface except for is covered with the polyimide film 5. Then, the entire semiconductor element 1, the die pad 8 and one end of the lead frame 3a are sealed with the sealing resin 2, and the back surface of the semiconductor element 1 is covered with the sealing resin 2 via the polyimide film 4 distributed in a scattered manner. Is in contact with.

FIG. 7 shows an example in which the transfer sheet of the present invention is used for a semiconductor device using a lead frame having a die pad whose die pad area is smaller than the back surface of the semiconductor element. As shown in the figure, in this semiconductor device, the semiconductor element 1 is mounted on the die pad 10 smaller than the back surface of the semiconductor element 1. One end of the lead frame 3b is located near the side surface of the semiconductor element 1, and this end and the circuit of the semiconductor element 1 are connected by a metal wire 7. The back surface of the semiconductor element 1 is covered with a polyimide film 4 distributed in a scattered manner on the entire surface including the portion protruding from the die pad 10, and the front surface of the semiconductor element 1 except for the connecting portion of the metal wire 7. The entire surface is covered with the polyimide film 5. Then, the entire semiconductor element 1, the die pad 10, and one end of the lead frame 3b are sealed with the sealing resin 2, and the portion of the back surface of the semiconductor element 1 that protrudes from the die pad 10 is covered with the scattered polyimide film 4. Is in contact with the sealing resin 2.

FIG. 8 shows an example of a semiconductor device in which a dotted polyimide film is formed on the back surface of the die pad. As illustrated, the semiconductor chip 1a is mounted on the die pad 10a to form the semiconductor element 1. This semiconductor device 1
Then, since the area of the die pad 10a is larger than the area of the back surface of the semiconductor chip 1a, the back surface of the semiconductor chip 1a does not contact the sealing resin 2, but the back surface of the die pad 10a contacts. Other than this, the structure is the same as that of the semiconductor device shown in FIG. 4, and the same portions are denoted by the same reference numerals. As described above, when the dotted polyimide film is formed on the back surface of the die pad 10a (back surface of the semiconductor element 1), the adhesive force between the back surface of the die pad 10a and the sealing resin 2 is improved, and the moisture resistance reliability of the semiconductor device is improved. It will improve.

[0122]

As described above, in the transfer sheet of the present invention, the film formed of polyimide or the like is attached to the foam release sheet in a scattered manner. By using this transfer sheet, it becomes possible to form a polyimide film on the back surface of the semiconductor element while preventing contamination of the surface of the semiconductor element without providing a special device or process. As a result, it is possible to effectively prevent the occurrence of defective products in the manufacture of semiconductor devices. Further, by using the transfer sheet of the present invention, it is not necessary to use a special device or equipment such as a spinner in forming the polyimide film on the back surface of the semiconductor element. Then, the polyimide film formed using the transfer sheet of the present invention is distributed in a dotted manner,
It does not cover the entire back surface of the semiconductor element. Therefore, by adopting this transfer sheet, it is possible to reduce the material cost required for forming the polyimide film.

Further, the polyimide represented by the general formula (1) to the general formula (7), the general formula (8) to the general formula (1)
4) A transfer sheet using at least one of the polyamic acid represented by 4) and the partially imidized polyamic acid obtained by partially imidizing the polyamic acid. The adhesiveness with the antistatic resin is remarkably improved, and the obtained semiconductor device has further excellent moisture resistance reliability and thermal shock resistance.

Next, examples will be described together with comparative examples.

[0125]

Example 1 Using N-methyl-2-pyrrolidone as a solvent,
1 mol of 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride, 0.965 mol of 2,2-bis [4- (4-aminophenoxy) phenyl] propane and bis (3
-Aminopropyl) tetramethyldisiloxane to 0.0
After reacting at a ratio of 35 moles, it was aged and polyamic acid varnish (concentration: 20% by weight concentration, viscosity: 150 dPa
-S) was prepared.

On the other hand, a polyester film separator (thickness: 50 μm) whose surface is treated with a silicone coat is used.
m) was prepared. Then, the polyamic acid varnish,
Filled in a syringe equipped with a needle having an inner diameter of 0.18 mm, under the conditions of a pressure of 3 kg / cm ² and a discharge time of 0.5 seconds,
For the surface of the polyester film separator,
Dispensing coating was performed at a pitch of 1 mm. Then 1
Under the condition of 50 ° C. × 2 hours, heat drying treatment is performed in an oven to give a thickness of 5 on the surface of the polyester film separator.
A polyamic acid film having a thickness of μm was formed in a scattered manner to prepare a target adhesion sheet. The polyamic acid film is a partially imidized polyamic acid film mainly containing polyamic acid.

On the other hand, a foam release sheet (No. 3194)
M, manufactured by Nitto Denko Corporation) was prepared. This has a structure as shown in FIG. Then, as described above, the foam release sheet and the adhesion sheet are faced to each other (see FIG. 4), and pressure-pressed at room temperature to adhere the polyamic acid film to the foam release sheet, thereby transferring the desired transfer. A sheet (A type) was obtained.

Next, this transfer sheet was made to have a thickness of 50 m.
It was placed on the steel sheet of m with the transfer surface (polyamic acid film forming surface) facing upward with the silicone rubber cushioning material interposed therebetween. Then, a semiconductor element previously cut into 12 mm square chips by dicing from a silicon wafer was placed on the transfer sheet such that the back surface of the semiconductor element was in contact with the transfer surface. Then, using a hot bar, a temperature of 250
The polyamic acid film was transferred to the back surface of the semiconductor element under the conditions of temperature of 1 ° C., pressure of 1 kg / cm ² , and pressure time of 10 seconds while the chip was fixed. And, this semiconductor element is 300 ° C. × 2
A heat treatment was performed in an oven under the conditions of time, and the above polyamic acid was imide-converted into polyimide, and a polyimide film having a coverage of 30% and distributed in a dotted pattern was formed on the back surface of the semiconductor element. The surface of the semiconductor element was not contaminated during the formation of this polyimide film.

Next, this semiconductor element was mounted on a LOC type lead frame, electrically connected with a gold wire, and then resin-molded by transfer molding with an epoxy resin, and the epoxy resin Curing treatment (175 hours × 5 hours) was performed to manufacture a semiconductor device (see FIG. 5).

After curing the above epoxy resin (175 ° C. × 5
Diffusion coefficient of water at 1.89 exp (-4749)
/ T) and the solubility coefficient of water is 2.20E-6ex.
p (4911 / T). The water diffusion coefficient and the water solubility coefficient are values measured according to Fick's diffusion equation. In the above semiconductor device, the thickness of the sealing resin from the back surface of the semiconductor element to the bottom of the sealing resin is 0.963 mm. When an operation test was performed on this semiconductor device, the operation was normal.

Infrared rays (IR) of the film immediately after transfer (mainly polyamic acid) on the back surface of the semiconductor element and the film imide converted by the above heat treatment after transferred to the back surface of the semiconductor element.
The spectrum was measured. The results are shown in FIG. 10 and FIG.
It is shown in the graph of No. 1. The graph of FIG. 10 is an IR spectrum immediately after transfer (partially imidized polyamic acid), and the graph of FIG. 11 is the imide conversion (polyimide).
It is an IR spectrum of. From FIGS. 10 and 11, it can be seen that the partially imidized polyamic acid was completely imide converted by the heat treatment to form the polyimide film.

The solder crack resistance of the semiconductor device thus obtained was examined. That is,
Place the semiconductor device in a thermo-hygrostat at 85 ° C and 85% RH.
It was left for 36 hours. The water absorption rate of the sealing resin of the semiconductor device by this treatment was 0.55%. Immediately after the above treatment, it was immersed in a high-temperature solder bath at 260 ° C., and the time at which cracks occurred was measured. As a result, this Example 1
In the semiconductor device of No. 1, no crack was generated even after 2 minutes.

[0133]

Example 2 In place of 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride, 3,3', 4,4'-benzophenonetetracarboxylic dianhydride was used, and the back surface of the semiconductor device was used. The coating rate was 25%. A semiconductor device was manufactured in the same manner as in Example 1 except for the above. In the production of this semiconductor device, the surface of the semiconductor element was not contaminated, and the semiconductor device operated normally. When the solder package crack resistance of this semiconductor device was examined in the same manner as in Example 1, no crack was generated even after 2 minutes.

[0134]

Example 3 The same polyamic acid varnish as in Example 1 was used.
Using a metal screen capable of printing a 0.5 mm square pattern at a pitch of 0.3 mm, the same screen printing method as described above was applied to the transfer surface of the same polyester film separator as in Example 1, and the same treatment as in Example 1 was performed. An applied polyimide film was formed. Except for this, a transfer sheet was produced in the same manner as in Example 1, and using this, a semiconductor device was produced in the same manner as in Example 1. In this semiconductor device, the polyimide coating formed on the back surface of the semiconductor element had a thickness of 15 μm and a coverage of 35%. Further, in the fabrication of this semiconductor device, the surface of the semiconductor element was not contaminated, and the semiconductor device operated normally.
Then, when the semiconductor device was examined for solder package crack resistance in the same manner as in Example 1, no crack was generated even after 2 minutes.

[0135]

Example 4 The same polyamic acid varnish as in Example 1 was used.
Using a metal screen capable of printing a 0.5 mm square pattern at a pitch of 0.3 mm, the transfer surface of the same polyester film separator as in Example 1 was applied by the above-described screen printing method, and then the same treatment as in Example 1 was performed. Was applied to form a polyamic acid film, and then a transfer sheet was prepared in the same manner as in Example 1. Using this transfer sheet, a dotted polyimide film (thickness 6 μm) was formed on the back surface of the silicon wafer before dicing by the method described above. Then, after dicing, 12 m from the silicon wafer
A semiconductor chip having a size of m × 12 mm was cut out. This semiconductor chip is opened in a window die pad (13 mm × 13
It was mounted on a lead frame having a die pad having a size of mm and an opening of 11 mm × 11 mm formed therein. The semiconductor chip (semiconductor element) was fixed to the die pad of the lead frame using a die bond silver paste. A semiconductor device was manufactured in the same manner as in Example 1 except for this. In this semiconductor device, the coverage is 35
%Met. Further, in the fabrication of this semiconductor device, the surface of the semiconductor element was not contaminated, and the semiconductor device operated normally. Then, when the semiconductor device was examined for solder package crack resistance in the same manner as in Example 1, no crack was generated even after 2 minutes.

[0136]

[Embodiment 5] The coverage of the polyimide film distributed in a dotted pattern on the back surface of the semiconductor device was set to 10%. A semiconductor device was manufactured in the same manner as in Example 1 except for this. In manufacturing this semiconductor device, the surface of the semiconductor element was not contaminated, and the semiconductor device operated normally. Then, when the solder package crack resistance of this semiconductor device was examined in the same manner as in Example 1, no crack was generated even after 30 seconds had elapsed.

[0137]

Example 6 A transfer sheet having a polyimide-based film was prepared. That is, a polyamic acid varnish was prepared in the same manner as in Example 1, and was applied to the transfer surface of the polyester film separator in a scattered manner. And 2
Drying treatment was carried out under the condition of 20 ° C. × 1 hour to prepare a transfer sheet having a film mainly composed of polyimide.

Using the above transfer sheet, a semiconductor device was manufactured in the same manner as in Example 1. Then, when the solder crack resistance of this semiconductor device was examined in the same manner as in Example 1, no crack was generated even after 2 minutes.

[0139]

Example 7 A strong adhesion type foam release sheet (see FIG. 2) was prepared. In this foam release sheet, the thickness of the base material sheet 20a is 100 μm, the thickness of the rubber elastic layer 20c is 10 μm, and the thickness of the heating foaming agent-containing adhesive layer 20b is 2 μm.
0 μm and the thickness of the heating foaming agent-free adhesive layer 20d is 10
μm. Then, using this foam release sheet, a film was attached in the same manner as in Example 1 to produce a B type transfer sheet. Then, using this transfer sheet, a polyimide film was formed on the back surface of the semiconductor element in the same manner as in Example 1 to manufacture a semiconductor device. Then, a soldering resistance package crack test was conducted on this semiconductor device in the same manner as in Example 1. As a result, no crack was generated in this semiconductor device even after 2 minutes from immersion.

[0140]

Example 8 A transfer sheet (A type) was prepared in the same manner as in Example 1. Then, using this, a polyimide film is formed on the back surface of a die pad of a lead frame on which a semiconductor element is mounted, and then a semiconductor device is assembled by electrically connecting with a gold wire. The device was made. Then, when the semiconductor device was examined for solder package crack resistance in the same manner as in Example 1, no cracks were generated until 30 seconds had passed after immersion in the high temperature solder bath.

[0141]

[Embodiment 9] In dispenser coating, the coating pitch was widened (3 mm intervals), and the coverage of the back surface of the semiconductor element with the polyimide film distributed in a scattered manner was 5%. A semiconductor device was manufactured in the same manner as in Example 1 except for this. When the solder crack resistance of this semiconductor device was examined, cracks occurred in 24 seconds.

[0142]

Example 10 In place of 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride was replaced with 2,2-bis [4- (4-aminophenoxy) phenyl]. The same molar amount of 4,4'-diaminophenyl ether was used instead of propane. Further, the coverage of the back surface of the semiconductor element with the polyimide film distributed in a scattered manner was 37%. A semiconductor device was manufactured in the same manner as in Example 1 except for this. When the solder crack resistance of this semiconductor device was examined, a crack occurred in 28 seconds.

[0143]

Comparative Example Using the same polyamic acid varnish as in Example 1,
It was applied on the surface of a silicon wafer by spin coating and then dried and cured to form a polyimide film. No polyimide film was formed on the back surface of the silicon wafer. Then, a semiconductor device was manufactured in the same manner as in Example 1, and the resistance to package cracking was examined in the same manner as in Example 1. As a result, a crack occurred in this semiconductor device in 12 seconds.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an example of a transfer sheet of the present invention.

FIG. 2 is a cross-sectional view of another example of the transfer sheet of the present invention.

FIG. 3 is a cross-sectional view of an example of an attachment sheet used for producing the transfer sheet of the present invention.

FIG. 4 is an explanatory view illustrating the production of a transfer sheet using the above-mentioned attachment sheet.

FIG. 5 is a cross-sectional view showing the configuration of an example of a semiconductor device manufactured using the transfer sheet of the present invention.

FIG. 6 is a cross-sectional view showing the configuration of another embodiment of a semiconductor device manufactured using the transfer sheet of the present invention.

FIG. 7 is a cross-sectional view showing the structure of another example of a semiconductor device manufactured using the transfer sheet of the present invention.

FIG. 8 is a cross-sectional view showing the configuration of another example of a semiconductor device manufactured using the transfer sheet of the present invention.

FIG. 9 is a cross-sectional view showing a configuration of a conventional semiconductor device.

FIG. 10 is a graph of IR spectrum of partially imidized polyamic acid.

FIG. 11 is a graph showing an IR spectrum of polyimide.

[Explanation of symbols]

 20a Base sheet 20b Adhesive layer containing heating foaming agent 4a Film

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H01L 21/56 H01L 21/56 T

Claims (4)

[Claims] 1. An adhesive layer containing a heat-foaming agent is formed on the sheet surface of a substrate sheet, and a film formed from at least one of polyimide and a polyimide precursor is scattered on the surface of the adhesive layer. A transfer sheet characterized by being attached. 2. A rubber elastic layer is provided on the sheet surface of the substrate sheet,
An adhesive layer containing a heating foaming agent, an adhesive layer containing no heating foaming agent, laminated in this order, formed from at least one of polyimide and polyimide precursor on the surface of the adhesive layer containing no heating foaming agent A transfer sheet having a film attached in a scattered manner. 3. The transfer sheet according to claim 1, wherein the polyimide is at least one of the polyimides represented by the following general formulas (1) to (7). Embedded image Embedded image Embedded image [Chemical 4] Embedded image [Chemical 6] [Chemical 7] 4. The polyimide precursor comprises a polyamic acid represented by the following general formula (8) to general formula (14) and a polyamic acid represented by the following general formula (8) to general formula (14). The transfer sheet according to any one of claims 1 to 3, which is at least one of partially imidized polyamic acid which is partially imido-converted. Embedded image [Chemical 9] [Chemical 10] [Chemical 11] [Chemical 12] [Chemical 13] Embedded image