JP4915034B2 - Epoxy resin composition and semiconductor device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor sealing epoxy resin with improved storage stability and a semiconductor device excellent in solder crack resistance.
[0002]
[Prior art]
Transfer molding of an epoxy resin composition as a sealing method for semiconductor elements such as IC and LSI is suitable for mass production at low cost and has been used for a long time. Improvements have been made to improve properties.
However, due to the recent trend toward smaller, lighter, and higher performance electronic devices, semiconductors have become more highly integrated and surface mounting of semiconductor devices has been promoted. The demand for compositions has become increasingly severe. For this reason, the problem which cannot be solved with the conventional epoxy resin composition has also come out.
The biggest problem is that by adopting surface mounting, the semiconductor device is suddenly exposed to a high temperature of 200 ° C. or higher in the solder dipping or solder reflow process, and the moisture when moisture absorbed explosively vaporizes the semiconductor device. This is a phenomenon in which cracks occur or peeling occurs at the interface between various plated joints on the semiconductor element, lead frame, and inner lead and the cured product of the epoxy resin composition, and the reliability is significantly reduced.
[0003]
In order to improve the reliability degradation due to solder reflow treatment, increase the filling amount of fused silica powder in the epoxy resin composition to achieve low moisture absorption, high strength, low thermal expansion and improve solder resistance At the same time, it is becoming common to use a low melt viscosity resin to maintain a low viscosity and high fluidity during molding.
On the other hand, in the reliability by the solder reflow process, the adhesiveness at the interface between the cured product of the epoxy resin composition and the base material such as a semiconductor element or a lead frame present in the semiconductor device has become very important. If the adhesive force at the interface is weak, peeling occurs at the interface with the base material after the solder reflow process, and further cracks of the semiconductor device due to the peeling occur.
Many structures have been proposed for epoxy resins and phenolic resins from the viewpoint of improving the adhesive strength at the interface. Particularly, epoxy resins of general formula (1) and phenolic resins of general formula (2) were used as curing agents. It is known that the epoxy resin composition has the characteristics of flexibility and low hygroscopicity, so that the stress generated during solder reflow treatment after moisture absorption is low, and it has excellent solder crack resistance (Japanese Patent Laid-Open No. Hei 5). -343570, JP-A-6-80763, JP-A-8-143648, etc.).
[0004]
In recent years, electrical and electronic materials, especially sealing materials for semiconductors, have been required to improve their preservability in order to improve their production efficiency at the time of fast curing and logistics and storage. Yes. Conventionally, epoxy resins for the electric / electronic materials field include amines, imidazole compounds, nitrogen-containing heterocyclic compounds such as diazabicycloundecene, quaternary ammonium, phosphonium or arsonium compounds as curing accelerators. Various compounds have been used.
While amines, especially imidazoles, etc. show excellent curability, they cause corrosion of internal wiring under high-temperature and high-humidity conditions as semiconductor sealing materials, that is, moisture resistance reliability tends to decrease. There are problems with the use of phosphorous compounds such as phosphonium compounds.
These generally used curing accelerators often exhibit a curing accelerating action even at a relatively low temperature such as room temperature, which means that the viscosity increases during production and storage of the epoxy resin composition, and the fluidity decreases. This is a cause of deterioration in quality as an epoxy resin composition due to variations in curability and the like.
[0005]
In order to solve this problem, in recent years, researches on so-called latent curing accelerators that suppress a change in viscosity and fluidity at low temperatures with time and develop a curing reaction only by heating during molding have been actively conducted. As a means for this, a proposal has been made to express latency by protecting the active site of the curing accelerator with an ion pair. JP-A-8-41290 discloses salt structures of various organic acids and phosphonium ions. A latent cure accelerator is disclosed. However, this phosphonium salt does not have a specific high-order molecular structure, and the ion pair is relatively easily affected by the external environment. Therefore, the phosphonium salt is easily moved by molecules such as recent low-molecular epoxy resins and phenol aralkyl resins. In the sealing material for semiconductors using resin, the problem that storage property falls is produced.
[0006]
[Problems to be solved by the invention]
The present invention relates to an epoxy resin composition for semiconductor encapsulation which has improved curability and storage stability by using a novel curing accelerator, a resin having excellent flexibility and moisture absorption resistance, and a semiconductor having excellent solder crack resistance. A device is provided.
[0007]
[Means for Solving the Problems]
The present invention
[1] (A) Epoxy resin represented by general formula (1), (B) phenol resin represented by general formula (2), (C) fused silica powder, and (D) molecule represented by general formula (3) An epoxy resin composition for semiconductor encapsulation, characterized by comprising a compound,
[0008]
[Formula 4]
(R is a group selected from a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, which may be the same or different. N is a positive number of 1 to 5 on average. )
[0009]
[Chemical formula 5]
(R is a group selected from a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, which may be the same or different. N is a positive number of 1 to 5 on average. )
[0010]
[Chemical 6]
(P is a phosphorus atom, R ₁ is a substituted or unsubstituted aromatic group or an alkyl group, which may be the same or different. X is an alkyl group having 1 to 5 carbon atoms, an oxygen atom, R is a group selected from a sulfur atom and a sulfone group, and R is a group selected from an alkyl group having 1 to 4 carbon atoms, which may be the same or different, and m is 0 ≦ m ≦. Indicates the number of 1.)
[0011]
[2] The epoxy resin composition for semiconductor encapsulation according to item [1], wherein X of the molecular compound represented by the general formula (3) is a sulfone group,
[3] A semiconductor device comprising a semiconductor element sealed using the epoxy resin composition for semiconductor sealing according to [1] or [2],
It is.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
The epoxy resin represented by the general formula (1) used in the present invention is an epoxy resin having two or more epoxy groups in one molecule, and has a hydrophobic structure between the epoxy groups. The cured product of the combination of the epoxy resin and the phenol resin has a low crosslink density and a large hydrophobic structure. Therefore, the moisture absorption is low, and the thermal stress at the time of molding the epoxy resin composition or the semiconductor device which is a molded product. Reduces the thermal stress generated in the solder reflow treatment after moisture absorption and has excellent adhesion to the substrate. On the other hand, since the hydrophobic structure between epoxy groups is a rigid diphenylene skeleton, it has a feature that there is little decrease in heat resistance for a low crosslinking density.
[0013]
Specific examples of the epoxy resin represented by the general formula (1) are shown below, but are not limited thereto.
[Chemical 7]
[0014]
As long as the properties of the epoxy resin represented by the general formula (1) used in the present invention are not impaired, it can be used in combination with other epoxy resins. Examples of epoxy resins that can be used in combination include monomers, oligomers, and polymers having an epoxy group, such as biphenyl type epoxy resins, stilbene valve type epoxy resins, hydroquinone type epoxy resins, bisphenol F type epoxy resins and other crystalline epoxy resins, bisphenols. Examples include A-type epoxy resins, ortho-cresol novolac-type epoxy resins, dicyclopentadiene-modified phenol-type epoxy resins, triphenolmethane-type epoxy resins, and naphthol-type epoxy resins. These epoxy resins may be used alone or in combination. In particular, in order to increase the filling amount of the fused silica powder of the epoxy resin composition, the crystalline epoxy resin which exhibits crystallinity at room temperature and whose melt viscosity is remarkably reduced at the molding temperature is preferable.
[0015]
The characteristics of the phenol resin represented by the general formula (2) used in the present invention are the same as those of the epoxy resin represented by the general formula (1). When combined with the phenolic resin of (2), the maximum effect is obtained in reliability such as low moisture absorption of the semiconductor device, solder crack resistance in the solder reflow treatment after moisture absorption, and adhesion.
[0016]
Although the specific example of the phenol resin shown by General formula (1) is shown below, it is not limited to these.
[Chemical 8]
[0017]
In the range which does not impair the characteristic of the phenol resin shown by General formula (2) used for this invention, it can use together with another phenol resin. Examples of phenol resins that can be used in combination include monomers, oligomers, and polymers having phenolic hydroxyl groups, such as phenol novolac resins, cresol novolac resins, xylylene modified phenol resins, terpene modified phenol resins, dicyclopentadiene modified phenol resins, bisphenol A, Examples include triphenolmethane. These phenol resins may be used alone or in combination. In order to improve the low hygroscopicity of the cured product of the epoxy resin composition and the adhesion to the substrate, those having a hydroxyl equivalent weight of 130 to 210 are particularly suitable.
[0018]
Examples of the fused silica powder used in the present invention include natural silica melted in a flame and synthetic silica obtained by hydrolyzing tetramethoxysilane, tetraethoxysilane and the like. There are spherical silica and crushed silica depending on the shape and manufacturing method.
As a compounding quantity of a fused silica powder, 75 to 93 weight% is preferable in all the epoxy resin compositions. If it is less than 75% by weight, the moisture absorption of the cured product of the epoxy resin composition is increased, and the strength at the soldering process temperature is lowered. On the other hand, if it exceeds 93% by weight, the fluidity at the time of molding the epoxy resin composition is lowered, and unfilling, semiconductor element shift and pad shift are likely to occur, which is not preferable. In particular, in order to highly fill the fused silica powder, a spherical one is preferable. A wide particle size distribution is effective for reducing the melt viscosity of the resin composition during molding.
[0019]
The molecular compound represented by the general formula (3) that acts as a curing accelerator in the present invention is a molecular aggregate of a tetra-substituted phosphonium and a phenol compound. Consists of one tetra-substituted phosphonium cation, one or more and less than three phenolic hydroxyl groups and one phenoxide anion unit, and one or more and less than three phenolic groups around the positive charge of the tetra-substituted phosphonium ion It is considered that the hydroxyl group and one phenoxide anion surround and are a stabilized structure.
[0020]
R _{1 of the} molecular compound represented by the general formula (3) is a substituted or unsubstituted aromatic group or an alkyl group. Specifically, tetraaryl-substituted phosphonium such as tetraphenylphosphonium and tetratolylphosphonium, triphenylmethyl Examples thereof include triarylmonoalkylphosphonium synthesized from triarylphosphine such as phosnium and alkyl halide, and tetraalkyl-substituted phosphonium such as tetrabutylphosphonium.
Moreover, as a phenol compound which is another component which forms a molecular compound, the bis (4-hydroxyphenyl) sulfone (bisphenol S) shown by Formula (4) is the stability of a molecular compound, sclerosis | hardenability, and hardened | cured material property. Best in terms.
[0021]
[Chemical 9]
(P represents a phosphorus atom and Ph represents a phenyl group. M represents a number of 0 ≦ m ≦ 1.)
[0022]
Molecular compounds include the above-mentioned phenolic compounds and bases that ultimately help dehydrohalogenation, such as alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, organic bases such as pyridine and triethylamine, and solvents such as alcohols. Then, the tetra-substituted phosphonium halide dissolved in an appropriate solvent is added and reacted, and finally, it is taken out as a solid content by operations such as recrystallization and reprecipitation, or tetra-substituted phosphonium tetra-substituted borate And a phenol compound can be synthesized by a heat reaction in a solvent such as alcohol after a thermal reaction.
[0023]
The molecular compound used in the present invention has a phosphonium-phenoxide type salt in the structure as described above. However, the molecular compound is different from the conventional phosphonium-organic acid anion salt type compound in that the proton of the phenolic hydroxyl group is different in the molecular compound. The higher-order structure due to the hydrogen bonds involved surrounds this ionic bond. In the conventional salt, the reactivity was controlled only by the strength of the ionic bond, whereas in the molecular compound, the ion pair of the reaction active site is surrounded by a higher order structure at room temperature, and the active site is protected. On the other hand, in the actual molding stage, the higher-order structure is broken, so that the active sites are exposed, and so-called latency, which expresses reactivity, is imparted. There is no problem even if it is used in combination with a curing accelerator such as triphenylphosphine, 1,8-diazabicyclo (5,4,0) undecene-7, 2-methylimidazole, etc., as long as the properties of the molecular compound are not impaired.
[0024]
The compounding amount of the molecular compound acting as a curing accelerator used in the present invention is 0.5 when the total weight of all epoxy resins (A) and all phenol resins (B) acting as curing agents is 100 parts by weight. About 20 parts by weight is preferable because of good balance between curability, storage stability and other characteristics. Moreover, the compounding ratio of the total epoxy resin (A) and the total phenol resin (B) is the phenol contained in the phenolic hydroxyl group and the molecular compound of the total phenol resin (B) with respect to 1 mol of the epoxy group of the total epoxy resin (A). When used in a molar ratio of about 0.5 to 2 mol, preferably about 0.8 to 1.2 in total with the curable hydroxyl group, the curability, heat resistance, electrical properties, etc. are improved.
[0025]
In addition to the components (A) to (D), the epoxy resin composition of the present invention includes a coupling agent such as γ-glycidoxypropyltrimethoxysilane as necessary, a colorant such as carbon black, a phosphorus compound, and the like. Flame retardants, low stress components such as silicone oil and silicone rubber, natural wax, synthetic wax, higher fatty acids or metal salts thereof, mold release agents such as paraffin, and various additives such as antioxidants.
In the epoxy resin composition of the present invention, the components (A) to (D) and other additives are mixed using a mixer or the like, then heated and kneaded using a heating kneader or a hot roll, and then cooled and pulverized. It is obtained by doing.
In order to seal an electronic component such as a semiconductor element and produce a semiconductor device using the epoxy resin composition of the present invention, it may be cured by a conventional molding method such as a transfer mold, a compression mold, or an injection mold. .
[0026]
Hereinafter, the present invention will be specifically described with reference to Examples. The blending unit is parts by weight.
[Synthesis of curing accelerator]
Hereinafter, the structure of the synthesized molecular compound was confirmed by NMR, elemental analysis, and neutralization titration (measurement of phosphonium phenoxide equivalent) by the following method.
The synthesized molecular compound is reacted with an excess amount of oxalic acid with a known weight in a methanol / water solvent, and the remaining oxalic acid is quantified with an aqueous sodium hydroxide solution with a known normality. N / g) was calculated. The reciprocal of this value is the phosphonium phenoxide equivalent.
[0027]
In a 1-liter separable flask equipped with a stirrer, 37.5 g (0.15 mol) of BPS-N (mainly composed of 4,4′-bisphenol S) manufactured by Nikka Chemical Co., Ltd. and 100 ml of methanol The solution was charged and dissolved with stirring at room temperature, and a solution prepared by dissolving 4.0 g (0.1 mol) of sodium hydroxide in advance with 50 ml of methanol was added with further stirring. Next, a solution prepared by previously dissolving 41.9 g (0.1 mol) of tetraphenylphosphonium bromide in 150 ml of methanol was added. After stirring for a while and adding 300 ml of methanol, the solution in the flask was added dropwise to a large amount of water with stirring to obtain a white precipitate. The precipitate was filtered and dried to obtain 66.0 g of white crystals. This compound is designated as C1. C1 is a target molecular compound in which one molecule of tetraphenylphosphonium and 4,4′-bisphenol S are complexed at a molar ratio of 1: 1.5 from the results of NMR, maspectrum and elemental analysis. It was done. Further, from the value of neutralization titration, the phosphonium phenoxide equivalent was close to the theoretical value 713, and the structure of the formula (4) was confirmed. The synthesis yield was 92.6%. This is designated as a curing accelerator (a).
[0028]
Example 1
5.9 parts by weight of epoxy resin of formula (5) (epoxy equivalent 274, softening point 60 ° C.)
[0029]
Phenol aralkyl resin of formula (6) (hydroxyl equivalent: 203, softening point: 67 ° C.)
4.3 parts by weight
[0030]
Curing accelerator (a) 0.3 parts by weight fused spherical silica powder 88.0 parts by weight Inorganic ion exchanger 0.5 parts by weight carbon black 0.3 parts by weight γ-glycidoxypropyltrimethoxysilane 0.3 parts by weight After mixing 0.4 parts by weight of carnauba wax using a mixer, kneading 30 times using two rolls having surface temperatures of 90 ° C. and 45 ° C. A resin composition was obtained. The obtained epoxy resin composition was evaluated by the following methods. The results are shown in Table 1.
[0031]
Evaluation Method Spiral Flow: Using a mold for spiral flow measurement according to EMMI-1-66, measurement was performed at a mold temperature of 175 ° C., an injection pressure of 70 kg / cm ² , and a curing time of 2 minutes. The unit is cm.
Water absorption: Using a transfer molding machine, a molded product having a mold temperature of 175 ° C., an injection pressure of 75 kg / cm ² , a curing time of 2 minutes and a diameter of 50 mm and a thickness of 3 mm is molded and post-cured at 175 ° C. for 8 hours. The molded product thus obtained was allowed to stand for 168 hours in an environment of 85 ° C. and a relative humidity of 85%, and the weight change before and after water absorption was measured to calculate the water absorption rate. Unit is% by weight
Solder crack resistance: 100-pin TQFP (package size: 14 x 14 mm, thickness: 1.4 mm, silicon chip size: 8.0 x 8.0 mm, lead frame made of 42 alloy) Mold temperature: 175 ° C, injection pressure: 75 kg / Cm ² , transfer molding at a curing time of 2 minutes, and post-curing at 175 ° C. for 8 hours. The obtained semiconductor package was left in an environment of 85 ° C. and relative humidity 85% for 168 hours, and then immersed in a solder bath at 240 ° C. for 10 seconds. External cracks were observed with a microscope, and the number of cracks [(number of crack generating packages) / (total number of packages) × 100] was displayed in%. Further, the ratio of the peeled area between the chip and the cured resin composition was measured using an ultrasonic flaw detector, and the peel rate [(peeled area) / (chip area) × 100] was the average value of the five packages. Was expressed in%.
Storage at 30 ° C .: Spiral flow immediately after adjustment and after storage for 1 week at 30 ° C. was measured and expressed as a percentage after storage relative to the spiral flow immediately after adjustment. Units%.
[0032]
Examples 2-4, Comparative Examples 1-3
Each component was mix | blended in the ratio shown in Table 1, the resin composition was obtained like Example 1, and it evaluated similarly to Example 1. FIG. The results are shown in Table 1. The biphenyl type epoxy resin YX-4000H is manufactured by Jaban Epoxy Resin Co., Ltd., melting point 105 ° C., epoxy equivalent 191, and the phenol aralkyl resin XL-225 is manufactured by Mitsui Chemicals, Inc., softening point 75 ° C., hydroxyl group equivalent. 174.
[0033]
[Table 1]
[0034]
【Effect of the invention】
In the present invention, an epoxy resin composition for encapsulating a semiconductor having excellent curability and storability by using a novel curing accelerator is obtained, and the semiconductor device using this has good moisture resistance. Excellent solder crack resistance.

Claims (2)

(A) An epoxy resin represented by general formula (1), (B) a phenol resin represented by general formula (2), (C) fused silica powder, and (D) a molecular compound represented by general formula (3). In the epoxy resin composition for semiconductor encapsulation, characterized in that the epoxy resin represented by the general formula (1) is 39/56 × 100 wt% or more and 100 wt% or less in all epoxy resins, The total phenol resin contains (B) the phenol resin represented by the general formula (2) in an amount of 29/42 × 100 wt% or more and 100 wt% or less, and (C) 88 wt% of the fused silica powder in the total epoxy resin composition. For semiconductor encapsulation, characterized in that it contains 2% × 100 wt% or more and 100 wt% of the molecular compound represented by the general formula (3) in the entire curing accelerator, Epoxy resin composition .
(R is a group selected from a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, which may be the same or different. N is a positive number of 1 to 5 on average. )
(R is a group selected from a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, which may be the same or different. N is a positive number of 1 to 5 on average. )
(P is a phosphorus atom, R ₁ is a substituted or unsubstituted aromatic group or alkyl group, which may be the same or different from each other. X is a sulfone group, and R is 1 to 4 carbon atoms. And may be the same or different from each other, and m represents a number of 0 ≦ m ≦ 1.) A semiconductor device obtained by sealing a semiconductor element using the epoxy resin composition for sealing a semiconductor according to claim 1.