The present invention relates to an epoxy resin composition and the application thereof. The epoxy resin composition of the present invention can be used in various electronic applications, such as in environmentally friendly, high voltage SMD packages.

As a package material for semiconductor, an epoxy resin composition must have a fire retardance of UL-94V-0. To this end, the main means is to add a certain amount of fire retardant in the prior art, which comprises various types of fire retardants, among which, the bromine fire retardant and antimony fire retardant are the major traditional (non-environment-friendly) fire retardants. However, as the rise in environment protection consciousness in the whole world, individual countries constitute environment protection acts to prevent fire retardant containing bromide and lead from being used in electronic products. Date back to early 90's of last century, US, Europe and Japan had found that attention must be paid to the harm of lead in lead-tin solder in a great amount of industrial waste resulted from rapid development of electronic products each year. Today, China has become a major export country of household appliances which are subjected to the limitation by regulations, such as ROHS, etc., when entering international markets. According to the requirements of The Restriction of the use of certain Hazardous substances in Electronic and Electrical Equipment issued by Europe Parliament and EU Council, China prohibited lead, antimony, mercury, cadmium, 6-valence chromium, PBB or PBDE, etc., from being contained in the electronic and information products listed in the catalog of key products under nation supervision. Therefore, the traditional bromine fire retardant and antimony fire retardant will be gradually replaced by environment-friendly fire retardants. However, currently used environment-friendly fire retardants are inferior than Br/Sb fire retardants in fire retardant effect and requires a larger amount to accomplish fire retardant effect. Utilizing a great amount of fire retardant will influence the fluidity, molding property, reliability and related electrical property of the epoxy resin composition. In semiconductor package, the change from the traditional high-temperature lead solder reflow process at 240°C to green high temperature lead-free solder reflow process at 260°C sets a higher requirement on the reliability of epoxy resin molding plastic. In the package of green environment friendly surface mounting device (SMD), typically, the high temperature reliability (JEDE MSL1/260degC) and the related electrical properties (HTRB, HAST, etc.) tests are made. In the JEDEC MSL1/260degC assessment test, the semiconductor package are often innerly layered due to the heat resistance, water absorption, adhesion, stress of epoxy molding plastic, among others; in the electrical property assessment test, the HTRB, HAST and other electrical properties come to a failure because the epoxy molding plastic has a higher water absorption, a stress and a higher ion content. Therefore, during the SMD packaging, epoxy molding plastic must firstly meet the requirements for the high temperature reflow of lead-free packaging technology in reliability, high heat resistance, high adhesion, low water absorption, and low stress, etc., so as to reduce or avoid layering between the epoxy molding plastic and chip/basal island/frame after a high temperature reflow. Secondly, the epoxy molding plastic must further have a good electrical property and a molding property. In short, in the SMD package, the epoxy molding plastic must have a higher reliability, an excellent electrical property and a good molding property, so as to reduce or avoid the internal layering of semiconductor packages, a poor electrical property, and an improved packaging molding efficiency.

The technical problem to be solved by the present invention is aimed to overcome the environmental problems resulting from introducing bromine- or antimony-based fire retardants to conventional epoxy resin compositions, and the shortcomings resulting from current environment-friendly fire retardants which have difficulties in satisfying the requirements of lead-free reflow soldering processes and high voltage electrical applications. In addition the present invention aims to provide an epoxy resin composition having the capability to satisfy the requirements of lead-free high temperature reflow processes. Furthermore the epoxy resin composition of the present invention should exhibit high reliability and excellent high voltage electrical properties. The present invention provides an epoxy resin composition, which contains or consist of an epoxy resin mixture, a phenolic resin, a curing promoter, an inorganic filler, and as optional components a release agent, and a coupling agent.

As used in the present invention, the singular "a", "an" and "the" includes the plural reference unless the context clearly indicates otherwise.

The epoxy resin mixture of the inventive epoxy resin composition comprises at least the epoxy resin represented b formula I,

formula I wherein R-i and R ₂ are independently H or Ci to C ₄ alkyl, and n is an integer from 0 to 50.

In one embodiment R-i and R ₂ are independently methyl and/or n is an integer from 1 to 40, preferably from 3 to 30, and more preferably from 5 to 15.

In another embodiment of the present invention, said epoxy resin mixture additionally comprises at least one e oxy resin represented by formulae II and/or III;

wherein m and I are independently integers from 0 to 50, preferably from 3 to 30, and more preferably from 5 to 15.

In the present invention, the content of the epoxy resin represented by formula I is preferably more than 50%, more preferably from 70 to 90%. The content of the epoxy resin represented by formula II is preferably less than 30%, more preferably from 10 to 20%. The content of the epoxy resin represented by formula III is preferably less than 30%, more preferably from 15 to 25%. As used above, the content of each epoxy resin is the percentage relative to the total mass of epoxy resin mixture. The epoxy resin mixture of the present invention can effectively contribute to the improvement of electrical properties of semiconductor products.

The content of said epoxy resin mixture of the present invention is preferably from 6 to 25%, more preferably from 8 to 16% by mass of the epoxy resin composition.

The phenolic resin of the present invention is mainly used as a curing agent. Preferably the phenolic resin is selected from phenolic resins having low water absorption.

The ratio of the number of phenolic hydroxyl groups of the phenolic resin to the number of epoxy groups of the epoxy resin mixture is preferably from 0.8 to 1.2, more preferably from 0.9 to 1.1.

The curing promoter of the present invention is a substance which can promote the curing of the epoxy resin composition. The curing promoter is preferably triphenylphosphine and/or a nitrogen-containing compound. Suitable nitrogen-containing compounds which can be used as curing promoters are known to a person skilled in the art. Preferred nitrogen-containing compounds are selected from imidazole compounds, such as substituted or unsubstituted imidazoles, amine compounds and compounds comprising a diazabicyclo structural element; said imidazole compound is preferably imidazole, said amine compound is preferably benzyldimethylamine; and said nitrogen-containing compound is preferably benzyldimethylamine and/or a compound comprising a diazabicyclo structural element. The content of the curing promoter is preferably less than or equal to 1 % of the epoxy resin composition by mass.

The inorganic filler of the present invention is used to further reduce the water absorption of the epoxy resin composition of the present invention. Suitable inorganic filler are known to a person skilled in the art. Preferred inorganic fillers are selected from fused silica and/or crystalline silica. The inorganic filler of the present invention may have any form or shape without any limitation, wherein an angular and/or spherical form or shape is preferred. The content of said inorganic filler is preferably from 60 to 88%, more preferably from 68 to 84% of the epoxy resin composition by mass.

The release agent of the present invention, if present, is preferably selected from waxes. The wax can be of natural or synthetic origin and can optionally also be in chemically modified form. Naturally occurring waxes that can be added are vegetable waxes, animal waxes, mineral waxes or petrochemical waxes. Suitable chemically modified waxes are hard waxes, such as Montan ester waxes, Sasol waxes, etc. Suitable synthetic waxes are polyalkylene waxes and

polyethylene glycol waxes. Petrochemical waxes are preferably added such as petrolatum, paraffin waxes, microcrystalline waxes as well as synthetic waxes. Preferred release agents are selected from Brazil waxes, polyethene waxes, and adipose waxes and/or mixtures thereof, wherein particular preferred release agents are Brazil wax, polyethene wax, and/or ester wax and/or mixtures thereof. The content of said release agent is preferably from 0.6 to 0.9 % of the epoxy resin composition by mass.

The coupling agent of present invention, if present, improves the compatibility between the epoxy resin mixture and the inorganic filler and increases the adhesion of the epoxy resin composition to a specific surface, such as a chip. The coupling agent is preferably selected from compounds comprising at least one oxirane group and at least one group, which is capable of interacting with the inorganic filler material. More preferably the coupling agent includes compounds having at least one oxirane group and at least one silane or siloxane group. In the present invention such compounds are preferably identified as epoxy-based silanes or epoxy-based siloxanes. In one embodiment of the present invention the coupling agent is an epoxy-based silane or epoxy-based siloxane. The release agent of the present invention is preferably added in an amount from 0.5 to 0.7 % of the epoxy resin composition by mass.

In one preferred embodiment of the present invention the epoxy resin composition further contains a fire retardant which is preferably selected from environmentally friendly fire retardants, which are substantially free of bromine and/or antiomony. More preferably the fire retardant used in the epoxy resin composition of the present invention is selected from nitrogen-containing fire retardants, boron-containing fire retardants and metal hydroxide fire retardants and/or mixtures thereof. The content of the fire retardant is preferably less than or equal to 12 %, more preferably less than or equal to 10% of the epoxy resin composition by mass.

By using environmentally friendly fire retardants an epoxy resin composition of the present invention can be obtained which is substantially free of bromine and/or is substantially free of antimony.

The term "substantially free of bromine", as used in the present invention, refers to a composition, which comprises less than 5 wt.% of bromine, preferably less than 1 wt.% of bromine, more preferably less than 0.1 wt.% of bromine, and particularly preferably less than 0.001 wt.% of bromine, each based on the total amount of the composition.

The term "substantially free of antimony", as used in the present invention, refers to a composition, which comprises less than 5 wt.% of antimony, preferably less than 1 wt.% of antimony, more preferably less than 0.1 wt.% of antimony, and particularly preferably less than 0.001 wt.% of antimony, each based on the total amount of the composition.

According to the actual requirements of application, the epoxy resin composition of the present invention may further comprise one or more of a colouring agent, a toughener, an adhesion promoter, and an ion scavanger, and/or mixtures thereof. The ion scavanger is used to reduce the content of free ions in the epoxy resin composition.

In one preferred embodiment of the present invention, said epoxy resin composition comprises or consist of an epoxy resin mixture, a phenolic resin, a curing promoter, an inorganic filler, a colouring agent, a release agent, a coupling agent, a fire retardant, a toughener and an ion scavanger.

In one embodiment of the present invention, the epoxy resin composition contains by weight: from 9 to 14% of an epoxy resin mixture of the present invention,

from 4 to 8% of a phenolic resin,

from 0.4 to 0.6% of a curing promoter,

from 68 to 80% of an inorganic filler,

from 0 to 0.5%, preferably from 0.2 to 0.4% of a colouring agent,

from 0 to 1 %, preferably from 0.6 to 0.9% of a release agent,

from 0 to 1 %, preferably from 0.5 to 0.7% of a coupling agent,

from 4 to 10% of a fire retardant,

from 0 to 1.5%, preferably from 0.5 to 1 % of a toughener, and

from 0 to 1 %, preferably from 0.3 to 0.5% of an ion scavenger.

In the aforementioned epoxy resin composition it is preferred that

- with respect to the epoxy resin mixture, n, m and I in formula I, and formulae II or III are independently an integer from 5 to 15, and/or

- the ratio of the number of phenolic hydroxyl groups of the phenolic resin to the number of epoxy groups of the epoxy resin mixture is from 0.9 to 1.1 and/or

- the inorganic filler has an angular and/or spherical shape.

When the release agent of the epoxy resin composition of the present invention consits of 30 to 35 wt% Brazil wax, 40 to 50 wt% polyethene wax and 20-25 wt% ester wax, it is preferred that the epoxy resin composition further contains 1 % or less of a toughener. The use of a toughener is advantageous because the corresponding epoxy resin compositions exhibit very good molding properties.

The present invention further provides a preparation method for said epoxy resin composition, which comprises the steps of:

extruding each component of the epoxy resin composition of the present invention in an extruder to obtain an extrusion product;

milling and cooling the extrusion product to obtain the epoxy resin composition of the present invention in pulverized form.

The extruder can be a twin-screw. The extrusion should preferably be performed at elevated temperatures, such as temperatures above 50°C, wherein extrusion temperatures of 100°C to 110°C are preferred.

Another aspect of the present invention is the cured product of the epoxy resin composition of the present invention.

Further aspects of the present invention are a surface mounting device (SMD) coated with the epoxy resin composition of the present invention or a surface mounting device (SMD) adhered to a surface, such as a chip, with the cured product of the of the epoxy resin composition of the present invention.

Another aspect of the present invention is the use of the epoxy resin composition of the present invention in surface mounting device packages.

The positive effects of the present invention lie in the following aspects:

1 . The epoxy resin composition exhibit excellent fluidity and fire retardance, high heat resistance, high adhesion, low water absorption and low stress, and meets the standard UL-94V-0, and satisfies the requirement of high temperature reliability for lead-free soldering package processes.

2. By optimizing the type and proportion of the release agent, the epoxy resin composition of the present invention has a better reliability and a very good molding property during SMD package molding, satisfying the requirement of cleaning the mold one time every continuous molding 24 hours (1000 times molding).

EXAMPLES

Brief Description of Drawings

Fig.1 is a schematic diagram for the adhesion as used in the present examples.

The epoxy resins of formulae I, II, III, which are utilized in the present examples, are shown below, wherein, each of the R-i and R ₂ is methyl in Examples 1-6, and hydrogen in Example 7, while in Example 8, Ri is butyl, and R ₂ is hydrogen:

The phenolic resin used in Examples is a linear phenolic resin and is represented by formula IV, wherein, n is an integer from 0 and 15.

Formula IV

Example 1

The formulation of the epoxy resin composition is listed in Table 1 , wherein, n of formula I is 10, the equivalent ratio of the linear phenolic resin to the epoxy resin is 1 .08.

The epoxy resin composition is prepared by extruding all components listed in Table 1 in a twin-screw extruder at a temperature of more than 110°C, followed by milling to pulverize the composition.

Example 2

The formulation of the epoxy resin composition is listed in Table 1 , wherein, n of formula I is 12, m of formula II is 10. The equivalent ratio of the linear phenolic resin to the epoxy resin is 0.89.

The epoxy resin composition is prepared by extruding all components listed in Table 1 in a twin-screw extruder at 100°C, followed by milling to pulverize the composition.

Example 3

The formulation of the epoxy resin composition is listed in Table 1 , wherein, n of formula I is 15, I of formula III is 10. The equivalent ratio of the linear phenolic resin to the epoxy resin is 0.91.

The epoxy resin composition is prepared by extruding all components listed in Table 1 in a twin-screw extruder at 100°C, followed by milling to pulverize the composition.

Example 4

The formulation of the epoxy resin composition is listed in Table 1 , wherein, n of formula I is 15. The equivalent ratio of the linear phenolic resin to the epoxy resin is 0.96. The epoxy resin composition is prepared by extruding all components listed in Table 1 in a twin-screw extruder at 100°C, followed by milling to pulverize the composition.

Example 5

The formulation of the epoxy resin composition is listed in Table 1 , wherein, n of formula I is 15. The equivalent ratio of the linear phenolic resin to the epoxy resin is 0.96.

The epoxy resin composition is prepared by extruding all components listed in Table 1 in a twin-screw extruder at 100°C, followed by milling to pulverize the composition.

Example 6

The formulation of the epoxy resin composition is listed in Table 1 , wherein, n of formula I is 12, m of formula II is 10, I of formula III is 4. The equivalent ratio of the linear phenolic resin to the epoxy resin is 1 .08.

The epoxy resin composition is prepared by extruding all components listed in Table 1 in a twin-screw extruder at 100°C, followed by milling to pulverize the composition.

Example 7

The formulation of the epoxy resin composition is listed in Table 1 , wherein, n of formula I is 0. The equivalent ratio of the linear phenolic resin to the epoxy resin is 1 .1 .

The epoxy resin composition is prepared by extruding all components listed in Table 1 in a twin-screw extruder at 100°C, followed by milling to pulverize the composition.

Example 8

The formulation of the epoxy resin composition is listed in Table 1 , wherein, n of formula I is 50, m of formula II is 50, I of formula III is 50. The equivalent ratio of the linear phenolic resin to the epoxy resin is 1 .05. The epoxy resin composition is prepared by extruding all components listed in Table 1 in a twin-screw extruder at 100°C, followed by milling to pulverize the composition.

Comparative Example 1

The formulation of the epoxy resin composition is listed in Table 1 , wherein, n of formula I is 5. The equivalent ratio of the linear phenolic resin to the epoxy resin is 1 .00.

The epoxy resin composition is prepared by extruding all components listed in Table 1 in a twin-screw extruder at 100°C, followed by milling to pulverize the composition.

Table 1

Test procedures and results

The major performance of the epoxy resin composition obtained in Examples 1 to 8, and Comparative Example 1 were tested. The test results are listed in Table 2.

1. Gelation time (GT): HW/ZL/JS015-HPGT

2. Spiral flowing length (SF): HW/ZL/JS015-SF

3. Ash: HW/ZL/JS015-ASH

4. Fire retardance (UL 94): HW/ZL/JS015-UL

5. Water absorption (PCT24): 121 C/100%/24H

6. Glass transition temperature/thermal expansion coefficient (Tg/CTE1 &2): HW/ZL/JS015TMA

7. Adhesion: the epoxy resin composition is packaged in the frame as shown in Fig.1 , cured in an oven at 175 °C for 6 hours, subjected to moisture-absorbing treatment under condition of

JEDEC MSL3 (30°C/60%/168h), then reflowed for 3 times at 260°C, at last the adhesion between the epoxy resin composition and a metal frame is tested with pull force tester, wherein the contact area between the epoxy resin composition and the frame is 0.784 sq.in, and arrow indicates the pull direction.

In addition the layering reliability, electrical properties, and molding properties of the epoxy resin composition obtained in Examples 1 to 6, and Comparative Example 1 were tested. The test results are listed in Table 3.

1. Layering reliability test: the sample is packaged in a SOT23 Cu/Ag frame (parameters for packaging are set as temperature: 185°C, curing time 60 seconds), then JEDEC MSL1

(85/85/100%) is performed at 260°C, reflowing pre-treatment is performed for 3 times, at last the internal layering of SOT23 packaging is scanned with C-sam.

2. Electrical property test: the packaged SOT23 sample is placed in a H(3)TRB box, and treated under a certain temperature and humidity for a certain period (reference can be made to Table 3 for the treatment condition), then the treated SOT23 sample is tested with respect to electrical property failure. 3. Molding property test: a continuous molding packaging test is made on TOWA SOT23 mold, wherein the major package parameters are set as follows, temperature is 185°C, turning time is 9 seconds, and curing time is 60 seconds.

Table 2

Table 3

In table 3, the number before " is the number of failure samples, the number behind 7" is the number of total samples.

Tables 2 and 3 indicate that the epoxy resin composition of the present invention has a good MSL1 layering reliability, good electrical properties and good molding properties. Especially, no failure is found in MSL1/260 and electrical property tests for the samples obtained in Examples 1 and 6; the samples obtained in Examples 1 and 4 have very good molding properties and the continuous molding time is up to 1000.