JPH08154364A - Resin molded body and its manufacture - Google Patents

Abstract

PURPOSE: To obtain a resin molded body in which cracks inside resin can be suppressed by a method wherein molding resin is divided into two as an inner- layer resin and an outer-layer resin and the glass transition temperature of the inner-layer resin is made lower than the glass transition temperature of the outer-layer resin. CONSTITUTION: Molding resin 2 is composed of an inner-layer resin 3 constituted so as to cover an insert material 1 and of an outer-layer resin 4 constituted so as to cover the inner-layer resin. Resin whose glass transition temperature is lower than that of the outer-layer resin 4 is selected to be used for the inner- layer resin 3. As a method to select a resin having a low glass transition temperature, various methods to select the chemical composition of a resin main ingredient (such as an epoxy resin or the like), to select a hardener (an acid anhydride or the like) and a catalyst, to change their mixture ratio and to change a molding condition such as a molding temperature, a molding time or the like are available. In order to obtain a molded structure which is hard to deform with reference to an external force even under the high temperature condition of external surroundings and whose shape reliability is high, a resin whose glass transition temperature is comparatively high is used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a generator rotor coil,
The present invention relates to a mold structure of a resin mold body such as a generator stator coil, a ground coil for a magnetic levitation train, a coil for automobile parts, and a semiconductor package, and a manufacturing method thereof.

[0002]

2. Description of the Related Art FIG. 6 is a sectional view showing a ground coil for a magnetic levitation train manufactured by a conventional technique. In the figure, the outer periphery of the insert material 1 composed of an aluminum coil conductor is covered with a mold resin 2 composed of an epoxy resin in which silica is kneaded as a filler. The resin molding is performed by injection molding. That is, a liquid resin obtained by mixing a thermosetting resin main agent which is liquid at room temperature with a curing agent, a catalyst, a filler and the like is poured into a mold, heated to accelerate the curing reaction, and then removed from the mold. In this state, the mold resin exhibits rubber-like elastic behavior at high temperature. After that, the whole is gradually cooled, taking care to minimize the residual stress that causes cracks, deformation, and strength reduction.

[0003]

When molding a resin molded body by injection molding, the inside of the molding resin is caused by hardening shrinkage of the resin and difference in heat shrinkage amount between the resin and the insert material during cooling. Stress is generated. Since the cured resin is a brittle material at room temperature below the glass transition temperature, the generation of stress inside the resin causes cracks, deformation, and strength reduction. From the viscoelastic properties of thermosetting resin,
Most of the residual stress during resin molding is due to the temperature difference between the glass transition temperature and the glass transition temperature at which the resin transitions from the rubber-like elastic body to the glass-like elastic body during cooling after the curing reaction of the resin. It is already known that the difference is in the coefficient of thermal expansion and the thermal stress caused by the glass elastic constant of the mold resin. In order to prevent this thermal stress from being generated as much as possible, the insert material and the molding resin are molded by selecting materials having thermal expansion coefficients that are as close as possible to each other.

Changing the coefficient of thermal expansion of the mold resin is generally performed by adjusting the type and amount of the filler to be kneaded with the thermosetting resin. For example, the coefficient of thermal expansion of a cured epoxy resin containing no filler is 8.0 to 10.
Although it is 0 × 10 ⁵ / ° C., the coefficient of thermal expansion is reduced to about 3.0 to 3.6 × 10 ⁵ / ° C. by kneading the silica filler. However, increasing the amount of filler
Since the viscosity of the liquid resin is increased and the workability at the time of molding is impaired, it is difficult to increase the amount of the filler until the thermal expansion coefficients of the insert material and the molding resin are completely the same. Further, the thermosetting resin becomes a rubber-like elastic body having a very small elastic modulus under the temperature condition of the glass transition temperature (Tg) or higher, and it is considered that the strain generation due to the temperature change hardly contributes to the stress generation. Get better. Therefore, it is considered that lowering the glass transition temperature of the mold resin is also effective for reducing the stress inside the resin. However, if the glass transition temperature of the mold resin is lowered, the mold resin will become a rubber-like elastic body under the high temperature conditions of the external environment during use, and will be easily deformed by external force, resulting in loss of shape reliability. . Therefore, it has been difficult in the past to use a material having a low glass transition temperature for the mold resin.

From the above reason, it can be imagined that stress is generated at the interface with the insert material inside the mold resin layer due to the difference in thermal expansion coefficient between the insert material and the mold resin layer. It is considered that this leads to the generation of cracks 5 at the corners of the insert material.

An object of the present invention is to obtain a resin molded body which is resistant to cracks inside the molding resin during molding and under the use environment, and which is resistant to deformation by external force and has strength and shape stability. Especially.

[0007]

In order to solve the above-mentioned problems, according to the present invention, the insert material made of metal or the like and the outer circumference of the insert material are covered over at least one cross section thereof over the entire circumference. In a resin mold body comprising a mold resin, the mold resin comprises two different resin layers, an inner layer resin and an outer layer resin, and the glass transition temperature (Tg) of the inner layer resin is higher than the glass transition temperature of the outer layer resin. Is also low.

Further, the inner layer resin and the outer layer resin are made of the same resin base material.

Further, the inner layer resin and the outer layer resin are both epoxy resins.

The glass transition temperature of the inner layer resin is room temperature or higher.

Further, in a resin mold die comprising a liquid resin flow channel wall made of metal or the like and an insert material installed in the flow channel, the resin flow channel has a thin partition wall, It is divided into an inner part including an insert material and an outer part in contact with the flow path wall, and when the liquid resin is injected, the resin inside the partition wall and the resin outside do not mix with each other. And

Further, in the resin molding method using the resin molding die, different liquid resins are respectively poured into the inner side and the outer side of the partition wall and simultaneously cured to be molded.

[0013]

In the structure of the present invention, the cause of cracks in the mold resin during molding of the molded body is due to the thermal residual stress caused by the difference in linear expansion coefficient between the insert material and the mold resin and the elastic constant of the mold resin. Moreover, due to the viscoelastic properties of the thermosetting resin, thermal stress is generated in the thermosetting resin in a temperature range below the glass transition temperature (Tg) at which the resin transitions from a high temperature rubber state to a low temperature glass state. It was obtained based on the finding that it is limited. That is, the inner resin layer having a glass transition temperature (Tg) lower than that of the outer resin layer is formed in close contact with both the insert material and the outer resin layer, which causes a crack in the mold resin. Since the resin layer can be replaced with the inner resin layer having a low glass transition temperature, the thermal residual stress at the time of molding the molded body can be relaxed. Further, since the glass transition temperature of the inner resin layer is lowered, the heat shrinkage amount of the inner resin layer during cooling is increased, and it is possible to compensate for the small heat shrinkage amount of the insert material and to approach the heat shrinkage amount of the outer resin layer. It is also possible to reduce the residual thermal stress during molding that occurs at the interface with the inner resin layer inside the outer resin layer. As a result, the effect of avoiding the occurrence of cracks in the molding resin at the time of molding to reduce defects during manufacturing is obtained, and cracks and deformation are less likely to occur due to external force when the mold body is used. In addition, a thin partition wall is provided in the molding die so as to separate the inner resin layer and the outer resin layer, and different resins are injected into the inner and outer sides of the partition wall to simultaneously cure and mold the inner resin layer. The layer and the outer resin layer can be molded in a single process, and the process can be rationalized.

[0014]

EXAMPLES The present invention will be described below based on examples.
FIG. 1 is a sectional view showing a mold coil according to an embodiment of the present invention. In the figure, a mold resin 2 is formed so as to cover an insert material 1 and an inner layer resin 3 and an inner layer resin. A resin having a lower glass transition temperature (Tg) than the outer layer resin is selected and used as the inner layer resin. In addition to selecting the chemical composition of the resin base (epoxy resin, melamine resin, polyester, polystyrene, methyl methacrylate, phenolic resin, etc.), a method of selecting a resin with a low glass transition temperature, a curing agent (acid anhydride, There are various methods such as changing the molding conditions such as selection of amine, polyamide, etc.), catalyst and their mixing ratio, molding temperature, molding time. Also,
When the glass transition temperature of the cured resin is changed by the above method, other physical properties such as mechanical strength, thermal characteristics, and insulation characteristics of the resin may change significantly. Therefore, comprehensively judge these points. It is necessary to determine the molding conditions.

Further, as the outer layer resin, a resin having a relatively high glass transition temperature is used in order to obtain a mold structure which is not easily deformed by an external force even under high temperature conditions of the external environment and has high shape reliability.

The glass transition temperature of the outer layer resin is preferably about 120 ° C. to 150 ° C. so that the resin is not softened by the external temperature condition under the use environment and the shape stability is not lost. Further, the glass transition temperature of the inner layer resin is set sufficiently high and lower than the glass transition temperature of the outer layer resin so as not to be softened by heat generation of the inner conductor during use and lose the stability of the shape. Specifically, the glass transition temperature of the inner layer resin is 80 ° C to 100 ° C.
Desirably.

As a method for molding the inner layer resin and the outer layer resin, injection molding is generally used. First, the inner conductor is molded by injection molding with the inner layer resin, and then by injection molding with the outer layer resin. At this time, in order to enhance the adhesiveness between the inner layer resin and the outer layer resin, the surface of the inner layer resin is previously subjected to surface roughening treatment using sandpaper or the like, or surface treatment such as coating with a coupling agent. It is desirable to keep.

In estimating the residual stress during molding at the interface with the internal conductor of the inner layer resin of such a resin mold, the residual stress is the thermal expansion between the conductor and the resin due to the temperature change below the glass transition temperature. The calculation is generally performed on the assumption that the thermal stress is due to the coefficient difference and the glass elasticity coefficient of the resin. In this case, the residual stress σ _{r at the} interface is approximately given by the following equation.

Σ _r ∝ E (Tg−Tr) (α ₁ −α ₀ ) where E is the elastic modulus of the resin, Tr is the temperature of the resin mold body after molding (generally room temperature), and Tg is the inner layer resin. Glass transition temperature, α ₁ is thermal expansion coefficient of inner layer resin, α ₀
Is the coefficient of thermal expansion of the inner conductor. FIG. 2 shows the relationship between the residual stress during molding of the inner layer resin of the resin mold body and the thermal expansion coefficient of the resin. From the figure, it can be seen that in order to reduce the residual stress during molding that occurs at the interface between the inner layer resin of the resin mold body and the internal conductor, the thermal expansion coefficient of the resin should be made as small as the internal conductor. In order to reduce the coefficient of thermal expansion of the resin, it is sufficient to increase the proportion of the filler at the time of molding, but this also increases the viscosity of the resin before curing, which leads to deterioration of workability in injection molding. In particular, if the mold is large and has a complicated mold shape, the resin may be insufficiently filled. For this reason,
Generally, the coefficient of thermal expansion of the resin is larger than that of the inner conductor. As a result, tensile circumferential stress is generated at the interface of the mold resin with the internal conductor, which causes cracks in the resin during molding.

Therefore, in order to reduce the residual stress generated at the interface with the internal conductor in the mold resin, it is understood that the glass transition temperature of the resin should be made small as shown in FIG. By lowering the glass transition temperature of the resin, the difference in shrinkage amount between the insert material and the resin at the glass transition temperature or less is reduced, and as a result, the circumferential stress of tension generated at the interface with the internal conductor in the inner layer resin is reduced. Can be made.

The tensile circumferential stress generated at the interface with the inner layer resin inside the outer layer resin is due to the apparent shrinkage amount of the inner layer resin in the region below the relatively high glass transition temperature of the outer layer resin and the outer layer resin. It occurs due to the difference from the shrinkage amount. However, the apparent shrinkage of the inner layer resin is the sum of the free shrinkage of the inner conductor and the free shrinkage of the inner layer resin. Here, if the glass transition temperature of the inner layer resin decreases, the amount of free shrinkage of the inner layer resin increases. Therefore, the apparent shrinkage amount of the inner layer resin increases and the difference with the shrinkage amount of the outer layer resin decreases, so that the tensile circumferential stress generated at the interface with the inner layer resin in the outer layer resin is reduced. In other words, the high heat shrinkage of the inner layer resin compensates for the low heat shrinkage of the insert material to bring the apparent heat shrinkage of the inner layer resin closer to the heat shrinkage of the outer layer resin. The residual stress of is reduced. From the above, it is understood that by using a resin having a low glass transition temperature as the inner layer resin, it is possible to reduce the residual stress in the outer layer resin having a relatively high glass transition temperature.

That is, by using a resin having a low glass transition temperature as the inner layer resin which is in direct contact with the inner conductor having a small thermal expansion coefficient, the circumferential tensile stress generated at the interface with the inner conductor in the inner layer resin is reduced, Further, due to the effect of increasing the thermal contraction amount of the inner layer resin, it is possible to reduce the circumferential tensile stress generated at the interface between the inner layer resin and the inner layer resin. As a result, the tensile stress in the resin is reduced, and the occurrence of cracks in the resin can be prevented.

FIG. 4 is a sectional view of a semiconductor package showing a different embodiment of the present invention. In the figure, the inner layer resin 3 is configured to cover the outer periphery of the silicon element 6 and the metal lead frame 7, and the outer layer resin 4 is configured to cover the inner layer resin 3. An epoxy resin filled with silica is used for both the inner layer resin and the outer layer resin. An epoxy resin having a relatively low glass transition temperature is used as the inner layer resin to reduce the residual stress generated at the interface of the inner layer resin with the silicon element and the lead frame. As the outer layer resin, an epoxy resin having a relatively high glass transition temperature is used to ensure high shape stability against external force under a use environment. The glass transition temperature of the outer layer resin is preferably 130 ° C. or higher, ideally 150 ° C. or higher in consideration of the reliability test conditions of semiconductor products. On the other hand, the glass transition temperature of the inner layer resin is 90 ° C. or higher in consideration of the temperature of the device surface during operation,
In addition, the glass transition temperature of the outer layer resin is not higher than the glass transition temperature. Specifically, it is desirable to set the temperature to about 100 to 120 ° C.

FIG. 5 is a sectional view showing a molding die used for manufacturing the resin molded body of the present invention. In the figure,
The resin flow path 10 inside the mold 8 is partitioned by a thin partition wall 9 such as a glass cloth impregnated with a curing agent in advance, and the resin inside the partition wall and the resin outside the partition wall are made of liquid resin. It does not mix when injecting. In the mold configured as shown in the figure, inside the partition wall, the inner layer resin with a low glass transition temperature after curing is placed on the side that directly contacts the insert material, and on the outside of the partition wall, the glass transition temperature after curing is relatively low. The high outer layer resin is injected, and the temperature is raised to cure at the same time. By doing so, the resin mold body of the embodiment of the present invention can be molded without increasing the number of times of curing and cooling, which occupies a large amount of time in the molding process. At this time, if the rigidity of the partition wall is too high, residual stress may occur at the interface between the inner layer resin and the partition wall and the interface between the outer layer resin and the partition wall during cooling. Therefore, it is desirable to make the partition wall as rigid as possible.

[0025]

As described above, according to the present invention, the mold resin layer has a two-layer structure composed of different resin cured products, and the resin forming the inner layer is a glass of the resin forming the outer layer. It was constructed using a resin having a temperature lower than the transition temperature. As a result, the thermal residual stress at the interface between the insert material and the mold resin layer, which causes cracks inside the mold resin during resin molding, is reduced, and a mold coil that does not easily crack inside the mold resin layer during molding. Can be provided.

Further, since the amount of free shrinkage of the resin forming the inner layer becomes large, the apparent amount of heat shrinkage of the inner layer resin becomes large and approaches the amount of heat shrinkage of the outer layer resin. It is also possible to reduce the residual stress during molding that occurs at the interface with and, and it is possible to avoid the occurrence of cracks inside the mold resin layer during molding.

Further, the resin flow path in the molding die is divided by a thin partition wall, and different liquid resins are injected into the inside and outside of the partition wall, and at the same time, the resin is cured and cooled to thereby form the inner layer resin and the outer layer resin. Can be configured at the same time, so that the manufacturing process can be shortened and the manufacturing efficiency can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a molded coil of an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a relationship between a residual stress during molding of an inner layer resin of a resin mold body and a thermal expansion coefficient of the resin.

FIG. 3 is an explanatory diagram showing the relationship between the residual stress during molding of the inner layer resin of the resin mold body and the glass transition temperature (Tg) of the resin.

FIG. 4 is a sectional view of a semiconductor package showing a different embodiment of the present invention.

FIG. 5 is a sectional view showing a molding die and a molding method according to an embodiment of the present invention.

FIG. 6 is a cross-sectional view showing a ground coil for a magnetic levitation train manufactured by a conventional technique.

[Explanation of symbols]

1 ... Insert material, 2 ... Mold resin, 3 ... Inner layer resin,
4 ... Outer layer resin.

Claims (6)

[Claims] 1. A resin mold body comprising an insert material made of a metal or an inorganic material, and a mold resin covering the outer circumference of the insert material at least in one section over the entire circumference, wherein the mold resin is an inner layer resin. A resin mold body, which is divided into two layers of an outer layer resin and a glass transition temperature of the inner layer resin is lower than a glass transition temperature of the outer layer resin. 2. The resin mold body according to claim 1, wherein the inner layer resin and the outer layer resin are made of the same resin base material. 3. The resin molded body according to claim 1, wherein both the inner layer resin and the outer layer resin are epoxy resins. 4. The resin mold body according to claim 1, wherein the glass transition temperature of the inner layer resin is room temperature or higher. 5. A resin molding die comprising a flow channel wall of a liquid resin made of a metal or an inorganic substance and an insert material installed in the flow channel, wherein the resin flow channel has a thin partition wall, It is divided into an inner part including the insert material and an outer part in contact with the flow path wall, and when the liquid resin is injected, the resin inside the partition wall and the resin outside do not mix with each other. Mold for resin molding characterized by. 6. The method according to claim 1, 2, 3, 4 or 5.
A resin molding method for molding a resin molded body in which different liquid resins are poured into the inside and outside of a partition wall and the inside resin and the outside resin are simultaneously cured into the resin molding die.