JP2000151071A - Lead frame insertion mold substrate and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve substrate quality, solder wetting and reliability by insert molding a first resin material onto the surface of a circuit pattern-like conductive lead frame, and forming a second resin layer in a prescribed form by means of insert-molding a second resin material onto the surface of the lead frame after the frame is formed. SOLUTION: In a primary formation process for insert-molding a first resin material onto the surface of a conductive lead frame worked into a circuit pattern form and forming the first resin layer of a prescribed form, a thermosetting resin material is used for the first resin material and the setting reaction is stopped to a stage B. Since the thickness of an oxide film formed on a land part 2 is about 60-70 angstroms, the wettability of solder at the time of mounting parts improves and the reliability of a module improves. The lead frame is worked into the prescribed form and a second resin material is insert-molded onto the surface. At the time of forming a second resin layer, the first resin material is set to a stage C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a lead frame insert molded substrate used as a substrate for a large current circuit, and a method of manufacturing the same.

[0002]

2. Description of the Related Art A lead frame insert molded substrate in which a circuit is formed by a copper lead frame having a thickness of about 0.5 mm and the periphery thereof is covered with a molding resin is a conventional thickness of about 0.035 to 0.105 mm. Compared with a printed circuit board using copper foil, it is possible to pass a large current with the same circuit area, and it is possible to reduce the area if it is a circuit that passes the same amount of current ,
In recent years, it has attracted much attention because it can be easily processed into a desired shape.

[0003] Hereinafter, an example of a conventional lead frame insert mold substrate and a manufacturing process thereof will be described with reference to FIG. As shown in FIG. 1A, a first resin layer is formed by injection molding on a surface of a lead frame 1 previously processed into a circuit pattern shape, around a component mounting land 2 on which components such as capacitors are arranged. 3 (hereinafter, referred to as a primary molding step). Next, the lead frame 1 is processed into a desired shape. For example, FIG.
In (b), an unnecessary portion at the end of the lead frame 1 is cut and then bent upward. Further, as shown in FIG. 1C, a second resin layer 4 is formed on the exposed portion of the lead frame 1 excluding the land portion 2 by injection molding (hereinafter, referred to as a secondary molding step). The component 5 is mounted on the land 2 of the substrate processed as described above,
A desired module as shown in FIG. 1 (d) is obtained.

[0004]

In the manufacture of the substrate as described above, a resin molding step in which the land portion 2 of the lead frame 1 is exposed to a high temperature is performed twice. Oxidation of the surface proceeds. For example, when epoxy resin is used as the first resin material, the mold temperature is set to 1
The temperature is set to about 80 ° C., and a lead frame made of copper is held therein for 5 minutes to form the first resin layer 3. Therefore, an oxide film of about 200 Å is formed on the surface of the land portion 2. If the same epoxy resin is used as the second resin material, the same thermal history is applied, so that the thickness of the oxide film formed on the land portion 2 becomes 400 Å or more. When such an oxide film is formed on the surface of the land portion 2, the wettability of the solder deteriorates in a later component mounting step, or the connection resistance value between the mounted component and the lead frame increases. .

Further, in the primary molding step, since the first resin material is sufficiently cured, a chemical bond does not occur between the first resin layer and the second resin layer due to an interaction between molecules.
The connection between the two is only a physical (mechanical) connection. Therefore, the bonding property between the first resin layer 3 and the second resin layer 4 is poor, and peeling and cracking are likely to occur at the interface 6 between them. Therefore, the insulation resistance and the heat conduction are likely to be reduced by the water absorption at the interface 6.

The present invention solves the above problems,
It is an object of the present invention to provide a lead frame insert molded board which is excellent in board quality and solder wettability at the time of component mounting and can obtain a highly reliable module. Another object of the present invention is to provide a method for manufacturing the above-described lead frame insert mold substrate.

[0007]

According to the present invention, a first resin material having a predetermined shape is formed by insert-molding a first resin material on a surface of a conductive lead frame processed into a circuit pattern shape. A primary molding step, a frame molding step of processing the lead frame into a predetermined shape, and forming a second resin layer of a predetermined shape by insert molding a second resin material on the surface of the lead frame after the frame molding A method for manufacturing a lead frame insert mold substrate comprising a secondary molding step, wherein a thermosetting resin material is used as the first resin material, and the resin material reacts to a B stage in a primary molding step. In the secondary molding process, the resin material is reacted up to the stage of C stage.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In a method for manufacturing a lead frame insert molded substrate according to the present invention, a first resin material is insert-molded on a surface of a conductive lead frame processed into a circuit pattern shape, and a predetermined shape of a first resin material is formed. In the primary molding step of forming one resin layer, a thermosetting resin material is used as the first resin material, and this curing reaction is stopped up to the stage of the B stage. Curing reaction of thermosetting resin material is B
In order to stop at the stage, the processing time is shortened or the processing temperature, that is, the heating temperature of the mold, is reduced as compared with the molding conditions when the conventional thermosetting material is completely solidified. is there. With any method, even if the first resin material is reacted to the stage of the B stage, the heat history applied to the component land portion of the lead frame in the primary molding process can be reduced as compared with the conventional method, and the oxidation at the component land portion can be reduced. The formation of a layer is suppressed.

For example, when an epoxy resin is used as the first resin material, in a primary molding step, a copper lead frame is heated at 170 ° C. for 30 seconds or 150 ° C. for 1 minute, so that the epoxy resin is in the B stage. When cured, the thickness of the oxide film formed on the land portion 2 becomes 60 to
It is about 70 angstroms. Therefore, solder wettability at the time of component mounting is improved, and as a result, the reliability of the module is improved. After the primary molding step, after processing the lead frame into a predetermined shape, during the secondary molding step of insert molding a second resin material on the surface of the lead frame to form a second resin layer of a predetermined shape The first resin material is cured up to the stage C.

In the secondary molding step, an intermolecular force or the like acts between an unreacted monomer of the first resin material and a portion of the second resin material in contact with the first resin layer.
A chemical bond occurs between the first resin layer and the second resin layer. Therefore, the first resin layer and the second resin layer are bonded by a chemical bond, and the occurrence of peeling and cracks at the interface between the first resin layer and the second resin layer due to impact or the like is reduced. .
Therefore, it is possible to prevent a decrease in insulation resistance and a deterioration in heat conduction due to the absorption of water at the interface, thereby improving the quality of the substrate. In addition, it is more preferable that the resin is further cured by performing after-curing after the secondary molding step, as in the related art, because the performance is improved.

As described above, in the present invention, a thermosetting resin material is used as the first resin material. Usually, injection molding (injection molding) is used for the insert mold. In injection molding, a rapidly heated resin material is
A desired molded product is obtained by injecting into a cavity of a mold heated to a predetermined temperature and performing heat treatment in the cavity for a predetermined time. Hereinafter, a method of stopping the reaction of the first resin material at the B stage in the primary molding process will be described.

First, the processing time is shortened or the processing temperature, ie, the heating temperature of the mold, is reduced as compared with the conventional molding conditions when the thermosetting material is reacted to the stage of C stage at which the thermosetting material is completely solidified. There is a way. When the processing time is shortened, the manufacturing lead time is shortened, and the heat history of the component land portion of the lead frame is reduced, so that the formation of an oxide film on the component land portion can be suppressed. Therefore, solder wettability at the time of component mounting is improved, and module reliability is improved. On the other hand, when the processing temperature is lower than the conventional molding conditions, the plating flow on the surface of the lead frame can be prevented, and the range of usable plating can be widened. Further, the amount of heat of the heater required to heat the mold can be reduced, and the manufacturing cost can be reduced.

In addition, in the injection molding of a thermosetting resin, the resin material is injected into the cavity at a higher speed than in the injection molding of a thermoplastic resin. Fever. Therefore, if the injection speed and the injection pressure are made lower than in the conventional case, the temperature rise of the resin material can be suppressed, and the curing reaction of the resin material can be stopped halfway even if the other molding conditions are the same as those in the related art. In this case, since the load on the molding machine can be reduced, the durability of the equipment is improved, and the manufacturing cost can be reduced.

The use of a thermoplastic resin as the second resin material has the following advantages and is preferred. Thermosetting resins, once cured, are difficult to reuse thereafter, whereas thermoplastic resins are resins that are easy to reuse. Therefore, by using the thermoplastic resin, the utilization rate of the material in the process can be increased, and the material cost can be reduced. In addition, it can be easily separated and collected even after molding the substrate, and is excellent in environmental measures.

In general, the molding time required for curing a thermoplastic resin is shorter than that of a thermosetting resin. Further, since the molding temperature of the thermoplastic resin is higher than that of the thermosetting resin, the molding time in the primary molding step can be shortened. Therefore, the manufacturing lead time can be shortened. Further, since the melt viscosity of the thermoplastic resin is higher than that of the thermosetting resin, burrs are less generated during molding. Therefore, burrs do not adhere to the component lands, and the wettability of the solder during subsequent component mounting is improved. Therefore, the reliability of the module is improved. Furthermore, compared to thermosetting resins, thermoplastic resins have less contamination of the mold during molding and are easier to maintain, improving the durability of the equipment, resulting in lower manufacturing costs and lower mass production. improves.

Here, when the second resin material is a thermosetting resin different from the first resin material, a lead frame insert mold substrate having new features can be obtained. It is preferable to use a thermosetting resin having a high thermal conductivity for the first resin material or the second resin material because the heat radiation of the substrate is improved. For example, when a heat-generating component such as a resistor is mounted on the component land portion, the use of a resin having a high thermal conductivity as the first resin material can improve the heat dissipation of the heat-generating component. Stress is reduced. As a result, the durability of the component is improved, and the reliability of the module is improved.

Further, when the first resin material or the second resin material is a thermosetting resin having a high pull-out strength with respect to the lead frame, the adhesion between the lead frame and the resin is improved. For example, when a heat-generating component is mounted on a component land, close contact between the lead frame and the resin is required around the heat-generating component. Therefore, if a resin having a high pull-out strength is used as the first resin material, peeling and cracking at the interface between the first resin layer and the lead frame due to an impact or the like can be reduced, and the insulation resistance decreases due to water absorption and heat dissipation. It is possible to prevent deterioration of sex. Therefore, the quality of the substrate can be improved.

Further, when the first resin material or the second resin material is a thermosetting resin having a small specific gravity, the weight of the substrate is reduced. By reducing the weight of the substrate, the load on equipment and the like during transportation or use of the product is reduced, the durability of the equipment is improved, and the manufacturing cost is reduced, which is preferable.

[0019]

The present invention will be described below in more detail with reference to specific examples. Example 1 An epoxy resin containing 30% of carbon black (manufactured by Mitsui Chemicals, Inc., product number TY-228) as a first resin material, and a ceramic filler (alumina) as a second resin material Polyphenylene sulfide (manufactured by Dainippon Ink and Chemicals, Inc., product number FZ-6600J2, hereinafter referred to as P
It is called PS. ) Was used. Table 1 shows the physical properties of each material.

[0020]

[Table 1]

A lead frame made of copper processed into the shape of a circuit pattern is placed in a mold set at 150 ° C., and the first resin material heated to 90 to 105 ° C. is injected into the mold at an injection pressure of 30 kgf / cm ² . Injected. After maintaining this state for 15 seconds, the mold was opened and the lead frame was taken out. Next, an unnecessary portion at the end of the lead frame was cut, and the lead portion was bent upward. This lead frame is
C., and the second resin material heated to 90 to 105.degree. C. was injected into the mold. After cooling as it was to sufficiently cool the resin, the substrate was taken out. The component land portion of the obtained substrate had a metallic luster, and the wettability of the solder was good. Further, almost no crack was generated at the interface between the first resin layer and the second resin layer. The adhesion at the interface between the lead frame and the first and second resin layers was also excellent.

Comparative Example 1 A lead frame insert molded substrate was produced in the same manner as in Example 1 except that the temperature of the mold for the primary molding step was set at 180 ° C. and the holding time was set at 5 minutes. The component land portion of the obtained substrate did not have metallic luster, and the solder wettability was not good. In addition, cracks occurred at the interface between the first resin layer and the second resin layer, and the adhesion at the interface between the lead frame and the first resin layer was not good.

[0023]

As described above, according to the present invention, it is possible to provide a lead frame insert molded substrate having excellent quality.

[Brief description of the drawings]

FIG. 1 is a view showing a manufacturing process of a conventional lead frame insert mold substrate.

[Description of Signs] 1 Lead frame 2 Component land portion 3 First resin layer 4 Second resin layer 5 Component 6 Interface between first resin layer and second resin layer

Claims (10)

[Claims] A first molding step of insert-molding a first resin material on a surface of a conductive lead frame processed into a circuit pattern shape to form a first resin layer having a predetermined shape; A frame forming step of processing into a predetermined shape, and a secondary forming step of forming a second resin layer of a predetermined shape by insert-molding a second resin material on the surface of the lead frame after the frame is formed. A method for manufacturing a lead frame insert mold substrate, wherein a thermosetting resin material is used as the first resin material, and in a primary molding process, the resin material is reacted up to a B stage, and in a secondary molding process, A method for manufacturing a lead frame insert mold substrate, wherein a resin material is reacted up to a C stage. 2. The method for manufacturing a lead frame insert mold substrate according to claim 1, wherein in the primary molding step, curing of the resin material is controlled by a heating time. 3. The method according to claim 1, wherein in the primary molding step, curing of the resin material is controlled by a heating temperature. 4. The method according to claim 3, wherein the heating temperature of the resin material is controlled by the temperature of a molding die. 5. The method of manufacturing a lead frame insert mold substrate according to claim 1, wherein in the primary molding step, curing of the resin material is controlled by an injection speed or an injection pressure into the mold. 6. The method according to claim 1, wherein a thermoplastic resin material is used as the second resin material. 7. A conductive lead frame processed into a circuit pattern shape, a first resin layer formed by molding the lead frame in a desired shape, and an exposed portion of the lead frame excluding a component land portion are molded. A lead frame insert mold substrate comprising a second resin layer, wherein the first resin layer or the second resin layer is made of a thermosetting resin having high thermal conductivity. 8. A conductive lead frame processed into a circuit pattern shape, a first resin layer formed by molding the lead frame in a predetermined shape, and an exposed portion of the lead frame excluding a component land portion are molded. A lead frame insert mold substrate comprising a second resin layer, wherein the first resin layer or the second resin layer is made of a thermosetting resin having a high pull-out strength with respect to a lead frame. 9. A conductive lead frame processed into a circuit pattern shape, a first resin layer molded with the lead frame in a predetermined shape, and an exposed portion of the lead frame excluding a component land portion are molded. A lead frame insert mold substrate comprising a second resin layer, wherein the first resin layer or the second resin layer is made of a thermosetting resin having a low specific gravity. 10. The lead frame insert mold substrate according to claim 7, wherein said second resin layer is made of a thermoplastic resin.