JPS6138862B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a package forming method for airtightly housing semiconductor elements such as diodes and transistors, and integrated circuits of these semiconductors (hereinafter referred to as semiconductors). Two thermoplastic resin plate-shaped molded products (hereinafter referred to as plate-shaped molded products) having at least one recess for accommodating semiconductors are housed in a mold for combination and heated, and then the semiconductors are heated. In the package forming method for semiconductors, which involves sandwiching and pressurizing lead frames equipped with semiconductors, it is possible to ensure reliability by ensuring that no flash occurs during the assembly stage, which may impede the appearance or, in some cases, the operating function of the semiconductors. The present invention relates to a method for molding packages such as flat packages and dual-in-line packages to obtain excellent sealing properties.

In the transfer sealing molding method of epoxy resin, which is the most widely used conventional method, the resin viscosity during molding is on the order of 10 ^{to 2} poise at most, so there are variations in the thickness of the lead frame, precision of mold processing, and molding usage. Epoxy resin flashing is likely to occur on the lead frame due to wear and dimensional deviations, which can cause not only appearance problems but also uneven plating, poor contact between leads and sockets, and interference with soldering work. Therefore, it had drawbacks such as requiring removal work.

In addition, in a semiconductor package molding method using two plate-shaped molded products, the essential flow characteristics of the thermoplastic resin composition used and the fact that at least only the combined surfaces of the plate-shaped molded products need to be melted and flowed are explained. Due to the special nature of the molding method, the viscosity of the resin composition when combined is on the order of 10 ³ to 10 ⁴ poise, which is much higher than that of epoxy resins, and although it has the advantage that flashing is essentially less likely to occur, it is still A conventionally proposed mold with a recess 1 as shown in Fig. 1,
1' to the plate-shaped molded products 3, 3' melted melt 2, 2'
In the case of a joining method in which there is a pronounced However, due to structural problems, it was not possible to completely eliminate flash.

For this reason, an improved method as shown in FIG. 2 has been proposed. That is, at least one preformed
Each piece (both pieces in FIG. 2) has a recess 5, 5' for accommodating the semiconductor, and includes surfaces in contact with the front surface 6 or back surface 7 of the lead frame 4 after the molten material is formed, respectively, in the same plane. Two plate-shaped molded products 3, 3' each having a shape in which the contours of the virtual cross-sections 8,8' are the maximum contours of the plane parallel to the lead frame surface are assembled to At least the plate-shaped molded product 3, which has the same shape as the outline of the parts in contact with the front and back surfaces of the lead frame, respectively, in the product.
The depth is equal to the thickness of the molten metal parts 2, 2' of 3', and the mold surfaces 10 of the merging molds 9, 9' to which the molten metal parts 2, 2' of the plate-shaped molded products fix the lead frame before merging. , 10', and the molten product is softened and melted by various heating means such as conduction from various heating sources, radiation, etc. A plate-shaped molded product crimping machine 12, 1 that clamps and fixes a lead frame from both front and back sides between two merging dies, and crimps a plate-shaped molded product to the lead frame independently of the merging dies.
2' proposes a method in which a plate-shaped molded product is crimped and integrated with a lead frame.

This improved method is an effective joining method in that it does not easily cause harmful flashing, but after softening and melting the molten material of the two plate-shaped molded products, the semiconductor is applied to the joining part of the two joining molds. It is necessary to either move the mounted lead frame or move the joining mold containing the plate-shaped molded product toward the lead frame fixed to the combined part, and the process of moving the molded plate-shaped product as it heats up. Some flashing due to thermal expansion is unavoidable, and it is essential to minimize the time required for this movement and maintain a softened and molten state in order to obtain good and reliable sealing. Semiconductors with defective sealing properties due to disturbance factors that are difficult to control, which is thought to be caused by a temperature drop on the combined surface of plate-shaped molded products and lead frames that are open to the surrounding atmosphere during this time of movement. There was a problem that the package of 2000 occurred, although it was rare.

The present invention has been made in view of these drawbacks, and will be described in detail below with reference to drawings showing embodiments.

In FIG. 3, the lead frame 4 is sandwiched between the pair of joining dies 9 and 9', and the joining surface 16 of the plate-shaped molded product 3 on the side that accommodates the semiconductors 15 is brought into contact with the lead frame 4. In this state, it is placed in the recess 17 of the combining mold 9', and the other combining mold 9' is placed in the recess 17' of the combining mold 9' with a portion 18 in contact with the lead frame of the combining mold remaining on at least one side. With the heating element 20 inserted into the recess 17' of the combining mold through the introduction hole, the other heating element is inserted into the recess of the combining mold so as not to come into contact with the heating element. The plastic resin plate-shaped molded product 3' is placed, heated in this state by the heating element 20, the heating element 20 is removed from the recess 17' of the combining mold, and then the plate-shaped molded product mounted in the recess is crimped. Machine 12,
12', the plate-shaped molded products are combined by opposing heating.

As mentioned above, in the present invention, before the lead frame is heated and pressurized into a plate-shaped molded product, (1) the lead frame is placed in a state in advance between the joining surfaces of the pair of joining molds ( 2) The contact mold surfaces of the merging molds that sandwich the lead frame are combined with the part of the merging mold that contacts the lead frame left open so that the periphery of the recess for storing the plate-shaped molded product is closed. A heating element introduction hole is formed on at least one side of the mold. (3) The surface of the lead frame on which semiconductors are mounted and the combined surface of the plate-shaped molded product on the side that houses semiconductors are substantially connected to each other. (4) The other plate-shaped molded product must be placed in the recess in the combination mold with its combined surface facing the lead frame, and (5) After heating is completed. After the heating element is removed, a plate-shaped molded product crimping machine must be installed in the recess of the combination mold in order to combine the two plate-shaped molded products and the lead frame.

Due to (1) and (2) above, the lead frame is sandwiched between the combined surfaces of the pair of combined types, and the periphery of the plate-shaped molded product is completely closed, preventing the occurrence of harmful flash. It has a remarkable effect on

That is, since the lead frame is closely fixed on both the front and back sides by the mold surfaces of the joining mold, the joining molds 9, 9' and lead frame 4 in FIG. Although the resin flows into the intended flash reservoir 14 formed by the dam, it cannot flow between the mold surface and the front and back surfaces of the lead, thereby preventing the formation of harmful flash.

More preferably, as mentioned above, the viscosity of the thermoplastic resin constituting the plate-shaped molded product used in the present invention during flow is on the order of 10 ³ to ^{10 4} poise, which is much higher than that of epoxy resin, and the lead frame itself Even if a minute gap is created between the lead frame and the mold surface of the lead frame and the mold surface due to variations in the thickness of the lead frame, machining accuracy of the lead frame, wear due to the use of the mold, or deviations in dimensions, harmful flash may be formed. It is possible to prevent this.

The greatest effect of the present invention is that (3), which was conventionally done by softening and melting the plate-shaped body, moves the lead frame with the semiconductor attached to the combined part, or moves it towards the lead frame fixed to the combined part. This eliminates the need for the process of moving the combined body containing the plate-shaped molded product a certain distance, and the process of moving the combined molded body containing the plate-shaped molded product a certain distance is no longer necessary, and the plate-shaped molded product and lead frame that are exposed to an atmosphere with a relatively low temperature compared to the heating temperature in conventional methods can be removed. In contrast, in the present invention, the movement of the plate-shaped molded product is limited to an extremely limited space that is almost closed, and furthermore, the temperature drop during the movement of the molded product is unavoidable. The time required is also shortened compared to conventional methods due to the reduction in the number of steps after heating, so the softened and molten state of the total surface of the plate-shaped molded product can be easily maintained close to the intended favorable coalescence conditions, resulting in highly reliable and good sealing. This has an extremely large effect on obtaining antistatic properties.

When heating, it is important that the surface of the lead frame on which the semiconductors are mounted and the combined surface of the plate-shaped molded product on the side that houses the semiconductors must be in substantial contact, so that the leads cannot be heated in a non-contact state. When heating from the frame side, the combined surface of the plate-shaped molded product corresponding to the shadow of the lead frame is shielded from the heating element by the lead frame, so the softening and melting state due to heating is insufficient, resulting in a highly reliable sealing state. It will be difficult to secure.

By heating through the lead frame while the lead frame surface and the plate-shaped molded product are in contact with each other, the contact joining surface is sufficiently melted by heat conduction from the lead frame, making it possible to form a lead frame that requires the most adhesion. The thermoplastic resin forming the plate-shaped molded product will be firmly combined with the thermoplastic resin.

In this case, the joining surface of the plate-shaped molded product that is not shadowed by the lead frame, which corresponds to the gap between the leads, naturally reaches a sufficiently softened and molten state by heating, and is then sufficiently joined by the pressurizing process. This will give you strength.

The side of the lead frame on which semiconductors are attached generally refers to the side on which the pellet is attached on the tab.
In this case, since heating is performed from the lead frame surface opposite to the pellet mounting surface, damage to the semiconductors due to heating can be prevented.

However, the surface of the lead frame on which the semiconductors are attached is not limited to this. For example, in the case where the tab 21 is offset in the lead frame 4 as shown in FIG. As shown in the figure, heating can also be carried out from the lead frame side of the pellet mounting surface using a heating element provided with a shielding material to protect the semiconductors from damage due to heating, if necessary.

The heating element used in the present invention is not particularly limited in its style, structure, etc., and must be one that can be easily inserted into and removed from the heating element introduction hole and has the ability to soften and melt the combined surface of the plate-shaped molded product in a short time. It is enough as long as it is.

Particularly, indirect heating, such as heating with hot air or radiant heating, can be preferably used.

In hot air heating, the heating source is placed outside the mold.
As shown in the figure, it is also possible to introduce only hot air into the cavity 17' of the mold through the hot air introduction hole 22 and discharge it through the hot air discharge hole 23, which is a preferred heating method especially when space is limited.

Various types of thermoplastic resins are used in the present invention depending on the characteristics required for the package of each semiconductor type, but the thermoplastic resins have high heat resistance (heat deformation resistance and heat deterioration resistance), low moisture permeability, and constant In addition to electrical and mechanical properties that exceed standards, it is also necessary to have moldability that exceeds a certain level.

Typical examples are polyphenylene oxide,
A grade with low water absorption among ether resins such as polyether sulfon, polysulfon, phenoxy resin, and polyacetal, ester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyarylate, carbonate ester resins such as polycarbonate, and polyamide resins. Examples include resins such as polyphenylene sulfide, and combinations of some of these resins and fillers, mainly glass fibers.

Further, as the material for the joining mold, a metal mold having excellent thermal conductivity and durability is preferable, but a so-called resin mold made by homogeneously mixing a thermosetting resin with metal powder or the like can also be used.

Example A recess for accommodating a semiconductor in the shape shown in Figure 6 using polyphenylene sulfide resin with a heat distortion temperature (ASTM D-648, 18.6 Kg/cm ² load) of 260°C or higher. A pair of plate-shaped molded products each having a cavity 24 for accommodating a part of the melted resin and a part of the molten resin were molded by injection molding.

Next, a mold for combining the plate-shaped molded product and a 16-pin DIP type lead frame whose surface is plated with silver, and a side wall of the mold for combining after placing the plate-shaped molded product crimping machine in the position as shown in Fig. 3. Height: 10mm, width
An electric hot air heater with a structure that uniformly blows hot air up and down from a 6.4mm heating element introduction hole is inserted, and the temperature is 450℃±.
Apply hot air at 5℃ (near the air outlet) at a flow rate of 30/min for 4 seconds to the plate-shaped molded product on the side housing the semiconductors from the side opposite to the side where the semiconductors are mounted. The other plate-shaped molded product was sprayed onto the combined surface through the lead frame that was in contact with the lead frame.

Next, the hot air heater was extracted from the heating element introduction hole, and the plate-shaped molded products were joined together with a lead frame sandwiched therebetween by applying a load of 50 kg using a plate-shaped molded product crimping machine.
The time required from removing the hot air heater from the heating element introduction hole to crimping was 0.5 seconds, and after a cooling time of 2 seconds, the combining mold was opened and the combined product was taken out. 1000
In all of these combined products, flash was only formed in the intended flash reservoir formed by the dam of the lead frame, the combined surface of the mold for combination, and the lead, and there was no harmful flash around the plate-shaped molded product. No occurrence was observed.

In addition, the obtained combined product was immersed in a red alcohol solution under pressure for 24 hours at a pressure of 5Kg/cm ² , and no red material was observed to enter the package.
In the 85°C-85% relative humidity bias test, it was confirmed that all the samples (500 pieces) had good characteristics.

As detailed above, according to the present invention, the following effects can be obtained. In other words, the lead frame is sandwiched between the combined surfaces of the pair of combined types, and the plate-shaped molded products are combined with the periphery completely closed, making it possible to eliminate harmful flash and also to prevent semiconductors from being damaged. By heating the combined side surface of the plate-shaped molded product on the storage side through the lead frame while in contact with the surface of the lead frame, the combined surface of the plate-shaped molded product can be sufficiently homogeneously softened and melted. It is possible to extremely shorten the time required from completion to pressurization and to minimize the drop in temperature of the heated joining surfaces, ensuring strong joining and making it possible to manufacture highly reliable semiconductor packages. Summer.

[Brief explanation of the drawing]

Figures 1 and 2 are cross-sectional views showing the conventionally proposed combining method, Figures 3, 4, and 5 are cross-sectional views showing the combining method according to the present invention, and Figures 6 A and B are respectively FIG. 7 is a cross-sectional and plan view of the plastic resin plate-shaped molded product, and a perspective view showing the state of the semiconductor package after being combined. Explanation of symbols, 1, 1'...Mold with depression, 2,
2'... Molten metal material, 3, 3'... Plate-shaped molded product, 4
...Lead frame, 5, 5'...Semiconductor storage recess, 6...Surface of lead frame, 7...Back surface of lead frame, 8, 8'...Virtual cross section, 9...
Mold for merging, 10, 10'... Mold surface of the merging mold, 1
1, 11'... Plate-shaped molded product storage recess, 12, 1
2'...Plate molded product crimping machine, 13...Dam, 14
... Intended flash reservoir, 15... Semiconductors, 16, 16'... Merging surface, 17, 17'... Recess, 18... Part in contact with the lead frame of the joining mold, 19... Heating body introduction hole , 20... heating element,
21...Tab, 22...Hot air introduction hole, 23...Hot air discharge hole, 24...Gap.

Claims (1)

[Claims] 1. Two thermoplastic resin plate-shaped molded products, at least one of which has a recess for accommodating a semiconductor, are molten and fused together to form a hypothetical cross-sectional outline that includes surfaces in contact with both the front and back surfaces of a lead frame, respectively, in the same plane. The thermoplastic resin plate-shaped molded product is placed in the recess of the combination mold, which has a maximum outline on a plane parallel to the lead frame surface and has recesses having the same shape as the outline on at least the sides in contact with the front and back surfaces of the lead frame. In a semiconductor package molding method in which a lead frame with semiconductors attached thereto is sandwiched and heated and pressurized, the combined side surface of the thermoplastic resin plate-shaped molded product on the side housing the semiconductors is aligned with the surface of the lead frame. The leads are placed in contact with each other in one of the merging molds, and a heating element introduction hole is provided on the side surface of the other merging mold to penetrate into the recess in the merging mold, leaving a portion for holding the lead frame. With the heating element introduced into the merging mold through the heating element introduction hole, the merging side surface of the other thermoplastic resin plate molded product is placed in the merging mold recess so as not to come into contact with the heating element, and the semiconductor After heating the joining surface of the thermoplastic resin plate-shaped molded product on the side that houses the items through the lead frame, and directly on the joining surface of the other thermoplastic resin plate-shaped molded product, the heating element is removed from the joining mold, and then the joining surface is heated. A method for molding packages for semiconductors, characterized in that thermoplastic resin plate-shaped molded products are joined together under opposing pressure by a plate-shaped molded product crimping machine installed in the recess of a mold.