JPH0360649B2 - - Google Patents

Description

[Detailed Description of the Invention] (1) Technical Field of the Invention The present invention relates to a method for forming a plastic mold, and more specifically, a method for forming a plastic mold, in which a heating furnace is disposed close to the mold, and the plastic material is heated in the mold for a short period of time. The present invention relates to a mold forming method in which the mold is subsequently hardened by heating in the heating furnace.

(2) Background of the Technology Semiconductor integrated circuit ICs using a lead frame as shown in the plan view of FIG. 1 are widely used. In these figures, 1 is a plastic mold, 2 is a semiconductor chip (this semiconductor chip is covered by the mold 1 and cannot be seen from the outside), 3 is a lead, and 4 is a feeding cradle. Note that predetermined portions of the semiconductor chip 2 are connected to respective leads 3 by bonding wires (not shown).

A molding device is used to form the mold 1 in the process of manufacturing such a semiconductor IC. FIG. 2 schematically shows the lower mold 11 of the molding device in a plan view. In the same figure, 12 is a cull into which plastic is injected, and 13 is a runner which is a channel through which molten plastic flows. indicates, semiconductor
The ICs are arranged in pairs on both sides of the runner 13.
In actual use, more runners are formed and more semiconductor ICs are sealed with resin, but these are shown in a simplified manner in the figure.

In operation, referring to FIG. 3, which schematically shows a cross-sectional view of the molding device, the semiconductor IC is placed in the second
The molds are arranged as shown in the figure, and after being pressurized by the mold press 14, the plastic is injected from the injection cylinder 15, and after the plastic is semi-hardened, the product is taken out and completely cured in a constant temperature bath. In addition, in FIG. 3, 11A indicates the upper mold.

(3) Conventional technology and problems The above-mentioned plastic has a temperature of 70 to 80°C during injection.
℃, and when placed in a mold heated to 160 to 180 degrees Celsius for about 1 to 2 minutes, it becomes semi-cured. This means that after the plastic is injected, the molding equipment, including the mold die and pressure press, is used only to heat the plastic to harden it.
Then 1-2 minutes of time is wasted. this is,
Taking into account that molding equipment is very expensive, this means that the investment in equipment is underutilized. Also, from the standpoint of work efficiency, the heating time of 1 to 2 minutes is not utilized at all.

(4) Purpose of the Invention In view of the above-mentioned conventional problems, the present invention provides a mold forming method that can increase the operating rate of expensive equipment and at the same time completely cure the plastic without going through the process of keeping it at a constant room temperature. It is on offer.

(5) Structure of the Invention According to the present invention, a molding device including a mold die and a press is used only for the original plastic injection work, and the plastic is only used to the extent that the plastic can be handled within the mold, that is, the mold This is achieved by a mold forming method in which the plastic is hardened to such an extent that it does not deform, and then the plastic is placed in a heating furnace provided close to the mold without lowering its temperature to harden the plastic.

(6) Examples of the invention Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 4 schematically shows a molding apparatus used for carrying out the method of the present invention in cross-section, and the same parts as those already shown in the figure are designated by the same reference numerals.

Plastic is injected from the plastic injection cylinder 13 as in the prior art. The temperature of the plastic material at this time is 70 to 80℃ as mentioned above.
It is. On the other hand, the molds, namely the lower mold 11 and the upper mold 11
A is heated to 160-180℃. Under these conditions, the plastic hardens in, for example, 10 to 20 seconds to the extent that it can be handled, ie, to the extent that the mold does not deform.

In the prior art, it takes, for example, 60 to 90 seconds to cure the plastic, during which time the molding device including the mold die and the press is used only for the purpose of curing the plastic. The inventor of the present application focused on the characteristics of the change in hardness of molten plastic over time, which is shown in the diagram of FIG. i.e. the bottom of the boat or U in the graph of fig.
In region A, such as the bottom of the letter, the plastic hardness changes little over time. In the prior art, the plastic was left in the mold for 60 to 90 seconds at this hardness. Mold equipment is currently expensive, costing around 10,000,000 yen, and it is wasteful to leave such expensive equipment unused for up to two minutes in some cases.

The inventor of the present application further states that the plastic is 160 to 180
They noticed that when placed in a mold heated to ℃ for 10 to 20 seconds, it hardened to the extent that it could be handled. In the method of the present invention, after 10 to 20 seconds have elapsed after plastic injection and the plastic mold has become hard enough not to be deformed, the plastic mold is removed from the mold, and the molding device is turned on without leaving it at room temperature. It is transferred to a heating furnace 16 located nearby. This heating furnace 16 is heated to the same temperature as the mold temperature (160 to 180°C) when the plastic is injected, and the plastic is hardened in the same way as conventionally in the mold. be.

Such a heating furnace 16 is schematically shown in FIG. 4, but since it is sufficient to heat the inside of the furnace to 160 to 180 DEG C., it can be easily manufactured using known techniques. Further, the semiconductor IC is moved by placing it on a conveyor 17 using, for example, a chuck means (not shown), and transferring it into the heating furnace 16 by this conveyor. After the plastic is left in the heating furnace 16 for, for example, 90 seconds to sufficiently harden, the semiconductor IC is transferred to a constant temperature bath as in the conventional case. Thus,
The temporal relationship in the method of the present invention can be summarized by the following equation, where the left side is for the method of the present invention and the right side is for the prior art. (Time in the mold) + (Time in the heating furnace) = (Time in the conventional mold) (7) Effects of the Invention As explained above in detail, in molding a semiconductor IC by the method of the present invention, The time the mold remains in the mold of the molding equipment is greatly reduced, increasing the availability of expensive equipment while achieving complete curing of the plastic and improving semiconductor production.
Hardening is very important in improving the yield of IC manufacturing.

In the above description, a semiconductor IC was taken as an example, but the scope of application of the present invention is not limited to that case, but is also applicable to all other cases of plastic mold formation.

[Brief explanation of drawings]

Fig. 1 is a plan view of a semiconductor IC, Fig. 2 is a schematic plan view of the lower mold of a molding device, Fig. 3 is a schematic cross-sectional view of a conventional molding device, and Fig. 4 is a schematic cross-sectional view of a conventional molding device. FIG. 5 is a diagram showing the relationship between the hardness of the molten plastic and the time. 1...Plastic mold, 11...Lower mold,
11A...Upper mold, 12...Cull, 13...Runner, 14...Mold pressure press, 15...Plastic injection cylinder, 16...Heating furnace, 17...
conveyor.

Claims (1)

[Claims] 1. In a method of forming a plastic mold using a molding device consisting of a mold die and a press for pressurizing the mold, a heating furnace is provided in close proximity to the molding device to the extent that the plastic material injected into the molding device is not deformed. 1. A method of forming a plastic mold, which comprises keeping the plastic material in the mold until the plastic material is hardened, and then transferring the plastic material to a heating furnace heated to approximately the same temperature as the mold and hardening it.