JPH0260500B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a resin sealing method using a transfer molding method and a high frequency preheating device used in the method.

In the process of manufacturing semiconductor devices, a resin tablet is supplied to a molding machine with a mold, heated and melted, and the molten resin is injected under pressure into the cavity of the mold to produce semiconductor elements and There is a resin sealing process using a so-called transfer molding method in which a resin sealant is formed to cover a part of a metal lead connected to an electrode of a semiconductor element. In this method, a resin tablet is placed in a pot of a mold heated to approximately 170°C.
The resin is heated and melted and pressed with a plunger to inject the resin into the cavity. In addition, in order to efficiently heat and melt the resin tablet in the mold pot, the resin tablet is softened by heating to a temperature of, for example, about 100° C. to an extent that it does not melt before being put into the mold pot. A high frequency preheating device is used as a means for preheating the resin tablet. A conventional high-frequency preheating device has a lower electrode for high-frequency heating consisting of a pair of rotatable rollers arranged horizontally apart from each other, and an upper electrode for high-frequency heating arranged on the lower electrode. , so that a high frequency voltage can be applied between the electrodes. When heating, a resin tablet having a circular cross section and a predetermined length is placed on the lower electrode consisting of the pair of rollers, and while rotating the resin tablet by rotating the rollers, the upper electrode is heated. A high frequency voltage is applied between the electrode and the lower electrode to heat it. The inventor of this application has discovered that this method has a problem in that more high-frequency energy is absorbed at the outer periphery of the resin tablet than at the center of the cross section, and that the outer periphery is heated to a higher temperature than the center. , only the outer periphery softens and melts first,
It was discovered that there are disadvantages in that it is difficult to handle and resin sealing cannot be performed efficiently.

The present invention has been made by focusing on the problems and drawbacks of the prior art described above, and its purpose is to preheat the resin tablet so that the central part of the tablet is softer than the outer periphery. It is an object of the present invention to provide a high-frequency preheating device that enables easy handling of rets and efficient resin sealing.

The gist of the present invention is to provide a cylindrical resin tablet, an upper electrode and a lower electrode disposed above and below the resin tablet, respectively, for high-frequency heating of the resin tablet, and the upper electrode and the lower electrode. In a high-frequency preheating device having a high-frequency power supply for applying a high-frequency voltage between , and the energy per unit time applied to the resin tablet by applying the high frequency voltage is higher in the central portion of the circular cross section of the resin tablet than in the circular cross section. The high frequency preheating device is characterized in that the shape and relative positional relationship of the upper electrode and the lower electrode are defined so that the upper electrode and the lower electrode are larger than the outer peripheral portion of the cross section.

FIG. 1 is a reference example and shows a preheated state of a resin tablet. FIG. 1a is a perspective view, and FIG. 1b is a sectional view taken along the line -' in FIG. 1a. A resin tablet 1 having a circular cross section and a predetermined length is placed on two rollers 2 and 3 spaced apart from each other. 4,5
are the upper and lower electrodes of a high-frequency heating device placed above and below the resin tablet 1 placed on the two rollers 2 and 3, respectively. The width W of the upper and lower electrodes is smaller than the diameter W' of the resin tablet. Further, the length L of the upper electrode and the lower electrode is larger than the length L' of the resin tablet. For example, by rotating the two rollers 2 and 3 in the same direction as shown by arrow A in the figure, the resin tablet 1 is
While rotating the resin tablet in the direction shown by arrow B in the figure, a high frequency voltage is applied between the upper electrode 4 and the lower electrode 5 to heat the resin tablet. According to this type of heating, energy is applied to the outer periphery of the resin tablet only when it is located between two electrodes due to rotation, but energy is applied to the center of the cross section always when it is located between two electrodes. The energy applied to the resin tablet 1 per unit time is greater at the center than at the outer periphery, and as a result, the center is heated to a higher temperature than the outer periphery, resulting in a softened state. The resin tablet 1 thus preheated to a temperature of about 100° C. is placed into a pot (not shown) provided in a mold of a molding machine. Preheat the mold to about 170℃. The preheated resin tablet is placed into a mold pot heated to approximately 170°C, whereupon it is further heated to a high temperature and melted. The resin melted in this pot is pressurized by a plunger (not shown) provided in the molding machine, passes through a flow path (runner) provided in the mold, and is injected into each cavity. In this way, the semiconductor element sealed in each cavity and a portion of the metal lead connected to the electrode of the semiconductor element are covered with the injected resin.

FIG. 2 shows a preheating state of a resin tablet in a high frequency preheating device which is an embodiment of the present invention. Figure 2a is a perspective view, Figure 2b
is a sectional view taken along the line -' in FIG. 2a.
A resin tablet 6 having a circular cross section and a predetermined length is placed on a support plate 7 made of an insulating material that is heat resistant and has poor adhesion to resin, such as fluororesin. An opening 8 having a diameter smaller than the diameter of the resin tablet 6 is formed in the support plate 7. The tablet 6 is placed so that the center of its cross section is exposed within the opening. 9 and 10 are an upper electrode and a lower electrode for high frequency heating, respectively. The electrodes 9 and 10 are, for example, circular and have a diameter smaller than the diameter of the resin tablet. The resin tablet and electrodes 9 and 10 are placed concentrically, and a high frequency voltage is applied between the upper electrode 9 and the lower electrode 10 to apply the resin tablet. According to such a heating method, the diameter of the electrodes 9 and 10 is smaller than the diameter of the resin tablet, and since they are located concentrically with the resin tablet, the outer periphery of the resin tablet 6 is exposed to the electrodes 9 and 10 at a high frequency. Since the resin tablet is removed from the high-frequency electric field formed by applying a voltage, a large amount of energy is applied to the center of the cross section of the resin tablet, causing it to be heated. Therefore, the center part of the resin tablet can be made softer than the outer peripheral part. In this way about
A resin tablet 6 preheated to a temperature of about 100° C. is put into a pot (not shown) provided in a mold of a molding machine. The mold is preheated to a high temperature of approximately 170°C. The resin tablet placed in the mold pot is heated to a higher temperature and melts. The resin melted in this pot is applied by a plunger (not shown) provided in the molding machine, passes through a runner provided in the mold, and is injected into each cavity of the mold. In this way, the object to be sealed, such as a semiconductor element, sealed in each cavity is covered with the injected resin.

FIG. 3 shows a preheating state of a resin tablet in a high frequency preheating device according to another embodiment of the present invention. FIG. 3a is a perspective view thereof, and FIG. 3b is a sectional view taken along the line -' of FIG. 3a. In this embodiment, by using hemispherical upper electrode 11 and lower electrode 12 in place of the disc-shaped electrodes shown in the embodiment of FIG. 2, the electric field is strongest at the point where the distance between the electrodes is closest. Taking advantage of this fact, the center of the resin tablet 6 can be heated to the highest temperature, and the heating temperature can be linearly varied from the center toward the outer periphery.

As described above in the examples, according to the present invention, the center of the resin tablet can be preheated to a state where it is softer than the outer periphery, so deformation of the resin tablet can be prevented and handling is easier. This makes it easy to perform resin sealing effectively. In addition, since it is possible to prevent the resin tablet from deforming, it is possible to prevent the generation of air bubbles during resin molding, which is caused by the deformation of the resin tablet as in the past, thereby improving the yield of resin sealing. be able to.

[Brief explanation of drawings]

FIG. 1a is a perspective view showing a preheating state of a resin tablet in a high-frequency preheating device as a reference example, and FIG. 1b is a sectional view taken along the line -' of FIG. 1a. FIG. 2a is a perspective view showing a preheating state of a resin tablet in a high-frequency preheating device according to an embodiment of the present invention, and FIG.
FIG. FIG. 3a is a perspective view showing a preheating state of a resin tablet in a high frequency preheating device according to another embodiment of the present invention;
Figure b is a sectional view taken along the line -' of figure a. 1, 6... Resin tablet, 2, 3... Roller, 4, 9, 11... Upper electrode for high frequency heating,
5, 10, 12... lower electrode for high frequency heating, 7...
...Support plate.

Claims (1)

[Claims] 1. A cylindrical resin tablet, an upper electrode and a lower electrode arranged respectively above and below the resin tablet in order to heat the resin tablet with high frequency, and a high frequency In a high-frequency preheating device having a high-frequency power supply for applying a voltage, the upper electrode is disposed above one end of the resin tablet, the lower electrode is arranged opposite to the upper electrode, and the upper electrode is disposed above one end of the resin tablet. The resin tablet is disposed above the other end of the tablet, and the energy per unit time applied to the resin tablet by applying the high frequency voltage is higher at the center of the circular cross section of the resin tablet than at the outer periphery of the circular cross section. A high-frequency preheating device, characterized in that the shape and relative positional relationship of the upper electrode and the lower electrode are defined so that the upper electrode and the lower electrode are larger than the lower electrode.