JPH10214853A - Semiconductor sealing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the moldability of low-viscosity sealing material under low injection pressure, by providing the screw of an injection molding machine with a reverse flow preventing mechanism. SOLUTION: Sealing material fed into a hopper stays in the front part of a cylinder 3 through the rotation of a screw 1. The amount of the sealing material stayed is controlled by the position to which the screw 1 is retreated, and the sealing material is returned along the groove of the screw 1 at the next shot. Depending on the amount of this back-flow, products may develop filling failure or sink mark due to short shot. To cope with this, the screw 1 of the injection molding machine is provided with a mechanism to prevent or reduce back flow. Specifically, back flow is reduced by installing a barrier 5 in the groove of the screw 1 or installing a plunger at the tip 4 of the screw to prevent sealing material from being returned to the groove of the screw 1, immediately before the screw 1 advances farthest in the final stage of injection filing when the amount of back flow is maximized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for sealing a semiconductor by injection molding using an epoxy resin sealing material.

[0002]

2. Description of the Related Art For sealing semiconductor elements such as ICs, LSIs, and discretes, transfer molding of an epoxy resin sealing material has conventionally been used as a method suitable for low cost, high reliability and productivity. In transfer molding, the epoxy resin sealing material is preformed in the form of a tablet, poured into a pot in a mold, and heated and melted, and is pressed into the mold cavity, transferred to the mold cavity, and cured. Is common. However, in this molding method, it is premised that the epoxy resin sealing material is preformed in a tablet shape, so that a tablet molding step is required. Since the shape of the tablet varies depending on the shape and size of the semiconductor to be molded, many mold devices for tablet molding are required.

In addition, since tablet injection and heat melting are required for each molding, the molding cycle cannot be made shorter than a certain time. From these points, there is a limit in cost reduction and mass productivity, and since a pre-process such as tablet molding is required, there is a high possibility that impurities are mixed in the sealing material. Furthermore, in transfer molding, the runner part, which is the flow path until the sealing material put into the pot flows in the mold and reaches the cavity, and the remaining cull part in the pot are completely cured. In addition, there is a problem that reuse is impossible and a large amount of resin waste is generated in a part other than a necessary semiconductor package part.

On the other hand, an injection molding method has been conventionally studied as a molding of a thermosetting resin molding material containing an epoxy resin. In injection molding, an epoxy resin molding material is supplied in a powder or granular form into an injection molding machine, and is injected into a mold by a screw while being kept in a molten state in a cylinder. For this reason, the problem of the transfer molding can be solved, for example, a tablet preforming step is not required.

However, at present, injection molding has not been put to practical use as a method for molding an epoxy resin sealing material. The reason is that there is a problem in the stability of injection molding at low pressure. This is because the reliability of the obtained semiconductor package is significantly impaired due to the deformation or cutting of the bonding wire on the semiconductor element in the injection molding, or in the case of diodes etc., the reduction of the electrical performance due to the pressure applied to the internal element. And the injection pressure needs to be low. As a result, when the screw advances at the time of injection, a phenomenon in which the resin molding material melted and measured at the screw tip is returned backward along the screw groove due to the flow resistance of the nozzle, the mold flow path, the gate, and the like. As a result, the amount of the injected resin varies, the transmission efficiency of the pressure is increased, and the molding is not stable.

[0006]

The present invention can be formed by a conventional low-pressure transfer molding method. In the method of sealing semiconductor by low pressure and low speed injection molding using epoxy resin sealing material for injection molding, various methods are used to solve the problem that the sealing material melted and measured at the screw tip part is returned to the back. The result of the examination of
An object of the present invention is to provide a semiconductor encapsulation method in which the moldability of a low-viscosity encapsulating material at a low injection pressure is improved.

[0007]

According to the present invention, a lead frame to which a semiconductor is joined and a wire frame to which a wire is bonded or a semiconductor element is joined is fixed to an injection mold as an insert, and thereafter, the mold is fixed. In a semiconductor encapsulation method in which an epoxy resin, a phenolic resin curing agent, a curing accelerator, and an injection molding epoxy resin encapsulating material having an inorganic filler as essential components are injected by an injection molding machine and cured, the injection molding machine has A semiconductor sealing method characterized in that a backflow prevention mechanism is provided on a screw.

The screw for an injection molding machine used in the present invention is provided with a backflow prevention mechanism at a tip end thereof. In general injection molding of a thermosetting resin, the full flight screw shown in FIG. 1 is used. Have been. In FIG. 1, 21 is a screw, 22 is a flight of the screw, and 23 is a cylinder. With this screw, when the material has a low viscosity, for example, 3000 centipoise or less, the backflow of the resin is large and the shot quantity is not stable.
In order to eliminate such disadvantages, the screw used in the present invention has a structure in which a flight groove at the tip of the screw is narrowed and a barrier (a crevice for reducing the return of the resin) is provided (FIG. 2), or the resin is filled in the mold cavity. It has a structure having a plunger at the tip of the screw (FIG. 3) and the like, which is designed to eliminate the gap with the nozzle at the time of filling and when the pressure starts to rise. In FIG. 2, 1 is a screw, 2 is a flight of the screw,
Reference numeral 3 denotes a cylinder, 4 denotes a screw tip, and 5 denotes a barrier. In FIG. 3, 11 is a screw, 12 is a flight of the screw, 13 is a cylinder, 14 is a plunger at the tip of the screw, and 15 is a nozzle sleeve corresponding to the plunger. With such a structure, the backflow of the resin during injection molding can be effectively prevented.

[0009] As a general operation of the injection molding, the sealing material put into the hopper is rotated by the rotation of the screw.
It is transported to the front of the cylinder, and at the same time melts due to heat conduction from the cylinder and heat generated by the shear, and stays at the front of the cylinder. In this case, the stagnation amount is one shot, and the weighing is controlled by the position of the screw retreat. The metered sealing material is ejected from the nozzle in the next shot, but is then returned along the screw groove depending on the pressure on the sealing material and the viscosity of the resin. This is called a backflow, and depending on the amount of the backflow, a product may cause a defective filling due to a short shot, sink, or the like. According to the present invention, a screw is provided with a mechanism for preventing or reducing backflow in an injection molding machine. More specifically, for example, a screw (barrier) is provided in the screw groove, or the sealing material is not returned to the screw groove from just before the screw, which is the final stage of the injection filling in which the backflow is largest, is most advanced. By providing a plunger at the tip of the screw, backflow is reduced.

[0010]

Embodiments of the present invention will be described below. As an epoxy resin encapsulating material, an ortho-cresol novolak type epoxy resin (epoxy equivalent: 200), phenol novolak (hydroxyl equivalent: 103), a diazabicyclounzecene compound (curing accelerator), and fused silica are used as main components. What mixed a molding agent, a coloring agent, etc. was used.

The barrier screw (FIG. 2) of the present invention was mounted on an injection molding machine having a mold clamping force of 50 tons and an injection cylinder inner diameter of 32 mm. The mold has 2 rows and 10 rows of 2
10 continuous copper leadframes 2 with no IC chip (20pSOP) bonded and gold wire bonded
The book was set in a mold, the mold temperature was set to 175 ° C., and 200 shots were continuously molded in a molding cycle of 80 seconds. In the case of the conventional full-flight screw (FIG. 1), molding was performed in the same manner, and the variation (standard deviation) and the variation rate for each shot were obtained. The results of comparison are shown in Table 1.

[0012]

The variation in shot amount was obtained by measuring the weight of a molded product for each shot, and the variation was shown by a standard deviation, and the variation was shown by a value obtained by dividing the standard deviation by the average shot amount.
As a result, the variation rate was about 2/3 to 1/2, and the variation in shot amount could be reduced by reducing the backflow. In addition, the appearance, filling property, wire sweep, and void of the molded product were also evaluated, and it was confirmed that there was no problem at least as high as the conventional product.

[0014]

According to the present invention, it is possible to perform continuous molding with a stable shot amount by injection molding of semiconductor encapsulation using an epoxy resin encapsulating material for injection molding, and to prevent poor filling and poor appearance. be able to. More stable products can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a front part of an injection molding machine having a conventional full flight screw.

FIG. 2 is a sectional view of a front part of an injection molding machine having a screw provided with a barrier.

FIG. 3 is a sectional view of a front part of an injection molding machine having a screw provided with a plunger mechanism.

[Explanation of symbols]

 1,11,21 Screw 2,12,22 Flight of screw 3,13,23 Cylinder 4 Screw tip 5 Barrier 14 Plunger at screw tip 15 Nozzle sleeve

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁶ Identification code FI // B29L 31:34

Claims (2)

[Claims] 1. A lead frame to which a semiconductor is joined and wire-bonded or a lead wire to which a semiconductor element is joined is fixed as an insert to an injection molding die, and thereafter, an epoxy resin and a phenol resin curing agent are fixed to the die. ,
In a semiconductor encapsulation method of injecting and curing an epoxy resin sealing material for injection molding containing a curing accelerator and an inorganic filler as essential components by using an injection molding machine, a screw for the injection molding machine was provided with a backflow prevention mechanism. A semiconductor sealing method characterized by the above-mentioned. 2. The semiconductor sealing method according to claim 1, wherein the screw provided with the backflow prevention mechanism is a barrier screw or a screw having a plunger at a tip.