JPH0148126B2 - - Google Patents

Description

[Detailed Description of the Invention] (1) Technical Field of the Invention The present invention relates to a transfer molding device, specifically, a transfer molding device equipped with a mechanism in which the resin injection speed of one stroke is changed in multiple steps or continuously (stepless speed). The present invention relates to a transfer molding device.

(2) Background of the technology Tree-encapsulated semiconductor devices are manufactured using transfer molding equipment.

Figure 1 shows a resin-encapsulated semiconductor device (plastic
Lead frame 1 for (also called IC)
A plan view of a part of the die is shown, and in the figure, 2 is a cradle, 3 is a die stage for mounting a semiconductor chip, 4 is a pinch for connecting the die stage 3 to the cradle 2, and 5 is a lead.

The die stage to which the semiconductor chip of the lead frame 1 is attached, and the inner lead portion of the lead frame 5, which is located close to the die stage and on which the wires connecting the semiconductor chip and the leads are attached, are sealed with resin. The machine is stopped and a mold is made. This molding area is shown surrounded by dotted lines in FIG.

The above-mentioned resin sealing is performed using a transfer molding apparatus shown in a schematic cross-sectional view in FIG. 16 is a cull, 17 is a runner, 18 is a cavity, and 19 is a resin tablet, in which the mold described above is formed. Although only three cavities are shown in FIG. 2 for the sake of simplicity, in reality there are from several tens to over a hundred cavities. When the tablet 19 is heated to about 90°C and melted, the plunger 14 is driven downward by the cylinder 15, and the molten resin is transferred to the cull 16, the runner 17, (not shown), etc.
Send it into cavity 18 via the gate,
When the resin injection ends, the plunger 14 returns to the top dead center, completing one stroke. The upper part of the plunger 14 at top dead center is shown in dotted lines in the figure.

Recently, in order to increase the effectiveness of mass production, methods have been adopted to increase the number of cavities per shot, that is, the number of products, and to reduce the amount of resin used per product, resulting in larger mold sizes. Ta. On the other hand, in order to keep the resin flow time constant in the end cavity in the mold, design considerations such as making the length of the runners uniform are taken.

(3) Conventional technology and problems When observing the resin inflow speed for each cavity in conventional transfer molding equipment, it is found that in the cavities where the resin flows in at the initial stage of one stroke, the runner part is filled and the cavity is filled. It is divided into two parts. When the filling of the runner part is completed, only the cavities are filled, and the above-mentioned difference in dispersion becomes small, and the inflow speed becomes faster as it approaches the end cavities. This is shown schematically in FIG. Note that in FIG. 3 and subsequent figures, parts that are the same as those already illustrated are designated by the same reference numerals.

Although four cavities are shown along the runner 17 in FIG. 3 for the sake of simplicity, in reality more cavities are disposed on both sides of the runner 17, as described above. When the cavity closest to the cull 16 is filled (resin is shown as sand in the figure), the cavity at the end, that is, the one farthest from the cull 16, is only slightly filled. At the end of a stroke, the resin rapidly flows into the end cavity, and the flow rate is quite high.

When a rapid inflow of resin occurs in this way,
It has been experienced that the wires that connect the semiconductor chip and the leads are washed away and deformed, or connected to adjacent leads or wires, or even bubbles are generated due to the intrusion of resin, making plastic ICs defective. It was done.

In order to solve the above problem, it has been proposed to complete one stroke at a slow speed from the beginning, but this takes too much time. The molten resin usually remains in a molten state for several seconds to several tens of seconds, and then begins to harden. Since the injection of resin into the cavity must be completed while the resin is in a molten state, the above proposal does not solve the problems of the prior art. In addition, the above proposal is disadvantageous because it increases the working time per shot.

(4) Purpose of the Invention In view of the above-mentioned conventional problems, the present invention provides a transfer molding apparatus in which resin does not rapidly flow into the end cavity at the end of one stroke in transfer molding of semiconductor devices. The purpose is to

(5) Structure of the Invention According to the present invention, a plurality of switches are arranged in the path of the plunger used for resin injection so that the resin injection speed changes in multiple steps and the resin inflow speed into the end cavity is slowed down. This is achieved by providing a transfer molding device configured to connect these switches to a speed controller, and to control a plunger driving cylinder by the speed controller so as to vary the transfer speed in multiple steps. be done. Alternatively, this can be achieved by providing a continuously variable (continuously variable transmission) device in place of the above-mentioned speed change.

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

The relationship between the transfer speed (which corresponds to the driving speed of the plunger 14) and time in a conventional transfer molding device is shown in the diagram of FIG. 4, in which the vertical axis represents the transfer speed S,
The horizontal axis represents the passage of time T. That is, the driving force of the plunger 14 is high in the initial stage, and the speed is reduced at the end of the initial stage t, and the resin is injected at that speed.

In order to achieve the above, in conventional equipment,
The first switch 21 is placed at the top dead center, and the second switch 22 is placed at the point corresponding to the time t elapsed.
A third switch 23 is also disposed at a position corresponding to the lowest position of the plunger 14, and these switches are connected to a speed controller 31.
On the other hand, from the speed controller 31, the oil sent from the pump 25 is sent at a predetermined pressure through the line 24 and a speed control signal is sent to the cylinder 15 as shown by the arrow, so that the transfer speed shown in FIG. 4 is obtained.

In the first embodiment of the present invention, the injection speed of the mold resin is changed in multiple steps, that is, the transfer speed of the transfer molding device is changed as shown in the diagram of FIG. 5, which is similar to FIG. .
The plunger 14 starts driving at the SO speed, and when the time t1 has elapsed, the transfer speed is reduced to S1 to start resin injection, and then, when the time t2 has elapsed, the transfer speed is changed to S2 and the runner section is After starting filling, when time t3 has elapsed, change the transfer speed to S3 and start filling the cavity in the center, and when time t4 has elapsed, transfer speed S3 is further reduced to transfer speed S4. The distal cavity is filled by. By doing this, the problems experienced in the prior art due to rapid resin injection in the end cavity are solved, and since the plunger is driven at a considerable speed in the first half of the stroke, the entire stroke is reduced to one stroke. The time required is not too long and the injection into the cavity is completed while the resin is in the molten state.

In order to realize the above-mentioned multi-step change in transfer speed, an apparatus shown in FIG. 6 is used. In FIG. 6, 14 and 15 are a plunger and a cylinder, respectively, as in the conventional example, and .
, are the transfer speeds S1, S2, S3, S4
speed control valve to obtain the speed corresponding to,
A, B, and C indicate hydraulic on-off valves for valves , , , and these hydraulic on-off valves are connected to the pump 25. Furthermore, the hydraulic on-off valves A, B, and C are the second
In the device shown, it is connected to three switches arranged between switches 22 and 23. This means that the conventional switch 22 has been replaced with four switches 41, 42, 43, and 44 arranged in sequence. Thus, as the plunger 14 descends, the hydraulic on-off valves A, B, and C are operated and closed in sequence upon receiving signals, and the speed control valves through which the oil sent to the cylinder 15 passes are sequentially reduced.
Controls the speed of plunger 14.

The operation of obtaining the speed change shown in FIG. 5 using the apparatus shown in FIG. 6 will be described below. When the plunger 14 descends from the top dead center at a speed S0 and time t1 has elapsed, the switch 41 is turned on, the hydraulic on-off valve 2 is closed, and the transfer speed is controlled by the pressure of the oil passing through the speed control valves. Start resin injection as S1.

When the time t2 has elapsed, the switch 42 is turned on, the hydraulic on-off valve A is closed, and the transfer speed is set to S2 and the filling of the runner section is started by the pressure of the oil that has passed through the speed control valve but not through the speed control valve. When the time t3 has elapsed, the switch 43 is turned on and the hydraulic on-off valve B closes, and the speed control valve
Filling of the cavity in the center is started by setting the transfer speed to S3 by the pressure of the oil that has passed through the pipe. Next, when the time t4 has elapsed, the switch 44 is turned on and the hydraulic opening/closing valve C is closed, and the transfer speed is set to S4 by the pressure of the oil passed only through the speed control valve, and the cavity at the end is filled. The cavities at the end are gradually filled with resin, and when all the cavities are filled, the plunger 14 is stopped while the hydraulic pressure is applied.

In the second embodiment of the present invention, the injection speed of the mold resin is continuously changed (continuously variable speed).
The situation is shown in the diagram of FIG. 7, which is similar to FIG. The transfer speed starts at S00, and when the time t11 has elapsed, the transfer speed is reduced to S11 to start injection of mold resin, and thereafter the transfer speed decreases at a predetermined rate as time passes, and reaches t12. After a period of time has passed, the transfer speed becomes S12.
Filling of the end cavity begins at this point. In this second embodiment, as is clear from FIG. 7, the transfer speed is continuously changed as the mold resin moves toward the end of the mold 11.

To realize the above-mentioned continuously variable transfer speed, a device shown in FIG. 8 is used. In the same figure,
Reference numeral 31 designates the speed controller of the apparatus of FIG. In operation, the motor 33 is activated from the start time t11 of mold resin injection, and returns to its initial state after the resin injection is finished.

(7) Effects of the invention As explained in detail above, according to the present invention, it is possible to slow down the resin injection speed into the end cavity by changing the plunger speed in multiple steps or steplessly during resin injection. This prevents damage to wires and air bubbles in the mold, which were previously experienced, and reduces plastic damage.
This is highly effective in improving IC manufacturing yield.

[Brief explanation of drawings]

Fig. 1 is a plan view of a part of a lead frame for making a plastic IC, Fig. 2 is a schematic sectional view of a transfer molding device, and Fig. 3 is a partial plan view of the lower mold of the device shown in Fig. 2. FIG. 4 is a diagram showing the relationship between transfer speed and time in the conventional transfer molding apparatus, FIGS. 5 and 7 are diagrams showing the relationship between transfer speed and time in the apparatus of the present invention, and FIG. The figure shows a device according to an embodiment of the present invention;
FIG. 8 is a diagram showing the speed control mechanism of the device of the present invention. 11...mold, 12...upper mold, 13...lower mold,
14...Plunger, 15...Cylinder, 16
... Cal, 17 ... Runner, 18 ... Cavity, 19 ... Resin tablet, 21, 22, 23
...Switch, 24...Signal line, 25...Pump, 31...Speed controller, 32...Speed controller knob, 33...Motor, 34...Motor speed controller,,,,...Speed control valve, i,
B, C...Hydraulic on/off valve.

Claims (1)

[Scope of Claims] 1 A mold consisting of an upper mold and a lower mold, a plunger for injecting molten resin through a cavity of the lower mold, a runner, and a cylinder for driving the plunger;
In a transfer molding device used for manufacturing a resin-sealed semiconductor device, the device has a speed controller connected to the cylinder to control the drive of the cylinder.
The speed controller includes a plurality of speed control valves that effect multi-step changes in the transfer speed of the plunger, and these valves are connected to the cylinder at one end and to a hydraulic on-off valve at the other end, and the hydraulic on-off valves are connected to the cylinder at one end and to a hydraulic on-off valve at the other end. A transfer molding device characterized in that it is connected to a plurality of switches arranged at different positions between positions corresponding to the top dead center and the lowest point of a plunger in response to changes in transfer speed. 2. the speed controller knob is connected to a motor, the motor is connected to a motor speed controller;
2. The transfer molding apparatus according to claim 1, wherein the motor is configured to operate from a resin injection starting point and return to an initial state after resin injection is completed.