JP2005340353A - Manufacturing method of electronic component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the occurrence of the non-filled part of resin which influences electric performance such as defective withstand voltage without raising a manufacturing cost of a mold by reducing the occurrence of defective appearance in a resin sealing process. <P>SOLUTION: When molten resin flows into a cavity from a runner via a gate, the molten resin is injected so as to collide the side wall of the cavity just after the resin flows into the cavity. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing an electronic component formed by resin-sealing an electronic element such as a semiconductor element.

As an example of an electronic component to be resin-sealed, a resin-sealed semiconductor device in which a semiconductor element is mounted on a lead frame will be described as an example.
A resin-encapsulated semiconductor device has a semiconductor element mounted on a lead frame that is punched into the same pattern and continuously arranged adjacent to it, and wire bonding is performed between the electrode pad of the semiconductor element and the inner lead of the lead frame. Then, resin sealing is performed for the protection, and the tie bar portion of the lead frame is cut to form individual semiconductor devices. There may be a plurality of semiconductor elements mounted on the lead frame, or other electronic elements such as resistance elements may be mounted together.
FIG. 4 is a diagram showing a state in the middle of a resin sealing process by a conventional manufacturing method. In order to grasp the inflow state of the sealing resin, a short shot is performed in which the resin injection is stopped halfway, and the upper mold is removed after the resin injection is stopped.

In FIG. 4, the resin 2 melted at the portion of the cal 1 is pressurized by a hydraulic control press (not shown) and flows out to the runner 3. It passes through the gate 10 of the cavity 5 connected to the runner 3 and flows into the cavity 5 of the mold on which the lead frame 4 is mounted. The molten resin 2 fills the cavity 5 and the resin sealing is completed. The gate 10 is disposed substantially at the center of the side of the cavity 5 on the runner 3 side, and the molten resin flows into the cavity 5 so as to be orthogonal to the side of the runner 3 side.
The heated and melted resin 2 flows through the runner 3, passes through the gate 10, and flows into the cavity 5. However, in the conventional method, before the interior of the runner 3 is completely filled with the molten resin, the cal 1 In the upstream portion close to, the molten resin flows into the cavity 5 through the gate 10. On the other hand, even when the molten resin is completely filled in the cavity 5 in the upstream portion of the runner 3, the cavity 5 in the vicinity of the end of the runner 3 is still unfilled, and in the upstream portion and the end portion of the runner 3, A time difference occurs in the filling of the resin 2 into the cavity 5. Due to such a filling time difference, particularly in the upstream cavity, the filling is completed before the molten resin has spread into the cavity, and an unfilled portion is generated, causing a defective appearance of the resin portion.

Conventionally, as a method for reducing a resin portion appearance defect of a resin-encapsulated semiconductor element, a mold mold that does not generate a gap at a boundary portion between gate inserts is used (for example, Patent Document 1), or a resin-encapsulating apparatus It is known to use a mold that reduces or eliminates the accumulated error in (for example, Patent Document 2).
JP-A-6-238672 JP 2003-17519 A

In a resin-encapsulated semiconductor device equipped with a power semiconductor element, a heat-dissipating hole that thins a part of the encapsulating resin to the vicinity of the lead frame in a part where the electronic element of the lead frame is not mounted for heat dissipation measures Screw holes 21 are provided for attachment to 20 and other substrates.
FIG. 5 is an enlarged view of the vicinity of the heat dissipation hole 20 and the screw hole 21 of the resin-encapsulated semiconductor device, in which a resin unfilled portion 22 is generated on the side wall portions of the heat dissipation hole 20 and the screw hole 21 (O in the figure). Inside). The resin-unfilled portion 22 is mainly generated in the vicinity of the protrusion in the cavity serving as the mold of the heat radiation hole 20 and the screw hole 21 and downstream of the resin flow path.
In the resin-encapsulated semiconductor element, such an unfilled portion of the resin is defective in appearance. Furthermore, depending on the size and depth, an unfilled portion may be the starting point and cause a withstand voltage failure.

However, although each of the above-mentioned patent documents describes improving the appearance defect due to the deviation of the upper and lower molds, as described above, the unfilled defect in the shadowed portion of the projection in the cavity is as described above. No measures are taken.
In addition, it is described that the appearance defect can be improved by changing the cross-sectional shape of the gate part between the runner side and the cavity side, but such a complicated shape mold increases the cost for its manufacture. There is.
The present invention reduces the occurrence of defective appearance in the resin sealing step in the conventional manufacturing method as described above, and does not increase the manufacturing cost of the mold, and without affecting the electrical performance such as defective withstand voltage. The object is to suppress the occurrence of unfilled portions.

In the conventional method for manufacturing a resin-encapsulated semiconductor element, the occurrence of unfilled resin as shown in FIG. 5 occurs more frequently in the upstream cavity near the cull, and decreases as the runner end comes closer.
The inventor investigated the cause of the unfilled resin portion by the following method.
FIG. 6 shows the result of investigating the relationship between the resin injection time and the unfilled resin occurrence rate using a transfer mold machine having 14 cavities on one side. The angle between the gate and the side of the cavity on the runner side is 90 °, and the width of the gate is 4 mm. This result indicates that the resin injection time is deeply involved, and that the resin unfilling occurrence rate is greatly reduced as the injection time becomes longer.
Furthermore, considering this result, the position of the cavity where the resin unfilled part was generated was almost 100% in the upstream cavity near the cull regardless of the injection time, whereas in the cavity near the runner end, It was found that the injection time decreased as the injection time became slower.

The cause of the unfilled portion of the sealing resin as described above is that when the resin heated and melted by the cal flows into the cavity after passing through the gate and into the cavity after passing through the gate, the upstream cavity near the cal and the cavity near the end of the runner It is considered that there is a time difference in resin filling between
For these reasons, it is necessary to approach the state in which all the cavities are filled with the molten resin at the same time, and to reduce the flow rate of the molten resin into the cavities.
Next, the result of investigating the hydraulic control mechanism of the mold press of the transfer machine is shown below.
FIG. 7 shows the change over time in the plunger injection pressure when the molding pressure is set to 4.5 tons and the injection time is set to 20 seconds. The plunger for transferring the molten resin is hydraulically controlled, and since the flow resistance load is small at the initial stage when pressure is applied, the plunger speed changes at a high speed until constant pressure molding is reached (Period 1) ). In this region, the molten resin flows out into the runner at a high speed, and the resin begins to flow into the upstream cavity near the cull at a high speed.

FIG. 8 is a view showing the flow of the molten resin in the cavity. As shown in FIG. 8A, when the gate is provided at the center of the cavity, the flow resistance of the molten resin is small and the molten resin reaches the end of the runner. Before filling with, the flow of molten resin into the cavity begins.
Eventually, the resin is filled in parallel to the runner and cavity, and the plunger load gradually increases (period 2)).
As the runner and cavity are filled, the load on the plunger gradually increases, the hydraulic pressure rises and the speed can be controlled, and the speed is controlled to a constant speed to become a constant pressure injection region (period 3)). When the resin is further filled and the injection pressure rises to the resin flow stop set pressure (period 4)), the filling is completed.

By the way, due to the performance of the hydraulic control mechanism of the mold press, even if the injection time is changed, the period 1) is a short-time operation and the same operation is performed, so the speed of the molten resin does not change.
From this, during the period 2) (until the constant pressure injection area is reached), it is difficult for the molten resin to flow into the cavity, and when this area is reached (when the runner end is filled), the cavity enters the cavity. If it is made to flow, it will be understood that the flow rate can be controlled and defective resin filling can be reduced.
In order to solve the above problems, the invention according to claim 1 is to form a cavity by an upper mold and a lower mold, and flow a molten resin into the cavity from a runner through a gate to encapsulate an electronic component. In the method of stopping, the molten resin is injected so as to collide with the side wall of the cavity immediately after flowing into the cavity.

According to a second aspect of the present invention, a connection opening with the gate of the cavity is provided in the vicinity of the side wall of the cavity so that the resin flowing into the cavity through the gate collides with the side wall of the cavity. In the connection opening, the angle formed by the gate and the cavity is shallower than 90 ° so that the molten resin flows in an inflow direction.
In any of the above, the gate width is preferably 2 mm or less.
Here, the gate width is the case where the gate depth is 0.4 mm. The flow resistance r is expressed by the equation (1) from the gate width w, the gate height h, the resin melt viscosity η, and the resin flow rate Q.

(Equation 1)
It is represented by Therefore, since the cross-sectional area of the gate is 0.8 mm 2 when the width of the gate is 2 mm, the cross-sectional area of the gate may be 0.8 mm or less. Even if the cross-sectional area of the gate is defined, the flow resistance can be increased similarly.

In a method of manufacturing an electronic component mounted on an electronic element lead frame such as a semiconductor element and sealed with resin, the molten resin collides with a side wall of the cavity immediately after the molten resin flows into the cavity formed by the upper mold and the lower mold. By injecting the molten resin into the mold, it becomes difficult for the molten resin to flow into the cavity until the pressure of the plunger for injecting the molten resin into the mold reaches the constant pressure injection region, and the inflow timing of the molten resin into the cavity is made closer, The filling time difference between the upstream cavity and the downstream cavity can be reduced. Mold costs will not increase.
By reducing the difference in filling time of the molten resin into the cavity, it is possible to reduce the occurrence rate of unfilled resin portions that particularly affect the electrical performance among the resin portion appearance defects and reduce the yield rate.

When the superheated and melted resin flows through the runner and flows into the cavity after passing through the gate, the flow rate into the cavity is increased to reduce the inflow speed. By doing so, the resin filling time difference between the upstream cavity near the cull and the cavity near the runner end is reduced, and the state of simultaneous filling is approached.
(Example)
FIG. 1 is a diagram illustrating a state in the middle of a resin sealing process according to an embodiment of the present invention. In order to grasp the inflow state of the sealing resin, a short shot is performed in which the resin injection is stopped halfway, and the upper mold is removed.
In FIG. 1, the gate 6 is provided in the vicinity of the end portion (corner portion) of the side of the cavity 5 on the runner 3 side. Immediately after the molten resin 2 passes through the gate 6 and flows into the cavity 5, the gate 6 is disposed at the corner of the cavity so as to collide with the side wall of the cavity (side perpendicular to the side on the runner side). The angle made with the side of the runner side is smaller than 90 °. In the example of FIG. 1, the gate 6 forms an angle of 45 ° with the side of the cavity 5 on the runner 3 side, and the width is 4 mm.

When the flow rate of the molten resin into the cavities is represented by an angle θ formed by a line (dotted line in FIG. 1) connecting the tip of the resin flowing into each cavity and the runner, θ = 12 ° in the example of FIG. .
When the gate 10 is provided at the center of the side on the runner side of the cavity and is at right angles to the runner as in the conventional example of FIG. 4, a line connecting the tips of the resin flowing into each cavity (dotted line in FIG. 4) The angle θ formed by the runner and the runner is 17 °.
Comparing the example of FIG. 1 with the conventional example of FIG. 4, as shown in equation (2):

(Equation 2)
tan12 ° / tan17 ° = 0.695 (2)
Thus, in comparison with the conventional example, the inflow velocity flowing into the upstream cavity near the cull is about 30% slower. This indicates that the state of simultaneous injection of resin into each cavity has been approached.
Further, in the case where the angle between the side of the cavity 5 of the gate 6 and the side of the runner 3 is 40 ° and 30 °, the results of examining θ in the same manner are shown in Table 1.

As a result, it can be seen that as the collision angle with the cavity wall surface increases, the velocity of flowing into the upstream cavity near the cull is reduced.
FIG. 2 is a diagram showing a state in the middle of the resin sealing step when the gate width is 1 mm and the angle between the gate and the cavity is 30 °.
Similar to FIG. 1, the angle θ formed by the line (dotted line in FIG. 2) connecting the tip of the resin flowing into each cavity and the runner is 4.7 °. Compared to the example of FIG. 1, the state of simultaneous injection into each cavity is closer.
In this way, by increasing the flow resistance of the resin flowing into the cavity, the molten resin first flows on the runner side, which is relatively easy to flow, and after the resin reaches the end of the runner, the plunger pressure increases and the resin enters the cavity. Will flow in. At this point, some cavities are filled in the upstream portion near the cull, but as shown in FIG. 4, the upstream portion near the cull is compared to the case where the gate is at the center and is perpendicular to the runner. The filling difference into the cavity near the end of the runner is reduced.

  Comparing the example of FIG. 2 with the conventional example of FIG. 4, as shown in equation (3):

(Equation 3)
tan 4.7 ° / tan 17 ° = 0.27 (3)
Thus, the resin inflow rate is improved by 73% compared to the conventional example, which is closer to the simultaneous injection.
Table 2 shows the result of comparing the flow rate in the cavity with the conventional example by changing the conditions of the gate angle and the gate width with respect to the cavity.

From Tables 1 and 2, it is effective to reduce the angle of the gate with respect to the cavity and to narrow the width of the gate in order to reduce the inflow rate of the resin and approach the simultaneous injection into each cavity.
FIG. 3 is a diagram illustrating a state of change in the plunger pressure with time when the gate is changed to the gate of this embodiment. Compared to the conventional example shown in FIG. 7, the constant pressure control region (period 3)) is expanded. This indicates that the resin injection speed into the cavity is slow, and the time during which the resin is simultaneously injected into a plurality of cavities is long.
In this embodiment, as shown in FIG. 8B, immediately after the molten resin flows into the cavity from the gate, the molten resin once collides with the side wall of the cavity, and spreads in the cavity at a reduced flow velocity. The molten resin has a large flow resistance from the runner to the cavity, and the molten resin flows through the runner having a smaller flow resistance. The molten resin does not easily flow into the cavity until the runner is filled with the molten resin.

  Table 3 shows the relationship between the resin injection time and the unfilled occurrence rate, and the width of the gate is changed.

As is clear from Table 3, it can be seen that the unfilling rate is lower as the injection time is longer.
The injection time of the resin is controlled by controlling the plunger pressure. As shown in FIG. 3, increasing the constant pressure control region (period 3)) approaches the simultaneous injection state to each cavity.
Lowering the plunger pressure increases the injection time, but simply increasing the injection time does not replace the fact that the upstream cavity close to the cull is filled first, and simultaneous injection into each cavity. It cannot be close to.
By defining the angle of the gate with respect to the cavity and the width of the gate, the resin begins to flow through the runner and the flow pressure changes at high speed1), and the plunger load increases as the resin begins to flow into the cavity. It is effective to lengthen the constant pressure control region (period 3)) after shortening the length of period 2).

For example, in the constant pressure control region (period 3)), the plunger pressure is suppressed to about 3 to 3.5 tons and the constant pressure control region (period 3)) is extended to about 15 seconds, so that the injection time is about 26 seconds. By doing so, unfilled defects can be suppressed as shown in FIG.
If the gate width is narrowed, unfilled defects are suppressed as described above. If the gate width is narrowed, the plunger pressure may be increased according to the setting of the injection time.
Even if an unfilled portion occurs, depending on the criteria, it may be determined to be a non-defective product by appearance inspection. FIG. 10 shows an example of this, and although a slight unfilled portion remains in the circle in the figure, it does not affect the characteristics of the semiconductor device and is determined as a non-defective product. In this way, when a certain amount of unfilled parts are allowed and mass productivity is important, the resin injection time can be shortened (plunger pressure increased), and unfilled parts can be generated more than mass production. When it is desired to suppress as much as possible, the resin injection time may be increased.

Moreover, although the arrangement | positioning of the cavity with respect to a runner may be sufficient as one side of a runner as shown in FIG. 1, FIG. 2, you may arrange | position in a zigzag form on both sides of a runner as shown in FIG.
At this time, as shown in the gate 6a, even if it is in the same direction as the flow direction of the resin (shown above the runner 3 in FIG. 11), if it is connected to the cavity at an angle shallower than 90 °, the resin Since it spreads inside after colliding with a side wall in a cavity and reducing a flow velocity, generation | occurrence | production of an unfilled part can be suppressed. In FIG. 11, the direction of all the gates may be the direction of the gate 6a.
Further, as in the gate 6b, the flow resistance can be further increased by guiding the resin in the direction opposite to the resin flow direction (shown below the runner 3 in FIG. 11). In FIG. 11, all the gates may be in the direction of the gate 6b.

The figure which shows the Example of this invention. The figure which shows the other Example of this invention. The figure which shows the state of the time-dependent change of the plunger pressure by this invention. The figure which shows a prior art example. The enlarged view of the resin unfilled part. Diagram showing the relationship between the incidence of unfilled resin and injection time The figure which shows the state of the time-dependent change of the conventional plunger pressure. Diagram showing resin flow in cavity The figure which shows the gate width and injection time dependence of the unfilling defect. The enlarged view of the improved resin unfilled part. The figure which shows the other example of arrangement | positioning of the direction of a gate, and a cavity.

Explanation of symbols

1 Cal 2 Resin 3 Runner 4 Lead frame 5 Cavity 6, 10 Gate 20 Heat dissipation hole 21 Screw hole 22 Unfilled part

Claims (3)

In a method of forming a cavity with an upper mold and a lower mold, and injecting a molten resin into the cavity through a gate from a runner and resin-sealing an electronic component,
The method of manufacturing an electronic component, wherein the molten resin is injected so as to collide with a side wall of the cavity immediately after flowing into the cavity. In a method of forming a cavity with an upper mold and a lower mold, and injecting a molten resin into the cavity through a gate from a runner and resin-sealing an electronic component,
In the connection opening, the connection opening with the gate of the cavity is provided in the vicinity of the side wall of the cavity, and the resin flowing into the cavity through the gate collides with the side wall of the cavity. An electronic component manufacturing method, characterized in that an angle formed by a gate and the cavity is shallower than 90 ° so as to have an angle in a flowing direction of a molten resin. In the manufacturing method of the electronic component of Claim 1 or Claim 2,
A method for manufacturing an electronic component, wherein a width of the gate is 2 mm or less.