JP2596252B2 - Method for manufacturing resin-encapsulated semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a resin-sealed semiconductor device, and more particularly to a method for melting and injecting a resin tablet in a mold to perform resin sealing.

[0002]

2. Description of the Related Art Resin sealing of a semiconductor device is performed using a resin molding machine. An upper mold and a lower mold are set in a resin molding machine, and a molten resin is injected and injected into a cavity formed by both molds. The encapsulating resin is in the form of a tablet in which thermosetting resin powder is formed in a cylindrical shape in advance. The lower mold has a pot for loading the sealing resin, a plunger for pressing the loaded sealing resin against the cull of the upper mold and injecting the same, and a runner for flowing the molten resin into the cavity. Further, each of the upper and lower molds has a heater for heating and melting the sealing resin. Using this resin molding machine, a lead frame on which a semiconductor element is mounted and wire-bonded is sandwiched between an upper mold and a lower mold, and a resin-encapsulated semiconductor device is manufactured by injection molding of a sealing resin.

Next, this manufacturing method will be described with reference to FIGS.
This will be described in more detail using (c). In the resin injection section of the resin molding machine, the plunger 6 descends to the origin position as shown in FIG. 4A, and the sealing resin 7 is filled in a space surrounded by the upper surface of the plunger 6 and the side wall of the pot portion 5.
And the upper mold 1 and the lower mold 2 are clamped by hydraulic pressure. Next, the plunger 6 is raised to press the sealing resin 7 against the cull portion 3 as shown in FIG. The injected encapsulating resin 7 flows into the cavity (not shown) via the runner 4 as shown in FIG. 3C, and all the cavities are filled with the encapsulating resin.
Thereafter, after a predetermined period of time, the curing of the encapsulating resin is completed, the mold is opened, the molded product and the encapsulating resin in the cull portion and the runner portion are integrally released, and a series of resin molding is completed. After the mold is opened as required, a step of cleaning the mold surface is added.

The above-described conventional resin sealing method for a semiconductor device is disclosed in Japanese Unexamined Patent Application Publication No.
-86938. In any case, after the resin tablet is loaded into the resin molding machine, the process immediately shifts to the pressure molding step.

[0005]

The conventional manufacturing method has the following disadvantages. First, as shown in the plan view of FIG. 7, the bonding wire 15 connecting the bonding pad 13 of the semiconductor element 12 mounted on the lead frame 8 and the inner lead 14 is usually stretched linearly when viewed from above. However, the wire 15 is greatly distorted due to the flow resistance of the encapsulating resin and causes a short circuit. As shown in the plan view of FIG. 8, the corner portion near the gate portion 16 on the surface of the cavity portion 9 of the lower mold 2 is a portion where the sealing resin that newly flows in through the runner portion 4 always comes into contact. Resins such as low-molecular components of the encapsulating resin, waxes, unreacted curing agents, etc. are easily attached and appear as mold stains 17. The stains appear as irregularities on the resin surface of the semiconductor device, which is a molded product, and cause poor appearance of the molded product and insufficient marking strength.

[0006] The mold contamination causes the following problems at the time of mold release. Generally, the operation at the time of mold release is such that either the upper mold or the lower mold moves relatively away,
The mold is opened. For example, as shown in the cross-sectional view of FIG. 9, when the lower mold 2 moves downward, the ejector pins 10 of the upper mold 1 are simultaneously pushed out, and the cured resin is released from the upper mold 1. . Next, when the lower mold 2 moves down to the bottom dead center, which is a knockout position, the ejector pins 11 of the lower mold 2 are pushed out, and the encapsulating resin 7 is released from the lower mold 2. However, in the conventional manufacturing method, since the ejector pins 11 do not rise evenly even when they are pushed out by the ejector pins 11, uniform release cannot be performed, resulting in uneven release. 4 causes resin breakage.

An object of the present invention is to provide a method of manufacturing a resin-encapsulated semiconductor device which can easily inject and release an encapsulating resin.

Another object of the present invention is to provide a method of manufacturing a resin-encapsulated semiconductor device which can perform resin encapsulation without significantly deforming a bonding wire.

The present invention is based on the new finding that the above-mentioned disadvantages of the prior art are caused by insufficient or insufficient preheating of the resin tablet before injection. That is, in the conventional method, the injected resin is not preheated or the preheating is insufficient, so that the injection resin is incompletely melted, has a high melt viscosity, and the progress of the curing reaction is incomplete. The present invention is characterized in that the loaded resin tablet is preheated for a predetermined time before injection, thereby lowering the viscosity of the encapsulated resin and improving the fluidity.

[0010]

According to the present invention, a resin tablet is abutted against a cull portion, held for a predetermined time in a slightly crushed state, and is preheated by heat from upper and lower molds and then injected. Perform By holding the crushed state, the cylindrical side surface of the resin tablet and the inner wall of the pot portion are in close contact with each other, the contact area between the resin tablet and the mold surface is maximized, and preheating is effectively performed. The preheating lowers the viscosity of the injected resin, the bonding wire is hardly deformed by the flow of the injection resin, and the mold is easily released from the mold.

The time for preheating varies depending on the type and amount of the sealing resin, but is limited by the time required for injection and the required fluidity of the resin.
The thermosetting resin which is molded to the extent of about 5 to 20 cm has a spiral flow value indicating the fluidity of the resin of 50 to 120 cm and a gel time of 10 to 50 seconds.
Preferably between seconds. Particularly preferred is around 10 seconds.

The method for manufacturing a resin-encapsulated semiconductor device according to the present invention does not require a major remodeling, a design change, or a new addition of a preheating device for the encapsulating resin, and changes the sequence of the injection operation. It can be realized only by doing.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a manufacturing process of a first embodiment of the present invention will be described with reference to FIGS. The encapsulating resin used in this embodiment is an epoxy resin, the resin tablet has a diameter of 13 mm and a height of 11 mm, and four resin tablets are used for one set of dies. The temperatures of the upper and lower molds are set to 180 ° C. in advance. Eight semiconductor elements having a size of 4 mm × 15 mm are mounted on one lead frame. This lead frame is set in the cavity of two dies, and injection is performed simultaneously from four culls. FIG. 1 shows one of these culls and the vicinity thereof.

First, as shown in FIG. 1A, a tablet-shaped encapsulating resin 7 is loaded into a pot portion 5 provided in the lower mold 2 and into which a plunger 6 is inserted, and the plunger 6 is inserted.
The upper mold 1 and the lower mold 2 are placed on top of each other, and the upper mold 1 and the lower mold 2 are clamped by hydraulic pressure. When the encapsulating resin 7 is loaded,
In the cylindrical outer shape, there is a clearance between the side surface and the inner wall of the pot portion 5, and the upper surface is also spaced because of the cull space, and only the lower surface is in contact with the upper surface of the plunger 6. Therefore, at this stage, the heat received from the lower mold 2 through the plunger 6 is very limited.

As shown in FIG. 2B, the plunger 6 is then raised, and the sealing resin 7 is pressed against the cull 3 of the upper mold 1 to stop the plunger 6 from rising slightly. For a predetermined time. As a result of the crushing, the encapsulating resin 7 has a side surface in close contact with the inner wall of the pot portion 5 and an upper surface in close contact with the cull portion 3 with a slightly larger area. Therefore, it is preheated sufficiently by receiving heat from the upper and lower molds. Next, as shown in FIG. 3C, the plunger 6 is restarted to move upward,
Is pressurized and melted and flows out to the runner section 4. Next, as shown in FIG. 4D, the plunger 6 is further raised to feed the sealing resin 7 into the cavity (not shown), and the injection is completed. In this state, the flow of the sealing resin 7 stops,
Curing proceeds.

The subsequent release and discharge of the cured resin will be described with reference to the sectional view of FIG. FIG. 10 also shows the cavities 9 on both sides of the pot portion 5. First, the lower mold 2 moves downward. At the same time, the ejector pins 10 of the upper mold 1 are extruded, and the cured encapsulating resin 7 is released from the upper mold 1. Next, when the lower mold 2 moves down to the bottom dead center, which is the knockout position, the ejector pins 11 of the lower mold 2 are pushed out, and the hardened encapsulating resin 7 separates the cavity 9, the runner 4, and the cull 3 from each other. The portion that has filled the space is integrally released from the lower mold 2. Then, it is discharged from the mold together with the semiconductor element (not shown) resin-sealed in the lead frame 8.

Next, the timing operation of the manufacturing process described with reference to FIG. 1 will be described in detail with reference to FIG. In FIG. 3, the vertical axis shows the operation stroke of the lower mold and the plunger, and the horizontal axis shows the required time. Incidentally required time is elapsed time from the clamping start T _1. After the resin tablet 7 is loaded, the lower mold 2 starts to rise at the same time as the mold clamping starts, and the origin D
_It rises by 40 mm from ₀ to reach the speed conversion point P _1, and rises by 45 mm at 7 seconds to complete the mold clamping. At 10 seconds (injection start T ₂ ), the plunger 6 starts to rise. At 11 seconds when the plunger 6 rises 2 mm from the origin P ₀ , it comes to the start T ₃ of the sealing resin 7 against the cull portion ₃ , and the tablet abutment position P Reach ₆ and the plunger stops for 5 seconds. That is, preheating is performed for 5 seconds. Injection Resume T ₄ becomes a 16 second time point, the plunger rises to 12mm injection end point P
₄ reached, the completion of injection T ₅ at 23 seconds. Curing the encapsulating resin in situ, next to the mold opening start T ₆ 127 seconds when the curing was completed, the lower die 2 the descent began,
At 129 seconds, the speed conversion point P ₁ drops by 5 mm, and 4
It returns to the origin D0 at 134 seconds after moving down by ₀ mm. One more
Beginning lowering of raised and the lower mold 2 of the plunger 6 at the same time at 40 seconds time, the plunger 6 reaches the lower die bitterness position P ₃ rises to 14 mm, the lower mold 2 reaches the knockout position P ₂ Both are stopped for one second and knockout by the ejector pin 11 is performed. Then 142
At 2 seconds, the lower mold 2 starts to rise, and at 143 seconds, the origin D
Returning to _0, the plunger 6 is the origin P Disconnect sticking the cull part resin by ₀ may fall head down position P ₅ of a height of 2.5mm from then plunger lower die bitterness position P ₃ again After returning to the origin P ₀ at 147 seconds, one injection step is completed. in this way,
5 seconds reaching the exit Resume T ₄ from the start T ₃ butting out of 13 seconds until the completion of injection T ₅ from the start of injection T ₂ are plunger operation is stopped, is performed preheating.

Referring to FIG. 2, a manufacturing process according to a second embodiment of the present invention will be described with reference to FIGS. The conditions for the description are the same as in the first embodiment. FIG.
As shown in FIG. 7, the tablet-shaped encapsulating resin 7 loaded in the pot portion 5 is
The upper mold 1 and the lower mold 2 are clamped in a state where they abut against the cull portion 3. That is, the plunger 6 starts to rise at the timing of the start of the mold clamping, and the sealing resin 7 has already been preheated at the end of the mold clamping. Next, FIG.
As shown in FIG.
Is melted, injection is started, and flows out to the runner section 4. Next, as shown in FIG. 3C, the plunger 6 is further raised, and the sealing resin 7 is fed into a cavity (not shown) and cured. The subsequent release and discharge of the encapsulated resin
This is the same as described with reference to FIG. In this embodiment, the plunger 6 abuts against the cull portion 3 at the same time as the mold clamping. However, before the mold clamping, the sealing resin 7 is already taken out of the upper surface of the lower mold 2, and after the mold clamping, the sealing resin 7 is the cull part 3
The adjustment may be performed so that Next, the timing operation of the manufacturing process described with reference to FIG. 2 will be described with reference to FIG. The numerical values and the like in the description are the same as those described in FIG. In this embodiment, a mold clamping start T ₁ and the injection start T ₂ simultaneously, the mold clamping start and rise of the plunger 6 and the lower die 2 at the same time has begun. As it, butting faster the timing of starting T ₃ and the injection resumed T _4, so that the take long curing time to the mold opening start T _6.

Referring to the graph of FIG. 5, the hot hardness (Shore D rubber hardness) of the sealing resin at 175 ° C. molding
The change in the molding time from the end of the injection to the elapse of the molding time is shown by comparing the normal manufacturing method 50 with the first embodiment 51 and the second embodiment 52 of the present invention. In both the first embodiment 51 and the second embodiment 52, the hot hardness rises in a shorter time than in the normal manufacturing method 50, and it can be seen that the curing is progressing. This means that the cycle time is shortened according to the present invention, and it is understood that the manufacturing method is excellent in mass productivity.

Table 1 shows that 100 shots (one shot corresponds to one shot) for the conventional method and two embodiments of the invention.
Times), the number of shots in which a mold release failure occurred (the time during which operation was not possible due to the mold release failure is also described), and of the molded product obtained by performing 100 shots on a lead frame mounting eight semiconductor elements, The number of defective units due to the distortion is shown, and the encapsulation yield (%) calculated separately is described. The right column shows the number of shots from immediately after the mold cleaning until the next cleaning is required. According to the embodiment of the present invention, mold release defects and the number of defects are significantly reduced, the encapsulation yield is greatly increased,
Moreover, it can be seen that the mold frequency is reduced and the frequency of cleaning is reduced.

[0021]

[Table 1]

[0022]

According to the present invention, the preheating of the encapsulating resin is sufficiently performed, the flowability of the encapsulating resin is improved, the progress of the curing reaction is completed, the melt viscosity is reduced, and the encapsulating semiconductor device is improved. The flow resistance received by the bonding wire is reduced and deformation is less likely to occur. Further, resin components such as low molecular components of the encapsulating resin, waxes, unreacted curing agent, and the like hardly remain on the inner surface of the mold, and mold contamination is reduced. Further, the release is performed uniformly, and the resin breakage and the like can be prevented.

[Brief description of the drawings]

FIG. 1 is a view for explaining a first embodiment of the present invention, and FIGS. 1 (a) to 1 (d) are partial cross-sectional views of a resin injection section showing manufacturing steps.

FIGS. 2A to 2C are views for explaining a second embodiment of the present invention, and FIGS. 2A to 2C are partial cross-sectional views of a resin injection section showing a manufacturing process.

FIG. 3 is a timing chart of the operation of the lower mold and the plunger according to the first embodiment of the present invention.

FIG. 4 is a timing chart of the operation of the lower mold and the plunger according to the second embodiment of the present invention.

FIG. 5 is a graph comparing resin hardness between two examples of the present invention and a normal manufacturing method.

FIG. 6 is a view for explaining a conventional manufacturing method, and FIGS.
(C) is a partial cross-sectional view of the resin injection unit showing a manufacturing process.

FIG. 7 is a plan view showing a conventional bonding wire bend.

FIG. 8 is a plan view showing a conventional mold stain.

FIG. 9 is a cross-sectional view showing a conventional mold release defect.

FIG. 10 is a cross-sectional view of a mold for explaining mold release of a sealing resin.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Upper mold 2 Lower mold 3 Cull part 4 Runner part 5 Pot part 6 Plunger 7 Encapsulation resin 8 Lead frame 9 Cavity part 10, 11 Ejector pin 12 Semiconductor element 13 Bonding pad 14 Inner lead 15 Bonding wire 16 Gate part 17 Mold contamination 50 Normal manufacturing method 51 Manufacturing method of the first embodiment 52 Manufacturing method of the second embodiment

Claims (6)

(57) [Claims] In a method of manufacturing a resin-sealed semiconductor device in which a resin molding machine is used to seal a semiconductor device with a resin, a sealing resin is charged into the resin molding machine, and the sealing resin is filled into a cull portion by a plunger. A method for manufacturing a resin-encapsulated semiconductor device, comprising preheating the sealing resin by pressing and holding the resin for a predetermined time. 2. A step of loading a sealing resin on a plunger mounted on one of two molds, a step of clamping the two molds, and extruding the plunger to remove the sealing resin from the mold. A step of pressing against the other cull of one mold and a step of preheating by holding the sealing resin for a predetermined time,
Thereafter, a method of manufacturing a resin-encapsulated semiconductor device including a step of further extruding the plunger to terminate injection, a step of curing the sealing resin, and a step of separating the cured sealing resin from the two molds. . 3. The method according to claim 2, wherein the extrusion of the plunger is stopped during the preheating step. 4. The method according to claim 2, wherein the step of clamping and the step of pressing are performed simultaneously. 5. The method for manufacturing a resin-encapsulated semiconductor device according to claim 2, wherein one of the dies is a lower die, and the raising of the lower die and the raising of the plunger are started simultaneously. 6. The method for manufacturing a resin-encapsulated semiconductor device according to claim 2, wherein said predetermined time in said preheating step is 5 to 20 seconds.