JP2897396B2 - External lead molding method for resin-encapsulated semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a QFP (quad flat package) type
The present invention relates to an external lead forming method for a resin-sealed semiconductor device having a gull-wing-shaped external lead such as an OP (small outline package) type.

[Conventional technology]

A conventional method of molding external leads of a resin-sealed semiconductor device will be described with reference to the cross-sectional view of FIG.

After the resin sealing, the semiconductor device 14 (hereinafter abbreviated as IC) that has completed the steps such as tie bar cutting and plating processing has external leads 15a projecting laterally from the resin sealing portion. The die 12 fixed to the lower die of the lead forming die has a convex portion that supports the external lead 15a near the resin sealing portion. Further, the upper mold pad 13a of the molding die is disposed above the die 12, and a downwardly protruding portion is provided at the outer edge thereof. Further, a rectangular cylindrical punch 11a is provided so as to surround the pad 13a. The upper die including the pad 13a and the punch 11a moves up and down by a driving device. A spring is interposed between the pad 13a and the upper base plate, and the pad 13 functions by the reaction force of the spring.

First, the IC 14 is mounted with the base end of the external lead 15a in contact with the projection of the die 12. Next, when the upper die is lowered from above the IC 14 as shown by the arrow, the IC 14 is connected to the external lead 15a between the convex portion of the die 12 and the convex portion of the pad 13 which has been lowered.
Is held in a straight line, and when the upper mold is further lowered, it is pressed and fixed by the reaction force of the spring. Further, the upper die is lowered, and the punch 11a is lowered to a predetermined position along the side surface of the pad 13 as indicated by an arrow. Due to the lowered punch 11, the external lead 15a is formed into a gull-wing-shaped external lead 15 having first and second curved portions following the shape of the die 12. Then punch
11 and the pad 13 are sequentially raised, and the forming of the external lead 15 is completed.

FIG. 6 is a sectional view taken along the line AA of FIG. 5 with the pad 13 and the punch 11 lowered, and FIG. 7 is a sectional view taken along the line BB of FIG. Conventionally, the IC 14 is fixed by holding the base end of the external lead 15a in a straight line between the die and the pad, and pressing the tip end of the external lead 15 in a straight line with the die 12 and the punch 11. The external lead is formed in a gull wing shape by being clamped.

[Problems to be solved by the invention]

However, in general, an IC is configured such that a semiconductor chip fixed on a lead frame is arranged in a space of an injection mold including an upper mold and a lower mold, and a resin is injection-molded in the space of the mold. Sealed. Then, after the resin is temporarily cured, when the mold is emptied and removed, only the upper mold is removed while the sealing resin remains in the lower mold, so the upper part of the sealing resin contacts the outside air and Cools and shrinks.

Also, the thermal expansion coefficient of the sealing resin is different from that of the lead frame portion located near the middle layer of the sealing resin, and the thermal expansion coefficient of the lead frame portion is generally about two digits smaller. For these reasons, in general, warpage occurs such that the end of the sealing resin is pulled up. Usually, the difference in the relative height between the base of the external lead and the end of the semiconductor device after resin sealing is about 20 μm to 50 μm.

In the conventional external lead forming method described above, since the base end of the external lead is sandwiched between the pad 13 and the die 12, this warpage is temporarily corrected. Then, since the external lead 15a is formed into a gull wing shape in this state, when the punch 11 and the pad 13 are raised after the forming, the warpage is restored as shown in the sectional view of FIG. Then, as shown in the side view of FIG. 9, the tips of the external leads of the IC do not line up on the same plane, and the flatness is poor.

In recent years, the pitch between external leads has tended to be reduced with the increase in the density of ICs and the increase in the number of pins. Therefore, the fine pitch of the printed circuit board is promoted, and the application amount of the solder paste applied at the time of mounting the IC to prevent the solder bridge is reduced. For example, for an IC with an external lead pitch of 0.65 mm, the thickness of the applied solder is 150 μm
It is about. However, as described above, since the external leads of the IC formed by the conventional method have poor flatness, there has been a problem that a soldering failure occurs during mounting on a printed circuit board.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has been made in view of the above circumstances. It is an object of the present invention to provide a method for molding external leads of a mold semiconductor device.

[Means for solving the problem]

The method for molding an external lead of a resin-encapsulated semiconductor device according to the present invention includes the steps of: forming a base end of a plurality of external leads protruding laterally from a resin-encapsulated portion of the resin-encapsulated semiconductor device with a die of a molding die; A resin having a step of pressing and clamping with a pad, and a step of forming the external lead into a gull wing shape by bending two points of a base end portion and a tip end portion of the external lead with a punch of the forming die. In the method of molding an external lead of a sealed semiconductor device, the die and the pad are separated into corresponding individual pieces, and a vertical relative displacement of a base end portion between the external leads caused by a resin sealing process is detected. The positions of the constituent surfaces for pressing and holding the base ends of the external leads of the separated die and pad are changed based on the displacement amount,
This is a molding method in which the external lead is bent while the relative displacement of the base end of the external lead in the vertical direction is approximated to the position of the separated clamping surface of the die and pad.

〔Example〕

Next, the present invention will be described with reference to the drawings. 1 (a) and 1 (b) are cross-sectional views of a lead molding die for explaining a first embodiment, FIG. 2 is a plan view showing a stage configuration of the lead molding die of the first embodiment, and FIG. FIG. 5 is a configuration diagram showing a method for controlling the position of a die (supporting portion) according to the first embodiment.

The difference from the conventional example of the present invention is that a step of detecting a vertical relative displacement of a base end portion of an external lead of an IC mainly generated in a resin sealing step before lead molding is provided.

First, as shown in FIG. 2, the IC 4 separated from the lead frame into individual pieces is placed on the sealing resin receiving convex portion 2e of the lead displacement detection stage 2d so that the sealing resin is in contact therewith.
With respect to the base ends of all the external leads 5 from the vertical direction, the vertical position is measured using a laser displacement meter or the like, the displacement from the reference position calculated back from the standoff value is obtained, and the data is stored.

Next, the arrangement of the dies (support portions) 2d of the lead forming stage 2c is approximated to the relative displacement state. The die (supporting portion) 2d is not an integral structure as in the conventional example, but is divided into individual pieces of a minimum unit so as to correspond to a small number of external leads, and independently in the vertical direction inside the die guide 7. Exercise is possible. The displacement amount of the die (support portion) 2b is set based on the data. When there are a plurality of corresponding external leads 5, the average value of the displacement of the base end is fed back. The aim value of the position of the die (support portion) 2b is obtained by adding the displacement to a reference position based on the standoff value.

While feeding back the measured value of the vertical position of the die (support) 2b by the laser displacement meter 101 with respect to the aim value of each die (support) 2b, the piezoelectric actuator 105
By controlling the voltage with the controller 103 and the actuator amplifier 104 using the as a drive source, vertical positioning is performed with respect to each die (support portion) 2b with an accuracy of about ± 1 μm. Note that, for the piezoelectric actuator 105, for example, a laminated type of lead magnesium niobate-based ceramic material is used.

After the positioning of the die (supporting portion) 2b is completed, the die (forming portion) is pressed from the inside of the die (supporting portion) 2b by a pusher or the like.
2a, the die (supporting portion) 2b stands by in a state similar to the displacement of the base end of the external lead 5 of the IC 4, as shown in FIG. 1 (a). The IC 4 is moved from the lead displacement detection stage 2d to the lead forming stage 2c, and is mounted so as to be in contact with the base end of the external lead 5 and the die (support portion) 2b.

Next, when the upper die is lowered from above the IC 4, the IC 4 is clamped between the die (supporting portion) 2 b and the lowered pad 3. At this time, the pad 3 is an independent die (support part)
Similarly, each pad is provided with a spring 9 so as to correspond to 2b.
Allows independent movement in the vertical direction.
Therefore, the pad 3 stops at a position corresponding to the displacement of each die (support portion) 2b, and starts to press and clamp the base end of the external lead 5.

When the upper die is further lowered, the punch 1 starts to bend the external lead 5 downward from the base end side. When the punch is further lowered, the external lead 5 finally contacts the die (molded portion) 2a as shown in FIG. 1 (b). The end of the lead 5 is clamped and stopped, and the external lead 5 is formed into a gull wing shape. Then, punch 1 and pad 3
Sequentially rise, and the molding of the external lead 5 is completed.

As described above, by detecting the relative displacement in the vertical direction of the base end between the external leads generated in the resin sealing process, the separated die and the pad are respectively configured to hold the base end of the external lead of the pad. Is changed based on the displacement amount to approximate the vertical relative displacement of the base end portion of the external lead and the pressure holding surface of the die and pad, and the external lead is bent. As in the example, the base end of the external lead hardly springs back after the lead is formed. In the conventional example, the flatness of the distal end of the external lead is poor, and the variation of the distal end exceeds 100 μm. However, according to the present embodiment, the maximum can be reduced to 30 μm or less, the solderability when mounting the IC on the printed circuit board is significantly improved, and inconveniences such as poor contact can be avoided. Because of the reliability of IC Improve.

FIGS. 4 (a), (b) and (c) are cross-sectional views of a lead forming die according to a second embodiment. This embodiment differs from the first embodiment in the method of detecting the relative displacement of the base end of the external lead of the IC in the vertical direction and the method of feeding back the relative displacement state to the die (support portion). .

As shown in FIG. 4 (a), a displacement detecting spring 9a is provided between the die (supporting portion) 2b and the base plate 8a which are divided into individual pieces so as to correspond to a small number of external leads. doing. At this point, the die (support portion) 2b is in a uniform state.

Next, as shown in FIG. 4 (b), the IC 4 is placed so that the base end of the external lead 5 is in contact with the die (supporting portion) 2b, and the displacement detecting pusher 10 is vertically moved from above the sealing resin. Then, IC4 is lowered to a certain position. At this time, since the dies (supporting portions) 2b are independently supported by the springs 9a, an array reflecting the relative displacement state of the base end of the external lead 5 is formed. A spring having a spring constant such that the load applied to the base end of the external lead 5 is several g per external lead is used.

Next, the arrangement of the dies (supporting portions) 2b is
Is held by pressing the die (molded portion) 2a side with a pusher or the like from inside. Then, the displacement detection pusher 10 is raised. The following steps are the same as those in the first embodiment. When the upper die is lowered as shown in FIG. 4 (c), the pads 3 are respectively positioned at positions corresponding to the displacement of the die (support portion) 2b. It stops and starts pressurizing the base end of the external lead 5.
When the punch 1 is further lowered, the punch 1 begins to bend the external lead 5 downward from the base end side, and finally stops by holding the distal end side of the external lead 5 with the die (molded portion) 2a, and stops the external lead. Form into gull wings. Thereafter, the punch 1 and the pad 3 are sequentially raised, and the molding of the external lead 5 is completed.

This embodiment has the same effects as the first embodiment, and has the advantage that the lead molding die can be manufactured at low cost.

〔The invention's effect〕

As described above, according to the present invention, the relative displacement of the base end between the external leads in the vertical direction generated mainly in the resin sealing step of the IC is detected, and the die and the pad separated into individual pieces are detected. Since the external lead is bent and lowered in a state in which the position of the component surface holding the base end of the external lead is changed to approximate the vertical relative displacement of the base end between the external leads, As shown in the example, after the lead molding, the base end of the external lead hardly springs back. In the conventional example, the flatness of the distal end of the external lead is poor, and the variation of the distal end of the external lead exceeds 100 μm. On the other hand, according to the present invention, the thickness can be reduced to 30 μm or less at maximum, so that the solderability at the time of mounting the IC on the printed circuit board becomes extremely good, and problems such as poor contact can be avoided. Because of this, IC
Significantly improves the reliability.

[Brief description of the drawings]

1 (a) and 1 (b) are sectional views of a lead molding die used in the first embodiment of the present invention, and FIG. 2 is a stage configuration of the lead molding die used in the first embodiment of the present invention. FIG. 3 is a configuration diagram illustrating a method of controlling the position of a die (supporting portion) used in the first embodiment of the present invention, and FIGS.
(B) and (c) are cross-sectional views of a lead forming die used in the second embodiment of the present invention, FIG. 5 is a cross-sectional view for explaining a conventional external lead forming method of an IC, and FIG. FIG. 7 is a cross-sectional view taken along line AA of FIG. 7, FIG. 7 is a cross-sectional view taken along line BB of FIG. 5, and FIG. 8 is a cross-sectional view showing a position of a base end of an external lead when a conventional pad is raised. FIG. 9 is a side view showing an IC after external leads are formed by a conventional method. 1,11,11a Punch, 2a Die (molding part), 2b Die (support part), 2c Lead molding stage, 2d Lead displacement detection stage, 2e Sealing resin receiver Convex, 3,1
3,13a… pad, 1,14… IC, 5,15,15a… External leads, 6… pad guide, 7… die guide, 8,8a…
Base plate, 9: Spring, 9a: Displacement detection spring, 10: Displacement detection pusher, 12: Die, 101: Laser displacement meter, 102: Data processing unit, 103
…… Controller, 104 …… Actuator amplifier, 105
…… Piezoelectric actuator, 106 …… Die drive pad.

Claims (1)

(57) [Claims] A step of clamping the base ends of a plurality of external leads protruding laterally from a resin-sealed portion of a resin-sealed semiconductor device with a die and a pad of a molding die; Forming a gull wing shape by bending the external lead at two points, a base end portion and a tip end portion, with a die punch. And the pads are separated into corresponding pieces, and the relative displacement of the base end between the external leads caused by the resin sealing process in the vertical direction is detected, and the separated base ends of the external leads of the die and pad are separated. The positions of the constituent surfaces for pressing and holding the respective parts are displaced based on the displacement amount, and the relative displacement in the vertical direction of the base end of the external lead,
An external lead forming method for a resin-encapsulated semiconductor device, characterized in that the external lead is bent in a state in which the position of the separated die and pad is close to the pressure holding surface.