JPS6313358A - Manufacture of semiconductor device and lead frame used for said manufacture - Google Patents

Abstract

PURPOSE:To inhibit the generation of a resin flash, and to improve solder dipping properties by flattening and treating a lead frame through coining before chip bonding before a resin mold process and flatly correcting the surface, an edge of which is rounded by punching a lead. CONSTITUTION:A lead frame 15 manufactured from a metallic plate through punching molding is coining-treated before chip bonding. Consequently, the whole lead frame 15 is coined and flattened, and the roundness (sagging) of each section edge of the main surface of the lead frame 15 is removed. Since the lead frame 15 is coining-treated on molding, the surface and the rear are flattened. As a result, the surface and rear of the lead frame 15 are fast stuck to a bottom force 3 and a top force 4. Accordingly, the resin component of a resin 6 does not leak also to the surface and rear of a lead 1, thus generating no flash. Consequently, when solder dipping treatment is executed to the surface of the lead after the molding, trouble in which solder 10 is difficult to adhere on the surface of the lead, thus improving the yield of solder dipping.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a semiconductor device and a lead frame used in the manufacturing.

[Conventional technology]

Transfer mold presses are generally used for sealing (packaging) in the manufacture of resin molded semiconductor devices. In this device, the lead frame with chips mounted and wire tensioned is sandwiched between the upper and lower molds of the mold (mold clamping), and then placed into a pot in the center of the lower mold. The resin tablet placed on top of the mold is heated under pressure with a plunger to melt it, and the melted resin is sent into the cavity through the resin flow path (main runner, sub-runner, gate) formed by the upper and lower molds. The lead frame part located at the front is covered with resin. In addition, since the resin in the cavity and resin flow path is cured and hardened, the upper and lower molds of the cured molded product are separated (
After opening the mold, it is taken out.

With this type of transfer mold press, lead flash and other flashes occur during resin molding, so
These particles are removed after resin molding. For example, in "Electronic Materials J 1981 Special Issue, Published November 10, 1981, P170-P175" published by Kogyo Kenkyukai,
After molding, a surface treatment is performed to ensure the soldering properties of the outer leads of the IC, but it is stated that as a pretreatment, lead flash generated during molding must be removed in advance. In addition, the same document describes methods for removing this paris, including a mechanical plasto method and a chemical treatment method using chemicals.

Dry blasting, in which particles (media) such as polystyrene are sprayed with high-pressure air, and wet blasting, in which particles are mixed with a solvent such as water, are sprayed (it is stated that they are widely used).

On the other hand, the lead frame attached to the mold of the aforementioned transfer mold press is formed by forming a metal plate by pressing (punching) or etching. Regarding lead frames, please refer to "Electronic Materials J, August 1982 issue, published by Kogyo Kenkyukai, 1982.
Published August 1, 2015, described on pages 6-9 to 74.

This document describes trends in press working of lead frames, such as the occurrence of warpage due to punching of ultra-thin plates.

[Problem that the invention seeks to solve]

As mentioned above, the occurrence of Paris during resin molding is as follows:
Affects product quality, productivity and yield.

The inventor has revealed that lead frames formed by punching as described above are inherently prone to flashing.

That is, in general, a plate punched by a press consisting of a punch and a goo has a rounded surface on the punch side (hereinafter simply referred to as the main surface).

Therefore, even when the lead frame is punched and formed, roundness (sag) also occurs. For example, as shown in FIG. It begins to take on a tinge of color. Generally, the first
As shown in Figure 0, when molding is performed by sandwiching the lead frame between the lower mold 3 and upper mold 4 of the mold, in order to take out the lead frame without any trouble after molding, the lead frame must be A gap 5 is provided on both sides of each part of the first class as necessary. For this reason, the melted resin 6 infiltrates both sides of the lead 1 as shown by the dots, and as shown by the hatching in FIG. , a barrier consisting of a mold release agent, etc. is formed. Since this barrier has a certain thickness and is composed of the entire composition of the resin 6, it can be removed relatively easily by the blasting method or the like as described above.

However, since the lead frame formed by punching has the roundness 2 at the edge of the main surface as described above, as shown in FIG. It was found that an unexpectedly narrow gap 8 was created, and the resin component of the resin 6 oozed out along this unexpectedly narrow gap 8, causing a flash 9. As shown by dots in FIG. 11, the flash 9 exists along the rounded portions 2 on both edges of the main surface of the lead 1, and therefore often reaches the tip of the lead 1.

This flash 9 is made of resin, and although it is not visible, it can be confirmed by the fact that no solder adheres to it when it is dipped in solder. Furthermore, the inventors have revealed that punched lead frames have problems with solder dips, in addition to the above-mentioned problem of flash generation.

That is, when lead 1 is dipped in solder, if roundness 2 exists on both edges of the main surface of lead 1, as shown in FIG. A phenomenon occurs in which the solder 1o adheres only thinly. Further, the product name and the like of semiconductor devices are stamped on the surface of the package. In this stamping, the stamped ink is baked at, for example, 160° C. for 1 to 2 hours. The heat during baking causes the a of the lead 1 to
Since the solder in the , Jl region is thin, it becomes Pb-rich or Sn-rich, resulting in a change in composition and oxidation. For this reason, when surface-mounting a completed semiconductor device on the wiring board 11, the layout of the wiring board 11 is particularly important. FFA layer 1
A solder cream 13 is provided on 2, and this solder cream 13
When the lead 1 is placed on top of the lead 1 and mounted by reflowing, the oxide film 14 exists on the rounded portion 2 of the top surface of the lead 1, so even if the solder cream 13 melts, the lead 1 It is not possible to reliably solder to cover the entire circumference of the lead 1 because it is not attracted to the top of the lead 1.

This type of soldering not only poses a problem in terms of reliability, but also is often judged to have poor appearance during inspection (there is also a problem in terms of yield).

An object of the present invention is to provide a lead frame with less occurrence of resin flash.

Another object of the present invention is to provide a lead frame suitable for the solder dip method.

Another object of the present invention is to provide a method for manufacturing a semiconductor device that can suppress the occurrence of resin flash.

Another object of the present invention is to provide a method for manufacturing a semiconductor device with high packaging yield and high packaging reliability.

The above and other objects and novel features of the present invention include:
It will become clear from the description of this specification and the accompanying drawings.

[Means for solving problems]

A brief overview of typical inventions disclosed in this application is as follows.

That is, according to the present invention, a lead frame formed by punching used in the manufacture of semiconductor devices is subjected to the following steps before chip bonding before the resin molding process:
It has been flattened by coining, and the rounded edges have been corrected to be flat by punching out the leads.

[Effect]

According to the above method, the lead surface with rounded edges due to punching is corrected to be flat, so when the lead frame is held between the upper and lower molds during resin molding and molded, the lead surface is flattened. Although flash occurs on the side surfaces of the lead, since the front and back surfaces of the lead are in close contact with the upper and lower molds, not only flash but also flash will not occur.

As a result, when the solder is applied to the lead surface after the molding process, the solder is applied uniformly. In addition, when solder is applied using the dip method, the cross section of the lead is rectangular due to coining, so the solder adheres well to the four sides of the lead, resulting in high yield and reliability even when surface-mounting semiconductor devices. It can be easily implemented.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a flowchart showing a method for manufacturing a semiconductor device according to an embodiment of the present invention, FIG. 2 is a plan view showing a lead frame of the present invention, and FIG. 3 is an enlarged sectional view of the lead.
FIG. 4 is an enlarged cross-sectional view showing the lead part during molding, FIG. 5 is an enlarged cross-sectional view showing the lead after molding, FIG. 6 is an enlarged cross-sectional view showing the lead dipped in solder, and FIG. FIG. 2 is an enlarged cross-sectional view showing a lead portion of the semiconductor device in a mounted state.

According to the present invention, as shown in the flowchart of FIG. It is manufactured through each process.

The lead frame 15 manufactured from a metal plate by stamping is subjected to a coining process. Lead frame 1
Reference numeral 5 denotes a lead frame for assembling a dual in-line semiconductor device, which has a pattern as shown in FIG. 2, for example.

The lead frame 15 includes a pair of outer frames 16 extending in parallel.
and thin inner frames 17 that connect these outer frames 16 at predetermined intervals.
and a plurality of leads 1 having a cantilever structure extending parallel to the outer frames 16 from the inner edges of the pair of outer frames 16 facing each other;
It consists of a lead 1 at the end extending parallel to the inner frame 17, an outer frame 16, and a dam 18 connecting the leads 1, respectively.

Further, a rectangular tab 19 is provided at the center of the lead frame pattern formed by the outer frame 16 and the inner frame 17. This tab 19 is supported at both ends by a thin tab suspension lead 20 whose one end is connected to the outer frame 16.

On the other hand, the lead 1 portions outside the dam 18, that is, the outer leads 21 are arranged at equal intervals, and
All of them extend parallel to each other, but the portion of the lead 1 inside the dam 18, that is, the inner lead 22, is parallel to each other up to the middle, but its tip ends toward the tab 19. It is curved and extended.

Further, since this lead frame 15 is formed by punching a metal plate using a precision press, the edge of the lead frame surface on the punch side of the press is rounded (sag), as described above. Therefore, in this embodiment, the entire lead frame 15 is flattened by coining, and the roundness (sagging) of the edges of the main surface of the lead frame 15 is eliminated. As a result, as shown in FIG. 3, the cross section of the lead 1 has a rectangular shape 9 with no rounding (sagging) at the edges of the main surface.

Incidentally, the lead frame 15 is used after being coated.

When manufacturing a semiconductor device using such a lead frame 15, chip bonding is first performed, and as shown by the two-dot chain line in FIG.
A semiconductor element (chip) 23 is bonded thereon.

Next, wire bonding is performed, and the chip 23
The electrodes and the inner ends of the grid 1 corresponding to these electrodes are connected by wires 24.

Next, resin molding is done. In this resin mold, the lead frame 15 is held between a lower die 3 and an upper die 4 of a mold die of a transfer mold press, and resin 6 is injected into a cavity formed by the mold die. This molding is performed on the area surrounded by the outer frame 16 and dam 18 of the lead frame 15. As a result, the chip 23 and
Wire 24. The inner end portion of lead 1 is covered.

At this time, in the mold, each part is formed taking into account variations in manufacturing dimensions of the lead frame 15, etc., so a gap 5 is generated on the side surface of the lead 1.
As shown in the diagram of the lead l taken out from the mold in FIG. 5, this causes the formation of a barrier. However, since this barrier is formed by all the components constituting the resin 6, it can be removed by deburring treatment in a post-process.

Moreover, this is one of the characteristics of the present invention, since the lead frame 15 is subjected to a coining process,
The front and back surfaces are flat. Therefore, the front and back surfaces of the lead frame 15 are in close contact with the lower mold 3 and the upper mold 4. Fourth
The figure shows the state of lead 1 during molding.
The front and back surfaces of the mold are in close contact with the lower mold 3 and the upper mold 4. As a result, the resin component of the resin 6 does not leak from the front and back surfaces of the lead 10, and as shown in FIG. 5, no flash occurs.

In manufacturing the lead frame 15, it is necessary to determine the plate thickness taking into account that the lead frame 15 will be coined.

After the molding process, the lead frame 15 is subjected to deburring treatment, for example, by dry blasting. This deburring process removes the barrier. Also,
In this embodiment, since there is hardly any flash that is difficult to remove on the surface of the lead 1, the deburring operation described above is also simplified.

Next, the lead frame 15 is subjected to a molding process. In this molding process, the tab hanging lead 20 and the lead 1 are separated from the outer frame 16 and the inner frame 17, and the dam 18 is cut and removed. Also, Pancake 25
The leads 1 protruding from the top are bent in the same direction midway to manufacture a dual in-line type semiconductor device.

Next, solder 10 is applied to the lead 1 portion of the semiconductor device using a solder dip. The solder paste 10 is attached to the circumferential surface of the lead 1, as shown in FIG. At this time, since the lead 1 has a rectangular cross section, the solder 10 is difficult to adhere to each vertex of the rectangle, and the portion to which the solder 10 is not applied extends linearly along the longitudinal direction of the lead 1.

Furthermore, this semiconductor device is subjected to characteristic inspection and marking before being shipped.

When mounting such a semiconductor device, for example, when folding back the leads 1 and surface mounting the semiconductor device on a wiring board, etc., the leads 1 are placed around the entire circumference of the leads 1, as shown in FIG. The solder 10 is rotated over the area to ensure reliable bonding.

That is, since the lead 1 has a rectangular cross section as shown in FIG. 6, the solder 10 is sufficiently attached to areas other than the corners. In addition, since the portions to which the solder 10 does not adhere are linear along the corners of the leads 1, even if the portions to which the solder does not adhere are oxidized by the heat during drying of the marking process in semiconductor device manufacturing, the portions to which the solder does not adhere are oxidized. is linear, and as shown in FIG.
Even if solder cream (not shown in the figure) is printed on F12, and lead 1 is placed on top of this solder cream, and soldering is performed by melting the solder cream by reflow, the solder 10 that adheres to lead 1 will not form a line. The solder in the form of solder mixes across the non-existent part, and the melted solder 10 below
is reliably sucked up onto the lead 1 by the surface tension of the solder. Therefore, good soldering can be performed.

According to such an embodiment, the following effects can be obtained.

(1) According to the present invention, since the lead frame is coined before molding, the sag on the edge of the main surface of the lead frame caused by punching has disappeared, so the front and back surfaces of the lead frame are It adheres closely to the parting surfaces of the lower and upper molds, preventing resin flash and improving mold yield.

(2) According to the above (1), according to the present invention, resin flash does not occur on the front and back surfaces of the lead frame during molding, so when the solder dip treatment is performed on the lead surface afterwards, the solder does not adhere to the lead surface. The effect of improving the yield of solder dips is achieved without causing any inconveniences such as difficulty in soldering.

(3) According to the above (1), according to the present invention, there is no sag on the main surface edge of the lead due to coining, and the lead cross section is rectangular. Since it is formed thickly except for the solder dip, the yield of solder dip is improved.

(4) According to the above (3), according to the present invention, since the lead is formed with thick solder except for the ridgeline, when a semiconductor device is mounted, the solder on the circumferential surface of the lead is applied to the ridgeline of the lead where no solder is present. Since the parts melt into each other and become integrated, the surface tension of the solder causes the solder to wrap around the entire circumference of the lead, ensuring reliable soldering, resulting in improved mounting reliability and yield.

(5) According to the above (1) to (4), according to the present invention, if a semiconductor device is manufactured using the lead frame of the present invention, an improvement in the yield of semiconductor devices can be achieved, and a semiconductor device with high mounting performance can be achieved. A synergistic effect can be obtained in that it can be provided at low cost.

Although the invention made by the present inventor has been specifically explained above based on Examples, it goes without saying that the present invention is not limited to the above Examples and can be modified in various ways without departing from the gist thereof. For example, even if the coining is performed not on the entire lead frame but only on the lead portion, the same effect as in the embodiment described above can be obtained.

Furthermore, as shown in FIG. 8, the present invention is highly effective for a semiconductor device 26 in which the lead 1 protruding from the package 25 is short and only a few parts need to be soldered during mounting.

That is, for the semiconductor device 26, which requires only a few parts to be soldered during mounting, the presence of a resin flash in the lead 1 portion is a fatal defect because solder cannot be applied. Furthermore, if the edges of the circumferential surface of the lead 1 are bent and no solder is applied to this portion, the solder will not spread around the entire circumference of the lead 1 during mounting, which is a fatal defect. Therefore, for the semiconductor device 26, which requires only a few parts to be soldered during mounting, the cross section of the lead 1 is rectangular, there is no resin flash, and the solder is attached to the entire surface, which improves the mounting performance. .

In the above description, the invention made by the present inventor is mainly applied to the manufacturing technology of semiconductor devices, which is the background field of application, but the invention is not limited thereto.

The present invention can be applied to a technique in which a part or all of an article, at least a part of which is formed by punching, is molded with resin.

〔Effect of the invention〕

A brief explanation of the effects obtained by typical inventions disclosed in this application is as follows.

According to the present invention, a lead frame formed by punching used in the manufacture of semiconductor devices is flattened by coining before chinbonding before the resin molding process, and the edges are rounded by punching the leads. The surface has been flattened. Therefore, during resin molding, when the lead frame is sandwiched between the upper and lower molds and molded, resin flakes occur on the sides of the leads, but since the front and back surfaces of the leads are in close contact with the upper and lower molds, Of course, flashes will no longer occur in Paris. As a result, when the solder is applied to the lead surface after the molding process, the solder is applied uniformly. Also, when attaching solder to the leads using the dip method,
Since the cross section of the lead is rectangular due to coining, solder adheres well to the four sides of the lead, and even if the semiconductor device is surface mounted, it can be mounted with high yield and reliability.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing a method for manufacturing a semiconductor device according to an embodiment of the present invention, FIG. 2 is a plan view showing a lead frame of the present invention, FIG. 3 is an enlarged cross-sectional view of the lead, and FIG. 4 is the same. FIG. 5 is an enlarged sectional view showing the leads after molding; FIG. 6 is an enlarged sectional view showing the leads dipped in solder; FIG. 7 is an enlarged sectional view of the semiconductor device. FIG. 8 is a front view showing a semiconductor device according to another embodiment of the present invention; FIG. 9 is an enlarged sectional view of a lead in a conventional lead frame; FIG. 10 is the same FIG. 11 is an enlarged perspective view showing the lead after molding; FIG. 12 is an enlarged sectional view showing the lead dipped in solder; FIG. 13 is an enlarged sectional view of the semiconductor device. FIG. 14 is an enlarged cross-sectional view showing the lead portion before mounting, and FIG. 14 is an enlarged cross-sectional view showing the lead portion after mounting the semiconductor device.

Claims (1)

[Claims] 1. A step of manufacturing a lead frame having leads by punching out a metal plate into a desired pattern, a step of performing chip bonding and wire bonding to the lead frame, and a step of placing the lead frame on a mold.・Manufacturing a semiconductor device, which includes the step of packaging a desired portion of the lead frame with resin after sandwiching it between lower molds, and before the molding step, coining at least the leads of the lead frame to make the edges rounded. 1. A method of manufacturing a semiconductor device, comprising flattening a lead surface having a tinge. 2. A lead frame having a lead formed by punching a metal plate, wherein at least the lead surface is made flat by coining.