JPS59169162A - Lead frame - Google Patents

Abstract

PURPOSE:To enable to cut off a dam even if a shearing blade is not used by providing a notch on a cutting line of the dam, thereby concentrating a stress at the notch. CONSTITUTION:Notches 9 are formed on the front and back surfaces of a dam 5 simultaneously at the time of punching a lead frame 1. The leads 7 of the lead frame 1 after forming a package are placed on the respective projections 14 of a die 12, the dams 5 bridged between the adjacent leads 7 are contacted with the respective projections 13 of a punch 11, and the punch 11 is then pressed down. Then, the dams 5 are sheared along the notches 9 at both side ends and cut off between the adjacent leads 7 and 7. Since the shearing stress is concentrated to the notch 9, a shearing blade is not necessary to be provided at the projections 13, 14 of the punch and the die.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a lead frame used in a semiconductor device, and particularly to a technique for cutting off a dam in a lead frame.

[Background Art] Generally, lead frames used for mounting semiconductor integrated circuit elements (pellets) are equipped with a molding material to prevent synthetic resin (resin) as a molding material from flowing out from the cavity used to form the package. , a resin stopper called a dam is installed.

Since this dam is built between each lead, it is cut off after package molding, but as packaging density increases, the spaces between the leads become narrower (and the shearing blade of the cutting machine used to cut off the dam becomes trapped). The inventor of the present invention has revealed that a problem arises in that the blade is easily broken.

"Object of the Invention" An object of the present invention is to provide a lead frame equipped with a dam that can be easily cut off.

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

[Summary of the Invention] A brief overview of typical inventions disclosed in this application is as follows.

In other words, by providing a notch on the cutting line of the dam,
Stress is concentrated in the notch, making it possible to cut off the dam without using shear blades.

[Example] Fig. 1 is a plan view showing an embodiment of a lead frame according to the present invention, Fig. 2 is an enlarged partial side sectional view taken along the line ■-■ in Fig. 1, and Fig. 3 is a dam cut-off situation. FIG. 4 is an enlarged partial side sectional view showing the state of molding the package.

In this embodiment, the lead frame 1 is generally formed by stamping a thin plate, and includes a pair of outer frames 2. A tab hanging lead 4 that supports the tab 3 at its tip is protruded from the outer frame 2. A pair of connecting parts are formed symmetrically around the tab 3 and are installed between both outer frames 2.2, and a plurality of glued parts 7 are attached to each end of the connecting part 6 with approximately equal pinches. It is installed protrudingly. The width of the lead 7 is changed from the middle, and the outer part 8 on the connecting part side
a and an inner portion 8b on the tab side.

The tip of the inner portion 8b of the lead 7 is arranged so as to surround the tab 3. A dam 5 is protruded from the middle of each lead 7 so as to bridge between adjacent leads 7 or the outer frame 2.

Notches 9 are provided on the front and back surfaces of the dam 5 for each lead 7.
The notches 9 are formed on extension lines of the ends of the outer frame 2, and the notches 9 are formed into narrow grooves having a triangular cross-sectional shape. The notches 9.9 on the front and back surfaces are formed such that their pointed ends face each other with a slight extra thickness of the dam 5 in between. It is desirable that this notch 9 be formed at the same time as the lead frame 1 is punched and formed.

In addition, in FIG. 1, only a part of the lead frame 1 is shown, and the rest is omitted. That is, the lead frame 1 is repeatedly and continuously provided in the direction in which the outer frame 2 extends, with the structure shown in FIG. 1 surrounded by the outer frame 2 and the connecting portion 6 as a basic repeating unit.

An embodiment of a method for cutting off the dam in the lead frame having the above structure after forming the package will be described with reference to FIG.

In FIG. 3, a cutting device (only the main parts are shown) 10
is equipped with a punch 11 and a die 12 that are paired with each other, and the punch 11 and die 12 have convex portions 13 that engage with each other.
and 14 are provided protrudingly from each other. The respective convex portions 13 and 14 of both are arranged so as to correspond to each dam 5 and each lead 7, respectively.

When the cutting operation is carried out, as shown in FIG. The bridged dam 5 is brought into contact with each convex portion 13 of the punch 11 and sandwiched between the punch 11 and the die 12. In this state, when the punch 11 is pushed down relatively, the dam 5 is sheared along the notches 9 at both ends, and is cut off between the adjacent leads 7.7. At this time, since shearing stress is concentrated in the notch 9, it is not necessary to provide shearing blades between the protrusions 13 and 14 of the punch and die.

In order to effectively generate stress concentration, it is desirable to provide notches on the front and back surfaces of the dam, and to form the tip to be sharp to reduce the excess thickness.

Here, the operation in molding a non-hermetically sealed package using the lead frame according to the above structure will be briefly explained with reference to the fourth drawing.

FIG. 4 shows the molding situation of a package by a transfer molding machine, and this molding machine 20 has an upper mold 21 and a lower mold 22.
It is equipped with A cavity 23 is formed in the mating surfaces of the upper mold 21 and the lower mold 22, and this cavity 23
A resin (none of which is shown) as a molding material is press-fitted from a pot through a runner and a gate. A clamping part 24 for strongly clamping the dam 5 and the lead 7 is formed on the outer mating surfaces of the upper and lower cavities 23, and relief parts 25 are formed on the outside of the clamping part 24 to increase surface pressure. has been done.

On the other hand, a pellet 26 is bonded to the tab 3 of the lead frame 1, and the pellet I-26 is electrically connected to the inner portion 8b of each lead 7 by a bonding wire 27.

Lead frame 1 with bellet 26 mounted in this way
When the resin is sandwiched between the upper and lower molds 21 and 22 as shown in FIG. 4, the resin is press-fitted into the cavity 23.

In order to press-fit this resin, the cavity 23 must be
It is necessary to vent the air inside, and an air vent is usually provided for this purpose. However, since it is not possible to provide a large number of air vents, a problem has been found in that voids occur inside the molded product at locations away from the air vents.

However, when the lead frame having the above structure is used, the air in the cavity 23 is discharged from the many notches 9 formed in the dam 5 to the surface pressure relief part 25 in all directions, as shown by the arrows in FIG. Therefore, there is no risk of voids occurring due to poor air discharge.

Although there is a concern that resin may leak from the notch 9, there is a large difference in flow path resistance between air and resin, so there is almost no resin leakage. However, it is more desirable to take measures such as, for example, providing cutouts 9 separately on the front and back surfaces of the dam 5 to reduce the cross-sectional area of a single cutout 9 and increase the flow resistance. - [Effects] (1) By providing a notch in the dam, stress concentration occurs in the notch when the dam is cut off, so the dam can be easily cut off and shearing blades can be omitted. Therefore, it is possible to avoid the problem of damage to the shearing blades when the gap between the leads becomes narrow.

(2) By providing notches on the front and back surfaces of the dam, stress concentration can be made more pronounced, making cutting off easier.

(3) By making the tip of the notch sharp, stress concentration can be made more pronounced, making it easier to cut off.

(4) By providing a notch in the dam, the air in the cavity during package molding is discharged in all directions through the notch, so it is possible to prevent voids from forming inside the pan cage after molding.

(5) By separately providing notches on the front and back surfaces of the dam, flow path resistance can be increased, thereby preventing leakage of resin from the notches.

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-mentioned examples and can be modified in various ways without departing from the gist thereof. Nor.

For example, the shape, number, etc. of the notches are not limited to those in the embodiments described above, and the shape, structure, etc. of the dam-shaped lead frame itself are not limited to those in the embodiments described above.

[Brief explanation of the drawing]

Fig. 1 is a plan view showing one embodiment of the present invention, and Fig. 2 is a plan view showing an embodiment of the present invention.
FIG. 3 is an enlarged partial side sectional view taken along line nn in the figure; FIG. 3 is an enlarged partial side sectional view showing how the dam is cut off; and FIG. 4 is an enlarged partial side sectional view showing how the package is formed. DESCRIPTION OF SYMBOLS 1...Lead frame, 2...Outer frame, 3...Tab, 4...Tab hanging lead, 5...Dam, 7...Lead, 8a...Outer part, 8b...・Inner part, 9・
... Notch, 11... Punch, 12... Gui, 13.
14...Convex part, 21...Upper mold, 22...Lower mold, 2
2... Cavity, 24... Dam clamping part, 25...
・Surface pressure relief part. Figure 1/ Figure 2 Figure 3/θ Figure 4

Claims (1)

[Claims] 1. A lead frame characterized in that a notch is provided on the cutting line of the dam. 2. The lead frame according to claim 1, wherein the notch is provided on both the front surface and the back surface. 3. The lead frame according to claim 1, wherein the tip of the notch is formed to be sharp.