JPH0444255A - Manufacture of lead frame - Google Patents

Abstract

PURPOSE:To obtain an accurate lead frame having high reliability by forming a shape at the tips of inner leads in a state that connecting parts remain, coining them to reduce the tips in thickness, then so forming uneven parts as to absorb excess parts formed by elongation, heat-treating them, and then removing the connecting parts to individually separate them. CONSTITUTION:A stripe material made mainly of steel is mounted in a mold having punching dies for punching parts of inner leads 1, tie bars 2, outer leads 3 of desired shape from four corners of a lead frame unit, and pressed to be patterned except the tip face of the inner leads. Then, it is coined to reduce them (a) in thickness. Thereafter, protrusions T are so formed partly at a region to become a cavity region as to absorb excess parts elongated by the coining (b), (c). Subsequently, in order to remove an inner stress, they are heat treated. Further, the cativy region C is punched to include the protrusion T, a die pad 11 is formed, and the tip edge of the inner lead is formed to complete patterning (d).

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a lead frame, and particularly to high-precision machining of inner leads.

[Conventional technology]

Lead frames used for mounting semiconductor devices such as ICs and LSIs are formed by forming a plate-shaped body made of iron-based or copper-based metal material into a desired pattern by press working or etching.

In recent years, with the increasing integration and miniaturization of semiconductor devices, the width of inner leads has become extremely narrow, and the spacing between them has also become smaller, creating a situation where even minute deformation of inner leads cannot be tolerated. ing.

Therefore, in order to prevent deformation of the leads, methods have been proposed such as attaching an insulating tape such as polyimide to the inner leads or fixing the inner leads to each other with ultraviolet curing resin.

However, these methods cannot correct the deformation of the inner lead due to processing strain (residual stress) that occurs during shaping of the lead frame by press working.

In order to solve this problem, a method is used in which a shape is stamped that leaves a connecting piece that connects the inner leads to each other on the end face of the inner lead, and after heat treatment is performed to remove residual stress, the connecting piece is removed. has been proposed (Japanese Patent Publication No. 62-44422).

However, even with this method, as shown in Figure 3, the connecting piece that connects the inner leads must be made thin in consideration of the later cutting process, and the material is thin to form a fine pattern, so it is difficult to machine. The mechanical strength is low, and the tension on the lead frame during heat treatment (annealing) in the reeled state deforms the connecting piece itself that is supposed to fix the inner lead, and the inner lead also deforms accordingly. was there.

In order to solve this problem, for example, heat treatment can be performed with the inner lead and pad connected without forming a cavity region. Coining is done to ensure a flat width, and there is no part to absorb the resulting elongation of the inner lead.
After the heat treatment process, there is a problem in that the position of the pad changes due to the extended inner lead.

(Problems to be Solved by the Invention) As described above, in the conventional method, there is no part to absorb the elongation of the inner lead caused by coining, so the position of the pad changes due to the elongated inner lead. There was a problem.

The present invention was made in view of the above-mentioned circumstances, and an object of the present invention is to provide a highly accurate and reliable lead frame.

[Structure of the invention]

(Means for Solving the Problems) Accordingly, in the first aspect of the present invention, after shaping the tip of the inner lead with a connecting portion left and performing coining to thin the tip of the inner lead, In order to absorb the extra thickness formed in the coining process, after forming the unevenness, heat treatment is performed, and after that, the connection part at the tip of the inner lead is removed and the inner lead is separated into individual leads.

In the second aspect of the present invention, after shaping the tip of the inner lead with the connecting portion left and performing coining to make the tip of the inner lead thin, the remaining portion formed in the coining process is removed. In order to absorb the flesh, the inner lead is pressed down from the part that will become the tip of the inner lead, and after heat treatment is performed to remove internal stress, the tip of the inner lead is pressed down to include the depressed part of the inner lead tip. The connecting parts of the die pads are removed, the die pads are separated individually, and the die pads are finally pressed down to a predetermined depth.

(Function) According to the above method, the tip of the inner lead is not a thin connecting piece, but is firmly connected with the cavity area in an unprocessed state, so that the inner lead is not deformed due to tensile run in the longitudinal direction during heat treatment. Moreover, since the elongation caused by coining is sufficiently absorbed by the formation of the unevenness, it is possible to obtain a lead frame with extremely high precision.

Further, according to the second aspect of the present invention, in addition to the above-mentioned effects, since the position of the die pad is lowered, the bonding wire can be shortened, and defects such as short circuits in the semiconductor device can be prevented.

(Example) Hereinafter, examples of the present invention will be described in detail with reference to the drawings.

Example 1 First, as shown in FIG. 1(a), a strip-shaped material containing copper as a main component is inserted into the desired shape of the inner lead (excluding the tip surface) 1, tie bar 2, A part of the outer lead 3 or the like is mounted in a mold equipped with a cutting die, and press working is performed to pattern the inner lead, leaving only the tip end face.

Next, the tip of the inner lead is subjected to a coining process to form a thin portion.

Thereafter, as shown in FIG. 1(b) and FIG. 1(C), a convex portion T is formed in a part of the region that will become the cavity region in order to absorb all the meat extended by coining.

After this, in order to remove internal stress,
Heat treatment is performed for 80 minutes.

Furthermore, as shown in FIG. 1(d), the cavity region C is punched out so as to include this convex portion T, and the die pad 11 and the inner lead tip are separated to form the die pad 11 and the end face of the inner lead tip. and complete the patterning.

Thereafter, a plating process or a taping process is performed as necessary to complete the lead frame.

The lead frame formed in this manner is highly accurate and reliable, with no deformation due to elongation of the material, and no variation in the length of the inner leads.

This lead frame is completed as a semiconductor device through processes such as chip mounting, wire bonding, and resin sealing, but because it is well formed with internal stress removed, it has extremely high precision. There is.

Example 2 Next, a second embodiment of the present invention will be described.

In the first embodiment, the elongation due to coining was absorbed by forming a convex portion, but in this example, after the entire area that will become the cavity area is pushed down to absorb the elongation due to coining, heat treatment is performed, When the die pad and the inner lead are finally separated from each other, the push-down portion is cut off from the inner lead portion, so that the die pad portion can be pushed down even deeper.

First, as shown in FIG. 2(a), as in Example 1, a strip-shaped material containing copper as a main component is inserted into the inner leads (excluding the tip surface) 1 and 1 in the desired shape from the four corners of the lead frame unit.
By attaching the tie bar 2, a part of the outer lead 3, etc. to a mold equipped with a cutting die, and performing press processing,
Pattern the inner lead leaving the tip end surface intact.

Next, the tip of the inner lead is subjected to a coining process to form a thin portion.

Thereafter, as shown in FIG. 2(b) and FIG. 2(C), the entire cavity area is pushed down to absorb the entire length of meat that has been extended by coining.

After this, in order to remove internal stress,
, heat treatment for 80 minutes.

Furthermore, as shown in FIG. 2(d), the die pad 11 is punched out to include the push-down portion, and the push-down portion is cut off at the inner lead portion.
and the tips of the inner leads are separated to form a die pad 11 and an end surface of the tips of the inner leads.

Finally, as shown in FIG. 2(e), the support bar is bent so that the die pad portion is pressed down further.

Thereafter, as in Example 1, a plating process and a taping process are further performed as necessary to complete the lead frame.

The lead frame formed in this manner is highly accurate and reliable, with no deformation due to elongation of the material, and no variation in the length of the inner leads.

This lead frame can be completed as a semiconductor device with light processes such as chip mounting, wire bonding, and resin sealing, but because it is well formed with internal stress removed, it has extremely high precision. ing.

Furthermore, since the position of the die pad is lowered, the bonding wire can be shortened, and defects such as short circuits in the semiconductor device can be prevented.

Note that the position and shape of this through hole are not limited to the embodiments and can be modified as appropriate.

Further, the positions and shapes of the unevenness and the push-down portion are not limited to the embodiments, and can be modified as appropriate.

〔Effect of the invention〕

As explained above, according to the lead frame manufacturing method of the present invention, the inner lead is shaped with the connecting portion left at the tip, and after coining, the unevenness is created to absorb the excess thickness. After forming, heat treatment is performed, and then the connection part at the tip of the inner lead is removed and separated individually, so the inner lead does not deform due to tension in the longitudinal direction and does not elongate due to coining. Since the unevenness is sufficiently absorbed by the formation of the unevenness, it is possible to obtain a lead frame with extremely high precision.

[Brief explanation of the drawing]

FIGS. 1(a) to 1(d) are manufacturing process diagrams of a lead frame according to the first embodiment of the present invention, and FIGS. 2(a) to 1(d) are
FIG. 3(e) is a diagram showing a manufacturing process of a lead frame according to a second embodiment of the present invention, and FIG. 3 is a diagram showing a part of a manufacturing process of a conventional lead frame. 11... Die pad, 12... Inner lead, 1
3... Tie bar 14... Outer lead, 15.
16...Side par 17...Support bar T.
...Protrusion. Figure 7 (Nine Figures (+/l Lilo) ＼II Figure 2 is the 2 Noah Figure 3

Claims (2)

[Claims] (1) A state including a plurality of inner leads formed radially so as to surround the semiconductor chip mounting part, and an outer lead connected to each inner lead, with a connecting part remaining at the tip of the inner lead. a first forming step in which the inner lead is shaped, a coining step in which the tip of the inner lead is thinned, and a second forming step in which unevenness is formed in order to absorb the excess thickness formed by the elongation in the coining step. A lead characterized in that it includes a molding step, a heat treatment step of performing heat treatment to remove internal stress, and a third molding step of removing the connecting portion at the tip of the inner lead and separating it into individual leads. How the frame is manufactured. (2) A state including a plurality of inner leads formed radially so as to surround the semiconductor chip mounting part, and an outer lead connected to each inner lead, with a connecting part remaining at the tip of the inner lead. a first forming step in which the tip of the inner lead is shaped, a coining step in which the tip of the inner lead is thinned, and a portion that will become the tip end surface of the inner lead is made to absorb the excess thickness formed by the elongation in the coining step. a second molding step in which a pressing process is performed to further push down the inner lead; a heat treatment step in which heat treatment is performed to remove internal stress; and a connecting portion at the tip of the inner lead is removed to include the depressed portion at the tip of the inner lead. 1. A method for manufacturing a lead frame, comprising a third molding step of separating each lead frame.