JP2781070B2 - Lead frame manufacturing method - 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 lead frame for a resin-encapsulated semiconductor device or the like, and more particularly to a method for manufacturing a lead frame suitable for a narrow-pitch multi-pin package. .

[0002]

2. Description of the Related Art In the manufacture of a resin-encapsulated semiconductor device, first, as shown in FIG. 6, a lead frame 2 having a central portion provided with a plated portion 1 such as gold plating or silver plating is prepared. The sectional shape of the outer lead 3 and the outer lead 4 is generally square or rectangular as shown by the dotted line in FIG. 7, that is, the upper surface and the lower surface have the same dimensions. As shown in FIG. 9, a semiconductor pellet 6 is adhered to the island portion 5, and a bonding pad portion of the semiconductor pellet 6 and a plated portion 1 of the inner lead 3 are wire-bonded with a gold wire 7 or the like. And
After the bonding is completed, the tie bar portion 9 (see FIGS. 6 to 8) is cut off while being sealed with the sealing resin 8.
Solder plating is applied to the surface 10 of the externally exposed portion of the lead frame 2, and the outer lead 4 is cut and bent to manufacture a product.

[0003]

However, according to the conventional lead frame 2, since the cross-sectional shape of the inner lead 3 and the outer lead 4 is square or rectangular, that is, the upper surface and the lower surface have the same width, In a multi-pin package or a narrow-pitch package, the inner leads 3 are thinner, so that the space on the upper surface to be generally wire-bonded is narrowed, and it is difficult to perform wire bonding at a favorable position. In the worst case, there is a problem that bonding is performed in the vicinity of the edge of the inner lead 3 and the strength of the wire bond and the availability of the equipment are reduced.

FIG. 8 shows a lead frame which addresses this problem. This lead frame 11
In order to secure a space for wire bonding, the cross-sectional shape of the inner lead 12 and the outer lead 13 is inverted trapezoidal, that is, the upper surface is wider than the lower surface. According to the lead frame 11, since the bonding space is generally increased by the length of the upper surface serving as the bonding surface, the wire bonding can be easily performed at a favorable position.

However, this lead frame 11
Since the upper and lower surfaces of the outer lead 13 have different width dimensions, stress is applied in different directions in the step of performing lead cutting and bending of the outer lead 13, and as shown in FIG. Can occur,
As shown in FIG. 11, there is another problem that the flatness of the lower end of the outer lead 13 is deteriorated.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problem. A lead which does not cause displacement of the outer lead or deteriorates the flatness of the lower end of the outer lead while easily performing wire bonding at a favorable position. An object of the present invention is to provide a method for manufacturing a frame.

[0007]

In order to solve the above-mentioned problems, a method for manufacturing a lead frame according to the present invention is characterized in that the outer lead portion is etched at the same speed with the masking dimensions being the same for the upper and lower surfaces and the inner lead is etched. In the part, the masking dimension is made wider on the wire bonding surface side than the width of the surface facing the wire bonding surface, and the etching rate of the wire bonding surface is
The etching rate of the surface opposite to the wire bonding surface is set to be faster than that of the portion other than the outer lead and the inner lead.

[0008]

According to the method for manufacturing a lead frame having the above-described structure,
A lead frame can be manufactured in which the upper and lower surfaces of the outer lead have the same width, and the width of the wire bonding surface of the inner lead is wider than the width of the surface facing the wire bonding surface.

[0009]

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

First, a lead frame to be manufactured according to the present invention will be described. Dotted line part in FIG. 1 and FIG.
As shown in FIGS. 3A and 3B, the inner leads 21 (portion A in FIG. 3) of the lead frame 20 are:
The upper surface 21a serving as the wire bonding surface has an inverted trapezoidal cross-sectional shape wider than the lower surface 21b facing the wire bonding surface, and the outer lead 22 (portion B in FIG. 3) has the same width as the upper surface 22a and the lower surface 22b. Square or rectangular cross section. 1 and 3, reference numeral 23 denotes a tie bar portion, reference numeral 24 denotes an island portion on which semiconductor pellets are mounted, and reference numeral 25 denotes a plating portion of the inner lead 21.

In general, in a narrow pitch package, the width of the inner lead 21 must be necessarily reduced. However, as shown in FIG. 4, the slit width W of the inner lead 21 is mechanically determined by the material thickness T of the metal plate of the lead frame 20. The width L itself must be reduced. Further, even in the case of a multi-pin package, it is necessary to bring the inner leads 21 closer to the island portions 24, so that the inner lead width L must be reduced as in the case of the narrow pitch package.

However, due to the above configuration, the inner leads 21 are connected to the upper surface 21a serving as a wire bonding surface.
Is wide, wire bonding can be easily performed at a favorable position, and the outer lead 22 has the same width on the upper surface 22a and the lower surface 22b.
Also in the step of performing lead cutting and bending, stress in different directions is less likely to be applied, and the outer lead 22 is not displaced and the lead flatness is not deteriorated.

Next, a method of manufacturing the lead frame 20 will be described.

The semiconductor device lead frame 20 is formed by forming a portion of the lead frame 20 that should remain, such as a lead frame skeleton portion including the inner lead 21, outer lead 22, and island portion 24, on the resist layer 30.
And then etching.

That is, as shown in FIG. 4, the width L of the resist layer 30 is made equal to the upper and lower surfaces of the portion to be the outer lead 22, and the etching process is performed at the same upper and lower speed so that the upper surface 22a and the lower surface 22b are the same. So that it is as wide as possible. On the other hand, in the portion to be the inner lead 21, as shown in FIG. 5, the width L of the resist layer 30 is masked so that the upper surface is wider and the lower surface is narrower. The inner lead 2 having a wide upper surface 21a while reducing the pitch P by suppressing the etching on the side and accelerating the etching speed on the lower surface.
1 is manufactured. In this way, it is possible to appropriately manufacture the lead frame 20 having a different cross section at each location.

[0016]

As described above, according to the method for manufacturing a lead frame of the present invention, the upper surface and the lower surface of the outer lead have the same width, and the width of the wire bonding surface of the inner lead faces the wire bonding surface. A lead frame wider than the width of the surface, that is, a lead frame having a different cross-sectional shape at each portion can be easily manufactured while accurately controlling a predetermined area, and the same manufacturing equipment that can be used to improve a conventional etching apparatus can be used. Therefore, cost increase can be minimized.

[Brief description of the drawings]

FIG. 1 is a perspective view of a main part of a lead frame according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view taken along positions aa and bb in FIG.

FIG. 3 is a partially cutaway plan view of a lead frame according to one embodiment of the present invention.

FIG. 4 is a cross-sectional view of an outer lead for describing a method of manufacturing a lead frame according to one embodiment of the present invention.

FIG. 5 is a cross-sectional view of an inner lead for describing a method of manufacturing a lead frame according to one embodiment of the present invention.

FIG. 6 is a plan view of a conventional lead frame.

FIG. 7 is a perspective view of a main part of a conventional lead frame.

FIG. 8 is a perspective view of a main part of a conventional lead frame.

FIG. 9 is a partially cutaway perspective view of a conventional resin-encapsulated semiconductor device.

FIG. 10 is a partially cutaway side view of a conventional resin-encapsulated semiconductor device.

FIG. 11 is a partially cutaway side view of a conventional resin-sealed semiconductor device.

[Explanation of symbols]

Reference Signs List 20 lead frame 21 inner lead 21a upper surface of inner lead (wire bonding surface) 21b lower surface of inner lead (wire bonding facing surface) 22 outer lead 22a upper surface of outer lead 22b lower surface of outer lead 30 resist layer

Claims (1)

(57) [Claims] 1. A method of manufacturing a lead frame, comprising masking a portion of the lead frame to be left with a resist layer and etching the same, wherein the outer lead portion has the same masking dimension for the upper surface and the lower surface. Etching is performed at a speed, and the inner lead portion has a masking dimension wider on the wire bonding surface side than the width of the surface facing the wire bonding surface,
The etching rate of the wire bonding surface is slower than the parts other than the outer leads and inner leads, and the etching rate of the surface facing the wire bonding surface is faster than the parts other than the outer leads and the inner leads. Are the same width,
A lead frame manufacturing method for manufacturing a lead frame in which a width of a wire bonding surface of an inner lead is wider than a width of a surface facing the wire bonding surface.