JPH07211849A - Lead frame - Google Patents

Abstract

PURPOSE:To avoid the phenomenon that a bonding part protrudes the side surface of an inner lead and becomes wider by forming the bonding part of the tip part of the inner lead so that the part is narrower than the base part of the lead. CONSTITUTION:An inner lead 1 of a lead frame is formed so that a width Wb of a bonding part 5 is narrower than a width Wa of the base part. Therefore, even if the width of the bonding part 5 is expanded by single bonding, the width does not exceed Wa. In this way, even if the bonding part 5 expands by the bonding, the width at a expanded part 6 does not exceed Wa. Therefore, it is not possible that an interval G between the neighboring inner leads 1 become narrower in thc vicinity of the part of bonding in the bonding work. In this way, a pitch P can be made small without narrowing the width Wa of the inner lead 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lead frame, and more particularly to a novel lead frame capable of achieving a fine pitch while ensuring strength.

[0002]

2. Description of the Related Art As a lead frame, a metal layer made of, for example, copper having a different thickness is formed on both surfaces of an intermediate metal layer made of aluminum to be an etching stop layer,
A thick outer lead and a thin inner lead are formed by selectively etching the metal layers on both sides, and thereafter, unnecessary portions of the intermediate metal layer are removed by etching using the outer lead and the inner lead as a mask. The one manufactured by the above method and the manufacturing method thereof are disclosed in JP-A-3-148856 or JP-A-5-58856.
-198716, etc.

In such a lead frame, the outer lead maintains the strength of the lead frame as a whole, and the inner lead is miniaturized, so that the IC can be made to have a large number of pins. In order to cope with a further increase in the number of pins, a technique has been developed in which inner leads are formed by a method of plating using a resist film formed in a negative pattern for the inner lead pattern as a mask. This is because the conventional method of forming a metal layer on the entire surface and etching the metal layer using the resist film as a mask causes side etching to limit fine pitching, but plating is performed using the resist film as a mask. This is because such a method does not cause such side etching.

[0004]

By the way, in the conventional lead frame, as shown in FIGS. 4 (A) and 4 (B), the tips of the inner leads are crushed and widened by single point bonding by ultrasonic waves. However, there has been a problem that a short circuit accident between adjacent inner leads is likely to occur. 4A is a plan view showing the IC and the inner leads bonded or bonded to the IC and its bonding pad, and FIG. 4B is an enlarged view of the actual inner leads after bonding in another example of the lead frame. It is the figure which expanded and copied what was photographed. In the drawings, 1 is an inner lead, 2 is a portion whose width is expanded by crushing, 3 is an IC, 4 is a bonding pad, and 5 is a scratch caused by a cross-shaped tip of a bonding tool.

To explain this problem concretely,
There are various inner lead widths and pitches,
For example, taking a pitch of 70 μm and a width of 40 μm as an example, the distance between adjacent inner leads is originally only 30 μm. However, when the crushing occurs due to the bonding, it spreads by about 10 μm on both side pieces of each inner lead. Then, the distance between the bonding portions between the adjacent inner leads is narrowed to about 10 μm, which in turn causes a short-circuit accident. However, by narrowing the width of the inner leads, it is possible to widen the distance between the adjacent inner leads at the bonding location with the same pitch, but doing so causes a problem that the strength of the inner leads decreases. ..

The present invention has been made to solve the above problems, and an object thereof is to achieve a fine pitch while ensuring the strength of the inner leads.

[0007]

A lead frame according to a first aspect of the present invention is characterized in that a portion of a tip portion of an inner lead to be bonded is made narrower than a base portion side thereof. A lead frame according to a second aspect of the present invention is the lead frame according to the first aspect, wherein the tip side is wider than the portion where the inner lead is bonded.

[0008]

According to the lead frame of the first aspect, since the width of the bonding portion is originally formed to be narrow even if the bonding portion is crushed by the bonding and expanded, it is possible to prevent the bonding portion from protruding from the side surface of the inner lead to be widened. Therefore, it is possible to avoid the problem that a short-circuit accident is likely to occur. According to the lead frame of the second aspect, the inner leads can be plated more easily than in the case where the width is narrowed from the portion to be bonded to the tip. That is, when the inner lead is formed by plating copper or the like using copper or the like as a base with the selectively formed resist film as a mask, if the narrow portion is long, it is difficult to plate, but the portion to be bonded The narrow part is narrowed and the tip side is made wider than that, so the narrow part can be short. Therefore, it is possible to reduce the risk that the inner leads will not be easily plated.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The lead frame of the present invention will be described in detail below with reference to the illustrated embodiments. FIG. 1 is a plan view showing one embodiment of the lead frame of the present invention. The inner lead 1, 1, ... Of this lead frame has a portion 5 to be bonded which is narrower in width than the base side thereof. P is the arrangement pitch of the inner leads 1, 1, ..., For example, 70 μm. G is an interval between the adjacent inner leads, for example, 20
μm. Wa is a width of the inner leads 1, 1, ... On the side closer to the base than the bonded portion 5 is, for example, 50 μm. Wb is the width at the portion 5 to be bonded and is, for example, 20 μm. The width Wb of the bonded portion 5 can be narrowed within a range determined by the resolution of photolithography using a resist used as a mask when forming the inner lead by plating, and even now, the thickness of the resist film is 20 μm. In this case, the width can be narrowed to, for example, 30 μm or 20 μm, and it is expected that the width can be further narrowed depending on the progress of the resist process technology.

Therefore, according to such a lead frame, even if the width of the bonding 5 is expanded from Wb by single point bonding, it does not exceed Wa.
Therefore, even if the bonding portion 5 is expanded by bonding, the width of the expanded portion 6 is not wider than Wa. Therefore, there is no fear that the gap G between the adjacent inner leads 1 will be narrowed near the bonding location due to the bonding. Then, by narrowing the width Wb of the bonded portion 5, the inner lead 1
The pitch P can be reduced without narrowing the width Wa (on the side closer to the base than the portion to be bonded). That is, it is possible to achieve a fine pitch while ensuring strength.

FIG. 2 is a plan view showing an essential part of a modification of the lead frame shown in FIG. 1. The difference between this lead frame and the lead frame shown in FIG. That is, the portion between and is tapered. That is, in the lead frame shown in FIG. 1, a portion between the portion 5 to be bonded and the portion having the width Wa has a bottleneck shape, that is, a portion indicated by 7 in FIG. However, the lead frame shown in FIG. 2 has a tapered shape. As described above, the shape between the portion 5 to be bonded and the portion having the width Wa is not limited to that shown in FIG. However, since stress concentrates on the edges of the lead frame shown in FIG. 2, cracks may occur.

FIG. 3 is a plan view showing an essential part of another embodiment of the lead frame of the present invention. The present lead frame is formed such that the tip side of each inner lead 1 is wider than the bonding point 5. This is done in order to avoid the difficulty of plating in the vicinity of the bonding portion 5. That is, when the inner lead is formed by plating copper or the like with copper or the like as a base using the resist film selectively formed as a mask, it is difficult to plate if the narrow width portion is long, but bonding is performed. Since only the part is narrowed and the tip side is wider than that, the narrow part can be short. Therefore, it is possible to reduce the risk that the inner leads will not be easily plated.

[0013]

The lead frame according to the present invention is characterized in that the width of the bonding portion of the tip end portion of the inner lead is narrower than that of the base portion side thereof. Therefore, according to the lead frame of the first aspect, since the width is originally formed to be narrow even if the bonding portion is crushed and expanded by the bonding, it is possible to prevent the bonding portion from protruding from the side surface of the inner lead to be widened. Therefore, it is possible to avoid the problem that a short-circuit accident is likely to occur.

A lead frame according to a second aspect of the present invention is the lead frame according to the first aspect, characterized in that the tip side is wider than the portion where the inner lead is bonded. Therefore, according to the lead frame of the second aspect, it is easier to plate the inner leads as compared with the case where the width is narrowed from the portion to be bonded to the tip.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a lead frame of the present invention.

FIG. 2 is a plan view showing a main part of a modified example of the lead frame of FIG.

FIG. 3 is a plan view showing a main part of another embodiment of the lead frame of the present invention.

4A and 4B are problems to be solved by the invention, FIG. 4A is a plan view of an inner lead, and FIG. 4B is an enlarged view of another type of inner lead taken. FIG.

[Explanation of symbols]

 1 Inner lead 5 Place to be bonded

Claims (2)

[Claims] 1. A lead frame characterized in that a portion of a tip end portion of an inner lead to be bonded is made narrower than a base portion side thereof. 2. The lead frame according to claim 1, wherein a width of the tip end side is wider than a portion of the inner lead to be bonded.