JPH0365023B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a lead frame for electrically connecting a semiconductor chip and external terminals.

[Prior art and its problems]

Generally, lead frames are electrically connected to semiconductor chips by wire bonding.
An aluminum cladding layer is formed at the tip of the inner lead.

FIG. 2a shows a conventional inner lead 1, to the tip of which an aluminum cladding layer 2 is bonded by pressure bonding or the like. When the inner leads 1 are punched out by pressing from a plate strip on which the aluminum cladding layer 2 has been formed, sagging occurs at the shoulders and the surface of the aluminum cladding layer 2 becomes uneven, so when wire bonding with the semiconductor chip is performed. There is a risk of bonding failure.

Conventionally, the aluminum cladding layer 2 at the tip of the inner lead 1 was coined to form a flat surface, as shown in FIG. 2b.

However, since the boundary edge 2a of the aluminum cladding layer 2 was conventionally provided parallel to the coining line 3, the inner lead 1 may be misaligned due to misalignment of the aluminum cladding layer 2 formed on the strip from which the inner lead 1 is punched. If the boundary edge 2a and the coining line 3 come close to each other or overlap, the stress that acts during coining will be concentrated over the entire length of the boundary edge 2a of the aluminum clad layer 2, which is the joint between the two members. However, there was a problem in that the aluminum cladding layer 2 peeled off at the boundary edge 2a.

In this way, the aluminum cladding layer 2 forms the boundary edge 2a.
If the aluminum cladding layer 2 itself peels off from the base material portion of the inner lead 1, there is a possibility that the aluminum cladding layer 2 itself will peel off from the base material portion of the inner lead 1, resulting in a connection failure in wire bonding with the semiconductor chip.

[Purpose of the invention]

The present invention has been made in view of these points, and the boundary edge of the aluminum clad layer formed on the inner lead does not peel off even when coining is performed, and the wire bonding state between the inner lead and the semiconductor chip is maintained. Our goal is to provide highly reliable lead frames that can be maintained in good condition at all times.

[Summary of the invention]

The lead frame of the present invention is a lead frame in which an aluminum clad layer is formed on the surface of the tip of the inner lead and coining is performed, and the coining line of the tip of the inner lead is provided so that the boundary edge of the aluminum clad layer intersects with the coining line of the tip of the inner lead. It is characterized by:

[Embodiments of the invention]

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

As shown in FIG. 1b, in this example,
A coining line 3 is provided so as to intersect with the boundary edge 2a of the aluminum cladding layer 2 pressed to the tip of the inner lead 1 at an inclination angle θ. The angle of inclination θ is determined in relation to the coining depth, the thickness of the aluminum clad layer 2, etc., so that the boundary edge 2a of the aluminum clad layer 2 does not peel off. According to experiments, the inclination angle θ is preferably 10 degrees or more.

In this embodiment, the coining of the aluminum cladding layer 2 is performed so that the coining line 3 is the boundary edge 2a.
Since the aluminum clad layer 2 and the aluminum clad layer 2 intersect with each other at an inclination angle θ, the boundary edge 2a of the aluminum cladding layer 2 does not peel off.

This is because, in FIG. 1b, the boundary edge 2a of the aluminum cladding layer 2 is completely coined in the area A, and the boundary edge 2a and the coining line 3 are sufficiently far apart. There is no possibility that 2a will peel off. In the B part between the A part and the C part, the boundary edge 2a and the coining line 3 overlap and are close to each other. Since the aluminum cladding layer 2 and the inner lead 1 are firmly pressed together, it is possible to prevent the boundary edge 2a from peeling off. Therefore, in this embodiment, even if the boundary edge 2a of the aluminum cladding layer 2 and the coining line 3 overlap or come close to each other, the boundary edge 2a never separates.

Therefore, the aluminum cladding layer 2, which is the wire bonding portion to the semiconductor chip, does not peel off from the inner lead 1, unlike in the conventional case.

Note that depending on the inclination angle θ or the position where the boundary edge 2a intersects with the coining line 3, B in FIG.
It is possible that the part B is located at the side edge of the inner lead 1 and the part B is slightly peeled off, but in this case, the part A will inevitably become larger and an anchor effect will occur.
Peeling of the aluminum cladding layer 2 can be prevented. In addition,
If the boundary edge 2a of the aluminum cladding layer 2 and the coining line 3 are sufficiently apart as shown in Figure 1a, even if coining is performed on the aluminum cladding layer 2 portion, the boundary edge 2a will not peel off. However, the bonding area becomes narrower. Also, peeling does not occur when coining is performed so that the coining line 3 is located completely outside the boundary edge 2a (on the opposite side from the tip of the inner lead), but in this case, coining is performed over a wide range. However, various problems such as distortion occur.

〔Effect of the invention〕

Since the lead frame of the present invention is constructed and operates in this manner, the aluminum cladding layer formed on the inner lead does not peel off even when coining is performed, and wire bonding between the inner lead and the semiconductor chip is prevented. It is possible to maintain a good connection state at all times, and the reliability is also improved.

[Brief explanation of drawings]

1A is a comparative example, FIG. 1B is a partial perspective view showing an embodiment of the lead frame of the present invention, and FIGS. 2A and 2B are partial perspective views showing a conventional example. 1... Inner lead, 2... Aluminum cladding layer, 2a... Boundary edge, 3... Coining line.

Claims (1)

[Claims] 1. In a lead frame having an aluminum cladding layer on the surface of the tip of the inner lead and coining the tip, the coining line of the tip of the inner lead is provided so that the boundary edge of the aluminum cladding layer intersects with the coining line of the tip of the inner lead. A lead frame characterized by: