JPH04364061A - Manufacture of lead frame - Google Patents

Abstract

PURPOSE:To increase material hardness and to make the material constitution finer by performing a ultra low temperature processing, after completing the shape processing of the main part in a state that the material hardness is low. CONSTITUTION:Stamping is done using a band material and a progressive metal mold so as to form the side edges of inner leads 2 and outer leads 3 successively and let the inner lead tips and a pad 4 link together. And a ultra low temperature processing at -150 deg.C is performed for 30min in a state that the inner lead tips and the pad are linked together, after the formation of the side edges of the inner leads 2 or outer leads 3. And cavity regions are punched off and the inner lead tips are separated individually. Besides coining is performed for ensuring flat breadth needed for wire bonding in the inner lead 2 tips. Namely, processability is excellent since the punching of the main part is completed in a state that the material hardness is low. Besides the ultra low temperature processing makes the material constitution fine and stabilizes it.

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, and more particularly to a method for manufacturing a lead frame using a punching method.

0002

[Prior Art] In recent years, there has been a growing trend toward smaller and thinner IC packages, and the current mainstream sizes are 0.25 mm and 0.2 mm.
0mm, 0.15mm material is made even thinner to 0.1mm
Or even less.

[0003] Under these circumstances, requirements for lead frames are becoming stricter. In particular, with the increase in the number of leads and their miniaturization, the lead spacing has become narrower, and even minute distortions in the leads can no longer be tolerated because they cause positional deviations.

[0004] Furthermore, since it is necessary to maintain accurate positional accuracy during mounting, the thinner the material of the outer lead, the greater the strength required.

However, when forming a lead frame by the stamping method, there is a limit to the strength of the punch.
Furthermore, if a material with high hardness is used, the workability will be significantly reduced, making it difficult to form fine patterns with high precision.

[0006] When forming a lead frame with a fine pattern by the stamping method, in order to improve precision, a method is used in which the inner lead tip and pad are stamped in a continuous shape, and then heat treatment is performed to remove processing distortion. is proposed.

[0007] According to this method, it is possible to manufacture a lead frame with less distortion and stable lead tips.

However, this method has a problem in that the hardness of the material decreases due to the heat treatment during annealing.

[0009] It is possible to select a material with high hardness as a starting material in anticipation of the decrease in material hardness due to this heat treatment, but if a material with high hardness is used, the workability will be significantly reduced as described above. However, it becomes difficult to form fine patterns with high precision.

0010

As described above, in the conventional method, the hardness of the material decreases due to the annealing treatment, so there is a problem in that sufficient strength cannot be maintained.

The present invention was made in view of the above-mentioned circumstances, and an object of the present invention is to provide a lead frame with good dimensional accuracy and high reliability.

0012

[Means for Solving the Problems] Accordingly, the present invention is characterized in that when manufacturing a lead frame using a stamping method, cryogenic treatment is performed in place of annealing treatment to remove strain caused by stamping.

[0013]

[Operation] According to the above method, when the material hardness is low,
Because we are trying to complete the punching of the main part,
It has good workability and can produce highly accurate punching patterns. In this way, after completing the main shape processing, we perform cryogenic treatment at temperatures below -150 degrees Celsius to make the structure of the material denser and more stable, as well as to increase its hardness. can be increased.

[0014] Therefore, it is possible to obtain a lead frame with high strength and good dimensional accuracy. In this method, cryogenic treatment is performed at least after punching out the side edges of the inner lead.

For example, the side edge of the inner lead is punched out so that the tip of the inner lead and the semiconductor element mounting part are connected, the lead frame is shaped, and then subjected to cryogenic treatment. The cavity area between the tip of the inner lead and the semiconductor element mounting area is punched out, the inner leads are separated from each other, a coining process is performed to make the tip of the inner lead wider, and a precious metal plating process is performed. Tape is attached to fix the separated inner leads to each other.

[0016] Furthermore, cryogenic treatment may be performed after the cavity extraction process or after the completion of plating.

Furthermore, after the cavity extraction process, the inner leads are molded so that they are connected by the connecting piece, and then cryogenic treatment is performed and the connecting piece is removed at the end. good.

[0018]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIGS. 1 to 5 are diagrams showing the manufacturing process of a lead frame according to an embodiment of the present invention.

First, as shown in FIG. 1, using a strip material 1 designated as alloy 42, the side edges of the inner lead 2 and the outer lead 3 are sequentially formed using a progressive mold to form the tips of the inner leads and Stamping is performed so that the pad 4 has a continuous shape.

After forming the side edges of the inner leads and outer leads in this manner, a cryogenic treatment is performed at -150° C. for 30 minutes while the inner lead tips and pads remain continuous.

Then, as shown in FIG. 2, the space between the inner lead tip and the periphery of the pad, ie, the so-called cavity region, is punched out to separate the inner lead tip portions individually.

Furthermore, as shown in FIG.
Coining is performed at the tip to ensure the flat width required for wire bonding. Here, flat beating is performed to force twisting of the inner lead as necessary.

Then, as shown in FIG. 4, a noble metal plating layer M such as Ag is formed on the tips of the inner leads and the pad portions.

Finally, as shown in FIG. 5, a polyimide tape T is attached to connect and fix the inner leads to each other, and the lead frame is completed.

The lead frame thus obtained is punched with the leading edge of the inner lead connected to the die pad, and then subjected to cryogenic treatment to remove distortion and improve hardness. After punching, coining, and plating the cavity area, taping is performed, resulting in high strength, good dimensional accuracy, and high reliability.

Note that the same effect can be obtained even if the coining process is performed before the cavity extraction process.

Further, in the above embodiment, this cryogenic treatment was performed after punching out the side edge of the inner lead, but it may be performed after the main punching, and can be changed as appropriate. The cryogenic treatment may be performed after the shape processing is completely completed or after the precious metal plating process is also completed.

[0029]Furthermore, the cryogenic treatment may be performed after other shape processing is performed while leaving the connecting member that connects the inner leads.

[0030] Furthermore, the treatment temperature and time of this cryogenic treatment can be changed as appropriate. In addition, the lead frame formed by annealing may be further subjected to cryogenic treatment.

[0031]

As explained above, according to the method of the present invention, after completing the shape machining of the main part in a state where the material hardness is small, cryogenic treatment is performed to improve the material hardness and improve the material structure. Since densification is performed, a lead frame with high precision and high strength can be obtained.

[Brief explanation of the drawing]

[Fig. 1] Manufacturing process diagram of a lead frame according to an embodiment of the present invention

[
Figure 2: Manufacturing process diagram of lead frame according to the embodiment of the present invention

[Fig. 3] Manufacturing process diagram of a lead frame according to an embodiment of the present invention

[Figure 4
] Manufacturing process diagram of a lead frame according to an embodiment of the present invention

[Figure 5]
Manufacturing process diagram of a lead frame according to an embodiment of the present invention

[Explanation of symbols]

1 Strip material 2 Inner lead 3 Outer lead 4 Pad C Cavity area M Plating layer

Claims (1)

[Claims] 1. A method for manufacturing a lead frame comprising a plurality of leads arranged at predetermined intervals, including a shaping step of shaping the lead frame by a stamping method; and during the shaping step or during the shaping step. A method for manufacturing a lead frame, comprising a cryogenic treatment step of holding the lead frame at a cryogenic temperature for a predetermined period of time after the processing step.