Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Metallic housing or support
Reexamination Certificate
2003-02-26
2004-11-23
Flynn, Nathan J. (Department: 2826)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Metallic housing or support
C257S666000, C257S674000, C257S677000
Reexamination Certificate
active
06821820
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the Invention
The present invention relates to a lead frame manufacturing method and, more particularly, a method of manufacturing a lead frame employed in a leadless package such as QFN, SON, etc.
2) Description of the Related Art
In recent years, development of the LSI technology as the key technology for implementing the multimedia devices is advanced steadily toward the higher speed and the larger capacity of the data transmission. The higher density of the packaging technology serving as the interface between the LSI and the electronic device is also advanced with the advance of such development.
As the package corresponding to the high-density packaging, various packages are developed up to now. As the package for the high-density packaging using the lead frame, the leadless package such as QFN (Quad Flat Non-leaded Package), SON (Small Outline Non-leaded Package), etc, in which the leads are not extended outward, for example, is well known.
FIG. 1A
is a sectional view showing an example of the semiconductor device in which an IC chip is mounted on the leadless package, and
FIG. 1B
is an enlarged sectional view taken along a II—II line in FIG.
1
A.
FIG. 2A
is a sectional view showing an example of the lead portions of the lead frame employed in the leadless package, and
FIG. 2B
is a sectional view taken along a III—III line in FIG.
2
A.
As shown in
FIG. 1A
, in a semiconductor device
110
having a QFN structure, an IC chip
104
is mounted on a die pad
102
and also a connection electrode of this IC chip
104
and a lead portion
100
are connected electrically to each other via a wire
108
. Then, this IC chip
104
is sealed with molding resin
106
that covers up to a top end portion of the lead portion
100
.
In this manner, in the semiconductor device
110
having the QFN structure, an upper surface and side surfaces of the lead portion
100
are covered with the lead portion
100
. Therefore, if a sectional shape of this lead portion
100
is a vertical shape, it is possible that the lead portion
100
buried in the molding resin
106
is come off from the molding resin
106
.
Therefore, as shown in FIG.
2
A and
FIG. 2B
, a sectional structure of the lead portion
100
of the lead frame is shaped into such a stepped shape that a width of a surface (surface that is connected to the connection electrode of the IC chip) is thicker than a width of a back surface (surface that is connected to the wiring substrate, or the like).
As a result, as shown in
FIG. 1B
, the molding resin
106
is buried to cut into the side surface of the lead portion
100
. Thus, coming-off of the lead portion
100
from the molding resin
106
can be prevented by the so-called anchor effect.
In the prior art, as the method of forming the lead portion
100
having the above sectional structure, mainly wet etching is employed. If wet etching is employed, a substantially same pattern of a resist film is formed on both surfaces of a metal plate, and then the metal plate is etched from both sides by the drug using the pattern of the resist film as a mask. At this time, if etchings of the front and back surfaces of the metal plate are not executed under the same conditions and, for example, such a condition is set that etching of the back surface is executed excessively, the lead portion in which the width of the surface is thicker than the width of the back surface can be formed.
However, the method of working the metal plate by wet etching has drawbacks such that a cost is expensive and a working speed is slow. Hence, stamping using the die, which makes possible a low cost and a quick working speed, is gradually employed.
FIGS. 3A
to
3
C are views showing a method of forming a stepwise shape, etc. in the lead portion by the stamping (prior art).
FIG. 3A
is a sectional view taken along a IV-IV line in FIG.
3
C.
In the method of forming the stepwise shape, etc. in the lead portion by the stamping in the prior art, as shown in
FIGS. 3A
to
3
C, first the lead portion
100
, which has crushed margin portions
100
a
in predetermined portions on both side surfaces, is formed by punching predetermined portions of the metal plate by the stamping. Then, as shown in
FIG. 3B
, the die having a punch
112
and a supporting member
114
is prepared and then the crushed margin portions
100
a
are pushed by using the punch
112
of the die to reduce a thickness. Thus, the stepped shape is formed from both side surface portions to the center portion of the lead portion
100
.
In this manner, in the prior art, the crushed margin portion
100
a
is provided in the predetermined portions on both side surfaces of the lead portion
100
, and then the crushed margin portions
100
a
are pushed/crushed by the punch
112
of the die to shape the lead portions into the stepped shape.
FIGS. 4A
to
4
D are views showing problems in the method of forming the stepwise shape, etc. in the lead portion by the stamping in the prior art. As shown in
FIGS. 4A and 4C
, if a crushed portion
100
b
is formed while setting a crushed depth of the crushed margin portions
100
a
, which is crushed by the punch
112
, shallow (e.g., about ⅓ of a metal plate thickness), spread of the metal is small on the surface S (surface that is connected to the connection electrode of the IC chip) side of the lead portion
100
and thus a sufficient bonding area cannot be assured. Also, as shown in an A portion of
FIG. 4A
, if the crushed depth is shallow, only an upper portion of the crushed portion
100
b
is extended in the lateral direction to form a shaving shape and thus the shape to attain a desired anchor effect cannot be obtained.
In contrast, as shown in
FIGS. 4B and 4D
, if the crushed portion
100
c
is formed while setting the crushed depth of the crushed margin portions
100
a
, which is crushed by the punch
112
, deep (e.g., about ½ or more of the metal plate thickness), the sufficient bonding area can be assured on the surface S of the lead portion
100
, nevertheless there is such a possibility that the crushed portion
100
c
that is pushed/spread by the punch
112
is spread excessively to contact mutually.
As the countermeasure against the above, there is such a method that the crushed portion
100
c
is formed by pushing the crushed margin portions
100
a
up to a depth at which a plurality of lead portions
100
come into contact with each other or come close to each other and then top end portions of a plurality of neighboring crushed portion
100
c
(portions surrounded by a chain line in
FIG. 4D
) are punched by the punch of the die such that a plurality of lead portions
100
can assure a desired interval therebetween.
However, since the portions that are punched by the punch are not united together, a punched metal residuum is separated into two pieces freely after the punching. As a result, the punched metal residuum does not stick to the side surface of the supporting member of the die but to the punch, and thus the so-called metal residuum lifting is generated.
In addition, a width of the crushed margin portion
100
a
of the lead portion
100
will be mentioned. If the width of the crushed margin portion
100
a
is narrow, the top end portion of the crushed portion is readily shaped into the above shaving shape. If the width of the crushed margin portion
100
a
is wide, an interval between neighboring lead portions
100
cannot be sufficiently assured since a pitch of the lead portions is decided previously. That is, it is extremely difficult to set the width of the crushed margin portion
100
a
that makes it possible to get the lead portion
100
with a desired sectional shape.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a lead frame manufacturing method capable of manufacturing a lead frame, which is employed in a leadless package and has lead portions each having a desired sectional shape, by the stamping not to cause any problem.
The present invention provides a lead frame manufacturing method of m
Armstrong Kratz Quintos Hanson & Brooks, LLP
Flynn Nathan J.
Mandala Jr. Victor A.
Shinko Electric Industries Co. Ltd.
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