Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor
Reexamination Certificate
2000-03-08
2002-09-24
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
C438S108000, C438S111000, C438S112000, C438S123000, C438S124000, C438S125000, C257S666000, C257S667000, C257S676000, C257S678000
Reexamination Certificate
active
06455348
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a resin-molded semiconductor device in which a semiconductor chip and signal-connecting leads to be connected to the chip are encapsulated with a resin encapsulant, a method for manufacturing such a device, and a lead frame suitable for manufacturing the resin-molded semiconductor device. In particular, the present invention relates to an improved device with a reduced thickness.
In recent years, in order to catch up with rapidly advancing downsizing of electronic appliances, it has become increasingly necessary to mount semiconductor components with higher and higher density. Correspondingly, sizes and thicknesses of semiconductor components have also been noticeably reduced.
Hereinafter, a conventional resin-molded semiconductor device will be described.
FIG. 20
is a cross-sectional view of a conventional resin-molded semiconductor device. As shown in
FIG. 20
, this semiconductor device includes external electrodes on its back surface.
The semiconductor device further includes a lead frame consisting of: inner leads
101
; a die pad
102
; and support leads (not shown) for supporting the die pad
102
. A semiconductor chip
104
is bonded onto the die pad
102
with an adhesive, and electrode pads (not shown) of the chip
104
are electrically connected to the inner leads
101
with metal fine wires
105
. And the die pad
102
, semiconductor chip
104
, part of the inner leads
101
, support leads and metal fine wires
105
are encapsulated with a resin encapsulant
106
. In this structure, no resin encapsulant
106
exists on the back surface of the inner leads
101
. In other words, the respective back surfaces of the inner leads
101
are exposed and the respective lower parts of the inner leads
101
, including the exposed back surfaces thereof, are used as external electrodes
107
. To improve the adhesion between the resin encapsulant
106
and the inner leads
101
or the die pad
102
, the side faces of the leads
101
and the pad
102
are formed like a taper with an upwardly increasing thickness, not to extend perpendicularly to their upper and lower surfaces.
In such a resin-molded semiconductor device, the respective back surfaces of the resin encapsulant
106
and the die pad
102
are both located on the same plane. Stated otherwise, the back surface of the lead frame is not substantially encapsulated. Accordingly, the thickness of such a semiconductor device is thinner than usual.
A resin-molded semiconductor device having such a structure as that shown in
FIG. 20
is manufactured in the following manner. First, a lead frame including inner leads
101
and a die pad
102
is prepared and then wrought mechanically or chemically to shape the side faces of the lead frame like a taper. Next, a semiconductor chip
104
is bonded onto the die pad
102
of the lead frame prepared, and is electrically connected to the inner leads
101
with metal fine wires
105
. As the metal fine wires
105
, aluminum (Al) or gold (Au) wires may be appropriately used, for example. Then, the die pad
102
, semiconductor chip
104
, inner leads
101
, support leads and metal fine wires
105
are encapsulated with a resin encapsulant
106
. In this case, the lead frame, on which the semiconductor chip
104
has been bonded, is introduced into a die assembly and transfer-molded. In particular, resin molding is performed with the back surface of the lead frame in contact with an upper or lower die of the die assembly. Finally, parts of outer leads, protruding outward from the resin encapsulant
106
, are cut off, thereby completing a resin-molded semiconductor device.
Although a conventional resin-molded semiconductor device of this type has a reduced thickness, the device has the following problems.
Firstly, a resin encapsulant covers the upper and side faces of a die pad, but does not exist on the back surface thereof. Accordingly, the resin encapsulant cannot hold the die pad and the semiconductor chip so strong as that of other thicker devices, resulting in deterioration in reliability of the device.
Secondly, stress applied by the resin encapsulant or stress applied after assembling might have unwanted effects on a semiconductor chip or the resin encapsulant might possibly crack. Particularly when moisture penetrates between the die pad and the resin encapsulant, the adhesion therebetween decreases to a noticeable degree or considerable cracking is created. As a result, the reliability of the device further deteriorates.
Thirdly, although a resin-molded semiconductor device can be generally mounted accurately on a motherboard to be self-aligned with its desired position using the tension of solder, the time taken to settle the self alignment is still to be shortened and the mounting accuracy is still to be improved.
Fourthly, if part of a resin encapsulant sticks out of the back surface of a die pad in bonding the die pad and a motherboard (i.e., if so-called resin burr exists), then desired characteristics might not be attained in terms of heat radiation, for example. This is because the die pad cannot be in satisfactory contact with a heat-radiating pad in such a case. Such resin burr can be removed by using water jet or the like. However, such a process is not just troublesome, but causes additional problems. Specifically, if a water jet process is carried out, then a nickel, palladium or gold plated layer might peel off and impurity might deposit on the exposed parts. Accordingly, such parts exposed on the resin encapsulant should be plated once again after the encapsulation. As a result, work efficiency and reliability of the device might possibly deteriorate.
SUMMARY OF THE INVENTION
A first object of this invention is providing a resin-molded semiconductor device suppressing delamination of a die pad by making a resin encapsulant hold the pad more strongly when the lower surface of the pad is exposed on the encapsulant, and a lead frame suitable for manufacturing such a device.
A second object is providing a resin-molded semiconductor device, preventing a resin encapsulant from cracking due to penetration of water or moisture between a die pad and the encapsulant, and a lead frame suitable for manufacturing such a device.
A third object is providing a resin-molded semiconductor device that can be self-aligned with a desired position on a motherboard more accurately by using a structure where the lower surface of a die pad is exposed on the resin encapsulant, and a method for manufacturing the same.
A fourth object is providing a resin-molded semiconductor device with heat radiation characteristics improved by preventing the formation of resin burr even if the lower surface of a die pad is exposed on the encapsulant, a manufacturing method thereof, and a lead frame suitable for manufacturing such a device.
A fifth object is providing a resin-molded semiconductor device in which solder balls need not be interposed between a die pad and a heat-radiating pad, and a method for manufacturing the same.
A first lead frame according to the present invention includes: an outer frame surrounding a region in which a semiconductor chip is mounted; a die pad formed in the region surrounded by the outer frame; a support portion for supporting the die pad by connecting the die pad to the outer frame; and signal-connecting leads connected to the outer frame. A convex portion protruding downward and a flange portion surrounding the convex portion are formed as lower part of the die pad.
In this structure, even if the lower surface of the convex portion of the die pad is not covered with the resin encapsulant in mounting a semiconductor chip on this lead frame and encapsulating the chip and the lead frame with a resin encapsulant, the encapsulant exists under the flange portion of the die pad. As a result, a resin-molded semiconductor device, where a resin encapsulant can hold the die pad more strongly, is obtained. That is to say, the first object is accomplished. In addition, since the adhesion between the resin encapsulant and
Lee Jr. Granvill D
Smith Matthew
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