Active solid-state devices (e.g. – transistors – solid-state diode – Lead frame – With structure for mounting semiconductor chip to lead frame
Reexamination Certificate
2001-05-18
2003-08-19
Flynn, Nathan J. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Lead frame
With structure for mounting semiconductor chip to lead frame
C257S673000, C257S692000, C257S666000, C257S678000, C257S674000, C438S127000, C438S123000
Reexamination Certificate
active
06608369
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to lead frames, semiconductor devices and a manufacturing method therefor, circuit boards and electronic equipment.
DESCRIPTION OF THE RELATED ART
A package having a bottom surface of a die pad of a lead frame exposed is known. In manufacturing this type of package, a molding process is conducted to mold resin while pressing the die pad against a molding die. However, the resin enters between the die pad and the molding die such that burrs are formed in the bottom surface of the die pad. Also, in this type of package, the die pad and the resin are likely to be delaminated from each other at their interface.
The present invention has been made to solve the problems described above. It is an object of the present invention to provide a highly reliable lead frame in spite of its structure in which the bottom rear surface of a die pad is exposed, a semiconductor device and a method for manufacturing the same, a circuit board and electronic equipment.
SUMMARY OF THE INVENTION
(1) A lead frame according to the present invention is a lead frame having an outer frame and a die pad,
the die pad having an end section formed with a thin portion thinner than a central section thereof,
one surface of the thin portion being formed in the same plane ash one surface of the central section, and
the die pad being shifted from the outer frame in a direction in which the surfaces of the thin portion and the central section formed in the same plane face.
According to the present invention, because the thin portion is formed at an end section of the die pad, a sealing material can be readily placed thereon. Accordingly, the die pad can be readily pressed against a mold in the molding step. Furthermore, the sealing material does not enter between the die pad and the mold, and therefore it is unlikely that burrs will be be formed. Also, by forming a thin portion at an end section of the die pad, the distance from one surface of the die pad to the other surface thereof becomes longer even when one surface of the die pad is exposed and sealed with a sealing material. Therefore, even when the die pad and the sealing material are delaminated from one another at their interface, penetration of water can be reduced.
(2) In the lead frame,
the die pad is connected to the outer frame by hanger pins,
the thin portion is formed at the end section of the die pad avoiding a portion thereof,
the hanger pins may be connected to the portion of the die pad in which the thin portion has not been formed.
As a result, since the hanger pin is connected to the die pad while avoiding the thin portion thereof, reduction in strength at the connecting section between the two can be prevented.
(3) In the lead frame,
the die pad has a step formed at the end section to thereby form the thin portion,
wherein of surfaces that form the step an end surface that rises in a direction of thickness of the die pad may be formed with a recessed surface.
Accordingly, a sealing material can be provided so that it enters into the recessed surface, whereby the adhesion between the recessed surface and the sealing material is improved.
(4) A semiconductor device according to the present invention comprises a semiconductor chip,
a die pad on which the semiconductor chip is mounted, the die pad having an end section formed with a thin portion thinner than a central section thereof, and
a sealing material that seals the semiconductor chip,
wherein one surface of the thin portion of the die pad is formed in the same plane as one surface of the central section, and
the sealing material leaves exposed the surfaces of the thin portion and the central section in the coplanar surface of the die pad, and seals the end section of the die pad.
According to the present invention, since the thin portion is formed at the end section of the die pad, the distance from one surface of the die pad to the other surface thereof becomes longer, penetration of water can be reduced even when the die pad and the sealing material are delaminated from one another at their interface. Also, because the thin portion is formed at the end section of the die pad, the sealing material can be readily placed thereon. Accordingly, the die pad can be readily pressed against a mold in the molding step, the sealing material will not enter between the die pad and the mold, and therefore it is unlikely that burrs will be formed.
(5) In the semiconductor device,
the die pad has a step formed at the end section to thereby form the thin portion,
wherein of surfaces that forms the step an end surface that rises in a direction of thickness of the die pad may be formed with a recessed surface.
Accordingly, a sealing material can enter into the recessed surface, whereby the adhesion between the recessed surface and the sealing material is improved.
(6) In the semiconductor device,
a brazing material may be provided on the surface of the die pad that the sealing material has left exposed.
As a result, the exposed surface on the die pad can be protected by the brazing material, and the brazing material can be used to facilitate bonding between the die pad and other members.
(7) A circuit board according to the present invention comprises the semiconductor device.
(8) A circuit board according to the present invention comprises the semiconductor device, and is provided with a heat dissipating member that is bonded to the die pad by the brazing material.
As a result, heat that is generated in the semiconductor chip can be dissipated through the heat dissipating member bonded to the die pad.
(9) Electronic equipment according to the present invention comprises the semiconductor device.
(10) Electronic equipment according to the present invention comprises the semiconductor device, and is provided with a heat dissipating member that is bonded to the die pad by the brazing material.
As a result, heat that is generated in the semiconductor chip can be dissipated through the heat dissipating member bonded to the die pad.
(11) A method for manufacturing a semiconductor device according to the present invention includes a molding step that is conducted by setting on a mold a lead frame having a semiconductor chip mounted on a die pad, wherein
the die pad has an end section formed with a thin portion thinner than a central section thereof,
one surface of the thin portion is formed in the same plane as one surface of the central section, and
a sealing material is placed on the thin portion to thereby bring the die pad into contact with the inner surface of the mold, whereby the molding step is conducted.
According to the present invention, because the thin portion is formed at an end section of the die pad, a sealing material can be readily placed thereon, and therefore the die pad on which the sealing material is placed can be pressed against the mold. Accordingly, the molding step can be conducted without allowing the sealing material to enter between the die pad and the mold. In this manner, a semiconductor device can be manufactured so that burrs will not formed on the die pad.
(12) The method for manufacturing a semiconductor device includes
an electrolytic plating step to be conducted for the lead frame after the molding step,
wherein the lead frame has an outer frame and a hanger pin that connects the outer frame to the die pad, and
wherein the electrolytic plating step may be conducted before the hanger pin is cut.
Accordingly, the hanger pin can be used to maintain electrical connection between the outer frame and the die pad to conduct an electrolytic plating.
(13) In the method for manufacturing a semiconductor device, the lead frame includes a plurality of leads that are connected to one another by a dam bar, wherein the electrolytic plating step may be conducted after the dam bar is cut.
As a result, cut surfaces at the dam bar in the leads can also be electrolytically plated.
REFERENCES:
patent: 5252783 (1993-10-01), Baird
patent: 5648682 (1997-07-01), Nakazawa et al.
patent: 5777380 (1998-07-01), Otsuki et al.
patent: 6081029 (2000-06
Erdem Fazli
Flynn Nathan J.
Oliff & Berridge PLC.
Seiko Epson Corporation
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