Semiconductor device and method of making the same
A semiconductor device and a method of making a semiconductor device are provided, wherein the device includes a die-pad, a semiconductor chip and a sealing resin. The die-pad has a first surface and a second surface opposite to the first surface. The second surface includes an exposed portion and a retreated portion around the exposed portion. The semiconductor chip is mounted on the first surface of the die-pad. The sealing resin covers the die-pad and the semiconductor chip, exposes the exposed portion, and is held in contact with the retreated portion.
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This application is a divisional application under 37 CFR § 1.53(b) of Ser. No. 10/027,856, filed on 19 Oct. 2001, entitled SEMICONDUCTOR DEVICE AND METHOD OF MAKING THE SAME.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention relates to a semiconductor device of the Quad Flat Non-leaded (QFN) package type, and a method of making the same.
2. Description of the Related Art
In the semiconductor device S3, the lower surface 32b of the die-pad 32 is exposed to the outside. Therefore, as indicated by the arrow A in
It is therefore an object of the present invention to provide a semiconductor device having a high reliability by preventing the removal of a sealing resin due to water infiltration.
According to a first aspect of the present invention, a semiconductor device is provided. The semiconductor device comprises; a die-pad having a first surface and a second surface opposite to the first surface, the second surface including an exposed portion and a retreated portion around the exposed portion; a semiconductor chip mounted on the first surface of the die-pad; a sealing resin for covering the die-pad and the semiconductor chip, wherein the resin is held in contact with the retreated portion while exposing the exposed portion.
Preferably, the retreated portion comprises a retreated surface and a side surface which adjoins the exposed portion, and the retreated surface forms an acute angle together with the retreated surface.
Preferably, the die-pad includes a slit opening at the retreated surface of the second surface and at the first surface.
Preferably, the die-pad includes a plurality of slits opening at the retreated surface of the second surface and at the first surface, and the plurality of slits are arranged to surround the semiconductor chip.
Preferably, the semiconductor chip is electrically connected to the die-pad via a first wire, and the first wire is connected to the first surface of the die-pad at a portion between a peripheral edge of the die-pad and the slit.
Preferably, the semiconductor device further comprises a terminal electrically connected to the semiconductor chip via a second wire. The terminal is retained by the sealing resin so as to expose a part thereof.
According to a second aspect of the present invention, another semiconductor device is provided. The semiconductor device comprises; a semiconductor chip; a die-pad which has an upper surface on which the semiconductor chip is mounted and a lower surface opposite to the first surface, the die-pad being electrically connected to the semiconductor chip via a first wire; and a plurality of leads electrically connected to the semiconductor chip via second wires, the semiconductor chip being sealed with a sealing resin with the lower surface of the die-pad exposed. The die-pad includes a thin-walled portion formed by removing the lower surface along a peripheral edge of the die-pad and also includes at least one slit penetrating through the thin-walled portion.
Preferably, the sealing resin extends under the thin-walled portion so as not to expose an opening of the slit.
Preferably, the slit is provided along a side surface of the semiconductor chip so as to surround the semiconductor chip.
Preferably, the first wire is connected at one end thereof to the semiconductor chip and connected at the other end thereof to the die-pad at a portion between a peripheral edge and the slit.
According to a third aspect of the present invention, a semiconductor device making method comprises the steps of; punching a conductive frame to form a die-pad having an upper surface and a lower surface opposite to the upper surface, and to form a slit penetrating through the die-pad adjacent the peripheral edge of the die-pad; performing etching with respect to the lower surface along the peripheral edge of the die-pad to form a thin-walled portion in the die-pad so that the slit opens at the thin-walled portion; mounting a semiconductor chip on the upper surface of the die-pad; bonding the semiconductor chip and the die-pad via a wire; and sealing the semiconductor chip with a sealing resin so that the lower surface of the die-pad is exposed.
Other features and advantages of the present invention will become clearer from the detailed description given below with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the present invention will be described below in detail with reference to
The semiconductor chip 1, which maybe an LSI chip or another kind of IC chip for example, is a silicon chip having one surface on which desired integrated electronic circuit is formed. The upper surface la of the semiconductor chip 1 is provided with a plurality of electrode pads (not shown). For obtaining good conductivity, the electrode pads may be formed by gold-plating electrodes of aluminum formed on the upper surface la of the semiconductor chip 1.
The first wire 11, which may be formed of gold for example, is bonded, at one end thereof, to the electrode pad for ground connection of the semiconductor chip 1. The other end of the first wire 11 is connected to the upper surface 2a of the die-pad 2. Generally, when the semiconductor device S1 is surface-mounted onto a mother board (not shown), the lower surface 2b of the die-pad 2 is connected to a ground pattern formed on the mother board. In this way, the grounding of the semiconductor chip 1 is realized via the first wire 11.
Each of the second wires 12, which may be formed of gold for example, is bonded, at one end thereof, to a respective one of other electrode pads on the semiconductor chip 1. The other end of the second wire 12 is connected to the upper surface 3a of a corresponding one of the leads 3 arranged around the semiconductor chip 1.
The die-pad 2 is a thin metal plate of a predetermined thickness formed of copper for example and larger than the semiconductor chip 1. The semiconductor chip 1 is bonded, via an adhesive, to a central portion on the upper surface 2a of the die-pad 2. The die-pad 2 includes a thin-walled portion 5 formed by cutting away peripheral portions of the lower surface 2b.
The thin-walled portion 5 has a thickness which is about one half of that of other portions of the die-pad 2. On the lower surface side 2b of the die-pad 2, the thin-walled portion 5 is defined by a retreated surface 6a and a side surface 6b. In this embodiment, the side surface 6b extends generally perpendicularly to the retreated surface 6a. The thin-walled portion 5 is formed with a plurality of thicknesswise penetrating slits 9 arranged to surround the semiconductor chip 1. As clearly shown in
Similarly to the die-pad 2, the leads 3 are formed from a thin metal plate of copper for example. The leads 3 are spaced from each other along the side surfaces 1b of the semiconductor chip 1.
The sealing resin 4 may be formed of a thermosetting resin such as an epoxy resin. As clearly shown in
To surface-mount the semiconductor device S1 onto a substrate (not shown), solder paste is applied to the wiring pattern formed on the substrate. Then, the device S1 is placed on the substrate so that the lower surface 2b of the die-pad 2 and the lower surfaces 3b of the respective leads 3 come into contact with the solder-applied wiring pattern. Precisely, the lower surface 2b of the die-pad 2 is brought into contact with the grounding portion of the wiring pattern. After the device S1 is properly positioned on the substrate, the applied solder paste is heated up so as to perform reflow soldering. As a result, the device S1 is electrically connected to the substrate via the die-pad 2 and the leads 3.
According to the semiconductor device S1 having the above structure, water infiltration to the upper surface 2a of the die-pad 2 can be prevented or lessened. In the semiconductor device S1, since the die-pad 2 and the sealing resin 4 have a boundary exposed to the outside, water may enter through the gap between the side surface 6b and the sealing resin 4. However, owing to the retreated surface 6a extending perpendicularly to the side surface 6b, the progress of water can be terminated. Thus, water is unable to reach or less likely to reach the upper surface 2a of the die-pad 2, whereby the removal of the sealing resin 4 in the reflowing process is reliably prevented. Consequently, it is possible to provide a reliable semiconductor device in which the breakage of the first wire 11 due to the removal of the sealing resin 4 does not occur.
In the semiconductor device S1, the sealing resin 4 surrounds the thin-walled portion 5 and fills the slits 9 provided at the thin-walled portion 5. This provides an ‘anchoring effect’ contributing to secure bonding between the die-pad 2 and the sealing resin 4. Thus, the die-pad 2 and the sealing resin 4 are irremovably attached to each other. Since the sealing resin 4, extending around and under the thin-walled portion 5, fills the openings 9aof the slits 9, water filtration through the slits 9 can be completely prevented or significantly lessened.
Further, in the semiconductor device S1, part of the sealing resin 4 extends into the plurality of slits 9 formed in the die-pad 2 for engagement therewith. Therefore, even if water reaches the upper surface 2a of the die-pad 2, thereby causing the sealing resin 4 to come off the surface at a location adjacent to the semiconductor chip 1, the slits 9 around the semiconductor chip 1 prevent the resin removal from propagating toward the peripheral edges of the die-pad 2 beyond the slits. Since the first wire 11 is connected at one end to the semiconductor chip 1 and at the other end to a portion of the die-pad 2 that is located between the slit 9 and the peripheral edge of the die-pad 2, the removal of the sealing resin does not affect the first wire 11. Therefore, the bonding condition of the first wire 11 to the die-pad 2 is kept good.
For preventing the removal of the resin seal 4, each of the slits 9 may be formed in the die-pad 2 at a portion inward from the thin-walled portion 5. In such a case, however, the opening 9a of the slit 9 is exposed to the outside, which increases the possibility that water advances along the inner surfaces of the slit 9 to reach the upper surface 2a of the die-pad 2. Therefore, in view of the prevention of water infiltration, it is preferable that the slit 9 is so formed as to penetrate through the thin-walled portion 5. Instead of the slit 9, the upper surface of the die-pad 2 may be formed with a recess for engagement with the sealing resin 4. In this case, since the recess is not open at the lower surface 2b of the die-pad 2, water filtration can be prevented even when the recess is provided inward from the thin-walled portion 5 in the die-pad 2.
In the semiconductor device S2, the sealing resin 4 comes into more secure contact with the die-pad 2, so that the die-pad 2 and the sealing resin 4 are held together more stably. However, the configuration of the side surface 6b is not limited to those described above, and another configuration may be employed as long as it ensures close contact between the die-pad 2 and the sealing resin 4.
Referring now to
Subsequently, with respect to each of the die-pads 2, portions of the lower surface 2b adjacent the peripheral edges thereof are removed by etching so that a thin-walled portion 5 is provided. The portions etched include portions in which the slits 9 are formed. At this time, the portions adjacent the peripheral edges of the die-pad 2 may be etched by e.g. wet etching to a thickness which is about one half of that of other portions. Alternatively, the thin-walled portion 5 may be formed by a punching process together with other portions if these other portions have a sufficiently large thickness. The configuration of the frame 15 shown in
Next, a semiconductor chip 1 is mounted by die-bonding to the center of the upper surface 2a of each die-pad 2. Then, a first wire 11 is bonded to the electrode pad for grounding of the semiconductor chip l and the upper surface 2a of the die-pad 2. With respect to the die-pad 2, the first wire 11 is bonded at a portion between the slit 9 and the peripheral edge of the die-pad 2. Then, a second wire 12 is bonded to connect each of other electrode pads of the semiconductor chip 1 to a corresponding one of the leads 3.
Then, as shown in
The semiconductor device S2 can also be formed by the above-described fabrication method. In forming the thin-walled portion 5 of the semiconductor device S2, the side surface 6b, which forms an acute angle together with the retreated surface 6a, may be formed by performing over-etching.
The scope of the present invention is not limited to the above-described embodiments. For example, the structure of the semiconductor chip 1, and the material, configuration, size of the die-pad 2 are not limited to the above-described embodiments.
Claims
1-10. (canceled)
11. A method of making a semiconductor device comprising the steps of:
- punching a conductive frame to form a die-pad with a slit, the die-pad including an upper surface and a lower surface opposite to the upper surface, the slit extending through the die-pad at a location adjacent to a peripheral edge of the die-pad;
- etching the lower surface along the peripheral edge of the die-pad so as to form a thin-walled portion in the die-pad in a manner such that the slit is opened at the thin-walled portion;
- mounting a semiconductor chip on the upper surface of the die-pad;
- bonding a wire to the semiconductor chip and to the die-pad; and
- sealing the semiconductor chip with a sealing resin in a manner such that the lower surface of the die-pad is exposed.
12. The method according to claim 11, wherein the thin-walled portion is defined by a retreated surface.
13. The method according to claim 11, wherein the sealing resin extends under the thin-walled portion so as not to expose an opening of the slit.
14. The method according to claim 11, wherein the slit extends along a side surface of the semiconductor chip around the semiconductor chip.
15. The method according to claim 11, wherein the wire is connected at one end thereof to the semiconductor chip and connected at another end thereof to the die-pad at a portion between a peripheral edge of the die-pad and the slit.
Type: Application
Filed: Apr 7, 2006
Publication Date: Aug 10, 2006
Applicant: ROHM CO., LTD. (Kyoto-shi)
Inventor: Yasumasa Kasuya (Kyoto-shi)
Application Number: 11/399,871
International Classification: H01L 23/28 (20060101);