Patent Application
20080265385
The invention relates to a semiconductor package and a wire bonding method for the same. More particularly, the invention relates to a semiconductor package using copper wires for electrically connecting a carrier to a chip mounted on the carrier and a wire bonding method for the same.
In conventional semiconductor packages, gold wires are generally used to electrically connect a chip to a chip carrier such as a leadframe or a substrate, since gold wires can form good bonding with a silver-coated layer on fingers of the leadframe or a Ni/Au layer on fingers of the substrate, a good bonding quality between the gold wires and the fingers can be ensured. Due to high cost of gold, however, there is a trend in the art to migrate from using gold wires to using other materials such as Copper (Cu). But copper cannot form good bonding with the silver-coated layer on the fingers of a leadframe or the Ni/Au layer on the fingers of a substrate, which thus may lead to short tail of the stitch ends of copper wires bonded to the fingers and further lead to uneven tail ends and inconsistent tail length of copper wires remained beyond the capillary after a bonding process, thus adversely affecting formation of free air balls (FAB) for a subsequent wire bonding process and resulting in nonuniform size of free air balls. Nonuniform size of the free air balls can easily result in poor bonding between the free air balls and the bond pads of the chip, thus adversely and ultimately causing a ball lift problem in the fabrication process.
As depicted in
In the case of using copper wires as shown in
To overcome the problems described above, as shown in
Therefore, it is highly desirable and beneficial to develop a semiconductor package using copper wires and a wire bonding method for the same that can overcome the conventional problems of ball lift and stitch lift so as to enhance bonding reliability of copper wires.
In light of the drawback associated with the conventional techniques as described above, an objective of the present invention is to provide a semiconductor package using copper wires and a wire bonding method for the same, which enhances bondability of copper wires on fingers of a carrier by implanting on the fingers of the carrier Au stud bumps that have good bonding with the copper wires, thereby overcoming the stitch lift problem of the prior art.
Another objective of the present invention is to provide a semiconductor package using copper wires and a wire bonding method for the same, which prevents the ball lift problem from occurring to copper wires bonded to bond pads of a chip by implanting on fingers of a carrier Au stud bumps that have good bonding with the copper wires.
Another objective of the present invention is to provide a semiconductor package using copper wires and a wire bonding method for the same. By implanting Au stud bumps on fingers of a carrier, wherein the Au stud bumps have good bonding with copper wires, residues of copper wires remained beyond the capillary after a bonding process have an even tail end and uniform tail length, and thus enabling formation of uniform free air balls before subsequent wire bonding process so as to form good bonding between the copper wires and bond pads of a chip without the need of implanting Au stud bumps on the bond pads of the chip.
In accordance with the foregoing and other objectives, a semiconductor package using copper wires according to the present invention comprises a carrier with a plurality of fingers, wherein the carrier may be a leadframe or a substrate; a plurality of stud bumps made of such as Au implanted on the fingers of the carrier; a chip mounted on the carrier, the active surface of the chip having a plurality of bond pads; a plurality of copper wires, wherein each of the copper wires has one end bonded to each of the bond pads of the chip and the other end bonded to each of the stud bumps on the carrier such that the chip can be electrically connected to the carrier through the copper wires; and an encapsulant formed on the carrier for encapsulating the chip, the copper wires and the stud bumps.
The present invention further provides a wire bonding method applied to the semiconductor package using copper wires described above. The method comprises the steps of: providing a carrier such as a leadframe or a substrate with a chip mounted thereon, wherein the carrier is provided with a plurality of fingers and a plurality of stud bumps is implanted on the fingers; and bonding one end of each of the copper wires to each of bond pads of the chip and bonding the other end of each of the copper wires to each of the stud bumps on the fingers, thereby electrically connecting the chip to the carrier through the copper wires.
Accordingly, the semiconductor package using copper wires and the wire bonding method for the same according to the present invention is characterized in that Au stud bumps that have good bonding with copper wires are implanted on fingers of a carrier so as to enhance bondability of the copper wires to the fingers and overcome the stitch lift problem of the prior art. With good bonding and enhanced bondability, residues of copper wires remained beyond a capillary after a bonding process have even tail ends and uniform tail length, which in turn facilitates fabrication of solder balls of uniform size before subsequent wire bonding process and thus eliminates the necessity to implant Au stud bumps on the bond pads of a chip and meanwhile overcomes the ball lift problem of the prior art, thereby enhancing the bonding reliability of copper wires. Therefore, the present invention offers advantages over the prior art and has high industrial applicability.
Other features and advantages of the invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings, in which
The present invention is described in the following with specific embodiments, so that one skilled in the pertinent art can easily understand other advantages and effects of the present invention from the disclosure of the invention. The present invention may also be implemented and applied according to other embodiments, and the details may be modified based on different views and applications without departing from the spirit of the invention.
The substrate 11 has a plurality of fingers 111 formed thereon such that the Au stud bumps 13 can be implanted on the fingers 111, thus allowing stitch end 142 of the copper wire 14 to be stitch bonded to the Au stud bump 13. The substrate 11 may be a conventional epoxy resin substrate, a polyimide substrate, a glass substrate or a ceramic substrate. Since manufacture of the substrate 11 is well known in the art, there will be no further description about the formation of the fingers 111 on the substrate 11 for the sake of brevity. Also, It should be noted that the use of the substrate 11 as a carrier for carrying the chip 12 is only exemplary and the invention is not limited thereto. For instance, a leadframe may be employed for carrying the chip 12.
The chip 12 has a plurality of bond pads 121 formed thereon for allowing solder ball 141 formed on one end of the copper wire 14 to be bonded thereon such that after the two ends of the copper wire 14 are bonded to the finger 111 of the substrate 11 and the bond pad 121 of the chip 12 respectively, the chip 12 can be electrically connected to the substrate 11 through the copper wires 14.
Since the molding process for forming the encapsulant 15 and the die bond process for bonding the chip 12 to the substrate 11 are well known in the art, detailed descriptions of the both processes will be purposely omitted herein for the sake of brevity. The efficacy of the semiconductor package I will be described in more detail in the following wire bonding method proposed by the invention.
As shown in
Since the Au stud bumps 13 on the fingers 111 have good bonding with the stitch ends 142 of the copper wires 14, the conventional problem of short tail of the stitch ends 142 is prevented, and accordingly stitch lift of the stitch ends 142 from the Au stud bumps 13 caused by short tail is avoided. With good bonding, residues of copper wires 143 remained beyond the capillary after a bonding process have even tail end and uniform tail length, which in turn facilitates formation of solder balls 141 of uniform size and eliminates the necessity to implant Au stud bumps on the bond pads of the chip and meanwhile solves the ball lift problem as encountered in the prior art, thereby enhancing bondability between the copper wires and the chip as well as the carrier and ensuring reliability of the semiconductor package.
It will be understood that the invention may be embodied in other specific forms without departing from the spirit or central characteristics thereof. The present examples and embodiments, therefore, are to be considered in all respects as illustrative and not restrictive, and the invention is not to be limited to the details given herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 096112654 | Apr 2007 | TW | national |
| 096123660 | Jun 2007 | TW | national |
