Patent Application
20070105280
The present invention relates to wire bonding in general and more specifically to a brace for a long wire loop.
Wire bonding typically involves connecting a bond pad on an integrated circuit (IC) die to a lead finger of a lead frame with a bonding wire. Referring to
Bonding wires of a substantial length, like the bond wire 22, are often needed to connect the inboard bond pads to the lead frame lead fingers. Correspondingly, wire loops of a significant length are usually formed between the inboard bond pads and the lead frame lead fingers. To prevent wire-to-die shorting, a height clearance of at least two (2) times the diameter of the bonding wire must be maintained over the surface of the IC die. However, creating a wire loop with the required height clearance throughout an inboard length of the bonding wire, that is, a length of the bonding wire extending over the surface of the IC die, often leads to performance issues, such as decreased stability and inconsistency. This problem is particularly acute in cases where the inboard length of the bonding wire is greater than about 60% of the total length of the bonding wire.
In view of the foregoing, it would be desirable to have a method of forming a stable and consistent wire loop with an appropriate height clearance throughout its inboard length to prevent wire-to-die shorting.
The following detailed description of preferred embodiments of the invention will be better understood when read in conjunction with the appended drawings. The present invention is illustrated by way of example and is not limited by the accompanying figures, in which like references indicate similar elements. It is to be understood that the drawings are not to scale and have been simplified for ease of understanding the invention.
The detailed description set forth below in connection with the appended drawings is intended as a description of the presently preferred embodiments of the invention, and is not intended to represent the only form in which the present invention may be practiced. It is to be understood that the same or equivalent functions may be accomplished by different embodiments that are intended to be encompassed within the spirit and scope of the invention.
The present invention provides a method of connecting a lead frame lead finger to a bond pad on an integrated circuit (IC) die. The method includes the step of bonding a first bonding wire from the lead finger to an intermediate point. A second bonding wire is bonded from the lead finger to the bond pad such that the first bonding wire supports the second bonding wire.
The present invention also provides a semiconductor package including a lead frame having a die support area and a plurality of lead fingers located around the die support area. An integrated circuit (IC) die having a plurality of bond pads is attached to the die support area. Respective lead fingers are connected to respective bond pads with respective bonding wires: a first bonding wire connects a first lead finger to an intermediate point; and a second bonding wire connects the first lead finger to a first bond pad such that the first bonding wire supports the second bonding wire.
The present invention further provides a method of making a semiconductor package including the step of attaching an integrated circuit (IC) die having a plurality of bond pads to a die support area of a lead frame having a plurality of lead fingers located around the die support area. Respective lead fingers are connected to respective bond pads with respective bonding wires: a first bonding wire connects a first lead finger to an intermediate point; and a second bonding wire connects the first lead finger to a first bond pad such that the first bonding wire supports the second bonding wire. The lead frame, the IC die and the bonding wires are encapsulated with a molding compound.
Referring now to
The IC die 30 includes a plurality of bond pads 38, each of which is connected to respective ones of the lead fingers 36 with respective ones of a plurality of bonding wires 40. While it is typical for one lead finger to connect to one bond pad, as can be seen, sometimes one lead finger is connected to more than one bond pad. Many of the bond pads 38 are located along a periphery of the IC die 30. However, as shown in
The bonding wires 40 may be made of gold (Au), copper (Cu), aluminium (Al) or other electrically conductive materials as are known in the art and commercially available. The layout of the bond pads 38 on the IC die 30 and the arrangement of the bonding wires 40 in
Referring again to
Referring now to
As shown in
With the support provided by the short bonding wire 48, the long bonding wire 42 has a stable and consistent wire loop with an appropriate height clearance C throughout its inboard length L2 to prevent wire-to-die shorting. In this particular embodiment, an inboard length L1 of the short bonding wire 48, that is, a length of the short bonding wire 48 extending over the surface 56 of the IC die 30, is less than about 55% of a total length LT1 of the short bonding wire 48, while an inboard length L2 of the long bonding wire 42, that is, a length of the long bonding wire 42 extending over the surface 56 of the IC die 30, is greater than about 65% of a total length LT2 of the long bonding wire 42.
In one embodiment, each of the long and short bonding wires 42 and 48 has a diameter of about 1.3 mil, lengths LT1 and LT2 of about 63.7 and about 88.5 mil, respectively, and loop heights H1 and H2 of about 6.5˜7.5 mil and about 8.5˜9.5 mil, respectively. Although specific and relative dimensions of the long and short bonding wires 42 and 48 are described herein, those of skill in the art will understand that the present invention is not limited to the described dimensions.
First ends 58 and 60 of the long and short bonding wires 42 and 48 are bonded to the centrally located bond pad 46 and the intermediate point 50, respectively, while second ends 59 and 61 of the long and short bonding wires 42 and 48 are bonded to the lead finger 44. As can be seen, the bonding wires 40 in this particular embodiment are bonded to the bond pads 38 of the IC die 30 and the lead fingers 36 by ball bonding. Nevertheless, those of skill in art will understand that the present invention is not limited to any single wire bonding technique. In the described embodiment, the intermediate point 50 is a bond pad. However, it should be understood that the present invention is not limited to bonding the first end 60 of the short bonding wire 48 to a bond pad. Further, in this particular embodiment, the respective second ends 59 and 61 of the long and short bonding wires 42 and 48 are bonded to nearby spots on the lead finger 44; in an alternative embodiment, the respective second ends 59 and 61 of the long and short bonding wires 42 and 48 are bonded to the same spot on the lead finger 44. It would also be possible to bond the long and short bond wires 42 and 48 to different ones of the lead fingers 44.
As is evident from the foregoing discussion, the present invention provides a method of forming a stable and consistent wire loop by providing a brace in the form of a shorter, and therefore inherently more stable, wire loop to support the longer wire loop. The shorter wire loop also prevents the longer wire loop from contacting a surface of an IC die.
While the preferred embodiments of the invention have been illustrated and described, it will be clear that the invention is not limited to these embodiments only. Numerous modifications, changes, variations, substitutions and equivalents will be apparent to those skilled in the art without departing from the spirit and scope of the invention as described in the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 200510124613.7 | Nov 2005 | CN | national |
