Solution to mold wire sweep in fine pitch devices

A method of preventing non-uniform bonding wire sweep during an encapsulating process of an integrated circuit package includes the step of forming an encapsulating material flow restricting element between two widely spaced functional bonding wires. The integrated circuit package includes an array of electrically conductive leads for electrically connecting the package to other electrical elements and an integrated circuit die having a plurality of input/output terminal pads. A plurality of functional bonding wires electrically connects certain ones of the input/output terminal pads to associated electrically conductive leads such that the functional bonding wires have a predetermined pitch which defines an approximate minimum desired spacing between adjacent functional bonding wires. The plurality of functional bonding wires includes two widely spaced functional bonding wires which are spaced apart from one another by a distance substantially greater than the predetermined minimum desired spacing. An encapsulating material surrounds the die, the bonding wires, and at least portions of the leads. The encapsulating material flow restricting element restricts the flow of the encapsulating material in the area between the two widely spaced functional bonding wires during the encapsulating process of the package thereby preventing excessive, non-uniform bonding wire sweep of either of the two widely spaced functional bonding wires during the encapsulating process. In one embodiment, the encapsulating material flow restricting element is at least one additional non-functional bonding wire formed between the two widely spaced functional bonding wires.

BACKGROUND OF THE INVENTION 
The present invention relates generally to integrated circuit packages and 
more specifically to a method and arrangement for preventing non-uniform 
bonding wire sweep during the encapsulating process of a fine pitch 
integrated circuit package. 
In the integrated circuit packaging industry, there is a continuous desire 
to provide higher and higher density integrated circuit packages for 
integrated circuit die having increasing numbers of input/output terminal 
pads. When using a conventional wire bonding packaging technique, the 
pitch, or spacing between adjacent bonding wires becomes finer and finer 
as the number of input/output terminal pads increases for a given size 
die. This presents the problem of having two adjacent bonding wires 
electrically short to one another due to bonding wire sweep during the 
encapsulating process of producing the integrated circuit package. 
Although a variety of approaches have been suggested for reducing the 
bonding wire sweep during the encapsulating process of an integrated 
circuit package, many of these approaches require additional process steps 
or require specialized equipment. These requirements for additional 
process steps or specialized equipment add to the costs of producing the 
package and are therefore undesirable. 
FIG. 1 illustrates a partial cut away plan view of one corner of a typical 
integrated circuit package 10. The package includes an integrated circuit 
die 12 having a plurality of input/output terminal pads 14 located on the 
top surface of the die. Die 12 is supported by a die attach pad 16 of an 
overall lead frame 18. Lead frame 18 also includes a plurality of 
electrically conductive leads 20 for electrically connecting integrated 
circuit package 10 to other electrical elements. Furthermore, lead frame 
18 includes tie bars 22 (only one of which is shown in FIG. 1) for 
maintaining die attach pad 16 in position relative to leads 20 during the 
assembly of the package. An array of bonding wires 24 electrically connect 
respective ones of input/output terminal pads 14 to associated leads 20. 
Bonding wires 24 are arranged to have a predetermined pitch which defines 
a minimum desired spacing between adjacent bonding wires. This pitch, or 
minimum spacing, is indicated by the reference letter S in FIG. 1. 
As indicated by arrow 26 in FIG. 1, an encapsulating material, indicated by 
wavy lines 28, is injected into a mold 30 to encapsulate die 12, bonding 
wires 24, and at least portions of leads 20. In this example, 
encapsulating material 28 is injected into one of the corners of mold 30 
such that the encapsulating material flows diagonally across the assembly 
of components making up the package. As the encapsulating material flows 
diagonally across the assembly, the leading edge of the encapsulating 
material impacts each successive bonding wire causing them to displace 
slightly in the direction of the flow of the material. This is referred to 
as bonding wire sweep or mold wire sweep. 
In most cases, the relative bonding wire sweep of each successive bonding 
wire is fairly consistent from bonding wire to bonding wire and therefore 
the adjacent bonding wires do not normally come into contact with one 
another causing an electrical short. However, applicants have discovered 
that in situations where the spacing between two widely spaced bonding 
wires is substantially larger than the predetermined minimum spacing, the 
wire sweep of the downstream bonding wire relative to the flow of the 
encapsulating material can be substantially greater than the wire sweep of 
other consistently spaced bonding wires. This greater wire sweep of the 
downstream bonding wire of the two widely spaced bonding wires may lead to 
shorting between this downstream bonding wire and the next successive 
downstream bonding wire. 
The tie bar region of a typical integrated circuit package is one region in 
which two widely spaced bonding wires are commonly found. As illustrated 
in FIG. 1, two widely spaced bonding wires 24a and 24b are positioned on 
opposite sides of tie bar 22 and are spaced apart by a distance indicated 
by the reference letter D. For many package configurations, because of the 
tie bar and the physical configuration of the package, distance D is often 
substantially greater than the minimum desired spacing S described above 
which is defined by the pitch of package 10. Because of this larger 
distance D between widely spaced bonding wires 24a and 24b, the resistance 
to the flow of the encapsulating material is lower in this tie bar region 
between widely spaced bonding wires 24a and 24b. This lower resistance 
allows the flow of the encapsulating material to pick up speed and 
momentum. Therefore, when the flow of the encapsulating material indicated 
by lines 28 impacts the downstream bonding wire 24b of the two widely 
spaced bonding wires, it causes a greater amount of bonding wire sweep 
compared to other bonding wires within the package. This greater bonding 
wire sweep may result in an electrical short between the downstream 
bonding wire 24b of the two widely spaced bonding wires and a next 
successive downstream bonding wire 24c as illustrated in FIG. 1. The 
present invention provides methods and arrangements for eliminating or 
substantially reducing this greater bonding wire sweep problem associated 
with widely spaced bonding wires. 
SUMMARY OF THE INVENTION 
As will be described in more detail hereinafter, a method of preventing 
non-uniform bonding wire sweep during an encapsulating process of an 
integrated circuit package is herein disclosed. The integrated circuit 
package includes an array of electrically conductive leads for 
electrically connecting the package to other electrical elements and an 
integrated circuit die having a plurality of input/output terminal pads. A 
plurality of functional bonding wires electrically connects certain ones 
of the input/output terminal pads to associated electrically conductive 
leads such that the functional bonding wires have a predetermined pitch 
which defines an approximate minimum desired spacing between adjacent 
functional bonding wires. The plurality of functional bonding wires 
includes two widely spaced functional bonding wires which are spaced apart 
from one another by a distance substantially greater than the 
predetermined minimum desired spacing. An encapsulating material surrounds 
the die, the bonding wires, and at least portions of the leads. The method 
includes the step of, prior to the encapsulating process of the package, 
forming an encapsulating material flow restricting element between the two 
widely spaced functional bonding wires. The encapsulating material flow 
restricting element restricts the flow of the encapsulating material in 
the area between the two widely spaced functional bonding wires during the 
encapsulating process of the package thereby preventing excessive, 
non-uniform bonding wire sweep of either of the two widely spaced 
functional bonding wires during the encapsulating process. 
In one embodiment of the method the direction of the flow of the 
encapsulating material during the encapsulating process is generally 
perpendicular to the two widely spaced functional bonding wires. 
In another embodiment, the step of forming an encapsulating material flow 
restricting element includes the step of forming at least one additional 
non-functional bonding wire such that the non-functional bonding wire is 
positioned between the two widely spaced functional bonding wires. Also, 
the array of electrically conductive leads is provided as part of a lead 
frame with the lead frame further including a die attach pad for 
supporting the die and at least one tie bar for supporting the die attach 
pad in a predetermined location relative to the leads. The two widely 
spaced functional bonding wires are positioned on opposite sides of the 
tie bar and the step of forming the non-functional bonding wire includes 
the step of bonding one end of the non-functional bonding wire to the tie 
bar. In one version of this embodiment, the other end of the 
non-functional bonding wire is bonded to the die attach pad. 
Alternatively, the die may include a non-functional input/output terminal 
pad and the other end of the non-functional bonding wire may be bonded to 
the non-functional input/output terminal pad. 
An integrated circuit package is also herein disclosed. The package 
includes an integrated circuit die having a plurality of die input/output 
terminal pads and an array of electrically conductive leads for 
electrically connecting the package to other electrical elements. A 
plurality of functional bonding wires electrically connects certain ones 
of the input/output terminal pads to associated electrically conductive 
leads such that the functional bonding wires have a predetermined pitch 
which defines an approximate minimum desired spacing between adjacent 
functional bonding wires. The plurality of functional bonding wires 
includes two widely spaced functional bonding wires which are spaced apart 
from one another by a distance substantially greater than the 
predetermined minimum desired spacing. An encapsulating material flow 
restricting element is located between the two widely spaced functional 
bonding wires for restricting the flow of the encapsulating material in 
the area between the two widely spaced functional bonding wires during an 
encapsulating process of the package. And finally, an encapsulating 
material surrounds the die, the functional bonding wires, the 
encapsulating material flow restricting element, and at least portions of 
the leads. 
In one embodiment of the package, the encapsulating material flow 
restricting element is at least one additional non-functional bonding wire 
positioned between the two widely spaced functional bonding wires. Also, 
the array of electrically conductive leads is part of a lead frame and the 
lead frame further includes a die attach pad for supporting the die and at 
least one tie bar for supporting the die attach pad in a predetermined 
location relative to the leads. The two widely spaced functional bonding 
wires are located on opposite sides of the tie bar and one end of the 
non-functional bonding wire is connected to the tie bar. In a first 
version of this embodiment, the other end of the non-functional bonding 
wire is connected to the die attach pad. Alternatively, the die may 
include a non-functional input/output terminal pad and the other end of 
the non-functional bonding wire may be connected to the non-functional 
input/output terminal pad.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An invention is herein described for providing methods and apparatus for 
preventing non-uniform bonding wire sweep in an integrated circuit package 
during an encapsulating process of the package. These methods and 
apparatus are most applicable to integrated circuit packages having a 
certain pitch which defines a minimum desired spacing between adjacent 
bonding wires and which includes two widely spaced bonding wires that are 
spaced apart from one another by a distance substantially greater than the 
minimum desired spacing defined by the pitch. 
In the following description, numerous specific details are set forth in 
order to provide a thorough understanding of the present invention. 
However, in view of this description, it will be obvious to one skilled in 
the art that the present invention may be embodied in a wide variety of 
specific configurations. Also, well known integrated circuit manufacturing 
processes such as conventional wire bonding processes, integrated circuit 
package encapsulating or molding processes, and other such conventional 
integrated circuit manufacturing processes will not be described in detail 
in order not to unnecessarily obscure the present invention. 
Referring initially to FIG. 2, a first embodiment of an integrated circuit 
package designed in accordance with the invention will be described. FIG. 
2 illustrates a partial cut away plan view of one corner of a integrated 
circuit package 40 designed in accordance with the invention. For 
illustrative purposes, package 40 of FIG. 2 has a configuration similar to 
that of integrated circuit package 10 of FIG. 1. As will be the case 
throughout the various figures of this description, like components of the 
various figures are designated by like reference numerals. 
As described for package 10, package 40 includes an integrated circuit die 
12 having a plurality of input/output terminal pads 14 located on the top 
surface of the die. Die 12 is supported by a die attach pad 16 of an 
overall lead frame 18. Lead frame 18 also includes a plurality of 
electrically conductive leads 20 for electrically connecting integrated 
circuit package 40 to other electrical elements. Furthermore, lead frame 
18 includes tie bars 22 (only one of which is shown in FIG. 2) for 
maintaining die attach pad 16 in position relative to leads 20 during the 
assembly of the package. An array of functional bonding wires 24 
electrically connect respective ones of input/output terminal pads 14 to 
associated leads 20. Functional bonding wires 24 are arranged to have a 
predetermined pitch which defines a minimum desired spacing between 
adjacent bonding wires. This pitch, or minimum spacing, is indicated by 
the reference letter S. 
Although package 40 has been described as including a conventional lead 
frame having a plurality of leads, a die attach pad, and tie bars, these 
specific features are not a requirement of the invention. Instead, it 
should be understood that the invention would apply to packages including 
a wide variety of lead frames having a wide variety of configurations. 
Also, the lead frame may be replaced with a variety of other conventional 
arrangements, such as flex tape substrates, that provide the electrical 
connection between the bonding wires and an external element to which the 
package is to be connected. All of these other various arrangements and 
lead frame configurations would equally fall within the scope of the 
invention so long as bonding wires are used to electrically connect the 
die to the lead frame or other electrical connecting arrangement. 
As described above in the background for package 10 of FIG. 1, package 40 
of FIG. 2 has two widely spaced functional bonding wires 24a and 24b 
positioned on opposite sides of tie bar 22 and are spaced apart by a 
distance indicated by the reference letter D. This distance D is 
substantially greater than the minimum desired spacing S which is defined 
by the pitch of package 40. However, in accordance with the invention, 
package 40 also includes an encapsulating material flow restricting 
element positioned between widely spaced functional bonding wires 24a and 
24b. As will be described in more detail hereinafter, the encapsulating 
material flow restricting element restricts the flow of the encapsulating 
material between the widely spaced functional bonding wires during the 
encapsulation process of the package thereby preventing or substantially 
reducing non-uniform bonding wire sweep of downstream functional bonding 
wire 24b. 
In the embodiment shown in FIG. 2, the encapsulating material flow 
restricting element takes the form of a non-functional bonding wire 42. 
Also, die 12 includes a non-functional input/output terminal pad 44. Pad 
44 is not electrically connected to any of the functional electrical 
components making up die 12 and its only purpose is to provide a point of 
attachment for one end of non-functional bonding wire 42. The other end of 
non-functional bonding wire 42 is attached to tie bar 22. 
As indicated by arrow 26 in FIG. 2 and as described above for FIG. 1, the 
encapsulating material, which is indicated by wavy lines 28, is injected 
into a mold 30 to encapsulate die 12, functional bonding wires 24, 
non-functional bonding wire 42, and at least portions of leads 20. As 
described above in the background, when the encapsulating material flows 
diagonally across the assembly, the leading edge of the encapsulating 
material impacts each successive bonding wire causing them to displace 
slightly in the direction of the flow of the material. Although the 
encapsulating material has been described as being injected into the mold 
so that is flows diagonally across the assembly, this is not a requirement 
of the invention. Instead, it should be understood that the encapsulating 
material may be injected in any appropriate manner such that it flows 
across the assembly in any predetermined direction. 
In accordance with the invention, non-functional bonding wire 42 acts as a 
encapsulating material flow restricting element restricting the 
encapsulating material from picking up speed and momentum between widely 
spaced functional bonding wires 24a and 24b as described above in the 
background. Without this increased speed and momentum, the impact of the 
flow of the encapsulating material on downstream functional bonding wire 
24b of the two widely spaced functional bonding wires is not substantially 
different than the impact of the flow of the encapsulating material on 
other bonding wires. Therefore, the flow of the encapsulating material 
does not cause functional bonding wire 24b to have a substantially greater 
amount of bonding wire sweep when compared to other bonding wires within 
the package. This eliminates or substantially reduces the chances of an 
electrical short between downstream functional bonding wire 24b of the two 
widely spaced bonding wires and a next successive downstream bonding wire 
24c as illustrated in FIG. 2. 
Although the encapsulating material flow restricting element of FIG. 2 has 
been described and illustrated as a single non-functional bonding wire, 
this is not a requirement. Instead, any number of non-functional bonding 
wires may be used depending on the requirements of the specific integrated 
circuit package. For Example, in situations in which the spacing between 
the two widely spaced functional bonding wires is several times the 
desired minimum spacing defined by the pitch of the package, multiple 
non-functional bonding wires may be formed between the two widely spaced 
functional bonding wires. 
One of the advantages of the approach of using a non-functional bonding 
wire to act as the encapsulating material flow restricting element is that 
the same wire bonding equipment that is used to form the functional 
bonding wires may be used to form the non-functional bonding wire flow 
restricting element. This means that no additional process steps are 
required to form the restricting element. This minimizes the cost of using 
this approach. Also, in designs in which the die attach pad and the tie 
bar are not electrically grounded, this approach will still produce a good 
overall package even if the non-functional bonding wire or wires which act 
as the flow restricting element end up making contact with one of the 
functional bonding wires due to bonding wire sweep. 
Although the die of FIG. 2 has been described as including an extra 
non-functional input/output terminal pad 44 to which one end of the 
non-functional bonding wire is attached, this is not a requirement. FIG. 3 
illustrates an second embodiment of an integrated circuit package 50 
designed in accordance with the invention which does not require the die 
to include an extra non-functional input/output terminal pad. Package 50 
of FIG. 3 includes all of the elements of package 40 of FIG. 2 with the 
exception of non-functional input/output terminal pad 44. As shown in FIG. 
3, for this embodiment, one end of non-functional bonding wire 42 is 
attached to tie bar 22 as described above for package 40. However, in this 
case, the other end of non-functional bonding wire 42 is attached to die 
attach pad 16 at attachment point 52 adjacent to die 12 and between widely 
spaced functional bonding wires 24a and 24b. 
The configuration of FIG. 3 provides still another advantage of this 
approach. That is, this approach may easily be applied to existing 
integrated circuit package designs which are exhibiting bonding wire sweep 
problems due to widely spaced functional bonding wires without requiring 
any change in any of the components making up the existing integrated 
circuit package design. In many package designs, particularly problematic 
regions of the package design can account for an overwhelming majority of 
problems causing failures in the package and reducing the manufacturing 
yield for that package design. An example of one of these potentially 
problematic regions is the tie bar region described above in which two 
widely spaced functional bonding wires are positioned on opposite sides of 
the tie bar. The method of the present invention may be easily applied to 
these problematic regions at a minimal cost without requiring any changes 
to the package design and without requiring any additional process steps. 
In many cases this can result in dramatic increases in the manufacturing 
yield for a particular package design. 
Although the above described embodiments have been describe as using a 
non-functional bonding wire as the encapsulating material flow restricting 
element, this is not a requirement of the invention. Instead, a wide 
variety of flow restricting structures or elements may be utilized to 
restrict the flow of the encapsulating material in the space between the 
two widely spaced functional bonding wires. Any of these various 
structures or elements would equally fall within the scope of the 
invention so long as they restrict the increase in speed and momentum of 
the encapsulating material in the space between the widely spaced 
functional bonding wires. Also, although the integrated circuit package 
has been described with the various components having particular 
respective orientations, it should be understood that the present 
invention may take on a wide variety of specific configurations with the 
various components being located in a wide variety of positions and mutual 
orientations and still remain within the scope of the present invention. 
Therefore, the present examples are to be considered as illustrative and 
not restrictive, and the invention is not to be limited to the details 
given herein, but may be modified within the scope of the appended claims.