Active solid-state devices (e.g. – transistors – solid-state diode – Lead frame – With separate tie bar element or plural tie bars
Reexamination Certificate
2000-08-23
2003-02-04
Chaudhuri, Olik (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Lead frame
With separate tie bar element or plural tie bars
C257S680000, C257S773000, C257S774000, C257S775000
Reexamination Certificate
active
06515354
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to integrated circuit packages, and more particularly to an integrated circuit package having beam leads approaching die bonding pads from more than one direction.
BACKGROUND ART
Semiconductor chips or wafers are used in applications including integrated circuits (ICs) or flash memory, which may be used in portable electronic devices. It is desirable that a semiconductor chip hold as many circuits or memory cells as possible per unit area to minimize the size, weight, and energy consumption of devices using the semiconductor chips. ICs, whether individual active devices, individual passive devices, multiple active devices within a single chip, or multiple active and passive devices within a single chip, require suitable input/output (I/O) connections between themselves and other circuit elements or structures. These semiconductor devices are typically small and fragile and commonly carried on substrates or carrier members for support. These devices are also frequently encapsulated to protect the device from unfavorable environments, such as dust, mechanical or electrical loads, and moisture.
As the density of semiconductor chip integrated circuits increases, the density of I/O terminals, such as contacts and leads must also increase through, for example, smaller contacts and leads and/or different I/O configurations. Chip-scale packages (CSPs) offer one advantageously compact geometry, requiring a package having dimensions no more than 1.2 times the dimensions of die
10
. CSPs find particular applicability in portable devices such as pagers, camcorders, cell phones, cameras, personal information managers, laptop computers, and global positioning devices, where size and weight are important considerations. Of these chip-scale packages, one increasingly important high density I/O configuration is a micro-ball grid array (&mgr;BGA) package.
FIGS. 1 and 2
illustrate a chip-scale &mgr;BGA package.
FIG. 1
shows a cross-section of the &mgr;BGA package including a die
10
, an elastomer or epoxy-based thermoset adhesive
20
applied to a lower surface of die
10
, and a tape or sheetlike interposer
30
, such as an insulating organic film of polyimide. The tape
30
has an adhesive
25
formed on one side and also has metal traces or wirings
40
formed thereon or embedded therein. The metal traces
40
are made, for example, by forming a thin metallic film on the tape
30
such as by evaporation or deposition and wet-etching the metallic film. At one end, each of the metal traces
40
is attached to a respective die bonding pad
60
. The traces
40
are routed across tape
30
, as shown in
FIG. 2
, to terminate in a conductive land
45
. The lands
45
collectively form a matrix pattern and vias or holes
50
are formed in the tape
30
to overlie these lands
45
. As shown in
FIG. 1
, conductive balls
65
such as solder balls are formed in vias
50
to contact lands
45
and permit electrical connection of the I/O terminals or bonding pads
60
of the die
10
to corresponding bonding pads disposed on the surface of a printed circuit board (PCB) or other substrate. The pitch, a distance from a center line of one ball to a center line of an adjacent ball, is designated by P. An encapsulant
80
, such as an epoxy thermoset, is provided to protect the electrical connections from damage caused by unfavorable environments, such as described above.
As shown in
FIG. 2
, tape windows
70
are selectively formed at either end of die
10
in areas corresponding to the die I/O bonding pads
60
. Subsequent to connection of tape
30
to die
10
, traces
40
are connected to bonding pads
60
. One approach to connecting trace
40
and bonding pad
60
is “wire bonding”, wherein a separate wire is used to connect a bonding pad provided at an end portion of trace
40
to bonding pad
60
. The separate wire is bonded to each of the bonding pads by bonding means including ultrasonic bonding, thermal bonding, and compression bonding. Another approach to connection of traces
40
and bonding pads
60
which is better suited for the particular design constraints of &mgr;BGA and limitations of conventional manufacturing equipment, is a “beam lead” connection illustrated by
FIGS. 1 and 2
. The beam lead connection is achieved by forming a portion
55
of each trace
40
to project into tape window
50
and overlie a position to be occupied by a bonding pad
60
. When a die
10
is disposed in a die receiving area
15
of tape
30
, the bonding pads
60
are exposed within the tape window
50
and are displaced (e.g., vertically) from a projecting portion
55
of a corresponding trace
40
. The projecting portion
55
is mechanically deformed (e.g., vertically) to contact a bonding pad
60
, where it is bonded to the bonding pad
60
by conventional bonding techniques and tools, such as an ultrasonic wedge bonder, to form a beam lead connection.
FIG. 3
illustrates a non-linear distribution of die bonding pads
60
wherein two groupings of bonding pads are disposed substantially perpendicular to one another. As with the previous example, a portion
55
of each trace
40
projects into tape window
50
to overlie a bonding pad
60
. Portions
55
span a width of the tape window
50
or project into the tape window from the side and terminate in a tie bar or beam lead support
75
. The tie bar
75
is typically a ganged support common to a plurality of beam leads. To form an electrical connection between the portion
55
, or beam lead, to the die
10
bonding pad
60
, the portion
55
is mechanically deformed to contact a respective bonding pad
60
. This deformation and bonding may be achieved by conventional bonding techniques and tools, such as an ultrasonic wedge bonder, thermode, or thermosonic bonder to form the beam lead connection. Portions
55
may have a notch adjacent tie bar
75
to facilitate separation of the beam lead
55
from the tie bar
75
during formation of the electrical contact.
However, despite its advantages, &mgr;BGA packaging is not as robust as conventional packaging and die evolution to increasingly smaller die sizes, particularly to CSPs, imposes additional constraints on design, manufacture and reliability of the die packaging. One important parameter is the bending profile of the beam lead, the exposed portion of the trace
40
extending into the tape window
70
to contact the die
10
bonding pad
60
. If the bending profile, such as the radius of curvature of the points of beam inflection, is too severe hairline cracks may develop and lead to device failure. Conventionally, to ensure that the beam lead bending profile is maintained, a predetermined tape window
70
size or width is kept constant and a predetermined beam length is maintained.
Dies may be designed with a non-linear distribution of bonding pads. For example, bonding pads
60
may be distributed around a comer of the die
10
, as shown in FIG.
3
. In such a case, beam leads
55
may be required to approach the die bonding pads from more than one direction. Conventionally, a tie bar or beam lead support
75
is formed to support and maintain the beam lead protruding portions
55
above a corresponding bonding pad
60
until they are separated from the tie bar during the bonding operation. However, &mgr;BGA design rules require both a minimum space S between pads on adjacent sides of about 0.2 mm and require a minimum beam lead length L of about 0.9 mm, although the actual requirement may vary. These requirements, combined with the conventional reliance on a tie bar or beam lead support to preserve alignment of the beam leads during packaging and the requisite tolerances necessary to ensure that the beam lead support will not inadvertently short circuit a beam lead adjacent and parallel thereto, sacrifice valuable die and packaging space.
SUMMARY OF INVENTION
Accordingly, a need exists in the art for an improved ball grid array package that avoids a potential for short circuit due to beam lead support placement and provides additional flexibility
Fontecha Edwin R.
Valluri Viswanath
Vivares Valerie
Chaudhuri Olik
Ha Nathan W.
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