Stadium-stepped package for an integrated circuit with air dielectric

A package for containing an integrated circuit component is provided which includes one or more layers with exposed edges surrounding a central opening. The integrated circuit component is positioned in the central opening. Bond wires connect the bond pads of the integrated circuit component to the continuous shelves of the various stepped-back stadium-like layers as well as to individual insulated leads. The layers are spaced apart by beads or columns of insulative material and the major portion of the layers are separated from each other by a gaseous dielectric, preferably air. The R-C constant is reduced and the speed of transmission is increased by the presence of the low dielectric material providing a device which can function rapidly. The stepped portions of the layers are exposed to allow for electrical interconnections within the layers, as well as from each layer to the integrated circuit.

FiELD OF THE INVENTION 
The present invention relates to a package for housing an integrated 
circuit component and providing electrical connections thereto. In 
particular, the invention relates to a package having multiple layers 
arranged in a stadium-stepped shape with an air dielectric between layers. 
BACKGROUND OF THE INVENTION 
Integrated circuits or "dice" are of such a small size that direct 
connection of the electrical connection "pads" to other circuitry is 
impractical. Accordingly, integrated circuits are housed in a larger 
device known as a "package" which contains conductive leads for providing 
electrical connections to the integrated circuit bonding pads. 
Topology and manufacturing requirements for the conductive leads and other 
connections to the integrated circuit typically require that the package 
contain several overlying layers having conductive lines. To preserve the 
desired functionality of the device, these layers must be electrically 
insulated from one another. Typically, a layer of solid material such as a 
plastic, ceramic or glass has been provided between the layers to 
electrically insulate the layers from one another. 
Such a previous configuration is depicted in U.S. Pat. No. 3,676,748 issued 
July 11, 1972 to Kobayashi et al. Kobayashi et al. also disclose providing 
two layers of leads located on different stepped planes, formed by using 
lead frames vertically spaced and insulated from each other. 
SUMMARY OF THE INVENTION 
The present invention includes the recognition of certain problems found in 
previous devices. The material previously used to insulate one layer from 
another is typically a material having a relatively high dielectric 
constant. For example, plastics, ceramics and glasses typically have a 
static dielectric constant (at standard temperature and pressure) of 
between about 2 and 13. Applicants have recognized that the use of 
insulation materials with relatively high dielectric constants leads to 
slowing of the time required for typical operation of the device. This 
slowing is related to at least two phenomena. One limiting factor on the 
speed of operation is the time required to discharge certain capacitance 
devices. This 15 time is directly related to the resistance-capacitance 
constant ("R-C constant"). The second phenomenon relates to the speed of 
propagation of signals through electrically conductive media. The speed of 
transmission is reduced below the speed of light to a degree which is 
directly related to the dielectric constant of material adjacent to the 
conductor. 
The present invention involves providing a gas, preferably air, as the 
dielectric material between layers. Air has a dielectric constant which is 
quite low (about 1.0054), approaching that of a vacuum. The low dielectric 
constant reduces the effective R-C constant and thus reduces the time 
needed to discharge capacitive circuits. By providing a relatively 
low-dielectric constant insulator, propagation or transmission speed of 
signals is increased, approaching the speed of light. 
Providing an air dielectric also affords other advantages. The space 
between layers can be used for accommodating electronic components which 
thus can be positioned physically close to the layers. Certain package 
configurations provide a bypass capacitor which connects two layers, for 
example, for use in providing rapid charging of a layer or lead when the 
value of a supply voltage switches from a high to a low value. According 
to the present invention, the speed with which such switching can be 
accomplished is increased by positioning the capacitor closer to the 
layers in the region between layers. A further advantage of using an air 
dielectric is that the conductive layers can be placed relatively close to 
one another, for example, with a spacing of about 0.004 to 0.006 inches 
(about 0.1 to 0.15 millimeters). A thin package is particularly useful for 
providing a thin profile component, for example, for surface mount 
devices. 
Because packages are intended to be connected to other electronic 
components, a certain amount of handling and manipulation is necessary. 
For this reason, the leads extending from packages have been provided with 
a sufficient thickness to prevent damage during such manipulation and 
handling. The thickness of the leads, however, provides an undesirable 
amount of capacitance. The present invention includes providing leads 
which have a lesser thickness in the interior portion than in the portion 
of the leads which extends exterior to the package. 
The present invention also includes providing one or more of the 
stepped-plane layers in a stadium-like configuration, i.e. in which the 
area to which bond wires are attached is a continuous shelf-like 
structure, rather than a plurality of individual pads or leads. This 
configuration permits connection of the bond wires in the necessary 
configuration, avoiding crossing or shorting of the bond wires, while 
still requiring only a single lead frame or plane for many applications. 
The stadium configuration provides for flexibility of the package in the 
sense that the stadium package can be used with a large number of 
different integrated circuit components or bond wire configurations 
without redesigning the package. This is because some of the bond wires 
going to a particular level can be connected anywhere along the shelf, 
rather than having to be connected to a particular pad or lead. The 
stadium configuration also provides for flexibility in permitting 
inter-layer connections, thus avoiding the need for vias to provide an 
electric pathway between layers and also permitting a wide variety of 
possible inter-layer connections without redesigning the package. The 
present invention includes a package with a ground plane which aids in 
reducing inductance. 
The present invention also provides a superior thermal pathway from the 
integrated circuit component to a radiating surface of the package. In one 
embodiment, the integrated circuit component is mounted in direct contact 
with a base layer which has a relatively high thermal conductivity so that 
the base layer provides an efficient thermal transfer surface. In one 
embodiment, the base layer is also electrically conductive and an electric 
pathway is formed between portions of the integrated circuit component and 
the base layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present invention relates to a package for housing and connecting an 
integrated circuit component. FIG. 1 depicts a package 12 according to the 
present invention. The package 12 depicted in FIG. 1 also shows an 
integrated circuit component or die 14 positioned within the package 12. 
The package 12 includes a base layer 16. The base layer 16 can be composed 
of a variety of materials including metals, plastics, ceramics, and the 
like. When it is important to dissipate heat from the integrated circuit 
component 14, the base layer 16 is preferably a material with high heat 
conductance having a thermal conductivity greater than about 2 watt 
cm.sup.-1. K.sup.-1. In one preferred embodiment, the base layer 16 is at 
least 90 weight percent copper, e.g., copper alloy known as C19400. The 
integrated circuit component 14 can be mounted on the base layer 16 using 
a pedestal 18 as shown in FIG. 2. Pedestal 18 can also be made of a number 
of materials, for example, if high thermal conductivity is desired, with 
electrical isolation, materials such as BeO or AlN could be used. In an 
alternative embodiment of the package 12' depicted in FIG. 3, the 
integrated circuit component 14 is mounted directly on the base layer 16 
e.g., by an epoxy adhesive, to provide for efficient thermal transfer. 
In the embodiment depicted in FIG. 1, the first stadium layer 22 is mounted 
overlying, but spaced from the base layer 16. The layer 22 includes at 
least a first conductive area and is preferably a sheet of conductive 
material, e.g., copper or a copper alloy. The first stadium layer 22 has a 
first central opening 24 defined by an opening edge 26. The central 
opening 24 is aligned with the region in which the integrated circuit 
component 14 is to be placed. The first layer 22 is spaced from the base 
layer 16 by selectively disposed insulating material 28a,28b, typically 
glass, ceramic, plastic, or an organic material. Any insulating material 
28a,28b can be used which has sufficient insulating characteristics and 
which can be readily produced and manufactured and adhered to the base 
layer 16 and first layer 22. Preferably, the insulating material 28 is 
itself adhesive so that no additional adhesive material is required. The 
insulating material 28a,28b can be provided in the form of a continuous 
bead parallel to the edges of the first plate 22. Alternatively, either 
the interior insulating material 28b or exterior insulating material 28a 
can be in the form of spaced regions or pillars of insulating material, as 
depicted in FIG. 4, 28'c, 28d, 28e, 28f. Preferably, the exterior edge 
insulating material 28a is a continuous bead of glass or organic material 
and forms a seal between the base layer 16 and the first layer 22 so that, 
as explained below the entire package, when completed, will form a sealed 
housing for the integrated circuit component 14. Preferably, the pillars 
28'c-28'f are made of a polyimide material 
The insulating material 28a,28b results in the first layer 22 being spaced 
from the base layer 16. Preferably, the distance 32 (FIG. 2) between the 
base layer 16 and the first layer 22 is less than about 0.015 inches 
(about 0.4 millimeters), preferably less than about 0.01 inches (about 
0.25 millimeters) and most preferably about 0.004 to 0.006 inches (about 
0.1 to 0.15 millimeters). 
In those embodiments in which the base layer 16 is not electrically 
conductive, it may be preferable to mount the first layer 22 directly on 
the base layer 16. The volume 33 between the base layer 16 and first layer 
22 which is not occupied by the first insulating material 28 is preferably 
filled with a gaseous material, most preferably air. The surface area of 
the portion of the lower surface of the first layer 22 which is adjacent 
the gas-filled region 33 is greater than about 50%, preferably greater 
than about 80%, of the total surface area of the lower surface of the 
first layer 22. 
A second layer 34 is secured overlying and spaced from the first layer 22. 
The second layer 34 also has a central opening 36 defined by an edge 38. 
The central opening 38 of the second layer 34 is larger than the central 
opening 24 of the first layer 22 and thus exposes a portion 42 of the 
first layer 22 as well as the integrated circuit component 14. Preferably, 
the opening 36 exposes a region 42 entirely surrounding the central 
opening 24 of the first layer 22. At least a first continuous region of 
conductive material is exposed as part of the exposed portion 42. Since, 
in the preferred embodiment, the first layer 22 is a unitary sheet of 
conductive material, the exposed portion 42 is preferably a continuous 
shelf of conductive material. 
The second layer 34 is spaced from the first layer 22 by insulating 
material 44a,44b formed in a manner and made of materials similar to the 
insulating materials 28a,28b separating the first layer 22 from the base 
layer 16. Either region of insulation material 44a,44b can be provided in 
the form of pillars and preferably, the insulation material 44a adjacent 
the exterior edge is in the form of a continuous bead while the material 
44'c, 44'd, 44'e are in the form of pillars, as depicted in FIG. 4. 
The region 46 between the second layer 34 and first layer 22 which is not 
occupied by the first insulating material 44a,44b is preferably filled 
with a gaseous material such as air. The surface area of the portion of 
the lower surface of the second layer 34 which is adjacent to the 
gas-filled region 46 is at least about 50% and preferably at least about 
80% of the total lower surface area of the second layer 34. The distance 
48 between the first layer and the second layer is preferably less than 
0.015 inches (about 0.4 millimeters), more preferably less than about 0.01 
inches (about 0.25 millimeters), and most preferably about 0.004 to 0.006 
inches (about 0.1 to 0.15 millimeters). 
A plurality of leads are typically provided during assembly in the form of 
a metalized substrate or a unitary lead frame 52, overlying and spaced 
from the second layer 34. The lead frame 52 includes a frame portion 54 
and a plurality of inwardly extending, electrically conductive leads 
56a-56u. The leads 56 are made of a conductive material such as a 42/45 
copper alloy. The interior edges of the inwardly extending leads 56 define 
a central opening 58 of the lead frame 52. The end portions of the leads 
56 are embedded in an insulating material 62 so that the leads and the 
material 62 in which the leads are embedded form a substantially planar 
layer 64. 
The lead layer 64 is separated from the second layer 34 by insulating 
material 66a,66b. The configuration and materials of the insulating 
material 66a,66b are similar to those of the insulating materials 44a,44b, 
28a,28b separating the second layer 34 from the first layer 22 and the 
first layer 22 from the base layer 16. Either portion of insulating 
material 66a,66b can be in the form of pillars (not shown) rather than the 
continuous beads 66a,66b depicted in FIG. 1. 
The lead layer opening 58 is larger than the central opening 36 of the 
second layer 34 and thus exposes a portion 68 of the second layer 34. 
Since, in the preferred embodiment, the second layer 34 is a unitary sheet 
of conductive material, the exposed portion forms a continuous shelf 68 
surrounding the central opening 36 of the second layer 34 and stepped back 
from the exposed shelf 42 of the first layer 22. The distance 72 which 
separates the lead layer 64 from the second layer 34 is preferably less 
than about 0.015 inches (about 4 millimeters), more preferably less than 
about 0.01 inches (about 0.25 millimeters), and most preferably about 
0.004 to 0.006 inches (about 0.1 to 0.15 millimeters). 
In one preferred embodiment, one or more of the leads 56c, 56k has an 
interior portion having a thickness less than that of the exterior 
portion. As seen in FIG. 2, a lead 56c which has a thickness in the range 
of about 0.006 to 0.01 inches (about 0.15 to 0.25 millimeters) is reduced 
in thickness in the interior portion so as to have an interior thickness 
73 of about half the exterior thickness, or about 0.003 to 0.005 inches 
(about 0.07 to 0.12 millimeters). In this way, the lead 56c is 
sufficiently thick in the exterior portion to have the mechanical strength 
needed for manipulation and handling, while the reduced thickness in the 
interior portion provides for reduced capacitance. Preferably, all leads 
56a-56y have reduced interior thickness. 
In an alternative embodiment, depicted in FIg. 3, there is no second layer 
34. Accordingly, the lead layer 64 overlies and is separated from the 
first layer 22. 
The region 74 separating the lead layer 64 from the second layer 34 not 
occupied by the insulation material 66a,66b is preferably filled with a 
gaseous material such as air. The surface area of the lower surface of the 
lead layer 64 which is adjacent to the air-filled region 74 is greater 
than about 50%, preferably greater than about 80%, of the total lower 
surface area of the lead layer 64. 
A cap 76 overlies and seals the entire package 12 The cap is spaced from 
the lead layer 64 by a perimetrical bead of insulating material 78 thus 
leaving interior upper surfaces of the leads 56 exposed. The cap 76 can be 
made from a plurality of materials including ceramic, glass, metal, 
plastic and the like. 
Package 12 typically is hermetically sealed with the interior 82 being 
sealed by an envelope made up of the base layer 16, the cap 76 and 
perimetrical portions of the first, second and lead layers 22, 34, 64, and 
the insulating materials 28a, 44a, 66a, 78. The interior 82 of the sealed 
package 12 is preferably filled with a gaseous material, such as air. The 
insulating materials 28a, 44a, 66a, 78 extend a distance from the edge of 
the package towards the interior. In those packages for which hermeticity 
is desired, the width of the strip of insulating material 28a, 44a, 66a, 
78 which is needed to achieve hermeticity depends upon the material being 
used for the sealing layers. As an example, when the upper sealing layer 
78 is a polyimide material, hermeticity will typically require a width 83 
of about 0.03 inches (about 0.75 millimeters). As can be seen from FIG. 2, 
the amount of width 83 occupied by the sealing material 78, 66a, 66b, 44a, 
44b, 28 a, 28b reduces the volume available for the gas dielectric 33, 46, 
74, 82. Accordingly, in embodiments where hermeticity is critical, the 
amount of gas dielectric provided, and the consequent amount of reduction 
in capacitance, may be diminished compared to packages in which 
hermeticity is less critical, and in which the width 83 of the sealing 
layers 78, 66a, 66b, 44a, 44b, 28a, 28b can be relatively less. In 
instances in which both low capacitance and high hermeticity are needed, a 
smaller width 83 of the sealing layers, such as layer 78, can be achieved 
by using a material for the sealing layer 78, which is highly 
gas-impermeable. 
In one embodiment, as depicted in FIG. 3, a bypass capacitor 94 is provided 
in one of the air-filled dielectric regions between layers and thereby is 
positioned physically close to the adjacent layers. As discussed above, 
such physically close placement assists in providing for rapid operation 
or speed of the device. 
Interconnection or bond wires provide an electrical connection between one 
or more of the bonding pads 84a-84i of the integrated circuit component 14 
and one or more of the first layer 22, second layer 34 and leads 56. The 
particular connections which are made depends on the characteristics of 
the integrated circuit component 14 and the pins on the package. One 
configuration is partially depicted in FIG. 1. The connections can include 
bond wires running from the bonding pads 84 to the first layer 86a, second 
layer 86b, third layer 86c,86d or base layer 86e. Connections can be made 
between layers as depicted by the bond wire 88 which connects the second 
layer 34 to the base layer 16 and bond wire 89, which connects a lead 56 
to the second layer 34. The bond wires 86,88 can be made of a number of 
materials. Preferably, aluminum wire is used, but gold and copper are 
alternatives. Connections can be secured by soldering or welding. 
Preferably the maximum horizontal distance 87 between a bonding pad and 
any of the layers is about 0.15 inches (about 2.5 millimeters). 
A variety of configurations of connections using bonding wires are 
possible, as may be needed to effect the desired functioning of the 
device. A single pad 84 can have two or more bond wires connecting the pad 
to different layers. Similarly, a single layer 22, 34, 64 can have a 
plurality of wires connecting that layer to various bond pads 84. Because 
layers can be interconnected with bond wires 88, there is no need for 
inter-layer vias as found in many previous devices. In one preferred 
embodiment, the first and second layers 22, 34 are connected so as to 
provide different voltages on the first and second layers 22, 34. In this 
way the first and second layers can be used, e.g., as a power plane 22 and 
a ground plane 34, respectively. 
After the desired connections are made and the package 12 is sealed, the 
leads 56 are singulated by making a cut between the frame portion 54 and 
the leads 56 such as along line 92 and removing the frame portion 54. In 
use, the singulated leads 56 are connected to other circuitry components 
to provide the desired electrical connection to the integrated circuit 
component 14. 
Because the first and second layers 22, 34 contain extended regions, 
preferably shelves 42, 68 along which connections can be made to those 
layers, the wiring is simplified and the package is more flexible than 
previous packages. The wiring is simplified because a given pad 84 is 
always adjacent to the continuous shelves 42, 48 so that connection to the 
first or second layer 22, 34 can be made by a bond wire without the 
necessity for the bond wire to cross over or under another bond wire in 
order to make the desired connection. The package 12 is more flexible 
because a variety of bond wire configurations and integrated circuit 
components can be used in a single package 12. In previous packages in 
which layers were provided in the form of individual connection pads, a 
change in wiring configuration often required reconfiguring the location 
of the pads so that connection could be made without unwanted crossing of 
wires. In the present invention, because the shelves 42, 68 are preferably 
continuous and surround the integrated circuit component, a change in the 
configuration of the bond wiring does not require a redesign of the 
package 12. 
Because the major portion of the dielectric separating the various layers 
64, 34, 22 is a low-dielectric gaseous material such as air, the effective 
R-C constant for various circuitry components in the package 12 is less 
than it would be if a higher dielectric material were used. Because the 
R-C constant is less, the device is able to operate more rapidly. 
Similarly, the speed of transmission is increased, approaching the speed 
of light, because the value of the dielectric constant of the material 
next to the conductive layers 22, 34, 64 is decreased compared to that of 
previous devices. 
A number of advantages are provided by the package 12 of the present 
invention. The wiring between components and the package 12 can be easily 
provided in a variety of configurations. Inter-layer vias can be 
eliminated by using inter-layer bonding wires. Because wiring is 
simplified, it is typically not necessary to provide more than one layer 
of leads. This advantage is important because a lead frame is relatively 
more expensive than a simple planar layer. Components such as by-pass 
capacitors can be placed in the region between layers. The design is 
conducive to production of this low-profile packages. Configuration of the 
base layer is flexible in that it can be thermally conductive, relatively 
thermally nonconductive, electrically conductive, and/or relatively 
nonelectrically conductive. In this way, the package can be provided in a 
number of configurations depending on the desired use and can be both 
thermally enhanced and speed-enhanced (i.e. provide for rapidity of 
operation). The device uses readily available materials and can be made 
without providing or developing new types of materials. 
A number of variations and modifications of the present invention can be 
used. The present invention can be used with more or fewer layers than 
those described and depicted. Gaseous dielectric could be used to separate 
some layers while a solid dielectric is used next to other layers. It is 
possible to use more than one lead or tape layer and/or more than two 
stadium-type or shelf layers. The leads 56 can be provided in a manner 
other than by production using a lead frame. Connections could be made by 
leads extending through the top or bottom surface of the package 12, 
although such a configuration is typically relatively expensive. The order 
of the various layers can be changed such that any of the ground, power, 
lead or other layers can overlie or underlie the others. Some or all of 
the connections which are depicted as using wire bonds or leads in the 
lead frame can also be provided using tape automated bonding (TAB). The 
package could be configured so that the stadium-stepped shape is provided 
on fewer than the four sides of the opening as depicted. The package could 
be configured so that shelves of different layers are exposed on different 
sides or portions of sides of the central opening. The package can be 
configured so that the shelves extend only part way around the central 
opening or part way along a single side of the central opening. The 
dielectric material which spaces layers can be provided in forms other 
than beads or columns such as continuous or intermittent sinuous forms, 
regions spaced away from the edges of the layers and the like. In order to 
prevent corrosion or other degradation of materials, the air can be 
treated, such as by drying for removal of particulates or undesired 
components. A gaseous material other than air can be used such as 
nitrogen, argon and the like. The space between layers can be occupied by 
a vacuum rather than by air. 
EXAMPLE 
Electrical parameters of the package 12 as well as for a more conventional 
package were modeled using a boundary element method. In the model, the 
leads were taken to be 0.005 inches (about 0.13 millimeters) in thickness, 
with a 0.005 inch (about 0.13 millimeters) distance apart. In a first 
model of the present invention (Model "A"), the distance from the lead 
plane to the ground plane was 0.005 inches (about 0.13 millimeters). In 
the first model the leads were modeled as being formed of copper. In a 
second model of the present invention (Model "B"), the leads were modeled 
as being formed of alloy 42 which is a magnetic material. Model B was 
otherwise similar to Model A. In a model of the previously provided 
devices, the lead layer was separated from the ground plane by 0.05 inches 
(about 1.3 millimeters) and the dielectric constant of the material 
between the lead plane and the ground place was taken as 4.0, typical of 
the dielectric constant of plastics. The results of the modeling are 
depicted in Table 1. 
TABLE 1 
__________________________________________________________________________ 
Adjacent 
Lead-to- 
Adjacent 
Lead Self- Lead Mutual 
Ground Plane 
Lead 
Inductance Inductance 
Capacitance 
Capacitance 
(nanohenries (nanohenries 
(picofarad 
(picofarad 
cm.sup.-1) cm.sup.-1) 
cm.sup.-1) 
cm.sup.-1) 
__________________________________________________________________________ 
Model "A" 
3.06 1.08 0.42 0.15 
(present 
invention) 
Model "B" 
4.56 .about.1.5 
0.42 0.15 
(present 
invention) 
Model "C" 
6.97 4.72 1.15 0.81 
(previous 
devices) 
__________________________________________________________________________ 
As can be seen from Table 1, Models A and B indicate that the present 
invention would have a lead self-inductance, adjacent lead mutual 
inductance, lead-to-ground plane capacitance and adjacent lead capacitance 
less than the corresponding values for previous devices having plastic 
insulation material between layers. It is noted that because the modeled 
lead alloy in Model B is magnetic material, its inductance is increased 
with respect to Model A (though still less than Model C) and its 
capacitance is essentially unchanged with respect to Model A. 
Although the description of the present invention has included a 
description of the preferred embodiment and various modifications and 
variations, other modifications and variations can also be used which come 
within the scope of the present invention, the present invention being 
described by the following claims.