Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – With window means
Reexamination Certificate
2001-03-23
2002-10-08
Talbott, David L. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
With window means
C257S684000, C257S698000, C257S730000, C257S738000, C257S773000, C257S778000, C257S780000, C228S180220
Reexamination Certificate
active
06462407
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to an electronic device having a multiplicity of contact bumps that project from a housing and that are connected via rewiring configurations on an intermediate support and that also connect connecting lugs of the intermediate support to contact areas on a semiconductor chip.
Laterally directed mechanical stresses arise when a flat conductor bonding process is used to electrically and mechanically connect a semiconductor chip that is mounted on an organic intermediate support to conductive structures of the intermediate support material. These laterally directed mechanical stresses arise at a predetermined distance between the microscopically small contact areas on the semiconductor chip and the correspondingly dimensioned contact connecting lugs of the flat conductors of the intermediate support. This is because of the different coefficients of thermal expansion of the joining participants, namely the semiconductor chip and the plastic intermediate support. These laterally directed mechanical stresses, which can lead to cracking in the contact connecting lug up to a complete interruption of the connection, arise in the bonding bridge that includes an overhanging contact connecting lug. These laterally directed mechanical stresses increase with increasing distance between the bonded connection and the neutral point of the semiconductor.
Particularly in the case of semiconductor chips with a row of centrally positioned contact areas, the intermediate support material is open in the region of the contact areas, as a result of which a “bonding channel window” in the intermediate support is kept free of support material. The etched-free conductor circuit pattern of the intermediate support is located in the bonding channel window above the contact areas of the semiconductor chip. During the flat conductor bonding process, these flat conductor structures are interrupted in a targeted manner and then are thermomechanically connected to the contact areas of the semiconductor chip. Since the region of the bonding channel window in the intermediate support is conventionally embodied as a slot with parallel edges, all of the flat conductor transitions to the contact windows are of the same length, irrespective of the size and extent of the semiconductor in the longitudinal direction. This means that at a large distance from the centrally located neutral point of the semiconductor chip, the risk of mechanical overloading during thermal cycling of the electronic device increases, the further away the bonded connection is from the neutral point of the semiconductor chip.
A conventional structure of an electronic device having a multiplicity of contact bumps which project on one side from a housing of the electronic device is shown in FIG.
3
. The semiconductor chip
7
has a central row
13
of contact areas
6
, only four of which are shown by way of example. The housing
15
, whose contours are shown in
FIG. 3
, has an intermediate support
2
on which the multiplicity of contact bumps
1
is configured. The multiplicity of contact bumps
1
are connected via a multiplicity of flat conductors
3
, only one of which is shown by way of example, to contact connecting lugs exposed in the bonding channel window
4
of the intermediate support
2
and to the contact areas
6
of the semiconductor chip
7
which are situated underneath at a fixed distance. In the conventional embodiment of the electronic device, the bonding channel window
4
has edges
10
and
11
that run parallel in the longitudinal direction. The contact connecting lugs
5
of the flat conductors
3
thus have the same lengths within the bonding channel window
4
. Since these contact connecting lugs
5
are composed of flat conductor material, they are not round like the formerly customary bonding wires. These contact connecting lugs are thus at extreme risk of cracking if, because of the different expansion coefficients of the semiconductor chip
7
and of the intermediate support
2
, the electronic device is exposed to thermal cycling. For bonded connections of this type, the further away a bonded connection, which includes a contact connecting lug of the intermediate support
2
and a contact area
6
of the semiconductor chip
7
, is from the neutral point
8
of the semiconductor chip
7
, the greater the risk of cracking during thermal cycling of the electronic device. This is because tensile stresses increase in the bonding bridge and load-relieving cracks occur.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide an electronic device which overcomes the above-mentioned disadvantageous of the prior art apparatus of this general type. In particular, it is an object of the invention to provide an electronic device that is constructed to reduce the risk that the bonded connections will crack or break, where these bonded connections include contact connecting lugs and semiconductor contact areas in a bonding channel window of the electronic device.
With the foregoing and other objects in view there is provided, in accordance with the invention, an electronic device, that includes a housing having an intermediate support formed with a bonding channel window having a center. A semiconductor chip has a plurality of contact areas disposed in the bonding channel window of the intermediate support. A plurality of contact bumps are configured on the intermediate support and project from the housing. A plurality of flat conductors have contact connecting lugs exposed in the bonding channel window of the intermediate support and connected to the plurality of the contact areas. The plurality of the flat conductors connect the plurality of the contact areas to the plurality of the contact bumps. The semiconductor chip has a neutral point disposed in the center of the bonding channel window of the intermediate support. The bonding channel window is formed with a width that increases with increasing distance from the neutral point of the semiconductor chip.
The neutral point of the semiconductor chip is configured in the center of the bonding channel window, and the width of the bonding channel window is greater with increasing distance from the neutral point. This electronic device has the advantage that the contact connecting lugs which are subjected to higher loading during thermal cycling of the electronic device, because they are further away from the neutral point of the semiconductor chip, are made longer and the tensile stress is thus reduced on both sides of the neutral axis of the contact connecting lugs. Because of the reduction of these tensile stresses during thermal cycling of the electronic device, the risk of cracking in the contact connecting lugs composed of flat conductor material is reduced to the extent that electronic devices constructed according to the invention withstand a higher degree of thermal cycling.
The bonded contact connecting lugs are usually exposed to extreme thermal cycling as early as in the production process, because the soldering bumps are not furnished until after the bonding process. Therefore, the reject rate when the contact bumps projecting from the housing are finally furnished can also be reduced by the manufactured electronic device. Consequently, the solution according to the invention increases both the productivity of the process for producing the electronic devices and the thermal-cycling resistance of the electronic devices to be supplied.
In accordance with an added feature of the invention, the edges of the bonding channel window are curved in the longitudinal direction, the radius of curvature being a multiple of the semiconductor chip length, preferably three to six times the length. This preferred embodiment advantageously realizes a continuously increasing width of the bonding channel window, with the result that the contact connecting lugs which are the furthest away from the central point of the semiconductor chip are made significantly longer than the conta
Gebauer Uta
Münch Thomas
Wanninger Friedrich
Chambliss Alonzo
Greenberg Laurence A.
Infineon - Technologies AG
Locher Ralph E.
Stemer Werner H.
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