Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
2001-01-16
2002-11-26
Cuneo, K. (Department: 2827)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S261000, C174S265000
Reexamination Certificate
active
06486415
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an electrical interconnection arrangement for making connection between electronic substrates and, more particularly, to making electrical interconnection between a chip carrier and a printed wiring board.
BACKGROUND OF THE INVENTION
One of the problems encountered with some chip carrier substrate interconnections to the next level of packaging is the high stress on the interconnections caused by coefficient of thermal expansion (CTE) mismatch between the substrate and the next level of packaging. The CTE thermal mismatch is particularly large where a ceramic chip carrier substrate is connected to a printed wiring board typically made of an epoxy/glass material. When a high circuit density chip is attached to the chip carrier substrate, the heat generated by the chip compounds the CTE mismatch problem between the chip carrier substrate and the printed wiring board because of large temperature variations between the chip and the printed wiring board. In addition, certain applications, such as flip chip applications, have required encapsulation to ensure a reliable flip chip interconnection in the solder joints between the chip and the substrate. Such encapsulation typically employs a high strength epoxy which acts to reinforce the bond between the chip and the chip carrier substrate. During thermal cycling, this reinforcing of the chip to chip carrier substrate reduces solder joint stress between the chip and the chip carrier. When coupled with the CTE mismatch between a ceramic chip carrier attached by a solder interconnection to a printed wiring board, this reinforcement can cause high stress between the ceramic chip carrier substrate and the printed wiring board to which it is attached. Repeated thermal cycling can lead to cracking of the solder interconnection between the ceramic chip carrier and the printed wiring board, ultimately affecting reliability of the chip/substrate/printed wiring board package.
The above described high stresses on the solder interconnections are generally attributed to the fact that the bonding of chip to the ceramic chip carrier, including the encapsulant, forms a composite which acts during thermal cycling to cause this composite to act like a “bimetallic” element wherein the composite bends due to the different CTE of the materials. As a result of the large thermal mismatch between the composite and the printed wiring board, the thermal cycling induced bending over time can cause solder interconnection failure. In this regard, the CTE for a typical chip may be in the order of about 3 parts per million per degree Centigrade (ppm/degree C.). The CTE for a typical ceramic chip carrier may be in the order of about 3-5 ppm/degree C., while a typical printed wiring board CTE may be about 18-22 ppm/degree C.
In general, others have attempted to address the problems caused by CTE mismatch of materials in electronic packages by providing various interposing structures that attempt to reduce the CTE mismatch. For example, multiple layers of materials with varying CTEs may be employed to form an interposing layer between one level of packaging and the next, with the layers having a gradation of CTEs such that the layer contacting one level of packaging is selected to have a CTE which more closely matches the CTE of that level while the layer contacting the next level of packaging has a CTE more closely matching that level while layers between may gradually reduce the difference. In addition, efforts have also been made to use interposing layers which are flexible in nature such as to reduce the stress on electrical interconnections during thermal cycling created by thermal mismatch. However, these various efforts typically are either difficult to assemble or are not totally effective in their purpose.
The present invention is directed at overcoming the problems set forth above. It is desirable to have an electronic package and method to make the electronic package that significantly absorbs the stresses that occur between a chip carrier and a printed wiring board during thermal cycling. Electronic packages produced by this method will have increased operational field life.
SUMMARY OF THE INVENTION
Accordingly, it is the object of this invention to enhance the art of packaging technology.
It is another object of this invention to provide a novel method of producing an electronic package that provides an improved interconnection between a chip carrier substrate and a printed wiring board.
It is yet another object of this invention to provide an electronic package that will be manufactured with relatively lower costs than many current products.
Still another object of this invention to provide an electronic package having a layer of dielectric material between a chip carrier substrate and printed wiring board that substantially absorbs stress caused by thermal cycling resulting in a package having much improved operational field life.
Still yet another object of this invention is to provide an electronic package having at least one through hole in a layer of dielectric material substantially filled with a conductive material and having a conductive member positioned on the conductive material.
According to one aspect of the invention, there is provided an electronic package comprising a substrate having a first surface, the first surface having a plurality of conductive contacts thereon and a layer of dielectric material having a first and second surface, the first surface of the dielectric material positioned substantially on the first surface of said substrate. At least one through hole is positioned in the layer of dielectric material substantially aligned with at least one of the plurality of the conductive contacts, the at least one through hole having a side wall. A conductive material is positioned in the at least one through hole, the conductive material substantially filling the through hole and being in electrical contact with the at least one of the plurality of conductive contacts, and at least one conductive member positioned on the conductive material in the at least one through hole and in electrical contact with the conductive material.
According to another aspect of the invention, there is provided a method of making an electronic package comprising the steps of providing a substrate having a first surface, the first surface having a plurality of conductive contacts thereon, positioning a layer of dielectric material having a first and second surface substantially on the first surface of the substrate, and forming at least one through hole in the layer of dielectric material in alignment with the at least one of the plurality of said conductive contacts, the at least one through hole having a side wall. The method includes positioning a conductive material in the at least one through hole so as to substantially fill the through hole and to be in electrical contact with the at least one of the plurality of conductive contacts, and positioning at least one conductive member on the conductive material in the at least one through hole and in electrical contact with the conductive material.
The above objects, advantages, and features of the present invention will become more readily apparent from the following detailed description of the presently preferred embodiments as illustrated in the accompanying drawings.
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Jimarez Lisa J.
Jimarez Miguel A.
Markovich Voya R.
Milkovich Cynthia S.
Perry Charles H.
Cuneo K.
Fraley Lawrence R.
International Business Machines - Corporation
Jordan John A.
Norris Jeremy
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