Electricity: conductors and insulators – Boxes and housings – Hermetic sealed envelope type
Reexamination Certificate
1999-06-24
2001-03-06
Gerrity, Stephen F. (Department: 3729)
Electricity: conductors and insulators
Boxes and housings
Hermetic sealed envelope type
C029S831000, C029S827000, C174S050510, C361S760000
Reexamination Certificate
active
06198044
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method of manufacturing a microcircuit board the method comprising the steps of forming a cavity in a part of the thickness of the board made of insulating material for forming the support, and fixing the microcircuit within the cavity while connecting it to a network of conductors so as to establish electrical connections between the cavity and a surface of the board.
In particular, the invention relates to a method of installing the microcircuit and the network of conductors in order to reduce the stresses which can be transmitted to the microcircuit when the board undergoes distortion after it has been manufactured.
The invention also relates to a microcircuit board produced the implementation of such a process.
DESCRIPTION OF THE PRIOR ART
In the manufacturing of microcircuit boards, it is known to install the microcircuit in a cavity formed in a part of the thickness of the board made of plastics material forming the support. The cavity is open on one surface of this board. On this surface, at its bottom and on its sides, it is conventional to arrange a network of conductors allowing electrical connection of the connection zones of the microcircuit to external connection areas defined on the surface around the cavity. When such a network of conductors is used, it is advantageous to use a particular technique for installing the microcircuit, known by the name “flip-chip”. In fact, the microcircuit includes connection zones which are defined on one of its surfaces and which permit access to the microprocessor and to associated memories. This installing technique consists of fixing and electrically connecting, in a same operation, the microcircuit to the network of conductors and more particularly to parts of the latter which extend and adhere on the bottom of the cavity.
Because the microcircuit is rigidly fixed to the bottom of the cavity, any distortion of the board results in stresses which are transmitted to the microcircuit, which can damage or render the microcircuit unusable in particular during the cracking the material (silicon) forming the microcircuit or during the breaking of an electrical interconnection.
The invention enables these difficulties to be overcome and the reliability of such a microcircuit board to be improved.
SUMMARY OF THE INVENTION
The basic idea of the invention separately produces a module made from a sheet of electrically conductive material, intended to form the network of conductors and of fitting the microcircuit to it in such a way that it is fixed and connected to the conductors of the circuit before the whole is assembled with the board by fixing the external connection areas of the network to the surface of the board, all around the opening of the cavity. In other words, the microcircuit is separate from the bottom of the cavity (or “suspended” in it) and the network of conductors provides a flexible connection between the microcircuit and the board, which greatly reduces distortion stresses applied to the board.
More precisely, the invention relates to a method of manufacturing a microcircuit board comprising the steps of forming a cavity in a part of the thickness of a board made of insulating material for forming a support, the cavity open on one surface of the board, creating a network of conductors to establish electrical connections between the cavity and the surface of the board, and of connecting the microcircuit to the network of conductors, producing a module comprising the network and the microcircuit in such a manner that a blank of the network is shaped to at least partially define a container and that the microcircuit is fixed to the network while keeping different parts of the network in position relative to each other, cutting off outer parts of the blank to form external connection areas, placing the module in the cavity with the external connection areas resting on the surface, and fixing the external connection areas onto the surface.
In other words, in accordance with a first exemplary embodiment, the microcircuit is connected to the board by means of a limited numbers of flexible junctions formed by the tracks of the network of conductors itself, these tracks leading to the external connection areas adhered to the surface of the board, all around the cavity. This type of construction considerably reduces the stresses transmitted to the microcircuit. However, the remainder of the cavity may be filled with different types of resins or similar filler materials, which are more or less flexible and deformable.
The invention also relates to a microcircuit board produced by implementation of the process defined above.
REFERENCES:
patent: 3851223 (1974-11-01), Yonezuka et al.
patent: 4996411 (1991-02-01), Rbjock
patent: 5005282 (1991-04-01), Rose
patent: 5647122 (1997-07-01), Launay et al.
patent: 44 31 754 C1 (1995-11-01), None
patent: 0 371 855 A1 (1989-11-01), None
patent: 0 599 194 A1 (1993-11-01), None
patent: 0 688 0541 A1 (1995-06-01), None
Bouchez Francois
Venambre Jacques
De la rue Cartes et Systemes
Gerrity Stephen F.
Oliff & Berridg,e PLC
Sands Rhonda E.
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