Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Assembly of plural semiconductive substrates each possessing...
Reexamination Certificate
1999-04-23
2001-05-29
Graybill, David E. (Department: 2814)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Assembly of plural semiconductive substrates each possessing...
C438S615000, C438S613000, C228S180220
Reexamination Certificate
active
06238951
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for producing a ring ensuring the mechanical strength and sealing between a substrate and a chip (or any other electronic component) hybridized by bumps on the substrate, which can itself integrate active or passive components. It has applications in the fields of microelectronics, information processing or on-board electronics.
PRIOR ART
A method for the transfer of electronic components to an interconnection substrate making use of microbosses or bumps forms part of the prior art and is known as flip-chip. According to the flip-chip method, the bumps are produced around input/output connections of the electronic component, e.g. of a deposited meltable material, by electrolysis or evaporation. This meltable material can, e.g. be indium or a tin-lead alloy. The transfer of component to the substrate takes place at a heating temperature at least corresponding to the melting point of the chosen meltable material. This transfer operation can be likened to soldering or brazing.
Such a process is known as C4 (control collapse chip connection) and forms the subject matter of numerous publications, e.g. the work entitled “Micro-electronics packaging handbook” published by R. TUMMALA.
However, the ever more frequent use of multichips implies an optimization of the surface of the useful substrate. It is for this reason that the flip-chip method is generally used in the case of multichips. It is in particular used in broad distribution sectors, where costs are the vital factor.
There has also been a technical development of substrates leading to flip-chip interconnection needs with respect to supports other than conventional silicon supports. These supports can e.g. be of alumina and can also be printed circuits.
However, the known flip-chip transfer method is reliable when the thermal expansion coefficients of the chip (or other electronic component) and the substrate are very close. However, alumina and to an even more pronounced extent the printed circuits commonly used as substrates, have an expansion coefficient differing very considerably from that of the chip normally produced on silicon. Moreover, when these expansion coefficients of the chip and the substrate differ, the changes (time variations) of temperature lead to significant stresses occurring in the bumps, which has the effect of embrittling them and significantly reducing the reliability of the system produced by the chip hybridized on the substrate.
FIGS. 1A
,
1
B and
1
C are front views of different cases of hybridization bumps connecting a chip and a substrate.
FIG. 1A
shows the case of a bump in a medium raised to a mean temperature of approximately 20° C. In
FIG. 1A
, it is possible to see the chip
1
which a layer
2
a
of electrically conductive material, which is in contact with the connection point or connector
3
. An electrically insulating layer
2
b
covers the lower face of the layer
2
a
around the connector
3
.
FIG. 1A
also shows the substrate having an electrically conductive material layer
4
a
in contact with the connector
7
. An electrically insulating layer
4
b
covers the layer
4
a
around the connector
7
. The hybridization bump
9
ensures an electrical connection between the connector
3
of the chip
1
and the connector
7
of the substrate
5
. For an ambient temperature of approximately 20° C., the bump has a vertical position and the connectors
3
and
7
are positioned substantially facing one another.
FIG. 1B
shows the same hybridization bump when the ambient temperature is approximately −50° C. The difference in the thermal expansion coefficients between the chip and the substrate gives rise to a relative displacement of the connectors
3
and
7
, which then no longer face one another (the bump then being oblique).
Finally,
FIG. 1C
shows the hybridization bump in the case where the temperature is raised to +120° C., which also leads to a shift in the relative position of the connectors
3
and
7
, but in the direction opposite to that of FIG.
1
B.
On considering
FIGS. 1A
,
1
B and
1
C it is easy to see that when the expansion coefficient of the chip differs from that of the substrate, the hybridization bump is deformed (cf.
FIGS. 1B and 1C
) in order to accommodate the expansion or contraction during the temperature change. As shown in
FIGS. 1B and 1C
, non-alignment of the connector
7
of the substrate
5
with the connector
3
of the chip
1
leads to a non-vertical shape of the bump
9
.
In order to limit the expansion or contraction problem due to the differences of the expansion coefficients between the chip I and the substrate
5
, an attempt has been made to fill the space between the chip
1
and the substrate
5
so that the material filling said space can absorb part of the stresses. The material used for filling the space between the chip and substrate is called the encapsulating substance. The obtaining of this total filling by an encapsulating substance consists, following the hybridization of the chip by bumps on the substrate, of filling the space between the chip and substrate using a dispenser. This requires a certain number of stages and relatively costly means.
In parallel, every increasing use is being made of the flip-chip method for hybrid sensor-type components. Thus, for such components, transfer generally takes place by bumps of a sensitive cell to an electronic control circuit more particularly produced on silicon using a conventional procedure. In this case, the sensitive cells are individually deposited on the electronic circuit, are collectively hybridized and each sensor is then cut. For such a construction, it is important to protect the sensitive structures against external attacks such as through the cutting, fitting or as a result of atmospheric conditions.
In order to protect the sensitive structures, as described hereinbefore, it is possible to insulate the interior of the assembly, i.e. the sensor with respect to the outside world. For this purpose it is possible to use an encapsulating substance in the form of a ring placed on the periphery of the chip. For this purpose IBM has studied the geometrical aspect of peripheral encapsulation in order to permit insulation in the manner described hereinbefore. The article entitled “Encapsulating flip-chip device with epoxy-resin” published in “International Interconnection Intelligence Flip-Chip Technology Impact Report” describes this geometrical aspect of encapsulation.
Other documents also describe different peripheral encapsulation types. U.S. Pat. No. 3,657,610 describes a semiconductor device having a metallic material sealing ring placed between two structures by applying ultrasonic vibrations at 300° C. EP-A-522 461 and U.S. Pat. No. 3,591,839 describe semiconductor devices sealing rings produced from several layers of metallic materials.
Like the total encapsulation described hereinbefore for ensuring the mechanical strength of the chip-substrate assembly, the formation of said peripheral encapsulation for sealing the assembly requires numerous stages and costly equipment. In addition, an annealing stage is generally necessary for the polymerization of the ring of bead normally produced using an epoxy resin adhesive, whereby said stage can be critical for the bumps or chip.
DESCRIPTION OF THE INVENTION
The present invention aims at obviating the disadvantages referred to hereinbefore. To this end it proposes a process for producing a ring ensuring the sealing of the chip hybridized by bumps on the substrate, whilst improving the mechanical resistance to temperature variations of the assembly constituted by the chip, the substrate and the hybridization bumps, particularly when the substrate is made from a material other than silicon.
For reasons of simplicity, said mechanical strength and sealing ring is referred to as the second material ring or even ring.
More specifically, the invention relates to a process for producing a sealing and mechanical strength ring between an interconnection substrate and
Commissariat A l'Energie Atomique
Graybill David E.
Hayes Soloway Hennessey Grossman & Hage PC
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