Component hybridizing system allowing for defective planarity

Details Component hybridizing system allowing for defective planarity Component hybridizing system allowing for defective planarity

2000-03-06

2002-06-04

Cuneo, Kamand (Department: 2827)

Electricity: conductors and insulators

Conduits, cables or conductors

Preformed panel circuit arrangement

C174S261000, C174S263000, C361S768000, C361S770000

Reexamination Certificate

active

06399895

ABSTRACT:

FIELD OF THE INVENTION
This invention involves a system of components for hybridisation adapted to a technique for hybridisation by melting of solder projections, know as the “flip-chip” method, and which allows for uneven surfaces. The invention also involves a component substrate with hybridisation studs allowing for uneven surfaces.
In the context of the present invention, component means either an electronic component such as for example an electronic chip, an electronic circuit support, or an optoelectronic circuit support, or a mechanical component such as, for example, a cap or sensor of physical values.
The invention can be applied in the areas of electronics and optics in particular.
The invention can be used for example in the manufacturing of retinas for detection of electromagnetic waves, for hybridisation, on addressing circuits, laser matrices with vertical cavities for surface emission, or for hybridisation of optical detectors on reading circuits.
STATE OF THE PRIOR ART
There are two main techniques for hybridisation of components by solder projections.
A first technique, called “technique for hybridisation by melting” uses projections of meltable material such as an alloy of tin and lead SnPb or tin and indium SnIn for example. The technique of hybridisation by melting is illustrated by the appended drawings of
FIGS. 1 and 2
.
In these figures, the references
10
and
12
designate respectively a first and a second component to be interconnected. The first component
10
includes first studs
14
a
of a material wettable by the material of the projections of meltable material (solder). The studs
14
a
are surrounded respectively by an area
16
a
of material which is not wettable by the material of the projections. For the purpose of simplification, only two interconnection projections are shown in
FIGS. 1 and 2
. The components could however be equipped with a large number of projections.
In the same way, the second component
12
includes second studs
14
b,
also made of a material wettable by the projection material, and surrounded by an area
16
b
of non-wettable material.
The first and second studs
14
a
,
14
b
are associated to form pairs of studs. The studs of each pair of studs are essentially arranged face to face when the components to be hybridised
10
,
12
are brought together with their hybridisation sides facing, as shown in FIG.
1
.
The studs
14
a
of one of the components, in this case of the component
10
, are equipped with projections
18
of meltable material. These projections
18
are to create a mechanical and/or electric link between the studs
14
a
,
14
b
of each pair of studs.
For a hybridisation, the component
12
is brought against the component
10
so that the studs
14
b
come into contact with the corresponding projections
18
. The entire structure is then brought to the hybridisation temperature, greater than or equal to the melting point of the projections, in order to solder the projections
18
to the studs
14
b.
All of the projections
18
are thus soldered simultaneously to the studs of the component
12
which corresponds to them. After cooling, the structure in
FIG. 2
is obtained.
The accuracy of the mutual positioning of the components during the placement of the component
10
onto the component
12
is not critical. During melting of the projection material, the components
10
and
12
are automatically aligned due to the surface tension of the molten projection material.
As indicated previously, due to the process of hybridisation by melting, all of the solder joints between the projections and the receiving studs are made simultaneously. The process of hybridisation by melting is thus particularly suitable for hybridisation of several components such as chips to a receiving component which forms the substrate. A high hybridisation yield can be obtained for these structures.
FIGS. 1 and 2
illustrate the technique of hybridisation by melting in the ideal case where the first and second components are perfectly flat. In the preceding description, the uneven surfaces which often appear on components were not taken into account. This surface unevenness generally results in deflection and has a greater influence on large components.
This situation is illustrated in FIG.
3
.
A first component
110
has an essentially planar hybridisation side
111
equipped with projection receiving studs
120
a
,
122
a
,
124
a
,
126
a
and projections of meltable material
120
b
,
122
b
,
124
b
,
126
b
. A second component
112
has a hybridisation side
113
equipped with studs
120
c
,
122
c
,
124
c
,
126
c
for receiving the projections.
The second component is not perfectly planar but rather has a deflection curve f indicated in the figure.
The deflection is measured between a plane which goes through the base of stud
124
c
, i.e. the upper part of the component curve, and a plane parallel to the plane which goes through the base of stud
124
c
and passing through the furthest reception stud from the plan which is, in the case of the example of the figure, stud
126
c.
In
FIG. 3
, hb indicates the height of the projections which have not yet been soldered onto the receiving studs of the component
112
. The height hb is measured from the hybridisation surface
111
. h
1
indicates the distance separating the first plane of the surface
111
after hybridisation of the components
110
and
112
. The distance h
1
is referred to in the remainder of the description as the “hybridisation height.”
The absence of a connection between the studs
120
c,
126
c
and their corresponding projections
120
b,
126
b
is seen in FIG.
3
. This flaw is due to the excessive mechanical deflection of the component
112
.
Once the projections
122
b,
124
b
are soldered to the receiving studs
122
c
and
124
c,
the hybridisation height h
1
at the lowest point of the component
112
, i.e. the point closest to the hybridisation surface
111
of the component
110
, is defined.
One receiving stud of the component
112
does not come into contact with its corresponding solder projection if the distance F which separates it from the plane which goes through the base stud is such that h
1
+f>hb, i.e. f>hb−h
1
.
This is the case for studs
120
c
and
126
c.
The height of the solder projections can be easily calculated from the volume of meltable material from the projections and the wettable surface of the receiving studs
120
a
,
122
a
,
124
a
and
126
a
(sphere truncated by a disk). In the same way, the height h
1
can be calculated by taking into account the volume of meltable material of the projections and the wettable surfaces of the receiving studs of each component (sphere truncated by two disks).
Considering that the volume of meltable material is essentially the same for all of the projections, it is possible to determine the maximum allowable deflection f before connection flaws of the projections appear.
Thus in effect F=hb−h
1
.
It is immediately apparent that this problem gets worse when the dimensions of the projections, and thus their height hb, is smaller. The problem is also aggravated for hybridisation of large components for which the deflection is naturally larger.
As an example, for hybridisation of a component with a matrix distribution of projections with a pitch of 25 &mgr;m, the projections can have a thickness of 10 &mgr;m between the receiving studs of each component (after hybridisation and a diameter of 15 &mgr;m.
When, before hybridisation, these projections equip the receiving studs of a first component which has a diameter of 12 &mgr;m, the height hb of the projections (in the form of spheres) not connected is hb=12.6 &mgr;m. The hybridisation height h
1
is, for the same data, such that: h
1
=10.4 &mgr;m.
The maximum acceptable deflection f is thus 12.6−10.4=2.2 &mgr;m. Components with a deflection less than such a maximum deflection are generally small. If the components are larger however, for example components with 2 cm

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