Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Insulative housing or support
Reexamination Certificate
2000-12-18
2003-05-20
Loke, Steven (Department: 2811)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Insulative housing or support
C438S127000, C438S125000
Reexamination Certificate
active
06566170
ABSTRACT:
“This application is a national phase of PCT/FR99/01457 which was filed on Jun. 17, 1999 and was not published in English.”
TECHNICAL FIELD
The present invention relates to a method for encapsulating components and for forming a device having one or more components arranged in one or more cavities with a controlled atmosphere.
By cavity, with controlled atmosphere is meant both a cavity in which a vacuum has been set up and a cavity containing a gas with controlled composition and/or pressure.
Said cavity, defined for example by a cover applied to a substrate, can be used to house sensitive components such as electronic, electro-optic or micro-mechanical components.
In particular, the invention finds applications in the hermetic encapsulation of electronic chips, of pressure or acceleration sensors, or further of electromagnetic sensors such as bolometer sensors.
STATE OF THE PRIOR ART
Different techniques are known with which it is possible to bond a cover onto a carrier. For example glass bonding techniques may be cited, or metal-on-metal type bonding, or further anode bonding. In respect of these techniques, well known in themselves, reference may be made to documents (1), (2) and (3) whose references are given at the end of this description.
The bonding of a cover onto a carrier to form a controlled atmosphere cavity is described with reference to
FIGS. 1
to
4
.
A first operation, illustrated in
FIG. 1
, consists of positioning a cover
10
on a carrier
12
, such as a substrate, in a region containing a component
14
.
It is observed that cover
10
has a recess
16
oriented in the direction of the carrier
12
and intended to house the component
14
. Recess
16
is surrounded by a border
18
.
A strip of insulation
20
, in a suitable material such as a fusible material is provided on the surface of carrier
12
, so as to surround component
14
and to correspond with the shape of the border
18
in cover
10
.
The mutual positioning of cover
10
and carrier
12
is made by alignment means shown very schematically and denoted
22
. With these means it is possible to cause the recess
16
of the cover to coincide with the component
14
and to position the border
18
facing the strip of insulation
20
.
FIG. 1
shows that all parts to be assembled, and the alignment means, are placed in a chamber
24
in which the desired controlled atmosphere is set up.
The actual bonding step, carried out after positioning of the cover, is illustrated in FIG.
2
.
As shown by an arrow, cover
10
is applied to the carrier in such manner that the strip of insulation connects the border
18
in impervious manner to the upper surface of substrate
12
.
Optionally, if the strip of insulation is in a fusible material, the carrier and cover assembly may be brought to sufficient temperature to cause the fusible material to melt.
Heating of the cover and carrier, which always takes place in the chamber
24
having a controlled atmosphere, is conducted for example by means of a heating plate
28
on which carrier
12
rests.
FIG. 3
shows, by way of example, a carrier
12
to which three covers
10
a
,
10
b
and
10
c
have been applied.
Reference
10
a
designates a first cover already bonded to carrier
12
. Reference
10
b
designates a second cover being applied to carrier
12
, during the bonding phase.
Finally, a third cover
10
c
, not yet applied to the carrier, is positioned above a component
14
.
It will be noticed that the positioning of the covers and their bonding takes place successively. Also as in the example in
FIG. 1
, the cover alignment means
22
, even though voluminous and cumbersome, must be housed in the chamber
24
with a controlled atmosphere.
The method described with reference to
FIG. 3
therefore raises housing problems of the alignment means, and proves to be little adapted to the positioning of a high number of covers onto a carrier.
It is to pointed out that it is not possible with the equipment in
FIG. 3
to align and deposit on the carrier all the covers outside chamber
24
, and then to conduct the bonding or soldering operation in a controlled atmosphere. For when the cover is placed on the carrier previous to placing the assembly formed by the cover and carrier in a chamber in which a controlled atmosphere is set up, the passage of gas between the cover and the carrier is hindered and it is no longer possible to control precisely the atmosphere which is set up in the cavity formed by the cover and the carrier. This is especially the case when a vacuum is to be set up in the cavity.
One partial solution to the problems mentioned above is provided by a cover transfer system illustrated in FIG.
4
.
This system uses an intermediate support part
26
on which covers
10
a
,
10
b
,
10
c
are transferred via their surface which does not come into contact with the final carrier
12
.
The intermediate part
26
, comprising the covers, is inserted with carrier
12
in a chamber with a controlled atmosphere, and the bonding or sealing of the covers can be conducted collectively.
The method in
FIG. 4
nevertheless requires alignment means
22
for the intermediate part
24
with the carrier. Also, the intermediate part must be removed after the covers have been applied.
Another partial solution to the problem of encapsulating a plurality of components, consists of only applying to the carrier a single cover, that is sufficiently large to cover all the components and then to cut the cover individually around each component. This solution, which is not shown in the figures, requires special forming of the carrier and/or cover to form individual cavities around the components, and has recourse to delicate cutting operations.
DESCRIPTION OF THE INVENTION
The purpose of the present invention is to put forward a method for encapsulating one or more components, which does not have the difficulties or constraints described above.
The method is intended to encapsulate components which may either be previously applied to a substrate or directly integrated into the substrate (electronic chips, integrated sensors . . . ).
One purpose of the invention in particular is to provide such a method which may be conducted in a chamber with a controlled atmosphere free of means to align the covers on the components.
A further purpose is to provide such a method with which it is possible to align with precision and to bond collectively a great number of covers over corresponding components.
To attain these purposes, the subject of the invention is more precisely an encapsulation method in a controlled atmosphere of at least one component by bonding at least one cover onto at least one region of a carrier containing the component. In accordance with the method of the invention:
at least one of either the cover or the carrier is provided with bonding means surrounding a region corresponding to said component, and with at least one wedge in a fusible material,
the cover and substrate are mutually positioned so that the cover is arranged substantially opposite a region corresponding to the component,
the assembly formed by the cover and carrier is heated in a chamber with a controlled atmosphere at sufficient temperature to cause the wedge of fusible material to melt.
Also the wedge in fusible material is made with sufficient initial height before fusion to prevent the bonding means from joining the cover to the carrier in impervious manner, and such as to have a height after fusion that is sufficiently low to enable impervious contact of the bonding means both with the cover and with the carrier.
By means of the wedges in fusible material, it is possible to put in place and position the covers on the carrier before inserting the carrier in the controlled atmosphere chamber.
Indeed, the wedges prevent the space between the cover and the carrier from forming a closed, isolated cavity before final bonding. The controlled atmosphere, such as a vacuum for example, may therefore be set up around the component.
Advantage may also be taken of the wedges to serve as electric connection
Caillat Patrice
Marion François
Massit Claude
Pornin Jean-Louis
Commissariat a l'Energie Atomique
Krebs Robert E.
Loke Steven
Owens Douglas W.
Thelen Reid & Priest LLP
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