Electricity: conductors and insulators – Boxes and housings – Hermetic sealed envelope type
Reexamination Certificate
2000-04-25
2002-04-16
Reichard, Dean A. (Department: 2831)
Electricity: conductors and insulators
Boxes and housings
Hermetic sealed envelope type
C257S693000, C174S260000, C174S261000
Reexamination Certificate
active
06372985
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a package for electronic components and also relates to electronic components including such a package. The present invention particularly relates to a ceramic package for surface-mount type electronic components and electronic components using such a ceramic package.
2. Description of the Related Art
A conventional package for an electronic component includes wiring layers disposed in recesses provided on the side surfaces of a substrate (castellation), as well as, via-holes arranged along the direction of thickness of the substrate in order to electrically connect electrodes located on an upper surface of a base substrate and electrodes disposed on the bottom surface of the base substrate.
FIGS. 19
to
21
show common structures of a conventional ceramic package provided with recesses on the side surfaces of a substrate.
FIGS. 19 and 20
show a disassembled perspective top view and a perspective bottom view of the conventional package, respectively, while
FIG. 21
shows a partially enlarged perspective view of the package in FIG.
20
. The package
21
is composed of a base substrate
22
and a side wall
23
. The base substrate
22
and the side wall
23
include layer or a plurality of layers of a ceramic insulation substrate made of, for example, Al
2
O
3
. An electrode
24
(the area surrounded by a broken line in
FIG. 19
) for electrically connecting device elements (not shown) to the package
21
is provided on the element mounting surface for mounting device elements, or on the upper surface of the base substrate
22
. External electrode terminals
25
for electrically connecting the package
21
to a mounting substrate are formed on the bottom surface of the base substrate
22
. Recesses
26
and
30
communicating with the bottom surface of the base substrate
22
are provided at the side surfaces of the side wall
23
and base substrate
22
, and wiring layers
27
are disposed on the side surfaces of the recesses
26
provided on the base substrate
22
. The recesses
26
and
30
have the same cross-sectional shape as each other. The electrode
24
is electrically connected to the external electrode terminals
25
through lead patterns
28
(the area outside of the area surrounded by the broken line in FIG.
19
), which abut the electrode and extend outward, and the wiring layers
27
are disposed in the recesses
26
. Chamfers
31
and
31
are provided at the corners of the base substrate
22
and side wall
23
in order to prevent them from being chipped.
The method for manufacturing the package as described above will be described hereinafter. Through holes which define the recesses
26
and the chamfers
31
are formed on a mother sheet of a ceramic green sheet provided for forming the base substrate
22
, followed by depositing a metal film for forming the wiring layers
27
in the recesses
26
and on the electrodes
24
,
28
and
25
. Subsequently, the area surrounded by the side wall
23
is punched, and through holes defining the recesses
30
and chamfers
31
are formed through a mother sheet of a ceramic green sheet for forming the side wall
23
. These ceramic green sheets for forming the base substrates and side walls are laminated, press-bonded and fired in the next step. Then, the surfaces of the electrodes
24
and
25
, and the surfaces of the wiring layers
27
are plated. Finally, the laminated green sheet is cut along the lines passing through the centers of the through holes that define the recesses and chamfers to divide into a lot of substrates, thereby completing the package
21
.
FIG. 22
is a cross-sectional view showing the configuration when an electronic component
35
including the package
21
in which an electronic device element is accommodated is mounted on a substrate. The package
21
in
FIG. 22
corresponds to a cross-section of the package in
FIG. 20
on the surface Y. An electronic device element
32
such as an elastic surface wave element or a semiconductor element is mounted on the element mounting surface of the package
21
as shown in the drawing, and the package
21
is airtight-sealed with a lid
29
made of, for example, a metal. The electronic component formed as described above is mounted on the surface of a printed circuit board
34
using a solder for mounting. In mounting the electronic component, solder fillets
33
are formed by a reflow method using a solder paste. The solder fillets
33
are provided for electrically and mechanically connecting the electronic component
35
to the printed circuit board.
However, the conventional package
21
for an electronic component experienced the problems as described below. While the thickness
W
of the side wall
23
of the package is reduced as the electronic component is miniaturized, the thickness
W
of the side wall
23
as a sealing width should be ensured to a certain extent for airtight-sealing of the package using the lid
29
. Since the thickness
W
of the side wall
23
turns out to be a minimum (
Wmin
) particularly at the portions where the recesses
26
and
30
are formed, the recesses
26
and
30
are required to be as small as possible for providing a certain minimum required sealing width.
A thicker electrical continuity passage can be formed, on the other hand, between the external electrode terminal
25
and the electrode
24
on the element mounting surface as the contact area between the solder fillet
33
and the wiring layer
27
is wider, thereby impedance
Z
, for example resistance, between the electrodes is reduced. In addition, mechanical strength such as bonding strength and bending strength can be enhanced as the contact area between the solder fillet
33
and the wiring layer
27
is wider. Accordingly, the recesses
26
and
30
should be formed to be as large as possible, in order to increase the contact area between the solder fillet
33
and the wiring layer
27
, or to ensure a good electrical and mechanical continuity between the element and the printed circuit board.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide a package for electronic components having excellent electrical and mechanical continuity with a printed circuit board and being highly airtight, and electronic components using the same as a surface-mount type electronic component in which an electronic device element is accommodated in the package.
According to a preferred embodiment of the present invention, a package for electronic components includes a base substrate and a side wall in which recesses communicating with the bottom surface of the base substrate are provided on the base substrate and the side wall, and in which electrodes on the bottom surface of the base substrate are electrically connected to electrodes on the element mounting surface defining an upper surface of the base substrate though wiring layers disposed on a portion of the recesses, wherein the recesses are arranged on the base substrate to have a cross-sectional area that is wider than the cross-sectional area of the recesses disposed on the side wall.
When the recesses on the base substrate have a wider cross-sectional area than the cross-sectional area of the recesses on the side wall standing on the base substrate among the recesses on the base substrate and on the side wall, or when the recesses on the side wall are smaller and the recesses on the base substrate are larger, the thickness of the side wall of the package defining a sealing width can be ensured to a certain extent even at its narrowest portion, besides maintaining a sufficient a contact area between the wiring layer and solder fillets so as to ensure electrical continuity between the electrodes on the bottom surface of the base electrode and the electrodes on the element mounting surface. Consequently, excellent electrical and mechanical continuity between the electronic component and the printed circuit board are achieved while maintaining t
Keating & Bennett LLP
Murata Manufacturing Co. LTD
Oliva Carmelo
Reichard Dean A.
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