Conductive cap, electronic component, and method of forming...

Details Conductive cap, electronic component, and method of forming... Conductive cap, electronic component, and method of forming...

2000-08-18

2002-12-03

Reichard, Dean A. (Department: 2831)

Electricity: conductors and insulators

Boxes and housings

Hermetic sealed envelope type

C174S050510, C257S704000, C257S710000

Reexamination Certificate

active

06489558

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a conductive cap for covering an electronic element such as a piezoelectric element mounted on the upper surface of a substrate, an electronic component including such a conductive cap, and a method of forming an insulating film of the conductive cap.
2. Description of the Related Art
For conventional electronic component elements such as piezoelectric resonators or other suitable components, a package structure including a conductive cap has been used. Such a type of package structure will be described with reference to FIG.
6
.
The package structure contains a substrate
51
having a rectangular sheet shape, made of an insulating material such as alumina, and a metallic cap
52
. On the upper surface
51
a
of the substrate
51
, terminal electrodes
53
and
54
for achieving external electric connection are provided. The terminal electrodes
53
and
54
each are extended onto the side surfaces, the end surfaces, and the lower surface, in addition to the upper surface
51
a
, so that the package structure can be surface-mounted onto a printed circuit board.
Further, a piezoelectric element is mounted onto the upper surface
51
a
of the substrate
51
by solder, a conductive bonding agent such as a conductive adhesive, or the like, though not shown in FIG.
6
. The electrodes of the piezoelectric element are connected to the terminal electrodes
53
and
54
, respectively.
For the purpose of sealing the piezoelectric element, a metallic cap
52
having an opening at the lower portion thereof is bonded to the substrate
51
. A rectangular frame-shaped insulating film
55
is provided on the portion of the upper surface
51
a
of the substrate
51
that is arranged to be contacted with the end surface of the opening of the metallic cap
52
. The insulating film
55
is formed by printing synthetic resin, or printing and baking glass. The thickness of the insulating film
55
is about 0.1 mm. Accordingly, the height of the chip electronic component to be produced can be reduced, even though the metallic cap
52
is used.
In recent years, it has been required to reduce the mounting areas of electronic components. With even greater miniaturization of components, it has been very difficult to print and form the insulating film
55
on the upper surface
51
a
of the substrate
51
with high precision.
Further, Japanese Unexamined Patent Application Publication No. 6-132762 discloses an electronic component
71
having a cap shown in FIG.
7
. In this electronic component
71
, terminal electrodes
73
and
74
each extends on the upper surface, the side surfaces, and lower surface of a substrate
72
made of an insulating material. A piezoelectric element
75
is bonded to the terminal electrodes
73
and
74
via solder members
76
and
77
.
A metallic cap
78
is bonded to the upper surface of the substrate
72
by an insulating adhesive. In order to prevent the terminal electrodes
73
and
74
and the metallic cap
78
from short-circuiting, an insulating film
79
is disposed on the entire inner surface of the metallic cap
78
.
In the prior art, no method of forming the insulating film
79
is specifically described. It is presumed that the insulating layer is precoated on a sheet material before the material is shaped into the metallic cap
78
, and the precoated sheet material is formed to have the same shape as that of the cap.
When the metallic cap described in Japanese Unexamined Patent Application Publication No. 6-132762 is produced, the peripheral portion of the opening of the metallic cap
78
must be bent outward, as shown in
FIG. 7
, so that the insulating layer is always positioned on the portions of the terminal electrodes
73
and
74
to be contacted with the metallic cap
78
. Accordingly, the process of producing the metallic cap
78
becomes complicated. Further, in some cases, when such bending work is carried out, the insulating layer
79
is peeled, making it impossible to reliably provide electrical insulation between the metallic cap
78
and the terminal electrodes
73
and
74
.
In a chip electronic component in which an element such as a piezoelectric element or other electronic element is mounted onto a substrate, the piezoelectric vibration portion thereof is vibrated. As a result, the structure is such that the element is accommodated in a package that does not interfere with vibration of the element. After the element is mounted onto the surface of the substrate, a cap is fixed to the surface of the substrate to cover and seal the element.
FIG. 20
is a cross-sectional view showing an example of another conventional electronic component sealed with such a cap. In the conventional electronic component shown in
FIG. 20
, an insulating cap
30
is used. This is because the cap
30
is fixed to terminal electrodes
11
and
12
provided on a substrate
10
and must be insulative in order to prevent the terminal electrodes
11
and
12
from short-circuiting. An element such as a piezoelectric resonator is mounted onto the upper surface of the substrate
10
. The element
20
is bonded to the terminal electrode
11
via solder
21
and the terminal electrode
12
with solder
22
. A terminal electrode
13
is provided between the terminal electrodes
11
and
12
between the terminal electrodes
11
and
12
on the lower surface of the substrate
10
to produce a capacitor between the terminal electrodes
11
,
12
and
13
.
As the insulating cap
30
, a ceramic cap, a resin cap, or other cap is used. However, these caps must have a thickness of 0.25 mm or larger because of the forming capabilities and limitations. Accordingly, it is not possible to reduce the height of the electronic component, and the area of the substrate becomes larger.
For the purpose of reducing the height of the electronic component and enhancing the integration density of the circuit board, it is preferable to use a metallic cap. However, if the metallic cap alone is fixed to the substrate, the terminal electrodes short-circuit, as described above.
In order to prevent the terminal electrodes from short-circuiting as described above, a method in which an insulating layer
31
is disposed on the substrate
10
and the terminal electrodes
11
and
12
onto which the metallic cap
32
is to be mounted, and the cap
31
is mounted onto the insulating layer
31
, as shown in FIG.
21
. In
FIG. 21
, elements such as a piezoelectric resonation element mounted onto the substrate
10
are omitted.
According to a method as described above, the metallic cap can be used. Thus, the height of an electronic component can be reduced. On the other hand, there arises the problem that with further miniaturization of the electronic component, it becomes more difficult to form the insulating layer on the substrate with high precision.
Japanese Unexamined Utility Model Application Publication No. 62-158828 and Japanese Unexamined Patent Application Publication No. 8-204491 disclose an electronic component provided with a metallic cap that is made of an aluminum sheet having an anodized film on the surface thereof. However, for the metallic cap, a sheet material is anodized. Therefore, in the case where the sheet material is formed into a cap shape, the end surfaces of the cap to be contacted with terminal electrodes on a substrate have no anodized films thereon. Accordingly, the terminal electrodes can not be prevented from short-circuiting.
Moreover, Japanese Unexamined Patent Application Publication No. 6-132762 discloses a metallic cap provided with an insulating layer disposed on the inner surface thereof. Such a metallic cap is shaped so that the end portions of the cap to be contacted with a substrate are bent outward, and the inner surface of the cap can be contacted with terminal electrodes. Accordingly, the insulating layer disposed on the inner surface is contacted with the terminal electrodes. Thus, the insulating layer is interposed between the metallic cap and the terminal electrodes, whereb

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