Electronic device

Details Electronic device Electronic device

2003-04-05

2004-11-30

Martin, David (Department: 2841)

Electricity: electrical systems and devices

Housing or mounting assemblies with diverse electrical...

For electronic systems and devices

C361S818000, C361S800000, C361S720000, C257S704000, C174S034000, C174S051000

Reexamination Certificate

active

06826053

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electronic devices including a wiring substrate and at least two units provided thereon, and more particularly, to an improvement in the strength for fixing a metal case and surface mount electronic components to the wiring substrate or for fixing a plurality of surface mount electronic components thereto.
2. Description of the Related Art
High-frequency electronic devices, such as RF devices for mobile phones and wireless communication, include a wiring substrate and surface mount electronic components mounted thereon via soldering.
FIG. 8
is a schematic cross-sectional view of a related electronic device
101
, which is of interest to the present invention.
The electronic device
101
is a hybrid electronic device including a wiring substrate
102
. The wiring substrate
102
is a multilayer ceramic substrate. Although not shown in the figure, on end surfaces of the periphery or the bottom surface of the wiring substrate
102
, several terminal electrodes are provided, and on the top surface of the wiring substrate
102
, several conductive lands are provided.
At least two surface mount electronic components
103
and
104
are mounted on the top surface of the wiring substrate
102
by soldering. One electronic component
103
is an IC chip component and is soldered to the conductive lands provided on the top surface of the wiring substrate
102
with several solder bumps
105
provided therebetween. The other electronic component
104
is a chip component, such as a capacitor, inductor, or quartz oscillator, and is soldered to the conductive lands provided on the top surface of the wiring substrate
102
with solder fillets
106
formed via soldering.
In the electronic device
101
having the structure described above, a case (not shown) may be fixed to the wiring substrate
102
so as to cover the electronic components
103
and
104
.
However, the electronic device
101
shown in
FIG. 8
has the following problems.
First, when impact is applied to the wiring substrate
102
due to a fall, bending, or other external force, at least one of the electronic components
103
and
104
mounted on the wiring substrate
102
may fall therefrom or be damaged.
In addition, when the size of the electronic component mounted on the wiring substrate
102
is increased, such as an IC chip component, or when the number of electronic components mounted on the wiring substrate
102
is increased, the size of the wiring substrate
102
must be increased. In addition, since the electronic device
101
has been increasingly required to have a smaller height, the thickness of the wiring substrate
102
must be decreased. Accordingly, damage, such as breakage, caused by external forces are more likely to occur in the wiring substrate
102
.
In addition, when the solder bumps
105
provided for the electronic component
103
are formed of eutectic solder, when the electronic device
101
is mounted as a module component on an appropriate motherboard (not shown) via a solder reflow process or other suitable soldering method, the temperature applied when the device is mounted may be higher than that at which the eutectic solder is melted in many cases. In this case, when the solder bumps
105
are melted, the electronic component
103
may move with respect to the wiring substrate
102
, and in the worst case, electrical short circuiting caused by the solder will occur between the adjacent conductive lands which are to be connected to the respective solder bumps
105
, thereby producing electronic devices
101
which must be rejected.
In addition, in an electronic device provided with a case, when the case is made, for example, of a metal, soldering is frequently performed to fix the case to the wiring substrate. However, due to insufficient strength obtained by soldering, in some cases, the case falls off or is removed from the wiring substrate.
A technique which is of interest to the present invention is disclosed in Japanese Unexamined Patent Application Publication Nos. 5-47968 and 8-17853 in which a resin is provided in the case so as to contact the wiring substrate, and the electronic component thereon is covered with the resin. Since the resin is in contact with the case, the resin serves as an adhesive for adhering the case and the wiring substrate to each other, and hence, the strength of fixing the case to the wiring substrate is increased by the resin.
However, in the structure disclosed in Japanese Unexamined Patent Application Publication Nos. 5-47968 and 8-17853, since the resin covers the electronic component, the solder applied for mounting the electronic component on the wiring substrate is also covered with the resin, and the structure described above may cause the following problems.
That is, the electronic device described above is mounted on a mounting substrate such as a motherboard so that the wiring substrate is brought into contact therewith. In this step, when a solder reflow process is used, the temperature for solder reflow may be higher than the melting point of the solder used for mounting the electronic component to the wiring substrate. In this case, since the solder used for mounting the electronic component is expanded by melting, or volatile components of the solder is expanded, stress is applied to the resin covering the electronic component, the adhesion strength between the resin and the wiring substrate is decreased, and as a result, interface separation therebetween may occur.
Accordingly, when interface separation occurs, the melted solder flows in the portion at which the interface separation occurs, and as a result, the solder causes short circuiting between different terminal electrodes of the electronic component mounted on the wiring substrate, resulting in short-circuiting defects.
The short circuiting defects described above are more likely to occur when the resin is arranged in the case so as to cover the electronic component, and when the resin is not provided in the case, the defects might be prevented. However, when the resin is not provided in the case as described above, the fixing strength of the case to the wiring substrate is reduced.
SUMMARY OF THE INVENTION
To overcome the problems described above, preferred embodiments of the present invention provide an electronic device which increases the fixing strength of an electronic component to a wiring substrate, reduces the occurrences of damage thereto, and prevents undesirable movement of the electronic component in a solder reflow process.
In addition, the electronic device according to preferred embodiments of the present invention prevents short circuiting defects caused by a resin provided in a case while increasing the fixing strength of a case to the wiring substrate.
An electronic device according to a preferred embodiment of the present invention includes a wiring substrate, a first unit and a second unit which are mounted on the wiring substrate, and an adhesive resin which adheres the first unit to the second unit, wherein the adhesive resin is not in contact with the wiring substrate. Accordingly, the adhesive resin mechanically integrates the first unit with the second units via adhesion.
The first unit may preferably include at least one surface mount electronic component which is mounted on the wiring substrate via soldering, the second unit preferably includes a case fixed to the wiring substrate so as to cover the electronic component. The adhesive resin is preferably provided between the top surface of the electronic component and the bottom surface of the top wall of the case.
The adhesive resin increases the fixing strength of the case to the wiring substrate with the electronic component provided therebetween. In addition, since the adhesive resin is arranged so as not to contact the wiring substrate, interface separation between the wiring substrate and the resin is prevented even when solder used for mounting the electronic component on the wiring substrate is melted and expanded, a

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