Electronic device

According to one embodiment, an electronic device includes a housing, a first substrate having rigidity and including a slit, contained in the housing, a part mount portion provided on the first substrate and adjacent to the slit, an electronic part mounted on the part mount portion and a second substrate having flexibility. The second substrate is stacked on an inside of the first substrate and an inside of the part mount portion, and it crosses the slit, thereby supporting the part mount portion to be displaceable with respect to the first substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2009-156000, filed Jun. 30, 2009, the entire contents of which are incorporated herein by reference.

BACKGROUND

One embodiment of the present invention relates to an electronic device, for example, comprising a circuit module in which a flexible printed circuit board is arranged around a rigid printed circuit board.

2. Description of the Related Art

Inside an electronic device such as a portable computer, a circuit module is housed and the module contains a rigid printed circuit board and various types of electronic parts mounted on the rigid printed circuit board. Portable electronic devices of this type may be exposed to percussive impact from outside while being carried in, for example, a bag.

When an electronic is exposed to percussive impact, the impact propagates to the circuit module inside the device. When the circuit module is exposed to percussive impact, the circuit module may be warped or distorted in form. For example, due to this, a defect may occur in the connection between a rigid printed circuit board and an electronic part, which was made by soldering.

In order to prevent such a defect, there have been provided such a technique in which an adhesive is supplied to be across between a side edge of the electronic part and the rigid printed circuit board, and thus the connection between the electronic part and the rigid printed circuit board is reinforced. There is another technique such as disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 2003-332743, in which the flexible printed circuit board (to be called as FPC hereinafter) is exposed to a portion of the rigid printed circuit board, and electronic parts are mounted on the FPC.

Even in the case where the connection between an electronic part and a rigid printed circuit board is reinforced with use of an adhesive, a large portion of the percussive impact applied to the electronic device is propagated to the circuit module. For this reason, some defect may occur in the connection due to the percussive impact even if an adhesive is employed.

In the technique of mounting electronic parts on an FPC, the electronic parts may not be firmly mounted since the FPC has flexibility. For this reason, even in the case where electronic parts are mounted on an FPC, some defect may occur in the connection due to the percussive impact.

DETAILED DESCRIPTION

Various embodiments according to the invention will be described hereinafter with reference to the accompanying drawings. In general, according to one embodiment of the invention, an electronic device includes a housing, a first substrate having rigidity and including a slit, contained in the housing, a part mount portion provided on the first substrate and adjacent to the slit, an electronic part mounted on the part mount portion and a second substrate having flexibility. The second substrate is stacked on an inside of the first substrate and an inside of the part mount portion, and it crosses the slit, thereby supporting the part mount portion to be displaceable with respect to the first substrate.

FIG. 1shows an example of the electronic device, that is, a portable computer1. The portable computer1includes a main body2of the computer and a display module3.

The display module3is jointed to a rear end of the main body2via a pair of hinge portions4. The display module3is made pivotable between a closed position where the module is lied on the main body2of the computer and an open position where the module stands upright from the rear end of the main body2around the hinge portions4as axis.

The main body2of the computer includes a housing10having a flat box shape. A keyboard mount portion11is formed on the upper surface of the housing10. A keyboard12is supported on the keyboard mount portion11.

The display module3includes a display housing15having a flat box shape, and a liquid crystal display panel16housed in the display housing15. The liquid crystal display panel16includes a screen16a. The screen16ais exposed to the outside of the module display3through an opening17opened in the front surface of the display housing15.

As shown inFIG. 1, the housing10contains a circuit module19. The circuit module19comprises a module substrate20. The module substrate20comprises a first substrate21and a second substrate22. The first substrate21is the so-called rigid printed circuit board, which has solidity, whereas the second substrate22is the so-called flexible printed circuit board, which has flexibility.

A slit24, which is a frame-shaped hole made through the first substrate21in its thickness direction, is made in the first substrate21. With the slit24formed therein, a rectangular mount substrate26is formed inside the first substrate21.

The mount substrate26is an example of the part mount portion, and it has a solidity similar to that of the first substrate21. The mount substrate26is surrounded by the slit24, and is isolated from the first substrate21. Further, the mount substrate26includes a first mount surface35and a second mount surface42. The second mount surface42is located on an opposite side to the first mount surface35.

A ball grid array (BGA)30, which is an example of the electronic parts, is mounted on the first mount surface35of the mount substrate26. The BGA30includes four corners30a.

The BGA30includes a plurality of solder balls33arranged in matrix. The solder balls33are an example of connection terminals. The solder balls33are soldered to pads (not shown) provided in the first mount surface35. Further, other electronic parts31such as a capacitor and a resistor are mounted on the first substrate21and the second mount surface42of the mount substrate26.

As shown inFIG. 3, the second substrate22is laminated on the entire area inside the first substrate21and the entire area inside the mount substrate26such as to be across therebetween.

The second substrate22is provided to cross the slit24and to be across between the first substrate21and the mount substrate26. In more detail, the second substrate22is provided from four side edges26aof the rectangular mount substrate26to four side edges21aof the first substrate21which defines the outer peripheral circumference of the slit24. A portion of the second substrate22is exposed to the slit24.

The second substrate22connects the first substrate21to the mount substrate26. With this structure, the mount substrate26is held on substantially the same plane as that of the first substrate21. Since the second substrate22has flexibility, the mount substrate26can be slightly displaced with reference to the first substrate21. It should be noted that the second substrate22may be provided on the entire area of the slit24.

FIG. 4shows a multi-layered structure of the module substrate20before being molded. The first substrate21comprises a first pre-preg member50, a first adhesive layer51, a second adhesive layer52and a second pre-preg member53.

The first pre-preg member50includes a conductor pattern50aformed on one surface and a conductor pattern50bformed on the other surface. The second pre-preg member53includes a conductor pattern53aformed on one surface and a conductor pattern53bformed on the other surface.

The mount substrate26comprises a third pre-preg member54, a third adhesive layer55, a fourth adhesive layer56and a fourth pre-preg member57.

The third pre-preg member54includes a conductor pattern54aformed on one surface and a conductor pattern54bformed on the other surface. The fourth pre-preg member57includes a conductor pattern57aformed on one surface and a conductor pattern57bformed on the other surface.

The second substrate22is interposed between the first adhesive layer51and the second adhesive layer52of the first substrate21, and also between the third adhesive layer55and the fourth adhesive layer56of the mount substrate26.

Further, the second substrate22includes a first surface22aand a second surface22blocated on an opposite side to the first surface22a. A conductor pattern22cis formed on the first surface22aof the second substrate22, and the conductor pattern22cis electrically connected to the pads formed on the mount substrate26.

Next, the method of manufacturing the module substrate20will now be described.

The second adhesive layer52, the second pre-preg member53, the fourth adhesive layer56and the fourth pre-preg member57are overlaid on the first surface22aof the second substrate22. Then, the first adhesive layer51, the first pre-preg member50, the third adhesive layer55and the third pre-preg member54are overlaid on the second surface22bof the second substrate22.

A plurality of guide pins59are inserted to holes, respectively, formed in the first pre-preg member50, the first adhesive layer51, the second substrate22, the second adhesive layer52and the second pre-preg member53for alignment. With the guide pins59, the first pre-preg member50, the first adhesive layer51, the second substrate22, the second adhesive layer52and the second pre-preg member53are overlaid on one another while maintaining predetermined relative positions with each other.

A plurality of guide pins59are inserted to holes, respectively, formed in the third pre-preg member54, the third adhesive layer55, the second substrate22, the fourth adhesive layer56and the fourth pre-preg member57for alignment. With the guide pins59, the third pre-preg member54, the third adhesive layer55, the second substrate22, the fourth adhesive layer56and the fourth pre-preg member57are overlaid on one another while maintaining predetermined relative positions with each other.

After carrying out the alignment as above, all the guide pins59are removed. Then, while maintaining the alignment, the first to fourth pre-preg members50,53,54and57, the first to fourth adhesive layers51,52,55and56and the second substrate22are heated, and are also pressurized in the directed indicated by arrow A inFIG. 4. After that, through various steps including the formation of through holes, a module substrate20as shown inFIG. 3is formed.

It should be noted that the method of manufacturing the module substrate20is not limited to that described above. For example, it is alternatively possible to overlay the first to fourth pre-preg members50,53,54and57and the first to fourth adhesive layers51,52,55and56onto the second substrate22after inserting the guide pins59into the holes made in the second substrate22.

Next, the advantage of the portable computer1having the above-described structure will now be described.

Since the second substrate22, which has flexibility, supports the mount substrate26, the mount substrate26can be slightly displaced with respect to the first substrate21. With this structure, a possible percussive impact applied on the BGA30, which may be created when a percussive impact is applied to the portable computer and the impact is propagated to the circuit module19, can be relaxed.

More specifically, as the mount substrate26flexibly moves to follow the percussive impact applied thereto, the impact propagated to the BGA30can be relaxed. In this manner, it is possible to prevent a defect in the electric connection between the mount substrate26and the BGA30. With this structure, in particular, the stress applied to the corner portions30aof the BGA30, which is one of the main factors for a failure, can be relaxed. Therefore, a defect in the electric connection between the mount substrate26and the BGA30can be effectively prevented.

Further, in case where the module substrate20of the circuit module19is expanded due to heat, the second substrate22is warped by the expanded first substrate21and the expanded mount substrate26. In this manner, the stress applied on the mount substrate26and the BGA30can be relaxed. Therefore, a defect in the electric connection between the mount substrate26and the BGA30caused by thermal expansion can be effectively prevented.

Further, the first substrate21and the mount substrate26are connected to each other via the second substrate22, which is a flexible printed circuit board. With this structure, if such a structure as of this embodiment that can relax the possible impact applied on the BGA30, the degree of freedom in the circuit design of the circuit module19can be retained.

In addition, the other electronic parts31can be mounted on the second mount surface42of the mount substrate26which is located on the opposite side to the BGA30. With this structure, the packaging degree of the circuit module19can be increased.

Next, the second to fifth embodiments of the present invention will now be described with reference to the respective drawings. In these embodiments, structural parts which have the same functions as those of the portable computer1of the first embodiment will be designated by the same reference numerals, and the explanations therefore will be omitted.

FIGS. 5 and 6show the second embodiment of the present invention.

As shown inFIG. 5, a reinforcing portion60is provided at each of the corner portions30aof the BGA30. The reinforcing portions60are each made of a thermosetting adhesive filled between the BGA30and the mount substrate26such as to be across therebetween.

In more detail, as shown inFIG. 6, the reinforcing portions60are made from the side edges30bof the BGA30over to the first mount surface35of the mount substrate25to adhere each of them. The reinforcing portions60harden in the state which they adhere to the BGA30and the first mount surface35, and in this manner, they fixate the BGA30to the mount substrate26. It should be noted that the reinforcing portions60are formed even over to the upper surface30cof the BGA30.

In the portable computer1having the above-described structure, the reinforcing portions60fixate the BGA30to the mount substrate26, and thus the soldered portion between the BGA30and the mount substrate26is reinforced. With this structure, a possible defect of the electrical connection between the BGA30and the mount substrate26can be prevented even more effectively.

It should be noted that the adhesive which forms the reinforcing portions60is not limited to the thermosetting type, but it is alternatively possible to use some other type of adhesive, for example, one which is hardened by ultraviolet rays or hardens along with an elapse of time.

Next, the third embodiment of the present invention will now be described with reference toFIGS. 7 and 8.

As shown inFIG. 7, a plurality of shock absorbing members63are provided between the first substrate21and the mount substrate26to be across therebetween. Each of the shock absorbing members63is formed of, for example, a sheet-like gel which transforms kinetic energy into heat. When kinetic energy is applied to the shock absorbing members63, these members attenuate the kinetic energy by transforming it into heat.

As shown inFIG. 8, each of the shock absorbing members63is adhered to the first mount surface35of the mount substrate26by one end portion63athereof, and also to the upper surface21bof the first substrate21by the other end portion63b. With this structure, the shock absorbing members63cover a part of the slit24.

It should be noted that the arrangement of the shock absorbing members63is not limited to that shown inFIG. 7, but it is alternatively possible to, for example, dispose the shock absorbing members63obliquely and connect the neighboring side edges21aof the first substrate21to each other. Further, it is also possible to provide a single shock absorbing member63larger than the slit24such as to cover the first substrate21, the slit24and the mount substrate26.

Furthermore, the shock absorbing members63may be provided between the second mount surface42of the mount substrate26and the first substrate21. In other words, it suffices only if the shock absorbing members63are formed between at least a part of the first substrate21and at least a part of the mount substrate26to be across therebetween.

In the portable computer1having the above-described structure, the shock absorbing members63are provided between the first substrate21and the mount substrate26to be across therebetween. If the circuit module19is exposed to percussive impact, the shock absorbing members63transform the kinetic energy caused by the impact into heat, thereby relaxing the impact propagated to the BGA30. With this structure, a possible defect of the electrical connection between the BGA30and the mount substrate26can be prevented even more effectively.

Next, the fourth embodiment of the present invention will now be described with reference toFIG. 9.

As shown inFIG. 9, the flexible second substrate22is stacked on a portion inside the first substrate21and a portion inside the mount substrate26, such as to cross the slit24.

The portable computer1having the above-described structure is different from that of the first embodiment only in the respect that the flexible second substrate22is provided on only a portion inside the first substrate21and only a portion inside the mount substrate26. Therefore, the use of the flexible printed circuit board, which is more expansive than the adhesive layer, can be reduced, and therefore the product cost can be decreased.

Next, the fifth embodiment of the present invention will now be described with reference toFIG. 10.

The first substrate21comprises a slit66and a part mount portion67. The slit66is a hole made through the first substrate21in its thickness direction, and it includes first to third portions66a,66band66ceach formed in a liner shape.

The second portion66bextends from an end of the first portion66ain a direction normally crosses the first portion66a. The third portion66cextends from the other end of the first portion66ain a direction normally crosses the first portion66a. With this structure, the second portion66band the third portion66care arranged to be in parallel with each other with an interval therebetween.

The part mount portion67is defined by a region surrounded by the first to third portions66a,66band66cof the slit66from three directions, and it has a rectangular cantilever shape. The BGA30is mounted in the part mount portion67.

The second substrate22is provided to cross the first to third portions66a,66band66cof the slit66. In more detail, the second substrate22is provided from three side edges67aof the part mount portion67to the side edges21aof the first substrate21, which respectively face the side edges67asuch be across therebetween, and a part of the second substrate22is exposed to the slit66. It should be noted that the second substrate22may be provided on the entire area of the slit66.

The part mount portion67is connected to the first substrate21via a continuation portion68. Since the second substrate22has flexibility, the part mount potion67can be slightly displaced with respect to the first substrate21at the continuation portion68as a supporting point.

In the portable computer1having the above-described structure, the second substrate22has flexibility, and therefore the part mount potion67can be slightly displaced with respect to the first substrate21at the continuation portion68as a supporting point. With this structure, if the portable computer1is exposed to a percussive impact, and the impact is propagated to the circuit module19, the impact applied to the BGA30can be relaxed.

More specifically, as the part mount portion67flexibly moves to follow the percussive impact applied thereto, the impact propagated to the BGA30can be relaxed. In this manner, it is possible to prevent a defect in the electric connection between the part mount portion67and the EGA30. With this structure, in particular, the stress applied to the corner portions30aof the BGA30, which is one of the main factors for a failure, can be relaxed. Therefore, a defect in the electric connection between the part mount portion67and the BGA30can be effectively prevented.

Further, in case where the circuit module19is expanded due to heat, the second substrate22is warped by the expanded first substrate21and the expanded the part mount portion67. In this manner, the stress applied on the part mount portion67and the BGA30can be relaxed. Therefore, a defect in the electric connection between the part mount portion67and the BGA30caused by thermal expansion can be effectively prevented.

Further, the first substrate21and the part mount portion67are connected to each other via the continuation portion68and also the second substrate22, which is a flexible printed circuit board. With this structure, if such a structure as of this embodiment that can relax the possible impact applied on the BGA30, the degree of freedom in the circuit design of the circuit module19can be retained.

It should be noted that the shapes of the slit and the part mount portion are not limited to those described above. For example, it is alternatively possible to provide two slits extending in parallel with each other in the first substrate, and define the region interposed between the two slits as the part mount portion. Or it is also possible to provide a slit including a linear portion and another portion extending from one end of the linear portion in a direction normally crossing the portion in the first substrate and define the rectangular region adjacent to this slit as the part mount portion.

Moreover, in the first to fifth embodiments, the BGA is discussed as an example of the electronic parts, but some other type of electronic part may be applied. For example, an electronic part such as a pin grid array (PGA) which includes pin-like connection terminals, or a quad flat package (QFP) including connection terminals extending towards a lateral direction can be used.