Semiconductor device connecting structure, liquid crystal display unit based on the same connecting structure, and electronic apparatus using the same display unit

A semiconductor device connecting structure for connecting a semiconductor IC 7 onto a substrate 13. A bonding layer 31 is placed between the substrate 13 and the semiconductor IC 7 to accomplish adhesion therein. This bonding layer includes an ACF 32 as a bonding material for joining said semiconductor IC 7 onto said substrate 13 and a space 33 formed within the ACF 32. Even if the IC 7 deforms due to heat or the like, the deformation is absorbed by the space a 33, whereupon the connecting conditions of bumps 28, 29 can not be unstable.

TECHNICAL FIELD

The present invention relates to a semiconductor device connecting structure for connecting a semiconductor device onto a substrate (or board), a liquid crystal display unit based upon the semiconductor device connecting structure, and an electronic apparatus using-the liquid crystal display unit.

BACKGROUND ART

In recent years, liquid crystal display units for displaying visible information have come into widespread use for electronic equipment such as navigation systems, televisions, palm-top computers, electronic organizers and portable telephones. In general, these liquid crystal display units are constructed such that a liquid crystal driving IC, i.e., a semiconductor device, is connected to a liquid crystal panel and incidental parts such as a back light and a casing are mounted on the liquid crystal panel. This liquid crystal panel is commonly made in a manner that a liquid crystal is put in between at least two substrates for the liquid crystal, and a polarizing plate, a color filter and others are mounted when necessary.

Many kind of ways of the connection of the liquid crystal driving IC to the liquid crystal panel have been considered, for example, connecting methods based upon a COB (Chip On Board) method, a COG (Chip On Glass) method or the like. According to the COB method, the liquid crystal driving IC is joined through the use of an ACF (Anisotropic Conductive Film) or other joining materials to an insulating substrate having a wiring pattern thereon, and that insulating substrate is connected through a heat seal or the like to the liquid crystal panel.

On the other hand, according to the COG method, the liquid crystal driving IC is directly joined through the use of the ACF or the like to a glass substrate having electrode terminals. In both the COB method and the COG method, a semiconductor device such as the liquid crystal driving IC is connected onto the substrate such as the insulating substrate and the liquid crystal glass substrate.

In the above-mentioned prior connecting methods, the ACF or other joining materials are uniformly placed in between the substrate and the liquid crystal driving IC without making a space therein. For this reason, when the liquid crystal driving IC is joined thereto under pressure, warps take place on the IC itself, or when the liquid crystal driving IC and/or the substrate deform due to the variation of temperature, excessive stresses occur at the bump portions of the liquid crystal driving IC in direct contact with the electrodes on the substrate. As a result, the electrical connecting conditions can become unstable. In addition, for avoiding such problems, the pressure-joining conditions for the liquid crystal driving IC are required to be severely managed within a small tolerance. As a result, a complicated process management is demanded.

Moreover, in the Japanese Unexamined Patent Publication No. 2-42738, there has been disclosed a connecting structure in which, in a COB based packaged printed-circuit board, a flexible bonding layer is placed as a cushioning material between an IC chip and A substrate to improve the reliability of the bond. However, in the case of this prior connecting structure, it is required to provide the flexible bonding layer for exclusive use for the purpose of taking the cushioning action, which leads to higher component cost and manufacturing cost.

Accordingly, the present invention has been developed with a view to eliminating the problems which arise with the prior semiconductor device connecting structure. The object of this invention is to maintain steadily the connecting condition of a semiconductor device to a substrate only by adding an extremely simple construction.

DESCRIPTION OF THE INVENTION

For the purpose described above, in accordance with the present invention, in a semiconductor device connecting structure for joining a semiconductor device onto a substrate according to this invention, there is a bonding layer in between the substrate and the semiconductor device for adhesion of both of them. The bonding layer contains a bonding material for joining the semiconductor device to the substrate and a space(s) formed in the interior of the bonding material.

According to this connecting structure, the space(s) is specially made in the bonding material when conducting the adhesion between the semiconductor device and the substrate, and absorb the deformation of the semiconductor device and others, changing freely in shape in response to the deformation of the substrate or the semiconductor device. In consequence, even in the case of the deformation of the semiconductor device or the substrate, it is possible to prevent excessive loads from applying on the electrode portions of the semiconductor device, so that the electrical connecting condition of the semiconductor device can be maintained steadily in good condition.

The space(s) is formed in the bonding material by pressurizing an IC with a pressurizing head ahd by heating at the same time as described below. When the temperature of the pressurizing head is given to the bonding material, the viscosity of the bonding material rapidly decreases to flow out to the external. In this way the space(s)can be formed. Thus, by forming the space(s) in the bonding material, it is possible to relieve the deformation of the semiconductor device or the substrate.

In the structure described above, as the semiconductor device, an IC chip and an LSI chip can be considered. Further, when supposing a liquid crystal display unit, as the semiconductor device, a liquid crystal driving IC can be considered. As the substrate, an insulating substrate in the COB method, a transparent substrate for a liquid crystal in the COG method, and various substrates corresponding to other connecting methods can be considered. As the bonding material, an ACF (Anisotropic Conductive Film) and a common bonding material can be considered.

The ACF is produced by dispersing conductive particles into a thermoplastic film or a thermosetting resin film, and is a bonding material showing the conductivity in a single direction by receiving the thermocompression bonding.

On the other hand, the common bonding materials have a function to join a semiconductor device to a substrate only mechanically, not electrically.

In the case of using the ACF, the terminals on the substrate and the bumps of the semiconductor device are electrically coupled through the conductive particles to each other. On the contrary, in the case of using the common bonding material, the terminals on the substrate and the bumps of the semiconductor device are directly connected to establish an electrical conduction, and in this state, the semiconductor device is mechanically joined to the substrate by the common bonding material.

Considering the liquid crystal driving IC to be used for a liquid crystal display unit as the semiconductor device, a plurality of bumps are arranged in rows on an active surface of the liquid crystal driving IC. Various ways can be considered for that in-row arrangement. For instance, as shown inFIGS. 2 and 7, a pair of bump strings28,29arranged in rows (two rows in the illustrations) in the longitudinal direction and a pair of bump strings28,28arranged in rows (two rows in the illustrations) in the transverse direction are arranged in a ring-shape. Further, as shown inFIG. 8, a pair of bump strings28,29may be located only in the longitudinal direction or in the transverse direction.

For the connection of the semiconductor device with the foregoing bump arrangement onto the substrate, as shown inFIG. 2, spaces33are formed in an adhesive (bonding material) within an area surrounded by the ring-shaped arranged bumps, or as shown inFIG. 7, spaces33are formed between the respective bumps28,29or outside the bump strings.

The spaces to be formed inside the adhesive can be made as a single space with a large volume, or can be made by disposing a plurality of spaces with small volumes in mutually close conditions.

Preferably, the space rate to the adhesive assumes between 5% and 70%, more preferably between 10% and 30%. This is because, in the case that the space rate is below 5%, it is impossible to absorb the deformation (or stress) of the semiconductor device or the substrates On the contrary, when it assumes more than 70%, the reliability of the connection between the semiconductor device and the substrate (particularly, the terminals formed on the substrate) goes down. Accordingly, if the space(s) is formed at the rate of 5% to 70%, the connection reliability can be obtained. More preferably, if the space rate is set to between 10% and 30%, the structure with improved connection reliability can be formed.

The bonding layer is made of an epoxy-based adhesive. Further, this bonding layer absorbs the deformation of the semiconductor device or the substrate.

Furthermore, in accordance with the present invention, a feature of a connecting method of joining a semiconductor device onto a substrate is that a bonding layer is placed in between the substrate and the semiconductor device to join them to each other, and a pressurizing head heated up to a high temperature is pressed against the semiconductor device to pressurize and heat the mentioned bonding layer for joining the substrate to the semiconductor device, and a space(s) is formed in the mentioned bonding layer. With this construction, the deformation of the semiconductor device or the substrate can be reduced by the space(s) and a connecting structure with a higher reliability can be obtained. In addition, the bonding layer is made from an epoxy-based adhesive.

A liquid crystal display unit according to this invention is a liquid crystal display unit with the above-described semiconductor device connecting structure. In more detail, the liquid crystal display unit according to this invention is composed of a pair of substrates disposed in an opposed relation to each other to interpose a liquid crystal therein, a semiconductor device joined onto at least one of the substrates and a liquid crystal display apparatus with a bonding layer placed in between the substrate and the semiconductor device to join the semiconductor device to the substrate wherein the bonding layer contains an adhesive for adhering the semiconductor device to the liquid crystal holding substrate and a space(s) made in the interior of the adhesive.

As mentioned above, it is preferable that the space rate to the adhesive is set to reach 5% to 70%, more preferably 10% to 30%, so that the semiconductor device and the electrode terminals formed on the substrate can be connected with a high reliability.

Moreover, concrete examples of an electronic apparatus using a liquid crystal display unit according to this invention are various kinds of equipment such as a navigation system, a television, a palm-top computer, an electronic organizer and a portable telephone. More specifically, one of the examples is the electronic apparatus with output terminals for driving a plurality of semiconductors, a liquid crystal display unit connected to these output terminals for driving a semiconductor, and an input unit. The liquid crystal display unit includes a pair of substrates disposed in an opposed relation to each other to interpose a liquid crystal therein, a semiconductor device joined onto at least one of the liquid crystal holding substrates, and a bonding layer placed in between the liquid crystal holding substrate and the semiconductor device to join the semiconductor device to the substrates for liquid crystal. In this case, the bonding layer contains an adhesive for adhering the semiconductor device to the substrates for liquid crystal and a space(s) made in the interior of the adhesive.

DESCRIPTION OF THE BEST MODE OF CARRYING OUT THE INVENTION

FIG. 6shows a portable telephone as one example of electronic apparatus using a liquid crystal display unit according to an embodiment of the present invention. This portable telephone is equipped with an upper housing1and a lower housing2. The upper housing1includes a PCB (Printed Circuit Board) for controlling a keyboard10. In addition, the lower housing2includes a control circuit board3mounting a control LSI and a body board4mounting the circuit board3. A liquid crystal display unit5according to this invention is mounted on the body board4. A plurality of semiconductor driving output terminals6are formed as a wiring pattern on the surface of the body board4. The liquid crystal display unit5has a liquid crystal driving IC7, i.e., a semiconductor device, therein. The liquid crystal driving IC7is electrically connected to the semiconductor driving output terminals6with the liquid crystal display unit5mounted on the body board4. The liquid crystal display unit5and other necessary units are placed within the lower housing2and subsequently the upper housing1is placed thereon from above. In this way a portable telephone is completed. Incidentally, numeral20designates a speaker.

For instance, as shown inFIG. 4, the liquid crystal display unit5includes a liquid crystal panel8, a back light unit9, a shielded case11and an elastic connector12. The liquid crystal panel8includes, as shown inFIG. 3, a first liquid crystal holding substrate13made of a transparent glass and a second liquid crystal holding substrate14made of a transparent glass. A transparent electrode18is formed on an inner surface of the first liquid crystal holding substrate13, whereas a transparent electrode19is formed on an inner surface of the second liquid crystal holding substrate14. Both electrodes are made of an ITO (Indium Thin Oxide) and another transparent conductive material.

Furthermore, polarizing plates16a,16b,serving as polarizing means, are adhered to outer surfaces of the first and second liquid crystal holding substrates13,14, respectively. The first liquid crystal holding substrates13and second liquid crystal holding substrates14are joined in a liquid-proof condition to each other by a ring-like sealing compound17with a certain gap, so-called cell gap. Further, a liquid crystal is sealed in the cell gap. A semiconductor input terminal21is formed at a right-hand end portion on an inner surface of a section13aof the first liquid crystal holding substrate13protruding toward the exterior (the right side inFIG. 3) of the second liquid crystal holding substrate14. The liquid crystal driving IC7as a semiconductor device is directly adhered by a bonding layer31onto the first liquid crystal holding substrate13, whereupon an output bump28of the IC7is connected to the transparent electrode18while an input bump29of the IC7is connected to the semiconductor input terminal21.

Thus, this embodiment provides a liquid crystal display unit, that is, a COG (Chip On Glass) type liquid crystal display unit, where the liquid crystal driving IC7is directly joined to the liquid crystal holding substrate13constituting the liquid crystal panel8.

InFIG. 3, the back light unit9comprises a light guiding member22and a plurality of (for example, 4) LEDs (Light Emitting Diodes)23fixed to a left-hand end portion of the light guiding member22. Also, as shown inFIG. 4, a rectangular-parallelepiped-like guide hole24serving as a guide for the elastic connector12is made in a right-hand end portion of the light guiding member22. As shown inFIG. 3, this guide hole24is made to have a dimension accepting the elastic connector12without making a gap.

The elastic connector12is, as shown inFIG. 5, equipped with an elastic material with an electrical insulation, for example, an elastic proximal section25made of a silicone rubber to have a cross-sectional semi-circular column-like configuration, and a large number of conductive sections26provided in parallel to each other on a semi-circular outer circumferential surface of the elastic proximal section25. An elastic material is placed between the two conductive sections adjacent to each other to form a non-conductive section. The width of the non-conductive section is kept to be 15 μm to 25 μm. In the illustration, reference mark W represents the separation between the adjacent conductive section26, so-called inter-conductive-section pitch, which is commonly set to W=30 μm to 50 μm.

For mounting the liquid crystal display unit according to this embodiment on the body board4of the portable telephone (FIG.6), inFIG. 4, the elastic connector12is inserted into the guide hole24in the light guiding member22, and the back light unit9is placed at a given position on the body board4, and the liquid crystal panel8is placed at a given position on the back light unit9, and the shielded case11is put on the liquid crystal panel8and the back light unit9in a state where a pressurizing member30made of a silicone rubber or another elastic material is interposed therein. And further, as shown inFIG. 3, the body board4and the shielded case11are tightened and fixed to each other by deforming a caulking stopper27.

At this time, the elastic connector12is compressed and deformed elastically in the vertical direction due to the effect of the pressurizing member30, whereupon the conductive sections26(seeFIG. 5) firmly comes into contact with both the semiconductor input terminal21on the liquid crystal panel8side and the semiconductor driving output terminal6on the body board4side owing to the elastic restoring force of the elastic proximal section25.

Incidentally, in terms of the way of compressing the elastic connector12, it is also possible that, in place of preparing a dedicated component such as the pressurizing member30, the corresponding portion of the shielded case11is deformed to protrude inwardly to form a rib at that portion of the shielded case11so that the rib compresses the elastic connector12.

On the completion of the above-mentioned liquid crystal display unit attachment, an electric signal and a liquid crystal driving power are supplied from the control circuit board3(FIG.6), through the semiconductor driving output terminal6, the elastic connector12(FIG. 3) and the semiconductor input terminal21, to the liquid crystal driving IC7. According to that, the liquid crystal driving IC7controls the applied voltages to the electrodes18,19. Due to this voltage control, a visible image appears on an effective display region of the liquid crystal panel8.

In this embodiment, since only by disposing the elastic connector12between the semiconductor input terminal21on the liquid crystal panel8side and the semiconductor driving output terminal6on the portable telephone side, both of them can be electrically connected to each other, the assembling work becomes extremely easy. In addition, since the elastic connector12is put within the guide hole24, when a force works on the elastic connector12, the elastic connector12warps without deformation such as buckling. Therefore, the electrical connecting condition between the semiconductor input terminal21and the semiconductor driving output terminal6can always be maintained steadily.

In this embodiment, as shown inFIG. 1, the liquid crystal driving IC7is adhered onto the first liquid crystal substrate13by the bonding layer31. The bonding layer31is composed of an ACF (Anisotropic Conductive Film)32serving as an adhesive and a plurality of spaces33formed inside of the ACF32. The ACF32is formed by dispersing a large number of conductive particles34into an adhesive-property resin film, and the output bump28of the IC7is electrically connected through the conductive particles34to the transparent electrode18, whereas the input bump29is electrically connected through the conductive particles34to the semiconductor input terminal21. Further, the bump28, the bump29and the portions between the terminals are held in a insulated condition by an adhesive-property resin.

FIG. 2shows the joining portion of the liquid crystal driving IC7viewed from the direction indicated by an arrow A in FIG.1. Obviously from the illustration, the plurality of spaces33are positioned to be close to each other within an area surrounded by the bumps28,29arranged in two rows in the longitudinal direction and the bumps28,28arranged in two rows in the transverse direction, that is, within an area surrounded by the plurality of bumps28,29arranged to make a ring-like configuration. Incidentally, althoughFIG. 2is illustrated with the bumps28and29omitted, bumps are formed at the circumferential end portions of the substrates as well as illustrated.

In general, for joining the liquid crystal driving IC7onto the substrate13, the liquid crystal driving IC7is heated and pressed against the substrate13under a given pressure with the ACF32interposed between the IC7and the substrate13. In this case, preferably, the ACF32is made of an epoxy-based adhesive. Particularly, if it is formed with a molecule including an epoxy radical at a relatively. small molecular weight, an excellent adhesive property can be obtained.

At this heating and pressurizing processing, the liquid crystal driving IC7may warp, and when it warps, an excessive stress may occur in the connecting portions of the bumps28and29, causing the electrically connecting condition to be unstable. Further, when the temperature varies in the liquid crystal driving IC7, the IC7and/or the substrate13may deform, causing the connecting conditions of the bumps28and29to be unstable.

On the other hand, if the spaces33are provided inside the ACF32like this embodiment, when the liquid crystal driving IC7deforms, the spaces33freely can deform in accordance with the deformation of IC7and can absorb the deformation of the IC7. As a result, the excessive stress on the connecting portions of the bumps28,29can be prevented.

The way of forming the spaces33inside of the ACF32is not limited to a specific method. For example, if the pressure bonding condition for joining the liquid crystal driving IC7onto the substrate13is set to an appropriate condition for the liquid crystal driving IC to be used, the spaces33can be produced. The following requirements are listed as one example of the pressure-bonding condition.

InFIG. 2, this IC has a dimension of L×W=7.7 mm×2.8 mm, and the number of bumps is approximately 200 and the bump size is 80 μm ×120 μm.

In the case that the ACF is pressurized and heated by pressing the IC7with the pressurizing head heated up to a high temperature, if the temperature of the pressurizing head is set to 260 to 360° C. (central temperature=approximately 300° C.), the aforesaid ACF temperature can be obtained.

When the liquid crystal driving IC7was joined to the substrate13under the aforesaid (1) to (5) requirements, the plurality of spaces33shown inFIG. 2were formed inside the ACF32.

These spaces are formed in the ACF when, in the heating and pressurizing processing, the viscosity of the adhesive rapidly decreases at the initial-process heating (process for approximately 0.1 to 0.5 second) so that a portion of the bonding layer flows out toward the exterior of the semiconductor device. The space rate to the ACF is preferable to be in a range of 5% to 70%. This is because, in the case that the space rate is below 5%, the stress on the ACF can not be absorbed. On contrary, when the space rate exceeds 70%, the space rate is too high to connect the terminals (or the electrodes) to each other with a high reliability. Accordingly, the space rate is preferable to be set in this range. However, in order to connect with a particularly high reliability, it is preferable that the space rate is set in a range of 10% to 30%. When the space rate is set to be in this range, the internal stress can be reduced without losing the adhesion strength, connecting with a high reliability.

FIG. 7shows a modification of the method of making the spaces33. The difference of this modification from the above-described embodiment shown inFIG. 2is that, in addition to providing the spaces33between the bump strings28,29in the longitudinal direction and between the bump strings28,28in the transverse direction, the spaces33are formed between the respective bumps and outside the pair of bump strings. Even in the case of disposing the spaces33in this way, the connection of the semiconductor devices to the substrate can be maintained steadily. Incidentally, althoughFIG. 7is illustrated with the bumps28and29omitted, bumps are formed around the end portions of the substrate as well as the illustrated bumps28and29. Alternate long and short dash lines indicates the bumps. Likewise,FIGS. 8 and 2are illustrated with the bumps omitted, but the same bumps as the illustrated bumps28,29are formed around the substrate end portions.

FIG. 8shows a modification of the bump arrangement. The difference of this modification from the above-described embodiment shown inFIG. 2is that, instead of arranging the plurality of bumps28,29to make a ring-like configuration, the bumps are disposed in rows only in the longitudinal direction. In this modification, a plurality of spaces33are provided between the bump strings28,29. However, instead of or in addition to these spaces, the spaces33can also be provided between the respective bumps and/or outside the bump strings.

The present invention has been described with some preferred embodiments, but this invention is not limited to those embodiments, and includes various changes within the technical ranges described in the claims.

For instance, the semiconductor connecting structure and the liquid crystal display unit according to this invention are applicable to various electronic apparatus other than a portable telephone, such as a navigation system, a television, a palm-top computer and an electronic organizer, which require a visible information display.

FIGS. 3to5indicate the embodiments which this invention is applied to the COG (Chip On Glass) type liquid crystal display unit. However, this invention is also applicable to the other types of liquid crystal display units, for example, a COB (Chip On Board) type liquid crystal display unit.

Furthermore, in the embodiments shown inFIGS. 3to5, the output terminal6on the portable telephone side as an electronic apparatus and the input terminal21on the liquid crystal panel8side are electrically connected to each other by the elastic connector12. However, the connecting method for connecting both of them is not limited to this. For example, this invention-includes a case of connecting both terminals by using an FPC (Flexible Printed Circuit).

Still further, in the embodiment shown inFIG. 1the bonding layer31is constructed with the ACF32containing the conductive particles34. Instead, it can be made by using an adhesive which does not contain conductive particles. In this case, spaces33are formed inside the adhesive. In addition, in this case, the bumps for the liquid crystal driving IC7are directly connected to the electrode terminals on the liquid crystal panel side.