JP2013236175A - Piezoelectric vibration device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric vibration device which achieves high airtight reliability and reduces the costs.SOLUTION: A crystal oscillator 1 has a structure where a container 2 is joined to a lid 4. A plating layer (a second joining layer 82) is formed at a joining region between the container 2 and the lid 4, and an alloy layer (a first joining layer 81) corresponding to the plating layer is formed on the lid. A first metal layer 822 in the second joining layer 82 is formed so as to have the largest thickness in the second joining layer, and a second metal layer 823 is made of a metal having low wettability observed during fusing with the first joining layer 81. A third metal layer 825 is made of a metal that is the same kind as one of the metals forming the first joining layer 81. A diffusion inhibition layer 824 is provided between the second metal layer 823 and the third metal layer 825. At least the third metal layer 825 and the first joining layer 81 are fused to be integrated thereby joining the container 2 to the lid 4.

Description

  The present invention relates to a piezoelectric vibration device used for communication equipment and the like.

  Piezoelectric vibration devices typified by quartz resonators are widely used in mobile phones and mobile communication devices. For example, a crystal resonator includes a crystal vibrating piece, a container having a recess for housing the crystal vibrating piece, and a lid that hermetically seals the recess by joining the container. The container and the lid are joined in a heated atmosphere in a state where a metal film formed on the upper surface of the bank portion surrounding the recess and a metal film (joint material made of brazing material) formed on the lid are in contact with each other. This is done by melting and integrating these metal films below. For example, Patent Literature 1 discloses a crystal resonator that performs hermetic sealing by melting metal.

JP 2006-287423 A

  In the hermetic sealing of the container and the lid by melting the metal, for example, a gold plating layer is used for the metal film formed on the container side, and a gold-tin alloy is used for the metal film formed on the lid side. There is a method of joining a container and a lid by using it as a joining material.

In the above-described method of joining the container and the lid, when the gold plating layer on the container side and the gold-tin alloy on the lid side are in contact with each other and heated at a predetermined temperature to melt these metals, May be taken up (diffused) into the gold-tin alloy, and so-called "gold erosion" may occur.
Recently, due to the miniaturization of the piezoelectric vibration device, the width of the bank is extremely narrow, and the width of the metal film formed on the upper surface of the bank is also very narrow. In order to ensure airtightness, the metal film formed on the upper surface of the bank portion needs to be thick to some extent.

  The diffusion of gold into the gold-tin alloy requires a longer time for the gold in the gold plating layer to diffuse in the vertical direction as the thickness of the gold plating layer increases, so that the molten gold plating layer flows in the horizontal direction. It becomes difficult. That is, the diffusion of gold in the vertical direction is superior to the diffusion in the horizontal direction, and the gold-tin alloy that has taken in gold by melting is likely to stay on the lid side (see FIG. 6). As a result, as shown in FIG. 6, the molten gold-tin alloy (reference numeral 8) is less likely to flow to the sealing region (upper surface indicated by reference numeral 240) on the container side (reference numeral 2). If the thickness of the gold plating layer is made too thin in order to prevent this phenomenon, even if the above problem is improved, there arises a problem that the characteristics of the piezoelectric vibrating device deteriorate.

  Moreover, when a nickel layer exists in the lower layer of the said gold plating layer, nickel becomes easy to spread | diffuse in a gold plating layer by heat processing. When the gold plating layer in which nickel is diffused and the gold-tin alloy are mixed by melting, the wettability with respect to the metal film formed on the upper surface of the bank portion of the container is lowered. As a result, the molten gold-tin alloy does not spread sufficiently to the sealing region, and there is a possibility that problems such as poor airtightness and reduced bonding strength may occur. Further, since the gold plating layer formed on the container side needs to be in a thick film state to some extent, the cost becomes high.

  The present invention has been made in view of this point, and an object of the present invention is to provide a piezoelectric vibration device that has high hermetic reliability and can reduce costs.

In order to achieve the above object, the present invention provides a piezoelectric vibration device in which a container for accommodating an electronic component element is joined to a lid,
A plating layer formed of a laminated film of a plurality of different metals is formed in the bonding region of the container with the lid,
An alloy layer corresponding to the plating layer is formed on one main surface of the lid,
The plating layer is composed of a first metal layer, a second metal layer, and a third metal layer in order from the lowest layer side,
The first metal layer is formed in the thickest film in the plating layer,
The second metal layer is made of a metal having low wettability when melted with the alloy layer,
The third metal layer is a metal of the same kind as one of the metals constituting the alloy layer,
Between the second metal layer and the third metal layer, there is provided a diffusion suppression layer for suppressing metal diffusion between the second metal layer and the third metal layer,
At least the third metal layer and the alloy layer are integrated by melting, so that the container and the lid are joined.

  According to the said invention, the metal fuse | melted at the time of sealing can be rapidly distribute | arranged to the sealing area | region of a container and a lid | cover. This is due to the following reason. The plating layer is formed in a bonding region (sealing region) with the lid, and the uppermost layer of the plating layer is a third metal layer. The third metal layer is formed thinner than the first metal layer in the plating layer. A diffusion suppression layer is formed between the second metal layer and the third metal layer.

  The third metal layer is the uppermost layer of the plating layer and is easily diffused into the alloy layer because it is the same kind of metal as one of the metals constituting the alloy layer. The diffusion suppressing layer can suppress the diffusion of the second metal layer having low wettability with the alloy layer into the third metal layer. This is because the wettability of the alloy layer with respect to the third metal layer does not decrease, so that the molten alloy layer is arranged to slide with respect to the third metal layer. That is, the third metal is formed by forming a plating layer that needs to maintain a thick film state to a certain degree by a laminated film of a plurality of different metals and setting the first metal layer to be the thickest in the plating layer. The thickness of the layer can be reduced to such an extent that the characteristics of the piezoelectric vibration device are not deteriorated. This is because the diffusion suppression layer exists between the second metal layer and the third metal layer.

  As a result of reducing the thickness of the third metal layer, it is possible to shorten the diffusion of the metal of the plating layer into the alloy layer, that is, the time for the metal of the plating layer to diffuse in the vertical direction. As a result, the alloy layer that has taken in the metal of the plating layer by melting is less likely to stay on the lid side, and the molten alloy can be quickly disposed on the container side (sealing region).

  In order to achieve the above object, in the lid, an inclined surface inclined inward from the side surface of the lid is formed on the periphery of the main surface joined to the container, and the alloy is formed from the inclined surface to the diffusion suppression layer. A meniscus made of a melt of the layer and the plating layer may be formed.

  According to the said structure, the inclined surface inclined inward from the side surface of the lid | cover forms, and it becomes easy to form the meniscus of a molten metal from the said inclined surface to the said diffusion suppression layer. By forming the meniscus, the area wetted by the molten metal is expanded, so that more reliable hermetic sealing can be performed. At this time, according to the configuration of the present invention, the alloy layer that has taken in the third metal layer by melting is prevented from staying on the inclined surface side of the lid, and the molten alloy is quickly distributed to the sealing region on the container side. can do. As a result, the melted alloy can be sufficiently distributed to the sealing region, so that it is possible to prevent a hermetic failure and a decrease in bonding strength.

  As described above, according to the present invention, it is possible to provide a piezoelectric vibration device that has high hermetic reliability and can reduce the cost.

Schematic cross-sectional view of a crystal resonator showing an embodiment of the present invention 1 is an exploded schematic view of a crystal resonator showing an embodiment of the present invention. Part A enlarged view of FIG. B part enlarged view of FIG. The enlarged schematic diagram of the junction area | region of the crystal oscillator which shows embodiment of this invention Enlarged schematic diagram after bonding of conventional crystal unit

  Hereinafter, a crystal resonator will be described as an example of a piezoelectric vibration device, and will be described with reference to the drawings. The crystal resonator 1 according to the embodiment of the present invention includes a container 2 having a recess 20, a crystal vibrating piece 3 bonded to the inside of the recess 20 via a bonding member 6, and a lid 4 that seals the recess 20. It is a major component. The quartz crystal resonator element 3 is accommodated in an internal space 9 created by joining the lid 4 and the container 2 via the joining material 8 and is protected from the external environment.

  In FIG. 1, the container 2 is a box-shaped body made of borosilicate glass as a base material and has a substantially rectangular shape in plan view. The container 2 has a recess 20 for accommodating the crystal vibrating piece and an annular bank portion 24 surrounding the recess 20. A step portion 25 on which the crystal vibrating piece is mounted is formed along the entire short side of the recess portion 20 in the recess portion 20 that is substantially rectangular in plan view. A thinner region than the step portion 25 is an inner bottom surface 21 of the recess. The recess 20 is formed into a substantially rectangular shape in plan view by using a photolithography technique and wet etching on a glass wafer. In FIG. 1, the side surface of the region dug by wet etching is an inclined surface because the base material of the container is glass.

  As shown in FIG. 1, an internal wiring pattern 50 is formed in the recess 20 from the inner bottom surface 21 to the stepped portion upper surface 250. A pair of mounting pads 5, 5 are formed at the end of the stepped upper surface 250 of the internal wiring pattern 50, and one end side of the crystal vibrating piece 3 is cantilevered via the bonding member 6 on the mounting pad 5. Is done. In the present embodiment, conductive bumps (bumps made of gold) are used for the bonding member 6.

  A pair of penetrating electrodes (not shown) is formed on a container base portion (denoted as a bottom plate portion 23 for convenience of explanation) sandwiched between the inner bottom surface 21 of the recess and the outer bottom surface 22 of the container. In the pair of through electrodes, a sputtered film is deposited on a pair of through hole inner walls penetrating one main surface (inner bottom surface 21) and the other main surface (outer container bottom surface 22) of the bottom plate portion 23, and inside the sputtered film. It has a structure filled with resin material.

  A pair of external connection terminals 7 and 7 connected to an external substrate, an external wiring pattern (not shown), and a resin pattern (not shown) made of a resin material are formed on the outer bottom surface 22 of the container. The pair of mounting pads 5 and 5 are electrically connected to the internal wiring pattern 50, the pair of penetration electrodes (not shown) and the pair of external connection terminals 7 and 7 via the external wiring pattern, respectively. ing.

  Although not shown in FIGS. 1 and 2, the sputtered film is formed around the end of the through hole of the inner bottom surface 21 of the recess, the inner wall surface of the through hole, and the outer bottom surface 22 of the container. Here, the sputtered film is a film formed by sputtering. In the present embodiment, the sputtered film has a two-layer structure in which a sputtered film made of Cu is laminated on a sputtered film made of Mo, and a part of the sputtered film is an internal wiring pattern 50.

  In FIG. 1, a quartz crystal vibrating piece 3 is a quartz plate having a substantially rectangular shape in plan view cut by AT cut. A pair of excitation electrodes are formed in the center of the front and back main surfaces of the crystal vibrating piece 2 so as to face each other (not shown). An extraction electrode (not shown) is led out from each of the pair of excitation electrodes to one short side of the quartz crystal vibrating piece, and a connection electrode (not shown) is formed at each end of the extraction electrode.

  The pair of connection electrodes are conductively bonded to each other via a bonding member 6 so as to correspond to the pair of mounting pads 5 and 5 of the container 2. In the present embodiment, a plating bump made of gold is used for the bonding member 6, and is formed in advance on each of the pair of connection electrodes of the crystal vibrating piece 3. Then, after the crystal vibrating piece 3 is positioned and mounted on the mounting pad 5 so that the pair of plating bumps correspond to the pair of mounting pads 5 and 5 of the container 2, the crystal is crystallized by the FCB (Flip Chip Bonding) method. The vibrating piece 3 is joined to the container 2. The joining of the crystal vibrating piece 3 and the container 2 is not limited to the FCB method. For example, a conductive adhesive is used as a joining member and the conductive adhesive is joined by heating and curing. A joining method may be used. Further, the application of the present invention is not limited to the quartz-crystal vibrating piece cut by the AT cut, and may be a quartz-crystal vibrating piece having other cutting angles, for example, a tuning-fork type quartz vibrating piece. The present invention can also be applied to piezoelectric vibrating pieces other than the quartz vibrating piece.

  In FIG. 1, the lid 4 has a substantially rectangular shape in plan view. One main surface 41 of the lid 4 is a flat surface, and the other main surface 42 is formed with an annular wall 43 projecting downward at the peripheral edge. Both side surfaces 431 and 432 of the wall portion 43 are formed in a tapered shape. The outer surface 431 of the wall portion 43 is an inclined surface that is inclined inwardly (inner space side) from the outer surface 44 of the lid. Such a shape is formed by wet etching.

  The lid 4 and the container 2 are joined via the joining material 8, but in the state before joining, as shown in FIG. 2, the lid 4 has a first joining layer 81 on the upper surface of the wall 43, and the container 2. A second bonding layer 82 is formed on the top surface 240 of the bank portion.

As shown in FIG. 3, the first bonding layer 81 formed on the wall portion 43 of the lid 4 extends from the wall portion upper surface (top surface) 430 to the wall portion outer surface 431. The first bonding layer 81 has a configuration in which an alloy layer 812 is formed on a base layer 811 and an extremely thin strike plating layer 813 is formed on the alloy layer 812. In this embodiment, the underlayer 811 has a two-layer structure in which a sputtered film made of Cu is laminated on a sputtered film made of Ti. The alloy layer 812 is a gold-tin alloy (AuSn), and gold is higher in content than tin and is configured at a predetermined weight ratio. This alloy layer 812 serves as a bonding material for bonding the container 2 and the lid 4. The entire thickness of the first bonding layer 81 is about 0.006 mm, the thickness of the alloy layer is about 0.005 mm, and the strike plating layer is about 0.001 mm.
Note that the overall thickness of the first bonding layer 81 is not limited to the above thickness, and may be thinner than 0.006 mm. In FIG. 3, the base layer 811 is exaggerated and displayed thick, but this is for convenience of explanation, and is actually formed in a very thin film (the same applies to the base layer 821 in FIG. 4 described later). ).

  The strike plating layer 813 shown in FIG. 3 is made of Au and is formed by an electrolytic plating method. The strike plating layer 813 is the same kind of metal (Au) as the third metal layer of the uppermost layer of the plating layer of the container 2 and functions as an antioxidant film. Further, the strike plating layer 813 is also used to improve the adhesion with the alloy layer 812. In this embodiment, the strike plating layer is formed on the alloy layer, but the strike plating layer may not be formed and the alloy layer may be the uppermost layer.

  In FIG. 4, the upper surface 240 of the bank portion 24 is a flat surface, and a second bonding layer 82 made of a plurality of different metals is formed. The second bonding layer 82 is formed in an annular shape on the top surface 240 of the bank portion, and the layer configuration of the second bonding layer 82 is the same as the film configuration of the internal wiring pattern 50 except for the periphery of the end portion of the through hole described above. It has become.

  The second bonding layer 82 has a structure in which a first metal layer 822, a second metal layer 823, a diffusion suppression layer 824, and a third metal layer 825 are stacked in this order on the base layer 821. In this embodiment, the underlayer 821 has a two-layer structure in which a sputtered film made of Cu is laminated on a sputtered film made of Mo. The first metal layer 822 is a Cu plating layer, the second metal layer 823 is a Ni plating layer, and the diffusion suppression layer 824 is a Pd (palladium) plating layer, and the third metal layer 825 is an Au plating layer. All of these plating layers are formed by electrolytic plating. In this embodiment, the total thickness of the plating layer is about 0.006 mm, the thickness of the first metal layer 822 is about 0.0044 mm, the thickness of the second metal layer 823 is about 0.001 mm, and diffusion suppression is performed. The thickness of the layer 824 is about 0.0001 to 0.0003 mm, and the thickness of the third metal layer 825 is about 0.0001 to 0.0003 mm.

  In the present embodiment, the first metal layer 822 is formed as the thickest film in the second bonding layer 82. In this embodiment, Cu plating is used as the first metal layer 822. By using Cu plating for the first metal layer 822 and forming the Cu plating layer in the thickest film state in the second bonding layer 82, a large heat capacity can be obtained with Cu, which is a metal with good thermal conductivity. Can be secured. That is, the heat of the heating atmosphere at the time of bonding is quickly conducted to the second metal layer side by the first metal layer 822, and the temperature of the entire second bonding layer 82 can be quickly raised. Thereby, melting of the third metal layer 825 and the alloy layer 812 can be accelerated. By accelerating the melting of the third metal layer 825 and the alloy layer 812, retention of the alloy layer 812 that has taken in the third metal layer 825 by melting on the lid side can be suppressed.

  Further, the following effects can be obtained by forming the first metal layer 822 in the thickest film in the second bonding layer 82. For example, when performing temporary bonding (so-called FCB method (Flip Chip Bonding)) by metal diffusion using ultrasonic waves, the lid and the container are made to be ductile and malleable, such as Cu and Ag, as the first metal layer 822. By using a rich metal material, it is possible to perform more reliable temporary bonding. This is because Cu or Ag formed in a thick film state has a buffering function against a load applied at the time of joining by the FCB method. Further, in the state after the lid and the container are joined, the stress applied to the joining region due to the thermal expansion of the lid and the container can be dispersed by Cu or Ag formed in a thick film state.

  In this embodiment, a Cu plating layer is laminated on a sputtered film made of Cu. That is, for the first metal layer, the same kind of metal as that of the uppermost layer of the base layer 821 is used from the viewpoint of adhesion to the base layer. However, the present invention is not limited to the above combinations and can be applied to other combinations. For example, the uppermost layer of the base layer 821 may be an Ag sputtered film, and the first metal layer 822 may be an Ag plated layer.

  For the second metal layer 823, a metal (Ni) having low wettability when melted with the alloy layer 812 (AuSn) of the first bonding layer 81 formed on the lid is used. In this embodiment, it is difficult to directly form an Au plating layer (third metal layer 825) on the first metal layer 822 made of Cu plating by an electrolytic plating method. The metal layer 823) is formed on the first metal layer 822. Here, if an Au plating layer (third metal layer 825) is formed on the Ni plating layer, Ni diffuses into the Au plating layer due to heat generated when the lid and the container are joined. When the Au plating layer in which Ni is diffused and AuSn of the lid are mixed by melting, the wettability with respect to the metal film in the sealing region is lowered. For this reason, a diffusion suppression layer 824 for suppressing the mutual diffusion of Ni and Au is provided between the Ni plating layer and the Au plating layer.

  On the Ni plating layer (second metal layer 823), a diffusion suppression layer 824 made of Pd is formed. An Au plating layer (third metal layer 825) is formed on the diffusion suppression layer 824. The diffusion suppression layer 824 serves as a seed layer for forming the third metal layer 825, and between the second metal layer 823 (Ni) and the third metal layer 825 (Au). It has a function to suppress metal diffusion. As the diffusion suppressing layer 824, an Au strike plating layer can be used in addition to the Pd plating layer.

  By using the layer configuration as described above, the amount of Au used can be greatly reduced as compared with the case where the plating layer is formed of a single layer (excluding the base layer) made of a gold plating layer. As a result, the manufacturing cost of the piezoelectric vibration device can be reduced.

  In the present embodiment, the lid 4 and the container 2 are joined in a heated atmosphere in a state where the lid-side first joining layer 81 and the container-side second joining layer 82 are positioned and arranged to correspond to each other. Done. Specifically, the first bonding layer 81 and the second bonding layer 82 are 300 to 320 ° C. in a state where the strike plating layer 813 which is the uppermost layer of each bonding layer and the third metal layer 825 are in contact with each other. Bonding is performed by heating in a temperature environment.

  The state after the lid 4 and the container 2 are joined is as shown in the schematic diagram of FIG. The third metal layer 825 (Au) is diffused and integrated into the alloy layer 812 by heating and melting. In FIG. 5, this integrated part is shown as a molten alloy layer 83. As shown in FIG. 5, the presence of the diffusion suppression layer 824 can suppress the diffusion of the second metal layer 823 and the first metal layer 822 to the upper layer side than the diffusion suppression layer 824. In addition, the second metal layer 823 and the first metal layer 822 below the diffusion suppression layer 824 have a melting point higher than the ambient temperature and thus do not melt. Of the second bonding layer 82, not only the uppermost third metal layer but also other metal layers may be integrated with the alloy layer 812 by heating and melting.

  According to the embodiment of the present invention, the metal melted at the time of sealing can be quickly arranged in the sealing region between the container 2 and the lid 4. This is due to the following reason. The second bonding layer 82 is formed in a bonding region (sealing region) with the lid, and the uppermost layer of the second bonding layer 82 is a third metal layer 825. The third metal layer 825 is formed thinner than the first metal layer 822. A diffusion suppression layer 824 is formed between the second metal layer 823 and the third metal layer 825.

  Since the third metal layer 825 is the uppermost layer, it is easy to diffuse into the alloy layer 812. The diffusion suppression layer 824 can suppress the diffusion of the second metal layer 823 having low wettability with the alloy layer 812 into the third metal layer 825. This is because the wettability of the alloy layer with respect to the third metal layer does not decrease, so that the molten alloy layer is arranged to slide with respect to the third metal layer. That is, the second bonding layer 82 that needs to maintain a thick film state to some extent is configured by a laminated film of a plurality of different metals, and the first metal layer 822 is set to be the thickest in the second bonding layer 82. Thus, the thickness of the third metal layer 825 can be reduced to such an extent that the characteristics of the crystal resonator are not deteriorated. This is because the diffusion suppression layer 824 exists between the second metal layer 823 and the third metal layer 825.

  As a result of thinning the third metal layer 825, diffusion of the third metal layer 825 into the alloy layer 812, that is, time for Au of the Au plating layer to diffuse vertically upward can be shortened. . As a result, the AuSn alloy that has taken in the Au of the third metal layer 825 by melting is less likely to stay on the lid side, and the molten alloy can be quickly disposed on the container side (sealing region).

  Further, according to the above configuration, the lid 4 is formed with the wall outer surface 431 formed of an inclined surface inclined inward (internal space 9) from the lid outer surface 44. As a result, a meniscus M of molten metal is easily formed from the inclined surface to the diffusion suppression layer 824. By forming the meniscus, the area wetted by the molten metal is expanded, so that more reliable hermetic sealing can be performed. At this time, with the configuration of the present invention, the alloy layer 812 that has taken in the third metal layer 825 by melting is prevented from staying on the inclined surface side (lid outer surface 431) of the lid, and the molten alloy is removed from the container side. Can be quickly arranged in the sealing region. As a result, the melted alloy can be sufficiently distributed to the sealing region, so that it is possible to prevent a hermetic failure and a decrease in bonding strength.

  In the embodiment of the present invention, a quartz crystal resonator element is taken as an example of an electronic component element, and a crystal resonator in which the quartz crystal resonator element is accommodated is described. However, in addition to the quartz crystal resonator element, an IC, a thermistor, etc. The present invention can also be applied to a crystal oscillator on which elements are mounted, a crystal filter, or the like.

  The present invention can be implemented in various other forms without departing from the spirit or main features thereof. Therefore, the above-described embodiment is merely an example in all respects and should not be interpreted in a limited manner. The scope of the present invention is indicated by the claims, and is not restricted by the text of the specification. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

  It can be applied to mass production of piezoelectric vibration devices.

DESCRIPTION OF SYMBOLS 1 Quartz crystal resonator 2 Container 3 Crystal vibrating piece 4 Lid 8 Bonding material M Meniscus 24 Embankment 43 Wall portion 81 First bonding layer 812 Alloy layer 813 Strike plating layer 82 Second bonding layer 822 First metal layer 823 Second Metal layer 824 Diffusion suppression layer 825 Third metal layer 83 Alloy layer after melting

Claims (2)

A container for accommodating an electronic component element is a piezoelectric vibration device joined to a lid,
A plating layer formed of a laminated film of a plurality of different metals is formed in the bonding region of the container with the lid,
An alloy layer corresponding to the plating layer is formed on one main surface of the lid,
The plating layer is composed of a first metal layer, a second metal layer, and a third metal layer in order from the lowest layer side,
The first metal layer is formed in the thickest film in the plating layer,
The second metal layer is made of a metal having low wettability when melted with the alloy layer,
The third metal layer is a metal of the same kind as one of the metals constituting the alloy layer,
Between the second metal layer and the third metal layer, there is provided a diffusion suppression layer for suppressing metal diffusion between the second metal layer and the third metal layer,
A piezoelectric vibration device characterized in that at least the third metal layer and the alloy layer are integrated by fusion so that a container and a lid are joined.   In the lid, an inclined surface inclined inward from the side surface of the lid is formed on the periphery of the main surface joined to the container, and the melt of the alloy layer and the plating layer extends from the inclined surface to the diffusion suppression layer. The piezoelectric vibration device according to claim 1, wherein a meniscus made of is formed.

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