JP2006279483A - Surface acoustic wave device of surface mount type - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small-sized, low-profile and low-cost surface acoustic wave (SAW) device of a resin seal type for employing CSP structure without deteriorating moisture resistance. <P>SOLUTION: The surface acoustic wave device 1 is provided with: a mount board 2 including a single layer ceramic substrate 3, wiring patterns 5, mount electrodes 4, and inner conductors 6 each making conductive the mount electrode 4 and the wiring pattern 5; a SAW chip 25 including a piezoelectric substrate 8, IDT electrodes 17, and connection electrodes 16; and a sealing resin 20 for forming a hermetic space S between the IDT electrodes and the mount board. Embedded positions of the inner conductors are configured so that the positions are located within the width of a skirt part of the sealing resin for configuring an outer hull of the hermetic space, part of the wiring patterns including upper ends of the inner conductors is covered with an insulation coat layer containing the same principal constituent as that of the single layer ceramic substrate, and at least part of the insulation coat layer corresponding to the upper end of the inner conductor is covered with the sealing resin. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention provides a surface acoustic wave device having a structure in which a surface acoustic wave chip is mounted on a mounting substrate using bumps and then the surface acoustic wave chip is sealed with a resin, and a hole penetrating the mounting substrate is filled. The present invention relates to a surface-mount type surface acoustic wave device that eliminates a problem that causes an internal conductor to impair airtightness in a surface acoustic wave chip.

A surface acoustic wave device (SAW device) has a configuration in which an IDT (interdigital transducer) electrode composed of comb-like electrode fingers is disposed on a piezoelectric substrate such as a quartz crystal. For example, by applying a high frequency electric field to an IDT electrode Filter characteristics are obtained by exciting a surface acoustic wave and converting the surface acoustic wave into a high-frequency electric field by a piezoelectric action.
With the generalization of small packaging technology called CSP (Chip Size Package) in semiconductor parts, SAW devices are also easy to miniaturize and from the viewpoint of improving productivity by batch manufacturing methods. Production methods using CSP technology have been introduced. In the CSP technology, a sealing method using a resin is often used.
FIG. 3 shows an example of a SAW device having a CSP structure according to the prior art (for example, WO 97/02596, JP-A-9-162690).
This SAW device 101 is a mounting substrate comprising an insulating substrate (single layer alumina ceramic substrate) 103, an external electrode 104 for surface mounting provided on the bottom of the insulating substrate 103, and a wiring pattern 105 provided on the top surface of the insulating substrate. 102, a SAW chip 115 comprising a piezoelectric substrate 118 provided on the lower surface with connection pads 116 electrically connected to the wiring pattern 105 via conductor bumps 110, and an IDT electrode 117, and an upper surface of the wiring pattern 105 And a resin 120 that is coated and integrated with the side surface and the upper surface of the SAW chip 115. The resin 120 is coated and formed by screen printing or the like so that an airtight space S for SAW propagation that is not filled with resin is secured between the lower surface of the SAW chip 115 and the upper surface of the mounting substrate 102.

By the way, when the SAW device 101 has a minute dimension of several millimeters in length and width, the SAW device 101 is mass-produced by batch processing using a large-area mounting board base material in which a plurality of mounting boards 102 are connected in a sheet shape, and the mounting board base After the SAW chip 115 is flip-chip mounted on each individual region on the material, the resin 120 is coated by screen printing using a predetermined mask or application by a dispenser. At this time, the resin 120 is filled in the valleys between the SAW chips 115 and hermetically seals the space between the bottom of the SAW chip 115 and the upper surface of the mounting substrate, while closely adhering to the outer surface of the SAW chip. Covered.
The external electrodes 104 and the wiring pattern 105 provided on the bottom and top surfaces of the insulating substrate 103 are electrically connected by an internal conductor 106 filled in a through hole 103 a formed in the insulating substrate 103. The internal conductor 106 is formed by drilling a through hole 103a in a ceramic green sheet, filling the through hole 103a with a conductive paste, and firing it. If the conductor paste is insufficiently filled, there arises a problem that the airtightness of the inner conductor portion of the ceramic substrate deteriorates through a minute gap between the through hole 103a and the inner conductor 106 after firing.
In the structure of FIG. 3, the internal conductor 106 is disposed in the insulating substrate 103 positioned immediately below the airtight space S. Therefore, when the airtightness between the through hole 103 a and the internal conductor 106 is insufficient, moisture is externally applied. Enters the airtight space S, corrodes the metal present in the internal space, and causes the electrical characteristics of the SAW device to deteriorate.

Next, as in the SAW device 101 shown in FIG. 4, the insulating substrate 103 constituting the mounting substrate 102 is a multilayer ceramic substrate composed of the upper layer 103U and the lower layer 103L, and the vertical through holes 103a formed in the upper layer 103U and the lower layer 103L, respectively. In the case where the horizontal position of ', 103a "is shifted and both the vertical through-holes 103a' and 103a" are communicated by the lateral hole 103 '", the conductive paste is put in each of the communicated holes. When filled and fired, the lateral positions of the inner conductors 106U and 106L formed on the upper layer 103U and the lower layer 103L respectively do not overlap. With this configuration, the airtightness of the airtight space S can be ensured even when the conductors are not sufficiently filled in the vertical through holes 103a ′ and 103a ″ and the horizontal hole 103 ′ ″. it can.
However, when manufacturing a multilayer ceramic substrate, it is necessary to individually form through holes and fill conductors in each of the ceramic green sheets of the upper layer 103U and the lower layer 103L, which increases the manufacturing process. When the through-hole drilling method is punching with a mold, it is necessary to prepare both upper and lower molds, and a plurality of expensive punching molds are required, resulting in an increase in cost. . When drilling through holes with an NC machine instead of punching with a die, the number of through holes to be drilled is greater than with single-layer ceramic substrates, so the time to complete drilling is longer. turn into. Also, the wiring pattern on the multilayer ceramic substrate and the conductor pattern serving as the external electrode must be printed on each of the upper and lower ceramic green sheets, which also increases the number of manufacturing steps. Furthermore, since the mounting substrate is becoming thinner due to the recent thinning of devices, the work of laminating the thin ceramic green sheets on the upper and lower layers after through-hole drilling, conductor filling, and conductor pattern printing has been carried out. It has become very difficult.
As described above, the multilayer ceramic substrate as shown in FIG. 4 can ensure the airtightness of the internal space even when the conductor filling in the through hole is insufficient, but there are many disadvantages as described above. There is.

  Next, in the SAW device 101 shown in FIG. 5, the internal conductor 106 is disposed inside the insulating substrate corresponding to the position immediately below the outer edge of the SAW chip 115, and the wiring pattern 105 including the upper end portion of the internal conductor 106 is provided. A structure in which the sealing resin 120 is covered with a skirt is provided. According to this structure, even when the conductor filling into the through-hole 103a is insufficient, it seems that moisture can be prevented from entering the airtight space S by the skirt of the sealing resin 120 covering the upper surface of the inner conductor. However, in practice, the surface of the wiring pattern 105 of the mounting substrate 102 is plated with Au in order to bond with solder or Au bumps. Due to the poor adhesion between Au and resin, the inner conductor 106 and the through-hole are penetrated. Moisture that has entered from between the holes 103a enters the airtight space along the contact interface between the Au plating and the sealing resin skirt. Also, since the sealing resin has good adhesion to the alumina ceramic, the contact interface width F between the insulating substrate made of alumina ceramic and the sealing resin is set as much as possible in order to increase the adhesion strength between the sealing resin and the insulating substrate. Although it is desirable to make it large, it has become difficult to ensure a sufficient contact interface width F due to recent device miniaturization. A structure in which the upper surface of the inner conductor is covered with a sealing resin as in the SAW device of FIG. 5 is disclosed in, for example, Japanese Patent Application Laid-Open No. 2003-298389.

Next, FIG. 6 shows a structure in which the inner conductor 106 is disposed closer to the center than the conductor bump 110, and the upper end portion of the inner conductor 106 and the wiring pattern 105 are covered with the skirt portion of the sealing resin 120. In such a structure, the contact interface width between the surface of the insulating substrate 103 made of alumina ceramic and the sealing resin 120 is easy to ensure, but the inner conductor is disposed closer to the center than the conductor bump 110. Due to the presence of 110 (conductor bump becomes an obstacle), it may be difficult to sufficiently cover the upper end portion of the inner conductor and the upper surface of the surrounding wiring pattern with the sealing resin.
A structure in which the inner conductor 106 is disposed closer to the center than the conductor bump as shown in FIG. 6 and the upper end portion of the inner conductor and the upper surface of the wiring pattern are covered with a sealing resin is disclosed in, for example, Japanese Patent Laid-Open No. 11-74755. .
WO97 / 02596 JP 9-162690 A JP 2003-298389 A Japanese Patent Laid-Open No. 11-74755

  The present invention has been made in view of the above, and an object thereof is to realize a resin-encapsulated SAW device having a small, thin, and low-cost CSP structure without deteriorating moisture resistance.

In order to achieve the above object, the invention of claim 1 includes a single-layer ceramic substrate, an external electrode for surface mounting disposed at the bottom of the single-layer ceramic substrate, a wiring pattern disposed above the single-layer ceramic substrate, And a mounting substrate comprising a conductor filled in a through-hole formed in the single-layer ceramic substrate and an internal conductor that conducts between the external electrode and the wiring pattern, a piezoelectric substrate, and one surface of the piezoelectric substrate In a state where the formed IDT electrode and the SAW chip including the connection pattern connected to the wiring pattern via a conductor bump and the SAW chip are flip-chip mounted on the mounting substrate using the conductor bump, An airtight space is formed between the IDT electrode and the mounting substrate by covering the SAW chip from the outer surface to the upper surface of the mounting substrate. A surface acoustic wave device comprising a stop resin, wherein the embedded position of the internal conductor is positioned within the width of the bottom portion of the sealing resin that forms the outline of the hermetic space portion, A part of the wiring pattern including the upper end portion of the inner conductor is covered with an insulating coat layer using the same main component as the single-layer ceramic substrate, and at least a portion corresponding to the upper end portion of the inner conductor of the insulating coat is sealed. It is characterized by being covered with resin.
According to a second aspect of the present invention, in the first aspect of the present invention, the area covered by the insulating coating layer extends to the surface of the insulating substrate located at the periphery of the wiring pattern.
A third aspect of the present invention is the first or second aspect, wherein the insulating coating layer is an alumina coating when the insulating material of the mounting substrate is an alumina ceramic, and a glass ceramic coating when the insulating material is a glass ceramic. It is characterized by.

According to the SAW device of the present invention, since the internal conductor is not disposed in the insulating substrate portion corresponding to the position immediately below the airtight space, when the airtightness between the through hole and the internal conductor is insufficient, It is possible to prevent moisture and the like from directly entering the internal space.
In addition, since the upper end portion of the inner conductor and the surrounding wiring pattern portion, and further, the insulating substrate surface portion around the wiring pattern are covered with the insulating coating layer using the same main component as the single-layer ceramic substrate, the insulating coating layer and The adhesion strength between the Au film on the wiring pattern and the adhesion strength between the insulating coating layer and the sealing resin can be increased, and the moisture resistance can be improved.
Furthermore, since the inner conductor is provided outside the conductor bump (near the end face of the SAW device), the upper surface of the inner conductor cannot be covered with the sealing resin due to the presence of the conductor bump (the conductor bump becomes an obstacle). .
In addition, since the insulating substrate is composed of a single-layer ceramic substrate, manufacturing costs can be reduced and productivity can be increased.
According to the present invention having the above-described configuration, it is possible to realize a resin-encapsulated SAW device having a small, thin, and low-cost CSP structure without deteriorating moisture resistance.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings.
FIG. 1A is a longitudinal sectional view of a surface-mounted surface acoustic wave device (hereinafter referred to as a SAW device) according to an embodiment of the present invention, and FIG.
This SAW device 1 has a configuration in which a SAW chip 15 is mounted on a mounting substrate 2 and the outer surface of the SAW chip 15 is covered with a sealing resin 20.
The mounting substrate 2 is a flat insulating substrate 3 as a single-layer ceramic substrate, a mounting electrode 4 for surface mounting provided at the bottom of the insulating substrate 3, and an upper surface of the insulating substrate 3 and via an internal conductor 6. A wiring pattern 5 electrically connected to the mounting electrode 4 is provided. As the single layer ceramic substrate, for example, a single layer alumina ceramic substrate or a single layer glass ceramic can be used. The mounting electrode 4 and the wiring pattern 5 have a structure in which nickel plating layers 4b and 5b and Au plating layers 4c and 5c are sequentially laminated on bases 4a and 5a made of tungsten, respectively. The inner conductor 6 is made of tungsten.
The SAW chip 15 includes a connection pad 16 that is electrically and mechanically connected to each wiring pattern 5 provided on the upper surface of the insulating substrate 3 via the conductor bump 10 and an IDT electrode 17 on the lower surface of the piezoelectric substrate 18 such as crystal. In preparation. The connection pad 16 is disposed so as to surround the outer periphery of the IDT electrode 17. The IDT electrode 17 can obtain a filter characteristic by exciting a surface acoustic wave by applying a high-frequency electric field and converting the surface acoustic wave into a high-frequency electric field by a piezoelectric reaction. The IDT electrode 17 and the connection pad 16 are formed on the main surface of the piezoelectric substrate 18 by a fine processing technique such as photoetching.
The sealing resin 20 is coated over the outer surface excluding the lower surface of the SAW chip 15 and the upper surface of the mounting substrate by screen printing or filling with a dispenser, thereby fixing the SAW chip 15 on the mounting substrate 2 and the SAW chip 15. An airtight space S is formed between the lower surface of the SAW chip 15 and the upper surface of the mounting substrate 2 by filling the space between the skirt (the outer peripheral edge of the lower surface) of the chip 15 and the upper surface of the mounting substrate.
The internal conductor 6 is formed by burying a conductor in a through hole 3 a formed through the insulating substrate 3. Specifically, the through hole 3a is formed in the ceramic green sheet, and the through hole 3a is filled with a conductive paste and fired.

The characteristic configuration of this embodiment is such that the embedded position of the internal conductor 6 is positioned within the width F of the skirt 20a of the sealing resin 20 that forms the outline of the airtight space S, and further the internal conductor 6 A part of the upper end of the wiring pattern and a part of the peripheral wiring pattern 5 are covered with the insulating coating layer 30 using the same main component as the single-layer ceramic substrate 3, and at least correspond to the inner conductor upper end 6a of the insulating coating layer 30. The portion to be covered is covered with the sealing resin 20. The range covered by the insulating coat layer 30 is preferably extended to at least the upper end portion 6a of the internal conductor 6 and the surrounding wiring pattern 5 portion, and preferably further to the insulating substrate surface portion around the wiring pattern. The width F is a contact interface width between the skirt portion of the sealing resin 20 and the insulating coat layer 30.
The material of the insulating coating layer 30 is alumina when the single-layer ceramic substrate 3 is a single-layer alumina ceramic substrate, and glass ceramic when the single-layer ceramic substrate 3 is a single-layer glass ceramic substrate.
As shown in FIG. 1B, the insulating coating layer 30 has a range of required width from the outer edge of the tungsten base 5a before the nickel plating layer 5b and the Au plating layer 5c are laminated on the tungsten base 5a of the wiring pattern. Is laminated.

FIG. 2 is an explanatory diagram of the manufacturing procedure of the SAW device of the present invention, and shows the procedure for assembling the SAW chip 15 to the mounting substrate 2. Actually, manufacturing is performed by batch processing using a mounting substrate wafer having a large area, but in order to simplify the description, a manufacturing procedure for individual pieces is shown in this drawing.
First, a conductor (tungsten) for forming the mounting electrode 4, the wiring pattern 5, and the internal electrode 6 is formed on a ceramic sheet (green sheet) constituting the insulating substrate 3, and subsequently, within a required range on the upper surface of the insulating substrate 3. The insulating coat 30 (alumina coat) is applied and then fired. Thereafter, nickel plating layers 4b and 5b and Au plating layers 4c and 5c are sequentially formed on the mounting electrode base 4a, which is a metal pattern exposed on the insulating substrate, and the wiring pattern base 5a.
The insulating coat layer 30 is laminated in a strip shape with a required width along the outer peripheral edge of the upper surface of the mounting substrate 2, and the insulating coat layer 30 is within a range of the required width from the outer edge of the wiring pattern 5 (tungsten base 5 a). Are laminated so as to cover. In this state, the mounting substrate is baked. On the other hand, the bumps 10 are fixed to the connection positions on the wiring patterns 5 with the bumps 10 fixed to the connection pads 16 of the SAW chip 15 in advance. The SAW device 1 is mounted, and then the sealing resin 20 is applied and filled in a vacuum atmosphere to complete the SAW device 1.

The SAW device according to the present invention has the following effects.
That is, in the SAW device of the present invention, in order to block moisture that may permeate from the outside into the airtight space S through the minute gap between the through hole 3a of the insulating substrate and the internal conductor 6. Since the internal conductor 6 is not disposed on the insulating substrate portion corresponding to the position directly below the airtight space S, moisture or the like is directly applied when the airtightness between the through hole 3a and the internal conductor 6 is insufficient. Intrusion into the internal space can be prevented.
Furthermore, in order to improve the airtightness and waterproofness (moisture resistance) of the airtight space S, in this embodiment, the upper end portion 6a of the internal conductor 6 and the surrounding wiring pattern 5 portion, and further the insulating substrate surface around the wiring pattern The portion was covered with an insulating coat layer 30 using the same main component as the single-layer ceramic substrate. The insulating coat layer 30 is an alumina coat when the insulating material of the mounting substrate 3 is an alumina ceramic, and a glass ceramic coat when the insulating material is a glass ceramic. The insulating coat is formed by applying a paste-like insulating material onto a ceramic green sheet that has been subjected to through-hole drilling, conductor filling, and conductor pattern printing by a printing process, and is simultaneously fired and solidified together with the ceramic green sheet.
Other advantages of covering the insulating coat layer 30 are as follows. That is, after the firing step, a Ni plating film and an Au plating film are sequentially formed on the conductor pattern (wiring pattern: for example, tungsten film) on the insulating substrate 3 in order to improve the bonding property with solder or Au bumps. However, the plating film does not adhere on the insulating coat layer 30. Since there is no Au plating film on the insulating coat layer 30, the sealing resin 20 is firmly covered with the sealing resin 20 in close contact with at least the upper end portion of the inner conductor on the upper surface of the insulating coat layer 30 and the wiring pattern portion corresponding to the periphery thereof. be able to. That is, the contact interface can be formed by the insulating coating layer 30 mainly composed of a ceramic material such as alumina or glass ceramic and the sealing resin 20. Since the adhesion strength between the sealing resin 20 and the alumina coating layer 30 or the adhesion strength between the sealing resin 20 and the glass ceramic coating layer 30 is stronger than the adhesion strength between the sealing resin and the Au plating, the internal conductor 6 can be prevented from entering the airtight space S through the contact interface between the insulating coating layer 30 and the sealing resin. Furthermore, since the bonding strength between the insulating sheet layer 30 and the wiring pattern (tungsten film) is stronger than the bonding strength between the sealing resin and the Au film, the moisture resistance can be further improved.

Thus, according to the present invention, the contact interface width F between the ceramic insulating coating layer 30 and the sealing resin 20 is set to be larger than the bonding width F between the ceramic insulating substrate and the sealing resin in the conventional configuration shown in FIG. Since it can ensure large, the adhesive strength of sealing resin and a mounting board | substrate improves, and moisture resistance improves. Specifically, when the SAW device has a micro dimension of several millimeters in length and width, the contact interface width F between the ceramic and the sealing resin is desirably 0.15 mm or more. However, according to the present embodiment, the contact interface width F exceeding the above numerical value can be secured, so that the moisture resistance can be improved.
Furthermore, in the present invention, the inner conductor 6 is provided outside the conductor bump 10 (closer to the end face of the SAW device). Therefore, as in the conventional example shown in FIG. This prevents the upper surface of the inner conductor from being covered with the sealing resin.
In the present invention, since the insulating substrate 3 is constituted by a single-layer ceramic substrate, when the through hole 3a is punched by a die, the insulating substrate is constituted by a multilayer ceramic substrate. The number of punching dies to be used is small, and the manufacturing cost can be reduced. Further, when the through holes 3a are drilled by an NC processing machine instead of punching with a mold, the number of through holes 3a to be drilled is smaller than in the case of a multilayer ceramic substrate, so that the drilling operation can be performed for a single time. Can be completed, and total productivity can be increased. In particular, when a single-layer ceramic substrate is used, through holes are formed for each ceramic green sheet, which is required when a multilayer ceramic substrate is used, a conductive paste is filled in each through-hole, and a conductor pattern Since it is not necessary to laminate the printed ceramic green sheet on another ceramic green sheet, the number of manufacturing steps is greatly reduced. For this reason, it can contribute to thickness reduction of a SAW device.
According to the present invention having the above-described configuration, it is possible to realize a resin-encapsulated SAW device having a small, thin, and low-cost CSP structure without deteriorating moisture resistance.

(A) is a longitudinal cross-sectional view of the surface-mount type surface acoustic wave device according to one embodiment of the present invention, and (b) is an enlarged cross-sectional view of a main part. Explanatory drawing of the manufacture procedure of the SAW device of this invention. The structure explanatory view of the 1st conventional example. The structure explanatory view of the 2nd conventional example. The structure explanatory view of the 3rd conventional example. The structure explanatory view of the 4th conventional example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Surface acoustic wave device (SAW device), 2 mounting board, 3 insulating board, 4 mounting electrode, 5 wiring pattern, 5a exposed area, 6 internal conductor, 10 conductor bump, 15 SAW (surface acoustic wave) chip, 16 connection pad , 17 IDT electrode, 18 piezoelectric substrate, 20 sealing resin, 30 resin coating layer.

Claims (3)

A single-layer ceramic substrate, a surface-mount external electrode disposed at the bottom of the single-layer ceramic substrate, a wiring pattern disposed above the single-layer ceramic substrate, and a through-hole formed in the single-layer ceramic substrate are filled. A mounting board comprising an inner conductor formed between the external electrode and the wiring pattern formed by a conductor,
A SAW chip comprising a piezoelectric substrate, an IDT electrode formed on one surface of the piezoelectric substrate, and a connection electrode connected to the wiring pattern via a conductor bump;
In a state where the SAW chip is flip-chip mounted on the mounting substrate using the conductor bumps, the SAW chip is covered and formed from the outer surface of the SAW chip to the upper surface of the mounting substrate, thereby airtight between the IDT electrode and the mounting substrate. A surface acoustic wave device comprising: a sealing resin that forms a space;
The embedded position of the inner conductor is configured to be positioned within the width of the bottom portion of the sealing resin that forms the outline of the hermetic space portion,
A part of the wiring pattern including the upper end portion of the inner conductor is covered with an insulating coat layer using the same main component as the single-layer ceramic substrate, and at least a portion corresponding to the upper end portion of the inner conductor of the insulating coat is sealed. A surface-mount surface acoustic wave device that is covered with resin.   The surface-mount type surface acoustic wave device according to claim 1, wherein a coverage area by the insulating coat layer extends also to the insulating substrate surface located at a peripheral edge of the wiring pattern.   3. The surface mounting according to claim 1, wherein the insulating coating layer is an alumina coating when the insulating material of the mounting substrate is an alumina ceramic, and a glass ceramic coating when the insulating material is a glass ceramic. Type surface acoustic wave device.

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