Method of making printed wiring board and method of making printed circuit board unit

The first support body is pressed against the second support body in response to the softening of the adhesive sheet. The fillers are allowed to reliably contact with one another between the first electrically-conductive land and the second electrically-conductive land. The fillers melt after the adhesive sheet has been softened. The intermetallic compounds are formed between the fillers and the electrically-conductive lands and between the fillers. Electrical connection is in this manner established between the first electrically-conductive land and the second electrically-conductive land. The matrix material and the adhesive sheet are then cured. The first support body and the second support body are firmly bonded to each other.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2008-143664 filed on May 30, 2008, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to a technique of bonding substrates together or an electronic component and a substrate together.

BACKGROUND

An electrically-conductive paste is well known. The electrically-conductive paste includes matrix material made of a thermosetting resin and electrically-conductive particles dispersed in the matrix material. The electrically-conductive particles are metallic particles, for example. An adhesive sheet made of a resin material is sandwiched between printed wiring boards so as to bond the printed wiring boards to each other, for example. Lands on the printed wiring boards are opposed to each other through a through bore formed in the adhesive sheet. The through bore is filled with the electrically-conductive paste. The electrically-conductive paste is hardened or cured by heating. The adhesive sheet bonds the printed wiring boards to each other. An electric connection is established between the lands opposed to each other.

It is proposed to bond a build-up layer to a core substrate for establishment of a so-called build-up substrate. It is required to establish a stable electrical connection between a land on the core substrate and a land on the build-up layer when the build-up layer is bonded to the core substrate. The aforementioned electrically-conductive paste cannot provide a reliable bonding between the build-up layer and the core substrate.

SUMMARY

According to an aspect of the invention, a method of making a printed wiring board, includes: setting an adhesive sheet made of a thermosetting resin between a first support body and a second support body so that a first electrically-conductive land on the first support body is opposed to a second electrically-conductive land on the second support body through an opening formed in the adhesive sheet; filling the opening with an electrically-conductive binder including matrix material and fillers when the first electrically-conductive land is opposed to the second electrically-conducive land, the matrix material containing a thermosetting resin, the fillers dispersed in the matrix material so as to unite with the first and second electrically-conductive lands based on intermetallic compounds formed between the fillers and the first and second electrically-conductive lands, respectively; softening the adhesive sheet by heating while the first support body is pressed against the second support body; inducing melting of the fillers by heating after the adhesive sheet has been softened; curing the matrix material by heating after the fillers have molten; and curing the adhesive sheet by heating after the matrix material has been cured.

According to another aspect of the invention, a method of making a printed circuit board unit, includes: setting an adhesive sheet made of a thermosetting resin between a first support body and a second support body so that a first electrically-conductive land on the first support body is opposed to a second electrically-conductive land on the second support body through an opening formed in the adhesive sheet; filling the opening with an electrically-conductive binder including matrix material and fillers when the first electrically-conductive land is opposed to the second electrically-conducive land, the matrix material containing a thermosetting resin, the fillers dispersed in the matrix material so as to unite with the first and second electrically-conductive lands based on intermetallic compounds formed between the fillers and the first and second electrically-conductive lands, respectively; softening the adhesive sheet by heating while the first support body is pressed against the second support body; inducing melting of the fillers by heating after the adhesive sheet has been softened; curing the matrix material by heating after the fillers have molten; and curing the adhesive sheet by heating after the matrix material has been cured.

DESCRIPTION OF EMBODIMENT

FIG. 1schematically illustrates the cross-section of a printed wiring board11according to an embodiment of the present invention. The printed wiring board11is utilized as a probe card, for example. Such a probe card is set in a probe apparatus, for example. It should be noted that the printed wiring board11may be utilized in any other electronic apparatus.

The printed wiring board11includes a core substrate12. The core substrate12includes a core layer13in the form of a thin plate. The core layer13includes an electrically-conductive layer14. Carbon fiber cloth is embedded in the electrically-conductive layer14. The fibers of the carbon fiber cloth extend in the in-plane direction of the core layer13. This results in a significant restriction of the thermal expansion of the electrically-conductive layer14in the in-plane direction. The carbon fiber cloth has an electrical conductivity. The carbon fiber cloth is impregnated with a resin material so as to form the electrically-conductive layer14. The resin material is a thermosetting resin such as epoxy resin. The carbon fiber cloth is a woven or nonwoven cloth made of carbon fiber yarns.

The core layer13includes core insulating layers15,16overlaid on the front and back surfaces of the electrically-conductive layer14, respectively. The electrically-conductive layer14is sandwiched between the core insulating layers15,16. The core insulating layer15,16are insulative. Glass fiber cloth is embedded in the core insulating layers15,16. The fibers of the glass fiber cloth extend along the front and back surfaces of the core layer13. The glass fiber cloth is impregnated with a resin material so as to form the core insulating layers15,16. The resin material is a thermosetting resin such as epoxy resin. The glass fiber cloth is a woven or nonwoven cloth made of glass fiber yarns.

Through bores17are formed in the core layer13. The through bores17penetrate through the core layer13. The through bores17each define a columnar space. The longitudinal axis of the columnar space is set perpendicular to the front and back surfaces of the core layer13. The through bores17define circular openings on the front and back surfaces of the core layer13, respectively.

A large-sized via18having a large diameter is formed in the individual through bore17. The large-sized via18is electrically conductive. The large-sized via18is formed in the shape of a cylinder along the inward wall surface of the through bore17. The large-sized via18is connected to annular electrically-conductive lands19on the front and back surfaces of the core layer13. The electrically-conductive lands19extend on the front and back surface of the core layer13. The large-sized via18and the electrically-conductive lands19are made of an electrically-conductive material such as copper.

The inner space of the large-sized via18in the through bore17is filled with a filling material21made of a resin material. The filling material21takes the form of a cylinder along the inward wall surface of the large-sized via18. The filling material21is a thermosetting resin such as epoxy resin. A ceramic fillers are embedded in the epoxy resin, for example.

The core substrate12includes insulating layers22,23overlaid on the front and back surfaces of the core layer13, respectively. The back surfaces of the insulating layers22,23are received on the front and back surfaces of the core layer13, respectively. The core layer13is sandwiched between the insulating layers22,23. The insulating layers22,23cover over the exposed surfaces of the filling material21. The insulating layers22,23are insulative. Glass fiber cloth is embedded in the insulating layers22,23. The fibers of the glass fiber cloth extend along the front and back surfaces of the core layer13. The glass fiber cloth is impregnated with a resin material so as to form the insulating layers22,23. The resin material is a thermosetting resin such as epoxy resin. The glass fiber cloth is a woven or nonwoven cloth made of glass fiber yarns.

Through bores24are formed in the core substrate12. The through bores24penetrate through the core layer13and the insulating layers22,23. The individual through bore24is located inside the corresponding through bore17. The through bore24penetrates through the corresponding filling material21. Here, the through bores24each define a columnar space. The individual through bore24is coaxial with the corresponding through bore17. The individual through bore24defines circular openings on the front and back surfaces of the core substrate12, respectively.

A small-sized via25having a diameter smaller than that of the large-sized via18is formed in the individual through bore24. The small-sized via25is electrically conductive. The small-sized via25is formed in the shape of a cylinder along the inward wall surface of the through bore24. The filling material21serves to insulate the large-sized via18and the small-sized via25from each other. The small-sized via25is made of an electrically-conductive material such as copper.

Electrically-conductive lands26are formed on the surfaces of the insulating layers22,23. The small-seized via25is connected to the electrically-conductive lands26on the surfaces of the insulating layers22,23. The electrically-conductive lands26are made of an electrically-conductive material such as copper. The inner space of the small-sized via25is filled with a filling material27made of an insulating resin between the electrically-conductive lands26,26. The filling material27is formed in the shape of a column, for example. The filling material27is a thermosetting resin such as epoxy resin. Ceramic fillers are embedded in the epoxy resin.

Build-up layers28,29are formed on the surfaces of the insulating layers22,23, respectively. The back surfaces of the build-up layers28,29are received on the surfaces of the insulating layers22,23, respectively. The core layer13and the insulating layers22,23are sandwiched between the build-up layers28,29. The build-up layers28,29cover over the electrically-conductive lands26,26, respectively. The build-up layers28,29are insulative. Glass fiber cloth is embedded in the build-up layers28,29. The fibers of the glass fiber cloth extend along the surfaces of the insulating layers22,23. The glass fiber cloth is impregnated with a resin material so as to form the build-up layers28,29. The resin material is a thermosetting resin such as epoxy resin. The glass fiber cloth is a woven or nonwoven cloth made of glass fiber yarns.

Electrically-conductive lands31,31are formed on the front surfaces of the build-up layers28,29. The electrically-conductive lands31extend along the front surfaces of the build-up layers28,29. The electrically-conductive lands31are electrically connected to the corresponding electrically-conductive lands26. Vias32are formed in the build-up layers28,29to connect the electrically-conductive lands31to the electrically-conductive lands26. Through bores are formed in the build-up layers28,29at positions between the electrically-conductive lands31and the corresponding electrically-conductive lands26so as to form the vias32. The through bores are filled with an electrically-conductive material. The electrically-conductive lands31and the vias32are made of an electrically-conductive material such as copper.

The printed wiring board11includes build-up layer units33,34overlaid on the front and back surfaces of the core substrate12, respectively. The back surfaces of the build-up layer units33,34are received on the front and back surfaces of the core substrate12, respectively. The build-up layer units33,34each include a layered structure including insulating layers35and electrically-conductive patterns36. The insulating layers35and the electrically-conductive patterns36are alternatively overlaid on one another. The electrically-conductive patterns36in different layers are electrically connected to each other through a via or vias37. A through bore is formed in the insulating layer35at a position between the electrically-conductive patterns36so as to form the individual via37. The through bore is filled with an electrically-conductive material. The insulating layers35are made of a thermosetting resin such as epoxy resin. The electrically-conductive patterns36and the vias37are made of an electrically-conductive material such as copper.

Electrically-conductive pads38are exposed on the front surfaces of the build-up layer units33,34. The electrically-conductive pads38are made of an electrically-conductive material such as copper. An overcoat layer39is overlaid on the front surface of the each of the build-up layer units33,34at positions off the electrically-conductive pads38. The overcoat layer39is made of a resin material, for example.

Electrically-conductive lands41are exposed on the back surfaces of the build-up layer units33,34. The electrically-conductive lands41extend along the back surface of the lowest one of the insulating layers35in the individual build-up layer unit33,34. The electrically-conductive lands41are electrically connected to the corresponding electrically-conductive patterns36through the vias37. The electrically-conductive lands41are made of an electrically-conductive material such as copper. The electrically-conductive lands41are electrically connected to the corresponding electrically-conductive lands31as described later in detail. Electrical connection is thus established between the electrically-conductive pads38exposed on the front surface of the printed wiring board11and the corresponding electrically-conductive pads38exposed on the back surface of the printed wiring board11. When the printed wiring board11is set in a probe apparatus, the electrically-conductive pads38on the back surface of the printed wiring board11are connected to the corresponding electrode terminals of the probe apparatus, for example. When a semiconductor wafer is mounted on the front surface of the printed wiring board11, for example, the electrically-conductive pads38on the front surface of the printed wiring board11receive the corresponding electrode bumps of the semiconductor wafer, for example. The electrically-conductive pads38are connected to the corresponding electrode bumps. A heat cycle test is then executed so as to examine the semiconductor wafer, for example.

Bonding layers42,42are sandwiched between the core substrate12and the build-up layer units33,34, respectively. The bonding layers42each include an insulating base43. The insulating base43is insulative. The insulating base43is made of a thermosetting resin such as epoxy resin. Glass fiber cloth may be embedded in the insulating base43in the same manner as described above, for example.

Electrically-conductive bodies44are embedded in the bonding layers42. The individual electrically-conductive body44is sandwiched between the corresponding electrically-conductive lands31,41. The electrically-conductive body44includes a number of spherical conductive bodies45. The individual spherical conductive body45includes a metallic fine particle46such as a copper particle, as depicted inFIG. 2. The surface of the metallic fine particle46is coated with a copper-tin alloy layer47. The copper-tin alloy layer47on the metallic fine particle46is in contact with the copper-tin alloy layers47on the adjacent metallic fine particles46. The copper-tin alloy layers47serve to establish an electric connection between the electrically-conductive lands31,41. The melting point of the copper-tin alloy exceeds 400 degrees Celsius.

The metallic fine particles46are embedded in a bismuth material48. The bismuth material48fills a space between the metallic fine particles46in the electrically-conductive body44. This results in suppression of the electrical resistance of the electrically-conductive body44. A sufficient electrical conduction is established. Moreover, the bismuth material48has the melting point equal to 270 degrees Celsius. Bonding between the electrically-conductive lands31,41is thus reliably maintained unless the bismuth material48is heated to a temperature exceeding 271 degrees Celsius. The aforementioned insulating base43surrounds the bismuth material48.

Next, description will be made on a method of making the printed wiring board11. The core substrate12is first prepared. Simultaneously, the build-up layer units34,34are prepared. A method of making the build-up layer units33,34will be described later in detail. Adhesive sheets51are overlaid on the front and back surfaces of the core substrate12, respectively, as depicted inFIG. 3. The back surfaces of the adhesive sheets51are received on the front and back surfaces of the core substrate12, respectively. The build-up layer units33,34are overlaid on the corresponding front surfaces of the adhesive sheets51, respectively. The adhesive sheets51are made of a thermosetting resin such as epoxy resin. Glass fiber cloth may be embedded in the adhesive sheets51, for example.

An opening52is formed in the individual adhesive sheet51at a position between the electrically-conductive lands31,41. The opening52penetrates through the adhesive sheet51. The electrically-conductive lands31,41are opposed to each other through the opening52. The shape of the opening52may be determined depending on the shape of the electrically-conductive lands31,41. The opening52is filled with an electrically-conductive binder53. A screen printing process may be employed to fill the opening52with the electrically-conductive binder53.

The electrically-conductive binder53includes matrix material53amade of a thermosetting resin. The thermosetting resin is epoxy resin, for example. A hardener, such as a carboxyl group, an amino group or a phenolic group, is added to the epoxy resin. An activator, such as an adipic acid, a succinic acid, or a sebacic acid, is also added to the epoxy resin.

Fillers53bdisperse in the matrix material53a. The fillers53binclude metallic fine particles, namely copper particles, each having the surface fully coated with a tin-bismuth alloy. The tin-bismuth alloy contains bismuth in a range from 50 wt % to 60 wt % (preferably at 58 wt % approximately). The tin-bismuth alloy of this type is prevented from shrinkage to the utmost when the tin bismuth alloy is cured or hardened. The melting point of the tin-bismuth alloy resides in a range between 139 degrees Celsius and 150 degrees Celsius. The tin-bismuth alloy may be plated entirely over the surface of the individual copper particle. The thickness of such a tin-bismuth alloy layer may be set in a range from 1.0 μm to 5.0 μm. The thickness of the tin-bismuth alloy layer is preferably set in a range from 1.0 μm to 2.0 μm. A plating film having a thickness smaller than 1.0 μm cannot have sufficient stability and bonding properties. An increase in the thickness leads to an increase in a thermal energy required for the tin-bismuth alloy during a bonding process. Accordingly, it is desired to minimize an increase in the thickness.

A heat treatment is effected on the layered body of the core substrate12, the adhesive sheets51and the build-up layer units33,34. The temperature of heat is set in a range from 150 degrees Celsius to 180 degrees Celsius. Pressure is applied to the layered body in the direction perpendicular to the front and back surfaces of the core substrate12during the heat treatment. The core substrate12, the adhesive sheets51,51and the build-up layer units33,34are in this manner tightly united together. The adhesive sheets51are softened in response to a rise in the temperature. The adhesive sheets51thus deform in line with the surfaces of the core substrate12and the layered bodies. Such deformation of the adhesive sheets51serves to absorb the unevenness of the surfaces of the core substrate12and the layered bodies. Simultaneously, the softened adhesive sheets51allow the copper particles between the electrically-conductive lands31,41to reliably contact with one another. The flowability of the copper particles serves to absorb a change in the distance between the electrically-conductive lands31,41.

The tin-bismuth alloy melts after the adhesive sheets51have been softened. The tin forms intermetallic compounds, namely the copper-tin (Cu6Sn5) alloy layers47, on the surfaces of the electrically-conductive lands31,41and the surfaces of the copper particles. The activator serves to accelerate generation of the intermetallic compounds. The copper-tin alloy layers47on the copper particles are brought in contact with one another. The copper-tin alloy layers47serve to bond the copper particles to the electrically-conductive land31,41as well as the copper particles to one another. The spherical conductive bodies45are established. Simultaneously, bismuth fills a space between the copper-tin alloy layers47. The bismuth embeds the spherical conductive bodies45between the electrically-conductive lands31,41. The bismuth is hardened or cured. The bismuth material48is formed. Since the copper particles are kept in a solid state, the electrically-conductive binder53is prevented from being excessively flattened under an applied pressure.

The matrix material made of the thermosetting resin is then hardened and cured. The spherical conductive bodies45and the bismuth material48are wrapped or embedded in the cured matrix material. The adhesive sheets51are hardened or cured. The matrix material and the adhesive sheets51are united together. The matrix material and the adhesive sheets51in combination form the insulating bases43of the bonding layers42. When the curing of the adhesive sheets51is completed, the build-up layer units33,34are then coupled to the front and back surfaces of the core substrate12, respectively. The printed wiring board11is then released from the heat and pressure. The printed wiring board11is in this manner produced.

The bismuth material48in the printed wiring board11has the melting point of 271 degrees Celsius. In the case where an electronic component such as a semiconductor chip is mounted on the printed wiring board11, for example, the printed wiring board11is subjected to heat having a temperature equal to or higher than the melting point of solder. Solder generally melts at a temperature lower than the 271 degrees Celsius. The bismuth material48is thus kept in a solid state. A sufficient bonding strength is maintained. Since the thickness of the tin-bismuth alloy layer is set smaller than 5.0 μm (preferably smaller than 2.0 μm) as described above, a minimum amount of a thermal energy is sufficient to cause reaction of the tin with the copper.

Copper particles of a different kind may be added to the aforementioned electrically-conductive binder53in addition to the aforementioned copper particles. The copper particles of a different kind are each coated with a silver plating layer or a tin plating layer. The copper particles of the different kind contribute to improvement of the wettability of the copper. The bonding strength of the copper is thus improved.

FIG. 4is a graph presenting the relationship between the viscosity and the temperature for the adhesive sheet51made of a material according to a specific example. As is apparent fromFIG. 4, a rapid increase in the temperature results in a delay of softening of the adhesive sheet51. Moreover, the rapider pace the temperature increases at, a higher temperature the curing of the adhesive sheet51starts at. When the temperature of heat applied to the adhesive sheet51increases by 10 degrees Celsius per minute, for example, the adhesive sheet51starts to get cured at 146.3 degrees Celsius.FIG. 5is a graph presenting the relationship between the elapsed time and the rate of curing reaction during the heat treatment on the adhesive sheet51. It is obvious fromFIG. 5that, the higher the temperature of the heat is, the shorter time the adhesive sheet51is cured in. Accordingly, adjustment on the temperature of the heat and the pace of increasing the temperature of the heat can be utilized to control the start of softening, the start of curing, and the completion of curing, of the adhesive sheet51.

FIG. 6is a graph presenting the relationship between the viscosity and the temperature of the matrix material53acontained in the electrically-conductive binder53. As is apparent fromFIG. 6, the viscosity depends on the temperature irrespective of the pace of an increase in the temperature. Curing starts when the temperature reaches 140 degrees Celsius approximately at any pace of an increase in the temperature. As the temperature increases at a rapider pace, the curing occurs at a higher temperature.FIG. 7is a graph presenting the relationship between the elapsed time and the rate of curing reaction during the heat treatment on the matrix material53a. It is obvious fromFIG. 7that the higher the temperature of the heat gets, the shorter time the matrix material53ais cured in. Accordingly, adjustment on the temperature of the heat and the pace of increasing the temperature of the heat can be utilized to control the start of softening, the start of curing, and the completion of curing, of the matrix material53a.

Here, a brief description will be made on a method of making the build-up layer units33,34. As depicted inFIG. 8, a support body55is prepared. The support body55includes an epoxy resin base55a. Glass fiber cloth is embedded in the epoxy resin base55a. The fibers of the glass fiber cloth extend along the front and back surfaces of the epoxy resin base55a. The glass fiber cloth is impregnated with epoxy resin so as to form the epoxy resin base55a. The thickness of the epoxy resin base55ais set in a range from 0.3 mm to 0.4 mm. A copper foil55bhaving a thickness of 9.0 μm approximately is attached to the front surface of the epoxy resin base55a. The epoxy resin base55aexhibits a rigidity sufficient for preventing deformation such as shrinkage or curvature in the process of producing the build-up layer units33,34.

An adhesive film56, a first metallic film57and a second metallic film58are overlaid in this sequence on the front surface of the support body55. The adhesive film56is made of a thermosetting resin such as epoxy resin. The first metallic film57is made out of a copper foil having a thickness of 18.0 μm approximately, for example. The second metallic film58is made out of two layers of copper foils having a total thickness of 18.0 μm approximately, for example. An intermediate barrier layer is sandwiched between the copper foils of the second metallic film58. The intermediate barrier layer is made of nickel, for example. The intermediate barrier layer may be made of a material capable of remaining after the etching of a copper foil. The second metallic film58extends wider out of the contour of the first metallic film57. Vacuum pressing is applied to the support body55, the adhesive film56, the first metallic film57and the second metallic film58. A vacuum hot press is employed in the vacuum pressing. The second metallic film58is bonded to the front surface of the support body55outside the contour of the first metallic film57. The back surface of the second metallic film58coheres to the front surface of the first metallic film57.

As depicted inFIG. 9, photolithography is effected on a copper foil58aon the front side of the second metallic film58, for example. A photoresist61is formed on the surface of the copper foil58a. The copper foil58ais exposed to an etchant at a position off the photoresist61, for example. As depicted inFIG. 10, the copper foil58ais removed from the position off the photoresist film61. An intermediate barrier layer58bserves to block the etchant. A copper foil58con the back side of the second metallic film58thus remains as it is. An electrically-conductive pattern made of copper is in this manner formed on the surface of the intermediate barrier layer58b. The electrically-conductive pattern corresponds to the aforementioned electrically-conductive lands41.

As depicted inFIG. 11, an insulating sheet62is overlaid on the surface of the intermediate barrier layer58b. The insulating sheet62and the intermediate barrier layer58bare subjected to heat under pressure, so that the insulating sheet62is bonded to the surface of the intermediate barrier layer58b. The insulating sheet62covers over the electrically-conductive lands41. An adhesive sheet made of a thermosetting resin, a prepreg of a thermosetting resin containing glass fiber cloth, or the like, may be employed as the insulating sheet62.

As depicted inFIG. 12, through bores63are formed in the insulating sheet62at predetermined positions. A laser is utilized to form the through bores63. The through bore63defines a hollow space on the corresponding electrically-conductive land41. Copper plating is effected on the surface of the insulating sheet62, for example. An electrically-conductive layer64made of copper is in this manner formed on the surface of the insulating sheet62. A via65made of copper is established in the through bore63. As depicted inFIG. 13, a photoresist66is formed on the surface of the electrically-conductive layer64, for example. The photoresist66defines voids67in a predetermined pattern on the surface of the electrically-conductive layer64. The voids67are located at positions off the vias65. As depicted inFIG. 14, a predetermined electrically-conductive pattern68is formed out of the electrically-conductive layer64based on an etching process. Such lamination of insulating sheets69and formation of electrically-conductive patterns71are then repeated. A predetermined number of layers of the electrically-conductive patterns71are in this manner formed. A predetermined layered body72is formed on the intermediate barrier layer58b, as depicted inFIG. 15.

As depicted inFIG. 16, the support body55, the adhesive film56, the first metallic film57and the second metallic film58are cut out along the contour of the first metallic film57inside the contour of the first metallic film57. The copper foil58a, the intermediate barrier layer58band the layered body72are separated from the surface of the first metallic film57. The intermediate barrier layer58bis removed based on an etching process. The electrically-conductive lands41are exposed. The build-up layer units33,34are in this manner formed. Nickel and gold plating films may be formed on the surfaces of the electrically-conductive patterns71and the electrically-conductive lands41on the front and back surfaces of the build-up layer units33,34.

As depicted inFIG. 17, the aforementioned bonding layer42may be utilized for mounting an electronic component81such as a semiconductor chip in the process of making a printed circuit board unit79, for example. The bonding layer42can function as a so-called underfill material. The electrically-conductive body44in the bonding layer42serves to connect electrically-conductive lands83on the electronic component81to corresponding electrically-conductive lands84on the printed wiring board82. In this case, an adhesive sheet85is sandwiched between the electronic component81and the printed wiring board82in the same manner as described above, as depicted inFIG. 18, for example. An opening86is formed in the adhesive sheet85between the electrically-conductive land83on the electronic component81and the corresponding electrically-conductive land84on the printed wiring board82. The opening86penetrates through the adhesive sheet85. The electrically-conductive land83on the electronic component81is opposed to corresponding the electrically-conductive land84on the printed wiring board82in the opening86. The opening86is filled with the electrically-conductive binder53.