JPH10261737A - Wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation and progress of cracks of solder between connection pads which is generated by temperature change after wiring boards whose thermal expansion coefficients are largely different are bonded to each other. SOLUTION: When a solder ball 6 is soldered to each connection pad 3 of a ceramic board, a recessed part is so arranged at the center that the lowermost end part of the solder ball 6 becomes lower than the upper surface 3a of the connection pad 3. Since the ball 6 falls in the recessed part, is anchored in the transversal direction, and soldered with low melting point solder 5, the ball 6 is tough to the transversal direction. When the space between both connection pads of the ceramic board and a print board made of resin is soldered, the ball 6 is still in the state of falling in the recessed part. When cracks K are generated by the change of temperature, and progress in the vicinity of an interface of a pad 3 of the board side and the low melting point solder 5, the progress stops on the surface of the ball 6, and the ball 6 receives shearing force.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wiring board used as a substrate for a BGA (ball grid array) package used for an IC package or the like and a resin printed board (mother board) for mounting such a wiring board. Regarding the substrate.

[0002]

2. Description of the Related Art A conventional substrate for a BGA package has a large number of connection terminals on the main surface of a substrate made of an electrically insulating material such as alumina ceramic or resin. FIG. 16 shows an example of the structure of the terminals. There are things. In this device, a predetermined plating is applied to each connection pad (group) 3 metallized on the main surface 2 of the package substrate 1, and Pb
-Small solder of lead composition such as Sn eutectic solder (hereinafter, referred to as
Connection pads (hereinafter, also referred to as low melting point solder) 5
A metal ball such as a solder ball 6 made of a relatively high melting point solder having a large lead composition such as Pb90-Sn10 (hereinafter also referred to as a high melting point solder) is used as a gap maintaining means at the time of bonding between the pads. (A sphere) is soldered to form a connection terminal (bump) 7.

The wiring board 1 having such connection terminals 7
The electrical connection is made by positioning and overlaying the connection pads of both wiring boards on a printed circuit board having connection pads arranged and formed corresponding to the arrangement, and soldering between the connection pads. You. FIG. 17 shows a structure in which the BGA package substrate 1 having the connection terminals 7 shown in FIG.

[0004]

However, such a joint structure has the following problems. In other words, in the case of a substrate having a small coefficient of thermal expansion, such as a ceramic package substrate, which is soldered and integrated between both connection pads on a large resin printed circuit board, a subsequent temperature change causes As shown in FIG. 18, cracks K occur in the solder joints between the connection pads 3 and 23 due to the difference in the amount of expansion and contraction caused by the difference in the coefficient of thermal expansion between the materials of the wiring boards 1 and 21. There was something. This is because the low melting point solder has relatively low strength and cannot withstand the thermal stress (shear stress) acting along the main surface between the two substrates 1 and 21. It becomes maximum near the interface of the connection pad of the low melting point solder between the pads.

Furthermore, low-melting solder is relatively brittle and less sticky than high-melting solder, and therefore has the property of being less likely to be plastically deformed. In addition, the bonding interface between the low melting point solder and the connection pad is made of Au—Sn or Ni by diffusion of Au plating or Ni plating on the connection pad and Sn in the solder.
A hard and brittle intermetallic compound of -Sn is formed. For this reason, if there is a large temperature change after joining, FIG.
As shown in FIG.
The low melting point solder between them has a very small thickness T
1, a solder layer of T2, that is, one low-melting-point solder skin is left, and a crack (crack) is formed in the direction along the main surfaces 2, 22 of the wiring boards 1, 21 (the direction of the arrow shown in the figure) with the outer peripheral edge as a starting point. ) K occurred and tended to evolve. Once such a crack K has been generated, it tends to develop at once from the starting point toward the opposite side, and as a result, poor conduction (disconnection) between the pads 3 and 23 may be caused.

[0006] Such a problem is caused when the resin wiring boards are connected to each other, such as when connecting a resin IC package board to a resin printed board, when both have different coefficients of thermal expansion, or when the IC to be mounted is different from the IC to be mounted. There is a risk that the deformation may occur when the IC package substrate is deformed due to a difference in thermal expansion coefficient of the resin. And, as the difference in thermal expansion coefficient between the two wiring board materials is larger, and as the size of the wiring board is larger, it appears more remarkably, and depending on the size, there is a problem that a ceramic package board cannot be mounted on a resin printed board, Further, there has been a problem that the material of the other wiring board is restricted or the size cannot be increased depending on the material of the one wiring board.

[0007] As shown in FIGS. 18 and 19, solder cracks between the pads naturally occur not only in the package substrate 1 but also in the vicinity of the pads 23 on the printed circuit board 21 side. In the case of bonding between a package substrate (hereinafter, also referred to as a ceramic substrate) made of a resin and a printed circuit board made of a resin, in practice, cracks tend to occur in the solder near the interface between the pad and the solder on the ceramic substrate side. It hardly occurs near the interface between the pad and the solder on the printed circuit board side. The reason is as follows. In other words, the pads forming the connection terminals of the ceramic substrate are placed on a metallized layer of tungsten or the like,
On the other hand, on a printed circuit board, a pad formed on a resin plate is usually as thick as 20 to 30 μm of copper, and copper is extremely soft as compared with tungsten.

Therefore, when the pads of both wiring boards are joined by solder, the pads themselves are thick and soft on the printed circuit board side and easily deformed, so that the thermal stress generated by the temperature difference is reduced. While it is easy to absorb, such absorption is hardly expected on the ceramic substrate because the pad is hard and thin. For this reason,
In many cases, cracks occur near the interface between the pad on the ceramic substrate side and the low melting point solder.

According to the present invention, as in the case where a package substrate made of alumina ceramic is joined to a printed board made of resin or the like, wiring boards having greatly different coefficients of thermal expansion are joined to each other, and then the connection pads formed due to a temperature change are formed. It is an object of the present invention to provide a wiring board capable of preventing the occurrence and development of cracks in low-melting-point solder, eliminating disconnection (poor connection) between connection pads, and obtaining highly reliable bonding.

[0010]

In order to achieve the above object, the present invention has a plurality of connection pads having a solderable surface on a main surface, and the connection pads can be soldered as connection terminals to the connection pads. In the wiring board to which the metal balls are soldered, when the metal balls are soldered to the connection pads, the connection pads are so arranged that the lowermost end of the metal balls is lower than the upper surface of the connection pads. It is characterized in that a concave portion is provided at substantially the center thereof.

In the above means, a low-melting solder paste is printed or coated on the connection pad, and a solderable metal ball such as a solder ball having a higher melting point is mounted thereon. The connection terminals (solder bumps) are formed by soldering with solder. In this case, the lowermost end of the metal ball is positioned lower than the upper surface of the connection pad in a substantially central concave portion of the connection pad. Then, the solder is soldered to the connection pad with solder having a melting point lower than the melting point of the metal ball. As described above, in the above-described wiring board, the metal ball is dropped into the concave portion so as to be latched in the lateral direction and is soldered. The solder used for soldering the metal balls is selected from alloys containing lead-tin as the main component (Pb-Sn) having a low Pb component ratio (high Sn component ratio), such as eutectic solder. It may be appropriately selected and used.

A wiring board to which such metal balls are soldered is arranged to correspond to the arrangement of the respective connection terminals, and for example, a resin printed board having connection pads with low melting point solder is formed. When each connection pad of both wiring boards is positioned and overlapped, and the low melting point solder between them is melted and both connection pads are soldered,
The metal ball is in a state where the lowermost end of the metal ball is lowered below the upper surface of the connection pad in the recess of the connection pad.

Accordingly, there is a temperature change in such a joint structure portion, and due to a difference in thermal expansion coefficient between the two wiring boards (materials), the low-melting solder at each joint portion is subjected to a shearing force acting along the main surface thereof. When a crack occurs, the following effect is obtained. That is, when cracks occur on the outer peripheral edge of the low melting point solder and near the interface between the pad on the wiring board side according to the present invention and the low melting point solder, the crack easily spreads along the upper surface of the pad and spreads on the surface of the metal ball. If it reaches, the crack stops at the surface due to the difference in the material of the low melting point solder and the metal ball. And
The shear force acts on the metal ball, which falls into the recess and is restricted from moving in the lateral direction. Therefore, since such a shear force is received by the metal ball locked in the recess, the conventional force is applied. As a result, it is possible to prevent the crack from developing at a stretch and leading to disconnection.

Further, since the metal ball made of high melting point solder or copper containing a large amount of lead is soft and easily deformed by an external force and has an action of absorbing stress, it does not generate new cracks, and Reduce the risk of disconnection. In particular, metal balls made of high melting point solder or lead having a high proportion of Pb component are extremely flexible and extensible, and have a recrystallization temperature close to normal temperature, which causes a shear force in the direction along the main surface of the wiring board. When the metal ball acts, the metal ball itself deforms to allow and absorb the stress. In other words, by using such a metal ball, according to the present invention, the development of cracks that tend to occur near the interface with the pad on the ceramic substrate side, for example, at the outer peripheral edge of the low melting point solder, is caused by the metal ball. The progress can be stopped, and disconnection between the pads can be prevented by the ease of deformation of the metal ball itself.

As described above, the pads of the resin printed board are usually made of copper which is softer and thicker than the pads on the ceramic substrate side, and can deform itself to absorb stress. However, if the present invention is embodied with pads on both wiring boards to be joined, the risk of disconnection is further reduced and reliability is improved.

In the above means, when the metal ball is soldered to the connection pad, the lowermost end of the metal ball is lower than the upper surface of the connection pad.
Although the connection pad has a concave portion at substantially the center thereof, the following configuration may be adopted. That is, in a wiring board having a plurality of connection pads having a solderable surface on a main surface, and solderable metal balls serving as connection terminals to the connection pads, the metal pads are provided on the connection pads. Wherein the connection pads are formed in a ring shape such that the lowermost end of the metal ball is lower than the upper surface of the connection pads when soldered.

In this case, since the pads are formed in a ring shape, the soldering area is reduced by the space in the center, but the metal ball is located at the lowermost end on the inner peripheral side of the connection pad. Is lower than the upper surface of the connection pad, and is soldered to the connection pad with solder having a melting point lower than the melting point of the metal ball. Therefore, the same operation or effect as that of the wiring board is obtained.

The plane shape (outside contour) of the pad may be an appropriate shape such as a circle or a square, and the plane shape of the concave portion or the inner peripheral space of the pad is a circle or a polygon close to a circle. It is preferable to make the shape approximate to a circle. This is because the metal ball is well accommodated and the stress due to thermal expansion and contraction can be uniformly received in all directions. In addition, the diameter of the concave portion or the inner peripheral space or the depth (the thickness of the pad)
Set properly according to the type, material, flat (main surface) shape and size of the wiring board as long as the drop amount (locking depth) of the metal ball does not hinder the gap maintaining means between the pads. do it.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described in detail with reference to FIGS. However,
In this embodiment, the present invention is embodied in a ceramic substrate. In the drawing, reference numeral 1 denotes a substrate for a BGA package made of alumina ceramic, the one main surface 2 of which is formed in a substantially circular shape in plan view.
A large number of pads 3 and 3 made of metal whose surface is wetted by solder are formed vertically and horizontally. In this example, each of the pads 3 is formed in a mortar shape so that the vertical cross section is U-shaped or V-shaped, and a recess 4 is formed at the center. And its bottom surface 4a
However, in this example, the height is lower than the upper surface (main surface) 2 of the substrate 1.

Each of the pads 3 is connected to a plurality of internal circuit wirings (not shown) in the substrate 1, and the entire surface of the pad 3 is plated with Ni or Au by electrolytic or electroless plating. I have. Incidentally, in this example, the pad 3 has a thickness of about 20 μm, and the outer diameter D1 of the upper surface 3a.
The concave portion 4 has an upper edge diameter (inner diameter) D2 of the wall surface 4b of 400 μm and an inner diameter D3 of the bottom surface 4a of 2 μm.
The lower taper is set to 00 μm, and the depth H is set to 150 μm.

As shown in FIG. 3, for a wiring board having such a pad 3, a low melting point solder (Pb-Sn eutectic solder) is applied on the Au plating layer on the surface of the pad 3. 5, a solder ball (also simply referred to as a solder ball) 6 made of, for example, solder (for example, Pb 90% -Sn 10%) having a higher melting point is mounted, and the connection terminal 7 is formed by soldering with eutectic solder. Is done. In this case, the solder ball 6 is
b and the pad upper surface 3a are supported by the ridge line, and the lowermost end 6a is slightly dropped into the concave portion 4 by its own weight,
As a result, durability against lateral force is large. Thus, the solder ball 6 has its lowermost end 6
a is lower than the upper surface 3a of the connection pad 3 and soldered (bonded) with the low melting point solder 5 to form the BGA package substrate 1 forming the connection terminals (bumps) 7.
The solder ball 6 in this example has a diameter of 60.
0 μm. In this manner, a portion of the lower portion of the solder ball 6 that is approximately one-eighth of its diameter is lower than the upper surface of the concave portion 4 and can be brought into a state of falling into the concave portion 4.

Such a ceramic BGA package substrate 1 is provided with connection pads with low melting point solder 25 arranged and formed so as to correspond to the arrangement of the connection terminals 7 as shown by the two-dot chain line in FIG. Each of the pads 3 and 23 is positioned and overlapped with a conventional printed board (for example, a printed board made of glass-epoxy resin) 21 having a (group) 23 (see FIGS. 4 and 5). The melting point solder 25 is melted. Then, as shown in FIG. 6, the connection pads 3 and 23 are connected via the low-melting solders 5 and 25 and the solder balls 6, and the solder balls 6 are formed in the recesses 4 of the pads 3 of the ceramic substrate 1. The lowermost end 6 a is lower than the upper surface 3 a of the pad 3.

Thereafter, there is a temperature change in such a joint structure. For example, a shear stress S acts on the main surface 2 in the direction of the arrow in FIG. The pad 3 on the substrate 1 side and the low melting point solder 5
When a crack K occurs and propagates as shown in FIG. 7 starting from the vicinity of the interface with the interface (the position P indicated by the dashed arrow),
The crack K reaches the surface of the high melting point solder ball 6, but stops at the surface. Therefore, it is possible to prevent the crack from spreading to the opposite side of the terminal at a stretch and leading to disconnection as in the related art.

At this time, the shearing force S is applied to the solder ball 6, but the lower portion including the lowermost end portion 6a of the solder ball 6 falls into the concave portion 4 of the pad, and the movement in the lateral direction is restricted. That is, since the shearing force S is received by the solder ball 6 and the recess 4, the solder ball 6 is deformed above the pad upper surface 3 a as shown by a two-dot chain line in FIG. Absorb. Thus, the development of the first crack K stops at the surface of the solder ball 6 without generating a new crack, thereby preventing disconnection between the pads.

As shown in FIG. 8, when the depth Hb at which the solder ball 6 falls into the concave portion 4 is set to be approximately 15% or more of the diameter Db of the ball 6, the pad upper surface 3a becomes in contact with the ball surface (tangential line S ) Is 45 degrees or more,
Since the shearing force is reliably applied to the inside of the solder ball 6, the progress of the crack can be reliably stopped. That is, when a metal ball such as a solder ball 6 falls into the concave portion 4,
The ball 6 comes into contact with the wall surface 4 b of the recess 4, but the depth Hb at which the ball 6 drops from the upper edge of the recess 4 is equal to the ball 6.
If it is made to fall as deep as about 15% or more of the diameter Db of
This is because the ball 6 receives a shearing force in a (circular) cross section close to its diameter Db. Therefore, the diameter D of the ball 6
The size (inner diameter and depth) of b and the concave portion 4 may be set so that the angle θ between the surface of the ball 6 and the pad upper surface 3a is 45 degrees or more.

Next, a method for manufacturing the wiring board 1 or the connection terminals 7 will be described with reference to FIG. First,
Ceramic green sheet 11 containing alumina as a main component
(See FIG. 9-A), press-mold the concave portion 14 at a predetermined position, that is, a position forming each connection pad (see FIG. 9-B), and form a metallization made of a refractory metal such as tungsten on the surface thereof. A paste (also called a pad) 13 is applied and formed by printing or the like according to the pad shape (see FIG. 9C). Alternatively, after printing the metallized paste 13 on the green sheet 11 (see the right side of FIG. 9B), the recess may be formed by pressing. Then this sheet 11
A predetermined number of green sheets are laminated so that
By crimping them and firing them simultaneously (batch),
A ceramic substrate is formed in which a connection pad (group) 13 having a recess at the center of the surface exists on one main surface. Then, the connection pad 3 is formed by applying Ni plating 15 and Au plating 16 on the surface of the connection pad 13.
reference).

Then, a low-melting-point solder paste 15 is applied to the surface of the connection pad 3 by printing or the like.
When the high melting point solder ball 6 is placed on this (see FIG. 9-E) and heated to, for example, 220 ° C. to melt only the low melting point solder 15 and solder the high melting point solder ball 6 to the connection pad 3, As shown in FIG.
The wiring board 1 has the connection terminals 7 on which the balls 6 are soldered. In other words, the formation of the pad 3 and the formation of the solderable surface 3a of the surface 3a can be realized in substantially the same steps as in the case of a conventional ceramic package substrate. Alternatively, after sintering a ceramic substrate provided with a concave portion in advance, a paste such as Ag or Ag-Pd is applied to the concave portion and the vicinity thereof and baked.

In the above-described embodiment, the bottom surface 4 a of the recess 4 formed by the pad 3 is lower than the upper surface 2 of the substrate 1. Therefore, the lateral displacement of the pad 3 itself due to the shearing force is also effectively prevented. Moreover, since the bonding area can be increased as compared with a flat pad, the tensile strength is also improved. In addition, when the solder balls 6 are mounted in the formation of the connection terminals (solder bumps) 7, the balls 6 fall into the recesses 4, so that their positions are stabilized. In the connection pad 3 of the previous example, a case was described in which a high melting point solder ball 6 was used as a solder bump and this was formed by soldering with a low melting point solder 5. However, when a metal ball was used, a high melting point solder ball was used. Instead of 6, a Cu ball may be used. However, when a Cu ball is used, its surface is preferably coated with a low melting point solder to enhance the wettability of the solder.

FIGS. 10 and 11 show a modification of the previous example. This is different only in that the pad 33 itself is formed in a circular shape in plan view and has a concave shape in vertical section without depressing the surface 2 of the substrate 1, thereby forming the concave portion 34 in the center of the plane of the pad 33. Since the operation and effect are basically the same as those of the previous example, detailed description is omitted. However, the illustrated concave portion 34 is formed concentrically in a columnar shape. FIG. 12 shows a state in which the metal ball 6 is soldered to the pad 3 by the low melting point solder 5 in the same manner as described above. effective.

Next, an embodiment in which the pad 43 is formed in a ring shape and a space is formed on the inner peripheral side thereof will be described with reference to FIGS. However, this is only the point that the main surface (surface) 2 of the substrate 1 is not dented, and the shape of the pad 43 itself is formed on the flat surface 2 in a plan view, a ring shape or a cylindrical shape with a predetermined thickness. The functions and effects thereof are the same as those of the previous example, except for the above-described embodiment, and therefore detailed description is omitted. However, in this example, the pad 43
Since the insulating substrate is exposed at the bottom surface on the inner peripheral side (vacant space), the soldering area is reduced accordingly.

FIG. 15 shows that the metal ball 6
FIG. 9 is a view in which a low melting point solder is mounted and soldering is performed. Even when bonding is performed using such a wiring board, the same operation or effect as in the above-described embodiment is obtained. In this example, since the shape of the pad 43 is relatively simple, it can be easily formed.
Therefore, the present invention is suitable for a case where the connection terminal is small, such as a wiring board for connecting flip chips.

In the above description, the case where the present invention is embodied on a ceramic package substrate and this is mounted on a resin printed circuit board has been described. However, the present invention can be embodied on such a printed circuit board. When the above-described ceramic substrate is mounted on and connected to such a printed circuit board, disconnection between the pads of both wiring substrates is more effectively prevented. That is, the present invention is extremely effective when BGA-joining wiring boards having different coefficients of thermal expansion irrespective of the type of wiring board such as a package board or a printed board, or the material thereof.

When the present invention is embodied in a resin wiring board made of glass-epoxy resin or the like, the following forming method is exemplified. That is, when the pad 3 of FIG. 1 is embodied as a resin wiring board, for example, an insulating layer having a recess at the center of the pad forming portion is formed on the surface of the resin substrate by photolithography technology, and thereafter, A copper pad having a predetermined thickness may be formed by an additive method using electroless Cu plating or electrolytic Cu plating, or by a subtractive method.

When the pad 33 of FIG. 10 is embodied in a resin wiring board, for example, the pad portion of the resin substrate is formed by an additive method using electroless Cu plating or electrolytic Cu plating, A copper pad having a predetermined thickness is formed by an active method, and thereafter, a concave portion 34 can be formed by half-etching only a central portion of the pad 33 using an etching resist.

Further, when the pad 43 of FIG. 13 is embodied as a resin wiring board, for example, the pad portion of the resin substrate is formed by an additive method using electroless Cu plating or electrolytic Cu plating, or The copper pad having a predetermined thickness may be formed in a ring shape by an active method.

The surface of the pad of such a resin substrate is plated with Ni or Au, and then the low melting point solder paste is printed on the pad, and a metal ball is mounted and reflowed. In the same manner as the wiring board of the above, a wiring board formed by soldering metal balls can be obtained.

[0037]

As is apparent from the above description, in the wiring board according to the present invention, when the metal ball is soldered to the connection pad, the metal ball is in the concave portion of the connection pad or in the inner peripheral side of the ring-shaped one. In this case, the lowermost end of the metal ball can be soldered at a level lower than the upper surface of the connection pad. In other words, the metal ball drops into the recess or the inner peripheral side of the pad and can be soldered in a form that locks in the horizontal direction. The performance is improved.

In the case of bonding with such a wiring board, even if cracks are generated and propagate near the interface between the pad and the low melting point solder, the cracks reach the surface of the metal ball.
Crack growth stops at the surface. As described above, according to the wiring substrate of the present invention, it is possible to prevent a crack from developing at a stretch and leading to disconnection between connection terminals as in the related art, and to obtain a highly reliable joint.

[Brief description of the drawings]

FIG. 1 is a schematic front view of a configuration of an embodiment of a substrate for a BGA package according to the present invention, and an enlarged view illustrating connection pads.

FIG. 2 is an enlarged plan view of a connection pad part of FIG. 1;

FIG. 3 is a view in which solder balls are soldered to the connection pads of FIG. 2 via low-melting solder.

FIG. 4 is a schematic configuration front view of a BGA package substrate in which solder balls are soldered to connection pads.

FIG. 5 is an enlarged partial cross-sectional view of a connection terminal portion of both wiring boards when a BGA package substrate is superimposed on a ceramic substrate.

FIG. 6 is a view soldered in FIG. 5;

FIG. 7 is an explanatory cross-sectional view of a state in which a crack has occurred and its progress has stopped in FIG. 6;

FIG. 8 is a cross-sectional view illustrating an appropriate depth at which a solder ball falls into a concave portion.

FIG. 9 is a manufacturing process diagram of a wiring board or a connection pad.

FIG. 10 is a longitudinal sectional view showing a modification of the pad of FIG. 1;

FIG. 11 is a plan view of FIG. 10;

FIG. 12 is a longitudinal sectional view in which a metal ball is soldered to the pad of FIG. 10;

FIG. 13 is a longitudinal sectional view showing an embodiment in which pads are formed in a ring shape.

FIG. 14 is a plan view of FIG. 13;

FIG. 15 is a longitudinal sectional view in which a metal ball is soldered to the pad of FIG. 13;

FIG. 16 is a diagram illustrating connection terminals of a conventional BGA wiring board.

FIG. 17 is an explanatory cross-sectional view showing a state in which a conventional BGA wiring board is overlaid on a ceramic substrate and connection terminals are joined.

FIG. 18 is a cross-sectional view for explaining a state in which cracks occur in solder due to expansion and contraction of both wiring boards due to a temperature change in FIG. 17;

FIG. 19 is a partially enlarged view of FIG. 18;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 BGA package board 2 Main surface of BGA package board 3, 33, 43 Connection pad of BGA package board 3a Upper surface of connection pad 4, 34 Depression of connection pad 5 Low melting point solder 6 High melting point solder ball (metal ball) 7 connection terminal 21 printed circuit board 22 main surface of printed circuit board 23 connection pad of printed circuit board

Claims (4)

[Claims] 1. A wiring board having a plurality of connection pads on a main surface having a solderable surface, and a solderable metal ball being connected as a connection terminal to the connection pad. A wiring board, wherein the connection pad is provided with a concave portion at a substantially center thereof so that a lowermost portion of the metal ball is lower than an upper surface of the connection pad when the metal ball is soldered. . 2. In a substantially central recess of the connection pad, the lowermost end of the metal ball is lower than the upper surface of the connection pad, and the metal ball is connected to the connection pad with solder having a melting point lower than the melting point of the metal ball. 2. The wiring board according to claim 1, wherein the wiring board is soldered. 3. A wiring board having a plurality of connection pads on a main surface having a solderable surface on which solderable metal balls are soldered as connection terminals to the connection pads. The wiring board, wherein the connection pad is formed in a ring shape such that a lowermost end of the metal ball is lower than an upper surface of the connection pad when the metal ball is soldered. 4. An inner peripheral side of the connection pad, wherein the lowermost end of the metal ball is lower than the upper surface of the connection pad, and the connection pad is soldered with solder having a melting point lower than the melting point of the metal ball. The wiring board according to claim 3, which is attached.