Wiring board having lead pin, and lead pin

A wiring board having a lead pin is provided. The wiring board having the lead pin includes a connecting pad which is formed on the wiring board, and to which the lead pin is bonded through a conductive material. The lead pin includes: a shaft portion; a head portion which is provided on one end of the shaft portion; a protruded portion which is formed on a surface side of the head portion opposed to the connection pad; and a first taper portion which is formed between the head portion and a base part of the shaft portion.

This application claims priority from Japanese Patent Application No. 2008-313966, filed on Dec. 10, 2008, the entire contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a wiring board having a lead pin, and the lead pin, and more particularly to a wiring board having a lead pin which is obtained by bonding the lead pin to a connecting pad formed on the wiring board through a conductive material, and the lead pin to be used therein.

DESCRIPTION OF RELATED ART

A wiring board having a lead pin which is formed by bonding the lead pin as an external connecting terminal to a connecting pad provided on the wiring board includes a product which is offered by bonding a lead pin5through a solder14, for example, as a bonding material for a conduction to a connecting pad12formed on a wiring board10as shown inFIG. 13.FIG. 13shows a wiring board having a lead pin which is formed by bonding, to the connecting pad12, a head portion5aof the so-called flat pin type lead pin5with the head portion5aprovided like a flat disc.

In case of the wiring board having a lead pin which uses the lead pin5having the flat head portion5a, as shown inFIG. 14A, there is a problem in that a void A is apt to be generated between the head portion5aand the connecting pad12and the lead pin5is tilted from an upright position to cause a failure when the lead pin5is bonded to the connecting pad12by a heating reflow. As shown inFIG. 14B, moreover, there is a problem in that the solder14is protruded toward a surface at an opposite side to a bonding surface of the head portion5ato the connecting pad12and a variation in a bonding height of the lead pin5is thus caused when the lead pin5is bonded to the connecting pad12.

As a method of solving the problems, there has been investigated a method of setting a bonding surface of a head portion of a lead pin to a connecting pad to take a shape of a hemispherical surface or providing a projection on a surface of the head portion which is bonded to the connecting pad, thereby regulating a bonding height of the lead pin depending on a height of the projection when bonding the lead pin to the connecting pad.

In a wiring board having a lead pin, the number of pins has been increased, and furthermore, a diameter of the lead pin has been reduced. For this reason, a bonding strength of the lead pin and a connecting pad formed on the wiring board has been more important than that in a related art. In the related art, the bonding strength is insufficient due to a reduction in a bonding area of the lead pin and a conductive material because of a decrease in a diameter of the lead pin, and furthermore, a pull strength is insufficient depending on a strength of the lead pin itself. Moreover, an increase in the bonding strength is inhibited due to the fact that a void remains in the conductive material to be used for bonding the lead pin. Furthermore, the conductive material is protruded toward a shaft portion beyond a head portion of the lead pin so that a removing/attaching property from/to a socket causes a problem.

SUMMARY OF INVENTION

Illustrative aspects of the present invention provide a wiring board having a lead pin which can ensure a sufficient bonding strength of the lead pin and a connecting pad formed on the wiring board and can be offered as a product having a high reliability even if the lead pin has a small diameter, and the lead pin to be used therein.

According to a first aspect of the invention, a wiring board having a lead pin includes a connecting pad which is formed on the wiring board, and to which the lead pin is bonded through a conductive material. The lead pin includes: a shaft portion; a head portion which is provided on one end of the shaft portion; a protruded portion which is formed on a surface side of the head portion opposed to the connection pad; and a first taper portion which is formed between the head portion and a base part of the shaft portion.

According to a second aspect of the invention, a wiring board having a lead pin includes a connecting pad which is formed on the wiring board, and to which the lead pin is bonded through a conductive material. The lead pin includes: a shaft portion; a head portion which is provided on one end of the shaft portion; a protruded portion which is formed on a surface side of the head portion opposed to the connection pad; and a trench which is formed on a surface of the head portion opposed to the connection pad.

According to a third aspect of the invention, a wiring board having a lead pin includes a connecting pad which is formed on the wiring board, and to which the lead pin is bonded through a conductive material. The lead pin includes: a shaft portion; a head portion which is provided on one end of the shaft portion; a protruded portion which is formed on a surface side of the head portion opposed to the connection pad. And, an external surface of the protruded portion and a surface of the head portion opposed to the connection pad are smoothly connected to each other through a continuous curved surface.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

First Exemplary Embodiment

FIGS. 1A and 1Bare sectional views showing a wiring board30having a lead pin according to a first exemplary embodiment of the present invention.FIG. 1Ais a sectional view showing a structure of a main part of a wiring board30having a lead pin andFIG. 1Bshows the enlarged vicinity of a bonding portion of a lead pin20and a connecting pad12. InFIG. 1B, the lead pin20portion is illustrated in a front shape in order to easily understand a shape of the lead pin20. The drawing showing the enlarged bonding portion of the lead pin20will be given in the same manner.

The wiring board30having a lead pin is formed by bonding the lead pin20to the connecting pad12provided on one of surfaces of a wiring board10through a solder14as a bonding conductive material.

In the wiring board10, one of the surfaces is formed as a bonding surface of an external connecting terminal to bond the lead pin20and the other surface is formed as an element mounting surface for mounting a semiconductor device thereon. One of the surfaces in the wiring board10is covered with a covering material16such as a solder resist except for a region in which the connecting pad12is formed, and the connecting pad12takes a planar shape which is exposed circularly.

The connecting pad12is formed by a copper layer, and nickel plating and gold plating are carried out as protective plating over a surface of the copper layer in this order.

A method of forming a wiring pattern including the connecting pad12on a surface of a wiring board is based on a general wiring pattern forming method such as a build-up method.

An operation for bonding the lead pin20to the wiring board10is carried out in the following manner.

First of all, a solder paste is applied as a conductive material to an exposed surface of the connecting pad12. Subsequently, the lead pin20is supported in an arrangement which is coincident with a planar arrangement of the connecting pad12by means of a support jig, and is caused to pass through a heating reflow device in a state in which the support jig and the wiring board10are aligned with each other. Thus, the lead pin20is bonded to the wiring board10. After the lead pin20is bonded to the wiring board10, the support jig is removed to obtain the wiring board30having the lead pin.

The support jig has a function for aligning the lead pin20with the connecting pad12and supporting the lead pin20to be bonded to a substrate surface of the wiring board10in an upright state. A set hole for setting the lead pin20which is provided on the support jig is formed to have an inside diameter with a slight clearance with respect to a diameter of a shaft portion20aof the lead pin20in consideration of an operation for positioning the lead pin20and an operation for removing/inserting the shaft portion20aof the lead pin20therefrom/therein.

In the lead pin20to be used in the wiring board having the lead pin according to the first exemplary embodiment, one of ends of the shaft portion20ais provided with a head portion20btaking a planar shape of a circular plate, and a protruded portion20cis formed concentrically with the shaft portion20aon a surface of the head portion20bwhich is opposed to the connecting pad12as shown inFIG. 1B.

In the first exemplary embodiment, an outside diameter of the protruded portion20cis set to be equal to that of the shaft portion20a. Moreover, a tip of the protruded portion20cis formed to take a vertical cutting configuration with respect to an axial direction of the shaft portion20a, that is, the protruded portion20cis formed to take a shape of a short cylinder which has an end face to be a flat surface.

Furthermore, positions of base parts of the protruded portion20cand the head portion20bhave rectangular sections. On the other hand, a surface side of the head portion20bto which the shaft portion20ais integrally coupled is set to be a taper portion20dobtained by linearly chamfering a portion between a base part of the shaft portion20aand the head portion20bin a sectional shape.

In a state in which the lead pin20is bonded to the connecting pad12, the solder14is filled in a portion between a lower surface of the head portion20b(an opposed surface to the connecting pad12) and the connecting pad12. An outside diameter of the head portion20bof the lead pin20is slightly smaller than an opening diameter of the covering material16. In a state in which the lead pin20is bonded to the connecting pad12, a slight clearance is formed between an outer peripheral edge of the head portion20band an inner peripheral edge of the covering material16.

A quantity of the solder14supplied to the connecting pad12is almost equal to such a quantity as to fill a region surrounded by the connecting pad12, an opening side surface of the covering material16and the lower surface of the head portion20b.

The lead pin20is bonded to the connecting pad12with a protruded end face of the protruded portion20copposed to a surface of the connecting pad12. The solder14is also present thinly between the protruded end face of the protruded portion20cand the surface of the connecting pad12and fills in a portion between the surface of the connecting pad12and the lower surface of the head portion20bof the lead pin20. In other words, a bonding region of the solder14and the lead pin20in the bond of the lead pin20to the connecting pad12is obtained by putting an external surface of the protruded portion20cand the lower surface of the head portion20btogether.

In the wiring board30having the lead pin according to the first exemplary embodiment, there is used the lead pin20in which the protruded portion20cis provided on the head portion20b. As compared with the case in which a lead pin including a simple head portion is used, therefore, it is possible to increase a contact surface area in the bonding portion of the solder14and the lead pin20. Thus, it is possible to increase a bonding strength of the lead pin20and the connecting pad12.

Moreover, the end face of the protruded portion20cwhich is opposed to the connecting pad12is formed to be a flat surface. Therefore, the lead pin20is bonded in an erecting state with the end face of the protruded portion20cplaced in parallel with the surface of the connecting pad12. Consequently, the lead pin20can easily be bonded in an upright state.

Moreover, the protruded portion20cof the lead pin20has a function for controlling a height position from the surface of the connecting pad12to the lower surface of the head portion20bin the bond of the lead pin20to the connecting pad12. By regulating the height of the protruded portion20c, it is possible to define a height of a tip of the lead pin20in the bond of the lead pin20to the connecting pad12. Thus, it is possible to reduce a variation in the height of the lead pin20in a state in which the lead pin20is attached.

By regulating a distance from the surface of the connecting pad12to the lower surface of the head portion20b, furthermore, it is possible to regulate the filling state of the solder14in the bond of the lead pin20to the connecting pad12. Consequently, it is possible to prevent the solder14from being protruded toward a side surface of the head portion20bor the shaft portion20aside beyond the head portion20b.

In the first exemplary embodiment, moreover, the taper portion20dis provided on the side of the head portion20bto which the shaft portion20ais coupled. As compared with a lead pin formed to have a flat pin type, therefore, a strength of a coupling part of the head portion20band the shaft portion20acan be enhanced more greatly. When the lead pin20is pulled, thus, it is possible to prevent the coupling part from being broken, thereby enhancing a pull strength of the lead pin20.

In the first exemplary embodiment, the outside diameter of the protruded portion20cis set to be equal to that of the shaft portion20a. In a process for manufacturing the lead pin20, a wire having a predetermined diameter is subjected to a press processing to form the lead pin20having the head portion20b. In the case in which the protruded portion20cis set to have an equal diameter to that of the shaft portion20a, it is possible to easily carry out a process for performing the processing over the wire, thereby manufacturing the lead pin. The protruded portion20cdoes not need to have the equal diameter to that of the shaft portion20ain the lead pin20but may have a smaller or larger diameter than that of the shaft portion20a.

Second Exemplary Embodiment

FIG. 2Ais a sectional view showing a wiring board130having a lead pin according to a second exemplary embodiment of the present invention.

For a lead pin120according to the second exemplary embodiment which is to be used, similarly, a protruded portion120cis formed concentrically with a shaft portion120aat a surface side of a head portion120bwhich is to be bonded to a connecting pad12.

Referring to a different structure from the lead pin20used in the first exemplary embodiment, a taper portion120eto be a chamfered portion taking a linear sectional shape is provided between a base part of the protruded portion120cand the head portion120b. The other structures of the lead pin120of the second exemplary embodiment are the same as those of the lead pin20of the first exemplary embodiment shown inFIGS. 1A and 1B.

In the second exemplary embodiment, the taper portion120eis provided between the head portion120band the protruded portion120c. Therefore, a void remains in a solder14for bonding the lead pin120to the connecting pad12with difficulty.

The reason is as follows. The taper portion120eis provided on a lower surface of the head portion120b(an opposed surface to the connecting pad12). Consequently, the void generated in the solder14is easily moved along an inclined surface of the taper portion120e(is moved from a central side of the head portion120btoward an outside inFIGS. 2A and 2B). Thus, there is taken an action for discharging the void from an inside of the solder14.

According to a shape of the lead pin120in accordance with the second exemplary embodiment, the void is prevented from remaining in the solder14filled between the head portion120band the connecting pad12. As compared with the case in which the void remains in the solder14, therefore, it is possible to enhance a bonding strength of the lead pin120and the connecting pad12more greatly. By preventing the void from remaining in the solder14, moreover, it is possible to inhibit the lead pin120from being bonded with a tilt.

Furthermore, the taper portions120dand120eare respectively provided on the base parts of the head portion120band the shaft portion120aand those of the head portion120band the protruded portion120c. Consequently, it is possible to enhance a strength of a coupling part. Thus, it is possible to prevent the coupling part from being broken when the lead pin120is pulled, thereby enhancing a pull strength of the lead pin120.

Third Exemplary Embodiment

FIGS. 3A and 3Bare sectional views showing a wiring board230having a lead pin according to a third exemplary embodiment of the present invention.

In a lead pin220according to the third exemplary embodiment, similarly, a protruded portion220cis formed concentrically with a shaft portion220aat a surface side of a head portion220bwhich is to be bonded to a connecting pad12, and a taper portion220dis provided between a base part of the shaft portion220aand the head portion220band a taper portion220eis provided between a base part of the protruded portion220cand a lower surface of the head portion220b.

Referring to a different structure from the lead pin120used in the second exemplary embodiment shown inFIGS. 2A and 2B, the protruded portion220cis formed to take a shape of a hemisphere which is convexed toward the connecting pad12. In other words, the protruded portion220cis formed to take a shape of a projection which has a hemispherical external surface from the taper portion220e. The other structures of the lead pin220of the third exemplary embodiment are the same as those of the lead pin120of the second exemplary embodiment.

A protruding height of the protruded portion220cis set to fill a part between the connecting pad12and the lower surface of the head portion220bwith a solder14in a state in which the lead pin220is bonded to the connecting pad12. An external surface of the protruded portion220cis formed to take a shape of a hemispherical surface. Consequently, the lead pin220is bonded to the connecting pad12in a state in which a protruded end (a top part) of the protruded portion220calmost comes in contact with a surface of the connecting pad12.

In the wiring board230having the lead pin220according to the third exemplary embodiment, the external surface of the protruded portion220cis set to take the shape of the hemispherical surface which is convexed toward the connecting pad12. Consequently, a void can be prevented from being caught between an end face of the protruded portion220cand the connecting pad12. In addition, the void generated in the solder14is discharged more easily than in the first and second exemplary embodiments shown inFIGS. 1A to 2B.

In the lead pins20and120shown inFIGS. 1A to 2B, the protruded portion20cor120cis formed to take a shape of a short cylinder. For this reason, there is a possibility that the void might be caught between the end face of the protruded portion20cor120cwhich is opposed to the connecting pad12and the connecting pad12. In the third exemplary embodiment, the protruded portion220cis formed to take the hemispherical shape. Therefore, the void can be prevented from being caught between the top part of the protruded portion220cand the surface of the connecting pad12. The void generated in the solder14is moved from a lower part toward an upper part along the external surface taking the shape of the hemispherical surface in the protruded portion220cand can be thus discharged from an inside of the solder14easily.

FIG. 3Cshows a protruded portion221cin a lead pin221in which the external surface of the protruded portion221ctakes a shape of a smooth curved surface with an opposed side to the connecting pad12convexed. In the lead pin221, there is taken a conical shape in which a tip side of the protruded portion221chas a diameter reduced gradually toward the connecting pad12. The tip part of the protruded portion221cis chamfered to take the shape of the hemispherical surface. In the case of the protruded portion220cformed to take the hemispherical shape, an interval between the external surface of the protruded portion220cand the surface of the connecting pad12is reduced at the tip side of the protruded portion220cso that a void might remain in the small interval portion. On the other hand, in the case of the protruded portion221c, the external surface of the protruded portion221cis formed to be a taper surface in a sectional shape. Consequently, the interval between the connecting pad12and the external surface of the protruded portion221cis increased so that the void can easily be removed from the inside of the solder14.

Also in the third exemplary embodiment, the solder14is stuck to the taper portion220eand the external surface of the protruded portion220cor221c. As compared with the case of a flat pin, therefore, it is possible to increase a bonding area of the solder14and the lead pin220or221, thereby enhancing a bonding strength of the lead pin220or221and the connecting pad12more greatly.

Although an outside diameter of the protruded portion220cor221cin a position in which it is to be coupled to the head portion220bis set to be equal to that of the shaft portion220ain the third exemplary embodiment, the diameter of the protruded portion220cor221ccan be selected properly and may be set to be larger or smaller than the diameter of the shaft portion220a.

Fourth Exemplary Embodiment

FIGS. 4A and 4Bare sectional views showing a lead pins320and321according to a fourth exemplary embodiment of the present invention. In the fourth exemplary embodiment, an external surface of a protruded portion320cor321cand an external surface of a taper portion320eon a lower surface of a head portion320bare provided continuously through a smooth curved surface.

FIGS. 4A and 4Bshow example in which a coupling part of the external surface of the protruded portion320cor321cand the taper portion320eis chamfered like a curved surface for the lead pin320including the protruded portion320chaving the external surface taking the shape of the hemispherical surface and the lead pin321including the protruded portion321chaving the external surface taking the shape of the conical surface, respectively.

When the external surface of the protruded portion320cor321cand the lower surface of the head portion320bare formed to be a smooth and continuous curved surface, thus, a void generated in a solder14can be discharged more effectively as compared with that in the third exemplary embodiment of the lead pin220shown inFIGS. 3A to 3C.

FIGS. 4A and 4Btypically show, in an arrow, a condition in which a void A generated in the solder14is moved in the solder14and is thus discharged. An operation for bonding the lead pin320or321to a connecting pad12by using the solder14is based on a method of carrying out bonding by supporting the lead pin320or321in an upright state through a support jig and causing them to pass through a heating reflow device as described above. At the heating step, the lead pin320or321is bonded with a shaft portion320aset in a vertical and upward direction as shown inFIGS. 4A and 4B. Accordingly, the void A generated in the solder14to be fused between the head portion320bof the lead pin320or321and the connecting pad12is moved from a lower part toward an upper part in the drawing by an action of a buoyancy.

The void A generated in the vicinity of a center of the connecting pad12is moved in an upward direction along the external surface of the protruded portion320cor321cand the lower surface of the head portion320b. By setting the protruded portion320cor321cand the lower surface of the head portion320bto be the continuous and smooth curved surface, therefore, the void A can easily be moved and discharged from an inside of the solder14to an outside.

The method of setting the lower surface of the head portion320band the external surface of the protruded portion320cor321cin the lead pin320or321to be the smooth curved surface as in the fourth exemplary embodiment is not restricted to the exemplary embodiment but can also be applied to the lead pin including the protruded portion20cor120ctaking the shape of the short cylinder shown inFIGS. 1A to 2Band other exemplary embodiments.

Fifth Exemplary Embodiment

FIGS. 5A and 5Bare sectional views showing a wiring board430having a lead pin according to a fifth exemplary embodiment of the present invention.

In a lead pin420shown inFIGS. 5A and 5B, similarly, a head portion420bis provided with a protruded portion420cin an opposed arrangement to a connecting pad12.

In the lead pin420according to the fifth exemplary embodiment, both surfaces of the head portion420bon a side to which a shaft portion420ais to be coupled and a side to which the protruded portion420cis to be coupled are formed by taper portions420dand420e, respectively, and the taper portions420dand420eare formed to take such a shape as to divide the head portion420binto two parts in a vertical direction.

By taking such a configuration as to divide the head portion420binto two parts of the taper portions420dand420ein the vertical direction, it is possible to increase a tilt angle of the taper portion420eon a lower surface of the head portion420b(an opposed surface to the connecting pad12) more greatly as compared with the lead pin320,321of the fourth exemplary embodiment shown inFIGS. 4A and 4B, for example. In other words, if a design for forming the taper portions420dand420eto divide the head portion420binto two parts in the vertical direction is set on a condition that a thickness of the head portion420bis constant, it is possible to increase at least an angle of the taper portion420ein the head portion420bwhich is opposed to the connecting pad12more greatly as compared with a lead pin in which a base part of the protruded portion20cand the head portion20bare simply chamfered.

If the tilt angle of the taper portion420ecan be increased, a void can easily be discharged from an inside of a solder14and can be thus prevented from remaining in the solder14.

In the lead pin420according to the fifth exemplary embodiment, in the case in which the surface of the head portion420bwhich is opposed to the connecting pad12is set to be an inclined surface, the void can easily be discharged from the solder14by utilizing the thickness of the head portion420b.

Although both of the lower and upper surfaces of the head portion420bare set to be the taper portions in the fifth exemplary embodiment, it is preferable that the upper surface of the head portion420bshould be a flat surface and the lower surface of the head portion420bshould be an inclined surface corresponding to a total thickness of the head portion420bin order to maximize the tilt angle of the surface of the head portion420bwhich is opposed to the connecting pad12. In consideration of a strength of the lead pin420itself, it is suitable to take the configuration in which the taper portions420dand420eare provided on both of the upper and lower surfaces of the head portion420bas shown inFIGS. 5A to 5C.

FIGS. 5A and 5Bshow the lead pin420in which an external surface of the protruded portion420ctakes a shape of a spherical surface.FIG. 5Cshows a lead pin421in which a protruded portion421cis formed to take a shape of a short cylinder. The shape of the head portion420baccording to the fifth exemplary embodiment can be employed irrespective of the configuration of the protruded portion.

Sixth Exemplary Embodiment

FIGS. 6A and 6Bare sectional views showing a wiring board530having a lead pin according to a sixth exemplary embodiment of the present invention. A lead pin520to be used in the wiring board530according to the sixth exemplary embodiment includes a protruded portion520ctaking a shape of a short cylinder on a surface side of a head portion520bwhich is opposed to a connecting pad12, and includes a trench521for discharging a void on the surface of the head portion520bwhich is opposed to the connecting pad12.

FIG. 7Ais a front view showing the lead pin520andFIGS. 7B and 7Care plan views showing the lead pin520seen from the surface side on which the protruded portion520cis formed.FIG. 7Bshows the lead pin520in which the trench521is formed on the head portion520b, andFIG. 7Cshows the lead pin520in which a trench522is formed on the head portion520b. InFIG. 7B, the trench521is provided in eight places in a uniform arrangement in a circumferential direction with such a shape as to have an equal width from an outer peripheral edge of the protruded portion520cto that of the head portion520b. InFIG. 7C, the trench522is provided in six places in a uniform arrangement in a circumferential direction with such a shape as to gradually increase a width from the outer peripheral edge of the protruded portion520cto that of the head portion520b.

As shown inFIG. 7A, the trench521is formed to take a tilting shape from a position of a base part of the protruded portion520cto an outer periphery of the head portion520b.

FIG. 6Bshows a sectional view taken along a B-B line inFIG. 7B. In a portion of the lead pin520in which the trench521is formed, an internal surface (a side surface) of the trench521is formed as an inclined surface which is gradually separated from the connecting pad12from the position of the base part of the protruded portion520ctoward the outer peripheral edge of the head portion520b. Namely, the internal surface of the trench521is formed as an inclined surface which is gradually taken in a high position with respect to the surface of the connecting pad12from the position of the base part of the protruded portion520ctoward the outer peripheral edge of the head portion520b.

In the case of the lead pin520according to the sixth exemplary embodiment, accordingly, a void generated in a solder14filled between the head portion520band the connecting pad12can easily be discharged via the trench521. The lead pin520is formed to take a shape of a simple flat disc in an appearance. By forming the trench521on the head portion520b, however, it is possible to discharge the void from the solder14filled between the head portion520band the connecting pad12, thereby enhancing a bonding strength of the lead pin520and the connecting pad12.

It is possible to properly set the shape of the trench521to be formed on the head portion520band the number of the trenches521to be arranged.

FIGS. 8A to 8Cshow a variant of the sixth exemplary embodiment. A lead pin620to be used in the variant has a taper portion620dformed in positions of base parts of a head portion620band a shaft portion620a.FIGS. 8A and 8Bare sectional views showing a wiring board630having the lead pin620andFIG. 8Cis a front view showing the lead pin620. Referring to the lead pin620according to the variant, the taper portion620dis provided corresponding to an action for discharging a void generated in a solder14from a trench621. Consequently, it is possible to enhance a strength of a coupling part of the head portion620band the shaft portion620a, thereby preventing a breakage in the coupling part. In addition, it is possible to enhance a pull strength in a bond of the lead pin620to a connecting pad12more greatly as compared with the example shown inFIGS. 7A to 7C.

Moreover, the trench621is formed on the head portion620b. As compared with the case in which the head portion20bis formed to take a shape of a simple flat disc, consequently, it is possible to increase a bonding area of the solder14and the lead pin620, thereby enhancing a bonding strength of the lead pin620.

Seventh Exemplary Embodiment

FIGS. 9A and 9Bare sectional views showing a wiring board730having a lead pin according to the seventh present invention. A lead pin720to be used in the wiring board730having the lead pin according to the seventh exemplary embodiment includes a protruded portion720cwhich is protruded like a short cylinder from an opposite surface to a surface of a head portion720bto which a shaft portion720ais coupled, and a trench722for discharging a void is provided from the protruded portion720cto the head portion720b.

FIG. 10Ais a front view showing the lead pin720andFIGS. 10B and 10Care plan views showing the lead pin720as seen from a surface side on which the protruded portion720cis formed. The trench722is formed to take a communicating shape from a vicinal position of a center of the protruded portion720ctoward an outer peripheral edge of the head portion720b. Although a surface of the trench722which is opposed to a connecting pad12is formed to be a linear inclined surface in the seventh exemplary embodiment, the trench722may take a shape of a curve seen in a sectional direction.

FIG. 10Bshows an example in which the trench722is uniformly arranged on four sides in a circumferential direction of the head portion720bandFIG. 10Cshows an example in which the trench723is uniformly arranged on three sides of the head portion720b.

With the formation of the trench722to be the inclined surface in which an outside is placed in a higher position from the vicinal position of the center of a lower surface of the protruded portion720ctoward the outer peripheral edge of the head portion720b, thus, a void in a solder14is discharged along the trench722in a portion in which the trench722is formed (a position of a C-C line inFIG. 10B) as shown inFIG. 9B. In particular, the trench722is formed to communicate from the protruded portion720cto the head portion720b. Consequently, there is an advantage that it is possible to easily discharge, through the trench722, a void which is generated in the vicinity of the connecting pad12(a position of a bottom of the protruded portion720c) and is discharged with difficulty.

FIGS. 11A to 11Cshow a variant of the seventh exemplary embodiment. In the wiring board830having a lead pin according to the variant, there is used a lead pin820in which a taper portion820dis formed in positions of base parts of a head portion820band a shaft portion820a. The lead pin820includes a protruded portion820cwhich is protruded like a short cylinder from an opposite surface to a surface of a head portion820bto which a shaft portion820ais coupled, and a trench822for discharging a void is provided from the protruded portion820cto the head portion820b.

FIGS. 11A and 11Bare sectional views showing the wiring board830having the lead pin andFIG. 11Cis a front view showing the lead pin820.

In the variant, the taper portion820dis provided in the positions of the base parts of the head portion820band the shaft portion820a. Consequently, it is possible to enhance a strength of a coupling part of the head portion820band the shaft portion820a. Thus, it is possible to enhance a pull strength in a bond of the lead pin820to a connecting pad12more greatly as compared with the example shown inFIGS. 10A to 10C.

In the wiring board730having the lead pin and the lead pin720shown inFIGS. 9A to 10B, it is preferable to properly set the configuration of the trench722to be formed from the protruded portion720cto the head portion720band the number of the trenches722to be arranged in consideration of a discharging efficiency of the void. In the wiring board830having the lead pin and the lead pin820shown inFIGS. 11A to 11C, this configuration can also be employed.

In the lead pin720in which the trench722is formed on the protruded portion720cand the head portion720b, it is possible to increase the bonding area of the solder14to the lead pin720, thereby enhancing the bonding strength of the lead pin720more greatly as compared with a lead pin in which the protruded portion20cis simply formed.

Referring to the method of forming the trench722on the protruded portion720cand the head portion720b, moreover, there is also an advantage that it is possible to enhance a pull strength in the bond of the lead pin720to the connecting pad12without damaging the strength of the lead pin720itself.

In the seventh exemplary embodiments, it is possible to use various solders14as a conductive material for bonding the lead pin720to the connecting pad12. For example, also in the case in which a tin based solder such as a tin—antimony alloy solder is used as a lead-free conductive material, it is possible to obtain completely the same functions and effects. Moreover, it is a matter of course that a conductive material other than the solder can also be used as a conductive material for bonding.

Example of Design

FIG. 12shows an example of a design for a lead pin used actually in a wiring board having a lead pin and a connecting pad of the wiring board. In the lead pin used actually, a range of a diameter of a shaft portion was set to be 0.2 to 0.35 mm, a range of an outside diameter of a head portion was set to be 0.65 mm to 0.83 mm, a range of a height from an upper surface of the head portion to a tip of a protruded portion was set to be 0.2 to 0.45 mm, and a range of a height of the protruded portion protruded from the head portion was set to be 0.2 to 0.35 mm. A thickness of the head portion is set to be 0.1 mm or more in consideration of a prevention of a solder from being protruded toward the shaft portion upward and a formation of the trenches521,522,621,722,723and822on the head portion.

Referring to the wiring board, a range of a pad diameter P is set to be 0.75 to 1.18 mm, a range of a layer thickness D of a solder resist is set to be 0.01 to 0.1 mm, and a range of an opening diameter W of the solder resist is set to be 0.75 to 1.18 mm. An outside diameter of the head portion is set to be slightly smaller than the opening diameter of the solder resist. Moreover, the thickness of the solder resist is set to be smaller than a height of a projection.

The lead pin of this invention is formed by a metal such as a nickel-iron alloy like a “kovar” or “alloy 42”, or a copper alloy, etc. As a example, nickel plating and gold plating are carried out over a surface of the lead pin in this order, for protecting the surface or improving the solder wettability of the lead pin.

Based on the dimensions such as the pad diameter and the dimensions of the respective portions in the lead pin, it is possible to prevent the solder from being protruded toward the shaft portion side of the lead pin in an upward direction, thereby enhancing the bonding strength of the connecting pad and the lead pin.

The outside diameter of the protruded portion is usually set to be equal to that of the shaft portion. In the case in which a trench for discharging a void is formed, however, it is preferable that the outside diameter of the protruded portion should be larger than that of the shaft portion. By setting an angle θ formed by a base part of the protruded portion and the head portion to be 20 to 60 degrees, it is possible to take an action for discharging a void from an inside of a solder, thereby bonding the lead pin to the connecting pad.