Contact member

A contact member includes first and second bent portions provided between a joining part to be joined to a first board and a contacting part to come into contact with a second board, a first contact part to come into contact with the second bent portion when the first bent portion is caused to bend by the pressing of the contacting part by the second board, a second contact part to come into contact with the first bent portion when the second bent portion is caused to bend by the pressing of the contacting part by the second board after the first contact part comes into contact with the second bent portion, and a third contact part to come into contact with the first board by the pressing of the contacting part by the second board after the second contact part comes into contact with the first bent portion.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is based upon and claims the benefit of priority of Japanese Patent Application No. 2012-215290, filed on Sep. 27, 2012, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to contact members.

2. Description of the Related Art

Electronic apparatuses such as cellular phones and smartphones have been reduced in size and thickness, and in response to this, the form of mounting parts on a printed circuit board (hereinafter abbreviated to “board”) provided inside apparatuses has mostly shifted to the surface mounting of chip parts.

In these electronic apparatuses, a ground (GND) line of the board is connected to a conductor panel of the enclosure (so-called frame grounding [FG]) in order to protect electronic parts mounted on the board and to deal with noise. Frame grounding is also performed between boards. In this case, a surface-mount contact member is used to connect respective conductors of the boards.

The contact member used in FG is a member having a spring characteristic, which is formed by bending a leaf spring to have a predetermined amount of stroke. The contact member is joined to a conductor of one of the boards and is compressed by being pressed by the other of the boards to electrically connect the conductors of the boards. In order to establish a stable electrical connection, the contact member for such use is desired to have a spring stroke amount corresponding to the pressing stroke of a board and to have a contact pressure of contact with the board over a wide area in response to pressing by the board.

Furthermore, usually, an automatic mounting apparatus is used to mount electronic parts on the surface of a board. In the case of a large electronic part, the automatic mounting apparatus holds the electronic part by clamping the electronic part with claws, and mounts the electronic part at a predetermined position. On the other hand, in the case of a small electronic part, the electronic part is held by attraction and adhesion using a suction nozzle. Accordingly, such a small electronic part subjected to mounting by the automatic mounting apparatus has an attracted part that is attracted and adhered to the suction nozzle.

Such conventional contact members used for surface mounting include the following.

For example, Japanese Laid-Open Patent Application No. 2009-272237 discloses a surface-mount contact that obtains three levels of contact pressure because of two folded parts and a deformation restricting part and has an attracted surface that is attracted and adhered to a suction nozzle.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, a contact member that electrically connects a first board and a second board includes a joining part configured to be joined to the first board, a contacting part configured to come into contact with the second board, a first bent portion and a second bent portion provided between the joining part and the contacting part, a first contact part configured to come into contact with the second bent portion when the first bent portion is caused to bend by pressing of the contacting part by the second board, a second contact part configured to come into contact with the first bent portion when the second bent portion is caused to bend by the pressing of the contacting part by the second board after the first contact part comes into contact with the second bent portion, and a third contact part configured to come into contact with the first board by the pressing of the contacting part by the second board after the second contact part comes into contact with the first bent portion.

DESCRIPTION OF THE EMBODIMENTS

FIGS. 1A through 1FandFIG. 2are diagrams illustrating an embodiment of a contact member.FIGS. 1A,1B,10,1D,1E and1F are a plan view, a left side view, a front view, a right side view, a bottom view, and a perspective view, respectively, of a contact member1according to an embodiment.FIG. 2is a cross-sectional view of the contact member1, taken along a plane including line A-A inFIG. 1D.

The contact member1according to this embodiment has a spring characteristic and electrically connects respective contacts of two boards.

As a material for the contact member1, an electrically-conductive metal plate that has a spring characteristic is used. Examples of such metal plates include those of phosphor bronze, beryllium copper, and stainless steel. The contact member1is formed by processing a single metal plate of, for example, 0.08 mm to 0.15 mm in thickness (hereinafter referred to as “leaf spring”) into the shape illustrated in the drawings by press working. Furthermore, the contact member1may be partly or entirely plated with nickel, copper, or gold as desired.

Referring toFIGS. 1A through 1FandFIG. 2, the contact member1includes a horizontal part15. The horizontal part includes first and second opposite surfaces15-1and15-2, which face upward and downward, respectively, inFIG. 1CandFIG. 2. Furthermore, in order to describe the directions of bending of a leaf spring by press working, a direction in which a surface of the leaf spring on the same side as the first surface15-1of the horizontal part15is bent inward (folded in “valley fold”) is referred to as “first bending direction” and a direction in which a surface of the leaf spring on the same side as the first surface15-1of the horizontal part15is bent outward (folded in “mountain fold”) is referred to as “second bending direction.”

The contact member1includes a first joining part2to be joined to a board surface by, for example, soldering, a rising part3that is bent in the first bending direction from the first joining part2to rise from the board surface, an intermediate part4that is continuous with the rising part3, bent in the second bending direction, and spaced apart from the board surface, and a second joining part5that extends from an opening part4aformed in the intermediate part4to come into contact with the board surface.

Referring toFIG. 1E, the first joining part2includes a tapered part2athat is continuous with the rising part3. The tapered part2ais provided so that the width (a vertical dimension inFIG. 1E) of the first joining part2gradually increases to match the width of the rising part3.

Referring toFIG. 1E, the intermediate part4is pierced to have an opening of an angular letter C shape by pressing, and the opening becomes the opening part4aand a portion left surrounded by the opening becomes the second joining part5. Furthermore, as illustrated inFIG. 10, the second joining part5is so bent as to extend downward from a surface of the intermediate part4. The length of the second joining part5may be such that the second joining part5either comes into contact with the board surface or is slightly above the board surface when the contact member1is provided on the board with the first joining part2joined to the board surface.

The contact member1further includes a first bent part6that is bent obliquely upward in the first bending direction from the intermediate part4inFIG. 1C, a first spring part7that is continuous with the first bent part6, a second bent part8that is continuous with the first spring part7and is bent in the first bending direction, and a second spring part9that is continuous with the second bent part8.

The first bent part6, the first spring part7, the second bent part8, and the second spring part9form a “first bent portion” of the contact member1. The first bent portion has a first spring constant. The first spring constant may be determined by the shape of the first bent portion.

The contact member1further includes a third bent part10that is continuous with the second spring part9and is bent in the second bending direction, a third spring part11that is continuous with the third bent part10, a fourth bent part12that is continuous with the third spring part11and is bent in the second bending direction, a fourth spring part13that is continuous with the fourth bent part12, and a fifth bent part14that is continuous with the fourth spring part13and is bent in the second bending direction.

The third bent part10, the third spring part11, the fourth bent part12, and the fourth spring part13form a “second bent portion” of the contact member1. The second bent portion has a second spring constant. The second spring constant may be determined by the shape of the second bent portion.

The contact member1includes the horizontal part15, which is continuous with the fifth bent part14. The first surface15-1of the horizontal part15includes an attracted part15a, which is a surface that is attracted and adhered to a suction nozzle of an automatic mounting apparatus by its pickup operation. The horizontal part15is substantially parallel to the first joining part2, so that the horizontal part15may have the attracted part15aattracted and adhered by an automatic mounting apparatus when the first joining part2is placed on a horizontal plane.

The contact member1further includes a contacting part20that comes into contact with a second board200illustrated inFIGS. 3A through 3E. As illustrated inFIG. 1A, the horizontal part15extends in a direction away from the second bent portion relative to the contacting part20. That is, the contacting part20is positioned at the right end of the horizontal part15inFIG. 1A, so that a large area may be ensured for the attracted part15aon the first surface15-1of the horizontal part15. Furthermore, because the contacting part20is narrower in width (a vertical dimension inFIG. 1A) than the horizontal part15, it is possible to increase the contact pressure of contact with the second board200. In addition, as illustrated inFIG. 1C, the contacting part20has a shape projecting upward from the horizontal part15. Therefore, when the contact member1is pressed from above inFIG. 1Cby the second board200, the contacting part20comes into contact with the second board200.

Referring toFIG. 2, the contact member1further includes a first contact part21and a second contact part22. The first contact part21is an upper surface of the first joining part2that is approached and contacted by the vicinity of the third bent part10, which is part of the second bent portion, as a result of the bending of the first bent portion. Because the contact position of the second bent portion on the first joining part2moves because of the bending of the first bent portion even after the second bent portion comes into contact with the first joining part2, the first contact part21comes into contact with the second bent portion not at a point but over a certain area on the first joining part2.

The second contact part22is part of the second surface15-2of the horizontal part15, which approaches and comes into contact with the vicinity of the second bent part B, which is part of the first bent portion, as a result of further bending of the second bent portion after the first contact part21comes into contact with the second bent portion. Because the contact position of the first bent portion on the second surface15-2of the horizontal part15moves because of the bending of the second bent portion even after the first bent portion comes into contact with the second surface15-2of the horizontal part15, the second contact part22comes into contact with the first bent portion not at a point but over a certain area on the second surface15-2of the horizontal part15.

The contact member1further includes a sixth bent part16that is continuous with the horizontal part15and is bent in the second bending direction and a stopper part17that is continuous with the sixth bent part16and extends downward inFIG. 2. The stopper part17includes a third contact part23at its end. When the first bent portion and the second bent portion bend so that the stopper part17lowers, the third contact part23comes into contact with a first board100illustrated inFIGS. 3A through 3E. The stopper part17restricts the bending of the first bent portion and the second bent portion so as to prevent a stress applied from the second board200to the contact member1from being applied to the first bent portion and the second bent portion beyond their elastic limits. As a result, it is possible to prevent the contact member1from being damaged or plastically deformed.

Referring toFIGS. 1A through 1F, the contact member1further includes protection parts18aand18bthat are bent from the first joining part2to rise from a surface of the first joining part2. The protection parts18aand18bserve as a guide for proper bending of the first bent portion of the contact member1, and may also be used as a holding position in a clamping device of an automatic mounting apparatus.

The contact member1further includes guide parts19aand19b, which are so arranged as to enclose the stopper part17. As illustrated inFIGS. 1A and 1B, the guide parts19aand19bare formed by bending the protection parts18aand18b, respectively, so as to cover the left side of the stopper part17as illustrated inFIGS. 1A through 10.

As described above, according to this embodiment, bent parts and spring parts are integrally formed. The bent parts and spring parts of the first bent portion and the second bent portion, however, are not limited to the above-described configuration. For example, the first bent part6, the first spring part7, the second bent part8, and the second spring part9may be formed as a single bent part having the first spring constant. Likewise, the second bent portion as well is not limited to the shape illustrated in this embodiment. The shapes of the bent portions in this embodiment are examples of shapes as a contact member according to this embodiment.

Next, a displacement of the contact member1according to this embodiment is described with reference toFIGS. 3A,3B,3C,3D and3E andFIG. 4.FIGS. 3A through 3Eare diagrams sequentially illustrating, fromFIG. 3AtoFIG. 3E, a displacement of the contact member1, joined to the first board100by surface mounting, at the time of pressing on the contact member1with the second board200. InFIGS. 3A through 3E, the first board100has an electrically conductive part (not illustrated) on its upper surface. The contact member1is mounted on the upper surface of the first board100with the first joining part2being joined to the electrically conductive part on the upper surface by soldering or the like. The contacting part20of the contact member1comes into contact with an electrically conductive part (not illustrated) provided on a lower surface of the second board200. As a result, frame grounding (FG) is established between the first board100and the second board200.

FIG. 3Aillustrates a state where the second board200has first come into contact with the contact member1. InFIG. 3A, the contact member1has not received a downward force from the second board200, and the contact member1is not displaced. Accordingly, the horizontal part15is substantially horizontal. A dotted line inFIGS. 3B through 3Eindicates the position of the contact member1inFIG. 3A.

FIG. 3Billustrates a state at a time when the second board200is depressed. In this embodiment, the first spring constant is determined to be smaller than the second spring constant. Therefore, when a downward force is applied to the horizontal part15by the second board200, the first bent portion having a smaller spring constant bends more than the second bent portion having a larger spring constant.

The effect of the bending of the first bent portion and the bending of the second bent portion on the inclination of the horizontal part15is described. When the first bent portion bends, the surface of the horizontal part15rotates (moves) clockwise. On the other hand, when the second bent portion bends, the surface of the horizontal part15rotates (moves) counterclockwise. Accordingly, when both the first bent portion and the second bent portion bend, the rotation directions of the horizontal part15cancel out. Therefore, even when the entire contact member1is compressed by the pressure of the second board200, the surface of the horizontal part15is likely to be kept in a horizontal position. That is, this movement may be obtained by providing the horizontal part15ahead of the first bent portion and the second bent portion. The contact member1moves in the same manner when a suction nozzle of an automatic mounting apparatus depresses the attracted part15a. That is, even when the suction nozzle is pressed against the attracted part15a, the attracted part15ais less likely to be inclined, so that it is possible to reduce attraction errors.

The first spring constant and the second spring constant may be suitably determined in accordance with mechanical characteristics desired of the contact member1. For example, when the first spring constant is determined to be an even smaller value than the second spring constant, it is possible to cause the second bent portion to hardly bend before the first bent portion bends to have the first contact part21coming into contact with the second bent portion. On the other hand, when the first spring constant and the second spring constant are closer, the second bent portion also considerably bends in accordance with the second spring constant before the first contact part21stops the second bent portion.

The horizontal part15is so positioned as to have no effect on the respective spring constants of the first bent portion and the second bent portion. Therefore, in designing the respective shapes of the first bent portion and the second bent portion, the shape of the horizontal part15may not be taken into consideration in determining the spring performance.

FIG. 3Cillustrates a state where the first contact part21comes into contact with the vicinity of the third bent part10to restrict the bending of the first bent portion. The first bent portion bends with the first spring constant, so that the first contact part21comes into contact with the vicinity of the third bent part10of the second bent portion. The bending of the first bent portion is restricted by the contact of the first contact part21and the second bent portion. This state is referred to as “first restricted state.” The contact of the first contact part21with the second bent portion shortens the electrical distance of a conductor, so that it is possible to reduce the overall impedance of the contact member1. This reduction in impedance is particularly effective in the frame grounding of boards that use high frequencies.

Next, referring toFIG. 3D, when the second board200is further depressed to come closer to the first board100, the second bent portion bends on the first contact part21serving as a support, and the second contact part22comes into contact with the vicinity of the second bent part8of the first bent portion to restrict the bending of the second bent portion. This state is referred to as “second restricted state.” In the transition from the first restricted state to the second restricted state, friction with the second bent portion occurs in the first contact part21. Thus, a so-called wiping effect, which removes an oxide film on a surface with a frictional force, is produced, so that it is possible to improve the performance of a contact point.

In the transition from the first restricted state to the second restricted state, the horizontal part15rotates counterclockwise substantially about the first contact part21to be inclined. Therefore, a position of the electrically conductive part of the second board200at which the contacting part20comes into contact with the electrically conductive part gradually changes with the inclination of the contacting part20. As a result, friction with the electrically conductive part of the second board200occurs in the contacting part20. Thus, a so-called wiping effect, which removes an oxide film on a surface with a frictional force, is produced, so that it is possible to improve the performance of a contact point.

Next, referring toFIG. 3E, when the second board200is further depressed to come closer to the first board100after the bending of the first bent portion and the second bent portion is restricted, a bend in the shape of a chevron formed at the fifth bent part14between the fourth spring part13and the horizontal part15is pressed to widen, and at the same time, the first bent portion and the second bent portion are compressed so that the third contact part23comes into contact with the upper surface of the first board100. A state where the third contact part23is in contact with the first board100is referred to as “third restricted state.” In the third restricted state, a pressure on the contacting part20from the second substrate200is mostly received by the stopper part17, so that the first bent portion and the second bent portion are less likely to receive more pressure. As a result, it is possible to prevent damage to or plastic deformation of the first bent portion and the second bent portion. The amount of stroke of the contact member1between the second restricted state and the third restricted state for prevention of damage to the first bent portion and the second bent portion may be suitably determined by the length of the stopper part17, that is, the distance between the third contact part23and the first board100. In the transition from the second restricted state to the third restricted state, friction with the first bent portion occurs in the second contact part22. Thus, a so-called wiping effect, which removes an oxide film on a surface with a frictional force, is produced, so that it is possible to improve the performance of a contact point.

FIG. 4is an enlarged view of a contact point part where the contacting part20and the second board200are in contact. InFIG. 4, the initial position of the horizontal part15is denoted by15-I. The horizontal part15is substantially horizontal (parallel to the upper surface of the first board100) at the initial position15-I, while at a position15-II, where the second board200is most depressed, the horizontal part15is rotated counterclockwise relative to the initial position15-I with the bending of the second bent portion, so as to be inclined toward the lower left inFIG. 4. Therefore, the contact point part where the contacting part20and the second board200are in contact moves rightward (in the direction of the fifth bent part14ofFIGS. 3A through 3E) in accordance with the angle of inclination of the horizontal part15.

FIGS. 5A and 53are diagrams illustrating the mounting of the contact member1on the first board100.FIG. 5Bis a cross-sectional view ofFIG. 5Ataken along a plane including line A-A. Referring toFIGS. 5A and 5B, three contact members1, which are denoted by reference numerals1a,1b, and1c, are enclosed in recesses101a,101b, and101c, respectively, formed in the first board100. This mounting method makes it possible to perform frame grounding also in mounting in the case of joining the first board100and the second board200(not illustrated inFIGS. 5A and 5B), placed on the opening side (left side inFIG. 5B) of the recesses101athrough101c, with a gap (distance) smaller than the height of the contact member1in the third restricted state illustrated inFIG. 3E.

In the mounting illustrated inFIGS. 5A and 5B, the recesses101athrough101cfor enclosing the contact members1athrough1c, respectively, are provided in the first board100. Alternatively, for example, it is also possible to mount the contact members1athrough1con the first board100by attaching the contact members1athrough1cto a housing package, which is provided separately from the first board100, and attaching the housing package, to which the contact members1athrough1care attached, to the first board100.

Next, a method of soldering a contact member is described with reference toFIG. 6.

FIG. 6is a diagram illustrating soldering of a contact member. Referring toFIG. 6, the first joining part2and the second joining part5of the contact member1are placed on an electrically conductive part of the first board100on which solder paste300is printed by a suction nozzle of an automatic mounting apparatus (not illustrated). By heating the first board100, the contact member1is soldered to the first board100at the first joining part2and the second joining part5.

The contact member1includes the rising part3, which is slanted at an angle from the first joining part2to rise from the upper surface of the first board100, the intermediate part4, which is spaced apart from the upper surface of the first board100, and the second joining part5which extends from the opening part4aof the intermediate part4to be joined to the upper surface of the first board100. Therefore, an air gap is formed between the upper surface of the first board100and the intermediate part4, and solder or flux provided in this air gap is prevented from moving up from the first board100to the contact member1. Accordingly, it is possible to prevent problems such as so-called solder wicking or flux wicking, which causes solder or flux to adhere to a surface of the contact member1other than its surface facing the first board100.

InFIG. 6, soldering is performed on the entire surface of the first joining part2that is joined to the first board100. Alternatively, soldering may be performed in a spot manner on part of the surface of the first joining part2.

Furthermore, inFIG. 6, the length of the second joining part5is so determined that the end of the second joining part5comes into contact with the upper surface of the first board100when the contact member1is soldered to the first board100. Alternatively, the length of the second joining part5may be so determined that the end of the second joining part5does not come into contact with the upper surface of the first board100when the contact member1is soldered to the first board100.

If the second joining part5is excessively long, the bottom surface of the first joining part2that is in contact with the first board100may come off the first board100because of the contact of the end of the second joining part5with the upper surface of the first board100. Therefore, by determining the length of the second joining part5so that the end of the second joining part5does not come into contact with the upper surface of the first board100when the contact member1is soldered to the first board100, it is possible to prevent the first joining part2from coming off the first board100even when the length of the second joining part5includes processing error, as long as the error does not cause the second joining part5to be excessively long.

Furthermore, inFIG. 6, the first joining part2and the second joining part5are soldered at a distance from each other. This reduces the area of contact with the first board100so that it is possible to reduce the amount of solder for soldering the contact member1, compared with the case where the first joining part2extends to the first bent part6without the rising part3, the intermediate part4, and the second joining part5, and the entire bottom surface of the extended first joining part2comes into contact with the upper surface of the first board100, for example.

Furthermore, even in the case where the coefficient of thermal expansion differs between the first board100and the contact member1, an extended portion of the second joining part5having an extending shape deforms to eliminate the difference in expansion due to heat, so that it is possible to eliminate the distortion of the contact member1at the time of soldering.

FIG. 7is a graph illustrating a relationship between contact force and displacement of the contact member1. InFIG. 7, the displacement refers to a vertical displacement of the contact member1due to the pressing of the contacting part20by the second board200, and the contact force refers to the force of contact of the contacting part20and the second board200.FIG. 7illustrates a case where the first spring constant is smaller than the second spring constant.

Referring toFIG. 7, when the contact member1is not pressed by the second board200, the displacement is zero (0). When the contacting part20receives pressure from the second board200, the first bent portion and the second bent portion start to bend, and at displacement “x”, the first restricted state where the first contact part21is in contact with the lower surface of the second bent portion as illustrated inFIG. 3Cis entered. The contact force at displacement “x” is indicated by “f1.” In the case where the first spring constant is smaller than the second spring constant, basically, the first bent portion bends with the first spring constant from displacement “0” to displacement “x.”

When the contacting part20is pressed by the second board200from the state of displacement “x,” at displacement “y,” the second restricted state where the second contact part22is in contact with the upper surface of the first bent portion as illustrated inFIG. 3Dis entered. The contact force at displacement “y” is indicated by “f2.”When the contact member1is displaced from displacement “x” to displacement “y,” the bending of the first bent portion is restricted, and the second bent portion having the second spring constant larger than the first spring constant bends. Accordingly, the slope of the graph is steeper than from displacement “0” to displacement “x.”

When the contacting part20is further pressed by the second board200from the state of displacement “y,” at displacement “z,” the third restricted state where the third contact part23, which is the end point of the stopper part17, is in contact with the first board100as illustrated inFIG. 3Eis entered. The contact force at displacement “z” is indicated by “f3.” From displacement “y” to displacement “z,” the bending of the first bent portion and the bending of the second bent portion are restricted, so that the bend of the fifth bent part14widens and the bent part of the first bent portion and the bent part of the second bent portion are displaced in a compressed manner. Accordingly, the slope of the graph is steeper than from displacement “x” to displacement “y.”

By the above transitions of restricted states, in the displacement range from “0” to “x,” a large displacement (amount of stroke) may be obtained without much increase in the contact force. Furthermore, in the displacement range from “x” to “y,” a large change in the contact force may be obtained with a small displacement. Furthermore, in the displacement range from “y” to “z,” a large change in the contact force may be obtained with little change in the displacement. Furthermore, the bending of the first bent portion and the second bent portion is restricted at displacement “z,” so that it is possible to prevent damage to the contact member1. InFIG. 7, “f4” indicates the maximum value of the contact force that does not cause damage to the contact member1. Because of the stopper part17, the value of “f4” may be larger than the value of “f3”, so that the contact member1may be protected from damage.

For example, multiple joining parts that are shaped to extend toward a board surface like the second joining part5may be provided in contact members.

Furthermore, part of the first joining part2may be removed by piercing in order to reduce an area of placement of the first joining part2on a board.