Electrical parts for surface mounting

Abstract: A plurality of strip-like terminals (31) project out in parallel from an insulating body (21) of an electrical part and the surface of the terminals are held perpendicular to the bottom (21a) of the insulating body. The lower marginal edge of each terminal forms a straight connection edge, which lies in a plane parallel to the bottom of the insulating body and is soldered to the corresponding conductor land (14) on a printed circuit board (13).

Description: The present invention relates to electrical parts, such as a connector and a switch, which are particularly suitable for surface mounting use. Recently it has come into wide use to surface-mount electrical parts, such as a connector and a switch, and electronic parts such as various integrated circuits on printed circuit boards. In surface mounting, terminals of required electrical or electronic parts are disposed, by a positioning process, at predetermined sites for attachment on soldering paste printed on connecting conductor lands on a printed circuit board having predetermined wiring patterns and the conductor lands formed by copper layers, and the printed circuit board is heated in its entirety to reflow-melt the soldering paste, thereby simultaneously soldering the terminals of the respective parts to the corresponding conductor lands on the printed circuit board. Conventional surface-mounting electrical parts of this kind have such a construction as shown in Fig. 1, which is disclosed in US-A-4,991,059. A rectangular parallelepipedic body 11 has strip-like terminals 12 projecting out of its both sides. The terminals 12 have their base portions formed in parallel to the bottom of the body 11 but are bent toward the bottom side of the body 11 and then bent outwardly thereof in parallel to its bottom to form connection portions 12a. These connection portions 12a are soldered to conductor lands 14 formed on a printed circuit board 13. In conventional surface mounting, the terminals 12 in the case of Fig. 1 are bent in the vicinities of their base portions just projecting out of the body 11 and in the vicinities of their connection portions 12a in directions perpendicular to and parallel to the bottom of the body 11, respectively, as indicated by 15 and 16 so that the connection portions 12a are held in contact with the conductor lands 14 in parallel to the bottom of the body 11. However, since the bending accuracy is low, the parallelism between the connection portions 12a and the bottom of the body 11 and their heights are not accurate, and further, their reproducibility is low. On this account, there occasionally arises where the connection portions 12a incline with respect to or do not make close contact with the surfaces of the conductor lands 14. Hence, the electrical parts are not stable in posture and in position. Therefore, soldering of the connection portions 12a to the conductor lands 14 is bad and the soldering strength is also low. Moreover, the accuracy of the sites for the attachment of the terminals is low and their reproducibility is also low. In addition, since the bottom surface of each connection portion 12a is connected to the conductor land 14, a wide area is required for soldering and there is a limit to the reduction of terminal spacing. An electrical connector for surface mounting disclosed in EP-A-0 280 449 comprises strip-like flat stamped metal terminals. These metal terminals have, at a lower marginal edge of a projected end portion thereof, a straight connection edge extending in a plane parallel to the bottom plane of the connector body. EP-A-0 165 490 discloses a printed circuit board connector comprising a connector body made of three parts of which one is a terminal holding portion made of an insulating material and having positioning grooves for accommodating terminals. EP-A-0 430 105 discloses a printed circuit board connector having a sheet metal cover and a metal case. The cover has a front panel portion covering at least a portion of a front of an insulating connector body and side holding portions extending from both sides of said front panel portion toward opposed sides of said body to elastically grip the body therebetween. A downward extending tongue-like metal leg is formed integrally with a bottom portion of the cover, the leg projecting downwardly beyond the bottom of said body. The case has a top panel and a pair of side panels for covering at least a top and sides of said body, and a metal leg is formed integrally with the lower marginal edge of each of said side panels and projects therefrom downwardly beyond the bottom of said body. The cover has formed integrally therewith strip-like spring means extended from its upper marginal edge to the top of said body, said spring means extending between the top of said body and the top panel of said case and being bent so that it elastically contacts said top panel. SUMMARY OF THE INVENTION An object of the present invention is to provide an electrical part for surface mounting use which has terminals whose connection portions can be connected to conductor lands on a printed circuit board with excellent reproducibility and in parallel thereto and whose spacing can be reduced, and which can be soldered firmly to the printed circuit board by a small number of steps. This object is achieved with an electrical part as claimed in claim 1. Preferred embodiments of the invention are subject-matter of the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view showing the surface mounting of a conventional electrical part; Fig. 2 is a sectional view illustrating one part of an embodiment of the present invention applied to a connector; Fig. 3 is an exploded perspective view of the connector of Fig. 2; Fig. 4 is a perspective view illustrating the connector of Fig. 2 covered with a shield case; Fig. 5A is a sectional view taken on the line 5A-5A in Fig. 4; Fig. 5B is a front view showing an attachment leg and its vicinity in Fig. 4; Fig. 5C is a plan view showing the state in which the attachment leg is inserted in a through hole of a printed circuit board and soldered thereto; Fig. 6 is a perspective view illustrating an embodiment of the present invention applied to a connector; Fig. 7 is a sectional view taken on the line 7-7 in Fig. 6; Fig. 8A is a front view of a metal cover 37 in Fig. 6; Fig. 8B is a sectional view taken on the line 8B-8B in Fig. 8A; Fig. 9 is a front view of a shield case 38 in Fig. 6, showing its attachment leg in cross section; Fig. 10A is a sectional view taken on the line 10A-10A in Fig. 6; and Fig. 10B is a sectional view taken on the line 10B-10B in Fig. 6. DESCRIPTION OF THE PREFERRED EMBODIMENT Fig. 2 illustrates a connector as an electrical part to which the present invention can be applied and Fig. 3 shows its exploded perspective view. An insulating body 21 made of a synthetic resin material is substantially rectangular parallelepipedic in shape and has an annular groove 22 cut in its front and a plurality of contact receiving holes 23 extending through the body 21 inside of the annular groove 22 on the front thereof. The rear of the insulating body 21 is formed as an independent terminal holding portion 24. The terminal holding portion 24 is made of synthetic resin substantially in a plate-like form and has at both sides forwardly extending coupling arms 25 formed integrally therewith, the coupling arms 25 having formed integrally therewith claws 26 at their tip end portions in opposing relation to each other. In both sides of the insulating body 21 there are provided guide grooves 27 extending forwardly from the rear of the body 21, and each guide groove 27 has in its forward end a recess 28. The guide grooves 27 each receive one of the coupling arms 25 inserted thereinto and the claw 26 engages the recess 28. The terminal holding portion 24 is fitted between a floor portion 21B and a roof portion 21C extending rearwardly of the insulating body 21. Each contact receiving hole 23 has received therein a contact 29 inserted thereinto from behind. The contact 29 is a socket contact, which has a fallen U-shaped cross-section so that a pair of opposed side panels elastically grip therebetween a pin contact of the mating connector. Each contact 29 has its rear end coupled integrally with the upper front edge of the corresponding terminal 31 through a coupling portion 31c. The terminal 31 has a vertical portion 31a extended from the rear end of the coupling portion 31c toward the bottom 21a of the insulating body 21 (downward in Figs. 2 and 3) and a leg portion 31b extended rearwardly aslant from the lower end of the vertical portion 31a. The surfaces of the vertical portion 31a and the leg portion 31b are held perpendicular to the bottom 21a of the insulating body 21, and in this embodiment these surfaces lie in the same plane. Each leg portion 31b has a straight lower edge 32 extending in parallel to the bottom 21a of the insulating body 21. In the state in which the contact receiving holes 23 have received therein the corresponding contacts 29, respectively, the straight lower edges of the leg portions 31b of the terminals 31 are positioned in the same plane parallel to the bottom 21a of the insulating body 21 and disposed in the vicinity of the bottom 21a, forming edges for connection to the conductor lands 14 on the printed circuit board 13. The coupling portion 31c and the terminal 31 are formed as a unitary structure by press work of sheet metal. The terminal holding portion 24 has in its front parallel positioning grooves 33 extending perpendicularly to the bottom 21a of the insulating body 21 for receiving the rear marginal portions of the vertical portions 31a of the terminals 31 to position the terminals 31 in the direction at right angles thereto. Thus, the surfaces of the terminals 31 are held in parallel to one another. The rear end portion of the vertical portion 31a of each terminal 31 has a rearwardly projecting stepped portion 31d, against which the lower end face of the terminal holding portion 24 abuts to position the terminal 31 in the direction vertical to the insulating body 21. The leg portion 31b protrudes rearwardly of the back of the terminal holding portion 24. Furthermore, pairs of protrusions 34 each for gripping therebetween the lower rear margin of the vertical portion 31a of corresponding one of the terminals 31 are protrusively provided on the front of the terminal holding portion 24 along its lower marginal portion, and the front end faces of the protrusions 34 abut against the back of the insulating body 21. The terminal holding portion 24 also has stoppers 36 extending forwardly from its front in opposing relation to the respective contact receiving holes 23, and the tips of the stoppers 36 abut against the rear ends of the contacts 29 to limit their rearward movement. In this way, the terminals 31 are accurately positioned in the insulating body 21. The lower edge 32 of the leg portion 31b of each terminal 31, that is, the connection edge 32, can be held accurately at a predetermined height and in parallel to the bottom 21a of the insulating body 21. As described above, each terminal 31 of the electrical part has surfaces of its respective portions held perpendicular to the bottom 21a of the insulating body 21, that is, the terminal 31 has no surface portions extending in parallel to the bottom 21a of the insulating body 21. Since punching can be performed with more ease and at a higher degree of accuracy than bending, the connection edge 32 is always retained at a correct position and in a correct form with respect to the body 21 and is held accurately in parallel to the bottom 21a. Hence, when the insulating body 21 is mounted on the printed circuit board 13, it lies stably and the connection edge 32 contacts the conductor land 14 in parallel thereto and can be soldered thereto stably and firmly. Since the terminal 31 is connected to the conductor land 14 by the thickness of the edge 32 alone, the site for soldering each terminal 31 to the conductor land 14 is so narrow that the spacing of terminals, that is, the spacing of conductor lands can be reduced. In an ordinary electrical part such as a connector or switch, its insulating body is often covered with an electromagnetic shielding metal case. For instance, in the case where a connector having such a shield case is surface-mounted onto a printed circuit board, an appreciably large amount of external force is applied to the connector when it is engaged with or disengaged from the mating connector. Therefore, when the connector is soldered thin to the wiring pattern over a relatively small area as in ordinary surface mounting, the bonding strength of the solder is insufficient and the connector will readily come off the printed circuit board. Conventionally, such an electrical part to which a relatively large amount of external force is applied, is fixedly secured to the printed circuit board in such a manner as follows: Tongue-shaped attachment legs are each extended from the lower marginal edge of one of both side walls of the shield case, inserted through a circular through hole made in the printed circuit board and then soldered, for example, by dipping, to a conductor land on the back of printed circuit board in a step separate of the soldering step for surface mounting. This method poses a problem as it increases the number of steps involved in the surface mounting process. A description will be given, with reference to Figs. 4, 5A, 5B and 5C, of a shield case provided on the connector described above. Since the connector of this embodiment is basically identical in construction with the above-described embodiment except the shield case, reference is also made to Figs. 2 and 3. This embodiment is identical with the above-described embodiment in that the insulating body 21 is disposed on the printed circuit board 13 with the bottom 21a of the former downward and that the lower marginal edge (the connection edge) 32 of each terminal 31 is soldered to the conductor land 14 on the printed circuit board 13. In this embodiment, the insulating body 21 is covered with a rectangular parallelepipedic shield case 38 which has a top panel 38a, a rear panel 38b and both side panels 38c and 38d covering the top and both sides of the insulating body 21 and the back of the terminal holding portion 24, respectively, as depicted in Fig. 4. Attachment legs 38F, formed integrally with the shield case 38 and extending down from lower marginal edges of its both side panels 38c and 38d further than the bottom 21a of the insulating body 21, are each inserted into the corresponding through holes 41 in the printed circuit board 13 as shown in Fig. 5B. By soldering each leg 38F to a conductive layer on the inner peripheral surface of the through hole 41 simultaneously with the soldering of the connection edges 32 of the terminals 31 to the conductor land 14 as mentioned previously in conjunction with Fig. 2, it is possible to firmly fix the connector 20, i.e. the electrical part, to the printed circuit board 13 and hence reinforce the soldering of the edges 32 to the conductor lands 14. As shown in Figs. 4 and 5A, the attachment legs 38F, in particular, one of them is formed as a cylindrical member which has an axis substantially perpendicular to the plane containing the bottom 21a of the insulating body 21 (i.e. the bottom of the electrical part), that is, an axis substantially parallel to the direction in which the leg 38F extends. In this example, the shield case 38 is formed by press work of sheet metal and square portions, formed integrally with lower marginal edges of the side panels 38c of the shield case 38, are each rolled or bent into a cylindrical form with both side marginal edges 38Fa and 38Fb of the square portions opposed close to or partly overlapping each other. Thus, the legs 38F are formed. It is preferable that the cylindrical member forming each leg 38F be in the form of an inverted truncated cone which gradually tapers down. In this example, as shown in Fig. 5B, the one marginal edge 38Fb forming the cylindrical leg 38F has a press-fit claw 43 which is formed integrally with the marginal edge 38Fb at its intermediate portion in the vertical direction. The press-fit claw 43 is formed as a triangular claw which protrudes outwardly of the cylindrical form of the leg 38F and the protrusion decreases downward. The press-fit claw gets caught in the through hole 41 of the printed circuit board 13 when the leg 38F is pulled up. When other electrical or electronic parts are mounted on the printed circuit board 13, the electrical part (i.e. the connector) 20 is also mounted on the board 13, with the legs 38F each inserted in the through hole 41 of the board 13. A conductive layer 44 is deposited all over the inner peripheral surface of the through hole 41 and an area around its open end. It is preferable that the leg 38F be pressed into the through hole 41 or that the outer peripheral surface of the leg 38F be as close to the inner peripheral surface of the through hole 41 as possible. Thereafter, the whole printed circuit board 13 is heated to melt the soldering paste. In this instance, the soldering paste coated on the conductive layer surrounding the through hole 41 is molten and flows into the gap between the inner peripheral surface of the through hole 41 and the outer peripheral surface of the leg 38F, by which the both peripheral surfaces are bonded together by solder 42 as depicted in Fig. 5C. Thus, the leg 38F is firmly fixed to the through hole 41. As described above, since the legs for the attachment of the shield case covering the insulating body to the printed circuit board are cylindrical, the soldering paste molten during the surface mounting of the electrical part onto the printed circuit board, together with other pans, flows into the gap between the through hole and the leg inserted therein, by which the cylindrical leg is soldered over the entire area of its outer peripheral surface to the inner wall or peripheral surface of the through hole, and consequently, they are soldered over a wide area, and hence are firmly bonded together. This avoids the necessity of including the leg soldering step in the surface-mounting process, and hence permits simplification of the process. In the case where the legs 38F each have the press-fit claw 43 as in the above embodiment, once the leg 38F is pressed into the through hole 41, even if a force is applied to the electrical part in a direction in which the leg 38F comes out therefrom, the claw 43 engages the through hole 41, preventing the leg 38F from coming off. Furthermore, since the cylindrical legs 38F of the shield case 38 are pressed into the through holes 41 of the printed circuit board 13 prior to the soldering thereto of the terminals 31 of the connectors 20, the body 21 can be provisionally fixed to the printed circuit board 13 -- this facilitates the soldering work. By the provisional fixing of the body 21 to the printed circuit board 13, it is possible to perform, with ease, the positioning of the connection edges 32 of the terminals 31 relative to the conductor lands 14. In addition, the use of the legs 38F further ensures firm fixing of the insulating body 21 to the printed circuit board 13. Fig. 6 illustrates an embodiment according to the present invention. The surface-mounting electrical part employing the shield case is shown as being applied to a connector as in the case of Fig. 2. Fig. 7 is a sectional view taken on the line 7-7 in Fig. 6. the parts corresponding to those in Figs. 2 and 4 are identified by the same reference numerals. The insulating body 21, the terminal holding portion 24, the contacts 29 and the strip-like terminals 31 are essentially identical in construction with those of the afore-mentioned embodiment shown in Fig. 3 but this embodiment differs therefrom in that two pairs of engaging protrusions 35a and 35b (35b not seen) are provided on both sides of the insulating body 21 as indicated by broken lines in Fig. 3. The shield case 38 is also substantially identical in construction with that shown in the Fig. 4 embodiment except that the mounting leg 38F slightly differs in shape from the aforementioned leg 38F as will be described later on. The connector of this embodiment has its front covered with a metal cover 37. The cover 37 is made of an elastic metallic material. Figs. 8A and 8B are front and sectional views of the metal cover 37, respectively. The metal cover 37 includes a front panel 37a which is held against the front of the insulating body 21, a top plate portion 37b which is held against the top of the insulating body 21, left- and right-hand side holding portions 37c and 37d which are held against the left- and right-hand sides of the insulating body 21 to elastically grip it between them, and pressing tongue-like members projecting out from lower marginal edges of the side holding portions 37c and 37d, respectively, as shown in Figs. 8A and 8B. These portions of the metal cover 37 are punched out from a sheet of metal into one piece, which is bent into the metal cover 37. Accordingly, the cover 37 has no portions corresponding to the bottom 21a of the insulating body 21 and the back of the terminal holding portion 24. The pressing tongue-like members 37F have their base portions bent slightly inwardly toward each other and their intermediate portions bent slightly outwardly away from each other. When the connector 20 is mounted on the printed circuit board 13, the pressing tongue-like members 37F are inserted into the through holes 41 made in the printed circuit board 13 and the inwardly protruding intermediate portions of the tongue-like members 37F are each urged against lower edge of the through hole 41 as shown in Fig. 10B. The front panel 37a has a circular window 37W through which the annular groove 22 cut in the front of the insulating body 21 and the front portion surrounded by the groove 22 are exposed to the outside. Further, the front panel 37a has a plurality of spring pieces 37S which extend rearwardly from the circumferential edge of the circular window 37W and are inserted into the annular groove 22 of the insulating body 21. The left- and right-hand side holding portions 37c and 37d have rectangular small windows 37p and 37q, respectively. When the cover 37 is put on the insulating body 21 from the front, the small windows 37p and 37q engage the small protrusions 35a and 35b formed on the both sides of the insulating body 21 (only the protrusion 35a being indicated by the broken line in Fig. 3), and locking portions 37g and 37h, which project out from the lower marginal edges of the left- and right-hand side holding portions 37c and 37d, are bent toward the bottom 21a of the insulating body 21. Thus, the cover 37 is secured to the insulating body 21. Incidentally, the small projections 35a and 35b can be sloped backwardly so as to facilitate the mounting of the cover 37 onto the insulating body 21 from the front side thereof, but they may be formed to a constant thickness. A pair of spring strips 37U and 37V are extended rearwardly from the rear edge of the top plate portion 37b of the cover 37 and, in Fig. 8B, their rear ends are shown to extend upwardly, but when the shield case 38 is put on the cover 37 as described later on, the rear ends of the spring strips 37U and 37V are pressed against the inner wall surface of the shield case 38 to electrically interconnect the cover 37 and the shield case 38. The shield case 38 includes a top panel 38a which is held against the top of the insulating body 21 over the spring strips 37U, 37V of the cover 37, a rear panel 38b which is held against the back of the insulating body 21, left- and right-side panels 38c and 38d which are held against the left and right sides of the insulating body 21 over the side holding portions 37c, 37d of the cover 37, respectively, and mounting legs 38F which extend downward from the lower marginal edges of the side panels 38c and 38d. These portions are punched out from a sheet of metal (a conductive material) into one piece, which is bent into the shield case 38. As shown in Figs. 10A and 10B which are sectional views taken on the lines 10A-10A and 10B-10B in Fig. 6, respectively, each mounting leg 38F is provided at a position opposite the corresponding pressing tongue-like member 37F of the cover 37 and is shaped in a semi-cylindrical form so that its concaved side faces the tongue-like member 37F. When the connector 20 covered with the case 38 is mounted on the printed circuit board 13, each mounting leg 38F is inserted into the through hole 41 together with the pressing tongue-like member 37F and held in contact with the inner marginal edge of the through hole 41. In this case, since the intermediate portion of the pressing tongue-like member 37F is bent as mentioned above, the electrical part is clicked into engagement with the printed circuit board 13, and once the electrical part is thus mounted on the printed circuit board 13, the pressing tongue-like member 37F is elastically urged against the printed circuit board 13, thereby preventing the electrical part from not only rising but also disengaging from the printed circuit board 13. When other electrical parts are mounted on the printed circuit board 13, the electrical part according to the present invention is also disposed on the board 13 and then the board 13 is heated to reflow the soldering paste 42. On one or both sides of the printed circuit board 13 and on the inner peripheral surface of every through hole 41 there are deposited conductor lands 44 (for grounding use) by means similar to circuit printing means, and when the soldering paste 42 is molten, it is placed on the conductor lands 44. By this, the molten soldering paste 42 flows into the through hole 41 when the paste 42 is molten. As a result, the mounting legs 38F are each mechanically fixed to the periphery of the printed circuit board 13, and at the same time, the inner peripheral surface of the through hole 41 and the outer peripheral surface of the mounting leg 38F are fixed to each other. Thus, the electrical part is firmly fixed to the printed circuit board 13. As described above, according to the present invention, since the pressing tongue-like members of the cover are bent so that their intermediate portions protrude inwardly, the tongue-like members are clicked into the through holes when the electrical part is mounted on the printed circuit board. In this state, the mounting legs of the shield case are held in close contact with the through holes and the inwardly bent portions of the tongue-like members press the lower marginal edges of the through holes, ensuring to prevent the electrical part from rising up from the printed circuit board and to firmly fix the former to the latter. Since the soldering paste having flowed into the through holes during reflow mechanically couples the mounting legs and the pressing tongue-like members to the conductor lands around the through holes, the mounting of the electrical part onto the printed circuit board can be further strengthened. Moreover, the soldering paste enters into gaps between the pressing tongue-like members and the mounting legs and electrically connects them --this also produces a shielding effect. While in the above the present invention has been described as being applied to connectors alone, the invention is also applicable to a switch and other electrical parts for surface mounting use. It is also possible to omit the leg 31b extending rearwardly from each terminal 31 and use the lower marginal edge of the vertical portion 31a as the connection edge 32.

Claims: An electrical part adapted to be surface mounted on a printed circuit board (13), comprising: an insulating body (21), a plurality of strip-like terminals (31) projecting from said body (21), each of said terminals (31) having, at a lower marginal edge of a projected end portion (31b) thereof, a straight connection edge (32) extending in a plane parallel to the bottom of said body (21) in the vicinity of said bottom, a sheet metal cover (37) having a front panel portion (37a) covering at least a portion of a front of said body (21) and side holding portions (37c, 37d) extending from both sides of said front panel portion toward opposed sides of said body (21) to elastically grip the body (21) therebetween, an elastic tongue-like metal leg (37F) formed integrally with the lower marginal edge of each of said side holding portions (37c, 37d), projecting downwardly beyond the bottom of said body (21) and having an intermediate portion, wherein the intermediate portions of said tongue-like metal legs (37F) are bent inwardly toward each other, a metal case (38) having a top panel (38a) and a pair of side panels (38c, 38d) for covering at least a top and sides of said body (21), and a semi-cylindrical metal leg (38F) formed integrally with the lower marginal edge of each of said side panels (38c, 38d) and projecting therefrom downwardly beyond the bottom of said body (21), wherein each of said semi-cylindrical metal legs (38F) and the corresponding one of said tongue-like metal legs (37F) are adapted to be pressed as a pair into the same through hole in said printed circuit board (13) with the concave surface of the semi-cylindrical metal leg facing the outer surface of the tongue-like metal leg. The electrical part of claim 1 wherein said terminals (31) are substantially flat. The electrical part of claim 1 or 2 wherein said body (21) has a substantially flat terminal holding portion (24) made of an insulating material separately of said body (21) and forming at least one side thereof and said plurality of strip-like terminals (31) are inserted at one side marginal edge in parallel positioning grooves (33) made in the inner wall surface of said terminal holding portion (24) so that they are held in parallel to one another. The electrical part of claim 3 wherein the lower end portion (31b) of each terminal (31) has a leg extending under the lower end of said terminal holding portion (24) and projecting out to the outside and the lower marginal edge of said leg forms said straight connection edge (32). The electrical part of any of the preceding claims wherein said cover (37) has formed integrally therewith strip-like spring means (37U) extended from its upper marginal edge to the top of said body (21), said spring means extending between the top of said body (21) and said top panel (38a) of said case (38) and being bent so that it elastically contacts said top panel.

Inventors: ARAI TOSHIHIRO, ARAI, TOSHIHIRO
Applicants: HOSIDEN CORP, HOSIDEN CORPORATION
Application year: 1992
Main classification: H05K1
IPC codes: H05K1, H01R12, H05K3