Abstract:
In a method for fixing an electrical or an electronic component, particularly a printed-circuit board, in a housing used to accommodate the component, and a fixing element for fixing the component by clamping it in place, the component is fitted with at least one fixing element, which includes an elastically yielding press-on part which, during the clamping in place of the component in the housing, is brought to lie against a part of the housing and is pressed against it while being deformed.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method for fixing an electrical or an electronic component, particularly a printed-circuit board, in a housing used for accommodating the component, a fixing element for fixing an electrical or an electronic component in a housing by clamping it in place, and an electrical or an electronic component, particularly a printed-circuit board. 
     BACKGROUND INFORMATION 
     The most varied technical design approaches exist for fixing electrical or electronic components, particularly printed-circuit boards in a surrounding housing. The printed-circuit board may be firmly screwed or adhered into the housing, for example, or may be connected to the housing by clipping it on. However, such connections are not free of disadvantages. Whereas an adhesive connection is no longer detachable after manufacturing, and may additionally lead to damage of the printed-circuit board or of the components mounted on it because of the chemical substances contained in the adhesive, screwed connections and clip-on connections are detachable, to be sure, but they put high requirements on the tolerances of the printed-circuit board and the housing. The latter also applies to clamping connections that are already known per se, in which, for instance, a printed-circuit board is directly clamped in place between two halves of the housing, when the housing is closed. In addition, the mechanical stresses on the printed-circuit board may be very high in such a location. 
     SUMMARY 
     Example embodiment of the present invention provide a method, a fixing element and an electrical or an electronic component of the type mentioned at the outset, to the extent that a secure, firm and durable fixing of the component in the housing is possible without special tolerance requirements. 
     Example embodiments of the present invention provide for fitting the component with at least one fixing element which includes an elastically yielding press-on part which, when the component is clamped in place in the housing, is brought into contact with a part of the housing, and is pressed against it while undergoing deformation. 
     According to example embodiments of the present invention, at the interfaces between the electrical or the electronic component and the housing, that is, in the place where the clamping forces are transferred from the housing to the component, instead of having a direct transfer of the clamping forces, one should select an indirect transfer, via an elastically yielding intermediate member, that is fit in between the component and the housing, so as to compensate for tolerances or play that may possibly be present in the area of the clamping connection. Since the elastically yielding press-on part is able to be deformed more or less severely, in correspondence to the respective installment conditions, the tolerance requirements on the housing and on the component itself may be considerably reduced. Furthermore, the different thermal expansions of the component and the housing may be compensated for via the elastically yielding press-on part of the at least one fixing element. In addition, with the aid of the elastically yielding press-on part, the contact surface between the component and the housing is able to be enlarged, which, because of lower surface pressures, leads to a reduction in the mechanical stresses caused by the clamping connection, and thus to an extension in the service life of the component. In addition, if the material is selected suitably, the elastically yielding press-on part also acts as a damping member, which damps the transfer of vibrations from the housing to the component, and consequently ensures, at least partially, a decoupling of the component from the housing according to vibration technology. 
     The method according to example embodiments of the present invention provides that the fixing element is fastened on the component by soldering, especially if the latter is a printed-circuit board. This type of fastening has the advantage that the fixing element is able to be applied, using an already present placement system, in the same manner as other components that are to be mounted on the printed-circuit board, so that the printed-circuit board is able to be fitted with the fixing element(s) using only slight additional effort, in the course of its manufacture. 
     In the case of other electrical or electronic components, which are also able to be fixed in a housing by being clamped in place, such as electrolytic capacitors, tabs or the like, the fixing element is expediently able to be fixed to the component by adhesion, which is possible to do without great additional effort even before mounting the component in the housing. 
     The press-on part of the fixing element is made up advantageously, at least in part, of an elastic plastic material, such as polytetrafluoroethylene (PTFE) or an elastomer, such as polyurethane foam or a thermoplastic elastomer (TPE). A rubber elastic material may also be used, however, such as ethylenepropylenediene rubber (EPDM) or a silicone, as long as this material is elastically yielding when a clamping force is applied, and is able to be applied without difficulty onto a suitable carrier of the fixing element. 
     Example embodiments of the present invention provide also using the fixing element for contacting between the electrical or electronic component, such as the printed-circuit board, and the surrounding housing, by making the press-on part and a part of the housing acting on the press-on part at least partially of an electrically conductive material, which, in the case of the press-on part, is preferably made up of an elastomer filled with graphite, and in the case of the housing part may expediently be developed as a metallic contact finger. In this way, additional contact measures between the electrical or electronic component and its housing become superfluous. 
     Example embodiments of the present invention are explained below in more detail with the aid of the corresponding drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a printed-circuit board fitted with four fixing elements; 
         FIG. 2  is a top view of one of the fixing elements according to  FIG. 1 ; 
         FIG. 3  is a side view of the fixing element according to  FIG. 2  before being mounted on the printed-circuit board; 
         FIG. 4  is a side view of the fixing element according to  FIG. 2  after being mounted on the printed-circuit board; 
         FIG. 5  is a top view of a modified fixing element; 
         FIG. 6  is a side view of the fixing element according to  FIG. 5  before being mounted on a printed-circuit board; 
         FIG. 7  is a partially sectioned side view of the fixing element according to  FIG. 5  after being mounted on a printed-circuit board; 
         FIG. 8  is an enlarged view of cutaway portion A in  FIG. 7 ; 
         FIG. 9  is a side view and a top view of a part of a printed-circuit board having a fixing element that is in contact with ground, which has an electrically nonconductive press-on part; 
         FIG. 10  is a side view and a top view of a part of a printed-circuit board having a fixing element that is in contact with ground, which has an electrically conductive press-on part; 
         FIGS. 11 through 17  are side views and sectional views of fixing elements having differently shaped press-on parts. 
     
    
    
     DETAILED DESCRIPTION 
     The printed-circuit board  2 , shown best in a drawing in  FIG. 1 , is fixed in a housing a clamping connection, by pressing it on from above by its underside against a firm, even substratum  4 , for instance, a floor of the housing. The pressing-on of printed-circuit board  2  against substratum  4  takes place with the aid of a plurality of cylindrical holding pins or similar extended housing projections  6 , which project, for instance, above the lower side of the cover (not shown) of the housing, and, when the cover is closed, extend downwards into the vicinity of printed-circuit board  2 , past a plurality of electronic components mounted on the face of printed-circuit board  2 , such as capacitors  8 , memory chips  10 , processors  12  and the like, where they exert in each case a clamping force (arrows F) on a fixing element  14  that is rigidly mounted below each projection  6  on the face of printed-circuit board  2 , in order to press fixing element  14 , and via it, printed-circuit board  2 , downwards against substratum  4 , and thus ensure the fixing of printed-circuit board  2  in the housing. 
     As is shown best in  FIGS. 2 ,  3  and  4 , fixing elements  14  are made up substantially of a base carrier  16 , which is firmly soldered onto printed-circuit board  2  with the aid of four pins  18  that project laterally, and which is provided on its upper side, facing away from printed-circuit board  2 , with an elastically yielding or deformable press-on part  20 , with which housing projection  6  engages, in order to clamp in place printed-circuit board  2  between housing projection  6  and substratum  4 . 
     Whereas base carrier  16  and pins  18  are made of a metal that is easy to solder and is electrically conductive, such as copper, press-on part  20 , depending on the size of the tolerance to be compensated for and the exerted clamping force, may be made of an elastomer material, such as polyurethane foam or a thermoplastic elastomer (TPE), an elastically yielding thermoplastic material, such as polytetrafluoroethylene (PTFE) or a rubber elastic material, such as an ethylenepropylenediene rubber (EPDM) or a silicone, which is more or less severely elastically deformed when a clamping force is applied, and which returns to its initial position after being unstressed. 
     Whereas fixing element  14  shown in  FIGS. 2 ,  3  and  4  is mounted by the reflow soldering method on printed-circuit board  2 , by having soft solder  22 , that is used, applied before fitting printed-circuit board  2  with fixing element  14 , below the provided contact surfaces of the flat pins  18  that are connected in one piece with the base carrier on the face of printed-circuit board  2 , and is melted during the fitting with fixing element  14 , fixing element  14  shown in  FIGS. 5 ,  6 ,  7  and  8  is fastened by the usual soldering method on printed-circuit board  2 , in that pins  18 , that are wire-like and are bent over downwards and project beyond base carrier  16 , are introduced from above into corresponding through bores  24  of printed-circuit board  2 , and are connected rigidly to printed-circuit board  2  by firm soldering on the lower side of printed-circuit board  2 , as soon as base carrier  16 , by contrast to base carrier  16  of fixing element  14  shown in  FIGS. 2 ,  3  and  4 , lies with its underside on the face of printed-circuit board  2  (cf.  FIG. 7 ). 
     By contrast to fixing elements  14  in  FIG. 1 , which are fastened to printed-circuit board  2  at a distance from the circuit traces (not shown),  FIGS. 9 and 10  show a fixing element  14  whose pins  18  are soldered onto two circuit trace sections  26 ,  28 , that are connected in parallel with a ground circuit trace  30  connected to ground. However, while press-on part  20  of fixing element  14  shown in  FIG. 9  is made of an electrically nonconductive material, just as press-on parts  20  of fixing element  14  described above, so that a current path  32  between a tapered contact finger  34 , used for clamping in place printed-circuit board  2 , that is pressed from above against press-on part  20 , of the housing, on the one hand, and ground conductor  30  of printed-circuit board  2 , on the other hand, is interrupted in the vicinity of press-on part  20 , press-on part  20  of fixing element  14  shown in  FIG. 10  is made of an electrically conductive material, such as an elastomer filled with graphite, so that a contacting is produced via press-on part  20  between contact finger  34  and base carrier  16  of fixing element  14 , and consequently, current path  32  between contact finger  34  and ground conductor  30  is closed when contact finger  34  is pressed against press-on part  20  of fixing element  14 . In this manner, ground connections of components  8 ,  10 ,  12  that are mounted on printed-circuit board  2  and connected to ground conductor  30 , for instance, are able to be connected via contact finger  34  to an external ground connection lying outside the housing. 
     While press-on parts  20  of fixing elements  14  shown in  FIGS. 1 to 10  have a parallelepiped shape in the undeformed state, it may perhaps be more favorable, depending on the particular application, to give a different shape to press-on parts  20 , as shown in  FIGS. 1 to 17 . 
       FIG. 11 , for example, shows a fixing element  14  having a press-on part  20  that is anvil-shaped in cross section, using which one is able to compensate for a possible slight inclination between the front of printed-circuit board  2  or base carrier  16  and a level housing part (not shown) lying against the upper side of press-on part  20 . In this context, in a top view, press-on part  20  may have a square or rectangular outline or another outline that is not rotationally symmetrical, if the inclination occurs only in one direction, or a round outline if the inclination is able to occur in a directionally nonspecific manner. 
       FIG. 12  shows a fixing element having a press-on part  20  that is trapezoidal in cross section, using which, while having the same area content of the upper side of base carrier  16 , the contact area of press-on part  20  on the housing may be maximized, for instance, if press-on part  20  is lying with its upper side directly against the lower side of a housing cover, or the like. 
       FIG. 13  shows a fixing element  14 , whose press-on part  20  has a cross section having a flat upper and lower side  36 ,  38  and a convexly rounded side surface  40 , for absorbing high stresses or clamping forces, and is preferably made of a rubber elastic material which is compressed only slightly in the vertical direction by a clamping force F exerted on upper side  36  of press-on part  20  (cf.  FIG. 1 ). 
       FIG. 14  shows a fixing element  14  having a press-on part  20 , that is used for centering printed-circuit board  2  with respect to the housing, which, on its upper side  36 , is provided with a rotationally symmetrical depression  42 , which cooperates with a complementarily shaped end face (not shown) of a housing projection  6  or a contact finger  34 , to bring the center axis of depression  42  and the housing projection into alignment. 
       FIG. 15  shows a fixing element  14 , whose press-on part  20  has a spherical surface  44 , and with that, it is suitable for unspecified insertion positions, in which the clamping force F (cf.  FIG. 1 ) that is exerted on press-on part  20  is applied to press-on part  20  of fixing element  14  in a direction that is not orthogonal to the front side or the back side of the printed-circuit board and/or is applied at a distance from the center. 
       FIG. 16  shows a fixing element  14  having a press-on part  20 , that is provided with a cylindrical depression  46 , into which a pin or peg  50  projecting downwards beyond a housing part  48  engages, having a radial play, if an annular shoulder  52  that surrounds pin or peg  50  lies against the flat upper side of press-on part  20 , around depression  46 , or is pressed against it. 
     The same also applies for fixing element  14  that is shown in  FIG. 17 , whose elastically yielding press-on part  20  has an upwards projecting cylindrical projection  54 , which also extends with radial play into a complementary accommodating depression  56 , of a housing part  58 , that cooperates with fixing element  14 , if housing part  58  is pressed from above against press-on part  20  of fixing element  14 , for the purpose of clamping in place printed-circuit board  2 . In contrast to the press-on part in  FIG. 16 , projection  54  and depression  56  have larger cross sectional dimensions, and have a height or depth so that, at the first contact between housing part  58  and press-on part  20 , only the end face of projection  54  is pressed against the floor of depression  56 , and, only during the course of a beginning compression of press-on part  20 , contact is produced between housing part  58  and press-on part  20  around depression  56  and projection  54 .