Patent Document

FIELD OF THE INVENTION 
     This invention is related to fasteners for circuit boards, and more particularly to fasteners for coupling a circuit board to a back plate. 
     BACKGROUND OF THE INVENTION 
     In many applications it is advantageous to attach a back plate to a circuit board. The back plate is fairly rigid, fabricated out of a metal, and has about the same length and width as the circuit board. The circuit board is thin, on the order of 2 to 100 millimeters, and therefore difficult to handle and to work with because it bends and tends to warp. The additional thickness of an assembly of the circuit board attached to the back plate prevents the circuit board from bending and warping. This makes it easier to install components onto the circuit board, and easier to install the assembly into a device. The circuit board is made out of one or more layers. Some of the layers are made out of plastic or out of a plastic and glass compound. These layers have a conductor, such as copper, deposited on both sides to form a particular pattern of tracks that is the printed wiring. Other layers are made of an epoxy material and hold the circuit board together. Components attach to the circuit board and connect to the printed wiring. The back plate also acts as a heat sink to dissipate some of the heat generated by the components. 
     Typically, the back plate is attached to the circuit board with an epoxy. Some circuit boards can be attached to the back plates with solder. However, this is very expensive and would drastically increase the cost of the assembly. Other circuit boards, for example circuit boards with low glass transition temperatures, cannot be attached to the back plates with solder because this solder connection will melt when this assembly is heated to attach components to the assembly. Once the back plate and circuit board are attached, a solder paste stencil is applied to the circuit board. The solder paste stencil is a thin metal stencil that has areas cut out that correspond to the areas of the circuit board where the components will be attached. Solder is then applied. The solder goes through the areas cut out on the stencil such that solder is deposited on areas of the circuit board where the leads of the components will be attached. The leads of the components are placed on the solder, soldering the components onto the circuit board. Screws are then added to hold the back plate and circuit board together more securely. 
     A problem with fabricating the assemblies is that it is difficult and expensive to make an epoxy that can bond the metal back plate to the material of the circuit board. The epoxy must be tailored to the circuit board and back plate. The development of the epoxy takes both time and money, therefore increasing the cost and the time to start production. However, even when the epoxy is tailored to the circuit board and the back plate, the epoxy is not very reliable. A significant percentage of the circuit boards detach from back plates. This reduces the yield and therefore raises the cost and time of fabricating the assemblies. 
     Attaching the components to the circuit board prior to attaching the circuit board to the back plate solves the problem of using the epoxy, however, it creates a more serious problem. FIG. 1 shows circuit board  4  with components  6 ,  8  attached to circuit board  4  before circuit board  4  is attached to back plate  10 . Attaching components  6 ,  8  to thin circuit board  4  before circuit board  4  is reinforced with back plate  10  causes circuit board  4  to warp and bend due to the mismatch in the thermal expansion coefficient between the board and the components  6 ,  8 . This warped circuit board  4  is then screwed onto back plate  10 . Back plate  10  is more rigid than circuit board  4  causing warped circuit board  4  to bend when it is screwed on back plate  10 . This can cause the printed wiring on circuit board  4 , circuit board  4  itself, components  6 ,  8 , or the solder joints on components  6 ,  8 , to crack, which disrupts connections and causes open circuits. This is particularly problematic when the crack in the printed wiring is difficult to detect, and the assembly is placed in a product and fails in the field. 
     Attaching the back plate to the circuit board with screws before soldering eliminates the need for the epoxy but it creates a more serious problem. FIG. 2 shows assembly  12  with screws  14 ,  16  attaching circuit board  18  to back plate  20 . Back plate  20  also has openings  30  and  32 . Openings  30  and  32  can be used for fasteners that fasten assembly  12  to the devise that receives assembly  12 . Circuit board  18  also has openings  26  and  28 . Openings  26  and  28  can be used for fasteners that fasten assembly  12  to the device that receives assembly  12 . Back plate  20  and circuit board  18  include these openings  30 ,  32 , and  26 ,  28 , respectively, in addition to the opening for the screws  14 ,  16  that attach circuit board  18  to back plate  20 . Circuit board  18  is typically too soft to be able to have threads to hold screws  14 ,  16  in place if their heads  22 ,  24  are positioned at the bottom of back plate  20 . Therefore, heads  22 ,  24  need be positioned above circuit board  18 . Heads  22 ,  24  have to be above at least a portion of circuit board  18  otherwise they will not hold circuit board  18  to back plate  20 . In the cases of all but the thickest circuit boards, heads  22 ,  24  are taller than, or at least as tall as, the thickness of circuit board  18 . Since heads  22 ,  24  need to be positioned above at least a portion of circuit board  18 , at least a portion of heads  22 ,  24  protrudes above top surface  34  of circuit board  18 . 
     Heads  22 ,  24  protruding over the top surface of circuit board  18  create raised areas in the top surface of assembly  12 . If the solder paste stencil is placed on top surface  34  of circuit board  18 , a gap is created between circuit board  18  and the stencil. The solder is then applied and will leak out onto circuit board  18 . This will cause the solder to be deposited on areas of circuit board  18  where it does not belong, i.e. the areas of circuit board  18  where components do not need to be attached, resulting in short circuits. When components  36 ,  38  are attached to circuit board  18 , some components  36  may attach to the solder that is deposited where it does not belong, resulting in incorrect connections and to open and short circuits. Depositing solder manually onto the circuit board instead of using the solder paste stencil, to avoid the solder leaking over the assembly, increases the cost and the time needed to manufacture assembly  12  to the point where it is prohibitively expensive to manufacture assembly  12 . 
     SUMMARY OF THE INVENTION 
     The invention solves the above problems by providing a mechanical fastener that does not protrude above the surface of the assembly. The assembly includes a back plate and a circuit board coupled to the back plate with the mechanical fastener. The fastener has an end and a head with a top surface. The circuit board has an opening that receives the head of the fastener so that the top surface of the head is between the top and bottom surfaces of the circuit board, inclusively. A portion of this opening has a diameter at least as large as the diameter of the widest portion of the head. Another portion of this opening, located closer to the back plate has a smaller diameter. 
     The assembly is fabricated by forming an opening in the circuit board. A portion of the opening has a diameter as large as the largest diameter of the head of the fastener. An opening is formed in the back plate. The circuit board is attached to the back plate with the fastener. The top surface of the head of the fastener is placed entirely within the opening in the circuit board. If the circuit board is a multi-layer circuit board the circuit board is laminates. An opening is drilled through all of the layers in the circuit board. This opening has a diameter smaller than the largest diameter of the head. A larger opening is counterbored in the top layer of the circuit board around the drilled opening, at least portion of the opening in the top layer has a diameter as large as the largest diameter of the head of the fastener. If the circuit board is a singe-layer circuit board an opening is drilled through the layer. A portion of the opening has a diameter as large as the largest diameter of the head of the fastener. In either case, the circuit board is then plated. 
     Fasteners not protruding above the top surface of the assembly allow solder to be deposited onto the circuit board with an automated surface mounted assembly system and components to be attached to the circuit board after the circuit board is attached to back plate, saving both time and money, while at the same time increasing the yield for the assemblies. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     It should be noted that the Figures are drawn to best illustrate preferred embodiments of the invention and are not drawn to scale. 
     FIG. 1 is a cross-sectional view of a prior art back plate and a prior art circuit board to which components were attached before the circuit board was attached to the back plate; 
     FIG. 2 is a cross-section of a prior art assembly having a back plate attached to a circuit board by screws before solder is applied to the circuit board; 
     FIG. 3 is an exploded view of an assembly having a back plate, a circuit board, and components according to one embodiment of the present invention; 
     FIG. 4 is a cross-sectional view of an assembly having a back plate attached to a circuit board with countersunk rivets according to one embodiment of the present invention; 
     FIG. 5 is a cross-sectional view of an assembly having a back plate attached to a circuit board with button head rivets according to one embodiment of the present invention; 
     FIG. 6 a  is a cross-sectional view of an assembly having a back plate attached to a circuit board with eyelets according to one embodiment of the present invention; 
     FIG. 6 b  is a top view the head of an eyelet in an opening in a circuit board of FIG. 6 a  according to one embodiment of the present invention; 
     FIG. 6 c  is a cross-sectional view of an assembly having a back plate attached to a circuit board with funnel head eyelets according to one embodiment of the present invention; 
     FIG. 7 is a cross-sectional view of another assembly having a back plate attached to a circuit board with countersunk rivets according to one embodiment of the present invention; and 
     FIG. 8 is a cross-sectional view of an assembly having a back plate attached to a circuit board with rivets and washers according to the embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIGS. 3 and 4, an assembly according to an embodiment of the present invention is generally designated by reference numeral  100 . Assembly  100  includes back plate  102  coupled to circuit board  104  with mechanical fasteners  103 ,  105 . Optionally, the assembly can also include components  106 ,  108 . 
     Back plate  102  is made out of aluminum, or any other material that balances the desire to keep back plate  102  light and inexpensive, yet as highly thermally conductive as possible. Back plate  102  is thick enough to be rigid. Preferably, the length and width of back plate  102  are about the same as that of circuit board  104 , although back plate  102  can be larger or smaller than circuit board  104 . The length and width of back plate  102  should be large enough to keep circuit board  104  fairly rigid so that it does not bend, warp, or move. Keeping circuit board  104  fairly rigid makes circuit board  104  easier to work with as components  106 ,  108  are attached to assembly  100  and as circuit board  104  is installed in a device that receives assembly  100 . 
     Back plate  102  has fastener openings  110 ,  112  for fasteners that fasten back plate  102  to circuit board  104 . Depending on the shape of the fasteners, fastener openings  110 ,  112  either run through the entire depth of back plate  102 , or the fastener openings extend through only a part of back plate  102 . For fasteners such as rivets, fastener openings  110 ,  112  run through the entire depth of back plate  102 . The bottom of fastener openings  110 ,  112  have recessed areas  111 ,  113 . Back plate  102  also has other openings  114 ,  116 ,  118 . Opening  118  accommodates component  108 . Openings  114 ,  116  are for fasteners that fasten assembly  100  to the devise that receives assembly  100 . 
     Circuit board  104 , like the conventional circuit board, is typically thin, on the order of 2 to 10 millimeters, and is made out of one or more layers  120 ,  122 ,  124 ,  126 ,  128 . Layers  120 ,  124 ,  128  are made out of plastic or out of a plastic and glass compound, such as FR4. These layers  120 ,  124 ,  128  have a conductor, such as copper, deposited on either one or on both sides to form a particular pattern of tracks that is the printed wiring. Layers  122 ,  126  are made of an epoxy material and hold circuit board  104  together. Layer  128  has tracks that serve as power on one side, and tracks that serve as a power ground on the other. Layers  120 ,  124  have tracks that serve as connections for components  106 ,  108  on one side, and tracks that serves as ground on the other side, such as RF power and ground and digital power and ground. Circuit board  104  is laminated and electroplated. 
     Circuit board  104  has openings  130 ,  132  for fasteners that fasten circuit board  104  to back plate  102 , and openings  134 ,  136  for fasteners that fasten assembly  100  to the device that receives assembly  100 . Openings  130 ,  132 ,  134 ,  136  run through the entire depth of circuit board  104  and are positioned over openings  110 ,  112 ,  114 ,  116 , respectively. Openings  130 ,  132 ,  134 ,  136 ,  135 ,  137  are electroplated, which allows them to conduct some of the current to ground tracks located on other layer in addition to the ground tracks on the layer with the transmission lines that generated the current. Openings  130 ,  132 ,  134 ,  136  and grounding openings  135 ,  137  help to connect the different ground layers and thereby reduce interference between signals on the printed wiring to an acceptable performance level. Openings  130 ,  132 ,  134 ,  136  and grounding openings  135 ,  137  should be placed as needed, preferably near the transmission lines of the printed wiring that carry high current at low impedance. Openings  130 ,  132 ,  134 ,  136 .  135 ,  137  also conduct some the current to back plate  102 , which acts as a ground plane. 
     There should be enough openings  130 ,  132  and fasteners  103 ,  105  to make sure that circuit board  104  and back plate  102  are securely held together. Additionally, although only two grounding openings  135 ,  137  are shown, there should be enough grounding openings  135 ,  137  to make sure that current is conducted to ground to reduce any interference between signals to an acceptable performance level. 
     Circuit board  104  also has component openings  138 ,  140  that go through the entire depth of circuit board  104 . Components  106 ,  108  fit through component openings  138 ,  140 . Components  106 ,  108  are either integrated circuits or discrete devices that are connected to circuit board  104  through leads  142 ,  144 , and  146 ,  148 , respectively. Leads  142 ,  144 , and  146 ,  148  connect to the printed wiring on top surface  150  of circuit board  104 . 
     Fasteners fit into openings  130 ,  132 , of circuit board  104  and openings  110 ,  112  of back plate  112  to fasten circuit board  104  to back plate  102 . The fasteners are preferably countersunk rivets, such as flat head pop rivets  103 ,  105 . Although, they can be any fasteners that can be recessed into circuit board  104  and still attach circuit board  104  to back plate  102 , such as button-head pop rivets  170 ,  172  shown in FIG. 5, eyelets  180 ,  182  shown in FIG. 6 a,  funnel head eyelets shown in FIG. 6c, flat head press fit rivets, or button-head press fit rivets. 
     Fasteners that can be recessed into circuit board  104  and still attach circuit board  104  to back plate  102  can be of two basic types. The first type of fastener has a head whose height is smaller than the depth of circuit board  104 , such as the eyelet, the button head rivets, or some of the flat head rivets. The second type of fastener has a head whose height is larger than the depth of the circuit board, but a portion of the head fits into the fastener openings such as some flat head rivets. 
     The shape of openings  130 ,  132  in circuit board  104 , and the depth of recessed areas  111 ,  113  at the bottom of fastener openings  110 ,  112  is dependent on the shape of the fastener. The openings  130 ,  132  should have an upper portion and a lower portion. The breadth (i.e. the diameter where the heads are conical or cylindrical and either the length or width where the heads are shaped like a polygon) of the upper portion is larger than the breadth of the lower portion. 
     FIG. 4 shows assembly  100  having circuit board  104  attached to back plate  102  with countersunk flat head rivets  103 ,  105 . Openings  130 ,  132 , in circuit board  104  are conical to accommodate the conical shape of heads  210 ,  212  of flat head rivets  103 ,  105 . The bottom of each of openings  130 ,  132  has about the same diameter as the stems of flat head rivets  103 ,  105 . A portion of openings  130 ,  132  above the bottom has a diameter that is about the same as the largest diameter of heads  210 ,  212 . The height of heads  210 ,  212  is about equal to or smaller than the depth of circuit board  104 , so the entire head  210 ,  214  of each rivet  103 ,  105  fits between the top and bottom surface of circuit board  104 . This makes the top surface of each of heads  210 ,  212  either level with or below top surface  150  of circuit board  104 , such that no portion on flat head rivets  103 ,  105  protrudes above the top surface of assembly  100 . 
     The stems of rivet  103 ,  105  fit into fastener openings  110 ,  112 . The end of each of flat head rivets  103 ,  105  has round or oval balls  214 ,  216 . When the rivets are actuated, balls  214 ,  216  are pulled through the stems. The stems surround balls  214 ,  216 , widening the stems. Balls  214 ,  126  are pulled through the stems until fastener openings  110 ,  112  do not permit the stems to be further expanded in diameter. Recessed areas  111 ,  113  at the bottom of fastener openings  110 ,  112  are large enough to accommodate the widened stems surrounding balls  214 ,  216  such that no portion of the stems or balls  214 ,  216  protrudes below the bottom of back plate  102 . This allows the entire bottom surface of the back plate to be in contact with the equipment or device into which the assembly is inserted. The equipment or device provides a large surface area to assist components  106 ,  108  with heat dissipation. In an alternative embodiment of the invention, the back plate does not have recessed areas III,  113  and balls  214 ,  216  protrude below the bottom of the back plate. The back plate without recessed area is easier to manufacture, but it should be used where a large contact between the back plate and the equipment or device is not needed to assist with heat dissipation. 
     FIG. 5 shows an assembly  220  having circuit board  222  attached to back plate  102  with button-head rivets  170 ,  172 . Openings  224 ,  226  in circuit board  222  are cylindrical to accommodate the cylindrical shape of heads  230 ,  232  and of the stems of rivets  170 ,  172 . Openings  224 ,  226  have a top and bottom portion. The diameter of the top portion of each of openings  224 ,  226  is about the same as the largest diameter of heads  230 ,  232 . The diameter of the bottom portion of openings  224 ,  226  is about the a little larger than the diameter of the stems of rivets  170 ,  172  but smaller than the diameter of the heads  230 ,  232 . The height of heads  230 ,  232  is smaller than the depth of the top portion of openings  224 ,  226 , so the entire head of each of rivets  170 ,  172  fits between the top and bottom surface of circuit board  222 . This makes the top of surface of each of heads  230 ,  232  either level with or below the top surface of circuit board  222  such that no portion of button head rivets  170 ,  172  protrudes above the top surface of assembly  220 . 
     The stems of rivets  170 ,  172  fit into fastener openings  110 ,  112 . Like the flat head rivets, the ends of button-head rivets  170 ,  172  have a round or oval balls  234 ,  236  that widen the stems. Recessed areas  111 ,  113  at the bottom of fastener openings  110 ,  112  are large enough to accommodate the widened stems surrounding balls  234 ,  236  such that the no portion of stems or balls  234 ,  236  protrudes below the bottom of back plate  102 . 
     FIG. 6 a  shows an assembly  250  having circuit board  252  attached to back plate  254  with eyelets  180 ,  182 . Each eyelet  180 ,  182  is composed of one of tubular elements  256 ,  260 . Heads  30   264 ,  268  and ends  266 ,  270  of the eyelets are the edges of tubular elements  256 ,  260  bent to hold the material between heads  264 ,  268  and ends  266 ,  270 . As can be seen in FIG. 6 a,  the final shape of eyelets  180 ,  182  resembles the letter I. 
     FIG. 6 b  shows a top view of opening  272  in circuit board  252 . Referring to FIGS. 6 a  and  6   b,  openings  272 ,  274  are cylindrical to accommodate the shape of heads  264 ,  268  of eyelets  180 ,  182 . Openings  272 ,  274  have a top and bottom portion. The height of heads  264 ,  268  is smaller or about the same size as the depth of the top portion of openings  272 ,  274 . The heads  264 ,  268  of each of eyelets  180 ,  182  fit between the top and bottom surface of circuit board  252 . This makes the top of surface of heads  264 ,  268  either level with or below the top surface of circuit board  252  such that no portion of eyelets  180 ,  182  protrudes above the top surface of assembly  250 . 
     The diameter of the top portion of each of openings  272 ,  274  is about the same as the largest diameter of heads  230 ,  232 . The diameter of the bottom portion of openings  272 ,  274  is about the same as the diameter of the stem of each of eyelets  180 ,  182 . Recessed areas  276 ,  278  at the bottom of fastener openings  280 ,  282  are large enough to accommodate the bent in portion of tubular elements  256 ,  260  that forms ends  266 ,  270  of eyelets  180 ,  182  such that no portion of eyelets  180 ,  182  protrudes below the bottom of back plate  254 . 
     FIG. 6 c  shows an assembly  284  having circuit board  286  attached to back plate  254  with funnel head eyelets  288 ,  290 . Like eyelets  180 ,  182 , funnel head eyelets  288 ,  290  are composed of one tubular element. Heads  292 ,  294  and ends  266 ,  270  of the funnel head eyelets  288 ,  290  are the edges of tubular elements. One edge of the tubular elements are bent outward to press against the bottom of the recessed area  276 ,  278  of the back plate  254 , forming ends  266 ,  270 . The other edge of the tubular elements are bent outward to form a conical shape, forming heads  292 ,  294  of funnel head eyelets  288 ,  290 . 
     Openings  296 ,  298  in circuit board  286  are conical to accommodate the shape of heads  292 ,  294 . The bottom of each of openings  296 ,  298  has about the same diameter as the diameter of the stem of the funnel head eyelets  288 ,  290 . A portion of openings  296 ,  298  above the bottom has a diameter that is about the same as the largest diameter of heads  292 ,  294 . The height of heads  292 ,  294  is about equal to or smaller than the depth of circuit board  284 , so the entire head  292 ,  293  of funnel head eyelets  288 ,  290  fits between the top and bottom surface of circuit board  284 . Thus, the top surface of each of heads  292 ,  294  either level with or below top surface of circuit board  254  such that no portion of funnel head eyelets  288 ,  290  protrudes below the bottom of back plate  254 . 
     FIG. 7 illustrates the second type of fastener that can be recessed into the circuit board and still attach the circuit board to the back plate. The fasteners, such as flat head rivets  310 ,  312  have heads  320 ,  322  whose heights are larger than the depth of the circuit board  102 , and that are shaped such that a bottom portion of heads  320 ,  322  has a diameter that can fit into fastener openings  110 ,  112 . A second portion of heads  320 ,  322 , above the bottom portion, has a larger diameter. In this case, it is important to ensure that first portions  324 ,  326  of openings  314 ,  316  in circuit board  302  have a diameter smaller than the largest diameter of heads  320 ,  322 , and that second portions  328 ,  330  of openings  314 ,  316 , above first portions  324 ,  326  have a diameter about as large as the largest diameter of heads  320 ,  322 . Openings  314 ,  316 , in circuit board  304  are conical to accommodate the conical shape of heads  320 ,  322 . 
     A portion of heads  320 ,  322  and stems fit into fastener openings  110 ,  112 . The height of the portion of each of heads  320 ,  322  that does not fit into fastener openings  110 ,  112  is about equal to or smaller than the depth of circuit board  302 . As a result the top surface of heads  320 ,  322  is either level with or below the top surface of circuit board  302 , such that no portion on flat head rivets  310 ,  312  protrudes above the top surface of assembly  300 . 
     The end of rivets  310 ,  312  has round or oval balls  332 ,  334  that widen the stems. Recessed areas  111 ,  113  at the bottom of fastener openings  110 ,  112  are large enough to accommodate the widened stems surrounding balls  332 ,  334  such that the no portion of the stems or balls  332 ,  334  protrudes below the bottom of back plate  102 . 
     FIG. 8 shows assembly  350 , similar to assembly  100  of FIG. 4, fastened by countersunk rivets  103 ,  105 . Over time as circuit board  104  is exposed to natural elements and as force is exerted on the circuit board, the circuit board material may creep, which will reduce the thickness of the circuit board. A brace, preferably spring-type washer  354  or  356 , such as a Belleville washer, is added to the rivets  103 ,  105  to compensate for any creep in the circuit board material that may take place over time. The inner edge of each of washers  354 ,  356  goes around one of rivets  103 ,  105  at the junction of the widened portion of the stem, pressing against the widened portion of the stem. The outer edge of washers  354 ,  356  presses against the top surface of recessed areas  360 ,  362  of fastener opening  364 ,  366 . If the circuit board material or the back plate material creeps over time, the washer extends vertically extending pressure against the back plate and the widened portion of the stem. This keeps the circuit board and back plate tightly pressed together. 
     Referring again to FIGS. 3 and 4, a method of fabricating assembly  100  will now be described. Back plate  102  is machined. Fastener openings  110 ,  112  are then formed in back plate  102 . Recessed areas  111 ,  113  of fastener openings  110 ,  112  can be machined or counterbored when back plate  102  is fabricated, or they can be drilled after faster openings  110 ,  112  are made. Opening  118  in the back plate to accommodate component  108  is typically machined when back plate  102  is fabricated. Other openings  114 ,  116  are typically drilled or counterbored afterwards. 
     Openings  130 ,  132  are formed in circuit board  104 . The circuit board can be a multi-layer or a single layer circuit board. In a multi-layer circuit board  104 , circuit board  104  is first laminated. An opening having a diameter smaller than the largest diameter of the head is drilled through layers  120 ,  122 ,  124 ,  126 ,  128  of circuit board  104 . A larger opening is counterbored, countrsunk or drilled in top layer  120  of circuit board  104  around the drilled opening, at least portion of the opening in the top layer has a diameter as large as the largest diameter of the head of the fastener. A portion of each opening has a diameter as large as the diameter of the top surface of fasteners  103 ,  105 . Circuit board  104  is then electroplated. In a single layer circuit board, since there is only one layer, forming opening in the layers below the top layer is not needed. 
     The preferred fasteners have countersunk heads, such as the flat head rivets  103 ,  105 . It is easier to reliably plate countersunk openings  130 ,  132  than openings with two portions with different diameters that have straight wall, because the straight walls create a sharp edge between the two portions. It is more difficult to ensure that the plating solution is deposited in the sharp edges, which can cause the opening to not be completely electroplated This can prevent the opening from conducting current between the ground layers on the circuit board and between the ground layers and the back plate, which also acts as a grounding plane. 
     Rivets  103 ,  105  are then placed in fastener openings  110 ,  112  and openings  130 ,  132  in the circuit board. A riveting tool actuates rivets  103 ,  105  to attach circuit board  104  to back plate  102 . Because of the sizes of openings  130 ,  132  in circuit board  104 , the top surface of heads  210 ,  212  of the rivets fits entirely within the openings  130 ,  132  such that it is either flush with the top surface of assembly  100 , or below the top surface of assembly  100 . Optionally, braces are attached to rivets  103 ,  105  and to the outer surface of back plate  102 . The braces are preferably spring-type washers such as Belleville washers. The inner edge of the washers fit around rivets  103 ,  105 , at the junction of the widened part of the stems and the rest of the stems. The outer edge of the washers presses against the top surface of recessed areas  111 ,  113 . 
     A solder paste stencil is placed on the top surface of circuit board  104 . The solder paste stencil exposes areas of the circuit board where components  106 ,  108  need to be soldered onto circuit board  104 . Solder is placed over the solder paste stencil depositing solder on the exposed area of circuit board  104 . The solder paste stencil is then removed and leads  142 ,  144 , and  146 ,  148  of components  106 ,  108  are attached to solder on circuit board  104 . 
     Optionally, screws, not shown, can be added to the assembly, after the components are attached to the assembly. The screws further assist in ensuring that the back plate and circuit board are securely attached. 
     While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art having reference to the specification and drawings that various modifications may be made and various alternatives are possible therein without departing from the spirit and scope of the invention.

Technology Category: h