Patent Publication Number: US-2004046507-A1

Title: Lamp base comprising an eletronic component and a method for producing a lamp base

Description:
[0001] The invention relates to a lamp base in accordance with the preamble of patent claim 1, and to a production method for such a lamp base.  
       I. PRIOR ART  
       [0002] Patent specification U.S. Pat. No. 6,068,180 describes the making of contact with a semiconductor component on a mounting plate that has conductor tracks embedded in plastic. The contact surfaces of the conductor tracks are arranged at a different height in order to facilitate making contact with the terminals of the semiconductor component.  
       II. SUMMARY OF THE INVENTION  
       [0003] It is the object of the invention to provide a lamp base comprising an electronic assembly arranged therein, the electronic assembly of which lamp base is optimally adapted to the prescribed shape and the prescribed inside dimensions of the base housing. It is also the object of the invention to specify a production method for a lamp base having an electronic assembly.  
       [0004] This object is achieved according to the invention by the features of patent claim 1 and of patent claim 4, respectively. Particularly advantageous designs of the invention are described in the subclaims.  
       [0005] The lamp base according to the invention has an electronic assembly with a mounting plate and electronic SMD components fastened thereon. The mounting plate has a surface provided for mounting the electronic components, and metal webs that are embedded in a dimensionally stable, electrically insulating material and that serve as conductor tracks and/or for making electrical contact with the electronic components on the mounting plate. According to the invention, the mounting plate has bent sections such that the surface provided for mounting the electronic components has regions arranged in different planes. As a result, the electronic assembly can be fitted into a housing of prescribed shape and with prescribed inside dimensions. In particular, the size and the shape of the bent sections of the mounting plate can be tuned to the spatial conditions of a housing into which the electronic assembly is to be inserted. The electronic SMD components fastened on the surface of the mounting plate of the electronic assembly thereby make optimum use of the available space, because they are arranged no longer substantially in a planar fashion, but in three dimensions. A particularly good utilization of space can be achieved with a meandering mounting plate. The bent sections of the mounting plate are advantageously connected via curved regions. This permits surface mounting of the electronic SMD components by means of a PCB assembly machine on the mounting plate, which is still flat. The final shape is not acquired by the mounting plate or the electronic assembly until a following fabrication step by bending the mounting plate in the region of the bending sites. In this way, the advantages of an automatic assembly of the mounting plate with electronic SMD components and of an optimum arrangement of the electronic components in the lamp base that is adapted to the spatial conditions are combined.  
       [0006] The method of production according to the invention for this lamp base comprises the following steps:  
       [0007] providing a flat metal sheet with prescribed desired bending sites about which the metal sheet can be bent,  
       [0008] producing a continuous metal frame from the metal sheet that has a surface for making contact with electronic SMD components, and which has metal webs that are provided as electrical conductors and/or ensure the unity of the metal frame,  
       [0009] form-fitting embedding of the metal frame in an electrically insulating material that can be adapted to the shape of the metal frame and can be brought into a dimensionally stable state such that the surface, provided for making contact with electronic components, of the metal frame remains accessible for the mounting of electronic components,  
       [0010] bringing the electrically insulating material into a dimensionally stable state such that the metal frame and the dimensionally stabilized electrically insulating material form a mounting plate,  
       [0011] if appropriate, severing of metal webs no longer required,  
       [0012] fastening and making contact with electronic SMD components on the mounting plate,  
       [0013] bending the mounting plate in the region of the desired bending sites such that the surface, serving for making contact with the electronic SMD components, of the metal frame has regions arranged in different planes, and  
       [0014] mounting the mounting plate ( 20 ) with the electronic SMD components ( 10 ) fastened thereon in the interior of a base housing.  
       [0015] As has already been explained above, the method of production according to the invention permits automated surface mounting of the electronic SMD components on the mounting plate by means of a PCB assembly machine and adaptation of the shape of the electronic assembly to the inside dimensions of a housing. The production of the metal frame is advantageously performed by punching the conductor track structure and the supporting webs from the metal sheet. Etching methods are not so well suited because of the comparatively large sheet thickness. Simple embedding of the metal frame in a dimensionally stable, electrically insulating material is advantageously achieved by injection-coating the metal frame with a plastic. The metal sheet advantageously has a reduced thickness in the region of the desired bending sites in order to facilitate bending of the mounting plate in this region.  
       [0016] The lamp base according to the invention can be, for example, a constituent of a high-pressure discharge lamp that can be used as headlight lamp in a motor vehicle. The electronic assembly advantageously includes electronic components that are interconnected as voltage transformer for generating the lamp operating voltage, as well as further electronic components that are a constituent of the ignition device required to ignite the gas discharge in the high-pressure discharge lamp. 
     
    
    
     III. DESCRIPTION OF THE PREFERRED EXEMPLARY EMBODIMENT  
     [0017] The invention is explained in more detail below with the aid of a preferred exemplary embodiment. In the drawing:  
     [0018]FIG. 1 shows a schematic cross section through the electronic assembly of a lamp base according to the invention, and  
     [0019]FIG. 2 shows a cross section through the base of a high-pressure discharge lamp with an electronic assembly arranged therein. 
    
    
     [0020] The electronic assembly depicted in FIG. 1 comprises a multiplicity of electronic components  10 , in particular SMD (Surface-Mounted-Device) components that are fastened on a meandering mounting plate  20 . The mounting plate  20  substantially comprises a dimensionally stable, electrically insulating plastic in which metal webs  21  are embedded. The metal webs  21  serve the purpose of mounting and making electrical contact with the electronic components  10  on the mounting plate  20 . A few metal webs  21  additionally, or even exclusively, serve the purpose of preserving the unity and the mechanical stability of the mounting plate  20 . The metal webs  21  are arranged in such a way that their surface  21   a  provided for making contact with the electronic components  10  is accessible. The contacting surface  21   a  of the metal webs  21  preferably terminate with the surface  20   a  of the mounting plate  20  that is provided for mounting the electronic components  10 . In the case of the exemplary embodiment depicted in FIG. 1, the mounting plate  20  has five bent sections  201 - 205  that are connected via curved regions  206  of the mounting plate  20 . The surface  20   a  is correspondingly divided up into five regions  201   a - 205   a  that are arranged in five different planes. A three-dimensional arrangement of the electronic components  10  is thereby achieved instead of a substantially planar one. In the preferred exemplary embodiment, the shape and the dimensions of the sections  201 - 205 , as well as the placing of the curved regions  206  and the placing of the electronic components  10  on the mounting plate  20  are tuned to the inside dimensions of the base  30  of a motor vehicle high-pressure discharge lamp. The mounting plate  20  and the electronic components  10  mounted thereon are inserted as electronic assembly into the chamber, provided therefor, of the base  30  and are connected to the high-voltage transformer  31  arranged in a separate chamber and to the supply leads (not depicted) of the high-pressure discharge lamp (not depicted). Apart from the high-voltage transformer  31 , the electronic assembly comprises all the electronic components of the ignition device, and the electronic components of a full-bridge inverter serving to operate the high-pressure discharge lamp.  
     [0021] A unipartite bronze sheet or brass sheet approximately 0.3 mm thick is used to produce the electronic assembly. The bronze or brass sheet can have a reduced thickness, for example by being notched, in the region of the desired bending sites  206 . Stamped from this metal sheet in accordance with a prescribed mask is a continuous metal frame whose webs  21  form conductor tracks for the electronic components  10  mounted thereon, and/or serve to preserve the mechanical stability and the unity of the metal frame. Subsequently, the metal frame is injection-coated with a plastic, for example a polyamide. The webs  21  are embedded in a form-fitting fashion in the plastics material by the injection-coating of the metal frame with plastic. The injection-coating of the metal frame with plastic is performed, however, such that the surface  21   a  of the metal webs  21  that is provided for making contact with the electronic components  10  to be mounted remains accessible, that is to say remains uncovered by plastic. Likewise, neither are the desired bending sites  206  injection-coated with plastic. After the plastic has hardened and thus become dimensionally stable, the metal webs no longer required, which have served exclusively to preserve the mechanical stability and the unity of the metal frame, are removed. Their function is taken over by the now dimensionally stable plastic. The corresponding webs are therefore severed in a second stamping operation in order to avoid an electric short circuit between the electronic components  10  to be mounted. The dimensionally stable plastic and the metal webs  21  embedded therein form a mounting plate  20  with a substantially flat surface  20   a  that is provided for mounting electronic SMD components  10 . The contacting surfaces  21   a  of the metal webs  21  terminate with the surface  20   a  of the mounting plate  20 . A piece assembly machine is used to fix the electronic components  10 , designed using SMD technology, on the surface  20   a , and to solder them to the contacting surfaces  21   a  of the metal webs  21  serving as conductor tracks. A lead-free high-temperature solder is used for this purpose. Subsequently, the mounting plate  20  is bent in a meandering fashion in the region of the desired bending sites  206 . The electronic component obtained in this way is inserted into the lamp base  30  and connected to the high-voltage transformer  31  and the electrical terminals of the base  30  as well as to the supply leads of the lamp (not depicted). A receptacle  32  for the high-pressure discharge lamp (not depicted) is provided in the base  30 .