Abstract:
Sintering tool ( 10 ) with a cradle for receiving an electronic subassembly (BG) to be sintered, characterized by at least one support bracket ( 20 ), arranged at two locations opposite the cradle, for fixing a protective film ( 30 ) covering the electronic subassembly (BG).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a National Stage application of International Patent Application No. PCT/EP2015/070625, filed on Sep. 9, 2015, which claims priority to German Patent Application No. 102014114097.4, filed on Sep. 29, 2014, each of which is hereby incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to a sintering tool with a cradle for receiving an electronic subassembly to be sintered. The invention also relates to a method for sintering an electronic subassembly comprising the steps of: arranging the electronic subassembly on the cradle of a sintering tool, covering the electronic subassembly with a protective film, and sintering the electronic subassembly. 
       BACKGROUND 
       [0003]    Sintering devices for carrying out the low-temperature pressure sintering of electronic subassemblies are already known. These have an upper die and a (preferably heatable) lower die, which can be moved towards one another. In particular, such sintering devices are designed for sintering electronic subassemblies in such a way that a lower die is provided with a massive tool, which carries and heats the planar circuit carrier. A temperature-resistant elastic medium of the upper die tool in the form of a pressure pad, for example a silicone pad, produces an increasing pressure on the surface of the circuit carrier, whereby the latter is pressed onto the planar support of the lower die tool. 
         [0004]    If a silicone pad is used as the pressure pad, it is customary to cover the subassembly to be sintered with a protective film, for example a Teflon film, in order to avoid contamination of the electronic subassembly with silicone components. The protective film is placed between the upper die and the lower die, covering the electronic subassembly to be sintered, and is elastically deformable in such a way that as the pressure pad presses the Teflon film against the surface contour of the electronic subassembly, so that the latter adapts itself to the surface relief of the electronic subassembly under elevated pressure (up to approximately 30 MPa) and elevated temperature (up to approximately 350° C.). 
         [0005]    However, it has been found to be disadvantageous when using these protective films, that the protective film remains adapted to the contour of the electronic subassembly after the opening of the upper die and lower and the cooling down of the sintered electronic subassembly, and has to be carefully lifted off from the subassembly relief to avoid damage to the sintered electronic subassembly. 
       SUMMARY 
       [0006]    The object of the invention is therefore to provide a sintering tool and a method for sintering that facilitates the sintering operation, in particular the handling of the protective film. 
         [0007]    This object is achieved according to the invention by the tool for a sintering device comprising: a sintering tool with a cradle for receiving an electronic subassembly (BG) to be sintered, comprising at least one support bracket, arranged at two locations opposite the cradle, for fixing a protective film covering the electronic subassembly (BG) and the method comprising the steps of: a method for sintering an electronic subassembly (BG) comprising the steps of: arranging the electronic subassembly (BG) on the cradle of a sintering tool, covering the electronic subassembly (BG) with a protective film, and sintering the electronic subassembly (BG), whereby after the covering and before the sintering of the electronic subassembly (BG), the protective film is fixed to at least one support bracket which is in turn fixed at two locations on opposing sides of the cradle. The subclaims, which are respectively dependent on the independent claims, provide advantageous designs of the invention. 
         [0008]    The basic concept of the invention is to fix the protective film at its edges, or the edges of the cradle, or of the electronic subassembly, before the heating and the application of pressure. On account of the elastic properties of the protective film, although the protective film will deform to adapt to the relief of the subassembly under the effect of heat and the effect of pressure, it will contract during the cooling down once sintering has been performed, and withdraw itself of its own accord from the surface relief, so that this operation takes place automatically and no longer has to be carried out manually. 
         [0009]    The advantage of the invention is therefore that the protective film detaches itself of its own accord from the subassembly after the lifting off of the upper die and cooling down, and can be readily lifted off from the subassembly. 
         [0010]    The sintering tool designed according to the invention has a cradle for receiving an electronic subassembly to be sintered and at least one support bracket, fixed at two locations on opposing sides of the cradle, for fixing a protective film covering the electronic subassembly. 
         [0011]    Preferably, two sets of fixing points for the support bracket are provided, co-planarly arranged on either side of the cradle, and in orthogonal directions. A particularly advantageous design being achieved if the support bracket is of an annular form. 
         [0012]    The support bracket can optionally also be rectangular, elliptical, or formed as a polygon to provide an optimized use of space of the cradle. Advantageously, the support bracket is formed complementary in shape to an edge of the cradle. 
         [0013]    Easy fastening of the protective film to the sintering tool, the sintering tool preferably has a socket for receiving a connector formed on the support bracket. Specifically, the socket and the connector may be formed in the manner of a bayonet fastener. 
         [0014]    Advantageously a release device may be provided, by means of which the separation of the sintering tool, in particular of the support bracket, from the protective film, may be carried out by the upper die after a pressurization and a sintering process. The electronic subassembly is usually set loosely on a moveable lower die and is pressed against an upper die comprising a pressure pad. The pressure pad is usually made of silicone, wherein the protective film protects the electronic subassembly from sticking and contamination by silicone. After the sintering, the lower die moves down and away from the fixed upper die, with the risk that the protective film, and possibly the electronic subassembly, adheres to the pressure pad of the upper die. To ensure safe release of the protective film, and possibly the electronic subassembly, from the pressure pad, a release device, coming from the upper die of the sintering tool, preferably engages into receiving sockets of the support bracket in order to release the sintering mold from upper die. Such a release device may comprise, for example, two or more electrically, pneumatically or hydraulically moveable actuator bolts. Herby it is possible to obtain a safe detachment of the electronic subassembly and thus a trouble-free and efficient sintering process. 
         [0015]    The method concerning the invention for sintering an electronic subassembly then provides that the electronic subassembly is arranged on the cradle of a sintering tool, is covered with a protective film, and is sintered, the protective film being fixed to at least one support bracket which is in turn fixed at two locations on opposing sides of the cradle. 
         [0016]    Optionally, the protective film may be mechanically detached after sintering. 
         [0017]    According to a preferred embodiment, the protective film is fixed after the covering of the electronic subassembly by a clamping ring. 
         [0018]    The protective film is in particular a Teflon film. 
         [0019]    The protective film may be of a multi-layered or multi-ply construction, the one layer or ply of the protective film consisting of Teflon and another layer or ply consisting of Kapton. The Teflon layer or ply may, for example, have a thickness of 400 μm and the layer or ply of Kapton that is facing the electronic subassembly may be 50 μm thick, so that the risk of contamination of the electronic subassembly with Teflon is reduced. 
         [0020]    Most preferably, the protective film is formed such that a gas exchange through the protective film is ensured—this is made possible by means of pores or holes penetrating the protective film. The clearances provided in the protective film allow an evacuation of the area surrounding the process, without inclusions of air remaining between the Teflon film and the components, or exposure to process gases, which can be brought up to the components to be sintered through these clearances, holes or pores. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The invention is explained in more detail on the basis of an exemplary embodiment that is represented in the following figures. 
           [0022]      FIG. 1  shows a sectional view through an exemplary embodiment according to the invention that is of a particularly preferred design. 
           [0023]      FIG. 2  shows a sectional view through a second exemplary embodiment according to the invention with a release device for the separation of the sintering tool. 
           [0024]      FIG. 3  shows a flow diagram illustrating an exemplary embodiment of the method according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]      FIG. 1  shows a sintering tool  10 , which has a cradle, formed as a depression in the sintering tool  10 , for receiving an electronic subassembly BG to be sintered. The electronic subassembly BG is covered by a protective film  30 , for example a Teflon film, which is fastened to the sintering tool  10  by means of the support bracket  20  arranged on both sides of the cradle. 
         [0026]    In  FIG. 2  is shown a sintering press  100  which comprises an upper die  42  and a lower die  44 . A sintering tool  10  is mounted on the lower die  44 . For pressure sintering, the lower die  44  can be moved vertically in the direction of the upper die  42  to produce a sintering pressure in the range of 10 to 40 MPa. An electronic subassembly BG, comprising a circuit substrate and electronic components which are to be electrically connected to it by pressure sintering, is inserted into a cradle in the tool holder  52 . The sintering tool  10  includes a protective film  30  and a support bracket  20 , which is formed as an annular clamping ring around the tool holder  52 , and the protective film  30  is fixed on the tool holder  52  of the sintering tool  10 . The lower die  44  and the upper die  42  are electrically heated. The upper die  42  carries a pressure pad  56 , that creates a quasi-hydrostatic pressure distribution on the protective film  30  and the electronic assembly BG when the lower die  44  is pressed into the upper die  42 . After the pressure sintering process, the lower die  44  moves downwards away from the upper punch  42 . In order to prevent adhesion of the protective film  30 , and thus also the sintering tool  10  to the pressure pad  56 , receiving sockets  46  are provided in the support bracket  20  of the sintering tool  10 . A release device  40  is shown, comprising a lifting bar  50  which is vertically movable by a hydraulic or pneumatic actuator cylinder  54 . The lifting bar  50  includes two or more actuator bolts  48  which can engage in the receiving sockets  46  of the support bracket  20 . If the lifting bar  50  is lowered in the direction of the closed lower die  44 , preferably synchronously with the speed of lowering of the lower die  44 , a reliable separation of the protective film  30 , and thus the sintering tool  10 , from the pressure pad  56  is obtained. Thus the sintering tool  10  can be removed from the sintering press  100  to allow further processing steps. 
         [0027]      FIG. 3  shows a flow diagram illustrating an exemplary embodiment of the method according to the invention. The method  200  concerning the invention for sintering an electronic subassembly provides that the electronic subassembly is arranged  201  on the cradle of a sintering tool, is covered  202  with a protective film, and is sintered  203 , the protective film optionally being fixed  204  at least in a direction in front of and behind the electronic subassembly after the covering and before the sintering of the electronic subassembly. Optionally, the protective film may be mechanically detached  205  after sintering  203 . 
         [0028]    While the present disclosure has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this disclosure may be made without departing from the spirit and scope of the present disclosure.