Patent Publication Number: US-2005136740-A1

Title: Premolded housing

Description:
FIELD OF THE INVENTION  
      The present invention relates to a premolded housing for receiving a detector chip, a component made up of such a premolded housing and a chip received therein, as well as a device having a substrate and such a component.  
     BACKGROUND INFORMATION  
      Premolded housings have a housing body which may be made of a plastic material or a molding compound based on epoxy resin, and a generally multiple-piece supporting strip of metal, generally called the leadframe. The premolded housing is produced in a molding process by extrusion-coating the leadframe with the plastic material or molding compound. Connector pins or housing tabs for contacting on a circuit board protrude, generally parallel to the housing floor or a possible die pad, generally on two sides or on all four sides of the premolded housing. A detector chip may subsequently be set into the premolded housing—onto the housing floor or preferably onto a middle area of the leadframe used as a die pad—and affixed by soldering or gluing, and contacted with the connector pins via wire bonds. The premolded housing is then mounted flat on a substrate, for example a circuit board, for example by gluing or soldering.  
      In gas sensors, which are used in the automotive industry for example to detect leakage in a CO 2  air conditioning system or to determine gas concentrations in the air being breathed, generally the temperature difference caused by absorption of infrared radiation in gas-specific wavelength ranges is measured as thermoelectric voltage, using a source of infrared radiation, such as an incandescent lamp operated in the low current range, and a radiation detector such as a thermopile. For the radiation detector, a detector chip, which may be in particular a thermopile chip, is often placed in a premolded housing as described above. The thermopile chip is usually placed on the floor of the premolded housing, for example on a die pad, so that an optical axis runs at an angle of 90_ to the floor of the premolded housing and thus to the circuit board. Because of their mechanical, optical or thermal properties, generally the detector chips may not be completely coated with plastic or a molding compound, so that the use of molded housings is unsuitable; however, in the case of premolded housings the radiation may enter through the open front of the premolded housing. The radiation source is generally positioned on another substrate, for example an additional circuit board, which must be optically aligned and positioned using a relatively complex procedure with respect to the premolded housing of the radiation detector.  
     SUMMARY  
      A premolded housing, component, and device according to an example embodiment of the present invention may have the particular advantage that using relatively little manufacturing effort and relatively low manufacturing costs, a space-saving installation and simple and precise optical alignment is possible. According to the present invention, vertical installation of the premolded housing on a substrate—in particular a circuit board—is possible, whereby the generally tight lateral installation space may be significantly reduced.  
      According to the present invention, vertical mounting of the premolded housing saves substrate area, so that a smaller lateral installation space is needed. This is beneficial both for optical and for non-optical applications. With this type of vertical mounting, the premolded housing allows simple and inexpensive incorporation of stress-sensitive chips. With the vertical installation of a premolded housing having an optical component, the optical axis of the optical chip is not run vertical, but parallel or at a slight angle to the substrate. Thus, it is possible to mount a plurality of optical elements on a substrate, for example the premolded housing according to the present invention having an incorporated detector chip and a radiation source, so that it is possible using only one circuit board to design a complete optical system, e.g., a gas sensor having a radiation source and a radiation detector including an absorption path, and possibly a reflector device for focusing the radiation. In particular, a plurality of radiation detectors, each made up of a premolded housing and an incorporated detector chip, may be positioned on the substrate opposite a shared radiation source. A radiation filter may be provided at the open front side of the premolded housing, i.e., in the optical axis in front of the incorporated detector chip.  
      The manufacturing costs for a vertically mountable premolded housing are substantially the same as for conventional premolded housings, since no additional manufacturing steps are necessary. Since the premolded housing has an unstructured, smooth front side or upper face without connector pins, a standard populating process on the substrate is possible.  
      Above the leadframe in a lateral direction, a heat dispersing device and an electrical coupling to the substrate are possible, so that electromagnetic compatibility may be ensured. Furthermore, all relevant surfaces and contacts in the premolded housing may be passivated.  
      The design of the premolded housing according to the present invention, having a housing body and laterally extending side support areas that may be bent over in direction-changing areas, allows great stability and great variability in the installation when mounted vertically, depending on the installation space and the need for accessibility of the soldering points. The side support areas may optionally be bent in one of two directions, and furthermore, soldering tabs of the side support areas and of the connector pins may optionally also be bent in one of two directions.  
      Cost-effective and rapid manufacturing of the premolded housing is possible by molding the housing on a supporting strip or leadframe strip, followed by cutting or stamping out the leadframe, preferably with one cut, and bending over the side support areas. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The present invention is explained below based on some example embodiments.  
       FIG. 1  shows a section of a leadframe strip having a plurality of premolded housings which are extrusion molded around identical, repeating leadframe structures.  
       FIG. 2  shows a 10-pole premolded housing according to one embodiment, with a leadframe from  FIG. 1  after being stamped out of the leadframe strip and before the leadframe is bent.  
       FIG. 3  shows a front view into the premolded housing according to  FIG. 2  after all the soldering tabs, both from the side support areas and from the connections, have been bent over in one direction, and after the side support areas have been bent.  
       FIG. 4  shows a top view of a corresponding 6-pole premolded housing after the soldering tabs have been bent in the direction of the housing opening and the side support areas have been bent toward the rear of the premolded housing.  
       FIG. 5  shows a top view of an embodiment corresponding to  FIG. 4 , having the side support areas bent toward the front of the housing.  
       FIG. 6  shows a top view of an embodiment corresponding to  FIG. 5 , but having soldering tabs bent toward the outside, i.e., toward the rear of the housing.  
       FIGS. 7   a, b  show the premolded housing from  FIG. 4  in a side view and a section of a side view.  
       FIG. 8  shows a gas sensor on a substrate having a radiation detector and a radiation source according to the present invention.  
       FIG. 9  shows a top view of a gas sensor having multiple radiation detectors according to the present invention. 
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS  
      A leadframe strip  1  is manufactured, for example as a stamped part, from a metal, for example copper, and has a continuous ladder-shaped frame  4  with webs  4   a , and a plurality of leadframe structures  5 , prestamped in frame  4  and arranged in sequence in a direction of symmetry P, for leadframes  2  to be separated out later.  
      According to an example embodiment of the present invention, housing bodies  6  may be manufactured directly by extrusion coating leadframe structures  5  in unseparated leadframe strip  1  with a plastic material or a molding compound based on synthetic resin. In  FIG. 1  the positions of premolded housing  6  are already drawn in with lines on the individual leadframe structures  5 .  
      Each leadframe  2  has in its middle area a die pad  9 , which is connected in both lateral directions, i.e., orthogonally to the direction of symmetry P—through a direction-changing area  10  to a left and right side support area  11 . Side support areas  11  each extend downward, i.e., opposite the direction of arrow P—away from direction-changing areas  10 , and each have two soldering tabs  12  at their lower end.  
      In addition, each leadframe  2  has a plurality of connector pins  14 —according to  FIG. 1  ten of them—, which are not connected to middle die pad  9 , in order to enable differing contacting, via die pad  9  of the chip incorporated later and connector pins  14 . Connector pins  14  protrude downward from housing body  6 , and taper down to narrower soldering tabs  15  at their lower end.  
      According to  FIG. 2 , leadframe  2  is molded into premolded housing  9  in such a way that direction-changing areas  10  are each halfway covered with the injected material, and thus serve in the subsequent bending as articulations for adjoining side support areas  11 , which are positioned outside of premolded housing  6 . In addition, connector pins  14  are also partially—e.g., approximately halfway—cast into premolded housing  6 , so that their lower parts with soldering tabs  15  protrude outward.  
      Individual leadframe structures  5  are connected by their soldering tabs  12  and their soldering tabs  15  to the webs  4   a  of leadframe strip  1 , which run in the transverse direction. By separating or trimming along straight cutting lines  3 , the individual leadframes  2  are subsequently detached from leadframe strip  1 ; a premolded housing shown in  FIG. 2  may be separated by each cut along cutting line  3 .  
      Premolded housing  8  shown in  FIG. 3  is formed starting from  FIG. 2  by first bending soldering tabs  12 ,  15  of side support areas  11  and connector pins  14  by 9_, in order to permit mounting and contacting—as will be explained later—on a circuit board. Then, side support areas  11  are bent at right angles, i.e., by 90_ to the rear in direction-changing areas  10 , which function as articulations.  
       FIG. 4  shows an example embodiment of a six-pole premolded housing  8 , which is manufactured by molding in six connector pins  14  and a die pad  9  having direction-changing areas  10  and side areas  11 . Here, all soldering tabs  12  are bent toward the housing opening, and side support areas  11  are then bent toward the rear—i.e., toward the floor of housing body  6 .  
      In the example embodiment of  FIG. 5 , in contrast to the example embodiment of  FIG. 4 , side support areas  11  are bent toward the front, i.e., toward a front side  13  of housing body  6 , soldering tabs  12  here too being bent as in  FIG. 4 .  
      In the example embodiment of  FIG. 6 , in contrast to the example embodiments of  FIGS. 4 and 5 , soldering tabs  12  and  15  are bent in the other direction, and side support areas  11  are bent as in  FIG. 5 , so that soldering tabs  12  are bent outward—i.e., in the opposite direction from  FIG. 5 —in order to allow better inspection of the soldering points, which are offset laterally from housing body  6 .  
      The example embodiments shown in  FIGS. 3 through 6  may optionally be combined in regard to the direction in which side support areas  11 , soldering tabs  12  and  15  are bent, in conformity with the corresponding contacting conditions and installation conditions of premolded housing  8 .  
       FIGS. 7   a  and  7   b  show a side view and sectional view from the side of premolded housing  8  from  FIG. 4  before installation on a circuit board. Housing body  6  has in its interior a free space  18 , and is at least partially open on its front side  13 , in order to receive the radiation being detected, for example, in optical applications.  
       FIG. 8  shows the basic configuration of a radiation detector  21 , which is formed by premolded housing  8  and a thermopile chip  19  incorporated into premolded housing  8 , the chip being attached by its bottom to die pad  9  and making contact with the individual connector pins  14  through bonding wires  20 . Radiation detector  21  is bonded to a circuit board  22  through soldering tabs  12  and  15  of side support areas  11  and connector pins  14 , by means, for example, of solder  24  or contact adhesive. Here the entire premolded housing  8  made up of housing body  6  and leadframe  2  stands vertically, which means that die pad  9  and the floor of housing body  6  are perpendicular to circuit board  22 , so that incorporated thermopile chip  19  is able to receive and detect radiation S which is parallel to circuit board  22 . To this end, an incandescent lamp operated in the low current range as IR source  26  makes contact through its connections  27  with circuit board  22  and emits infrared radiation S, which is detectable by thermopile chip  19 . Distance d between IR source  26  and thermopile chip  19  functions as absorption path d, in which a gas component, for example CO 2 , is detectable. A cover and a radiation filter  25  may be placed on front  13  of housing body  6 , which allow only IR radiation of a selected wavelength range to pass.  
      According to  FIG. 9 , a plurality of radiation detectors  21  incorporated vertically on circuit board  22  are provided, each made up of a premolded housing  8  and a thermopile chip  19 , together with a shared IR radiation source  26 . It is possible here to provide different radiation filters  25   a ,  25   b  and  25   c  having different filter properties on front  13  of housing body  6 . For signal amplification, a reflector device  29  may be installed on circuit board  22 , which focuses and guides radiation S from the one IR radiation source  26  to the individual radiation detectors  21 .