Abstract:
The present invention relates to a TO-can type encapsulating element for enclosing, either hermetically or non-hermetically, optical-electrical chips with integrated optical element interfaces, detachable fibres and leadframes. The TO-can/encapsulating element enables the optical fibre ( 9 ) to be readily positioned relative to the chip ( 25 ) with the aid of a fix-able can-flange ( 7 ), and eliminates the risk of crack formation by virtue of the component leads of said TO-can having been provided with and connected to a leadframe ( 6 ).

Description:
FIELD OF INVENTION 
   The present invention relates to a can for the hermetic or non-hermetic enclosure of an optical-electric chip that includes an integrated optical element interface, a detachable fibre pigtail and a leadframe. 
   DESCRIPTION OF THE BACKGROUND ART 
   The technique of encapsulating optical-electric chip in so-called TO-cans (TO/Transistor Outline) provides obvious advantages with respect to maintaining stable positioning of, for instance, an optical fibre relative to an optical-electric chip in environments of changing temperatures. In present day technology, lenses are often used to maintain an acceptable coupling between fibres and chip, which renders the cost involved unacceptable in the case of certain applications. TO-cans/encapsulations may include a receptacle that can be detached from the can, although this optical element interface has often been produced in an unnecessarily expensive manner with regard to the choice of material and design. When TO-cans have been mounted on a printed circuit board, their component leads have normally been bent down towards the board, which may have a negative affect on the transmission properties at high frequencies in some contexts. There is also a risk of the formation of microcracks in the glass transit that embrace the component leads in the mounting base of the TO-can. Little account is often paid to the fact that transmission at high frequencies can be improved when the transmission conductor has conductors with 0-potential on two sides. 
   SUMMARY OF THE INVENTION 
   The structural design outlined in  FIG. 1  includes a component that has several significant properties. Positioning of an optical fibre in relation to an optical-electric chip can be achieved relatively simply, by moving a ferrule in two dimensions until coupling of the light is satisfactory (see  FIG. 2 ). The ferrule can then be fixed by laser welding, gluing or soldering processes. 
   The so-called TO-can shown in  FIG. 1  also includes a ferrule interface which enables two ferrules with optical fibres to be coupled in relation to each other in a guide sleeve. The optical interfaces of the fibre ends are brought into contact with each other with the aid of a locking sleeve that includes a bayonet fitting, which subsequent to being pressed and rotated ensures that a spring pressure can be maintained for mutual contact of said ends during operation. 
   To eliminate the risk of the formation of micorcracks among other things, the component leads of the TO-can have been provided with a leadframe, the construction of which can be seen from  FIG. 3 . The leadframe with its short lead-ins together with the positioning of the earth leads of the mounting base on both sides of the transmission conductor ensures that the transmission properties will be good and that stable positioning between a fibre and an optical-electric chip can be maintained. 
   The leadframe can be soldered to the mounting base leads or fastened thereto in some other way, to create a low-resistance connection. The leadframe can be further supported against the mounting base with a glue joint, an injection moulded joint or a compression moulded joint. At this stage, all leads are short-circuited to a common potential, which is beneficial from an electric discharge aspect (ESD). 
   As will be evident from the markings in  FIG. 3 , the leadframe can then be split up (clipped) to separate the individual leads and to adapt said leads for mounting on the printed circuit board. With the intention of achieving component stability when mounting the component on the printed circuit board, a combined support leg and mounting leg have been placed on the end wall of the can, as will be seen from  FIG. 1 . The entire component or parts thereof may be enclosed in a thermoplastic or thermosetting material. 
   The invention will now be described in more detail with reference to a preferred embodiment thereof and also with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a partially exploded outline view of the various structural elements for effecting an optical-fibre connection to a TO-can. 
       FIG. 2  is a cross-sectional view of a TO-can arranged in accordance with the invention and mounted in the absence of a leadframe. 
       FIG. 3  shows a leadframe mounted on the leads of the TO-can. 
       FIG. 4  is a cross-sectional view of the TO-can arranged in accordance with the invention and mounted with a leadframe. 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1  is a partially exploded perspective view of the various structural elements for connecting an optical fibre to a TO-can, where the can  1  includes a mounting base  2 , a leadframe  6  and an end wall  3 . The end wall  3  has a hook  4  and a hook leg  5 . A capsule ferrule  8  having a capsule flange  7  is shown fitted to the end wall  3 , with an optical fibre  9  disposed in a cylindrical cavity, where said optical fiber  9  is glued firmly inside the ferrule  8  or fastened thereto in some other way. An optical fibre  20  is shown partially bared and fitted in a ferrule  11  with its flange  12  and its guide  14 . The guide  14  is surrounded by a coil spring  13 . The capsule ferrule  8  with its optical fibre  9  is guided in relation to the ferrule  11  with its optical fibre  20  by means of a guide sleeve  10  which has been made resilient by slitting the sleeve or in some other way. A locking sleeve  15  runs on the optical fibre  20 . The locking sleeve  15  has at least two locking recesses  16   a  and  16   b , an end surface  17  and a guide hole  18 . To prevent the fibre being broken, the locking sleeve  15  includes an integrated anti-break element  19  formed integrally with the locking sleeve  15 . 
   The structural elements illustrated in  FIG. 1  are assembled by pressing one end of the guide sleeve  10  onto the ferrule  8 , wherewith the guide sleeve  10  yields slightly and therewith embrace the ferrule  8 . The ferrule  11  is pressed into the other end of the guide sleeve  10 , so as to be enclosed therein. The locking sleeve  15  with its locking recesses  16   a  and  16   b  is moved towards the hook  4  and the hook leg  5 , so that the hook  4  and the hook leg  5  can be guided into the locking recesses  16   a  and  16   b  and the guide  14  can enter the hole  18 , wherewith the coil spring is brought into contact with the end surface  17 . The locking sleeve  15  is pressed further towards the mounting base  2 , so as to compress the coil spring  13  between the flange  12  and the end surface  17 , therewith bringing the optical fibre  9  in the ferrule  8  into contact with the optical fibre  20  in the ferrule  9 , wherewith an optical contact element can be releasably attached to the capsule with the aid of the mutually opposing ferrule interfaces. A fibre pigtail can be releasably mounted on the component, by clockwise rotation of the locking sleeve  15  until the hook  4  and the hook leg  5  reach the end position of respective locking recesses  16   a ,  16   b.    
     FIG. 2  is a detailed cross-sectional view of the various structural elements of a TO-can according to the invention, where the cylindrical can  1  is fastened to the cylindrical mounting base  2  with the aid of a can joint  23 . At least one ground lead G is fastened to the mounting base  2  with the aid of a lead joint  31 , such that the ground lead is able to function as a cooling sink and as an electrical 0-potential from the mounting base  2  down towards a printed circuit board for instance. The mounting base also includes at least one transmission lead T and one current supply lead Vcc each having lead ledges  28   a  and  28   b . The leads are surrounded by electrically insulated transits or leadthroughs  32  at the places where the transmission lead T and the current supply lead Vcc penetrate the mounting base  2 . One or more carriers  27  are glued or soldered firmly to the upper side of the mounting base  2 , and one or more optical-electrical chips  25  are glued or soldered firmly to the upper surface of said carrier. Subsequent to being optimised, the cylindrical ferrule  8  with its fixable flange  7  and its cylindrical ferrule-part  33  are secured to the upper side of the can  1  with a so-called ferrule joint  22  by means of a laser welding, soldering or gluing process. An optical fibre  36  is secured within the ferrule  8 , by means of a clamping action, a gluing process or a soldering process. The optical fibre  36  has an outwardly protecting part  9  which is adapted so that the ferrule-part  33  will not come into contact with a bonding wire  26  or other wires. Because the can includes means for positioning a connected optical fibre to the optical-electrical component without the use of lens elements, and because the ferrule  8  is moved in an x-direction and a y-direction over the can  1  in its cylindrical recess  24 , optimisation can be achieved with respect to light incoming from the optical fibre  36  to the optical-electrical chip  25  with its optically active area  21  or, when the optical-electrical chip  25  is a light emitting component, the chip  25  can transmit light from the optical ares  21  to the optical fibre  36  in an optimised manner. 
     FIG. 3  is a view taken from beneath the mounting base  2  and shows the ground lead G, the transmission lead T and the power supply lead Vcc of said base, said leads having been connected to a leadframe  6 . The leadframe  6  is configured so that the ground lead G extends on both sides of the transmission lead T, therewith contributing towards limiting the distortion at high bit rates and, at the same time, functioning as symmetrical cooling sinks between the mounting base  2  and a printed circuit board  35  together with its metal conductors. The leadframe  6  is mounted with the leads in joins  37 , which have been produced by crimping, laser welding or soldering, or by some other appropriate joining method, whereafter the leadframe  6  has been divided at cutting locations  34 , so as to separate the various leads in the leadframe. The lead separated in the leadframe are length matched/impedance matched to obtain optimal transmission properties. 
     FIG. 4  is a detailed cross-sectional view illustrating the various structural elements in the TO-can, and shows the cylindrical can  1  secured to the cylindrical mounting base  2  by can joints  23 , and the leadframe  6  connected to the leads T, G and Vcc. The ground lead G is fastened to the mounting socket with the aid of lead joints in a manner to enable the ground lead to function as a cooling sink and an electric 0-potential from the mounting base down to a printed circuit board for instance. The mounting base includes at least one transmission lead T and one power supply lead Vcc, each having a respective lead ledge  28   a  and  28   b . The leads are surrounded by said electrically insulated transits or leadthroughs  32  at the place where the transmission lead T and the power supply lead Vcc penetrate the mounting base  2 . The leadframe  6  is configured so that the ground leads G will extend on respective sides of the transmission lead T. The leadframe  6  is fastened with the leads in joins  37 , which have been made by crimping, laser welding or soldering or in some other suitable way, whereafter the leadframe  6  has been divided at the cutting locations  34  so as to provide mutually separate and length-matched conductors to the various leads, which are then cut slightly beyond the joins  37 . 
   It will be understood that the invention is not restricted to the aforedescribed and illustrated exemplifying embodiments thereof and that modifications can be made within the scope of the accompanying claims.