Patent Publication Number: US-4545761-A

Title: Method and apparatus for securing articles in place on a substrate

Description:
TECHNICAL FIELD 
     This invention relates to a technique for securing a plurality of articles on a substrate. 
     BACKGROUND OF THE INVENTION 
     Only recently have chip carriers been developed for the packaging of semiconductor chips. A chip carrier is typically comprised of a case having a cavity therein in which a semiconductor chip is fixedly mounted. The semiconductor chip is connected, either by way of solid wires or leads which extend through the case, to bonding pads on the exterior thereof to permit electrical connection to the chip. The case is covered by a lid which is hermetically sealed thereto. 
     To assure the hermetic seal between the case and the lid, a thin film of a eutectic alloy is deposited in an earlier process on the periphery of a major surface of the lid which will contact its associated case. The alloy will reflow when heated and, upon subsequent cooling, will form the desired seal. The case must be maintained in intimate contact with the lid during heating thereof to prevent the lid from floating during the reflow of the eutectic alloy. In the past, various types of spring clips have been used to apply pressure to the lid and case during heating. One such spring clip has the configuration similar to that of a clothespin where the case and the lid of a chip carrier are held closely to one another between the tines of the spring clip. This type of clip can be configured to typically hold six chip carriers. The clip itself, with the captured chip carriers therein, is ultimately placed in a furnace to reflow the solder to seal the lids onto the cases. 
     These prior spring clips have not proven satisfactory from the standpoint that they must be manually employed. This necessarily results in slow packaging time and incurs additional expenses in the form of increased labor costs. Secondly, these prior spring clips are not easily adaptable to high volume production of chip carriers because of the additional time required to arrange a sizable number for large-scale simultaneous heating. 
     Therefore, there is a need for a spring clip adaptable to an automated and a high volume assembly of chip carriers which also holds the lid in intimate contact with the chip carrier cases during the heating thereof. 
     SUMMARY OF THE INVENTION 
     The foregoing problems are obviated by one aspect of the invention which is an apparatus comprising an elongated central member having first and second ends, means at the first end of the central member for lockably engaging a substrate, and a plurality of resilient arms extending radially out from the central member, for contacting and securing articles on the substrate in place when the first end of the central member is lockably engaged in the substrate. 
     Advantageously, the use of the instant apparatus which is amenable to an automated assembly process insures reliability of packaging by reducing labor and essentially replaces the workmanship required by the prior apparatus. In addition, the packaging operation is converted from a low volume and costly process to a high volume and less expensive one because a large number of chip carriers can be assembled quickly and sealed simultaneously by utilizing the apparatus and the pallet. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the invention, reference is made to the following description of an exemplary embodiment thereof, and to the accompanying drawings, wherein: 
     FIG. 1a is a top isometric view of a semiconductor chip carrier; 
     FIG. 1b is a bottom isometric view of the semiconductor chip carrier of FIG. 1a; 
     FIG. 2a is a top isometric view of a pallet containing the components of a chip carrier of FIGS. 1a, 1b and a spring clip; 
     FIG. 2b is a partial cross-sectional view of a receiving passage and a cavity of the pallet of FIG. 2a; 
     FIG. 3 is a top view of the spring clip which is inserted in the pallet of FIGS. 2a, 2b; 
     FIG. 4a is a cross-sectional view of the spring clip taken along 4a--4a shown in FIG. 3; and 
     FIG. 4b is an isometric view of a shaft component of the spring clip of FIGS. 3, 4a. 
    
    
     DETAILED DESCRIPTION 
     As illustrated in FIGS. 1a, 1b a chip carrier 10 is typically comprised of a case 12 having a cavity therein in which a semiconductor chip (not shown) is fixedly mounted. The semiconductor chip is connected, either by way of solid wires or leads which extend through the case 12, to bonding pads 13 on the exterior thereof to permit electrical connection to the chip. The case 12 is covered by a lid 14 which is hermetically sealed thereto by a thin film of eutectic alloy 15 such as 10UC Soldex alloy manufactured by Zirmex, Inc. of Tuscon, Ariz. The alloy 15 is deposited during an earlier process on the periphery of a major surface of the lid 14 which will contact the case 12. 
     FIG. 2a shows the structure of a pallet 20 which is utilized to contain and transport the components (i.e., the case 12 and the lid 14) of the chip carriers 10 through the assembly process. The pallet 20 has formed therein a plurality of through cavities 22 (one shown). Each cavity 22 has a tapered opening 22a in the upper portion thereof and an opening 22b in the lower portion surrounded by a ledge 23 for supporting a lid 14. Each cavity 22 is sized and shaped to permit receipt of a case 12 above an associated underlying lid 14 (see also FIG. 2b). In an exemplary embodiment, the cavities 22 are arranged in a ten row by six column array. 
     The pallet 20 also has formed therein a plurality of through receiving passages 24 (also see FIG. 2b). The passages 24 are arranged in a five row by three column array in such a manner that a group of four cavities 22 surround one passage 24. FIG. 2b  shows a cross-sectional view of the receiving passage 24 having shoulders 25 formed therein and a cavity 22 having a chip carrier lid 14 and a case 12 positioned therein. Also depicted in FIGS. 2a, 2b is a spring clip 30 which is inserted into a corresponding passage 24. 
     FIGS. 3, 4a and 4b show top, side and isometric views, respectively, of the spring clip 30 in detail. The spring clip 30 comprises an elongated member or central shaft 32 which extends through a passage (not shown) in a thin square metal plate 31. The metal plate 31 is loosely carried on the central shaft 32 between a pair of annular spaced-apart shoulders 33,34. In practice, the outer diameter of the lower shoulder 34 is smaller than the diameter of the passage through the plate 31 which in turn is smaller than the outer diameter of the upper shoulder 33. A small &#34;e&#34; ring 35 engages the central shaft 32 above the shoulder 34 to keep the metal plate 31 from slipping off the shaft 32. The plate 31 has four outstretched resilient arms 36, each sloping downwardly from a separate one of the sides thereof. Typically, each arm 36 has an upturned end 37. 
     As shown in FIG. 4b, the lower end 38 of the central shaft 32 is oblong-shaped and is sized for insertion into a corresponding through receiving passage 24 in the pallet 20. The upper end 40 of the central shaft 32 also has an oblong shape whose long dimension is oriented 90° from that of the lower end 38. Note that the long dimensions of the lower and upper ends 38 and 40, respectively, are each substantially normal to the axis of the central shaft 32. 
     Referring to FIG. 2b, in order to insert the spring clip 30 into a receiving passage 24, the shaft 32 is rotated such that the orientation of the long dimension of its lower end 38 is in alignment with the length of the surface opening of the passage 24. The shaft 32 is then inserted into the passage 24 without resistance because the upper dimension of the passage 24 is sized to accept the lower end 38. As the shaft 32 is inserted, the ends 37 of the arms 36 initially contact the chip carrier cases 12 also without resistance. Thereafter, a downward force must be exerted to continue the shaft 32 insertion. The shaft 32 enters the passage 24 until the annular shoulder 34 contacts the surface of pallet 20 and entry is stopped. The shaft 32 is then rotated once more in order that the long dimension of the lower end 38 is oriented 90° from its bearing when it was initially inserted. The long dimension of the lower end 38 is effectively positioned underneath the passage shoulders 25 and, consequently, the spring clip 30 cannot be lifted out of passage 24. The tolerances involved are such that arms 36 of an inserted spring clip 30, after being so positioned, extend over and press against each of the chip carrier cases 12 in the surrounding cavities 22. Note that the area of any one arm 36 in contact with the case 12 is minimized because the upturned end 37 directs all the force exerted by the arm 36 to a single line on the case 12. 
     In the manufacture of the semiconductor chip carriers 10, the components of the carriers are deposited into the cavities 22 of the pallet 20 (see FIG. 2a). Each lid 14, which is typically deposited first, rests on the bottom ledge 23 of the cavity 22 in which it sits. Each case 12, in turn, is deposited to overlie an associated lid 14. The eutectic alloy 15, which was previously applied on the periphery of a major surface of each lid 14, lies in between each lid 14 and case 12. 
     A plurality of the spring clips 30 are then inserted into the passages 24 of the pallet 20 as described previously. Each spring clip 30 secures in place all the unsealed chip carriers 10 in the cavities 22 surrounding the spring clip 30. Furthermore, the arms 36 of the spring clips 30 secure the cases 12 onto their associated lids 14 and provide a force which prevents relative movement therebetween during reflow of the eutectic material. 
     The pallet 20, now fully loaded, is placed in a furnace in order to reflow the eutectic alloy 15. A hermetic seal is formed between each lid 14 and case 12 as the chip carriers 10 are subsequently cooled. 
     After cooling, the spring clips 30 are removed from the pallet 20. The shaft 32 of each spring clip 30 is rotated 90° in order that the long dimension of its lower end 38 disengages the shoulders 25 of the passage 24 it is inserted in and aligns with the length of the passage 24 opening. The spring clips 30 are then slidably removed from the passages 24. Immediately thereafter, the newly sealed chip carriers 10 are also removed from the cavities 22. 
     It is to be understood that the embodiments described herein are merely illustrative of the principles of the invention. Various modifications may be made thereto by persons skilled in the art without departing from the spirit and scope of the invention. 
     For instance, although the instant embodiment is set forth in terms of a manual operation it is not so limited. An automated operation is described in a copending patent application entitled &#34;A Method and Apparatus for Automated Spring Clip Insertion and Removal&#34; to J. S. Cartwright filed in the U.S. Patent and Trademark Office on even date herewith, assigned to the instant assignee, and is incorporated by reference herein. 
     Additionally, the exemplary embodiment used a spring clip 30 that holds four chip carriers 10 in the cavities 22 of the pallet 20; however, it should be clear that the clips could be adapted to readily secure a smaller or larger number of carriers on the pallet. Furthermore, the pallet 20 can be arranged to handle a larger or smaller array of chip carriers 10 than is shown in the exemplary embodiment of FIG. 2a.