Abstract:
A multi-die encapsulation device has a plurality of die chambers. Each of the die chambers has parallel opposing walls, retaining edges which define an insertion void, and a retaining contact in contact with a printed circuit board. Each of the retaining contacts is characterized as having a compliant foot for making contact with a printed circuit board. The encapsulation device comprises a cap with a compression pad for protecting and biasing each of the bare die in its respective chamber.

Description:
This application is a continuation of U.S. patent application Ser. No. 08/353,769, filed Dec. 12, 1994, now U.S. Pat. No. 5,767,443, which is a continuation-in-part of the Application having Ser. No. 08/091,786 filed on Jul. 10, 1993, now abandoned and entitled A Multi-Die Encapsulation Device and Method and having inventors Warren M. Farnworth, Alan G. Wood, and Tim J. Corbett. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to packaging of semiconductor integrated circuits, and more particularly to a multi-die encapsulation device. 
     BACKGROUND OF THE INVENTION 
     AMP Corporation located Harrisburg, Pa. has developed an encapsulation device for retaining a plurality of bare semiconductor die. A cross sectional view of a simplified AMP encapsulation device is shown in FIG. 1. The AMP encapsulation device is typically molded plastic and has a chamber portion comprised of a plurality of die chambers 5 and is enclosed with a cap after the insertion of the die into the chambers 5. Each chamber has at least one beveled edge 10. A bare die is inserted by hand into a chamber 5 with the circuit side touching the beveled edge 10. The beveled edge 10 thus serves as a guide for the insertion of the bare die. However, since the circuit slides across the bevel the circuitry may be damaged during insertion. The bare die is inserted into a spring retaining and contact assembly 15. The retaining and contact assembly 15 holds the bare die in position in the encapsulation device. A spring portion 20 electrically contacts the bare die and a rigid foot portion 25 is provided for contacting a circuit board onto which the encapsulation device is mounted. Due to the rigidity of the foot portion 25 and inherent bowing of many circuit boards the failure rate of electrical contact between the bare die and the board is typically high. At times the failure runs as high as 80%. In addition to these problems solid caps secured over the chamber portion of the encapsulation device do not retain the die in the correct position and often are a cause of die damage subsequent to encapsulation of the die. 
     Thus a need exists for an encapsulation device for bare die which provides reliable electrical contact between the die and a mounting board and a need exists for a method for safely inserting the bare die into the encapsulation device. In addition there is a need to provide position retainment of the bare die within the encapsulation device without fear of die damage following encapsulation. 
     SUMMARY OF THE INVENTION 
     The invention is an encapsulation device for bare die. The encapsulation device comprises chambers having parallel walls, an insertion void, and a spring retention electrical contact having a compliant foot and comprises a cap having a compression pad. The encapsulation device of the invention provides a reliable contact between the die and a mounting board via the compliant foot. The insertion void allows for a safe insertion of a die into a chamber of the encapsulation device. The compression pad and the spring retention electrical contact provide positive retainment of the bare die within the encapsulation device. 
     The invention is a process for inserting bare die into the encapsulation device of the invention and is a vacuum insertion tool used in the insertion of the bare die into the encapsulation device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a simplified AMP encapsulation device of the related art. 
     FIG. 2 is three dimensional view of the encapsulation device of the invention prior to insertion of bare die and prior to final assembly. 
     FIG. 3 is simplified schematic of a bare die and the die pads thereon. 
     FIG. 4 is a cross sectional view of one chamber of the encapsulation device of the invention with a bare die inserted and seated therein. 
     FIG. 5 is a top view of one chamber of the encapsulation device of the invention with a bare die inserted therein. 
     FIG. 6 is a three dimensional view of a bare die insertion tool of the invention. 
     FIG. 7 is a side view of the three dimensional view of the bare die insertion tool of FIG. 6. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 2 is a three dimensional view of the encapsulation device 45 of the invention prior to insertion of bare die into the encapsulation device. A chamber portion 50 comprises a plurality of chambers 55 for accepting and retaining the bare die. The exact number of chambers 55 may vary depending on design considerations. Each chamber 55 comprises retaining edges 60 which define a chamber void 65. The chamber void 65 accepts a bare die insertion tool during the process of inserting the bare die into each chamber 55. 
     When the bare die have been inserted into the chambers 55 a cap 70 is sealed to the chamber portion. The cap 70 rests on lip 75 of the chamber portion 50. The final locking seal between the cap 70 and the lip 75 is typically an epoxy which when heated allows the cap to be removed and resealed, thereby allowing for the removal and the replacement of faulty die. However, other locking seals such as a snap seal, a grooved seal, and a pressure seal, may work equally well. The chamber portion 50 and the cap 70 are typically molded plastic. 
     FIG. 3 is representative of a single bare die 76 designed to fit into the encapsulation device 45. In this case the single die 76 has eight die pads 77 although it is possible for the bare die to have any number of die pads. 
     FIG. 4 is a cross sectional view of a single die chamber 55 having parallel walls 78. A bare die 76 inserted into the die chamber 55 is retained against the retaining edges 60 by retaining contact 85. The retaining contact 85 and electrical contacts one of the die pad 77 of bare die 76, see FIG. 3, at a spring portion 86 and electrically contacts a circuit board 90 with a compliant foot portion 95 when seated in the die chamber 55. Thus the retaining contact protrudes through a bottom portion 96 of the chamber portion 50. The compliant contact foot 95 provides reliable contact to the circuit board 90 even though the circuit board 90 may be bowed. It can be seen from FIG. 3 that the compliant foot 95 has a vertical displacement d. Therefore as long as the distance between the reference foot 100 and the circuit board 90 is less than d and the distance accommodates a width of the compliant foot 95 the compliant foot 95 makes contact with the circuit board 90. The number of retaining contact 85 is equal to the number of die pads 77 on the bare die 76. Therefore for the bare die of FIG. 2 there would be eight retaining contact 85 in a die chamber 55. 
     FIG. 5 is a top view of a single die chamber 55. In addition to elements previously named a pair of opposed parallel walls 101 is shown in FIG. 5. Preferably, the chamber portion 50 shown in FIG. 1 is oriented, during bare die insertion, such that the chambers 55 are stacked. This orientation allows for a simplified insertion process which can best be understood with reference to FIGS. 3, 4, 5, 6, and 7. 
     A bare die 76 is placed on an insertion tool 105, shown three dimensionally in FIG. 6 and cross sectionally in FIG. 7, with the circuit side of the bare die 76 up, thereby preventing damage to the circuitry of the bare die 76. The insertion tool 105 is then inserted into the chamber void 65 between the two retaining edges 60. The guide edge 110 of the insertion tool 105 is used to mechanically force the bare die 76 into the retaining contact 85, see FIG. 4. For best results a bare die 76 with a beveled edge 111 is used to eliminate breakage as the bare die 76 is forced into the retaining contact 85, again see FIG. 4. The bare die 76 is held in a correct orientation on the insertion tool 105 with a vacuum provided by a vacuum source, not shown. The vacuum source is connected to the insertion tool 105 at vacuum connection 115 through a means such as a plastic hose, not shown. 
     Internal passages 120 connected to the vacuum connection 115 directs the vacuum to suction depressions 125. Thus the die insertion tool 105 allows for insertion of the bare die 76 into chamber 55 without damage to die circuitry. Not only does the process and encapsulation device of the invention prevent damage to die circuitry there is also a space savings over the beveled wall chamber of the related art shown in FIG. 1. 
     However it should also be noted that the exact orientation of the parallel chamber walls is unimportant. For example they may be at an angle of less than 90 degrees to the circuit board to which the encapsulated device attaches. In this case the chambers may be slanted to form a low profile encapsulation device. 
     After the bare die 76 have been inserted into the desired chambers 55 the cap 70 is seated on lip 75, see FIG. 1, and retained and sealed to the chamber portion 50 with a sealant glue. The cap contains a compression pad 130 which provides a flexible bias to the bare die 76. Various substances may be used for the compression pad including a variety of springs, gels, or foams. Because of the flexible bias the compression pad 130 biases the bare die firmly into the retaining contact. Therefore the compression pad 130 of the cap 70 helps to eliminate breakage of the bare die even with jarring. The seating of the cap 70 on the lip 75 completes the encapsulation process. 
     Although the invention has been described with respect to specific embodiments the invention is limited only as claimed.