Abstract:
A packaging technology for silicon chips is similar to ball grid array packaging technology of the prior art without, however, the use of printed board substrate of the prior art Instead pins are used that are part of a planar frame, the pins folded to a position 90 degrees from the plane of the frame, after which the frame is disposed in contact with the chip, pads on the frame and the chip are connected, and then entire assembly is then encapsulated. The edges of the frame are then cut off, leaving the encapsulation to maintain the configuration of the package in place.

Description:
PROSECUTION HISTORY 
     This application is a continuation-in-part of U.S. Non-Provisional patent application Ser. No. 11/567,154 (Dec. 5, 2006) for a “Chip Packaging With Metal Frame Pin Grid Array”, which claims priority to U.S. Provisional Patent Application No. 60/742,265 (Dec. 6, 2005), for a “Chip Packaging With Metal Frame Pin Grid Array” and U.S. Provisional Patent Application No. 60/772,841 (Feb. 13, 2006), for a “Chip Packaging With Metal Frame Pin Grid Array”. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to the field of electronic packaging, and more specifically to the field of packaging of electronic chips containing microcircuits. 
     DESCRIPTION RELATIVE TO THE PRIOR ART 
     The packaging of electronic devices through time has taken different forms and shapes. It is not the purpose of this invention to describe each one. It is rather to the interest of this invention to refer to a couple of them in order to contrast the invention to prior art. In  FIG. 1 , the two types that have been used extensively in packaging DRAM silicon devices are of interest. Other types of packing techniques, not discussed herein, are also present in the prior art. 
     One type of prior art packages known as the GULL wing type  104  is constructed with a metallic frame that has the pins formed in the perimeter after encapsulation  103  of the silicon. This type of frame with GULL wing pins served the industry for devices whose operating frequencies were low and the space which the devices occupied on a printed circuit board was not quite at a premium. As the silicon processing geometries shrunk and the requirement for smaller package size and higher operating frequencies increased, the industry adapted a new package known as Ball Grid Array, referred to hereinafter as (BGA). Such a package is shown in  FIG. 1   100 . The BGA package is constructed in most cases with multilayered substrate  101  that has pads where the connection is made to pads of the silicon by known means. This connection propagates through substrate wiring to another pad of the substrate in a predefined location of the encapsulated package. At this terminal point a solder ball  102  is attached. The solder ball is the connecting point between a pad on the printed circuit board and a silicon pad. Utilization of space on the face of the package for interconnections instead of the perimeter makes the package smaller and allows for higher frequency operation. 
     The balls of a BGA package when are soldered on the circuit boards collapse to a solder mass. The solder mass sometimes creates a crack and the connection is compromised. This, eventually, will cause the device to fail. Another problem is when a BGA device is unsoldered from the circuit board no longer maintains the shape of the original balls. It cannot be re-soldered in that form. New balls would have to be attached. This process becomes expensive and as such is undesirable. Not a single unique package can satisfy all needs of the industry. 
     The method described herein is more applicable to devices of high volume such as memory devices of all kinds and other devices whose number of I/O pins do not present complexity of interconnections. 
     The package constructed with this invention would have metallic pins or solder balls for interconnection of the silicon I/O pads to the circuit board pads by use of metallic frame connecting paths. A metallic frame instead of a printed circuit board frame is used. Such a package is shown in  FIG. 9 . At re-flow time, the solder on the circuit board pads will engulf pin  901  to make the connection. When such device  900  is removed, it can be re-used on the same or other circuit boards. The process of construction of package  900  is less expensive than the present BGA process. 
     SUMMARY OF THE INVENTION 
     The present invention comprises an improved packaging system. This packaging system comprises a metallic frame, a silicon chip and the encapsulation of both. The metallic frame is constructed from a thin flat sheet of metal capable of allowing solder to adhere to it. On the face of the metal plate a pattern is exposed by known means and chemicals. The material under the pattern is protected from etching chemicals. The rest of the non-protected metal is allowed to be etched away or removed by known means. After the etching process, the metal of the intended patterns remains held together by the perimeter of un-etched metal material. This perimeter holds the patterned sections in their specified positions. Said etched patterns are formed to accommodate end pads, etched and or formed pins and connecting metal between said pins and respective pads and perimeter. Each etched pattern has an ending pad and a metallic path that connects it to the metal of the perimeter. 
     In accordance with one aspect of the invention, a method for manufacturing a pin grid array for electronic chip packaging includes the step of creating a frame comprising a multiplicity of printed wires and a multiplicity of corresponding pads, each wire connecting to a corresponding flattened pin and corresponding pad, all within the same plane. 
     In accordance with a second aspect of the invention, the method includes the further step of bending all of the flattened pins to an angle approximately 90 degrees relative to the plane. 
     In accordance with a third aspect of the invention the method includes the further step of disposing the frame above a chip comprising pads, aligning the pads of the chip with the corresponding pads of the frame. 
     In accordance with a fourth aspect of the invention the method includes the further step of electrically connecting each pad of the chip to the corresponding pad of the frame. 
     In accordance with a fifth aspect of the invention the method includes the further step of encapsulating the frame and chip with the pins extending through the encapsulation. 
     In accordance with a fifth aspect of the invention the frame further comprises a periphery having sides and ends, wherein each printed wire is attached to one of the ends. 
     In accordance with a sixth aspect of the invention the method further comprises the step of removing the frame ends where they attach to the flattened wires after encapsulation. 
     In accordance with a seventh aspect of the invention the connecting of each pad of the chip to the corresponding pad of the frame is done by wire bonding. 
     In accordance with an eighth aspect of the invention the connecting of each pad of the chip to the corresponding pad of the frame is done by direct connection. 
     In accordance with a ninth aspect of the invention the flattened pins are stamped, thereby creating a bulge in each pin extending at an angle of 90 degrees relative to the plane. 
     In another aspect of the invention, in the path and at a predetermined location, a rectangular extension of metal is formed in the form of a rectangular pin of certain length. The collection of the end pads of the pattern become the connecting points to pads of a silicon device. 
     In one method, the connections can be performed by bonding wires from a formed frame pad to the silicon pad. In another method, the connection can be made directly from pad to pad by solder re-flow means or with heat applied to pre-treated pads. The rectangular formed pins of the patterns are bent 90 degrees with the end of said pins in the perpendicular direction when the entire frame is in a horizontal position. The bending of all pins is accomplished with one operation by special apparatus or tool. This process is fast and accurate. After the pins are bent in a 90 degree position, the entire frame is placed on top of the silicon device in correct alignment of the silicon pads to the pads of the frame. 
     Then the connection is performed between respective pads by means mentioned above. The arrangement of the silicon and the frame is placed in an apparatus where the encapsulation is performed. The encapsulation apparatus could be the same one used for pin forming. Once the pins are rotated 90 degrees, the open areas of the slots used for the rotation would be plugged to prevent any encapsulation material from escaping. 
     Another approach would be to have the apparatus restrain the pins in position and separate the frame before encapsulation. In another approach and after the encapsulation, the exposed pins are sheared to the right length and the metal of the perimeter is removed with appropriate means. 
     The resulting package has the silicon chip and the patterns of the frame inside the encapsulating material. On one face of this package, the pins extend away from the package. On the sides of the package, the metal sections that held the patterns to the perimeter are exposed after the removal of the perimeter. Said exposed metals can serve as testing points for each pin connection to the silicon pad and to the circuit board wiring. Connection of the exposed pins to the circuit board pads is made by known solder re-flow process. 
     In another aspect of the invention, the pins of the frame described above are formed by methods of metal stretching. A flat section of each connecting metal strap of the patterned frame and at a strategic predefined location a pin protrusion is formed by stretching the metal into a forming cavity of the metal stretching apparatus. Said pin protrusions extend away from the encapsulating material after encapsulation. 
     In yet another aspect of the invention, the patterned sections of the frame do not have pins formed by any method. Instead, at encapsulation time, the encapsulating material is inhibited from touching the metal at the point where a pin or solder ball is required. After encapsulation, the exposed metal is used to either attach a solder ball or a metallic ball or pin so that the package has connection means to the pads of a printed circuit board at assembly time. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These, and further features of the invention, may be better understood with reference to the accompanying specification and drawings depicting the preferred embodiments, in which: 
         FIG. 1A  depicts the gull wing package of the prior art. 
         FIG. 1B  depicts the, the ball grid array package of the prior art. 
         FIG. 2   a  depicts a metal frame of the Frame Pin Grid Array showing pads, pins, connecting metal and perimeter of the first embodiment of the present invention. 
         FIG. 2   b  depicts a cross-section of the assembly, showing pin, after having been bent by 90 degrees, and extending through the encapsulation, in accordance with the first embodiment of the present invention. 
         FIG. 3  depicts a metal frame of the Frame Pin Grid Array with pads, connecting metal, perimeter and pins formed in a 90 degree rotation of the second embodiment of the present invention. 
         FIG. 4  depicts a face of a silicon device with I/O pads made for bonding wire connection to pads of the frame. 
         FIG. 5  depicts a frame of  FIG. 2  placed on top of silicon of  FIG. 4  and bonding wires connecting pads of frame to pads of silicon. 
         FIG. 6  depicts a face of a silicon device with I/O pads made for direct connection to frame pads. 
         FIG. 7  depicts a metal frame of the Frame Pin Grid Array with pads, connecting metal, perimeter and pins formed in a 90 degree rotation placed on top of the silicon of  FIG. 6  with pads of the silicon connected to the pads of the frame by the direct method. 
         FIG. 8  depicts a side view of the final package containing the silicon device and the frame with the pins of the frame protruding from the encapsulation material. 
         FIG. 9  depicts a view of the final package containing the silicon device and the frame with the pins of the frame protruding from the encapsulation material and in a grid arrangement under the encapsulated body. 
         FIG. 10  depicts a forming plate with forming wells and the frame, with pins disposed over the forming plate. 
         FIG. 11  depicts the pin bending apparatus. 
         FIG. 12  depicts the metal stretching apparatus. 
         FIG. 12A  depicts the cross section of a pin after being stretched by the metal stretching apparatus. 
         FIG. 13  depicts the metal exposing apparatus. 
         FIG. 13A  depicts the metal protrusions used in a third embodiment of the invention 
         FIG. 14  depicts the metal frame, showing the formed pattern, formed pad, and exposed metal. 
         FIG. 15  depicts the encapsulate package showing the wells and the exposed frame. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention comprises a system and a method of packaging silicon devices, with pins arranged in a grid formation, without the use of the customary balls of Ball Grid Array. 
     The final package produced by this invention includes a silicon device, such as a computer chip, contained within an encapsulation of non-conductive material, with an array of conducting contacts designed to mate with the contacts on a motherboard, so that electrical signals may be transmitted and received from the motherboard to the silicon device. The final package, as described above, will be referred to hereinafter as the “package” 
     The package described in the present invention preferably incorporates the use of a metal frame, and a plurality of metal pins formed as an integral part of the frame. 
     The preferred method incorporates the holding of the pins in a predetermined location, the forming of said pins by bending or by metal stretching, the exposing of the extended portions of the pins during encapsulation, a connecting of the pads of the frame to the silicon pads, and the encapsulation of the frame and silicon. 
       FIG. 2  illustrates a frame  200  with printed wires  202  with pads  203  and pins  201  created from a sheet of metal by well-known means in the prior art. Said printed wires  202  have one end connecting to the perimeter of the metal frame  200 , and the other end forming pads  203 , include integrally-formed rectangular pins  201 . 
     The shape of the printed frame wires could be adjusted to accommodate for thermal expansion and location of the end pads. One such alternative shape could include zigzag or letter “U” formations of the wires at strategic points to allow for thermal expansion and to prevent damage to pad connections. Another advantage of such alternative configurations is to adjust for overall line lengths as a function of temperature. 
     When manufactured, the frame starts as a flat sheet of metal of a certain rectangular dimension and thickness. The metal composition has properties that allow solder to adhere to metal pins in a solder re-flow process. There are several methods of creating such frame. 
     In one preferred embodiment and on one face of the metal plate, a pattern of the image of the frame is formed on the face of the metal and the metal is etched, so that the image remains intact, and the rest of the metal plate is removed, by photochemical means well-known in the prior art. 
     In a second preferred embodiment the image is formed by laser cutting means that eliminates the unwanted metal portion of the plate. 
     In a third preferred embodiment the patterns on the plate are formed by stamping out the unwanted portions of the metal with a tool and die apparatus. 
     In a fourth preferred embodiment the patterns on the plate are formed by conductive ink deposition on an insulating material. Solid pins may be formed or attached in predefined locations by mechanical means. Conductive paths may be formed by either ink deposition, or by deposition of conductive epoxy adhesive. 
     This image of the frame is designed to have pads  203  and pins  201  in pre-determined locations designed to match the approximate location of pads of the silicon chip with which the frame is to be connected. The frame pins, after bending or stretching into a final position, form the grid array of conducting contacts in the final package. A frame of this type, in accordance with the preferred embodiment, is shown in  FIG. 2 . 
     After fabrication, the entire frame may be treated with coatings such as melted solder, or may be plated with other metals such as silver, gold, nickel or tin, to improve conduction and to reduce the overall metal inductance and resistance. 
     The use of such a frame in the manufacturing of electronic devices is not limited to small chips, but is also practical in a variety of many different silicon devices various sizes and shapes. 
       FIG. 2   b  depicts a cross section of a small portion of the final package which includes the frame of  FIG. 2   a . In  FIG. 2   b  the pin  201  has been bent at an angel of 90 degrees relative to the plane of the frame, and extends through the encapsulation  207 . A protrusion  204  formed as part of pin  201  allows the pin to extend slightly above the layer of the encapsulation  206 . It can be seen from this figure that a small portion of the pin  201  extends below the layer of encapsulation, and it is the array of these protruding portions of the pins that forms the array of pins which mate with the mother board to which the package is to be connected. Not shown in  FIG. 2   b  is the silicon device, which is electrically connected to pad  205  of this figure, after which the silicon device is encapsulated. 
       FIG. 3  illustrates the frame  200  of  FIG. 2  with the rectangular pins  301  rotated by 90 degrees toward the observer, and facing the observer on end. 
     The method of rotating the pins is generally accomplished by mechanical means, typically by using a die to push all of the pins away from the plane of the frame in a single motion, using an apparatus with plungers in locations that correspond to locations of the frame pins that force the frame pins to rotate within predefined slots of the rigid plate. 
       FIG. 4  shows a silicon device with pads formed on the face of the silicon. As shown in this figure, the pads are located in correct alignment with the corresponding pads of the frame. After the frame pins have been rotated by 90 degrees away from the frame, the frame, having the rotated pins directed away from the silicon device, is place on the silicon device, with the pads of the frame and the silicon device aligned. Bonding wires are then connected between each pad of the frame and the corresponding pad of the silicon device, thus making the electrical connections required. 
       FIG. 5  shows the frame  500  placed and aligned over silicon device  501 , with the pads of the frame  502  aligned to silicon device pads  503 , and with bonding wires  504  connecting the corresponding pads. It is seen from this figure that the frame  500  is slightly larger than the silicon device, so that the edges of the frame may be removed after encapsulation of the entire package, without cutting into the silicon device. In the preferred embodiment, only the edges of the silicon frame are removed, typically by cutting or stamping. It is clear from this figure that the short ends (the “ends”) of the frame must be removed, otherwise all of the pads will be shorted together. The long sides (“sides”) of the frame need not be removed, however, and leaving the sides intact within the finished package does not negatively impact the performance of the package in any way. 
       FIG. 6  illustrates silicon device with pads designed to connect directly to pads of the frame without bonding wires. In this embodiment, which is an alternative to the embodiment of  FIG. 5 , the electrical connection will be made by simply allowing the pads of the frame to touch the pads of the silicon device. Solder is applied to the pads, and heat used to allow the solder to facilitate electrical conduction. The encapsulation which follows this process provides physical support, so that the pads remain in contact throughout the life of the package. 
       FIG. 7  illustrates silicon device  701  with pads  703  connected directly to pads  702  of frame  700 . Connection of pads  702  to  703  is made with re-flow of high temperature solder or with heat applied to two metals to create permanent connection between them. 
       FIG. 8  illustrates a cross-sectional view of the encapsulated, packaged device  800  with pins  801  protruding perpendicular to the encapsulation. Pins  801  take the place of balls  102  of the prior art, as shown in  FIG. 1B . 
       FIG. 9  depicts a perspective view of the finished package  900  with pins  901  protruding from the bottom of the package. In this view the place  902  where the ends of the frame have been removed after encapsulation is shown at the ends of the package. 
       FIG. 10  illustrates the mother board or base plate  10  with multiple wells  12  and the frame  11  and with pins  13  aligned over the wells  12 . This figure shows the pins before they have been rotated, and obviously before the frame and silicon device have been connected and encapsulated, and is included herein only to show how the final package will align with the motherboard. The pins will be rotated about pivoting point  14  so that the desirable length of the pins is obtained after pin rotation. 
       FIG. 11  shows a section of a preferred embodiment of the pin forming apparatus. This embodiment demonstrates how all of the pins could be rotated 90 degrees in a simplified way. Two plates  11   a  and  11   d  are aligned with dowel pins  11   m . Plate  11   d  is allowed to slide up and down the dowel pins. Plate  11   d  accommodates plunger  11   e . The plunger is allowed to slide up and down a predetermined distance. Plate  11   a  accommodates wells  11   b . Multiple wells populate the plate in predetermined locations to match the locations of the pins  11   c  of the frame when said frame pins are aligned to said wells. Pins  11   c  are aligned so that desirable length of the pin extends into the well. Then plate  11   d  is lowered and pressed against the frame that is placed between the plates. Finally the plungers are lowered to push pins  11   c  into the well and in a 90 degree rotation. This apparatus is easily automated for high-volume production. 
       FIG. 12  illustrates a section of an apparatus which performs contacts by means of metal stretching. This second embodiment demonstrates how a pin can be formed in a simplified way, and creates a contact extending 90 degrees from the plane of the frame without rotating the pins. Two plates  12   a  and  12   b  are aligned with dowel pins  12   c . Plate  12   b  is allowed to slide up and down the dowel pins to secure frame  12   e  between the plates. Plate  12   b  accommodates plunger  12   d . The plunger is allowed to slide up and down a predetermined distance. Plate  12   a  accommodates wells  12   f . Multiple wells populate the plate in predetermined locations. The frame is placed between plates  12   a  and  12   b  in correct alignment. Then plate  12   b  is pressed against the frame and plate  12   a . Then the plungers  12   d  are pressed to a predetermined extension. The pressure of the plungers forces the metal of the frame to stretch and to extend into the cavity  12   f . The well  12   f  has predetermined depth  12   h  and bottom diameter  12   g.    
     This resulting metal protrusion will become the point to connect to the pad of the printed circuit board. A cross-sectional view of a protrusion formed by the device of  FIG. 12  is shown in  FIG. 12A  as reference number  12   k . Reference number  12   e  is that portion of the pin parallel to the plane of the frame. 
     In another aspect of the invention where no pins are formed from the frame with any described method, an apparatus is used to expose the frame metal at strategic locations during the encapsulation of the device and frame. 
     This may be better understood by referring now to  FIG. 13 . A plate  13   a  is constructed so that metal protrusions  13   b  of certain height  13   c  and radius  13   d  are placed in the strategic locations, as shown in  FIG. 13A . During encapsulation, the frame with the silicon attached is pressed against the metal protrusions. The encapsulating material is allowed to flow around the protrusions to fill the total cavity that creates the final package. When the package is removed from the encapsulating apparatus, it will contain cavities of the diameter and depth of the apparatus and at the bottom of each cavity the frame metal will be exposed. This exposed metal will be used to be connected to a solder ball or a metallic ball or metallic pin or, simply, to be connected to solder that fills the cavity. 
     Referring next to  FIG. 14 , the frame  14   a , the frame pattern  14   c  with pad  14   d  and the protrusion  14   b  are shown looking perpendicular to the frame after the protrusions are formed. The protrusion locations could be where metal is exposed by the method described in  FIG. 13 . 
     Next referring to  FIG. 15 , a finished package is shown with created cavities and exposed metal inside the cavities. The package is not in its final stage since the exposed metal is not yet connected to any solder balls or pins of any kind. 
     Although it is not shown in any figure, the formation of the silicon pads in an outside perimeter of the silicon and the formation of the frame pads close to the perimeter of the frame to facilitate either wire bonding or direct connection is another method that does not depart from the object of the invention. 
     It will be apparent that improvements and modifications may be made within the purview of the invention without departing from the scope of the invention defined in the appended claims.