Abstract:
The present invention discloses an electronic package to contain and protect an integrated circuit (IC) chip. The electronic package further includes a leadframe, a flexible circuit or PCB type of substrate. The leadframe, flexible circuit or PCB type substrate further includes solder contacts, which are aligned with via holes in the molding layers on the top and bottom sides of the package. These via holes are for placing solder paste or solder balls from above and below for electrical access to the IC chip. These solder balls provide access for electrical testing after the package is mounted on a motherboard. They also provide the connection points for stacking multiple packages vertically.

Description:
This patent application is a Non-Provisional Application and claims the Priority dates of a first Provisional Application 60/836,419 on Aug. 8, 2006 and a second Provisional Application 60/918,279 filed on Mar. 15, 2007 filed by the Applicants of this Non-Provisional Patent Application. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to the electronic package. More particularly, this invention relates to a package configuration to provide low cost high performance electronic device packages that allows on-board testing and options for attaching electrical shielding, heat spreader or stack of multiple packages for highly integrated portable electronic products. 
     2. Description of the Prior Art 
     For conventional molded plastic packages using leadframe for interconnection substrates, packages such as QFP, SOIC, PLCC or SOJ, the IC chip and chip interconnects by either wire bonding or implementing a flip chip configuration, the packages are molded into square or rectangular body. All electrical paths are extended to outside of the molded plastic body along the perimeter of the plastic body. Since the outer lead pitch (OLP), typically 1 mm or greater, along the perimeter of the molded plastic body limits the connection density, for electronic devices that have large number of external electrical paths along the perimeters, it is generally required to make the plastic body to have a relatively large size. Presently, for a quad flat package (QFP), a practical limit is two hundred and eight (208), using 1.27 mm OLP. Furthermore, extended pins outside of the plastic body along the perimeters are very vulnerable to damage from handling or testing. 
     Plastic ball grid array (PBGA) was developed to address the issues caused by the limitation of the pin count for the conventional leadframe packages. In a PBGA package, the IC chip and the interconnecting wires or metal traces are bonded onto a PCB type of substrate. A plastic molding compound is used to encapsulate the IC chip and the interconnections on only one side of the substrate. All electrical signals are connected through via holes opened through the substrate to solder balls on the other side of substrate. Since the solder balls can be arranged in area array format, the number of signal connections can be much higher than that of the QFP packages. Therefore, a PBGA package that has a few hundreds of solder balls is quite common at the present packages. But, for one side molded BGA, the top and bottom structures are not symmetrical. As the bending or warping could occur throughout the hot processing steps or upon the heat cycles that occurs in the operational environment, it creates great stress onto IC chip and caused reliability vulnerability. Furthermore, all solder balls are placed under the substrate. Many of their connecting traces are routed through multi-layers inside of the motherboard, without any top surface pads. Thus, in most cases, individual PBGA cannot be probed or tested after it has been mounted on the motherboard. 
     For all existing molded packages, the electrical signal paths are either along the perimeters or from the bottom of molded body. For connections of these configurations, connections from the top of the molded body cannot be made for stacking or testing purposes. Therefore, a need still exits in the art to provide new and improved packaging configurations and also manufacturing procedures for resolving the above discussed problem and difficulties. 
     Additionally, the PBGA packages are still limited by the high cost of the substrate materials. The conventional quad flat pack (QFP) packages are not amiable to stacking to achieve a three-dimensional packaging configuration. Therefore, a need still exits in the art to provide low cost and improved packaging configurations and also manufacturing procedures for resolving the above discussed problems and difficulties. 
     SUMMARY OF THE PRESENT INVENTION 
     It is therefore an aspect of the present invention to provide an improved configuration and procedure for packaging an integrated circuit (IC) chip and assembling multiple IC packages together as modules by implementing a via-hole ball-grid-array (VHBGA) configuration. The VHBGA is implemented with a leadframe, flexible circuit or PCB type of substrate provided with via holes in the molding layers from the top and the bottom sides of the molded package. These via holes are filled with solder materials, thus providing top and bottom connections and electrical accesses features to the metal traces in the package substrate. Due to space limitation for some packages with high input-output (I/O) requirements, the via-holes in the molding layers may overlap with the metal traces in order for the solder to make electrical connections. The via holes and metal traces can be of different shapes or sizes but they have to be overlapping or touching each other in order to make solder connections. 
     Another aspect of the present invention to provide an improved via-hole in molded packaging configuration and method to achieve cost savings by replacing expensive substrate with low cost leadframe by making use of existing QFP equipment and eliminating the lead forming and replacing soldering steps with standard BGA solder ball placement processes. 
     Another aspect of the present invention to provide an improved via-hole in molded package configuration and method to improve the thermal performance of the packaged products by attaching ground shielding and heat spreader to the IC chip over the top of the VHBGA package or stacked modules. 
     Another aspect of the present invention to provide molded standoff features that will prevent the collapse of solder balls during mounting or stacking processes. 
     Another aspect of the present invention to provide an improved via-hole molded package configuration and method to allow more testing flexibilities with top and bottom solder balls for probing and testing after the VHMP packaging processes are completed, or after the VHMP package is mounted on the motherboard. 
     Another aspect of the present invention to provide an improved via-hole BGA packaging configuration and method to allow stack-mounting packages of different sizes by providing top and bottom solder balls on a VHBGA package thus achieving cost and space savings in manufacturing and assembling miniaturized electronic devices. 
     Another aspect of the present invention to provide an improved via-hole BGA packaging configuration and method to improve the electrical performance and product reliability with the leads all enclosed and protected in the plastic molding packages. Shortest electrical connections are achieved with direct surface mounting configuration made possible with the top and bottom solder balls on each of the VHBGA packages. 
     Briefly, in a preferred embodiment, the present invention comprises an electronic package for containing and protecting an integrated circuit chip therein. The electronic package includes a leadframe, or a flexible circuit or PCB type of substrate. The leadframe, flexible circuit or PCB type substrate further includes solder contact pads for placing solder paste or solder balls through via holes in the molding layers from above and below whereby electrical access to the IC chip is available from the top and bottom of the electronic package. 
     These and other objectives and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment, which is illustrated in the various drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the top view of a leadframe of this invention, including the locations of the intended via holes in the molding layers. 
         FIG. 2  shows the cross-section of the molding fixture. It has plugs for the intended via holes matching the contact pad locations. On the left-hand side, the contact pad locations have holes in the leadframe. On the right-hand side, the contact pad locations have no holes in the leadframe. In an actual design, the via-hole locations may be placed anywhere as needed. 
         FIG. 3  shows the top view of an as molded package. It has one chip and some bonded wires inside the mold compound, and via holes in the top molding layer and the peripheral supporting frame outside molded body has been trimmed off. 
         FIG. 4  shows three possible designs of contact placement to match the via-holes in the molding layers. 
         FIG. 5A  shows the cross-sectional view of the molded package of  FIG. 4 , and  FIG. 5B  shows the cross-sectional view after solder ball placement and reflow. 
         FIG. 6  shows that the via-holes in the molding layer on the topside may or may not align with those on the bottom side. The size of the via-holes could be different depending on the designed requirements. 
         FIG. 7  shows a cross sectional view of a VHBGA package with a ground shield covering the top that is immediately over the IC chip enclosed in a VHBGA of this invention. 
         FIG. 8  shows a cross sectional view of two stacked VHBGA package configuration by mounting the bottom solder balls of the top package on top of the top solder balls of the bottom package. 
         FIG. 9A  shows a cross-section view of a VHBGA package with molded standoff supporting structure to maintain the spacing between the package and the motherboard, thus reduce the risk of solder balls collapsing due to surface tensions during high temperature processing. 
         FIG. 9B  shows a cross-section view of a two stacked-VHBGA packages and heat spreader with standoff height supporting structure to reduce the risk of solder balls collapsing due to surface tensions during high temperature processing. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows a top view of a leadframe after the operation of a die bonding to form a molded ball grid array (BGA) package with via holes in the molding layers on both the top and bottom sides of the package according to an exemplary embodiment of this invention. The leadframe includes a peripheral supporting frame  110  with four peripheral frame stripes configured substantially with a square or rectangular shape. The leadframe further includes a plurality of metal lines  115  extended to the peripheral frame  110  from different predefined locations surrounding a central portion  105 , which is designated for placement of an integrated circuit (IC) chip  120 . Each of these metal lines  115  further includes at least one or several contact pads  125 . By applying a wire bonding process, the bonding wires  135  are formed to interconnect the integrated circuit (IC) chip  120  to the bonding wire fingers, which is at the inner end of the metal line  115 , and has proper local plating layer to enhance wire bonding. The contact pad locations are to match the solder-filled via holes in the molding layer shown in  FIG. 2  below. Note that some contact locations such as  129  do not have electric connection to the chip  120 . Such contact locations  129  are provided to serve as a “pass through” for a signal I/O in a future stacked dice above it as shown in  FIG. 8  and  FIG. 9B , to pass through the lower molded body and be connected to motherboard directly. It is another aspect of this invention that the solder ball at  129  enhances the mechanical strength of the VHBGA to motherboard attachment. The solder ball at  129  is completely surrounded by the top and bottom molding layers, and shares the shear stress with other metal connections between the VHBGA and the motherboard. Therefore, the solder balls at the contact location  129  will enhance the attachment reliability, an additional benefit of VHBGA package. 
       FIG. 2  shows a cross-sectional view of a molding fixture for forming a molded package having via holes in the molding layers above and below the leadframe shown in  FIG. 1 . A molding fixture includes a top-mold  155 -T and a bottom-mold  155 -B. The molding fixture also includes a molding gate  175  for injecting molding compound  130  to fill up the space above and below the leadframe. The molding fixture further includes a plurality of top mold plug  145 -T and bottom mold plug  145 -B matching the location of the contact pad  125  disposed on the metal lines  115 . The mold injection operation fills up the space above and below the leadframe, and extends to four sides with thin mold with bleeding stop at dam bar frame, which is a short distance away from the peripheral supporting frame  110 . Afterwards, the top mold  155 -T and bottom mold  155 -B are opened together with the top and bottom mold plugs  145 -T and  145 -B, leaving the top and bottom via holes  126  (shown in  FIGS. 4B ,  4 C &amp;  5 A). The top and bottom mold plugs  145 -T and  145 -B are coincident with the locations of the contact pads  125  thus the via-holes  126  are matched with the contact pads  125  as that shown in  FIG. 5A  below. 
       FIG. 3  is a top view for showing the molded package after the top and bottom molds  155 -T and  155 -B are removed and also the leadframe trimming process is completed to remove the peripheral supporting frames  110  with the molding compound layer  130  protects the package from the top and bottom of the leadframe. The top and bottom via holes  126  in the molding layer  130  are filled with solder material to establish electric contact to the contact pads  125  for electrically communicating with the IC chip  120  through the bonding wires  135  as that further shown in  FIG. 5A  below. 
       FIGS. 4A to 4C  show different possible configurations for each of the metal line  115 .  FIG. 4A  shows a metal line  115 - 1  that has a donut-shape hole  125  at the contact location.  FIG. 4B  shows a straight metal line  115 - 2  that is narrower than the size of the donut-hole shaped contact pad  125  shown in  FIG. 4A  and smaller than the via hole  126  formed in the molding layer  130 .  FIG. 4C  shows a smaller taper line  115 - 3  to form a contact with the solder material filling into the via-hole  126 . 
     Referring to  FIG. 5A  for a cross sectional view, wherein the bonding wires  135  are formed to connect the predefined terminals on the IC chip  120  to corresponding wire-bonding fingers, which are at the inner ends of the metal lines  115  for providing external electrical connections to the IC chip  120 . The via-holes  126  are extended through the molding layers  130  as shown in  FIG. 5A . The peripheral supporting frame  110  is removed after the package is molded in a molding compound as a protective enclosure  130  for enclosing and protecting the IC chip  120 . Referring to  FIG. 5B , the solder paste and solder balls  140 -T are placed and soldered on the top and  140 -B are placed and soldered on the bottom for each of the contact pads  125  that match the via-holes  126  along the metal lines fingers  115 . In this package, a top and bottom electrical connections are provided through the top and bottom solder balls  140 -T and  140 -B as shown in  FIG. 5B . 
       FIG. 6  is a cross sectional view of another exemplary embodiment of a package with the via-holes opened through the molding layers  130  and the associated solder balls  140 -T and  140 -B on both top and bottom sides respectively. These solder pastes or solder balls  140 -T and  140 -B on the top and bottom sides may be aligned as illustrated on the left half, or offset as illustrated in the right half. 
     Referring to  FIGS. 7 and 8  for alternate embodiments of this invention. In  FIG. 7 , an electrical ground shielding and heat spreader  150  is placed on top of the package to function as an electrical ground shield and also as a heat spreader. The ground shielding structure  150  is connected only to the solder balls  140 -BG at electrical ground voltage. A possible embodiment is to place these grounded solder balls on the four corners of the package module. Of course, the package as shown may have more grounded solder balls other than the corner locations. The grounded shield may be pre-pressed so that the corresponding positions to those four corner solder balls may be pushed downward so that the ground shield will be above the other solder balls, which are not to be connected to the ground voltage. Each of these pushed down position may have a concave bottom. This design will facilitate the placement and the self-alignment of the ground shield VHBGA package. The heat dissipation and electrical performance is improved. 
     In  FIG. 8 , two packages of this invention  100  and  200  are stacked with the bottom solder balls  140 -B of the top package  100  electrically connected to the top solder balls  240 -T of the bottom package  200 . The stacked packages further include a cooling fins  250  placed on top of the electrical ground shield and heat spreader  150  of the top module  100 . Refer to  FIGS. 9A and 9B  for improvement embodiments for providing stacked packages of the VHBGA packaged modules. In  FIG. 9A , the edges of the VHBGA package  100 ′ further includes a standoff height support  160  that can function to reduce the risk of solder balls collapse due to surface tension during high temperature processing. In  FIG. 9B , the standoff height supports  160  between the stacked modules  100 ′ and  200 ′ provide additional flexibility for the stacked modules with the surface tension relieved because structure flexibility is provided through these standoff height supports  160  placed between the upper and the bottom modules. 
     Although the present invention has been described in terms of the presently preferred embodiment, it is to be understood that such disclosure is not to be interpreted as limiting. Various alternations and modifications will no doubt become apparent to those skilled in the art after reading the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alternations and modifications as fall within the true spirit and scope of the invention.