Patent Publication Number: US-2010126764-A1

Title: die ground lead

Description:
SUMMARY  
     Hard disk drive (HDD) design continues to progress toward faster, smaller, lighter, and generally more efficient devices. Such designs necessarily lead to wires within such devices carrying or affecting signals with increasingly smaller amplitudes. These small amplitude signals are especially vulnerable to electronic interference from other nearby wires and/or devices. 
     In order to improve signal to noise ratio (SNR) and reduce electromagnetic interference (EMI) in an electronic package ground connection, a novel approach connects ground potential of an electrical circuit within an electronic package directly to a commonly grounded surface of an electrical system (e.g., a commonly grounded housing of an HDD). In one implementation, an improved die ground lead includes a first end internally connected to an electrical ground potential of the electrical circuit within the electronic package and a second end creating a compressive electrical connection with the commonly grounded surface. 
     The use of this configuration for the improved die ground connection between the electrical circuit and the commonly grounded surface results in significantly less physical distance than conventional ground paths for electronic packages. Conventional ground paths typically extend through a printed circuit board (PCB), along the PCB surface and then down through mounting screws to the commonly grounded housing. Since conventional ground paths typically utilize the PCB as an intermediary between the electronic package and the commonly grounded housing, the length of the ground connection is increased and therefore the resulting noise and possibility of EMI is increased. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Other features, details, utilities, and advantages of the claimed subject matter will be apparent from the following more particular written Detailed Description of various implementations and implementations as farther illustrated in the accompanying drawings and defined in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The described technology is best understood from the following Detailed Description describing various implementations read in connection with the accompanying drawings. 
         FIG. 1  illustrates a perspective view of an example HDD assembly with an electronic package mounted to a PCB and the PCB mounted to the commonly grounded housing of the HDD. 
         FIG. 2  illustrates a first sectional view of an example HDD assembly of  FIG. 1  utilizing a tie bar improved die ground lead. 
         FIG. 3  illustrates a second sectional view of an example HDD assembly of  FIG. 1  utilizing a pogo pin improved die ground lead. 
         FIG. 4  illustrates a plan view of the interior of an example electronic package with a tie bar extending out of one corner of the electronic package. 
         FIG. 5  illustrates a plan view of the exterior of an example electronic package with a tie bar extending outwardly from one corner and folded over the top of the electronic package. 
         FIG. 6  illustrates a perspective view of an example electronic package mounted on a PCB with a tie bar improved die ground lead contacting a commonly grounded surface. 
         FIG. 7  illustrates a perspective view of an example electronic package mounted on a PCB with a pogo pin improved die ground lead contacting a commonly grounded surface. 
         FIG. 8  is a flow chart illustrating an example process for assembling an electrical system with an improved die ground lead. 
         FIG. 9  is a flow chart illustrating another example process for assembling an electrical system with an improved die ground lead. 
     
    
    
     DETAILED DESCRIPTION  
     The market for HDDs continues to demand increased performance and storage capability from increasingly smaller and lighter devices while requiring less power to operate. This progression toward faster, smaller, lighter, and generally more efficient designs leads to wires within such devices carrying or affecting signals with increasingly smaller amplitudes. These small amplitude signals are especially vulnerable to electromagnetic interference from other nearby wires and/or devices. 
     By minimizing the length of ground connections associated with sensitive circuitry that relies on small amplitude signals, noise and EMI effects on such signals can be reduced. As such, an improved die ground lead described herein provides a reduced ground connection length and therefore results in a reduction in noise and EMI effects experienced by the sensitive circuitry. Specifically, the improved die ground lead reduces the distance the ground connection must travel from an electronic package to a commonly grounded surface of an electrical system. The commonly grounded surface may be any conductive surface that serves as a common ground for the electrical system, by example and not limitation, a commonly grounded housing. 
     Referring now to  FIG. 1 , an example perspective layout of a HDD  100  is shown generally comprising a commonly grounded housing  104  within which at least one platter  108  and at least one actuator  112  are mounted. A PCB  116  is mounted to an outer surface of the commonly grounded housing  104  using screws inserted through screw holes  120  in the PCB  116  and the housing  104 . At least one electronic package  124  through which the HDD  100  is controlled is mounted on the surface of the PCB  116  between the PCB  116  and the commonly grounded housing  104 . 
     According to the presently disclosed technology, an improved die ground connection from the electrical circuit within the electronic package  124  to a surface of the commonly grounded housing  104  is established via an improved die ground lead extending from ground potential within the electrical circuit to the surface of the commonly grounded housing  104  to establish a compressive contact with the commonly grounded housing  104 . The improved die ground lead may be any compressive electrical connection, including but not limited to, a compression connector, a tie bar, a pogo pin, a spring, and any other compressive electrical connection, such that the electrical connection maintains integrity with a surface of the commonly grounded housing  104  during operation without bonding or soldering or passing through or along the PCB  116 . Section A-A of the HDD  100  in the area of the PCB  116  is shown in detail in  FIGS. 2 and 3 . 
     The HDD  100  is used as an example only; the disclosed technology may be utilized in a variety of electrical systems utilizing a commonly grounded surface, a PCB  116 , and at least one electronic package  124 , e.g., cellular telephones, PDAs, and various computer components. Further, the electronic package  124  may be any type of electrical system where an improved die ground lead is desired, e.g., microprocessors, microcontrollers, application-specific integrated circuits, digital field processors, and field-programmable field arrays. 
     Additionally, the improved die ground lead may be adapted to a variety of electronic packaging styles, for example, ball grid array (BGA) packaging and lead frame packaging. In the BGA implementation, the interface between the PCB  116  and the electronic package  124  comprises a grid of solder balls on a surface of the electronic package  124  facing the PCB  116 . These solder balls conduct electrical signals from the electronic package  124  to the PCB  116  and vice versa. Example BGA implementations contemplated herein include but are not limited to, ceramic BGA, plastic BGA, fine BGA, ultra fine BGA, and micro BGA. 
     In the lead frame implementation, a die attach pad of the electronic package  124  is exposed and directly attached to the PCB  116 . Further, leads may extend from the die and attach to the PCB  116 . Depending on the style of lead frame packaging, the leads may extend out of the electronic package  124  before attaching to the PCB  116  or the leads may attach to the PCB  116  where the surface of the electronic package  124  adjoins the PCB  116  (e.g., is in direct physical contact with the PCB  116  or in indirect physical contact with the PCB  116 , such as through an adhesive and/or solder layer). Example lead frame implementations contemplated herein include but are not limited to, micro lead frame package (MLP), MLP quad, MLP micro, MLP dual, thin quad flat pack (TQFP), quad flat no leads (QFN), fusionquad, very very fine land grid array (WPLGA), thin array plastic package (TAPP), and thin substrate chip scale package (tsCSP). 
     Referring now to  FIG. 2 , an example electrical system  200  utilizing an improved die ground lead is shown. An electronic package  204  is shown with a die  208  mounted therein. At least one wire  212  connects the die  208  to at least one signal lead  216 . The connections between the die  208 , the wire  212 , and the signal lead  216  are sealed in an over mold  218  formed from Bakelite or any other electrically non-conductive moldable or non-moldable material. 
     The signal lead  216  connects the die  208  and wire(s)  212  (collectively, the electrical circuit) within the electronic package  204  to a PCB  220  via at least one soldered connection  224  to at least one contact pad  228  on the PCB  220 . The electronic package  204  may be further adjoined to the PCB  220  via a soldered connection  224  between two contact pads  228 , one on a surface of the PCB  220  and one on an adjacent surface of the electronic package  204 . This soldered connection  224  may further carry though the thickness of the PCB  220  via circuit pathways  230  to another contact pad  228  on the opposite side of the PCB  220 . Electrical signals transmitted to and from the electrical circuit and the PCB  220  via one or more contact pads  228  are carried along a length and/or thickness of the PCB  220  via the circuit pathways  230 . 
     In one implementation, the PCB  220  is physically mounted to a commonly grounded surface  232  via at least one conductive screw  236  extending through at least one screw hole  240  in the PCB  220  and into at least one conductive screw sleeve  244  mounted on the commonly grounded surface  232 . A traditional (ground connection between the electrical circuit and the commonly grounded surface  232  is illustrated by the arrow  248 . It should be understood, however, that the described technology may replace the traditional ground connection of arrow  248  in some implementations. In a typical electrical system  200  utilizing an electronic package  204  mounted on a PCB  220 , the ground connection is transmitted from the die  208  through a soldered connection  224  to a contact pad  228  on the PCB  220 . The ground connection then travels along a length of the PCB  220  via circuit pathways  230  to a screw hole  240 . Then a conductive screw  236  is inserted through the hole and carries the ground signal to the commonly grounded surface  232  through the interface of the conductive screw  236  with the conductive screw sleeve  244 . 
     In the implementation of  FIG. 2  consistent with presently disclosed technology, the improved die ground configuration connects ground potential of the electrical circuit within the electronic package  204  with the commonly grounded surface  232  directly, without relying on the PCB  220  as an intermediary. In one implementation, an electrical connection from the die  208  extends through the over mold  218  and out of the electronic package  204  away from the PCB  220 , compressively contacting the commonly grounded surface  232 . The improved die ground lead may be installed in lieu of the traditional ground connection or in addition to the traditional ground connection. 
     In the implementation shown in  FIG. 2 , an improved die ground lead  252  is connected to the die  208  with a wire  212 . The improved die ground lead  252  extends out of the side of the electronic package  204  and bends away from the PCB  220  and toward the commonly grounded surface  232  which is mounted in close proximity to but not contacting the electronic package  204 . As the PCB  220  is installed on the commonly grounded surface  232  via one or more conductive screws  236  and conductive screw sleeves  244 , the improved die ground lead  252  compressively contacts the commonly grounded surface  232  thereby creating an improved die ground connection from the electrical circuit to the commonly grounded surface  232  when compared with the traditional ground connection illustrated by the arrow  248 . The traditional ground connection illustrated by the arrow  248  includes bonded connections, such as soldering and welding, such that the ground connection travels through and/or along the PCB  220  and through mechanical structures, such as screws, press-fitting leads, and riveting to the commonly grounded surface  232 . Example structures for the improved die ground lead  252  include, but are not limited to, one or more compression connectors, tie bars, springs, and metal leads configured to electrically connect ground potential on the electrical circuit to the commonly grounded surface  232  by extending from the electronic package  204  and forming a compressive electrical connection to the commonly grounded surface  232 , rather than forming a bonded or soldered connection with structures of the PCB  220 , which is connected to the commonly grounded surface  232 . Further, the improved die ground lead may comprise multiple improved die ground leads  252  extending from the commonly grounded surface  232  and compressively contacting the commonly grounded surface  232 . 
       FIG. 3  illustrates another example implementation of an electrical system  300  utilizing an improved die ground lead. In this implementation, the over mold  318  in the electronic package  304  has an aperture  356  through the surface of the electronic package  304  facing the commonly grounded surface  332 . This aperture  356  extends through the over mold  318  and terminates at a wire  312  connected to ground potential on the die  308 . In other implementations, the aperture  356  may terminate at ground potential directly on the die  308  or at a signal lead  316  connected to ground potential on the die  308  via a wire  312 . 
     Within and extending out and away from the aperture  356  and toward the commonly grounded surface  332  is a pogo pin  360 . In other implementations, any other compressive lead may be used in place of the pogo pin  360 , e.g., a spring. As the PCB  320  is installed on the commonly grounded surface  332  via one or more conductive screws  336  and conductive screw sleeves  344 , the pogo pin  360  compressively contacts the commonly grounded surface  332  thereby creating an improved die ground connection from the electrical circuit within the electronic package  304  to the commonly grounded surface  332  when compared with a traditional ground connection illustrated by the arrow  348 . 
     The pogo pin  360  may be located anywhere on the face of the electronic package  304  where it can make electrical contact with ground potential of the electrical circuit. Further, there may be multiple pogo pins  360  creating multiple improved die ground connections between the electrical circuit and the commonly grounded surface  332 . In the implementation of  FIG. 3 , the commonly grounded surface  332  has an indention  388  in the commonly grounded surface that acts as a seat for one end of the pogo pin  360 . In other implementations, there is no seat in the commonly grounded surface  332  for receiving one end of the pogo pin  360 . 
     Referring now to  FIG. 4 , a plan view of the interior of an example electronic package  400  with a tie bar  464  extending out of one corner of the electronic package  400  is shown. The interior of this example electronic package  400 , shown in detail in View B, comprises a die  408  with signal wires  480  and ground wires  476  extending from die pads  468  mounted on the die  408 . The signal wires  480  extend to the periphery of the electronic package  400 . The ground wires extend to die pads  468  mounted on a lead frame  472 . The lead frame  472  serves as a common ground potential for the electrical circuit within the electronic package  400 . A non-conductive material, known as over mold  418 , may be used to encase the connections between the die  408 , die pad  468 , signal wires  480 , ground wires  476 , and lead frame  472  and protect them from potential damage from dirt, corrosion, or physical contact with another object. 
     Systems such as the electronic package  400  shown in  FIG. 4  are often manufactured in stripes containing multiple electronic packages. The stripes are then cut to yield each individual electronic package  400 . Normally the excess conductive material extending from the lead frame  472  out of the corners of the electronic package  400  is trimmed off when the stripes are cut. However, in the implementation shown in  FIG. 4 , a portion of the excess conductive material, known as a tie bar  464  is kept and may be used to provide the improved die ground connection as contemplated by the presently disclosed technology. Use of the tie bar  464  as an improved die ground lead is merely an example; other structures of making electrical contact with the lead frame  472  and/or ground wires  476  are contemplated to extend an improved die ground lead out of the electronic package  400 . 
     Referring now to  FIG. 5 , a plan view of the exterior of an example electronic package  500  with a tie bar  564  extending out of one corner of the electronic package  500  is shown. From the exterior, all that is visible are signal leads  516  protruding from each side of the electronic package  500 , the tie bar  564  protruding from one corner of the electronic package  500 , and over mold covering the internal components of the electronic package  500 . 
     The lead frame  572  is shown in broken lines to illustrate the connection between the tie bar  564  and the lead frame  572 , even though the lead frame  572  cannot actually be seen from this exterior view. The tie bar  564  extends out of a corner of the electronic package  500  and may be bent upwardly and over a first face of the electronic package  500 , thereby creating an improved die ground lead that may compressively contact anything that is placed adjacent the first face of the electronic package  500 . 
     Referring now to  FIG. 6 , the electronic package  500  of  FIG. 5  is shown mounted on a PCB  620  with a tie bar  664  improved die ground lead contacting a commonly grounded surface  632 . More specifically, the electronic package assembly  600  is shown in “before installation” and “after installation” illustrations. 
     In the bottom, before installation illustration, an electronic package  604  similar to the one depicted in  FIG. 5  is shown mounted on a plane representing a PCB  620 . Signal leads  616  protrude from the sides of the electronic package  604  and attach to the PCB  620 . The tie bar  664  emerges from a corner of the electronic package  604  and extends away from the PCB  620 . The tie bar  664  is further bent so that it passes over the first face of the electronic package  604  while continuing to extend away from the PCB  620 . A plane representing the commonly grounded surface  632  is shown above the electronic package  604  and arrows  634  indicate that the commonly grounded surface  632  will be moved in the direction of the electronic package  604 . 
     In the top, after installation illustration, the PCB  620  with an electronics package  604  mounted thereto is shown installed on the plane representing the commonly grounded surface  632 . After installation, a first face of the electronics package  604  is in close proximity, but not in contact with the commonly grounded surface  632 . However, the tie bar  664  is in compressive contact with the commonly grounded surface  632 , thereby connecting ground potential on the electrical circuit within the electronic package  604  to the commonly grounded surface  632  via the tie bar  664  without utilizing the PCB  620  as an intermediary. 
     Referring now to  FIG. 7 , an electronics package  704  is shown mounted on a PCB  720  with a pogo pin  760  improved die ground lead contacting a commonly grounded surface  732 . Similar to  FIG. 6 , the electronic package assembly  700  is shown in “before installation” and “after installation” illustrations. 
     In the bottom, before installation illustration, the electronic package  704  is shown mounted on a plane representing a PCB  720  in the same way described in  FIG. 6 . However, the electronic package  704  does not utilize a tie bar to extend an improved die ground connection out of the electronic package  704  and away from the PCB  720 . Instead, the electronic package  704  illustrated in  FIG. 7  utilizes a pogo pin  760  mounted within an aperture  756  in the over mold of the electronic package  704 . The aperture  756  extends into the electronic package  704  to ground potential of an electrical circuit within the electronic package  704 . A first end of the pogo pin  760  is in physical contact with ground potential on the electrical circuit within the electronic package  704 . A second end of the pogo pin  760  extends out of the aperture  756  and in the direction of the commonly grounded surface  732 . The commonly grounded surface  732  may optionally have an indention  788  for receiving the second end of the pogo pin  760 . The indention may improve the die ground connection between the electronic package  704  and the commonly grounded surface  732 . A plane representing the commonly grounded surface  732  is shown above the electronic package  704  and arrows  734  indicate that the commonly grounded surface  732  will be moved in the direction of the electronic package  704 . 
     In the top, after installation illustration, the PCB  720  with an electronics package  704  mounted thereto is shown installed on the plane representing the commonly grounded surface  732 . After installation, a first face of the electronics package  704  is in close proximity, but not in contact with the commonly grounded surface  732 . However, the pogo pin  760  is in compressive contact with the commonly grounded surface  732 , thereby connecting ground potential on the electrical circuit to the commonly grounded surface  732  without utilizing the PCB  720  as an intermediary. 
     Referring now to  FIG. 8 , a flow chart illustrates an example process  800  for assembling an electrical system with an improved die ground lead. While the process in  FIG. 8  is directed toward an implementation utilizing a tie bar as an improved die ground lead, other methods of attaching the improved die ground lead to an electronic package are contemplated. 
     The process begins with removing the electronic package from a stripe of electronic packages  810 . Normally, the process of removing an electronic package from the stripe would entail cutting the tie bars at the edge of the electronic package. However, in at least one implementation of the described technology, one or more tie bars extending from one or more corners of the electronic package are left intact and attached to the electronic package. The tie bars may then be folded over a first face of the electronic package while also extending away from the first face of the electronic package  820 . 
     Then the second face of the electronic package is attached to a PCB via signal and ground leads  830 . Finally, the first face of the PCB is mounted to the commonly grounded surface with the first face of the electronic package in close proximity to but not contacting the commonly grounded surface. Since the tie bar extends away from the first face of the electronic package, when the PCB is mounted to the commonly grounded surface, the tie bar compressively contacts the commonly grounded surface thereby establishing the improved die ground connection  840 . 
     Referring now to  FIG. 9 , a flow chart illustrates another example process  900  for assembling an electrical system with an improved die ground lead. While the process in  FIG. 9  is directed toward an implementation utilizing a pogo pin as an improved die ground lead, other methods of attaching the improved die ground lead to an electronic package are contemplated. 
     The process begins with creating an aperture in the over mold on a first face of an electronic package  910 . The aperture may be formed at the time the over mold is installed on the electronic package or afterward. Further, drilling, melting, punching, or any means of creating an aperture may be used to create the aperture in the over mold. At the bottom of the aperture in the over mold is a connection to ground potential of the electrical circuit within the electronic package. This connection to ground potential may be to the die directly, to the lead frame, or to a wire or lead connected to the die and/or the lead frame. 
     Next a pogo pin or other compressive conductive device, e.g., a spring, is inserted into the aperture  920 . Then the second face of the electronic package is attached to a PCB via signal and ground leads  930 . Finally, the first face of the PCB is mounted to the commonly grounded surface with the first face of the electronic package in close proximity to but not contacting the commonly grounded surface. Since the pogo pin extends away from the first face of the electronic package, when the PCB is mounted to the commonly grounded surface, the pogo pin compressively contacts, rather than being bonded or soldered to, the commonly grounded surface thereby establishing the improved die ground connection  940 . 
     The above specification and examples provide a complete description of the structures of example implementations of methods and apparatus that may be used for providing an improved die ground lead. Although various implementations of the methods and apparatus have been described above with a certain degree of particularity, or with reference to one or more individual implementations, those skilled in the art could make numerous alterations to the disclosed implementations without departing from the spirit or scope of the presently disclosed technology. It is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative only of particular implementations and not limiting. Changes in detail or structure may be made without departing from the basic elements of the presently disclosed technology as defined in the following claims.