Abstract:
An electronic package comprises a lead frame having a die pad for supporting a semiconductor chip. The electronic package is characterized by directly mounting at least a surface-mountable device on the lead frame thereby increasing the electric performance of the electronic package. According to an electronic package of the present invention, at least two leads of the lead frame have portions joined together to form a first pad and the die pad has a protruding portion to form a second pad thereby allowing the surface-mountable device to be connected across the first pad and the second pad. The present invention further provides another electronic package comprising a tape attached across the leads of the lead frame for supporting the surface-mountable device.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to electronic packages, and more particularly to lead frame packages characterized by directly mounting surface-mountable devices on lead frame. 
     2. Description of the Related Art 
     An electronic package typically includes a lead frame with one or more active devices attached thereon; packages including only one device are known as Single Chip Modules (SCM), while packages including a plurality of devices are called Multi Chip Modules (MCM). The active device is typically a chip commonly made of Silicon, Germanium or Gallium Arsenide. 
     FIG. 1 depicts a conventional electronic package comprising a lead frame for supporting a semiconductor chip  100 . The lead frame includes a plurality of leads having outer lead portions  106  and inner lead portions  107 . The chip  100  is attached onto a die pad  111  using a die attach adhesive such as silver paste  114 . The die pad  111  is connected to the lead frame by supporting bars (not shown in FIG.  1 ). The outer lead portions  106  are used for electrical coupling to an outside circuit. The chip  100  has bond pads electrically interconnected to the inner lead portions  107  of the lead frame through bonding wires  115 . The chip  100 , the die pad  111 , the inner lead portions  107  of the lead frame and bonding wires  115  are encapsulated in a package body  117  made of insulating material such as epoxy. 
     As the speed of semiconductor devices increase, noise in the DC power and ground lines increasingly becomes a problem. To reduce this noise, passive components such as decoupling capacitors are often used to reduce power supply noise which occurs due to change in potential difference between the ground voltage and the power-supply voltage supplied to the active device. The decoupling capacitors are typically surface-mountable devices (SMD&#39;s) used in the so-called surface-mounting technique. The decoupling capacitors are placed as close to the active device as practical to increase their effectiveness. For high pin count packages commonly encountered in the electronics manufacturing industry, as the number of I/O connections increases, finer pitches of the outer leads are required (i.e., below 0.5 mm) for the lead frame used therein. Therefore, lead frames for high pin count packages usually have a fine structure such that the decoupling capacitors cannot be directly mounted on the leads of the lead frames. Some wafers have capacitors built into the architecture of each chip, thereby significantly enhancing the electrical performance thereof. However, that will complicate the manufacturing process of wafer thereby increasing the production cost. 
     Accordingly, the present invention seeks to provide a method for directly mounting surface-mountable devices on a lead frame, which overcomes, or at least reduces the above-mentioned problems of the prior art. 
     SUMMARY OF THE INVENTION 
     It is a primary object of the present invention to provide an electronic package with surface-mountable devices built therein. The electronic package comprises a lead frame for supporting a semiconductor chip and is characterized in that the surface-mountable devices are directly mounted on the lead frame thereby increasing the electric performance of the electronic package. 
     The electronic package in accordance with the present invention mainly comprises a lead frame including a die pad and a plurality of conductive leads; a semiconductor chip disposed on the die pad and electrically connected to the leads; a surface-mountable device disposed on the lead frame; and a package body encapsulating a portion of the lead frame, the semiconductor chip and the surface-mountable device. Preferably, the surface-mountable device is a passive component such as a resistor, a capacitor or an inductor. 
     In a preferred embodiment of the present invention, at least two leads of the lead frame have portions joined together to form a first pad and the die pad has a protruding portion to form a second pad such that the surface-mountable device is connected across the first pad and the second pad. 
     In another preferred embodiment of the present invention, at least two adjacent leads of the lead frame have portions joined together to form a first pad and at least another two adjacent leads of the lead frame have portions joined together to form a second pad. In addition, the electronic package further comprises a tape that is attached across the leads of the lead frame and has two openings formed corresponding to the first pad and the second pad. In this embodiment, the surface-mountable device is supported by the tape and connected across the first pad and the second pad through the openings of the tape. 
     In a further preferred embodiment of the present invention, the electronic package further comprises a tape attached across the leads of the lead frame and at least one layer of electrical circuitry formed on the tape. The electrical circuitry comprises two first pads and two second pads respectively coupled to the first pads. Each of the first pads has an aperture formed corresponding to one predetermined lead. The tape has openings formed corresponding to the apertures of the first pads. In this embodiment, the surface-mountable device is supported by the tape and connected across the two second pads. The apertures and corresponding openings are filled with a conductive paste so as to electrically connect the surface-mountable device to the predetermined leads. 
     According to a still further preferred embodiment of the present invention, the electronic package further comprises a tape attached across the leads of the lead frame and at least one layer of electrical circuitry formed on the tape. The electrical circuitry comprises two first pads and two second pads respectively coupled to the first pads. In this embodiment, the two first pads are adapted to support the surface-mountable device and the two second pads are adapted for wire bonding to the semiconductor chip. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
     FIG. 1 is a cross sectional view of a conventional electronic package; 
     FIG. 2 is a top plan view of a lead frame according to a first preferred embodiment of the present invention illustrating a surface-mountable device and a chip mounted on the upper surface of the lead frame; 
     FIG. 3 is a top plan view showing a portion of the lead frame in FIG. 2 on an enlarged scale; 
     FIG. 4 illustrates, in an enlarged top plan view, a portion of the lead frame in FIG. 2 with the surface-mountable device mounted thereon; 
     FIG. 5 is a bottom plan view of a lead frame according to a second preferred embodiment of the present invention illustrating a surface-mountable device mounted on the lower surface of the lead frame and a chip mounted on the upper surface of the lead frame; 
     FIG. 6 is a top plan view showing a portion of the lead frame in FIG. 5 on an enlarged scale; 
     FIG. 7 illustrates, in an enlarged top plan view, a portion of the lead frame in FIG. 5 with the surface-mountable device mounted thereon; 
     FIG. 8 is a top plan view of a lead frame with a tape attached thereon according to a third preferred embodiment of the present invention illustrating a surface-mountable device mounted thereon; 
     FIG. 9 is a top plan view showing a portion of the lead frame and the tape attached thereon in FIG. 8 on an enlarged scale; 
     FIG. 10 illustrates, in an enlarged top plan view, a portion of the lead frame and the tape in FIG. 8 with the surface-mountable device mounted thereon; 
     FIG. 11 illustrates, in a top plan view, a tape having a layer of electrical circuitry according to a fourth preferred embodiment of the present invention attached on a lead frame and a surface-mountable device mounted on the tape; 
     FIG. 12 is a top plan view showing a portion of the lead frame and the tape attached thereon in FIG. 11 on an enlarged scale; 
     FIG. 13 illustrates, in an enlarged top plan view, a portion of the lead frame and the tape in FIG. 11 with the surface-mountable device mounted thereon; 
     FIG. 14 illustrates, in a top plan view, a tape having a layer of electrical circuitry according to a fifth preferred embodiment of the present invention attached on a lead frame and a surface-mountable device mounted on the tape; 
     FIG. 15 is a top plan view showing a portion of the lead frame and the tape attached thereon in FIG. 14 on an enlarged scale; and 
     FIG. 16 illustrates, in an enlarged top plan view, a portion of the lead frame and the tape in FIG. 14 with the surface-mountable device mounted thereon. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 2 shows a lead frame  200  according to a first preferred embodiment of the present invention. As shown, a surface-mountable device  300  and a chip  400  are mounted on the upper surface of the lead frame. Lead frames may be manufactured in long strips of many individual units (only one shown in FIG.  2 ). The lead frame  200  includes a plurality of conductive leads  210  arranged around a die pad  220 . The die pad  220  is connected to the lead frame  200  by four tie bars  230 . Usually, inner ends  210   a  of the leads  210  are plated with a layer of metal, such as silver, gold, or palladium, which bonds well with conventional bonding wire material. 
     Referring to FIG.  2  and FIG. 3, the lead frame  200  is characterized in that at least two leads have portions joined together to form a pad  240  and the die pad  220  has a protruding portion to form a pad  250 . It should be understood that the pads  240 ,  250  are formed between the inner ends  210   a  of the leads  210  and the die pad  220 . It is noted that the inner ends of the leads connected to the pad  240  are still ready for wire bonding. Usually, the surface-mountable device  300  (see FIG. 4) is secured to the pads  240 ,  250  through two end contacts of the device  300  by bonding materials such as solder paste. 
     FIG. 5 shows, in a bottom plan view, a lead frame  500  according to a second preferred embodiment of the present invention. As shown, a surface-mountable device  300  is mounted on the lower surface of the lead frame  500  and a chip  400  (indicated by dotted line shown in FIG. 5) is mounted on the upper surface of the lead frame  500 . 
     Referring to FIG. 6, the lead frame  500  is characterized in that at least two leads have portions joined together to form a pad  510  and the die pad  220  has a protruding portion to form a pad  520 . It is noted that only the pad  520  extends between the inner ends  210   a  of the leads  210  and the die pad  220 . As shown in FIG. 7, the surface-mountable device  300  is secured to the pads  510 ,  520  through two end contacts of the device  300  by bonding materials such as solder paste. It should be understood that since the pad  510  is formed on the lower surface of the lead frame  500 , the bonding material for SMT device will not contaminate the predetermined areas of leads (i.e., the upper surface of the inner ends) adapted for wire bonding. Therefore, before wire bonding, it is not necessary to treat the upper surface of the inner ends with a time-consuming plasma clean process. 
     It should be understood that, in the first and the second embodiments, the surface-mountable device may be a passive component such as a capacitor or a resistor, excluding resistor. Furthermore, the lead frame in accordance with the present invention is formed from a thin metal strip, which has been etched or stamped to form a pattern similar to that shown in FIG. 2 or FIG.  5 . Preferably, the lead frame is made of copper or alloys containing copper. Alternatively, the lead frame may be made of iron, nickel or alloys thereof, and then plated with copper. 
     FIG. 8 shows a lead frame  600  with a tape  650  attached thereon according to a third preferred embodiment of the present invention. As shown, a surface-mountable device  300  is mounted on the tape. Referring to FIG. 9, the lead frame  600  is characterized in that at least two adjacent leads have portions joined together to form a pad  610  and at least another two adjacent leads have portions joined together to form a pad  620 . The tape  650  is attached across the leads of the lead frame and has two openings  650   a  formed corresponding to the pads  610 ,  620 . In this embodiment, the surface-mountable device  300  (see FIG. 10) is supported by the tape  650  and connected across the pads  610 ,  620 . The tape  650  may be a lead-fixing tape composed of a polyimide resin or the like, which is punched and bonded to the leads of the lead frame with an adhesive layer. 
     FIG. 11 shows a tape  750  having a layer of electrical circuitry according to a fourth preferred embodiment of the present invention attached on a lead frame  700 . As shown in FIG. 12, the electrical circuitry comprises two pads  752  and another two pads  754  respectively coupled to the pads  752 . Each pad  754  has an aperture  754   a  formed corresponding to one predetermined lead  210 . The tape  750  has openings formed corresponding to the apertures  754   a  of each pad  754 . In this embodiment, a surface-mountable device  300  (see FIG. 13) is supported by the tape  750  and connected across the two pads  752 . The apertures  754   a  of the pads  754  and corresponding openings of the tape are filled with a conductive paste so as to electrically connect the surface-mountable device  300  to the predetermined leads. The conductive paste may be conductive epoxy (such as silver paste) or solder paste. The tape  750  may be formed from a dielectric film (suitable dielectric material such as polyimide). The film is punched and laminated with a conductive metal layer (such as a copper foil). Then the desired electric circuit is formed from the conductive metal layer on the dielectric film through photolithography and etching. 
     FIG. 14 shows a tape  770  having a layer of electrical circuitry according to a fifth preferred embodiment of the present invention attached on a lead frame  700 . As shown in FIG. 15, the electrical circuitry comprises two pads  772  and another two pads  774  respectively coupled to the pads  772  with a conductive trace. The pads  774  are formed at locations proximal to the inner ends  210   a  of the leads  210  for wire bonding to predetermined chip bonding pads. Preferably, the pads  774  are plated with a layer of metal, such as silver, gold, or palladium, which bonds well with conventional bonding wire material. In this embodiment, the surface-mountable device  300  (see FIG. 16) is supported by the tape  770  and connected across the two pads  772 . 
     Referring to FIG. 8, FIG.  11  and FIG. 14, even though the lead frame has a very fine lead structure, the surface-mountable device still can be mounted on the tape attached across the leads with good support. In the third, fourth, and fifth embodiments of the present invention, the surface-mountable device is preferably a passive component. It could be understood that the passive components may include capacitors, resistors and inductors arranged as filters to suppress power source noises and attain speed-up of the operation of the chip. 
     It should be understood that, in the electronic package of the present invention, the semiconductor chip is securely attached onto the die pad of the lead frame using a die attach adhesive such as silver paste. Usually, the semiconductor chip has a plurality of bond pads electrically interconnected to the lead frame through bonding wires such as gold wires (not shown). The gold wires are connected to the inner ends of the leads and the corresponding bond pads using known wire bonding techniques. The lead frame, the semiconductor chip, the bonding wires and the surface-mountable device are encapsulated in a package body (not shown) such that each lead of the lead frame has at least a portion left exposed for electrical connection to outside. Typically, the package body is formed by known plastic molding methods such as transfer molding. 
     Although the invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.