Abstract:
An integral impedence is formed on or within a lead frame pin of a semiconductor package and receives a connection from an electrode of a semiconductor die within the package to eliminate the need for adjustment and protective impedences external of the package. The impedence comprises passives such as resistors, capacitors, diodes or inductors which modify the performance of the package for new semiconductor device characteristics. The impedences may have positive or negative temperature coefficients and are in close thermal communication with the semiconductor die.

Description:
BACKGROUND OF THE INVENTION 
     Modern applications of semiconductor packages have an increasing demand for quick improvements in performance of their electric components and circuits. To keep up with the raising demand of better performance, higher power density, more efficiency, lower cost and space, more integration, higher functionality, increased digital content, etc., the silicon process technologies undergo continuous improvement steps. Correspondingly the technology development cycles of entire silicon process platforms have shrunk dramatically, sometimes with intermediate process upgrades on a yearly time base. 
     Consequently the market and the applications can take advantage of newer and better performing devices on shorter and shorter time scales. Existing products will be replaced by a next generation part with faster turn-around cycles than ever before. The quick adoption of a better performing silicon (or other semiconductor materials) process technology is advantageous to improve systems like electronic control units as quickly as possible. 
     On the other hand this quick replacement of existing parts by newer devices can also cause many problems for the system and circuit designs using those parts. Since the design-in of a newer or better performing devices normally requires changes or modifications of the circuit layout or the main system, such as an electronic control unit, unless the new part offers exactly the same layout, package, pin count, electric supply requirements, protective circuits, and the like. 
     Therefore, it is advantageous to produce a pin-compatible replacement product which provides a better performance (e.g. better electric behavior, higher power, etc.) while the user-application need not be changed. Thus, a printed circuit copper board or the like doesn&#39;t need to change its trace layout if the replacement part is in the same package and has the same footprint and layout as the older version. 
     This is especially important for applications such as automotive applications which do not change hardware generations as frequently as the silicon process technology offers improved parts. If the newer silicon technology offers a better performing device in the same package and with a pin-compatible layout, the application (e.g. an Electronic Control Unit “ECU”) can use the newer product without expensive changes of the system design. In that case a re-qualification of the system with the new component is sufficient. 
     Therefore, in many applications, especially automotive applications, it is preferred to implement a better performing part without sacrificing the existing system layout such as a printed circuit board (PCB). For this purpose it is a major market advantage and of great customer value to generate quasi-identical, pin-compatible replacement parts. 
     Unfortunately, even if pin-compatibility can be achieved, newer silicon or GaN technology might have different electric characteristics that require changes of the system circuitry even if the package outline and the footprint of the replacement part are identical to the predecessor package. Often the demand for higher integration and more functionality drives a newer silicon generation (especially IC circuits). Therefore, the newer silicon IC generations often implement more logic capabilities (e.g. CMOS logic, digital content, microcontroller capability, memory cells, etc.) which can turn a formerly very rugged and robust IC-process with less “smartness” into a more capable but less rugged device. 
     Thus, when converting IC or other devices to a more logic capable and higher integrated process, while some functions and parameters are more rugged than in the older process there are also some elements in the new designs that require additional protection or safety features. In such a case a customer who replaces a pin compatible part with a newer part still needs to redesign the application circuit and implement external protecting pre-resistors or other devices or circuits to limit certain current or voltage inputs. 
     With the need for those additional changes the advantage of a theoretically “pin-compatible” replacement part can be drastically reduced. In some cases a user might even be very reluctant to use it due to the need for additional changes in his system circuitry. In such a case a beneficial drop-in replacement of a newer part will be delayed until the application undergoes a re-design into a newer generation that can add the external protection elements for the newer part. In the automotive market, for example, this generation change is typically linked to car model design cycles which change typically every 3-5 years. This is a major drawback for the quick adaptation of replacement parts with newer silicon or other technology and better performance. 
     As previously stated, The required protection of sensitive sections or pins of an IC for example may be done with a pre-resistor (or other component) which is mounted externally on a PCB or other circuitry. Similarly, certain circuit blocks and contact pins of parts may need additional pre-resistors when used in the same application as the original part which did not need this resistor. 
     The disadvantages of this prior art solution are: 
     a) the user has to implement the changes on his system and carry the cost and time delay for changing the entire system such as a different PCB layout and changes in the assembly process to implement the pre-resistor or other component. 
     b) if the user is not aware of the need for a pre-resistor he might just replace the older generation part with the newer “pin-compatible” product and cause unaccepted failures in his application. 
     It would be very advantageous to implement the necessary new protection in a way that a new pin-compatible part does not need external protection. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The invention provides a solution for the above described problem of replacement parts that require additional protection compared to the replaced predecessor device. In accordance with the invention, a protecting pre-resistor or other device is integrated into the standard package of the new device without impact on footprint and pin compatibility. For example, a resistor, which may have a well controlled thermal coefficient of resistance may be added to the lead frame pine of the device. The package will then provide the protection needs of the new device without requiring the customer to redesign his circuit to accommodate the new part. 
     The invention offers the following advantages: 
     a) The customer has an identical 1:1 replacement of a newer better performing part, without the need for changing his application layout or electric circuit. 
     b) Cost and space savings as compared to the state of the art solution that requires an additional external passive component (like a pre-resistor) in the circuitry to protect the new replacement part. 
     c) Quick adoption of newer generation parts without cost and time intensive redesigns at the customer site. 
     d) Reduced risk of failures due to incorrect application use by the customer. 
     e) No need for disclosure of certain device weaknesses as compared to the predecessor part by implementing protection “hidden” in the package. 
     f) Additional functionality available inside of the package such as current sensing or temperature measurement. 
     g) Automatic adjustment of the protection (e.g. resistor value) with the operating temperature of the device. 
     The invention can be applied to all types of electric devices that need added protection or current limiter using a pre-resistor or other passive components (such as capacitors, diodes or inductors). 
     The invention is especially advantageous for markets with quick turn-around cycles or newer product generations such as the consumer and appliance markets, since the newer parts can be implemented without changing the external circuitry. The invention is also beneficial for markets with very slow turn around cycles of the application due to long system lifetimes such as automotive control units since the newer generation devices can be implemented without change of the circuitry design. Thus, only a re-qualification of an existing ECU with the new device may be required. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross sectional view of a first embodiment of the invention in which a pre-resistor is integrated into a lead or pin of the lead frame of an otherwise standard plastic package. 
         FIG. 1A  is a plan view of a full lead frame section. 
         FIG. 2  is a perspective view of the embodiment of  FIG. 1  with an added sense bond wire which bypasses the pre-resistor. 
         FIG. 3  is a modification of  FIG. 2  in which the lead frame pin has a lateral extension to more conveniently receive the sense bond wire. 
         FIG. 4  shows a further embodiment of the invention, like that of  FIG. 1  in which a pre-capacitor replaces the pre-resistor of  FIG. 1 . 
         FIG. 5  shows a further embodiment of the invention, like that of  FIG. 2  in which two adjacent lead frame pins have capacitive stack to enable measurement of current or temperature. 
         FIG. 6  shows a further embodiment of the invention in which the bond wire of  FIG. 2  is replaced by a rigid lead frame segment to form a bond-wireless package. 
         FIG. 7  shows a further embodiment of the invention in which the lead or pin of  FIG. 1  contains a series pre-resistor. 
         FIG. 8  shows a further embodiment of the invention in which the full lead frame pin is of resistive material. 
         FIGS. 9A ,  9 B and  9 C are top views of lead frame pins which are shaped to define an increased resistance as required by the pre-resistor of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, similar components in each Figure have the same identifying numeral. 
     Referring first to  FIG. 1 , there is shown a processed silicon die  20  mounted on a lead frame segment  21 . 
     Die  20  may be an IC or power device such as a MOSFET or IGBT or the like and may include process improvements over the processes used for part which it replaces. The die  20  may have any desired electrode pattern, including for example, electrodes  22 ,  23 ,  24  and  25  ( FIGS. 2 ,  3 ,  5  and  6 ) depending on the device  20  type. 
     Lead frame  21  ( FIGS. 1 ,  2 ,  3 ,  4 ,  5  and  6 ) has a plurality of extending leads or pins, only one of which, lead  30 , is shown in  FIG. 1 . A conventional wire bond  31  bonds electrode  24  to lead  30 . Other wire bonds may connect the other electrodes to other lead frame leads or pins (not shown). 
     In accordance with one embodiment of the invention, and as shown in  FIG. 1 , a pre-resistor  40  is fixed on lead frame lead  30  and receives the end of bond wire  31 . The resistor  40  has the same value as a prior art external resistor used to adapt the new die  20  to an existing application. 
     Resistor  40  may be a resistive layer, for example, manganese sized to exhibit a predetermined resistance change with temperature (and thus lead current) and is preferably deposited on the lead frame to a size needed to produce the desired resistance value. The resistor  40  may be formed by coating, plating, or sputtering or the like. A bond wire  31  is connected to its upper surface. The resistive metal layer  40  preferably has an upper top layer of, for example, nickel, which will suitably bond to conventional Al or Au bond wire  31  in a conventional wire bond application. 
     While only one lead of the lead frame is shown as receiving a pre-resistor, such pre-resistors can also be formed on other leads which are bond-wire connected to other electrodes of die  20 , and may have other respective resistive values, as desired.  FIG. 1A  shows a top view of such a lead frame with plural pre-resistors (or pre impedences)  40   a ,  40   b , and  40   c  on respective leads or pins extending from the central die support surface  30   a  which receives die or chip  20 . 
     The package of  FIG. 1  is preferably a plastic package and is conventionally overmolded with a suitable plastic housing  45 . 
     Referring next to  FIG. 2 , which shows the package of  FIG. 1  with housing  45  removed for clarity, a sense bond wire  50  added, extending from electrode  25  to lead  30 , by passing resistor  40 . 
     The optional bond wire  50  ( FIGS. 2 ,  3  and  5 ) is a current sense wire bond and permits the measurement of the voltage drop across resistor  40  to determine the current flow through resistor  40 . Thus resistor  40  acts as a shunt resistor, permits measurement of the temperature of the device (knowing the temperature co-efficient of the resistive material  40  and the current flow to pin  30 ). 
       FIG. 3  shows an embodiment like that of  FIG. 2 , where however, lead frame segment  55  replaces lead frame segment  30  and has a lateral extension  56  for receiving sense bond wire  50 . Significantly, in both  FIGS. 2 and 3  sense bond wire  50  is connected close to resistor  40  and is in close thermal communication with resistor  40 . As stated previously, the bond wire  50  and bond wire  31  of  FIGS. 2 and 3  can be used for temperature sensing measuring the voltage drop over resistor  40 . 
     By knowing the resistor  40  temperature coefficient and the current flow, the device&#39;s temperature can be measured via the voltage drop over the resistive layer  40 . Again the close proximity of bond wire  50  to the sensor element (resistive layer  40 ) and a suitable measurement device or circuit in the IC  20  will solve temperature difference problems existing in state-of-the-art solutions using external temperature sensor elements. Thus, temperature drifts during operation are compensated by having close thermal contact between the resistor  40  and the IC  20 . 
     Another advantage of the solution shown in  FIGS. 2 and 3  is that the resistive layer material  40  can be chosen with a positive or negative temperature coefficient. Thus, depending what is needed for the device, the value of the resistive layer  40  will change with the operating temperature of the device. Note that the silicon device  20  and the lead frame  21  will have a very similar temperatures due to their close proximity. Therefore, another advantage is provided compared to state of the art external resistors which are not in thermal contact with the device which they protect. The integrated resistive protection layer  40  can automatically change its resistive value depending on the operating temperature of the device. For example, if a device needs a higher pre-resistor value when it is hot the resistive material  40  can be chosen to increase the resistance with temperature and therefore be optimized over a broad temperature range. State-of-the art external resistors can only be optimized at one temperature point and need to cover the worst-case condition. 
     Other passive elements such as inductors or capacitors may be integrated on the lead frame pin of a device package. For example, a capacitor can be mounted and contacted in a similar way as the resistor  40  shown in the embodiments of  FIGS. 2 and 3 . Thus, instead of a resistive layer, a capacitive multilayer can be provided on one lead frame pin or between two lead frame pins. 
     Thus, as shown in  FIG. 4 , the resistor  40  is replaced by capacitor  60  which consists of a dielectric layer  61  between metal contacts  62 ,  63 . Capacitor  60  may be used as an isolating input element for decoupling pin  30  from the external circuit. Wire bond  31  is connected to top metal  63 . Metal  63  or a suitable plating is chosen to be conventionally bonded to aluminum or gold wires. 
       FIG. 5  shows a further embodiment of the invention in which a capacitive stack  70  is connected between lead frame pins  30  and  71  for purposes previously described. Notes that stack  70  can also be a resistive stack of layers of Cu, Mo and Cu which is soldered, sintered, welded or otherwise formed. 
       FIG. 6  shows a still further embodiment of the invention in which bond wire  31  of  FIG. 1 , for example, is replaced by a more rigid lead frame type copper strip  31   a  to connect resistive layer  40  to electrode  24  form a bond-wireless package. Note that resistor  40  could be replaced in  FIG. 6  by a capacitor or inductive part. 
       FIG. 7  shows a still further embodiment of the invention in which lead  30  of  FIG. 1  is replaced by composite lead  100  in which a resistive element  101  of manganese or the like is formed within and along the length of the lead. The bond wire  31  is fixed or wire-bonded to conductive (copper) segment  102  of the lead  100 . 
     As shown in  FIG. 8  it is also possible to make the full length of lead  105  of resistive material (manganese) with a wire bond  31  connected to a suitable plated segment  106  which may be nickel or the like. 
       FIGS. 9A ,  9 B and  9   c  show techniques for increasing the resistance of lead  30  without the need for a separate resistor  40  of  FIG. 1 . Thus, in  FIG. 9A , a pattern of spaced openings  110 ,  111 ,  112  is formed along the length of lead  30 . In  FIG. 9B  an elongated slot  113  is employed for the same purpose. Finally, in  FIG. 9C , side cut-outs  114 ,  115  form a controlled increased pre-resistor value in the lead  30 . The special shaping of the lead  30  is advantageous for introducing relatively small resistance values or for AC current resistance which takes advantage of skin effect at higher frequencies. 
     Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein.