Patent Publication Number: US-2011075387-A1

Title: Strain Measurement Chips For Printed Circuit Boards

Description:
BACKGROUND 
     The printed circuit boards of some computing devices exhibit relatively high failure rates. For example, the motherboards of mobile computers, such as notebook or “laptop” computers, tend to fail more often than the motherboards of stationary computers. Such failures can be due to manufacturing processes. For example, damage may occur when a printed circuit board is twisted to fit within a computer housing. Failures can also occur during use. For example, damage may occur when a notebook computer is subjected to undue physical and/or thermal stresses. 
     Such failures can be reduced by evaluating the stresses that are typically imposed on the printed circuit boards. For example, if it is determined that a current manufacturing process imposes too much stress on a circuit board, alternative manufacturing processes can be used. The stress imposed upon a given circuit board can be determined by gluing strain gauges to the printed circuit board and collecting strain readings with wires that are attached to the strain gauges. Although such a solution can be effective, the process of gluing the strain gauges to the board is labor intensive and time consuming. In addition, because of the variability with which the stain gauges are glued to the boards in terms of location and orientation, such a solution may not provide consistent, and therefore dependable, results. Furthermore, such a solution can only be implemented before assembly of the computer in which the circuit board is to be installed has been completed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosed strain measurement chips can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale. 
         FIG. 1  is a cut-away top perspective view of a first embodiment of a strain measurement chip. 
         FIG. 2  is a top view of the strain measurement&#39;chip of  FIG. 1 . 
         FIG. 3  is a bottom perspective view of a second embodiment of a strain measurement chip. 
         FIG. 4  is top perspective view of a printed circuit board having a strain measurement chip mounted thereon. 
         FIG. 5  is side view of the strain measurement chip of  FIG. 1  shown attached to a printed circuit board. 
         FIG. 6  is a top view of the strain measurement chip and printed circuit board of  FIG. 5 , illustrating electrical connection of the chip to conductive traces of the circuit board. 
         FIG. 7  is a schematic top view of a further printed circuit board to which a strain measurement chip has been mounted. 
         FIG. 8  is side view of the strain measurement chip of  FIG. 3  shown attached to a printed circuit board. 
         FIG. 9  is a perspective view of a computer that incorporates a strain measurement chip. 
         FIG. 10  is a block diagram of an embodiment of the computer of  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION 
     As described above, it is desirable to measure the strain within a printed circuit board, such as a computer motherboard. Although strain data can be collected by gluing strain gauges to the circuit board, such a solution is disadvantageous for various reasons. As described in the following, such disadvantages can be reduced or avoided by mounting a strain measurement chip to the board. In some embodiments, the strain measurement chip comprises a semiconductor chip similar to an integrated circuit (IC) chip. Like conventional IC chips, the strain measurement chip comprises electrical contacts that can be directly connected, for instance soldered, to contact pads or traces provided on the board. Unlike an IC chip, however, the strain measurement chip comprises internal strain gauges that measure strains within the circuit board. Due to the connection of the leads or contacts to the traces of the circuit board, strain data can be communicated through the board, as opposed to through auxiliary wires. 
     Referring now in more detail to the drawings, in which like numerals indicate corresponding parts throughout the several views,  FIG. 1  illustrates a first example strain measurement chip  100  that can be mounted to a printed circuit board, such as a computer motherboard. As indicated in  FIG. 1 , the chip  100  has the general configuration of an IC chip. Therefore, the chip  100  comprises a substantially block-shaped body  102  having multiple sides from which outwardly (e.g., laterally) extend lead frames  104 , each including multiple electrical leads  106 . By way of example, the body  102  is formed of a semiconductor (e.g., silicon-based) and/or a polymer material, such as a silicon-based material and the leads  104  are made of an electrically-conductive material, such as a metal. In some embodiments, the chip  100  comprises four lead frames  104 , one provided along each of the four sides of the chip (see  FIG. 2 ). Each of the leads  106  comprises a foot  108  that can be attached to an element (e.g., contact pad) of a printed circuit board. Therefore, the leads  106  can be used to securely mount the chip  100  to the board. As described below, one or more of the leads  106  can also be used to communicate strain data measured by one or more internal strain gauges provided within the body  102 . Although a particular number of leads  106  is shown in  FIG. 1 , it is to be understood that fewer or greater number of leads can be used depending, at least in part, on the strength of the bond desired between the chip  100  and its associated board. 
     As is further shown in  FIG. 1 , provided within the body  102  are one or more internal strain gauges  110 . By way of example, the strain gauges  110  comprise piezo strain gauges. In the embodiment of  FIG. 1 , three such strain gauges  110  are provided, each being completely encompassed or encapsulated by the material of the chip body  102 . As shown most clearly in the top view of  FIG. 2 , each strain gauge  110  has a different orientation within the chip  100  to enable measurement of strains in multiple different directions. In the embodiment of  FIGS. 1 and 2 , a first strain gauge  110  is aligned with an x direction, a second strain gauge  110  is aligned with a y direction, and a third strain gauge is aligned with a diagonal direction that forms an angle (e.g., 45°) with each of the x and y directions. 
     With further reference to  FIG. 1 , each strain gauge  110  is electrically coupled to at least one of the electrical leads  106 . In the embodiment of  FIG. 1 , the strain gauges  110  couple to the leads  106  with supplemental conductors  112 , such as internal wires. Alternatively, however, one or more of the leads  106  can be directly connected to each strain gauge  110 . 
       FIG. 3  illustrates a second example strain measurement chip  300 . The strain measurement chip  300  is similar to the chip  100  and therefore comprises a body  302  that encapsulates strain gauges (not shown). The chip  300 , however, does not comprise electrical leads that extend laterally from the body  302 . Instead, the chip  300  comprises a ball grid array  304  formed on a bottom surface  306  of the body  302 . The ball grid array  304  comprises a plurality rows and columns of solder balls or bumps  308 . Like the electrical leads  106  of the chip  100 , the solder bumps  306  can be used to securely mount the chip  300  to a printed circuit board. In addition, one or more of the solder bumps  306  can be used to communicate strain data measured by one or more of the internal strain gauges. 
       FIG. 4  illustrates an example printed circuit board  400 , such as a motherboard intended for use in a computer. As shown in  FIG. 4 , the circuit board  400  includes various electrical components that are mounted to a top surface  402  of the circuit board. Such components can include processor chips, memory elements, electrical connectors, power sources, and the like. Also shown mounted to the surface  402  of the circuit board  400  is a strain measurement chip  404 , which may have a configuration similar to that described above in relation to either  FIG. 1  or  FIG. 3 . In the embodiment of  FIG. 4 , the strain measurement chip  404  to mounted to a central region of the circuit board  400 . It is noted, however, that the chip  404  may be mounted in other locations. Furthermore, multiple such chips  404  may be mounted to the circuit board  400 , if desired. 
       FIGS. 5 and 6  illustrate mounting of the strain measurement chip  100  to a portion of the printed circuit board  400  shown in  FIG. 4 . As indicated in  FIG. 5 , each of the electrical leads  106  is mounted to the surface  402  of the circuit board  400 . For example, the feet  108  of the leads  106  are soldered to the surface  402 . As indicated in  FIG. 6 , the leads  106  can be soldered to contact pads  600  formed on the surface  402  of the circuit board  400 . As is further indicated in  FIG. 6 , one or more of the contact pads  600  can be electrically coupled to integral conductive traces  602  formed on or within the circuit board  400 . Such traces  602  can be used to communicate strain data measured by the strain measurement chip  100  to a memory element on the circuit board  400 , to another storage location within a computer in which the circuit board  400  is used (e.g., nonvolatile memory element), or to another device via a connector of the circuit board. The latter functionality is depicted in  FIG. 7 , in which a strain measurement chip  700  is mounted to a printed circuit board  702  and conductive traces  704  extend to an electrical connector  706  of the circuit board. By way of example, the connector  706  comprises a serial port or a universal serial bus (USB) connector. In such a case, strain data can be collected directly from the circuit board  702 , for example by booting the circuit board independent of a computer in which it is to be installed. Testing can then be performed, for example during installation of the circuit board  702  into a housing of the computer. 
       FIG. 8  illustrates mounting of the strain measurement chip  300  to a portion of the printed circuit board  400 . As with the chip  100 , the chip  300  can be soldered to the circuit board  400 . For example, the solder bumps  306  of the chip  300  can be soldered to contact pads (not shown) provided on the surface  402  of the circuit board  400 . Again, one or more of those pads can be electrically coupled to conductive traces (not shown) formed on or within the circuit board  400  to enable communication of strain data using the circuit board. 
     Although the stain measurement chips  100 ,  300  have described as being soldered to a printed circuit board, it is noted that the chips can further be glued to the circuit board to keep them in place until soldering is performed and/or to provide additional strength to the bond formed between the chip and the circuit board. 
     Given that the above-described strain measurement chips are similar to conventional IC chips that mount to circuit boards, conventional automated manufacturing techniques can be used to mount the strain measurement chips. Such automation not only saves time and effort but also ensures consistency in the positioning and orientation of the strain gauges relative to the circuit board. Once a secure bond is achieved between the strain measurement chip and the circuit board, stresses imposed upon the circuit board will be transmitted to the strain measurement chip and its internal strain gauges. Strain data measured by the strain gauges can then be communicated directly to contact pads and conductive traces of the circuit board, thereby obviating the need for the separate wires that are necessary when individual strain gauges are simply glued to a circuit board. In addition, because the strain measurement chip is mounted and electrically coupled to the circuit board in similar manner to other surface mounted components, strain data can be collected after completion of assembly of a computer or other device in which the circuit board is used. 
       FIG. 9  illustrates an example application for a strain measurement chip of the type described herein. More particularly,  FIG. 9  illustrates a notebook or “laptop” computer  900 . As indicated in the figure, the computer  900  includes a base portion  902  and a display portion  904  that are attached to each other with a hinge mechanism (not shown). The base portion  902  includes an outer housing  906  that surrounds various internal components of the computer  900 , including a motherboard that comprises a strain measurement chip that is mounted thereto. Also included in the base portion  902  are user input devices, including a keyboard  908 , a mouse pad  910 , and selection buttons  912 , and various ports or connectors  914  that are accessible through the housing  906 . The display portion  902  includes its own outer housing  916 . Formed within the housing  916  is an opening  918  through which a display device  920  may be viewed. 
     As indicated in  FIG. 10 , the computer  900  includes a processing device  1000 , memory  1002 , the strain measurement chip  1004 , and an output device  1006 , each of which is connected to an interface  1008 , such as an internal bus. Stored in memory  1002  is a strain monitor application  1010  that collects strain data from the strain measurement chip  1004 . With such an application  1010 , strain within the motherboard can be stored over time. In addition or exception, strain data can be output from the computer  900  via the output device  1006 , which can comprise a serial port, USB connector, Firewire connector, Ethernet connector, or other communication connector or device. 
     Although a notebook computer has been identified as a possible application for the strain measurement chip, it is to be appreciated that the strain measurement chip can be used with substantially any circuit board, whether it is present with a notebook computer or another device or machine. For example, the strain measurement chip can be provided on the circuit boards of any of desktop computers, tablet computers, personal digital assistants, mobile phones, portable game units, vehicles, appliances, and so forth.