Patent Publication Number: US-6714026-B2

Title: System and method for measuring the thickness or temperature of a circuit in a printed circuit board

Description:
CROSS REFERENCES TO RELATED ART 
     This application is a Continuation-In-Part application of application Ser. No. 09/892,850 filed Jun. 28, 2001, now U.S. Pat. No. 6,635,879, which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to systems and methods for measuring power characteristics of an electric circuit. More particularly, this invention relates to on-board systems and methods for measure power characteristics of a circuit or sub-circuit on a Printed Circuit Board, and for measuring temperature and thickness of the circuit or sub-circuit. 
     2. Description of the Related Art 
     Printed Circuit Boards (PCBs) are well known. PCBs are a convenient and effective way to manufacture and implement both analog and digital electronics, often referred to as integrated circuits. Today, integrated circuits on PCBs are used in a multitude of applications, such as in computers, networking equipment, electronic appliances, stereos, etc. 
     In general, a PCB is manufactured to design specifications and lays out the electronic circuits for the associated application, such as the wiring for an integrated circuit. Then, after the PCB has been manufactured, the elements and various components of the integrated circuit are mounted onto the PCB at touch points, such as by soldering, etc. 
     As integrated circuits have become more and more complex, their related power consumption and distribution becomes more demanding. Accordingly, accurate testing of an integrated circuit&#39;s power needs is essential to the production of quality integrated circuits, and in turn, electrical and electronic equipment. 
     Often, analytical tools such as component modeling tools or simulation tools (e.g., SPICE®, etc.) are used by design engineers to help predict power consumption and distribution across an integrated circuit. However, many factors make the accurate prediction of the characteristics of an integrated circuit unreliable. For example, it is common for a PCB to be manufactured to tolerances of up to ±10%. Similarly, component tolerances may vary. Thus, the modeling of an integrated circuit may be used for design purposes, but might not accurately predict the actual power consumption and power distribution characteristics of an integrated circuit on a PCB, which could change with the varying tolerances. Accordingly, electronics manufacturers still must rely on conventional, laboratory type testing of integrated circuits manufactured on PCBs. 
     The physical testing of a integrated circuit on a PCB is not without its problems. For example, it is a common practice to test an integrated circuit by “breaking up” or isolating sections of a circuit or sub-circuit on the PCB. In order to isolate a circuit or sub-circuit, a component (e.g., an inductor, etc.) is usually removed and a power source is then spliced in, such as by a wire. Then, various voltage and current measurements may be made using conventional meters (e.g., voltage and current meters, oscilloscopes, etc.). However, as electronic components become smaller, physically isolating circuits on a PCB and accurately attaching scopes and meters to the circuit becomes more cumbersome, and is often impossible. 
     Ideally, to perform such testing, a precision measurement of the current feeding a circuit is necessary, which can be achieved by providing a precision current source in series with the circuit, or by adding a precision resistor in series with a voltage source to a circuit. For example, referring to prior art FIG. 1, shown is a simple block diagram of a circuit  100  on a PCB. The circuit  100  has a load  102  and a voltage source  104 . The power plane or PCB has a trace resistance level which is represented by R 2 . A precision resistor R 1  is placed in series with the power plane (R 2 ), and a precision current can be measured feeding load  102 , such as by using a current meter across the precision resistor R 1 . However, by placing a component in series with the load (circuit)  102 , the reliability of the circuit is directly related to the reliability of the precision resistor R 1 . Accordingly, the reliability of the entire circuit may be reduced. 
     Adding components in series with the circuit itself could affect the inductances of the circuit and accordingly, affect overall performance. Moreover, precision resistors also have the problem that they often cannot handle high current. 
     Furthermore, many circuits on a PCB are powered and connected via embedded circuits. In the example described above, the power plane is most likely embedded in the PCB, and therefore, certain characteristics of the power plane, such as thickness, will not be known. These characteristics may vary from PCB to PCB due to manufacturing tolerances. It may be important to know certain characteristics of the power plane or other embedded circuits for on-board testing of circuits or for measuring power of a circuit on a PCB. 
     However, since these circuits are embedded, conventional methods of measuring their thickness or other characteristics might not succeed. For example, conventional surface thickness measuring devices cannot be contacted with a power plane which is embedded in a PCB. 
     In view of the aforementioned problems, there is a need for new and improved systems and methods for measuring the power of a circuit on a PCB that is accurate and non-intrusive, and for measuring other characteristics of embedded circuits in a PCB. Such systems and methods should limit the number of additional components added to the circuit being tested, and should allow testers better access to circuits or less cumbersome methods to make measurements. 
     SUMMARY OF THE INVENTION 
     The present invention provides a system for measuring a thickness of a circuit component on a printed circuit board (PCB) The system includes a first circuit, a power plane, a power strip, a calibration strip, a temperature sensor, and a second circuit. The power plane is coupled to the first circuit. The power strip is for providing power to the power plane and is disposed in said PCB connected to the power plane. The power strip has at least two vias. The calibration strip has a predetermined width and is disposed in the PCB. The calibration strip has at least two vias for measuring a voltage drop. The temperature sensor is coupled to the calibration strip and configured to measuring a temperature of the calibration strip. The second circuit is coupled to the temperature sensor and configured to determine the thickness of the calibration strip based on at least the temperature of the calibration strip. 
     According to another embodiment of the present invention, provided is a system for measuring a thickness of circuit components on a printed circuit board (PCB). the system includes a first circuit, a power plane, a power strip, a calibration strip, a temperature regulator, and a second circuit. The power plane is coupled the first circuit. The power strip is for providing power to the power plane disposed in the PCB connected to the power plane. The power strip has at least two vias. The calibration strip has a predetermined width and is disposed in the PCB,. The calibration strip has at least two vias for measuring a voltage drop. The temperature regulator is coupled to the PCB and configured to maintain the PCB at a set temperature. The second circuit is configured to determine the thickness of the calibration strip based on at least the set temperature of the calibration strip. 
     According to another embodiment of the present invention, provided is a method for determining a thickness of a power strip of a circuit on a printed circuit board (PCB). The method includes the steps following steps: disposing a circuit onto a PCB.; embedding a power strip having a first predetermined length and width into the PCB between a first power supply and the circuit during a manufacturing process; disposing a calibration strip having a second predetermined length and width into the PCB during the manufacturing process; providing a second power supply to the calibration strip and grounding the power strip to form a current flow through the power strip; measuring a first voltage across the power strip; measuring a second voltage across the calibration strip; determining a temperature of the PCB; and calculating a thickness of the power strip based on the first and second voltages, the temperature, the first predetermined length and width and the second predetermined length and width. 
     According to another embodiment of the present invention, provided is a method for determining a thickness of a component of a circuit on a printed circuit board (PCB). The method includes the following steps: disposing a circuit onto a PCB; embedding a power strip having a first predetermined length and width into the PCB between a first power supply during a manufacturing process; embedding a calibration strip having a second predetermined length and width into the PCB during the manufacturing process; providing a second power supply to the calibration strip and grounding the calibration strip so that a current flows through the calibration strip; regulating a temperature of the PCB to be a set temperature; measuring a first voltage across the power strip; measuring a second voltage across the calibration strip; and calculating the thickness of the power strip based on the first and second voltages, the set temperature, the first predetermined length and width and the second predetermined length and width. 
     According to another embodiment of the present invention, provided is a system for measuring a thickness of a circuit component on a printed circuit board (PCB). The system includes a first circuit means, a power plane means, a power strip means, a calibration strip means, a temperature sensor means, and a second circuit means. The power plane means is for providing power to the first circuit means. The power strip means is for providing power to the power plane means disposed in the PCB, the power strip means having at least two vias. The calibration strip means has a predetermined width and is disposed in the PCB. The calibration strip means has at least two vias for measuring a voltage drop. The temperature sensor means is for measuring a temperature of the calibration strip means. The second circuit means is for determining the thickness of the calibration strip means based on at least the temperature of the calibration strip means. 
     According to another embodiment of the present invention, provided is a system for measuring a thickness of circuit components on a printed circuit board (PCB). The system includes a first circuit means, a power plane means, a power strip means, a calibration strip means, a temperature regulator means, and a second circuit means. The power plane means is for providing power to the first circuit means. The power strip means is for providing power to the power plane means disposed in the PCB, the power strip means having at least two vias. The calibration strip means has a predetermined width and is disposed in the PCB. The calibration strip means has at least two vias for measuring a voltage drop. The temperature regulator means is for maintaining the PCB at a set temperature. The second circuit means is for determining the thickness of the calibration strip means based on at least the set temperature of the calibration strip means. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For full understanding of the present invention, reference should be made to the accompanying drawings, wherein: 
     FIG. 1 is a schematic of a prior art system for measure power of a circuit on a PCB; 
     FIG. 2 is a block diagram of an on-board system for measure power of a circuit on a PCB according to a first embodiment of this invention; 
     FIG. 3 is an expansion view of the power supply and power plane of the on-board system for measure power of a circuit on a PCB according to a first embodiment of this invention; 
     FIG. 4 is a block diagram of an on-board system for measure power of a circuit on a PCB and the thickness of a calibration strip embedded in the PCB according to a second embodiment of this invention; 
     FIG. 5 a  is a schematic block diagram of an on-board system for measure power of a circuit on a PCB and the thickness of a calibration strip embedded in the PCB according to a first embodiment of this invention; 
     FIG. 5 b  is a schematic block diagram of an alternative power configuration for an on-board system for measure power of a circuit and the thickness of a calibration strip embedded in the PCB on a PCB; 
     FIG. 6 is a schematic diagram of an on-board circuit for measuring power of a circuit on a PCB and the thickness of a calibration strip embedded in the PCB according to a second embodiment of this invention; 
     FIG. 7 is a schematic diagram of an on-board circuit for measuring power of a circuit on a PCB and the thickness of a calibration strip embedded in the PCB according to a second embodiment of this invention; 
     FIG. 8 is flow chart of a system for measuring the power of a circuit on a PCB according to a first embodiment of the present invention; 
     FIG. 9 is flow chart of a system for measuring the power of a circuit on a PCB according to a second embodiment of the present invention; and 
     FIG. 10 is flow chart of a system for measuring the thickness or a power strip or a calibration strip embedded in a PCB according to an embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 2, shown is an block diagram of a system for measuring the core power of a circuit on a printed circuit board (PCB) according to a first embodiment of the present invention. In particular, system  200  includes a power source  202  (VDC 1 ), such as a DC voltage source, which supplies power to a power plane  204  via a power strip  206  (e.g., a wide copper strip). The power plane  204  is used to supply power to a circuit  208 , which has a predetermined load. 
     The power strip  206  has vias a and b, voltage drop points, placed a predetermined distance apart. The voltage drop V 1  across the vias a and b are input into a differencing circuit  214  which measure the voltage drop V 1  and outputs a voltage signal equal to the voltage drop V 1  to a power determination circuit  216 . A temperature sensor  220  measures the temperature of the power strip  206  and outputs a temperature signal tmp to the power determination circuit  216 . The power determination circuit  216  calculates the core power P of the circuit  208  and outputs a power signal P. As will be explained in detail below, various calculations may be made to determine the power based on a number of factors which could include voltage drop V 1 , the size of power strip  206 , the material of each, the temperature tmp of the power strip  206 , and the load of circuit  208 . The power signal P can be output from power determination circuit  216  to a display circuit, calibrating circuit, or other circuit as desired. 
     The various power calculations are described in more detail with reference to FIG. 3, which shows a close-up view of the power plane  204  and voltage source  202  connected by the power strip  206 . Power strip  206  is shown having a length L, a width W and a thickness T. The material of the power strip can preferably be a good conductor, such as pure copper. According to a preferred embodiment, the power strip may be one ounce Cu with a thickness of 0.0012-0.0014 inches, but the present invention is not intended to be limited as such. The thickness T, resistivity of the material (ρ) and thermal coefficient of the material (e) are properties of the material used. The length L and width W may be controlled by design. The thickness T may be set at 0.001 inches as a default for the purposes of calculations. 
     In this embodiment of the present invention, the resistance R of the power strip  206  is calculated by taking into account the temperature (tmp) of the power strip  206 , thermal coefficient (e), resistivity (ρ), the thickness T, and the known length L and width W. Accordingly, the following formulas may be used to calculate power: 
     
       
           R =(1+( tmp− 20)* e )* L*ρ/W*T   
       
     
     
       
           P=VDC   1   *V   1 / R   
       
     
     Accordingly, the power determination circuit  216  may have the known values L, W, T, p and e stored in memory or input dynamically from an external source. 
     Since the thickness of the power strip  206  may be unknown or may vary depending on the manufacturing tolerances of the process used to manufacture the PCB, an on-board self calibrating circuit can be added to system  200  to eliminate the need for accurate measurement of the thickness, as described below in further detail. Furthermore, a system for measuring the thickness of the power strip  206  may be implemented on-board, and is also described in further detail below. 
     Referring to FIG. 4, shown is an block diagram of a system for measuring the core power of a circuit on a printed circuit board and the thickness of a calibration strip embedded in the PCB according to a second embodiment of the present invention. In particular, system  200  includes a power source  202 , such as a DC voltage source, which supplies power to a power plane  204  via a power strip  206 . The power plane  204  is used to supply power to a circuit  208 , which has a predetermined load. A second voltage supply  210  is connected to a calibration strip  212 , which may be aligned in the same proximity as the power strip  206  on the PCB for reasons that will be explained below. The calibration strip  212  is directly grounded so that there is no loading of power source  210  other than the strip itself. 
     The power strip  206  and the calibration strip  212  have vias a-d, also referred to as voltage drop points, placed at a predetermined distance apart. The voltage drops V 1  and V 2  across the vias are input into difference circuits  214  which measure the voltage drop across each via. As an example, two differencing circuits are shown. The voltage drops measured, V 1  and V 2 , are entered into a power determination circuit  216  which can calculate the core power of the circuit  208 . As will be explained in detail below, various calculations may be made to determine the power based on a number of factors which could include V 1  and V 2 , the dimensions of calibration strip  212  and power strip  206 , the material characteristics of calibration strip  212  and power strip  206 , the temperature of the calibration strip  212  and the power strip  206 , and the load of circuit  208 . Each of the dimensions and the material characteristics may be input into the power determination circuit  216  from an external source, such as a CPU or a memory device (not shown), or the power determination circuit  216  may be preprogrammed with these variables. The power can be output as a signal P from power determination circuit  216  to a display circuit, calibrating circuit, or other circuit as desired. Furthermore, the power determination circuit  216  may be configured to determine the resistance and the thickness of the power strip  206 , if unknown. 
     As shown and described with reference to FIG. 3, the power P consumed by the load  208  can be calculated based on the voltage drop V 1  across the power strip  206 , the temperature (tmp) of the power strip  206 , the thermal coefficient (e), resistivity (p), the thickness T, length L and width W. However, as explained above, the thickness T, thermal coefficient (e), and resistivity (ρ) may not always be controlled by design and may not be predicted with extreme accuracy because of varying manufacturing processes used to manufacture the PCB. Therefore, in this embodiment, the calibration strip  212  may be placed in a close proximity to the power strip  206  and may be made of the same material (e.g., copper or some other conductor or semi-conductor). Thus, regardless of the manufacturing process, the thickness T(cal) of the calibration strip  212  will be equal to or substantially equal to the thickness T(power) of the power strip  206 . Also, since the calibration strip  212  is placed very close to the power strip  206 , the temperature of calibration strip  212  on-board will be equal to or substantially equal to the temperature of the power strip  206  during operation. Accordingly, the need for accurate measurement of the temperature tmp or thickness T for power calculations can be eliminated, and the power calculations can be based on known and controlled, or easily measured variables. 
     Resistance can be determined in terms of the resistance of power strip  206  (R 1 ) and calibration strip  212  (R 2 ) as follows: 
       R 1 =( 1+( tmp −20)* e )* L   1 *ρ(power)/ W   1   *T (power) 
     
       
           R 2 =( 1+( tmp −20)* e )* L   2 *ρ(cal)/ W   2   *T (cal) 
       
     
     
       
           T (power)= T (cal)= T   
       
     
     
       
         ρ(power)=ρ(cal)=ρ 
       
     
     
       
         ρ= R   2   *W   2 * T /(1+(tmp−20)* e )* L   2 , therefore 
       
     
     
       
           R   1 = L   1 * R   2 * W   2 / W   1 * L   2   
       
     
     The resistance of the calibration strip  212  R 2  may be determined by accurate measurement of the current through the strip, such as by adding a precision resistor in series with calibration strip  212  or by providing a precision current source (not shown). Thus, the power of the circuit  208  may be determined without intrusive meters or without adding additional components to the voltage path of the circuit  208 . 
     It is possible to determine the thickness T of the power strip  206  or of the calibration strip  212 , if the temperature tmp is known and, likewise, it is possible to determine temperature tmp if the thickness T is known. The thickness T of the calibration strip  212  may be determined by the following formula: 
     
       
           T =( L   2 *ρ)*(1+(tmp−20)* e )/( R   2 *  W   2 ) 
       
     
     Since R 2  may already be determined as described above, the thickness of the power strip  206  may be determined by either measuring the temperature tmp or by setting the temperature tmp. For example, a temperature sensor  222  may be included in system  200  to measure the temperature tmp of the calibration strip  212  and input a signal tmp into power determination circuit  216 . 
     Alternatively, a thermal regulating device, such as a fan or thermal stream (not shown), may be used to heat the entire PCB to a specific temperature before taking measurements. In this case, the power determination circuit  216  may be configured to pre-set the temperature tmp equal to the temperature of the board for calculation purposes. This temperature tmp may be used to then solve for the thickness T. 
     Also, if the thickness T is known or estimated, then the temperature tmp may be calculated by the following formula: 
     
       
         Tmp=(( R   2 * W   2 * T )/( L   2 *ρ)−1)/( e +20) 
       
     
     Accordingly, the power determination circuit  216  may be configured to perform the preceding calculations. It is important to note that resistances and temperature each vary in accordance with one another, and in accordance with the amount of current within the material being measured. Therefore, calculations can be made instantaneously instead of over a period of time. 
     FIG. 5 a  is a block diagram of a system for measuring the core power of a circuit on a PCB and the thickness of a calibration strip embedded in the PCB according to a third embodiment of the present invention. This embodiment is similar to the second embodiment, but differs in that the power determination circuit  216  is replaced by an analog to digital (A/D) converter  218  and a CPU. Since the voltage drops V 1  and V 2  can be very small, a means for amplifying the voltage drops V 2  and V 2  may used. As an example, differencing circuits  214  may be operational amplifier circuits which feed an amplified voltage drops V 1  and V 2  to the A/D converters  218 , which can accurately convert the amplified voltages V 1  and V 2  into digital signals V 1 ′ and V 2 ′, which are fed to the CPU  220 . Temperature sensor  222  may input a signal directly into CPU  220 , or in the case of an analog sensor, may input into another A/D converter (not shown) before inputting the temperature detected into the CPU  220 . The CPU  220  can then calculate power P, the thickness T, or the temperature tmp using the calculations already described above. 
     In this embodiment, the temperature tmp may also be set for calculation purposes, and the board temperature may be regulated in accordance with the setting of the temperature tmp. A device, such as a heater or fan (not shown) may be used to regulate the temperature of the board. The board may be set to a predetermined temperature or may simply be regulated at a set temperature, which is then measured. 
     Although a CPU  220  is shown, the present invention is not meant to be limited to embodiments including a CPU. For example, one having ordinary skill in the art will understand that power calculations described herein may be performed using a variety of calculating means and methods, such as with digital and analog circuits. 
     FIG. 5 b  illustrates an alternate power configuration for the calibration strip  212 . In particular, rather than providing a precision resistor in series with the current supply, the calibration strip  212  is placed directly in parallel with a voltage source  210 , and the voltage drop V 2  is measured by the differencing circuit  214  from vias c and d, in the same manner as described above. The output of the differencing circuit may be connected to A/D converter  218  as shown in FIG. 5 a  or to a power determination circuit as shown in FIG.  4 . 
     Referring to FIG. 6, an exemplary operational amplifier (e.g., an instrumentational op. amp.) circuit is shown which could be used as a differencing circuit  214 . Circuit  300  includes an operational amplifier  302  having inputs IN+ and IN−, which can be connected to vias a or c, and b or d, respectively. One having ordinary skill in the art will readily understand the application of additional circuitry  306  in order to power, bias, and set the gain for an operational amplifier. Operational amplifier  302  has an amplified output  304  which can produce the signals V 1  and V 2 . 
     The output  304  (e.g., V 1  or V 2 ) of operational amplifier  302  may be input into an AID converter as shown in FIG. 5, a power calculation circuit as shown in FIG. 4, or may be conventionally measured, such as by a meter, oscilloscope or other suitable device. It will be understood by one having ordinary skill in the art that when measuring power across integrated circuits, measurements may be required to be amplified, such as by operational amplifiers or other means. However, the present invention is not meant to be limited as such, and it will be understood that an A/D converter may be provided that is accurate enough to measure such small voltages directly without amplification. 
     Referring now to FIG. 7, shown is a schematic diagram of an exemplary configuration of a differencing circuit  214  and A/D converter  218  used to deliver digital signals to CPU  220  or other processing means. In particular, an operational amplifier  302 , similarly configured to the operational amplifier circuit  300  shown in FIG. 6, receives the voltages from vias c and d, or a and b, of the calibration strip  212 . 
     The calibration strip  212  is placed in series with an input voltage source  210  and a precision resistor Rp, which is also shown in the expanded view of FIG.). The amplified output  47  ( 304 ) of the operational amplifier  310 , which is the amplified potential V 2  (or V 1 ) across the vias of the calibration strip  212  (or power strip  206 ), is input into a channel of A/D converter  218 . A/D converter  218  may be a 12 bit A/D converter with a scale of −0-5V DC, for example, but is not limited as such. The input voltage from voltage source  210  is also input into a channel of the A/D converter  218  as a reference voltage. The A/D converter  218  is powered and biased by circuit  218   a . The A/D converter outputs corresponding digital signals (V 2 ′ and V reference) which may be input into CPU  220  or other calculation means in order to perform the power calculations. One having ordinary skill in the art will readily understand that the described configuration may be modified to include any number of amplifiers and A/D converters in order to accommodate circuits having more power strips and/or calibration strips. 
     Referring to FIG. 8, shown is a flowchart of a method for measuring the power of a circuit on a PCB according to an embodiment of the present invention. Processing starts at step  8 - 1  and proceeds immediately to step  8 - 2 . At step  8 - 2 , a copper strip of known width, thickness and length and having vias, is placed between the voltage source and a power plane on a PCB during manufacturing of the PCB. Such a strip is shown and described above with reference to FIG.  3 . 
     Next at step  8 - 3 , the voltage drop across the power strip is measured, such as by a circuit connected to the strip at the vias. Such a circuit has already been described above with reference to FIGS. 2-7. 
     At step  8 - 4 , once the voltage drop has been measured, the power can be calculated based on the length, width, thickness, voltage across the vias, temperature of the board, resistivity of the strip, and temperature coefficient of the strip. Such a circuit has already been described above and could include a differencing circuit, operational amplifiers, A/D converters, a power calculation circuit, and a CPU. Processing terminates at step  8 - 5 . 
     Referring to FIG. 9, shown is a flowchart of a method for measuring the power of a circuit on a PCB according to another embodiment of the present invention. Processing starts at step  9 - 1  and proceeds immediately to step  9 - 2 . At step  9 - 2 , a copper strip of known width and length and having vias, is disposed between the voltage source and a power plane feeding a circuit to have its power measured, on a PCB during manufacturing of the PCB; i.e., the power strip may be added during the circuit design process before manufacturing of the PCB. In this way, the strip is part of the PCB. Such a strip is shown and described above with reference to FIG.  3 . 
     Next at step  9 - 3 , a separate calibration strip is disposed in close proximity (e.g., adjacent) to the power strip. Similar to the previous step, the calibration strip can be preferably disposed during the manufacturing of the PCB. This calibration strip is given a power source having a known current, and can be the calibration strip already defined above with reference to FIGS. 4 and 5. Then at step  9 - 4 , after manufacturing and during testing, a voltage drop V 1  across the vias of the power strip and a voltage drop V 2  across the vias of the calibration strip is measured. Measurement of the V 1  and V 2  can be done by conventional means or by the onboard circuitry described above with reference to FIGS. 2-7. Once V 1  and V 2  are known, the resistance of the power strip is determined at step  9 - 5 , and from the resistance, the power of the circuit is calculated at step  9 - 6 . The calculations can be performed via a CPU or a power determination circuit as shown and described with reference to FIGS. 2-7 above. Processing terminates at step  9 - 7 . 
     Referring to FIG. 10, shown is a flowchart of a method for determining the thickness of a power strip of a circuit on a PCB according to another embodiment of the present invention. Processing starts at step  10 - 1  and proceeds immediately to step  10 - 2 . At step  10 - 2 , a copper strip (power strip) of known width and length and having vias, is disposed between the voltage source and a power plane feeding a circuit to have its power measured, on a PCB during manufacturing of the PCB; i.e., the power strip may be added during the circuit design process before manufacturing of the PCB instead of being placed upon the PCB after it is manufactured. In this way, the strip embedded into the PCB. Such a power strip is shown and described above with reference to FIG.  3 . 
     Next at step  10 - 3 , a separate calibration strip is disposed in close proximity (e.g., adjacent) to the power strip. Similar to the previous step, the calibration strip can be preferably disposed during the manufacturing of the PCB. This calibration strip is given a power source having a known current, and can be the calibration strip already defined above with reference to FIGS. 4 and 5. Then at step  10 - 4 , after manufacturing and during testing, a voltage drop V 1  across the vias of the power strip and a voltage drop V 2  across the vias of the calibration strip is measured. Measurement of the V 1  and V 2  can be done by conventional methods or by the onboard circuitry described above with reference to FIGS. 2-7. Once V 1  and V 2  are known, the resistance of the calibration strip is determined at step  10 - 5 . 
     At step  10 - 6 , the temperature of the calibration strip is determined or set. As already described above, the temperature may be controlled via a device such as a heater, fan, or thermal stream, or may be measured using a sensor. Then, given the resistance of the calibration strip calculated at step  10 - 5 , and the and the temperature determined or set at step  10 - 6 , the thickness of the calibration strip is calculated at step  10 - 7 . The calculation can be performed via a CPU or a power determination circuit as shown and described with reference to FIGS. 2-7 above. Processing terminates at step  10 - 7 . 
     The thickness of the power strip may be assumed to be the same as the thickness of the calibration strip. Or alternatively, the resistance of the power strip may be calculated, and the thickness can then be calculated based on the temperature and the resistance of the power strip. As already described above, the thickness and temperature of the calibration strip should be an extremely accurate indicator of the temperature and thickness of the power strip. 
     Moreover, if the thickness of the calibration strip is known, then the temperature of the board or of the calibration can be calculated given the resistance and the thickness. 
     Thus, having fully described the invention by way of example with reference to the attached drawing figures, it will readily be appreciated that many changes and modifications may be made to the invention and to the embodiments disclosed without departing from the scope and spirit of the invention as defined by the appended claims. For example, the power strip and the calibration strip can be of any known conductor, semiconductor, or other suitable material. Also, if the temperature of an entire PCB at power is constant, then only one calibration strip is needed for making calculations for all circuits across the entire board (however, at least one power strip per circuit is still needed).