PATENT DOCUMENT

Publication Number: US-12135592-B2
Application Number: US-202318473567-A
Country: US
Kind Code: B2

Title: Printed circuits with embedded resistive thermal devices

Abstract:
An electronic device may include a printed circuit with a surface-mounted component. The component may produce resistive heating within the printed circuit. Resistive thermal devices (RTDs) may be embedded within the printed circuit. An RTD may at least partially overlap the electrical component. The RTD may include contact pads on a flexible substrate and a meandering conductive trace between the contact pads. The trace may have a resistance varying linearly as a function of temperature. A data acquisition system (DAQ) may measure the resistance of the RTD. Control circuitry may identify the temperature of the printed circuit based on the resistance of the RTD measured by the DAQ and may reduce power consumption by the component when the temperature exceeds a threshold. This may serve to prevent overheating in the printed circuit over time, thereby maximizing the operating life of the printed circuit.

Claims:
What is claimed is: 
     
       1. An electronic device comprising:
 a first substrate layer; 
 a second substrate layer on the first substrate layer; 
 an electrical component surface-mounted to the first substrate layer; and 
 a resistive thermal device (RTD) that is disposed between the first substrate layer and the second substrate layer and that at least partially overlaps the electrical component. 
 
     
     
       2. The electronic device of  claim 1 , wherein the RTD comprises:
 a flexible printed circuit substrate layered between the first substrate layer and the second substrate layer; and 
 conductive traces on the flexible printed circuit. 
 
     
     
       3. The electronic device of  claim 2 , wherein the conductive traces have one or more bends. 
     
     
       4. The electronic device of  claim 1 , wherein an entirety of the RTD overlaps the electrical component. 
     
     
       5. The electronic device of  claim 1 , further comprising:
 a printed circuit board that includes the first substrate layer and the second substrate layer. 
 
     
     
       6. The electronic device of  claim 1 , wherein the RTD is configured to measure a temperature. 
     
     
       7. The electronic device of  claim 6 , wherein the electrical component is adjusted based on the temperature. 
     
     
       8. An electronic device comprising:
 a printed circuit board; 
 an electrical component surface-mounted to the printed circuit board; and 
 a resistive thermal device (RTD) that is laminated within the printed circuit board. 
 
     
     
       9. The electronic device of  claim 8 , wherein the RTD is configured to measure heat produced by the electrical component. 
     
     
       10. The electronic device of  claim 8 , wherein the RTD at least partially overlaps the electrical component. 
     
     
       11. The electronic device of  claim 8 , wherein the electrical component is adjustable based on a temperature measured using the RTD. 
     
     
       12. The electronic device of  claim 8 , wherein the RTD comprises conductive traces on a flexible printed circuit that is different from the printed circuit board. 
     
     
       13. The electronic device of  claim 8 , wherein the printed circuit board is a rigid printed circuit board. 
     
     
       14. The electronic device of  claim 8 , wherein the RTD comprises meandering conductive traces. 
     
     
       15. A printed circuit board configured to receive a surface-mounted electrical component, the printed circuit board comprising:
 stacked layers; 
 a first contact pad and a second contact pad embedded within the stacked layers; and 
 a meandering conductive trace embedded within the stacked layers and extending from the first contact pad to the second contact pad, the meandering conductive trace having a resistance that varies linearly as a function of temperature across a range of operating temperatures associated with the surface-mounted electrical component. 
 
     
     
       16. The printed circuit board of  claim 15 , wherein the stacked layers are rigid. 
     
     
       17. The printed circuit board of  claim 15 , wherein the meandering conductive trace at least partially overlaps the surface-mounted electrical component. 
     
     
       18. The printed circuit board of  claim 17 , wherein an entirety of the meandering conductive trace overlaps the surface-mounted electrical component. 
     
     
       19. The printed circuit board of  claim 15 , further comprising:
 a flexible printed circuit substrate embedded in the stacked layers, the meandering conductive trace being disposed on the flexible printed circuit substrate. 
 
     
     
       20. The printed circuit board of  claim 15 , further comprising a resistive thermal device (RTD) that includes the meandering conductive trace, the first contact pad, and the second contact pad.

Description:
This application is a continuation of U.S. patent application Ser. No. 17/224,891, filed Apr. 7, 2021, which is hereby incorporated by reference herein in its entirety. 
    
    
     FIELD 
     This disclosure relates generally to electronic devices and, more particularly, to electronic devices with temperature sensors. 
     BACKGROUND 
     Electronic devices such as cellular telephones, computers, and other electronic devices contain integrated circuits and other electrical components. Components such as these may be mounted on printed circuits. During operation, the components draw current/power that increases the temperature at one or more locations within the electronic device. If care is not taken, the printed circuits, components, and/or other portions of the electronic device can be subjected to overheating. 
     SUMMARY 
     An electronic device may include a printed circuit and an electrical component mounted to a surface of the printed circuit. The electrical component may transmit and/or receive signals via the printed circuit. Each electrical component is powered using power and ground connections. The power and ground connections typically draw a large amount of current that produces resistive heating within the printed circuit. In order to measure resistive heating within the printed circuit, one or more resistive thermal devices (RTDs) may be embedded within the printed circuit. RTDs may additionally or alternatively be adhered to an exterior surface of the printed circuit. The RTDs may be located at resistive heating hotspots on the printed circuit. An RTD may, for example, at least partially overlap the electrical component. 
     The RTD may include first and second contact pads on a flexible substrate. The RTD may include a meandering conductive trace extending from the first contact pad to the second contact pad. The meandering conductive trace may be formed from a material having a resistance that varies linearly as a function of temperature across the operating temperatures of the printed circuit. The material can include nickel, nickel-iron, or platinum, as examples. The flexible substrate may have a very narrow thickness, such as a thickness less than or equal to 50 microns. This may allow the RTD to be embedded within the printed circuit. Conductive vias may be used to couple the contact pads to a data acquisition system (DAQ) that is mounted to the printed circuit or disposed elsewhere in the device. 
     The DAQ may include power supply terminals and reference resistors for a bridge circuit that includes the RTD. The DAQ may measure the resistance of the RTD. One or more processors may identify the temperature of the printed circuit at the location of the RTD based on the resistance of the RTD measured by the DAQ. The one or more processors may reduce activity or power consumption by the electrical component when the temperature exceeds a threshold temperature. In this way, the one or more processors can monitor points on the printed circuit most prone to resistive heating (e.g., locations within the interior of the printed circuit)—points which are otherwise inaccessible to surface-mount temperature sensors. This may serve to prevent overheating in the printed circuit over time, thereby maximizing the operating life of the printed circuit. 
     An aspect of the disclosure provides an electronic device. The electronic device can include a printed circuit having a surface. The electronic device can include an electrical component mounted to the surface of the printed circuit. The electronic device can include a resistive thermal device (RTD) embedded within the printed circuit. The electronic device can include one or more processors. The one or more processors can be configured to measure a resistance of the RTD. The one or more processors can identify a temperature of the printed circuit based on the measured resistance of the RTD. 
     An aspect of the disclosure provides a method of operating an electronic device having a printed circuit, a resistive thermal device (RTD) embedded within the printed circuit, a data acquisition system (DAQ) coupled to the RTD over conductive vias in the printed circuit, an electrical component mounted to the printed circuit, and one or more processors. The method can include, with the DAQ, measuring a resistance of the RTD. The method can include, with the one or more processors, identifying a temperature within the printed circuit based on the resistance of the RTD measured by the DAQ. The method can include, with the one or more processors, reducing power consumption by the electrical component when the identified temperature exceeds a threshold temperature. 
     An aspect of the disclosure provides a printed circuit having a range of operating temperatures. The printed circuit can be configured to receive a surface-mount electrical component that produces resistive heating in the printed circuit. The printed circuit can include stacked dielectric layers. The printed circuit can include stacked metal layers interleaved with the stacked dielectric layers. The printed circuit can include a substrate having a thickness less than 50 microns. The printed circuit can include a first contact pad and a second contact pad on the substrate. The printed circuit can include a conductive trace on the substrate that extends from the first contact pad to the second contact pad. The conductive trace can have a resistance that varies linearly as a function of temperature across the range of operating temperatures of the printed circuit. The conductive trace can have a length that configures the conductive trace to exhibit a nominal resistance at a predetermined temperature. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a functional block diagram of an illustrative electronic device having a temperature sensor with a resistive thermal device (RTD) in accordance with some embodiments. 
         FIG.  2    is a circuit diagram of an illustrative temperature sensor having a bridge circuit that includes an RTD for measuring temperature in accordance with some embodiments. 
         FIG.  3    is a plot of resistance as a function of temperature for an illustrative RTD in accordance with some embodiments. 
         FIG.  4    is a cross-sectional side view of an illustrative electronic device having a printed circuit and electrical components mounted to the printed circuit in accordance with some embodiments. 
         FIG.  5    is a perspective view of an illustrative electronic device having a printed circuit that extends between first and second housing portions in accordance with some embodiments. 
         FIG.  6    is a top view of an illustrative RTD having a meandering conductive trace extending between contact pads on an underlying substrate in accordance with some embodiments. 
         FIG.  7    is a cross-sectional side view of an illustrative printed circuit having one or more RTDs on and/or within the printed circuit in accordance with some embodiments. 
         FIG.  8    is a cross-sectional side view showing how an illustrative RTD may be laminated within the layers of a printed circuit in accordance with some embodiments. 
         FIG.  9    is a flow chart of illustrative operations involved in measuring temperature using an RTD on a printed circuit in accordance with some embodiments. 
         FIG.  10    is a plot of temperature error for temperature values measured by an illustrative RTD on a printed circuit as a function of mechanical microstrain on the printed circuit in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     An illustrative electronic device of the type that may be provided with a printed circuit board having a resistive thermal device (RTD) is shown in  FIG.  1   . Electronic device  10  of  FIG.  1    may be a computing device such as a laptop computer, a desktop computer, a computer monitor containing an embedded computer, a tablet computer, a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wristwatch device, a pendant device, a headphone or earpiece device, a device embedded in eyeglasses or other equipment worn on a user&#39;s head, or other wearable or miniature device, a television, a computer display that does not contain an embedded computer, a gaming device, a navigation device, an embedded system such as a system in which electronic equipment with a display is mounted in a kiosk or automobile, a wireless internet-connected voice-controlled speaker, a home entertainment device, a remote control device, a gaming controller, a peripheral user input device (e.g., a wireless track pad, wireless mouse, wireless keyboard, a peripheral device that combines two or more of these functions, etc.), a wireless base station or access point, equipment that implements the functionality of two or more of these devices, or other electronic equipment. 
     As shown in the functional block diagram of  FIG.  1   , device  10  may include components located on or within an electronic device housing such as housing  12 . Housing  12 , which may sometimes be referred to as a case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, metal alloys, etc.), other suitable materials, or a combination of these materials. In some situations, parts or all of housing  12  may be formed from dielectric or other low-conductivity material (e.g., glass, ceramic, plastic, sapphire, etc.). In other situations, housing  12  or at least some of the structures that make up housing  12  may be formed from metal elements. 
     Device  10  may include control circuitry  14 . Control circuitry  14  may include storage such as storage circuitry  16 . Storage circuitry  16  may include hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid-state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Storage circuitry  16  may include storage that is integrated within device  10  and/or removable storage media. 
     Control circuitry  14  may include processing circuitry such as processing circuitry  18 . Processing circuitry  18  may be used to control the operation of device  10 . Processing circuitry  18  may include on one or more microprocessors, microcontrollers, digital signal processors, host processors, baseband processor integrated circuits, application specific integrated circuits, central processing units (CPUs), etc. Control circuitry  14  may be configured to perform operations in device  10  using hardware (e.g., dedicated hardware or circuitry), firmware, and/or software. Software code for performing operations in device  10  may be stored on storage circuitry  16  (e.g., storage circuitry  16  may include non-transitory (tangible) computer readable storage media that stores the software code). The software code may sometimes be referred to as program instructions, software, data, instructions, or code. Software code stored on storage circuitry  16  may be executed by processing circuitry  18 . 
     Control circuitry  14  may be used to run software on device  10  such as satellite navigation applications, internet browsing applications, voice-over-internet-protocol (VOIP) telephone call applications, email applications, media playback applications, operating system functions, etc. To support interactions with external equipment, control circuitry  14  may be used in implementing communications protocols. Communications protocols that may be implemented using control circuitry  14  include internet protocols, wireless local area network (WLAN) protocols (e.g., IEEE 802.11 protocols—sometimes referred to as Wi-Fi®), protocols for other short-range wireless communications links such as the Bluetooth® protocol or other wireless personal area network (WPAN) protocols, IEEE 802.11 ad protocols (e.g., ultra-wideband protocols), cellular telephone protocols (e.g., 3G protocols, 4G (LTE) protocols, 5G protocols, etc.), antenna diversity protocols, satellite navigation system protocols (e.g., global positioning system (GPS) protocols, global navigation satellite system (GLONASS) protocols, etc.), antenna-based spatial ranging protocols (e.g., radio detection and ranging (RADAR) protocols or other desired range detection protocols for signals conveyed at millimeter and centimeter wave frequencies), or any other desired communications protocols. Each communications protocol may be associated with a corresponding radio access technology (RAT) that specifies the physical connection methodology used in implementing the protocol. 
     Input-output circuitry in device  10  such as input-output devices  20  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Input-output devices  20  may include buttons, joysticks, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, tone generators, vibrators, cameras, sensors, light-emitting diodes and other status indicators, data ports, etc. A user can control the operation of device  10  by supplying commands through input-output devices  20  and may receive status information and other output from device  10  using the output resources of input-output devices  20 . In some configurations, keyboards, headphones, displays, pointing devices such as trackpads, mice, and joysticks, and other input-output devices may be coupled to device  10  using wired or wireless connections (e.g., some of input-output devices  20  may be peripherals that are coupled to a main processing unit or other portion of device  10  via a wired or wireless link). 
     Input-output devices  20  may include one or more displays such as display  22 . Display  22  may be a touch screen display that includes a touch sensor for gathering touch input from a user or display  22  may be insensitive to touch. A touch sensor for display  22  may be based on an array of capacitive touch sensor electrodes, acoustic touch sensor structures, resistive touch components, force-based touch sensor structures, a light-based touch sensor, or other suitable touch sensor arrangements. 
     Input-output devices  20  may also include sensors  24 . Sensors  24  may include one or more strain gauge sensors  28  and other sensors such as proximity sensors, ambient light sensors, touch sensors, force sensors, temperature sensors, pressure sensors, magnetic sensors, and other sensors. Strain gauge sensors  28  may include sensors mounted on the surfaces of a printed circuit board and/or embedded within a printed circuit board. In order to measure the temperature at one or more points on and/or within device  10 , sensors  24  may include one or more temperature sensors such as temperature sensor  26 . 
     If desired, the input-output circuitry in device  10  may also include wireless circuitry  34  to support wireless communications and/or radio-based spatial ranging operations. Wireless circuitry  34  may include one or more antennas  36 . Wireless circuitry  34  may also include baseband processor circuitry, transceiver circuitry, amplifier circuitry, filter circuitry, switching circuitry, analog-to-digital converter (ADC) circuitry, digital-to-analog converter (DAC) circuitry, radio-frequency transmission lines, and/or any other circuitry for transmitting and/or receiving radio-frequency signals using antennas  36 . 
     Wireless circuitry  34  may use antenna(s)  36  to perform wireless communications within corresponding frequency bands at radio frequencies (sometimes referred to herein as a communications band or simply as a “band”). The frequency bands handled by wireless circuitry  34  may include wireless local area network (WLAN) frequency bands (e.g., Wi-Fi® (IEEE 802.11) or other WLAN communications bands) such as a 2.4 GHz WLAN band (e.g., from 2400 to 2480 MHz), a 5 GHz WLAN band (e.g., from 5180 to 5825 MHz), a Wi-Fi® 6E band (e.g., from 5925-7125 MHz), and/or other Wi-Fi® bands (e.g., from 1875-5160 MHz), wireless personal area network (WPAN) frequency bands such as the 2.4 GHz Bluetooth® band or other WPAN communications bands, cellular telephone frequency bands (e.g., bands from about 600 MHz to about 5 GHz, 3G bands, 4G LTE bands, 5G New Radio Frequency Range 1 (FR1) bands below 10 GHz, 5G New Radio Frequency Range 2 (FR2) bands between 20 and 60 GHz, etc.), other centimeter or millimeter wave frequency bands between 10-300 GHz, near-field communications frequency bands (e.g., at 13.56 MHz), satellite navigation frequency bands (e.g., a GPS band from 1565 to 1610 MHz, a Global Navigation Satellite System (GLONASS) band, a BeiDou Navigation Satellite System (BDS) band, etc.), ultra-wideband (UWB) frequency bands that operate under the IEEE 802.15.4 protocol and/or other ultra-wideband communications protocols, communications bands under the family of 3GPP wireless communications standards, communications bands under the IEEE 802.XX family of standards, and/or any other desired frequency bands of interest. 
     Control circuitry  14  may be used to run software on device  10  such as operating system code and applications. During operation of device  10 , the software running on control circuitry  14  may be used in gathering temperature sensor data (e.g., temperature measurements) from temperature sensor(s)  26  and in gathering strain gauge data from strain gauge(s)  28 . Strain gauge data may be analyzed during failure analysis (e.g., to help designers improve the design of a device and the printed circuits and other components within the device), may be monitored in real time to issue alerts and provide other information to a user or others, and/or may be used to take other suitable action in device  10 . 
     Some or all of control circuitry  14  (e.g., one or more CPUs, a system-on-chip (SOC), etc.), wireless circuitry  34 , input-output devices  20 , and/or other electrical components in device  10  may be mounted to substrates such as one or more printed circuits. The printed circuits may include rigid printed circuit boards and flexible printed circuits. These electrical components are powered and draw current during use (e.g., the electrical components have power and ground connections that draw relatively high amounts of current). Power density and current density can change rapidly depending on the size of the load. Current drawn by electrical components such as a CPU or SOC is higher when performing intensive calculations and lower when performing less-intensive activities. The rate of change of the current from low to high leads to increased resistive (Ohmic) heating on the printed circuit and within device  10 , thereby increasing the temperature of the printed circuit and the interior of device  10 . 
     Temperature detection within device  10  is important to preventative reliability in device  10 . Sensing temperature may allow for the electrical components (e.g., control circuitry  14 ) to throttle the load, thus decreasing the current drawn to limit the resistive heat generated in device  10 . If the temperature within device  10  is not known, the printed circuit may be subjected to overheating. The lifespan of the printed circuit may be decreased by cycles of heating/overheating and cooling, which can have long term effects on the materials in the stack up of the printed circuit. 
     The printed circuit generally includes multiple stacked dielectric layers interspersed with metallization layers. Resistive heating may be particularly pronounced at certain points within the printed circuit (e.g., at the dielectric or metallization layers near the center of the printed circuit stack up, beneath the power/ground connections of highly active components, etc.). In some scenarios, temperature sensor  26  is soldered to a surface of the printed circuit using surface-mount technology (SMT) (e.g., as an SMT temperature sensor). While SMT temperature sensors may measure the temperature at a surface of the printed circuit, SMT temperature sensors are typically unable to measure temperature at points within the interior of the printed circuit where resistive heating is most pronounced. In addition, SMT temperature sensors are bulky and are generally unable to be placed at pin-point areas around critical electrical components on the printed circuit (e.g., voltage regulators, processors, memory, etc.) where power density and thus resistive heat is highest. In some scenarios, the temperature sensor may be adhered or glued to the surface of the printed circuit after the SMT process using tape or glue. However, this typically requires either unused board area or relatively long distances between the temperature sensor and the point of interest, and may undesirably change position in heated environments. In order to mitigate these issues to allow for precise temperature measurements within the printed circuit while mitigating the printed circuit area used for measuring temperature, temperature sensor  26  may include one or more resistive thermal devices such as resistive thermal device (RTD)  30 . RTD  30  may be embedded within the layers of the printed circuit and/or placed at a surface of the printed circuit. RTD  30  may sometimes also be referred to as a resistive temperature device, resistive thermal detector, resistive temperature detector, resistance thermal device, resistance temperature device, resistance thermal detector, resistance temperature detector, resistive thermometer, or resistance thermometer. 
     RTD  30  may include a conductive material (e.g., a conductive trace, metal foil, etc.) on an underlying substrate. The temperature coefficient of resistance (TCR) of the conductive material, denoted by the Greek letter α in units of Ohms/Ohms*° C., is defined by the equation α=[R 100 −R 0 ]/[100−R 0 ], where R 100  is the resistance of the conductive material at 100° C. and R 0  is the resistance of the conductive material at 0° C. The conductive material in RTD  30  may exhibit a linear TCR (a) as a function of temperature over the expected temperature range of operation for the printed circuit (e.g., from −50° C. to 150° C. or other temperature ranges). Examples of such conductive materials that may be used to form RTD  30  include metals such as Nickel (Ni) or platinum (Pt) and alloys such as Nickel-Iron (Ni—Fe). RTD  30  may occupy a very small amount of space on the printed circuit. For example, RTD  30  may be thin enough to be placed between the layers of the printed circuit with nearly infinite lateral placement flexibility within the printed circuit. RTD  30  may be manufacturing using a silicon die wafer packaging manufacturing process or using any other desired processes. 
     In general, the resistance of RTD  30  changes as a function of temperature. Temperature sensor  26  may include a data acquisition system (DAQ)  32  coupled to RTD  30 . DAQ  32  may measure temperature on the printed circuit by measuring the resistance of RTD  30 . DAQ  32  may include one or more amplifiers, differential amplifiers, bridge circuit components (e.g., reference resistors), comparators, digital logic, analog circuitry, analog-to-digital converters (ADCs), power supply voltage sources, switching circuits, and/or any other desired components for measuring the resistance of RTD  30  and thus the temperature of the printed circuit. Temperature sensor  26  may include any desired number of RTDs  30  on one or more printed circuits in device  10 . Using multiple RTDs  30  may allow temperature sensor  26  to measure and track the temperature of multiple points within the printed circuit (e.g., the points on the printed circuit most subject to resistive heating). The resistance of each RTD  30  may be measured by the same DAQ  32  or each RTD  30  may be read by a respective DAQ  32 . If desired, DAQ  32  may also be used to gather strain gauge data using strain gauge(s)  28 . 
     The example of  FIG.  1    is merely illustrative. While control circuitry  14  is shown separately from temperature sensor  26  in the example of  FIG.  1    for the sake of clarity, DAQ  32  may include processing circuitry that forms a part of processing circuitry  18  (e.g., DAQ  32  may include one or more processors) and/or storage circuitry that forms a part of storage circuitry  16  (e.g., portions of control circuitry  14  may be implemented on DAQ  32 ). While temperature sensor  26  is shown separate from display  22  and wireless circuitry  34  for the sake of clarity, RTD  30  may form a part of display  22  and/or a part of wireless circuitry  34 . For example, RTD  30  may be formed on a printed circuit that feeds display signals to display  22  (e.g., a display flex) or that otherwise forms a part of display  22 . As another example, RTD  30  may be formed on a printed circuit in a radio-frequency front end (RFFE) module of wireless circuitry  34 , on a printed circuit used to support a transceiver and/or baseband processor in wireless circuitry  34 , on a printed circuit that is used to form one or more radio-frequency transmission lines for wireless circuitry  34 , on a printed circuit that is used to support one or more antennas  36 , etc. Wireless circuitry  34  and/or display  22  may be omitted if desired. 
       FIG.  2    is a circuit diagram of illustrative temperature sensor circuitry having RTD  30  on a printed circuit. Temperature sensor  26  may include a bridge circuit (e.g., a Wheatstone bridge) such as bridge circuit  40 . Bridge circuit  40  may include reference resistors  44  and RTD  30 . Reference resistors  44  may each have a known resistance R (e.g., each reference resistor  44  may have the same resistance or two or more of the reference resistors may have different resistances). RTD  30  has a resistance RV that varies as a function of temperature (e.g., linearly over the operating temperatures of the printed circuit) and therefore serves as a temperature sensing element. The illustrative bridge circuitry of  FIG.  2    includes one RTD  30  and three reference resistors  44 , but configurations with two RTDs  30  and two reference resistors  44  or other combinations of reference resistors  44  and RTDs  30  may be used, if desired. 
     Power supply terminals VP and VN may respectively apply a positive power supply voltage and a ground power supply voltage to bridge circuit  40 . Temperature sensor  26  may include measurement circuitry  42 . Measurement circuitry  42  may be used to measure voltages at measurement nodes N1 and N2 of bridge circuit  74 . Measurement circuitry  42  may include a differential amplifier having inputs coupled to nodes N1 and N2 and having an output coupled to an analog-to-digital converter, as one example. Measurement circuitry  42  may measure the resistance RV of RTD  30 , which changes based on the temperature of the printed circuit at the location of the RTD. Measurement circuitry  42  may store the measured resistance RV for later processing if desired. Measurement circuitry  42  may also convert the measured resistance RV to a corresponding temperature (e.g., the temperature under which RTD  30  exhibits that measured resistance RV) and may store the temperature for later processing. Measurement circuitry  42  may determine/generate the temperature using the Callendar-Van Dusen equations or by comparing the measured resistance to stored data mapping resistance RV to temperature (e.g., for the corresponding conductive material in RTD  30 ). Measurement circuitry  42 , power supply terminals VP and VN, and reference resistors  44  may all form part of DAQ  32 . The components of DAQ  32  may be formed from components mounted to the surface of the printed circuit (e.g., the printed circuit on which RTD  30  is formed) and/or may be formed on other substrates or printed circuits that are separate from the printed circuit that includes RTD  30 . 
       FIG.  3    includes a curve  50  that plots resistance as a function of temperature for the conductive material used to form RTD  30 . As shown by curve  50 , the resistance of RTD  30  is linear between temperatures T1 and T2. Temperatures T1 and T2 may define the operating temperatures of the printed circuit on which RTD  30  is located. Temperatures T1 and T2 may be, for example, −50° C. and 150° C., respectively. While curve  50  and the TCR of RTD  30  is described herein as being linear, curve  50  and the TCR may be substantially linear if desired (e.g., the slope of curve  50  may be constant or may vary by a small amount such as around 1% or less between temperatures T1 and T2). Conductive materials such as Ni, Ni—Fe, and Pt may exhibit a resistance characterized by curve  50 , as examples. These examples are merely illustrative and, in general, any desired conductive material having a resistance characterized by a linear curve between temperatures T1 and T2 such as curve  50  may be used to form RTD  30 . 
       FIG.  4    is a cross-sectional side view showing how a printed circuit may be mounted within device  4 . As shown in  FIG.  4   , device  10  may have a housing such as housing  12  in which electrical components  66  are mounted. Electrical components  66  may include integrated circuits (chips), integrated circuit packages or other packages, SOCs, voltage regulators, processors, memory, connectors, sensors, input-output devices, some or all of control circuitry  14  of  FIG.  1   , some or all of wireless circuitry  34  of  FIG.  1   , and/or other circuitry. Components  66  may be mounted to one or more substrates such as printed circuit  64 . Printed circuit  64  may be a rigid printed circuit board formed from fiberglass-filled epoxy, ceramic, or other rigid printed circuit board substrate material or may be a flexible printed circuit formed from a flexible layer of polyimide or flexible sheets of other polymer material. 
     Components  66  may be mounted to lateral surface  70  of printed circuit  64  (e.g., at the exterior of printed circuit  64 ). Components  66  may, for example, be mounted to lateral surface  70  using conductive interconnect structures  68 . Conductive interconnect structures  68  may include solder balls (e.g., components  66  may be SMT components), a ball grid array (BGA), conductive pins, conductive clips, radio-frequency connectors, and/or using any other desired conductive interconnect structures for coupling components  66  to lateral surface  70 . Conductive interconnect structures  68  may be coupled to contact pads on lateral surface  70  of printed circuit  64 . Conductive interconnect structures  68  may be used to route data signals, radio-frequency signals, reference signals, power supply voltages, control signals, baseband signals, intermediate frequency signals, and/or any other desired signals between component  66  and other components  66  on printed circuit  64  or external to printed circuit  64  (e.g., over metallization layers and/or conductive vias in printed circuit  64 ). 
     Display  22  may include display layers  62  (e.g., liquid crystal display layers, an organic light-emitting diode display, an electrophoretic display, etc.). Display layers  62  may sometimes be referred to herein as display module  62 . Display layers  62  may be mounted under display cover layer  60 . Display cover layer  60  may be mounted to housing  12  and may be formed from a layer of glass, transparent plastic, sapphire or other transparent crystalline material, etc. If desired, printed circuit  64  may be a flexible printed circuit coupled to display layers  62  (e.g., a display flex that conveys display signals to display layers  62  to produce display light that is emitted through display cover layer  60 ). If desired, a flexible printed circuit (e.g., a display flex) may couple display layers  62  to printed circuit  64  (e.g., printed circuit  64  may be a main logic board for device  10  or may include display driver circuitry used to drive display layers  62  through the display flex). 
     During device operation, components  66  draw current and power that produces resistive heating at printed circuit  64 . RTDs such as RTD  30  ( FIGS.  1  and  2   ) may be mounted at one or more locations on lateral surface  70  and/or within the layers of printed circuit  64 . The RTDs may be mounted at locations overlapping and/or adjacent to a corresponding component  66  to provide accurate measurements of the temperature of printed circuit  64  at locations where resistive heating is the highest. This may allow the control circuitry to accurately measure and track temperature in printed circuit  64  so that device operations can be selectively throttled when necessary to maximize the operating life and reliability of printed circuit  64 . 
     The example of  FIG.  4    is merely illustrative. Housing  12  may have other shapes. Display  22  may be omitted. If desired, printed circuit  64  may extend between multiple portions of housing  12 , such as in embodiments where device  10  is a laptop computer.  FIG.  5    is a perspective view of device  10  in configurations where device  10  is a laptop computer. As shown in  FIG.  5   , device  10  may have an upper housing portion (lid)  12 A and a lower housing portion (base)  12 B. Input-output devices  82  (e.g., a keyboard, trackpad, other buttons, etc.) may be disposed on lower housing portion  12 B. A battery or other power supply circuitry may be also be disposed within lower housing portion  12 B. Display  22  may be disposed on upper housing portion  12 A. If desired, one or more sensors such as camera  80  may be disposed on upper housing portion  12 A. Camera  80  may be a user-facing camera (e.g., webcam), as one example. Upper housing portion  12 A may rotate with respect to lower housing portion  12 B about a hinge axis or clutch barrel. 
     As shown in  FIG.  5   , printed circuit  64  may extend from the interior of lower housing portion  12 B to the interior of upper housing portion  12 A (e.g., across the hinge axis or clutch barrel). In this example, printed circuit  64  may be a display flex used to drive display  22 , may be a speaker flex used to drive speakers in upper housing portion  12 A, may be a camera flex used to mount camera  80  or any other sensors in upper housing portion  12 A (e.g., camera  80  may be mounted to printed circuit  64 ), may be an antenna flex used to convey radio-frequency signals between upper housing portion  12 A and lower housing portion  12 B, or may convey any other desired signals between upper housing portion  12 A and lower housing portion  12 B. If desired, one or more RTDs  30  may be disposed at one or more locations on or within printed circuit  64  within upper housing portion  12 A (e.g., to measure the temperature of the printed circuit when subjected to heating by display  22 ) and/or within lower housing portion  12 B (e.g., to measure the temperature of the printed circuit when subjected to heating by the battery or other components in lower housing portion  12 B). These examples are merely illustrative and, in general, device  10  may have any desired form factor. 
     An illustrative RTD such as RTD  30  of  FIGS.  1  and  2    is shown in  FIG.  6   . As shown in  FIG.  6   , RTD  30  includes an elongated conductive trace  92  that extends from a first contact pad  94  to a second contact pad  96  on the lateral surface of an underlying substrate such as substrate  90 . Substrate  90  may be flexible and inert and may include polyimide or other flexible polymers. The conductive material used to form conductive trace  92  has a linear resistance as a function of temperature over the operating temperatures of the printed circuit (e.g., the conductive material may be characterized by curve  50  of  FIG.  3   ). As examples, conductive trace  92  may be formed from Ni, Ni—Fe, or Pt (e.g., conductive trace  92  may be an Ni trace, an Ni—Fe trace, or a Pt trace). RTD  30  may be fabricated using a silicon die wafer process, for example. Contact pads  94  and  96  may, for example, be copper-plated contact pads (e.g., where the copper plate serves as a stop for micro vias that are laser drilled into the printed circuit over the contact pads). 
     Conductive trace  92  may follow a meandering (e.g., serpentine) path between contact pads  94  and  96 . As such, conductive trace  92  may include a series of interconnected segments that run parallel to the Y-axis and/or X-axis of  FIG.  6   . Conductive trace  92  may include one or more bends (e.g., around axes parallel to the Z-axis). Bends in conductive trace  92  may be used to maximize the amount of conductive material per lateral area on substrate  90  and thus the length of conductive trace  92 . The length of conductive trace  92  may be selected to set the nominal resistance of RTD  30  (e.g., the resistance of RTD  30  at a predetermined temperature such as room temperature). The nominal resistance of RTD  30  may be between 200-400 Ohms, for example. 
     The example of  FIG.  6    is merely illustrative and, in general, conductive trace  92  may have any desired number of segments extending in any desired directions, may follow any desired path having any desired shape, may have any desired number of bends, and may have edges with any desired shape. The layout of conductive trace  92  (e.g., the number and configuration of bends, the density of conductive traces on substrate  90 , etc.) may be selected so that RTD  30  exhibits a desired length that configures RTD  30  to exhibit the nominal resistance. If desired, conductive trace  92  may include one or more trim features  98 . Trim features  98  may be formed by routing portions of conductive trace  92  into pocket shapes, for example. Trim features  98  may be used to help configure RTD  30  to exhibit the desired length and thus the nominal resistance. Trim features  98  may be omitted if desired. RTD  30  may also include one or more visual alignment indicators  100  on substrate  90 . Visual alignment indicator  100  may help to ensure that RTD  30  is properly aligned after lamination within a printed circuit. 
     RTD  30  may be embedded within printed circuit  64  or may be adhered to a surface of printed circuit  64  ( FIGS.  4  and  5   ). At the same time, RTD  30  forms a part of bridge circuit  40  in temperature sensor  26  ( FIG.  2   ). For example, contact pad  94  may be coupled to a reference resistor  44  and power supply terminal VP of bridge circuit  40  (e.g., reference resistor  44  and power supply terminal VP may form part of DAQ  32  and may be coupled to contact pad  94  over one or more conductive vias in the printed circuit and/or other conductive interconnect structures). Contact pad  96  may be coupled to node N2 of bridge circuit  40  (e.g., node N2 may form a part of DAQ  32  and may be coupled to contact pad  96  over one or more conductive vias in the printed circuit and/or other conductive interconnect structures). DAQ  32  may measure the resistance of conductive trace  92  across terminals such as contact pads  94  and  96 . DAQ  32  may identify the temperature at RTD  30  (e.g., the temperature within printed circuit board  64 ) from the measured resistance. 
     RTD  30  (substrate  90 ) has a lateral area (footprint) defined by a length L and a perpendicular width W. Length L may be greater than width W or may be equal to width W. RTD  30  is relatively compact in size. For example, length L and width W may each be around 0.3-3 mm. This lateral size of RTD  30  may be on the same order of magnitude as an SMT capacitor or resistor. However, at the same time, RTD  30  is 10-100 times thinner than an SMT capacitor or resistor. RTD  30  may, for example, have a thickness (e.g., as measured parallel to the Z-axis) that is approximately 20-50 microns, 35-45 microns, less than 100 microns, less than 50 microns, less than 40 microns, etc. This may allow RTD  30  to be embedded within the layers of printed circuit  64  for measuring temperature at locations within the interior of printed circuit  64 . 
     Strain gauge(s)  28  ( FIG.  1   ) may also be embedded in the printed circuit for measuring strain on the printed circuit. The strain gauge also includes a meandering conductive trace between contact pads on an underlying substrate. When the printed circuit bends in response to strain, the bending alters the length of the conductive trace and thus the resistance of the strain gauge. DAQ  32  or a separate DAQ may measure these changes in resistance and may estimate the strain on the printed circuit based on the resistance. However, the conductive trace in the strain gauge is formed from metals such as nichrome, karma, or constantan that do not exhibit a linear resistance as a function of temperature across the operating temperatures of the printed circuit. RTD  30  may also occupy less lateral area than strain gauge  28  because, for the same nominal resistance value, the conductive material used in strain gauge  28  has higher resistance per unit length and thus RTD  30  will need a longer conductive trace to achieve the nominal resistive value (e.g., RTD  30  may occupy the lateral area of as many as three strain gauges  28 ). 
       FIG.  7    is a cross-sectional side view showing how RTD  30  may be disposed on printed circuit  64 . As shown in  FIG.  7   , printed circuit  64  may include a set of stacked (laminated) dielectric layers  110 . Dielectric layers  110  may be formed from a rigid material (e.g., fiberglass, ceramic, etc.) in embodiments where printed circuit  64  is a rigid printed circuit board or may be formed from a flexible material (e.g., polyimide, flexible polymer, etc.) in embodiments where printed circuit  64  is a flexible printed circuit. 
     Printed circuit  64  may also include a set of metal layers  112  (sometimes referred to herein as metallization layers) interspersed or interleaved among the dielectric layers. Metal layers  112  may include conductive (e.g., copper) traces patterned onto the surface of corresponding dielectric layers  110 . The conductive traces in metal layers  112  may be used to route any desired signals, power supply voltages, etc. around the printed circuit. The conductive traces in metal layers  112  may also include ground traces. Conductive vias may be used to couple metal layers  112  together and/or to conductive components at the surface of printed circuit  64  through dielectric layers  110 . 
     As shown in  FIG.  7   , printed circuit  64  may have contact pads  125  on lateral surface  70  (sometimes referred to herein as exterior surface  70  because it is the lateral surface of an outer-most dielectric layer  110  in printed circuit  64 ). Component  66  may be mounted to contact pads  125  using conductive interconnect structures  68  (e.g., conductive interconnect structures  68  may include a BGA, conductive pins, or solder balls coupled and/or affixed to contact pads  125 ). Conductive interconnect structures  68 , contact pads  125 , metal layers  112 , and conductive through vias in dielectric layers  110  may be used to route signals between component  66  and other components mounted to a surface of printed circuit  64  or elsewhere in device  10 . As current from these signals pass through metal layers  112 , the current produces Ohmic (resistive) heating in printed circuit  64 . This heating may be particularly pronounced at one or more points (hotspots) within printed circuit  64  such as locations at or adjacent to component  66 , locations within the interior of printed circuit  64  and overlapping component  66 , etc. 
     In order to fully monitor the temperature of printed circuit  64 , RTDs  30  may be disposed at each of the hotspots within printed circuit  64 . For example, a first RTD  30  may be embedded within printed circuit  64  at location  118 . When at location  118 , RTD  30  may partially or completely overlap electrical component  66  (e.g., when viewed in the direction of arrow  128 ). RTD  30  may be sufficiently thin (in the Z-direction) so as to allow RTD  30  to be fully laminated within the layers of printed circuit  64  while still retaining a flat or planar profile. RTD  30  may, for example, overlap or be placed beneath SMT pin pads of a BGA having high current power and ground solder ball pins (e.g., pins that support currents as high as 5 A/pin or higher). Location  118  may be at a distance D from lateral surface  70  (e.g., a depth within the printed circuit where current density and thus resistive heating is highest). Distance D may be a few mm, a few microns, etc. Distance D may be less than, equal to, or greater than half the thickness of printed circuit  64 . Conductive through vias such as conductive vias  122  (e.g., micro vias) may couple contact pads  94  and  96  of RTD  30  ( FIG.  6   ) to DAQ  32  (e.g., conductive vias  122  may extend to lateral surface  70  or may couple RTD  30  to DAQ  32  through conductive traces in one or more metal layers  112  and additional conductive vias that extend to lateral surface  70 ). 
     In another suitable implementation, RTD  30  may be embedded at location  120  within printed circuit  64  at distance D from lateral surface  114  (e.g., the lateral surface of printed circuit  64  opposite lateral surface  70 ). Location  120  may at least partially overlap component  66 . In other words, when RTD  30  is at location  118  or location  120 , RTD  30  may partially overlap component  66  or an entirety of RTD  30  may overlap component  66  (e.g., RTD  30  may completely overlap component  66 ). This is merely illustrative and, in general, locations  118  and  120  need not overlap component  66 . Location  120  may additionally or alternatively at least partially overlap an additional component mounted to lateral surface  114 . 
     If desired, RTD  30  may be mounted to lateral surface  70  such as at location  116 . When mounted to lateral surface  70 , a layer of glue or adhesive  126  may be used to affix RTD  30  to lateral surface  70 . Printed circuit  64  may include one RTD  30  or more than one RTD  30  (e.g., dozens of RTDs, hundreds of RTDs, a few RTDs, etc.). RTDs  30  may be mounted at location  118 , location  120 , location  116 , and/or any other desired locations on/within printed circuit  64  (e.g., at each current density hotspot and/or at any other desired locations on printed circuit  64 ). Embedding RTDs  30  into printed circuit  64  in this way may allow temperature sensor  26  to measure the temperature of printed circuit  64  at high current density locations such as locations within the printed circuit. SMT temperature sensors soldered to the exterior surface of printed circuit  64  are unable to measure the temperature of printed circuit  64  at these locations. 
       FIG.  8    is a cross-sectional side view showing how RTD  30  may be laminated within the layers of printed circuit  64 . As shown in  FIG.  8   , printed circuit  64  may include dielectric layers  110  such as a first dielectric layer  110 - 1 , a second dielectric layer  110 - 2  stacked under dielectric layer  110 - 1 , and a third dielectric layer  110 - 3  stacked under dielectric layer  110 - 2 . Metal layers  112  may be patterned onto dielectric layers  110 . For example, a first metal layer  112 - 1  may be patterned onto the top surface of dielectric layer  110 - 2  (or the bottom surface of layer  110 - 1 ), a second metal layer  112 - 2  may be patterned onto the top surface of dielectric layer  110 - 3  (or the bottom surface of layer  110 - 2 ), a third metal layer  112 - 3  may be patterned onto the bottom surface of dielectric layer  110 - 3 , etc. Additional dielectric layers  110  and/or metal layers  112  may be stacked over dielectric layer  110 - 1  and/or stacked under metal layer  112 - 3 . Layers  110 - 1 ,  110 - 3 , and/or  112 - 3  may be omitted if desired. 
     RTD  30  (e.g., substrate  90  and/or conductive trace  92  of  FIG.  6   ) may be coupled to metal layer  112 - 1  using a layer of adhesive such as adhesive  130 . Dielectric layer  110 - 2 , metal layer  112 - 2 , and additional layers of printed circuit  64  (e.g., dielectric layer  110 - 3 , metal layer  112 - 3 , additional layers under metal layer  112 - 3 , etc.) may be layered under RTD  30  and metal layer  112 - 1 . Conductive via  122  may couple the contact pads on RTD  30  to metal layer  112 - 2 , to other metal layers  112  in printed circuit  64 , and/or to contact pads on an exterior surface of the printed circuit). Adhesive  130  may be a heat and/or pressure activated adhesive, for example. 
     During manufacture of printed circuit  64 , RTD  30  may be deposited onto adhesive  130  using double sided tape or other manufacturing equipment. In this example, metal layer  112 - 1 , dielectric layer  110 - 1 , and the metal layers  112  and dielectric layers  110  stacked over dielectric layer  110 - 1  may form a multilayer core of printed circuit  64 . Dielectric layer  110 - 2  and any dielectric or metal layers under dielectric layer  110 - 2  are then laminated under RTD  30  and metal layer  112 - 1 . A heat press may be used to activate adhesive  130  and to adhere each of the layers together, for example. Milling equipment or other equipment may cut through vias into at least layer  110 - 2  and the through vias may be filled with conductive material to form conductive vias  122 . The silicon die wafer process used to form RTD  30  may configure RTD  30  to have a relatively thin thickness H (e.g., around 39 microns, 35-45 microns, less than 50 microns, etc.), thereby allowing RTD  30  to be embedded within printed circuit  64  in this way without requiring a cavity or recess to be cut into dielectric layer  110 - 2  to accommodate the RTD. 
       FIG.  9    is a flow chart of illustrative operations that may be performed by DAQ  32  to identify temperature on/within printed circuit  64  using RTD  30 . At operation  140 , DAQ  32  (e.g., measurement circuitry  42  of  FIG.  2   ) may measure the voltage across contact pads  94  and  96  ( FIG.  6   ) to measure the resistance RV of RTD  30  in bridge circuit  40 . The resistance RV of conductive trace  92  in RTD  30  depends on the temperature of RTD  30  (e.g., due to resistive heating within printed circuit  64  due to current drawn by component  66 ). 
     At optional operation  142 , DAQ  32  or a separate DAQ may measure strain on printed circuit  64  using one or more strain gauges  28  ( FIG.  1   ). The strain measurements may be used to identify wear and tear on printed circuit  64 , drop events or other mechanical stress events on device  10 , etc. The strain measurements may be stored (e.g., at storage circuitry  16  of  FIG.  1   ) for later processing. 
     At operation  144 , control circuitry  14  (e.g., DAQ  32 , one or more processors, other control circuitry in device  10 , etc.) may identify (e.g., determine, calculate, compute, generate, or infer) the temperature of RTD  30  and thus within printed circuit  64  based on the measured resistance RV of RTD  30 . If desired, control circuitry  14  may store predetermined tables or curves (e.g., curve  50  of  FIG.  3   ) that map the resistance of the conductive material in conducive trace  92  to temperature. For example, control circuitry  14  may identify the temperature corresponding to the measured resistance RV on curve  50  or may interpolate the temperature corresponding to resistance RV using a set of stored points on curve  50 . The temperature identified at operation  144  may sometimes be referred to herein as identified temperature, measured temperature, an identified temperature value, or a measured temperature value. 
     Additionally or alternatively, control circuitry  14  may calculate the temperature of RTD  30  using the Callendar-Van Dusen equation (e.g., using the measured resistance RV as an input to the Callendar-Van Dusen equation). In other words, control circuitry  14  may identify (e.g., generate, compute, or calculate) the temperature of RTD  30  by solving for temperature T in the Callendar-Van Dusen equation, which is shown in equation 1.
 
 RV=R 0[1+ AT+BT   2   +C ( T− 100° C.) T   3 ]  (1)
 
In equation 1, temperature T is in units of ° C., R0 is the resistance of the conductive material in conductive trace  92  at 0° C., and A, B, and C are Callendar-Van Dusen constants that are empirically derived for the given material in conductive trace  92  based on the measured resistance of the material at 0° C., 100° C., and 260° C. Calculating temperature T using the Callendar-Van Dusen equation may be more precise than performing interpolation on stored data curves, for example.
 
     In general, if care is not taken, non-zero strain applied to printed circuit  64  affects the resistance RV of RTD  30  and thus the temperatures identified by temperature sensor  26  (e.g., because the strain may cause small changes in the length of conductive trace  92 ). Similarly, different temperatures affect the resistance of strain gauge  28  and thus the strain measurements gathered using strain gauge  28  (e.g., because of thermal expansion of the conductive material in the strain gauge). At optional operation  146 , control circuitry  14  may normalize the identified temperature based on strain measured at operation  142  and/or may normalize the strain measured at operation  142  based on the temperature identified at operation  144 . 
     Control circuitry  14  may normalize the identified temperature value by applying (e.g., adding) an offset value to the identified temperature value that is based on the measured strain (e.g., as measured by a strain gauge adjacent to RTD  30  in printed circuit  64 ). If desired, the offset value may be identified using a stored curve that plots the effect of strain on temperature for conductive trace  92  (e.g., as predetermined experimentally). Control circuitry  14  may also calculate the offset value based on the measured strain (e.g., using a fourth order thermal compensation polynomial, etc.). Additionally or alternatively, control circuitry  14  may normalize the measured strain by applying (e.g., adding) an offset value to the measured strain that is based on the identified temperature value (e.g., as measured by an RTD  30  adjacent to the strain gauge in printed circuit  64 ). This offset value may also be identified using a stored curve that plots the effect of temperature on strain for conductive traces in strain gauge  38  or may be calculated as a function of the identified temperature value. 
     At operation  148 , control circuitry  14  may store the identified temperature for subsequent processing and/or may adjust device operations based on the identified temperature. For example, control circuitry  14  may track temperature over time to analyze the heating patterns within printed circuit  64 . Control circuitry  14  may reduce current/power drawn by one or more components  66  and/or by other components in device  10  (e.g., by disabling or powering off some or all of the component, reducing the number or speed of processing tasks performed by the component, terminating applications running on the component, reducing power supply voltages, disabling or reducing brightness on display  22  of  FIGS.  4  and  5   , etc.) when the identified temperature value exceeds a predetermined threshold value. This may serve to prevent overheating in device  10  and potential damage to printed circuit  64  or other components in device  10 , while also preserving battery life and maximizing the operating life of printed circuit  64  and the other components in device  10 . 
     When multiple RTDs  30  are disposed on printed circuit  64 , control circuitry  14  may also identify subsets of the printed circuit and/or subsets of the components  66  mounted to the printed circuit that are producing excessive resistive heating. Control circuitry  14  may thereby reduce current/power drawn by the identified subset of the components  66  or by other components on the identified subset of the printed circuit (e.g., without affecting operation of the other components  66  on printed circuit  64 ). If desired, switching circuitry may be used to route signals away from overheated portions of printed circuit  64  and towards portions of printed circuit  64  that are at relatively low temperatures. If desired, control circuitry  64  may monitor the identified temperature across and within printed circuit  64  over time to assess the general health of the printed circuit, components  66 , and device  10  over time. RTD  30  may allow control circuitry  14  to identify the temperature at locations within the interior of printed circuit  64  where resistive heating may be the highest. These locations are otherwise inaccessible to SMT temperature sensors. 
       FIG.  10    is a plot of temperature error for temperature values measured by RTD  30  as a function of mechanical microstrain on printed circuit  64 . The curve of  FIG.  10    may be predetermined and generated experimentally, for example. The curve of  FIG.  10    or similar data plotting temperature error as a function of mechanical microstrain may be stored on device  10  for use during temperature measurement normalization. As shown by the curve of  FIG.  10   , there may be no error or relatively little error in temperature measurements by RTD  30  when printed circuit  64  is subject to no microstrain. As non-zero microstrain is applied, the strain may produce changes in the resistance RV of RTD  30  that are unassociated with temperature, leading to the error in the temperature values identified by control circuitry  14  as shown by the curve of  FIG.  10   . The temperature error shown in  FIG.  10    may correspond to temperature offsets that are added to the temperature values identified by RTD  30 . For example, when strain gauge  38  measures a non-zero strain, control circuitry  14  may use the curve of  FIG.  10    to identify the temperature error corresponding to that measured strain. Control circuitry  14  may then normalize the measured temperature value by adding an offset to the measured temperature value that compensates for the identified temperature error. The example of  FIG.  10    is merely illustrative. The curve of  FIG.  10    may have other shapes in practice. 
     The methods and operations described above in connection with  FIGS.  1 - 9    may be performed by the components of device  10  using software, firmware, and/or hardware (e.g., dedicated circuitry or hardware). Software code for performing these operations may be stored on non-transitory computer readable storage media (e.g., tangible computer readable storage media) stored on one or more of the components of device  10  (e.g., storage circuitry  16  of  FIG.  1   ). The software code may sometimes be referred to as software, data, instructions, program instructions, or code. The non-transitory computer readable storage media may include drives, non-volatile memory such as non-volatile random-access memory (NVRAM), removable flash drives or other removable media, other types of random-access memory, etc. Software stored on the non-transitory computer readable storage media may be executed by processing circuitry on one or more of the components of device  10  (e.g., processing circuitry  18  of  FIG.  1   , etc.). The processing circuitry may include microprocessors, central processing units (CPUs), application-specific integrated circuits with processing circuitry, or other processing circuitry. 
     The foregoing is merely illustrative and various modifications can be made to the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20230925
Publication Date: 20241105
Grant Date: 20241105
Priority Date: 20210407
Inventors: MASON, ANNE M.
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F1/181", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K2201/10151", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01L1/22", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01K3/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01K7/16", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/32", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K2201/0154", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/09", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K1/111", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K1/0353", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K1/185", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K1/0268", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/0271", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K1/167", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/0201", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K2201/09263", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F1/203", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/206", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01L1/22", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01K7/18", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/206", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01K3/005", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05K2201/10151", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/0154", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/185", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K1/111", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K1/09", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K1/0353", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/32", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/181", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01L1/22", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01K7/16", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01K3/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/206", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 83509247