Device and method for isolating and detecting tin whiskers

Abstract

An apparatus for tin whisker isolation and detection includes a substrate having a plurality of pads for connection to electronic components placed on the substrate, and a shield placed on a surface of the substrate. The shield includes a plurality of cavities aligned over the plurality of pads. A plurality of sensing features, each associated with one of the plurality of cavities, are configured to sense conductive growth from a corresponding pad of the plurality of pads. The plurality of circuit connections are each configured to connect one of the sensing components to the detection circuit. The detection circuit is configured to receive one or more sensing signals from one or more of the sensing components and detect conductive growth from the corresponding pad based on the one or more sensing signals.

Description

Field of the Invention

[0001] The field of the present invention relates to electrical devices having tin-plated or soldered connections, or more specifically, to methods and apparatus for tin whisker isolation and detection. Background of the Invention

[0002] Whisker growth has been highlighted as a significant hazard and is unknown for high-reliability electronic product operation. Tin whiskers are metallic and crystalline filamentous structures that grow outwards from a metal surface and are more common in electrodeposited tin (Sn) coatings and tin-based alloys. Whiskers can take many forms, including filaments, straight, kinked, helical, nodular, and oddly shaped eruptions. Typically, whiskers have a length of 1 nanometer to 500 nanometers and a thickness of 0.5 micrometers to 50 micrometers. Lead (Pb)-free solder joints have led to the growth of tin whiskers between components and signals on printed wiring boards (PWBs), resulting in the formation of unintended conductive paths. In turn, this presents a catastrophic security and reliability threat in computer systems.

[0003] The U.S. government, avionics, and military groups have conducted extensive research to better understand the causes of whisker growth and methods to control or stop such growth. According to research by the National Aeronautics and Space Administration (NASA) of the United States, many failures are attributed to the growth of tin whiskers. To date, the mechanism of tin whisker growth is still not fully understood. Efforts are underway to slow down whisker growth, and this is one reason why tin / lead (SnPb) alloys are still allowed for a variety of mission-critical applications such as space, avionics, missile, and defense applications. There are various mitigation techniques, including alloy-purified electroplating, hot-dip reflow for pre-treating pins, post-soldering re-heating / reflow, and using a nickel barrier between tin (Sn) and copper (Cu) surfaces. Some of these existing mitigation techniques are useful for mission-critical systems but are quite expensive for general applications because they require a large amount of resource usage such as capital expenditure, training, maintenance / repair, materials, floor space, electricity, dedicated operator / personnel, and time. Summary of the Invention

[0004] In one embodiment, a device for tin whisker isolation and detection includes a substrate having a plurality of pads for connection to electronic components placed on a substrate, and a shield placed on the surface of the substrate, the shield having a plurality of cavities aligned above the plurality of pads. The device further includes a plurality of sensing components, each of the sensing components being associated with one of the plurality of cavities and configured to sense conductive growth from a corresponding pad of the plurality of pads. The device also includes a plurality of circuit connections, each of the plurality of circuit connections being configured to connect one of the sensing components to a detection circuit. The detection circuit is configured to receive one or more sensing signals from one or more of the sensing components and detect conductive growth from the corresponding pad based on the one or more sensing signals.

[0005] In one embodiment, the detection circuit is configured to identify the pads having conductive growth based on the one or more sensing signals. In one embodiment, the device further includes a plurality of contacts, each of the plurality of contacts being coupled to the output of a corresponding one of the plurality of sensing components. In one embodiment, each of the plurality of contacts is further coupled to the detection circuit.

[0006] In one embodiment, one or more of the plurality of sensing components include operational amplifiers. In another embodiment, the plurality of sensing components are housed within the shield. In another embodiment, the plurality of sensing components are placed on another substrate, and another surface is mounted to the outer surface of the shield.

[0007] In one embodiment, each of the plurality of sensing components includes a Hall effect sensor configured to sense a change in a magnetic field generated by a magnet within the cavity and generate the sensing signal based on the change in the magnetic field. In one embodiment, the detection circuit further includes a selection matrix coupled to each of the plurality of sensing components, the selection matrix being configured to select one of the sensing signals and detect conductive growth from the corresponding pad based on the selected sensing signal.

[0008] In one embodiment, the detection circuit is configured to output a status bit indicating the location of the detected conductive growth. In another embodiment, the detection circuit is configured to use time domain reflectometry to detect conductive growth. In another embodiment, the detection circuit is configured to use vector network analysis to detect conductive growth. In one embodiment, the shield is formed of a metallized ceramic substrate.

[0009] An embodiment of a method for detecting tin whiskers in an apparatus for detecting an electronic component placed on a substrate having a plurality of pads for connection to an electronic component includes placing a shield on a surface of the substrate, the shield having a plurality of cavities aligned above the plurality of pads. The method further includes using a sensing component associated with one of the plurality of cavities to sense conductive growth from a corresponding pad of the plurality of pads, each of the sensing components being associated with one of the plurality of cavities. The method further includes receiving, by a detection circuit, one or more sensing signals from one or more of the sensing components. The method further includes detecting, by the detection circuit, conductive growth from the corresponding pad based on the one or more sensing signals.

[0010] In one embodiment, the method further includes identifying, by the detection circuit, a pad having conductive growth based on the one or more sensing signals.

[0011] In one embodiment, detecting conductive growth from the corresponding pad further includes sensing a change in a magnetic field generated by a magnet within the cavity and generating a sensing signal based on the change in the magnetic field.

[0012] In one embodiment, the method further includes selecting one of the sensing signals and detecting conductive growth from the corresponding pad based on the selected sensing signal. In one embodiment, the method further includes outputting a status bit indicating a location of the detected conductive growth.

[0013] In one embodiment, detecting conductive growth further includes detecting conductive growth using time domain reflectometry. In another embodiment, detecting conductive growth further includes detecting conductive growth using vector network analysis.

[0014] The foregoing and other objects, features, and advantages of the present invention will become apparent from the following more particular description of exemplary embodiments of the invention as illustrated in the accompanying drawings, in which like reference numerals generally represent like parts of the exemplary embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A perspective view of a surface mount component mounted on a substrate is shown.

[0016] Figure 2 An embodiment of a shield placed above the pins of a surface mount component placed on Figure 1 is shown.

[0017] Figure 3 An embodiment is shown in which the shield placed on the pins of a surface mount component placed on Figure 1 is non-conductive but has a metal coating, and the inner surface of the walls of the shield also has a metal coating.

[0018] Figure 4 Shows a device for tin whisker isolation and detection according to an exemplary embodiment.

[0019] Figure 5 Shows a sensor component for sensing whisker growth according to an exemplary embodiment.

[0020] Figure 6 Shows a device for tin whisker isolation and detection according to another exemplary embodiment.

[0021] Figure 7 Shows a device for tin whisker isolation and detection according to another exemplary embodiment.

[0022] Figure 8 Shows a sensor component for sensing whisker growth according to another exemplary embodiment.

[0023] Figure 9 Shows a detection circuit for whisker detection and isolation according to an exemplary embodiment.

[0024] Figure 10 Shows according to an exemplary embodiment Figure 9 of the multiplexing / selection matrix circuit of the detection circuit.

[0025] Figure 11 Shows a device for tin whisker isolation and detection using time domain reflectometry (TDR) according to an exemplary embodiment.

[0026] Figure 12 Shows a device for tin whisker isolation and detection using vector network analysis (VNA) according to an exemplary embodiment.

[0027] Figures 13A - 13C Shows an embodiment of a shielding component according to an exemplary embodiment.

[0028] Figure 14 Shows Figures 13A - 13C an example of tin whisker growth within the cavity of the shield.

[0029] Figure 15 Illustrates a flowchart showing an exemplary method for tin whisker isolation and detection according to an exemplary embodiment. Detailed Description

[0030] Exemplary embodiments disclose an apparatus and method for tin whisker isolation and detection that mitigate damage to electronic components due to tin whisker growth. In a particular embodiment, an electronic component soldered to a substrate has a shield with a cavity that covers a corresponding pad of the electronic component to serve as a shield or barrier to limit tin whisker growth and prevent tin whisker physical contact with adjacent tinned or soldered connections. Particular embodiments also provide for the detection of whisker growth events at specific pads or leads of the electronic component and the identification of specific leads or pads of the electronic component associated with the whisker growth event.

[0031] Starting Figure 1 from, an exemplary method, apparatus, and product for tin whisker isolation and detection in accordance with the present invention will be described with reference to the accompanying drawings. Figure 1 A perspective view of a surface mount component 10 mounted on a substrate 12 is shown. In a particular embodiment, substrate 12 includes a printed circuit board. The particular surface mount component 10 shown is a thin small outline package (TSOP) that includes a semiconductor device mounted on a carrier, but the exemplary embodiments have broad applicability to other surface mount components such as, but not limited to, dual in-line packages (DIPs), quad flat packages (QFPs), small outline packages (SOPs), and JEDEC package types. The surface mount component 10 includes leads 14 that are joined to pads 16 on the surface of substrate 12 by solder ( Figure 1 not shown in). The leads 14 can be copper, for example, and are coated with tin to facilitate soldering to the pads 16. If tin whiskers grow from the solder (not shown) or the leads 14 and contact adjacent leads 14, pads 16, or solder, a short circuit or arc can occur, which can damage the surface mount component 10.

[0032] Now referring Figure 2 , Figure 2 an embodiment of a shield 44 placed above the lead 14 of the surface mount component 10 placed in Figure 1 is shown. In particular, Figure 2 an embodiment of the shield 44 described in U.S. Patent Application Publication No. 2021 / 0208190, which is incorporated herein by reference, is shown. The shield 44 has an opening (or cavity) 20 through which the leads 14 from the surface mount component 10 and the pads 16 on the surface of the printed circuit board 12 are visible. The shield 44 with the opening 20 forms a "carport-like" structure. In a particular embodiment, the leads 14 and pads 16 do not protrude from the shield 18. Each opening 20 includes a wall 22 that forms a barrier between adjacent leads 14, solder (not shown), and pads 16, so that if tin whiskers are to form, the adjacent leads 14, solder, and pads 16 will not contact, thereby avoiding the possibility of short circuits and arcs.

[0033] In a particular embodiment, the shield 44 is made of a metallic material such as copper or aluminum. An exemplary operation is to sense when a tin whisker contacts the wall 22 of the shield 44. When the shield 44 is made of a metallic material, the entire shield 44 is conductive, and when a tin whisker contacts the shield 44, an indication is output to the fault detection and error handling circuit 26 via the contact 24.

[0034] In another embodiment, the shield 44 is made of a non-metallic material such as epoxy resin. In some embodiments, to indicate the presence of tin whiskers, the wall 22 of the opening 20 is made conductive, such as by a metal coating on the wall 22, and the outer surface of the shield 44 is also made conductive by coating with a metallic material. In a particular embodiment, the metal coating for the wall 22 and the outer surface of the shield 44 can be, for example, copper. Any contact with a tin whisker on the wall 22 can conduct to the metallic outer surface of the shield 44 and then to the contact 24 to output an indication to the fault detection and error handling circuit 26 when the tin whisker contacts the shield 44.

[0035] Figure 3 An embodiment is shown where the shield 44 is non-conductive but has a metal coating 32, and the inner surface 28 of the wall 22 also has a metal coating, and the inner surface of the wall of the shield 44 also has a metal coating, as described in U.S. Patent Application Publication No. 2021 / 0208190. In one embodiment, the shield 44 can have internal wiring 30 such that when a tin whisker contacts the inner surface 28 of the wall 22, the contact conducts through the wiring 30 to the metal coating 32 and then to the contact 24 for output to the fault detection and error handling circuit 26. It should be understood that although the internal wiring 30 is shown from only one opening 20, in some embodiments, internal wiring 30 is used between each opening 20 and the contact 24 to enable detection of tin whiskers in any of the openings 20.

[0036] The embodiment described in U.S. Patent Application Publication No. 2021 / 0208190 provides a physical barrier to prevent / contain the growth of tin (Sn) whiskers by using a "canopy"-like structure that acts as a physical barrier to prevent dendritic growth of tin whiskers. If a tin whisker inadvertently grows from a component I / O pin, it prevents short-circuiting / arcing with nearby pins within the same device, adjacent devices, or any other conductive features on a printed circuit board assembly (PCBA) or other substrate.

[0037] The various embodiments described herein provide an enhanced whisker growth barrier that cannot be penetrated by tin whiskers, as well as enhanced whisker sensing in which whisker events (such as momentary short circuits) are identified. In certain embodiments, if a whisker grows long enough to contact the barrier, the sensing circuit and associated multiplexing or matrix selection circuit are configured to precisely locate the position of the whisker using system monitoring and / or characterization analysis modes as further described herein. In certain embodiments, the sensing circuit associated with each cavity of the shield is incorporated into the shield or mounted to the outer surface of the shield or near the shield (e.g., mounted on an external card). Various embodiments of the sensing and detection circuits are described herein, including operational amplifier-based sensor circuits, Hall effect sensor circuits, time domain reflectometry (TDR) detection circuits, and vector network analysis (VNA) detector circuits.

[0038] Figure 4 An apparatus 50 for tin whisker isolation and detection in accordance with an exemplary embodiment is shown. Apparatus 50 includes a shield 52 placed over pins 56 of surface mount components (not shown) mounted on a substrate 12. Shield 52 includes cavities 54 aligned over pins 56 of the surface mount components and corresponding pads on substrate 12 to which pins 56 are soldered. In Figure 4 the particular embodiment shown, shield 52 includes eight cavities 54 that are aligned over each pin / pad of the surface mount components. For illustrative purposes, cavities 54 are shown as open at one end; however, in one or more embodiments, each of cavities 54 includes additional walls (not shown) that completely surround cavity 54.

[0039] In Figure 4 an embodiment, the inner surface of each cavity 54 is metallized and internally wired via a circuit connection 60 to a case contact 58 on substrate 12. For illustrative purposes, a single connection of a single cavity 54 to a corresponding case contact 58 is shown. However, it should be understood that in Figure 4 an embodiment, each of cavities 54 is internally wired via a separate surface connection 60 to a corresponding case contact 58. Thus, each of cavities 54 is internally routed separately to a corresponding case contact 58. In Figure 4 an embodiment, shield 52 is not electrically coupled to case contacts 58. In Figure 4 the embodiment shown, four case contacts 58 are located on a first side of shield 52 and four case contacts (not shown) are located on an opposite side of shield 52.

[0040] Each of the housing contacts 58 is connected via a circuit connection 62 to a whisker detection circuit 70. The whisker detection circuit 70 is configured to receive a signal from one or more of the cavities 56 when a tin whisker 80 forms between a pin / pad and the wall of the cavity 54 (e.g., resulting in a short circuit or other fault). The whisker detection circuit 70 determines that a whisker event caused by the growth of the tin whisker 80 has occurred and identifies the location of the whisker event by identifying the particular cavity 54 associated with the growth of the tin whisker 80. In a particular embodiment, the whisker detection circuit 70 determines that a short circuit has occurred between the tin whisker 80 and the cavity 54 based on the received signal.

[0041] Figure 5 A sensor component 100 for sensing whisker growth according to an exemplary embodiment is shown. The sensor assembly 100 includes a resistor 102 having a resistance R1 and an operational amplifier (op-amp) circuit 104. In a particular embodiment, the op-amp circuit 104 includes an LM741 op-amp. A first terminal of the resistor 102 is connected to a single housing contact of a shield placed above a pin of a surface mount component (e.g., Figure 4 one of the housing contacts 58). A second terminal of the resistor 102 is connected to the non-inverting (+) input (3) of the op-amp circuit 104. The inverting (-) input (2) and the positive power supply (V+) input (7) of the op-amp circuit 104 are both connected to a positive power supply voltage (+V). The negative power (V-) input of the op-amp circuit 104 is connected to ground (GND). The output terminal (6) of the op-amp circuit 104 is coupled to a whisker detection circuit 106, which includes a multiplexing / selection matrix as further described herein. Although Figure 5 a single sensor component 100 is shown, it should be understood that in various embodiments, each of the housing contacts 58 of the shield is connected to a separate sensor component 100, and the output of each of the sensor components 100 is connected to the whisker detection circuit 106. In a particular embodiment, the sensor component 100 for each housing contact 58 is included in the shield. In another particular embodiment, the sensor component 100 for each housing contact 58 is included on a separate card / plate mounted to or near the shield.

[0042] During operation of the sensor component 100, the sensor component 100 functions as a current sensor to sense a signal having a current equal to or greater than a predetermined threshold current received from the corresponding housing contact 58. The resistance value R1 of the resistor 102 is determined by dividing the power supply voltage by the desired current threshold. In a particular embodiment, the sensor component 100 is configured with a power supply voltage of 10 volts (V) to detect a current threshold of 1 milliampere (mA). Thus, the resistance R1 for the resistor 102 is calculated to be equal to 10 kiloohms (10 V / 0.001 A). If a whisker grows between the cavity 54 corresponding to position "A" and the pin / pad, a current is generated and supplied to the associated housing contact 58. The op-amp circuit 104 receives the current via the resistor 102. If the current is equal to or exceeds the configured current threshold, the op-amp circuit 104 outputs an indication of the detected tin whisker event to the whisker detection circuit 106. Since the association between position "A" and the corresponding sensor component 100 is known, the occurrence of the tin whisker event and the associated position are determined by the whisker detection circuit 106.

[0043] Figure 6 FIG. 4 shows an apparatus 200 for tin whisker isolation and detection according to another exemplary embodiment. The apparatus 200 includes a shield 202 that is placed over the pins 56 of surface mount components (not shown) mounted on a substrate 12. The shield 202 includes cavities 54 that are aligned with the pins 56 of the surface mount components and corresponding pads on the substrate 12 to which the pins 56 are soldered. In Figure 6 the particular embodiment shown, the shield 202 includes eight cavities 54 that are aligned over each pin / pad of the surface mount components. For illustrative purposes, the cavities 54 are shown as being open at one end; however, in one or more embodiments, each of the cavities 54 includes additional walls (not shown) that completely surround the cavity 54. In a particular embodiment, the shield 202 is formed from a metallized ceramic substrate.

[0044] In Figure 6 an embodiment, the inner surface of each cavity 54 is connected to the input of the sensor component 100 described with respect to Figure 5 and the output of the sensor component 100 is connected to the corresponding housing contact 58 on the substrate 12. For illustrative purposes, a single sensor component 100 is shown connected between a separate cavity 54 and the corresponding housing contact 58. However, it should be understood that in Figure 5In the embodiments, each of the cavities 54 is connected to a corresponding housing contact 58 via a separate sensor component 100. Thus, each of the cavities 54 is individually connected to a corresponding housing contact 58 via the sensor component 100. In a particular embodiment, each of the sensor components 100 is formed of a thin film deposited circuit. In Figure 6 the embodiments, the shield 202 is not electrically coupled to the housing contacts 58. In Figure 6 the illustrated embodiment, four housing contacts 58 are located on a first side of the shield 202 and four housing contacts (not shown) are located on an opposite side of the shield 202.

[0045] Each of the housing contacts 58 is connected to a whisker detection circuit 106 via a circuit connection 62. The whisker detection circuit 106 is configured to receive a signal from one or more sensor components 100 when a tin whisker 80 is formed between a pin / pad and the wall of the cavity 54 (e.g., resulting in a short circuit or other fault). The whisker detection circuit 106 determines that a whisker event caused by the growth of the whisker 80 has occurred and identifies the location of the whisker event by identifying the particular cavity 54 that has caused the whisker event.

[0046] Figure 7 FIG. shows a device 300 for tin whisker isolation and detection according to another exemplary embodiment. The device 300 includes a shield 302 that is placed over the pins 56 of surface mount components (not shown) mounted on a substrate 12. The shield 302 includes cavities 54 that are aligned over the pins 56 of the surface mount components and corresponding pads on the substrate 12 to which the pins 56 are soldered. In Figure 7 the illustrated particular embodiment, the shield 302 includes eight cavities 54 that are aligned over each pin / pad of the surface mount components. For illustrative purposes, the cavities 54 are shown as open at one end; however, in one or more embodiments, each of the cavities 54 includes additional walls (not shown) that completely surround the cavity 54.

[0047] Figure 7 The device 300 of Figure 6 is similar to the device 200 of Figure 6 except that sensor components 305 are included on a second substrate 304 mounted on the outer surface of the shield 302 rather than within the shield 302 as discussed with respect to Figure 7 In the illustrated particular embodiment, the second substrate 304 includes an op-amp circuit 306, a resistor 308, and a selector circuit 310. In a particular embodiment, the second substrate 304 is included on an auxiliary card / plate. In Figure 7In the embodiments, the inner surface of each cavity 54 is connected to the input of the sensor component 305, and the output of the sensor component 305 is connected to the corresponding housing contact 58 on the substrate 12. Thus, each of the cavities 54 is individually connected to the corresponding housing contact 58 via the sensor component 305. In Figure 7 the embodiments, the shield 302 is not electrically coupled to the housing contact 58. In Figure 7 In the illustrated embodiment, four housing contacts 58 are located on the first side of the shield 302, and four housing contacts (not shown) are located on the opposite side of the shield 302.

[0048] Each of the housing contacts 58 is connected to the whisker detection circuit 106 via a circuit connection 62. The whisker detection circuit 106 is configured to receive a signal from one or more sensor components 100 when a tin whisker 80 is formed between the pin / pad and the wall of the cavity 54 (e.g., resulting in a short circuit or other fault). The whisker detection circuit 106 determines that a whisker event caused by the growth of the tin whisker 80 has occurred and identifies the location of the whisker event by identifying the specific cavity 54 that has caused the whisker event.

[0049] Figure 8 Shown is a sensor component 400 for sensing whisker growth according to another exemplary embodiment. The sensor component 400 includes a Hall effect sensor 402 mounted within a cavity 54 of a shield 202 of Figure 6 instead of the sensor component 400. The cavity 54 covers the pin / pad 404 of the surface mount component. The sensor component also includes one or more magnets 406 mounted within the cavity 54. In a particular embodiment, the one or more magnets are mounted to one or more walls of the cavity 54, such as a "garage door" (not shown) that encloses the cavity 54. The power terminal of the Hall effect sensor 402 is connected to a power supply voltage (+V), and the ground terminal of the Hall effect sensor 402 is connected to ground (GND). The output terminal of the Hall effect sensor 402 is connected to the housing contact 58.

[0050] One or more magnets 406 establish a magnetic field within the cavity 54. Whisker growth 408 occurring at the pin / pad 404 within the cavity 54 corresponding to position "B" causes interference with the magnetic field within the cavity 54. The Hall effect sensor 402 generates a signal in response to detecting the magnetic field interference and sends the signal to the housing contact 58. The signal is received by the multiplexing / select matrix of the whisker detection circuit as an indication of a detected tin whisker event. Since the association between position "B" and the corresponding Hall effect sensor 402 is known, the occurrence of the tin whisker event and the associated position are determined by the whisker detection circuit. To detect the tin whisker event, the whisker growth 408 need not contact the wall of the cavity 54. Instead, the tin whisker event can be detected before the whisker growth 408 reaches the wall of the cavity 54. Thus, the tin whisker event can be detected earlier compared to embodiments where contact of the whisker growth with the cavity wall triggers detection of the tin whisker event. In some embodiments, a baseline magnetic field is measured within each cavity 54 prior to any whisker growth. Detection of the whisker event is determined by measuring a deviation from the baseline magnetic field that exceeds a predetermined threshold. In other embodiments, the baseline magnetic field can be determined periodically.

[0051] Figure 9 A detection circuit 500 for whisker detection and isolation according to an exemplary embodiment is shown. The detection circuit 500 includes a multiplexing / select matrix 502 and a control register 504. The inputs of the multiplexing / select matrix 502 are connected to the housing contacts 58 of a shield (e.g., Figure 4 shield 52, Figure 6 shield 202, or Figure 7 shield 302) to receive signals indicative of tin whisker events associated with the corresponding cavities 54. The control register 504 is connected to the multiplexing / select matrix 502 and the system bus 514 and is configured to set the monitoring mode 506 of the multiplexing / select matrix 502. The output 510 of the multiplexing / select matrix 502 is provided to the status register 512. The status register 512 includes status bits associated with each housing contact channel to indicate whether a particular channel has triggered a tin whisker event. The status bits are provided to the system bus 514.

[0052] The control register 504 is further configured to control 508 which inputs from the housing contacts 58 are enabled to pass through the multiplexing / select matrix 502 at a particular time. In particular, the control register 504 is configured to use n controls to control 2 nInput of a housing contact channel. If the monitoring mode is set to the normal operation mode, all housing contact channels pass through the multiplexing / selection matrix 502 to allow monitoring / detection that interference due to a whisker event has occurred on one of the housing contacts 58. If the monitoring mode is set to the characterization / fault analysis mode, a single housing contact channel is selected to allow further or more detailed study of a given shielded cavity associated with the housing contact channel. In an embodiment, one or more of the housing contact channels are provided to a machine learning model configured to predict whether a particular shielded cavity is prone to tin whisker growth.

[0053] Figure 10 Shows a Figure 9 multiplexing / selection matrix circuit 600 of the detection circuit 500 according to an exemplary embodiment. In Figure 10 the embodiment, two controls (a, b) and four housing contacts 58 (A, B, C, D) are shown. Other embodiments may include any number of housing contacts and corresponding controls. The multiplexing / selection matrix circuit 600 includes a first OR gate 602 having inputs connected to the four housing contacts 58. Each housing contact 58 is also connected to a first input of one of the first AND gates 604. The control register 504 provides the two controls (a, b) to corresponding first inverters 606, and the inverter outputs from each of the first inverters 606 are provided to the second inputs of the two first AND gates 604. The non-inverted versions of each of the control signals (a, b) are provided to the third inputs of two of the first AND gates 604. The output of each of the first AND gates 604 is provided to the second OR gate 608. The monitoring mode control signal from the control register 504 is provided to the first input of the second AND gate 610 and the input of the second inverter 612 to set whether the multiplexing / selection matrix circuit system 600 is in the normal mode or in the characterization / fault analysis mode.

[0054] Still referring to Figure 10 , the output of the second OR gate 608 is connected to the first input of the third AND gate 614, and the output of the second inverter 612 is provided to the second input of the third AND gate 614. The output of the third AND gate 614 and the output of the second AND gate 614 are respectively provided to the first input and the second input of the third OR gate 616. The output of the third OR gate 616 is provided to the status register.

[0055] Figure 11 Shows a device 700 for tin whisker isolation and detection using a time domain reflectometer (TDR) according to an exemplary embodiment. Figure 11 The device 700 of Figure 4The apparatus 50, in addition, each of the housing contacts 58 is connected via a circuit connection 62 to a TDR detector 702. The TDR detector 702 is configured to isolate and characterize tin whisker events via reflected signals monitored from each of the cavities 54. As is known in the art, TDR is sometimes used to detect the location of faults in transmission lines and coaxial cables. A low voltage pulse signal is sent through the transmission line, and the TDR meter checks for any reflections that may be caused by impedance mismatches. If there are no impedance mismatches throughout the line, no reflections occur. However, if there is a discontinuity in the transmission line at a particular point, some portion of the pulse signal will be reflected back to the TDR meter. By measuring the time and propagation speed of the received pulse, the TDR meter calculates the location of the fault and the nature of the fault, such as an open circuit, short circuit, or impedance mismatch. The various embodiments described herein utilize TDR technology to determine whether tin whisker growth has occurred and the location of such tin whisker growth.

[0056] In Figure 11 an embodiment, the TDR detector 702 generates a series of pulses to each of the housing contact points 58 of the shield 52 to serve as monitoring points, determines whether a reflected signal indicating a tin whisker event caused by the growth of the whisker 80 is received back from one or more of the housing contacts 52, and identifies the location of the whisker event by identifying the particular cavity 54. In a particular embodiment, the TDR detector 702 determines that an instantaneous short circuit has occurred between the tin whisker 80 and the cavity 54 based on the shape and characteristics of the reflected signal. In a particular embodiment, the TDR detector 702 uses differential TDR to detect very small tin whisker growth.

[0057] Figure 12 An apparatus 800 for tin whisker isolation and detection using vector network analysis (VNA) in accordance with an exemplary embodiment is shown. Figure 12 The apparatus 800 is similar to Figure 4 the apparatus 50, except that each housing contact 58 is connected via a circuit connection 62 to a VNA system 802. The VNA system 802 is configured to isolate and characterize tin whisker events to perform a frequency domain analysis of the housing contacts 58 using VNA technology. The VNA system 802 uses a sensing circuit to characterize tin whisker events by detecting an energy interruption of the shield 52 of the card assembly in the case where the whisker has grown long enough to contact the cavity 54 of the shield 52.

[0058] The VNA system 802 learns the normal energy state (e.g., -100 db) of the card assembly including the shield 52 in the absence of tin whisker events. The VNA system 802 operates in the frequency domain to monitor network interference that occurs at the moment of tin whisker short - circuit and fusing events. Each housing contact 58 serves as a detection point, and the VNA system 802 monitors the housing contacts 58 to detect any interference in the network composed of the on - board shield / barrier housing and its associated contact pins. During whisker growth and fusing events, the VNA system 802 detects changes in the frequency distribution of the shield / barrier components that deviate from the normal state.

[0059] Figures 13A through 13C An embodiment of a shield 900 according to an exemplary embodiment is shown. Figure 13A A perspective view of the shield 900 placed above the pin 902 of the surface - mount component 904 is shown. The shield 900 includes a cavity 906 aligned above the pin 902 of the surface - mount component 904 and a corresponding pad 908 to which the pin 902 is soldered. In Figures 13A - 13C the particular embodiment shown, the shield 900 includes eight cavities 906 aligned on each pin / pad of the surface - mount component. For illustrative purposes, the cavity 906 is shown as open at one end; however, in one or more embodiments, each of the cavities 906 includes an additional wall (not shown) that completely encloses the cavity 906.

[0060] Figure 13B A front perspective view of the shield 900 is shown, which also includes a sensor circuit 910 disposed on the top surface of the shield 900. Figure 13C A rear perspective cross - sectional view of the shield 900 is shown.

[0061] Figure 14 An example of Figures 13A - 13C tin whisker growth inside the cavity of the shield is shown. In Figure 14 the example, several tin whiskers 1400 grow from the pin 902. The growth of the tin whiskers 1400 is detected by one or more of the devices and methods for tin whisker isolation and detection as described herein with respect to various embodiments.

[0062] For further explanation, Figure 15A flowchart illustrating an exemplary method for tin whisker isolation and detection in accordance with an exemplary embodiment is presented. For an apparatus having an electronic component placed on a substrate having a plurality of pads for connection to an electronic component, the method includes placing a shield on a surface of the substrate 1502. The shield has a plurality of cavities aligned above the plurality of pads. A sensing component associated with one of the plurality of cavities is used to sense 1504 a conductive growth from a corresponding pad of the plurality of pads. Each of the sensing components is associated with one of the plurality of cavities.

[0063] A detection circuit receives 1506 one or more sensing signals from one or more of the sensing components. The detection circuit detects 1508 a conductive growth from the corresponding pad based on the one or more sensing signals.

[0064] In one embodiment, detecting 1508 a conductive growth from the corresponding pad further includes sensing a change in a magnetic field generated by a magnet within the cavity and generating a sensing signal based on the change in the magnetic field. In another embodiment, detecting the conductive growth further includes using time domain reflectometry (TDR) to detect the conductive growth. In yet another embodiment, detecting the conductive growth further includes using vector network analysis to detect the conductive growth.

[0065] In one embodiment, the method further includes identifying 1510, by the detection circuit, a pad having a conductive growth based on the one or more sensing signals.

[0066] In one embodiment, the method further includes selecting one of the sensing signals and detecting a conductive growth from the corresponding pad based on the selected sensing signal. In another embodiment, the method further includes outputting a status bit indicating a location of the detected conductive growth.

[0067] In view of the foregoing explanation, the reader will recognize that benefits of tin whisker isolation and detection in accordance with embodiments of the present invention include providing an enhanced whisker growth barrier that cannot be penetrated by tin whiskers and enhanced whisker sensing in which whisker events such as momentary shorts are identified.

[0068] It will be understood from the foregoing description that modifications and changes can be made in various embodiments of the present invention without departing from the true spirit thereof. The description in this specification is for illustrative purposes only and should not be construed in a limiting sense. The scope of the present invention is limited only by the language of the appended claims.

Claims

1. An apparatus for tin whisker isolation and detection, the apparatus comprising: A substrate having a plurality of pads for connection to electronic components placed on the substrate; A shield placed on the surface of the substrate, the shield having a plurality of cavities aligned above the plurality of pads; A plurality of sensing components, each of the sensing components being associated with one of the plurality of cavities and configured to sense conductive growth from a corresponding pad of the plurality of pads; A plurality of circuit connections, each of the plurality of circuit connections being configured to connect one of the sensing components to a detection circuit; And The detection circuit configured to receive one or more sensing signals from one or more of the sensing components and detect conductive growth from the corresponding pad based on the one or more sensing signals.

2. The device according to claim 1, wherein, The detection circuit is configured to identify the pad having the conductive growth based on the one or more sensing signals.

3. The device according to claim 1, further comprising: A plurality of contacts, each of the plurality of contacts being coupled to the output of a corresponding one of the plurality of sensing components.

4. The device according to claim 3, wherein Each of the plurality of contacts is further coupled to the detection circuit.

5. The device according to claim 1, wherein One or more of the plurality of sensing components include operational amplifiers.

6. The device according to claim 1, wherein, The plurality of sensing components are housed within the shield.

7. The apparatus according to claim 1, wherein, The plurality of sensing components are placed on another substrate, the other surface being mounted to the outer surface of the shield.

8. The apparatus according to claim 1, wherein, Each of the plurality of sensing components includes a Hall effect sensor configured to sense a change in a magnetic field generated by a magnet within the cavity and generate the sensing signal based on the change in the magnetic field.

9. The device according to claim 1, wherein The detection circuit further includes a selection matrix coupled to each of the plurality of sensing components, the selection matrix being configured to select one of the sensing signals and detect the conductive growth from the corresponding pad based on the selected sensing signal.

10. The device according to claim 1, wherein, The detection circuit is configured to output a status bit indicating the location of the detected conductive growth.

11. The device according to claim 1, wherein, The detection circuit is configured to detect the conductive growth using time domain reflectometry.

12. The device according to claim 1, wherein, The detection circuit is configured to detect the conductive growth using vector network analysis.

13. The device according to claim 1, wherein, The shield is formed of a metallized ceramic substrate.

14. A method for detecting tin whiskers in a detection apparatus having electronic components placed on a substrate, the substrate having a plurality of pads for connection to the electronic components, the method comprising: Placing a shield on the surface of the substrate, the shield having a plurality of cavities aligned above the plurality of pads; Using a sensing component associated with one of the plurality of cavities to sense conductive growth from a corresponding pad of the plurality of pads, each of the sensing components being associated with one of the plurality of cavities; Receiving one or more sensing signals from one or more of the sensing components by a detection circuit; And Detecting conductive growth from the corresponding pad by the detection circuit based on the one or more sensing signals.

15. The method according to claim 14 further comprises: The detection circuit identifies the pad having the conductive growth based on the one or more sensing signals.

16. The method according to claim 14, wherein, Detecting the conductive growth from the corresponding pad further includes sensing a change in a magnetic field generated by a magnet within the cavity and generating the sensing signal based on the change in the magnetic field.

17. The method according to claim 14 further comprises: Select one sensing signal from the sensing signals and detect the conductive growth from the corresponding pad based on the selected sensing signal.

18. The method according to claim 14, outputting a status bit indicating the location of the detected conductive growth.

19. The method according to claim 14, wherein, Detecting the conductive growth further includes detecting the conductive growth using time domain reflectometry.

20. The method according to claim 14, wherein Detecting the conductive growth further includes detecting the conductive growth using vector network analysis.

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