Apparatus and method for the isolation and detection of tin whiskers

Abstract

The apparatus for isolating and detecting tin whiskers includes a substrate having a plurality of pads for connecting to electronic components disposed on the substrate, and a shield disposed on a surface of the substrate. The shield includes a plurality of cavities aligned over the plurality of pads. A plurality of sensing components, each associated with one of the plurality of cavities, are configured to detect electrically conductive growth from a corresponding pad of the plurality of pads. A plurality of circuit connections are each 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 electrically conductive growth from the corresponding pad based on the one or more sensing signals.

Description

[Technical Field]

[0001] The field of the invention relates to electrical devices having tin or solder connections, or more specifically to methods and apparatus for the isolation and detection of tin whiskers. [Background technology]

[0002] Whisker growth has been highlighted as a significant and unknown risk to the operation of high-reliability electronic products. Tin whiskers are metallic, crystalline, thread-like structures that grow outward from metal surfaces and are commonly found in electrodeposited tin (Sn) coatings and tin-based alloys. Whiskers can take many forms, including filaments, straight, kinked, spirals, nodules, and irregularly shaped extrusions. Whiskers typically range in length from 1 nanometer to 500 nanometers and in thickness from 0.5 microns to 50 microns. Lead-free solder joints can grow tin whiskers between components and signals on printed wiring boards (PWBs), thus leading to the formation of unintended conductive paths. Consequently, the safety and reliability of computer systems are compromised.

[0003] U.S. government, avionics, and military groups have conducted significant research to better understand the causes of whisker growth and how to control or halt this growth. According to National Aeronautics and Space Administration (NASA) research, many failures are attributed to tin whisker growth. To this day, the mechanism of tin whisker growth is still not fully understood. Efforts to mitigate whisker growth are ongoing, which is one of the reasons why tin / lead (SnPb) alloys are still permitted for use in a wide variety of mission-critical applications, including space, avionics, missile, and defense applications. Various mitigation techniques exist, including alloyed purge plating, pin pretreatment with molten metal reflow, post-soldering reheat / reflow, and the use of a nickel barrier between the tin (Sn) and copper (Cu) surfaces. While useful for mission-critical systems, some of these existing mitigation techniques are prohibitively expensive for universal application due to the significant resource requirements: capital investment, training, maintenance / repair, materials, floor space, electricity, dedicated operators / personnel, and time. Summary of the Invention

[0004] In one embodiment, an apparatus for isolating and detecting tin whiskers includes a substrate having a plurality of pads for connecting to an electronic component disposed on the substrate; and a shield disposed on a surface of the substrate, the shield having a plurality of cavities aligned over the plurality of pads. The apparatus further includes a plurality of sensing components, each of the sensing components associated with one of the plurality of cavities and configured to detect electrically conductive growth from a corresponding pad of the plurality of pads. The apparatus further includes a plurality of circuit connections, each of the plurality of circuit connections 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 electrically conductive growth from the corresponding pad based on the one or more sensing signals.

[0005] In one embodiment, a detection circuit is configured to identify the pad having the electrically conductive growth based on the one or more detection signals. In one embodiment, the device further comprises a plurality of contacts, each of the plurality of contacts coupled to an 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 includes an operational amplifier. In another embodiment, the plurality of sensing components is contained within the shield. In another embodiment, the plurality of sensing components is disposed on a separate substrate, the separate substrate being mounted to an outer surface of the shield.

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

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

[0009] One embodiment of a method includes a method for detecting tin whiskers in a device having an electronic component disposed on a substrate, the substrate including a plurality of pads for connecting to the electronic component, the method comprising: disposing a shield on a surface of the substrate, the shield including a plurality of cavities aligned over the plurality of pads. The method further comprises detecting electrically conductive growth from a corresponding pad of the plurality of pads using a sensing component associated with one of the plurality of cavities, each of the sensing components being associated with one of the plurality of cavities. The method further comprises receiving, by a detection circuit, one or more sensing signals from one or more of the sensing components. The method further comprises detecting, by the detection circuit, electrically conductive growth from the corresponding pad based on the one or more sensing signals.

[0010] In one embodiment, the method further comprises identifying, by the detection circuitry, the pads including the electrically conductive growth based on the one or more sense signals.

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

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

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

[0014] The above 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 explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a perspective view of a surface-mounted component mounted on a substrate.

[0016] [Figure 2] 2A and 2B are diagrams illustrating an embodiment of a shield placed over the leads of the surface mount component of FIG. 1.

[0017] [Figure 3] 1 shows an embodiment in which a shield placed on the leads of the surface mount component of FIG. 1 is non-electrically conductive but has a metallic coating, and the inner surface of the wall of the shield also has a metallic coating.

[0018] [Figure 4] FIG. 1 illustrates an apparatus for the isolation and detection of tin whiskers, according to an exemplary embodiment.

[0019] [Figure 5] 1A-1C illustrate sensor components for detecting whisker growth according to an exemplary embodiment.

[0020] [Figure 6] FIG. 1 illustrates an apparatus for the isolation and detection of tin whiskers according to another exemplary embodiment.

[0021] [Figure 7] FIG. 1 illustrates an apparatus for the isolation and detection of tin whiskers according to another exemplary embodiment.

[0022] [Figure 8] FIG. 10 illustrates a sensor component for detecting whisker growth according to another exemplary embodiment.

[0023] [Figure 9] FIG. 1 illustrates a detection circuit for whisker detection and isolation, according to an exemplary embodiment.

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

[0025] [Figure 11] FIG. 1 illustrates an apparatus for tin whisker isolation and detection using time domain reflectometry (TDR), according to an exemplary embodiment.

[0026] [Figure 12] FIG. 1 illustrates an apparatus for the isolation and detection of tin whiskers using vector network analysis (VNA), according to an exemplary embodiment.

[0027] [Figure 13] Figures 13A, 13B, and 13C are diagrams illustrating an embodiment of a shielding component according to an exemplary embodiment.

[0028] [Figure 14] FIG. 16 shows an example of tin whisker growth within the cavity of the shield of FIGS. 13A-13C.

[0029] [Figure 15]FIG. 1 shows a flowchart illustrating an exemplary method for whisker isolation and detection, according to an exemplary embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0030] Exemplary embodiments disclose an apparatus and method for tin whisker isolation and detection that mitigates damage to electrical components due to tin whisker growth. In certain embodiments, an electrical component soldered to a substrate has a shield that includes a cavity that covers a corresponding pad of the electrical component to limit tin whisker growth and act as a shield or barrier to prevent tin whiskers from physically contacting adjacent tin or solder connections. Certain embodiments further provide for detection of whisker growth events on specific pads or leads of the electrical component and identification of the specific leads or pads of the electrical component associated with the whisker growth event.

[0031] Exemplary methods, apparatus, and products for tin whisker isolation and detection according to the present invention are described with reference to the accompanying drawings, beginning with FIG. 1 . FIG. 1 illustrates a perspective view of a surface mount component 10 mounted on a substrate 12. In a particular embodiment, the substrate 12 comprises 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 embodiment is broadly applicable to other surface mount components, such as, but not limited to, dual in-line packages (DIPs), quad flat pack packages (QFPs), small outline packages (SOPs), and JEDEC package styles. The surface mount component 10 includes leads 14 that are joined by solder (not shown in FIG. 1 ) to pads 16 on the surface of the substrate 12. The leads 14 may be, for example, copper and coated with tin to facilitate soldering to the pads 16. If tin whiskers grow from the solder (not shown) or leads 14 and contact adjacent leads 14, pads 16, or solder, a short circuit or arc can occur, potentially damaging the surface mount component 10.

[0032] Referring now to FIG. 2, FIG. 2 illustrates one embodiment of a shield 44 disposed over the leads 14 of the surface mount component 10 of FIG. 1. In particular, FIG. 2 illustrates one embodiment of the shield 44 described in U.S. Patent Application Publication No. 2021 / 0208190, which is incorporated herein by reference. The shield 44 has openings (or cavities) 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 openings 20 forms a “carport-like” structure. In certain embodiments, the leads 14 and pads 16 do not protrude beyond the shield 18. Each opening 20 includes walls 22 that form a barrier between adjacent leads 14, solder (not shown), and pads 16. Therefore, even if tin whiskers form, the adjacent leads 14, solder, and pads 16 do not come into contact, thereby avoiding the possibility of short circuits and arcs.

[0033] In certain embodiments, the shield 44 is made of a metallic material, such as copper or aluminum. An exemplary operation is to detect when a tin whisker comes into contact with the wall 22 of the shield 44. If the shield 44 is made of a metallic material, the entire shield 44 is conductive, and when a tin whisker comes into contact with the shield 44, an indication is output via the contacts 24 to the fault detection and error handling circuitry 26.

[0034] In another embodiment, the shield 44 is made of a non-metallic material, such as epoxy. In some embodiments, to indicate the presence of a tin whisker, the walls 22 of the opening 20 are made conductive, such as by a metallic coating on the walls 22, and the outer surface of the shield 44 is also made conductive by being coated with a metallic material. In particular embodiments, the metallic coating on the walls 22 and the outer surface of the shield 44 may be copper, for example. Any tin whisker that contacts the walls 22 will be conducted to the metallic outer surface of the shield 44 and then to the contact 24, which can output an indication to the fault detection and error handling circuitry 26 when a tin whisker contacts the shield 44.

[0035] 3 illustrates an embodiment in which the shield 44 is non-electrically conductive but has a metal coating 32, 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 if a tin whisker contacts the inner surface 28 of the wall 22, the contact is conducted through the wiring 30 to the metal coating 32 and then to the contacts 24 for output to the fault detection and error handling circuitry 26. Although the internal wiring 30 is shown from only one opening 20, it should be understood that in some embodiments, internal wiring 30 between each opening 20 and the contact 24 is used so that tin whiskers can be detected in any of the openings 20.

[0036] The embodiments described in U.S. Patent Application Publication No. 2021 / 0208190 provide a physical barrier that inhibits / inhibits tin (Sn) whisker growth by using a "carport"-like structure that acts as a physical barrier to prevent dendritic growth of tin whiskers. If a tin whisker inadvertently grows from an I / O lead of a component, it can prevent shorting / arcing to nearby leads within the same device, adjacent devices, or other electrically conductive features on a printed circuit board assembly (PCBA) or any other substrate.

[0037] Various embodiments described herein provide an enhanced whisker growth barrier that cannot be penetrated by tin whiskers, and enhanced whisker detection in which whisker events such as momentary shorts are identified. In certain embodiments, if a whisker grows long enough to contact the barrier, the detection circuitry and associated multiplexing or matrix selection circuitry are configured to locate the whisker using a system monitoring and / or characterization mode, as described further herein. In certain embodiments, the detection circuitry associated with each cavity in the shield is integrated into the shield, mounted on the outer surface of the shield, or mounted in close proximity to the shield (e.g., mounted on an external card). Various embodiments of the detection and detection circuitry 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] FIG. 4 illustrates an apparatus 50 for tin whisker isolation and detection, according to an exemplary embodiment. The apparatus 50 includes a shield 52 disposed over leads 56 of a surface-mounted component (not shown) mounted on a substrate 12. The shield 52 includes cavities 54 aligned over the leads 56 of the surface-mounted component and over corresponding pads on the substrate 12 to which the leads 56 are soldered. In the particular embodiment illustrated in FIG. 4, the shield 52 includes eight cavities 54, one aligned over each lead / pad of the surface-mounted component. For purposes of illustration, the cavities 54 are shown as open at one end, but in one or more implementations, each of the cavities 54 includes an additional wall (not shown) that completely surrounds the cavity 54.

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

[0040] Each of the case contacts 58 is connected to a whisker detection circuit 70 via a circuit connection 62. The whisker detection circuit 70 is configured to receive a signal from one or more of the cavities 56, for example, when a tin whisker 80 that causes a short or other fault forms between a lead / pad and a wall of the cavity 54. The whisker detection circuit 70 determines that a whisker event caused by the growth of a 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 certain embodiments, the whisker detection circuit 70 determines that a short has occurred between the tin whisker 80 and the cavity 54 based on the received signal.

[0041] FIG. 5 illustrates a sensor component 100 for detecting whisker growth, according to an exemplary embodiment. The sensor component 100 includes a resistor 102, which includes a resistor R1, and an operational amplifier (op-amp) circuit 104. In a specific embodiment, the op-amp circuit 104 includes an LM741 op-amp. A first terminal of the resistor 102 is connected to a single case contact (e.g., one of the case contacts 58 in FIG. 4 ) of a shield located on a lead of a surface-mount component. 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 supply voltage (+V). The negative power supply (V−) input of the op-amp circuit 104 is connected to ground (GND). An 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. 5 shows a single sensor component 100, it should be understood that in various embodiments, each of the case 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 of the case contacts 58 is included on the shield. In another particular embodiment, the sensor component 100 for each of the case contacts 58 is included on a separate card / board mounted on or near the shield.

[0042] During operation of the sensor component 100, the sensor component 100 functions as a current sensor that detects signals having a current equal to or greater than a predetermined threshold current received from the corresponding case contact 58. The resistance value R1 of the resistor 102 is determined by dividing the supply voltage by the desired current threshold. In a specific embodiment, the sensor component 100 is configured with a supply voltage of 10 volts (V) to detect a current threshold of 1 milliamp (mA). Accordingly, the resistance R1 used for the resistor 102 is calculated as (10V / 0.001A) equals 10 kilohms. When whisker growth occurs between the lead / pad corresponding to location "A" and the cavity 54, a current is generated and provided to the associated case contact 58. The current is received by the op-amp circuit 104 via the resistor 102. If the current equals or exceeds the set current threshold, the op-amp circuit 104 outputs an indication of a detected tin whisker event to the whisker detection circuit 106. Since the association of location "A" and the corresponding sensor component 100 is known, the occurrence and associated location of a tin whisker event is determined by the whisker detection circuit 106.

[0043] FIG. 6 illustrates an apparatus 200 for tin whisker isolation and detection according to another illustrative embodiment. The apparatus 200 includes a shield 202 disposed over the leads 56 of a surface-mounted component (not shown) mounted on a substrate 12. The shield 202 includes cavities 54 aligned over the leads 56 of the surface-mounted component and over corresponding pads on the substrate 12 to which the leads 56 are soldered. In the particular embodiment illustrated in FIG. 6, the shield 202 includes eight cavities 54, one aligned over each lead / pad of the surface-mounted component. For purposes of illustration, the cavities 54 are shown as open at one end, but in one or more implementations, each of the cavities 54 includes an additional wall (not shown) that completely surrounds the cavity 54. In a particular embodiment, the shield 202 is formed of a metallized ceramic substrate.

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

[0045] Each of the case contacts 58 is connected via circuit connections 62 to a whisker detection circuit 106. The whisker detection circuit 106 is configured to receive a signal from one or more of the sensor components 100 when, for example, a tin whisker 80 that causes a short circuit or other fault forms between a lead / pad and a wall of a cavity 54. The whisker detection circuit 106 determines that a whisker event has occurred caused by the growth of a whisker 80 and identifies the location of the whisker event by identifying the particular cavity 54 that caused the whisker event.

[0046] FIG. 7 illustrates an apparatus 300 for tin whisker isolation and detection according to another illustrative embodiment. The apparatus 300 includes a shield 302 disposed over the leads 56 of a surface-mounted component (not shown) mounted on a substrate 12. The shield 302 includes cavities 54 aligned over the leads 56 of the surface-mounted component and over corresponding pads on the substrate 12 to which the leads 56 are soldered. In the particular embodiment illustrated in FIG. 7, the shield 302 includes eight cavities 54, one aligned over each lead / pad of the surface-mounted component. For purposes of illustration, the cavities 54 are shown as open at one end, however, in one or more implementations, each of the cavities 54 includes an additional wall (not shown) that completely surrounds the cavity 54.

[0047] The device 300 of FIG. 7 is similar to the device 200 of FIG. 6 , except that the sensor component 305 is 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 FIG. 6 . In the particular embodiment shown in FIG. 7 , the second substrate 304 includes an op-amp circuit 306, resistors 308, and a selector circuit 310. In particular embodiments, the second substrate 304 is included on a second card / board. In the embodiment of FIG. 7 , the inner surface of each cavity 54 is connected to an input of the sensor component 305, and the output of the sensor component 305 is connected to a corresponding case contact 58 on the substrate 12. Accordingly, each of the cavities 54 is individually connected to a corresponding case contact 58 via the sensor component 305. In the embodiment of FIG. 7 , the shield 302 is not electrically coupled to the case contacts 58. In the embodiment shown in FIG. 7, four case contacts 58 are located on a first side of shield 302 and four case contacts (not shown) are located on the opposite side of shield 302 .

[0048] Each of the case contacts 58 is connected via circuit connections 62 to a whisker detection circuit 106. The whisker detection circuit 106 is configured to receive a signal from one or more of the sensor components 100 when, for example, a tin whisker 80 that causes a short circuit or other fault forms between a lead / pad and a wall of a cavity 54. The whisker detection circuit 106 determines that a whisker event has occurred caused by the growth of a tin whisker 80 and identifies the location of the whisker event by identifying the particular cavity 54 that caused the whisker event.

[0049] FIG. 8 illustrates a sensor component 400 for detecting whisker growth according to another exemplary embodiment. Instead of the sensor component 400, the sensor component 400 includes a Hall Effect sensor 402 mounted within the cavity 54 of the shield 202 of FIG. 6 . The cavity 54 covers the leads / pads 404 of a surface-mount component. The sensor component further includes one or more magnets 406 mounted within the cavity 54. In certain embodiments, the one or more magnets are mounted to one or more walls of the cavity 54, such as a “garage door” (not shown) surrounding the cavity 54. A power terminal of the Hall Effect sensor 402 is connected to a supply voltage (+V), and a ground terminal of the Hall Effect sensor 402 is connected to ground (GND). An output terminal of the Hall Effect sensor 402 is connected to a case contact 58.

[0050] One or more magnets 406 create a magnetic field that is established within the cavity 54. When whisker growth 408 occurs from a lead / pad 404 within the cavity 54 corresponding to location "B," the magnetic field within the cavity 54 is disturbed. The Hall Effect sensor 402 generates a signal in response to detecting the magnetic field disturbance and transmits the signal to the case contact 58. The signal is received by the multiplexing / selection matrix of the whisker detection circuitry as an indication of a detected tin whisker event. Because the association of location "B" and the corresponding Hall Effect sensor 402 is known, the occurrence and associated location of the tin whisker event is determined by the whisker detection circuitry. The whisker growth 408 does not need to contact the wall of the cavity 54 to detect the tin whisker event. Instead, the tin whisker event can be detected before the whisker growth 408 reaches the wall of the cavity 54. Accordingly, tin whisker events can be detected more quickly than in embodiments in which contact of a growing whisker with a cavity wall triggers detection of a tin whisker event. In some embodiments, the baseline magnetic field within each cavity 54 is measured prior to any whisker growth. Detection of a whisker event is determined by measuring a deviation from the baseline magnetic field above a predetermined threshold. In other embodiments, the baseline magnetic field can be determined periodically.

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

[0052] The control register 504 is further configured to control which of the inputs from the case contacts 58 are enabled 508 for passage through the multiplex / select matrix 502 at a particular time. n The monitor mode is configured to use n controls to control the inputs for the case contact channels. When the monitor mode is set to a normal operation mode, all case contact channels are passed through the multiplexing / selection matrix 502 to monitor / detect the occurrence of a whisker event failure in one of the case contacts 58. When the monitor mode is set to a characterization / failure analysis mode, individual case contact channels are selected to further enable further or more detailed investigation of a given shield cavity associated with the case contact channel. In one embodiment, one or more of the case contact channels are provided to a machine learning model configured to predict whether a particular shield cavity is susceptible to tin whisker growth.

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

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

[0055] FIG. 11 illustrates an apparatus 700 for tin whisker isolation and detection using time-domain reflectometry (TDR), according to an exemplary embodiment. The apparatus 700 of FIG. 11 is similar to the apparatus 50 of FIG. 4 , except that each of the case contacts 58 is connected to a TDR detector 702 via a circuit connection 62. 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 fault locations in transmission lines and coaxial cables. A low-voltage pulsed signal is sent down the transmission line, and the TDR meter checks for any reflections that may be due to impedance mismatches. If there is no impedance mismatch along the entire line, no reflections will occur. However, if there is a discontinuity in the transmission line at a particular point, a portion of the pulsed signal will be reflected back to the TDR meter. By measuring the time and propagation velocity of the received pulse, the TDR meter calculates the location of the fault and the nature of the fault (e.g., open circuit, short circuit, impedance mismatch). Various embodiments described herein utilize TDR techniques to determine whether tin whisker growth has occurred and the location of such tin whisker growth.

[0056] 11 , the TDR detector 702 generates a series of pulses at each case contact 58 of the shield 52 to act as a monitoring point, determines whether a reflected signal is received back from one or more case contacts 52 indicative of a tin whisker event caused by whisker 80 growth, and identifies the location of the whisker event by identifying the particular cavity 54. In certain embodiments, the TDR detector 702 determines that a momentary short between the tin whisker 80 and the cavity 54 has occurred based on the shape and characteristics of the reflected signal. In certain embodiments, the TDR detector 702 uses differential TDR to detect even very small tin whisker growth.

[0057] 12 shows an apparatus 800 for tin whisker isolation and detection using vector network analysis (VNA), according to an exemplary embodiment. The apparatus 800 of FIG. 12 is similar to the apparatus 50 of FIG. 4, except that each of the case contacts 58 is connected to a VNA system 802 via circuit connections 62. The VNA system 802 is configured to isolate and characterize tin whisker events using VNA techniques to perform frequency domain analysis of the case contacts 58. The VNA system 802 uses sensing circuitry to characterize tin whisker events by detecting an interruption in the energy of the shield 52 of the card assembly when the whisker grows 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 without a tin whisker event. The VNA system 802 operates in the frequency domain and monitors the network faults that occur at the moment of tin whisker shorting and fusion events. The individual case contacts 58 act as detection points, and the VNA system 802 monitors the case contacts 58 to detect any faults in the network consisting of the mounted shield / barrier cases and their associated contact pins. When whisker growth and fusion events occur, the VNA system 802 detects any deviations from the normal state in the frequency distribution of the shield / barrier components.

[0059] 13A-13C illustrate one embodiment of a shield 900, according to an example embodiment. FIG. 13A illustrates a perspective view of the shield 900 positioned over the leads 902 of a surface-mount component 904. The shield 900 includes cavities 906 aligned over the leads 902 of the surface-mount component 904 and corresponding pads 908 to which the leads 902 are soldered. In the particular embodiment illustrated in FIGS. 13A-13C, the shield 900 includes eight cavities 906, one aligned over each lead / pad of the surface-mount component. For purposes of illustration, the cavities 906 are shown as open at one end, however, in one or more implementations, each of the cavities 906 includes an additional wall (not shown) that completely surrounds the cavity 906.

[0060] Figure 13B shows a front perspective view of shield 900 further including sensor circuitry 910 disposed on the top surface of shield 900. Figure 13C shows a rear perspective cutaway view of shield 900.

[0061] Figure 14 shows an example of tin whisker growth within the cavity of the shield of Figures 13A-13C. In the example of Figure 14, several tin whiskers 1400 have grown from the lead 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 described herein with respect to various embodiments.

[0062] For further explanation, FIG. 15 shows a flowchart illustrating an exemplary method for whisker isolation and detection according to an exemplary embodiment. For a device having an electronic component disposed on a substrate having a plurality of pads for connecting to the electronic component, the method includes disposing a shield 1502 on a surface of the substrate. The shield has a plurality of cavities aligned over the plurality of pads. Electrically conductive growth from a corresponding one of the plurality of pads is detected 1504 using a sensing component associated with one of the plurality of cavities. Each of the sensing components is associated with one of the plurality of cavities.

[0063] One or more sensing signals from one or more of the sensing components are received by a detection circuit 1506. The detection circuit detects 1508 electrically conductive growth from the corresponding pads based on the one or more sensing signals.

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

[0065] In one embodiment, the method further includes step 1510 of identifying, by the detection circuitry, pads having electrically conductive growth based on the one or more sensing signals.

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

[0067] In view of the above discussion, the reader will recognize that advantages of tin whisker isolation and detection according to embodiments of the present invention include providing an enhanced whisker growth barrier that is impenetrable by tin whiskers, and enhanced whisker detection in which whisker events such as momentary shorts are identified.

[0068] From the foregoing description, it will be understood that modifications and changes may be made in various embodiments of the present invention without departing from the true spirit thereof. The description herein is for purposes of illustration only and is not to be construed in a limiting sense. The scope of the present invention is limited only by the language of the following claims.

Claims

1. 1. An apparatus for the isolation and detection of tin whiskers, said apparatus comprising: a substrate having a plurality of pads for connecting to electronic components disposed on the substrate; a shield disposed on a surface of the substrate, the shield having a plurality of cavities aligned over the plurality of pads; a plurality of sensing components, each of the sensing components associated with one of the plurality of cavities and configured to sense electrically conductive growth from a corresponding pad of the plurality of pads; a plurality of circuit connections, each of the plurality of circuit connections configured to connect one of the sensing components to a detection circuit; and the detection circuit configured to receive one or more detection signals from one or more of the sensing components and detect electrically conductive growth from the corresponding pad based on the one or more detection signals; An apparatus comprising:

2. The apparatus of claim 1 , wherein the detection circuitry is configured to identify the pads having the electrically conductive growth based on the one or more sense signals.

3. The apparatus of claim 1 , further comprising a plurality of contacts, each of the plurality of contacts coupled to an output of a corresponding one of the plurality of sensing components.

4. 4. The apparatus of claim 3, wherein each of the plurality of contacts is further coupled to the detection circuit.

5. The apparatus of claim 1 , wherein one or more of the plurality of sensing components comprises an operational amplifier.

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

7. The apparatus of claim 1 , wherein the plurality of sensing components are disposed on a separate substrate, the separate substrate being mounted to an outer surface of the shield.

8. 2. The apparatus of claim 1, wherein each of the plurality of sensing components comprises a Hall Effect sensor configured to sense changes in a magnetic field generated by a magnet within the cavity and to generate the sensing signal based on the changes in the magnetic field.

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

10. The apparatus of claim 1 , wherein the detection circuitry is configured to output a status bit indicative of the location of the detected electrically conductive growth.

11. The apparatus of claim 1 , wherein the detection circuitry is configured to detect the electrically conductive growth using time domain reflectometry.

12. The apparatus of claim 1 , wherein the detection circuitry is configured to detect the electrically conductive growth using vector network analysis.

13. 10. The apparatus of claim 1, wherein the shield is formed from a metallized ceramic substrate.

14. 1. A method for detecting tin whiskers in a device having an electronic component disposed on a substrate, the substrate including a plurality of pads for connecting to the electronic component, the method comprising: disposing a shield on a surface of the substrate, the shield including a plurality of cavities aligned over the plurality of pads; detecting electrically conductive growth from a corresponding pad of the plurality of pads using a sensing component associated with one of the plurality of cavities, each of the sensing components associated with one of the plurality of cavities; receiving, by a detection circuit, one or more detection signals from one or more of the sensing components; and detecting, by the detection circuitry, an electrically conductive growth from the corresponding pad based on the one or more sense signals; A method for providing the above.

15. The method of claim 14 further comprising identifying, by the detection circuitry, the pads that include the electrically conductive growth based on the one or more sense signals.

16. 15. The method of claim 14, wherein detecting the electrically conductive growth from the corresponding pad further comprises sensing a change in a magnetic field generated by a magnet in the cavity, and generating the detection signal based on the change in the magnetic field.

17. 15. The method of claim 14, further comprising: selecting one of the sense signals; and detecting the electrically conductive growth from the corresponding pad based on the selected sense signal.

18. The method of claim 14 further comprising outputting a status bit indicative of the location of the detected electrically conductive growth.

19. The method of claim 14 , wherein detecting the electrically conductive growth further comprises detecting the electrically conductive growth using time domain reflectometry.

20. The method of claim 14 , wherein detecting the electrically conductive growth further comprises detecting the electrically conductive growth using vector network analysis.

Images