Low-current voltage source watchdog

Abstract

A voltage source watchdog includes a passive device placed in series between a voltage source and a load. The passive device includes an electromigration (EM) connection point of a known material that will form an electromigration void upon passage of a specified amount of current through the EM connection point. After a known amount of current is passed, a void is formed and a voltage is no longer sensed, providing a reliable safe mode condition. When the voltage source is a battery, battery life may be extended by selectively enabling voltage measurement operations of the proposed watchdog.

Description

Background Art

[0001] The present invention relates generally to the field of power management and, more particularly, to monitoring power in a voltage source.

[0002] According to the PCI (Payment Card Industry) data security standard, cryptographic cards require security protection when powered by batteries.

[0003] MEMs (micro-electromechanical systems) and their related micro-electromechanical and micro-systems constitute technologies for microscopic devices, especially those with moving parts. MEMs are tiny machines that have both mechanical and electronic components. MEMs can be embedded in silicon to perform certain mechanical tasks based on electrical inputs. Summary of the invention

[0004] In one aspect of the present invention, an apparatus includes: (i) an element substrate having a wire bonding site configured for electrical connection between a voltage source and an electronic device; (ii) a wire bonding comprising a wire having two terminals, the wire including a molten portion having a first length and two ends, each end including one of the two terminals, the molten portion having a diameter smaller than the two ends, the two terminals being attached to the element substrate at the wire bonding site; and (iii) a first electromigration (EM) connection point located at the first terminal, the EM connection point being formed at a ball bond connecting the first terminal of the wire to a metal pad at the wire bonding site.

[0005] In another aspect of the present invention, a battery backup circuit for a cryptographic card includes: (i) a cryptographic circuit board; (ii) a battery; (iii) a processor; and (iv) an electromigration (EM) connection point assembly including a first wire bond having a fused wire of a first length, the EM connection point assembly being electrically connected in series with the battery and the processor. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 is a schematic diagram of a circuit according to the present invention;

[0007] Figure 2 is a perspective view of a wire bond according to the present invention;

[0008] Figure 3 is a perspective view of an electromigration timer according to the present invention;

[0009] Figure 4 is a perspective view of an exemplary structure after depositing a first layer of material on a substrate; and

[0010] Figure 5 is a perspective view of an exemplary structure of an electromigration timer according to the present invention. DETAILED DESCRIPTION

[0011] Some embodiments of the present invention relate to a voltage source watchdog including a passive device placed in series between a voltage source and a load, having an electromigration (EM) junction made of a known material that forms an electromigration void after a specified amount of current passes through the EM junction. After a known amount of current passes, the void is formed and the voltage is no longer sensed, thereby providing a reliable safe mode condition. When the voltage source is a battery, the battery life can be extended by selectively enabling the voltage measurement operation of the proposed watchdog. Applications of the battery watchdog include processor memory that relies on a battery.

[0012] Low voltage applications often require a long battery life. For example, according to the PCI (Payment Card Industry) data security standard, password cards require security protection when powered by batteries. If continuous monitoring is performed to ensure that sufficient battery power is available, the batteries used in these applications will be consumed in advance. A low-current battery watchdog is proposed in this article for periodically ensuring battery power over a period of time that can be long (which may be, for example, one to five years). Other areas where low-current voltage source watchdogs may be applied include IoT (Internet of Things), automotive applications, and computing servers. IoT devices can be improved by using a disclosed watchdog that monitors the power of a voltage source using an EM connection point to monitor the operating status of a low-power circuit. For automotive applications, any circuit with a fuse can be improved by using a disclosed watchdog that monitors the power of a voltage source using an EM connection point. The use of an EM connection point eliminates the need for additional circuits to monitor overcurrent conditions because the EM connection point forms a disconnected state when exposed to an overcurrent condition.

[0013] When a low battery condition occurs, preemptive measures are usually taken, such as shutting down the system or destroying saved data for safety purposes. Sometimes the low battery condition is a false positive event. By inserting a low current voltage source watchdog (also referred to herein as a battery watchdog) that periodically verifies the battery charge and operates to identify a failed battery before the system takes preemptive low battery action in the existing circuit, managing battery life over the course of a five-year life is achieved. The voltage source watchdog device utilizes an EM controlled or EM regulated sensor.

[0014] By targeting the wire bond pad interface for failure, failures can be designed into the circuit, creating a predictable duration before failure. By establishing this predictable duration, it is known that the voltage source is still functional because it is able to generate the expected failure at the target time. Multiple electromigration-based sensors are set to fail at different times, creating a periodic voltage check for failure or no failure. Voltage measurement circuits can continuously or periodically monitor the voltage across the load or DUT.

[0015] Some embodiments of the present invention recognize the following facts, potential problems and / or potential areas of improvement relative to the current state of the art: (i) cryptographic hardware is subject to a three to five year maintenance-free battery capability requirement; (ii) if the cryptographic hardware detects a low voltage on the battery domain at any time, the hardware will automatically enter a safe mode and destroy any saved data; (iii) battery life conservation should be carefully considered to achieve a five year battery life; (iv) with sufficient current flow, metal can move by electromigration forming voids and / or shorts in microelectromechanical systems (MEMs); (v) electromigration depends on current flow, material, cross-sectional area and metallurgy; (vi) precise design of electromigration supports a known time when the expected Kirkendall void will appear; (vii) some cryptographic hardware maintains a current draw of less than 100 μA (approximately 30 to 60 μA); and (viii) monitoring battery life tends to consume battery power.

[0016] In one aspect of the invention, an apparatus comprises: (i) a component substrate having a wire bonding site configured for electrical connection between a voltage source and an electronic device; (ii) a wire bond comprising a wire having two terminals, the wire comprising a fused portion having a first length and two ends, each end comprising one of the two terminals, the fused portion having a diameter smaller than the two ends, the two terminals being attached to the component substrate at the wire bonding site; and (iii) a first electromigration (EM) connection point at the first terminal, the EM connection point being formed at a ball bond connecting the first terminal of the wire to a metal pad at the wire bonding site. The EM connection point advantageously provides a sensor of battery status because when the EM connection point carries current, the battery is indicated as being in good condition.

[0017] In another aspect of the invention, the diameter of the fused portion is set based on a specified current through the wire bond. By setting the diameter to a specified current associated with the application, the wire bond EM connection point can be designed to fail after a specified number of years of operation.

[0018] In yet another aspect of the present invention, the voltage source is a battery and the electronic device is a cryptographic card.Some embodiments of the present disclosure advantageously support battery-dependent memory of a cryptographic card.

[0019] In another aspect of the invention, the diameter and the first length of the molten portion are sized to carry a specified current for a specified number of years before an open circuit is formed due to electromigration at the EM junction. In this way, electromigration failure of the EM junction is designed so that as long as the EM junction passes current, the measured voltage will indicate the state of the battery, wherein failure before the specified number of years indicates damage to the battery and thus a potential bad battery.

[0020] In yet another aspect of the invention, the specified current is less than 100 μA. Some embodiments of the invention are directed to relatively low current applications less than 100 μA, with some applications as low as 30 μA.

[0021] In one aspect of the invention, a battery backup circuit for a cryptographic card includes: (i) a cryptographic circuit board; (ii) a battery; (iii) a processor; and (iv) an electromigration (EM) connection point assembly, the EM including a connection point assembly first wire bond, the first wire bond having a first length of fused wire, the EM connection point assembly being electrically connected in series with the battery and the processor. The EM connection point assembly advantageously provides a sensor of battery status because when the EM connection point assembly carries current, the battery is indicated as being in good condition.

[0022] In another aspect of the present invention, a battery backup circuit for a cryptographic card includes a voltage measurement circuit electrically connected in parallel with the processor to read the voltage across the processor. The voltage measurement circuit can advantageously provide battery charge monitoring while verifying current flow through the EM connection point assembly.

[0023] In another aspect of the present invention, an EM connection point assembly for a battery backup circuit for a cryptographic card includes a second wire bond having a second length of fused wire, the first wire bond and the second wire bond being electrically connected in conjunction, the second length being greater than the first length. A pair or more wire bonds in the EM connection point assembly allow for intermediate verification of normal function of the EM connection point assembly while providing a more controlled assurance of continued normal battery function.

[0024] In another aspect of the invention, the first length of fused wire is a middle portion of a wire having two ends, the first length of fused wire being between the two ends, each end including one of the two terminals, the fused portion having a smaller diameter than the two ends, the two terminals being attached to the component substrate of the EM connection point assembly. The EM connection point advantageously provides a sensor of battery status because the battery is indicated as being in good condition when the EM connection point carries current.

[0025] In yet another aspect of the invention, an EM connection point assembly for a battery-backed circuit for a cryptographic card includes an EM connection point at a first terminal, the EM connection point forming a ball bond connecting the first terminal of the wire to a metal pad at a wire bonding site on the component substrate. The EM connection point advantageously provides a sensor of battery status because when the EM connection point carries current, the battery is indicated as being in good condition.

[0026] Kirkendahl effect and Kirkendahl voids are the result of thermally driven or electrically (electromigration) driven atomic diffusion. The Kirkendahl effect is the movement of the interface between two metals due to the difference in the diffusion rate of metal atoms. If an atomic species diffuses faster from one element, phase or compound at the interface relative to the diffusion rate of another element, phase or compound, the resulting interface movement and the accumulation of atomic vacancy concentration at the interface lead to void formation. As diffusion proceeds, atomic vacancies aggregate into microscopic voids at the interface. The significant accumulation of voids at the interface may damage the mechanical and electrical integrity of the interface, which leads to electrical failure. Kirkendahl voids have been observed to occur in various electronic interconnects, including: (i) solder connection points; (ii) wire bonding; and (iii) sintered-co-fired metals and / or ceramics.

[0027] The mean time to failure (MTTF) due to electromigration can be calculated using Black's equation:

[0028]

[0029] Where A is a constant that depends on the cross-sectional area, j is the current density, n is a scaling factor (usually set to 2), and E a is the activation energy of electromigration, k is the Boltzmann constant, and T is the absolute temperature in Kelvin. Electrical failures caused by electromigration include: (i) atomic deposition, hillock, which leads to short circuits; and (ii) atomic depletion, voids, which leads to disconnections.

[0030] Some embodiments of the present invention are directed to identifying and / or monitoring the operating status of a battery backup of a cryptographic card over a period of years. By reliably identifying the operating status of a battery backup, false battery failures can be avoided, thereby reducing unnecessary repairs and / or replacements. Some embodiments of the present disclosure employ a series of EM fuses or EM / thermal fuses that allow monitoring of battery function at very low currents (typically less than 100uA).

[0031] According to some embodiments of the present invention, a passive device is placed in series between a voltage source and a load. The passive device is constructed and / or inserted to include an electromigration connection point. The electromigration connection point is made of a material known to form an electromigration void after a specified current density j flows through the connection point for a predetermined duration T. Therefore, in some embodiments of the present invention, when exposed to a specified current density for a specified amount of time or duration, a void is formed and the voltage will no longer be sensed, thereby providing a reliable safety mode condition. Alternatively, at a specified duration T, the circuit is evaluated to determine whether the passive device is in a disconnected state. If the disconnected state occurs for a specified duration, the voltage source charge is confirmed to be at an operating level. If the disconnection does not occur, the voltage source charge is marked as being below the operating level. Because the lack of a disconnected state indicates that the passive device has been exposed to a lower current density than required to operate the voltage source or battery cell, the voltage source charge is unreliable or marked. If the evaluation discloses that the disconnected state occurs before the designed duration T, it can be predicted that the voltage source may fail prematurely due to an excessively high current density flowing through the passive device.

[0032] Figure 1 1 is a circuit diagram showing a battery and a load having an electromigration (EM) connection point in which the battery is monitored for operating conditions. Circuit 100 includes: a voltage source 104, an EM connection point 102, a load or device under test (DUT) 106, and a voltage measurement circuit 108. In this example, the EM connection point contains a packaged battery watchdog. The EM connection point is designed to detect the voltage at a predetermined time interval (from T0 to T1). f , where T0 is the initial time, T f The electromigration that causes the open circuit at the EM junction (time of failure or open circuit) is known as the time of failure or open circuit. At the moment of failure, the EM junction interrupts the flow of current through the junction, resulting in an open circuit state.

[0033] According to some embodiments of the present invention, voltage measurements are made by a voltage measurement circuit 108 across the load / DUT 106 during normal operation to establish a baseline for the duration of the EM connection point. When the voltage source 104 is a battery, the voltage can be monitored periodically, such as, for example, 1 Hz, 0.1 Hz, once a minute, or once an hour. If battery life is critical, the voltage measurement circuit is disabled except when measurement operations are required. By disabling or limiting the frequency of voltage measurements, battery life is longer than if voltage measurements are continuously made. The load / DUT impedance may drop for a variety of reasons, including: (i) during tampering with the password card; and (ii) during operation that exceeds specifications and potentially damages the circuit being powered.

[0034] Some embodiments of the present invention are directed to multiple EM sensors with various designed durations to electromigration (EM) failure in a single system. For example, a first electromigration sensor may be designed for a duration to EM failure of T1, and a second electromigration sensor may be designed for a duration to EM failure of T2, where T2 is greater than T1. When the two EM sensors are arranged in a parallel circuit with a battery generating a known current, the first EM sensor will fail after the first duration, earlier than the second EM sensor. Intermediate determination of battery status is achieved with multiple EM sensors with various designed durations to electromigration (EM) failure in a single system.

[0035] Some embodiments of the present invention operate in applications with current demands in the range of 100μA to 300mA. Some embodiments of the present invention are deployed with on-chip metallization functions below 100μA. On-chip metallization can be implemented in new semiconductor chips, ASICs (application-specific integrated circuits), or independent smaller chips that work as part of a regulator feedback loop. In addition, with respect to the wire bonding embodiments of the present invention, the addition of prestress burns including high continuous current or high temperature thermal aging exposures used independently or in combination drives a large amount of interfacial degredation on the burned-in hardware, so that relatively low levels of current and lower temperatures in operation can cause electromigration connection points to fail within a specified functional time window.

[0036] Figure 2 Wire bonding according to an embodiment of the present invention. Wire bonding 200 includes: bonding wire 202, Rayleigh filament 204, ball bond 206 and wedge bond 208. The original diameter of the bonding wire is processed to form a Rayleigh filament of a specified length and diameter for interface failure caused by electromigration. Interface failure can be designed to occur at the ball bond or the wedge bond. Diffusion occurs at the weld of the bond.

[0037] Fused wire bonds can be initially prepared by a melting process and then installed. Initial preparation can involve applying an external heat treatment to the bond wire. The wire bond to pad interface may degrade after installation to drive eventual directional electromigration failure. The melting process can be applied to bond wires made of any noble metal, such as gold, that forms the filaments for the sensor.

[0038] According to some embodiments of the present invention, historical failures of certain wire bonds in the field provide the data needed to predictably form electromigration fuses for periodically verifying battery life.

[0039] According to some embodiments of the present invention, the time frame or duration within which a wire bond is targeted to fail may be from one month to six years.

[0040] Some embodiments of the present invention are directed to a stand-alone electronic package including one or more wire bonds attached to a substrate with the wire bond connections terminating at peripheral leads or array pads, which is presented as a sensor packaging solution.

[0041] One use case for electronic packaging is a battery watchdog in a cryptographic card application. Electromigration fuses are made extremely small to drive significant Joule heating into the interconnects of the fuse itself to ensure that electromigration driven diffusion can cause failure when used in an application. Small size is achieved by creating a wire bond package where the wire bonds are made small enough that their bonding interface can be significantly heated by applying a small current to form an electromigration fuse or series of fuses.

[0042] Figure 3 is for mounting to a circuit (e.g., circuit 100 ( Figure 1 )) is a package set of wire-bonded sensors. The wire-bonded sensor package 300 includes: a gold-plated pad 302; a wire-bonded jumper pad 304; a component substrate 306; and a group of wire-bonded timers or sensors 310a, 310b, 310c.

[0043] The current carrying limit for a wire bond of a given material and wire diameter at which it begins to melt (melt) in air is usually estimated using the Preece equation:

[0044]

[0045] Where i = maximum current (amps), D = wire diameter (in), and k is a material constant (k = 10,244 for Au). The formula is valid for individual wire bonds in air with wire lengths < 0.040".

[0046] For wire bonds of varying lengths, a modified Priss equation is used and highlighted in the MIL specification standard MIL-M-38510 and is based on a simplified form of the Joule heating model where the maximum current I (amps) required to melt is proportional to the following expression:

[0047]

[0048] Where k = thermal conductivity of the wire material, p = resistivity of the wire material, D = wire diameter, and l = length of the wire bond.

[0049] According to some embodiments of the present invention, a wire bonding post-processing method is provided that involves adding a short burst pulse current to cause individual bonding wires to melt and / or fuse. This is a way to make the wire bonds small enough to act as a cryptographic battery watchdog. Individual bonding wires are melted at their approximate centerline by the proposed method, where the molten metal retracts by capillary action and control of surface tension to form very fine filaments.

[0050] The very fine filaments described herein are also referred to as Rayleigh filaments. The formation and ultimate stability of the filaments were studied and determined by Lord Rayleigh, where the maximum fused gap or filament length is equal to 4.51*d, where d is the starting diameter of the wire. The specific current amount and duration of the pulsed applied current can be adjusted based on the specific bonding wire and wire bond length to form fused filaments of varying lengths on wire bonds of varying lengths, where the filament length is as high as the Rayleigh instability limit of 4.5*d. By making a wire bond package with Rayleigh filaments, very high operating temperatures of the wire bonds can be achieved at very low current levels.

[0051] The use of a sensor package with bonding wires having different lengths of fused segments will allow the duration T when battery operation is confirmed to be adjusted. The ability to create sensors that will fail in various durations can be used for various watchdog applications, including watchdog applications for password cards. Multiple wire bonds are connected in parallel to form current sharing and allow normal battery function detection over time, because the presence of wire bonds of different lengths with Rayleigh filaments of different lengths will fail at different times within the life of the product. According to some embodiments of the present invention, when a parallel wire fails, the remaining (one or more) wires will share more current, but this (one or more) wire and part of the "timer circuit" are also designed to be able to carry more current. For example, any remaining wire bonds can be made of relatively short lengths of wire and / or filaments of larger diameter. In that way, the longest wire / filament has the shortest failure time. When the wire fails, the voltage and / or impedance change is detected. This process continues because the parallel wires in the circuit fail over a long period of time.

[0052] For example, using a 0.8 mil diameter starting bonding wire (20 μA), a Rayleigh filament of approximately 0.08 mil (2 μA) can be created via a melting process. According to the Priest equation, the maximum current that can be carried in a 0.08 mil wire is 7.3 mA. The maximum current using the modified Priest equation for a Rayleigh filament of 125 microns in length at a temperature of 400°C with the properties of gold material is approximately 3.1 mA.

[0053] According to another embodiment of the present invention, the chip metallization establishes electromigration connection points via photolithography of the semiconductor structure. Figure 4 and Figure 5 As described, photolithographic techniques are used to create electromigration connection points with specific characteristics designed for electromigration failure when exposed to a specified current density for a defined period of time.

[0054] Reference now Figure 4 and Figure 5 An exemplary structure for forming an electromigration timer or sensor device includes a semiconductor substrate 402. A trench having a thickness less than the thickness of the substrate is formed on the semiconductor substrate 402. Material layers 406 and 408 are deposited on the surface of the trench using a thin film method known in the art to form Figure 4 The partial structure 400 in FIG. 406 may be one of the following metals: Cu, Al, Cr, Ag, Au, and Ni. The material layer 408 is a dielectric material for electrically isolating the material layer 406.

[0055] Electromigration (EM) timer 500 is formed by depositing a layer of substrate 402 and forming a trench through the deposited layer to the top surface of structure 400. A second layer of material is deposited over material layers 406 and 408, the second layer including metal layer 504. The second layer of material is placed so that metal layers 504 and 406 overlap a distance 506 forming electromigration interface 502. Metal layers 504 and 406 are made of different metals, including Cu, Al, chromium, Ag, Au, and Ni. Material layer 408 is a dielectric material that electrically isolates metal layers 504 and 406. Dielectric 510 in the second layer of material electrically isolates metal layers 504 and 406 except for the electrical connection at electromigration interface 502.

[0056] Electromigration interface 502 can be set for a specific duration before voids caused by electromigration make the electrical connection weak. Dimensions 508 and 512 are adjustable properties of thin current carrying member 514 that limit the current flow to a specified amount. When the current flow exceeds the specified current amount, EM interface 502 can produce EM-induced voids earlier than the specified duration. Alternatively, when the current flow exceeds the specified current amount, thin current member 514 fails, resulting in an open state across the thin member. Dimension 506 is an adjustable property of the EM interface. The surface area of ​​the EM interface combined with the current flow limitation establishes a failure time target for voids caused by electromigration to make the electrical connection weak. Figure 5 A single EM timer is shown. Multiple EM timers with various expiration time designs allow for periodic battery integrity checks based on the actual expiration time of each EM timer.

[0057] The electromigration interface may be based on the following metal layer EM pairs (404 / 406 pairs): Cu and Al, Al and Cr, Cu and Cr, Cu and Ag, Cu and Au, and Al and Au. Other EM paired metals may be used according to embodiments of the present invention.

[0058] According to some embodiments of the present invention, a construction and processing flow for forming a watchdog sensor package with an electromigration (EM) fuse includes: (i) constructing a watchdog element substrate; (ii) creating a wire bonding assembly; (iii) performing high current pretreatment on the wire bonding assembly to form Rayleigh filaments on each bonding wire; (iv) applying a protective cover on the assembly; and (v) assembling the wires into a target circuit, such as on a cryptographic circuit board for a security card.

[0059] The watchdog element substrate 306 can be created from (but is not limited to): (i) circuit board laminate, (ii) ceramic, and (iii) lead frame ( Figure 3). For example, the component substrate 306 includes a gold plated pad 302 suitable for wire bonding the device to an aluminum pad mounted thereon or an aluminum slug that can be mounted on the substrate. The component substrate can be made with a wire bonding jumper pad 304 that includes nickel plating and hard gold or doped gold. The component substrate can include a single wire bonding site 310a to create a single electromigration timed connection. The component substrate can include multiple wire bonding sites 310a, 310b, 310c for serial or parallel connection to create multiple timed watchdogs. The wire bonding sites can be within the component substrate, or connected to the substrate at the application component level.

[0060] The wire bond assembly can be created by thermosonic assembly, ultrasonic assembly, or other assembly techniques currently known or that may become known in the future. The individual bond wires can be made of materials including, but not limited to: (i) aluminum; (ii) copper; (iii) gold; (iv) silver; and (v) palladium.

[0061] Wire bond pre-treatment of the assembly with high heat can be achieved by varying the current / pulse to form filaments of desired length up to the Rayleigh instability limit of the material (4.51*d).

[0062] Assembling the packaged watchdog component into the target circuit can be accomplished using a variety of techniques, including but not limited to: (i) soldering; and (ii) separable connectors. The component can be a peripheral pin or array package for SMT soldering or connector insertion. The component can contain single or multiple wirebond wires, where the presence of parallel circuits of wirebonds can provide additional options for monitoring electromigration failures over time, particularly when the component package is made with wirebonds of varying lengths or different bond wire materials and / or diameters.

[0063] Some embodiments of the present invention may include one or more of the following features, characteristics and / or advantages: (i) detecting safe mode conditions through physical evidence of voids formed at strategically defined electromigration connection points; (ii) monitoring periodic failures based on an EM timer reduces the drain on the battery that would be found in continuous monitoring of the battery itself.

[0064] A variety of tuning parameters may be used by those skilled in the art. These various tuning parameters allow for a range of failure times throughout the duration of the product life when using multiple independent watchdog packages with separate wire bonds or when using a watchdog package with multiple wire bonds that can be connected in parallel with the application.

[0065] The failure time duration of a thermal diffusion / electromigration fuse package made with wire bonding can be adjusted by changing a variety of construction and / or watchdog processing parameters, including: (i) wire bond or chip / thin film wire length; (ii) substrate pad metallurgy (Al, Au and Ag) used for wire bond or chip metallization; (iii) pad electroplating dopant addition (for example, wire bond or chip pad made with hard gold plating containing palladium, iron, silver, platinum and silicon); (iv) pad metallurgy thickness; (v) wire bond or chip wire material, such as Au, Pd, Ag, Pt, Cu, Al; (vi) starting wire diameter or chip trace width; (vii) fuse current and time pulse (wire bond only); (viii) thermal pretreatment (burn-in) after wire bond or chip trace; and (ix) electrical pretreatment (burn-in) after wire bond or chip trace.

[0066] Some useful definitions are:

[0067] The present invention: should not be taken as an absolute indication that the subject matter described by the term "the present invention" is covered by the claims as filed or by claims that may ultimately issue after patent examination; although the term "the present invention" is used to help the reader gain a general sense of what is disclosed herein that is believed to be potentially new, such understanding, as indicated by the use of the term "the present invention", is tentative and provisional and is subject to change during the patent prosecution process as relevant information is clarified and the claims are potentially amended.

[0068] Embodiments: See above for the definition of "the present invention" - similar considerations apply to the term "embodiments".

[0069] And / or: inclusive; for example, A, B "and / or" C means at least one of A or B or C is true and applicable.

Claims

1. A device comprising: a component substrate having wire bonding sites configured for electrical connection between a voltage source and an electronic device; a wire bond including a wire having two terminals, the wire including a fused portion having a first length and two ends, each end including one of the two terminals, the fused portion having a smaller diameter than the two ends, the two terminals being attached to the component substrate at the wire bond site; as well as A first electromigration (EM) connection point at a first terminal is formed at a ball bond connecting the first terminal of the conductive line to a metal pad at the wire bonding site. 2 . The apparatus according to claim 1 , wherein a diameter of the molten portion is set according to a specified current passed through the wire bonding.

3. The device according to claim 1, wherein: The voltage source is a battery. The apparatus according to claim 1 , wherein the electronic device is a password card.

5. The apparatus of claim 1, wherein the diameter and the first length of the molten portion are sized to carry a specified current for a specified number of years before an open circuit is formed due to electromigration at the EM junction. The device of claim 5 , wherein the specified current is less than 100 μA.

7. A battery backup circuit for a password card, comprising: Password circuit board; Battery; processor; as well as An electromigration (EM) connection point assembly including a first wire bond having a fused wire of a first length, the EM connection point assembly being electrically connected in series with the battery and the processor.

8. The circuit according to claim 7, further comprising: A voltage measurement circuit is electrically connected in parallel with the processor to read the voltage across the processor.

9. The circuit of claim 8, wherein: The voltage measurement circuit is normally open and measures the voltage when the circuit is closed, thereby allowing periodic voltage measurement.

10. The circuit of claim 7, wherein the EM connection point assembly further comprises: A second wire bond has a second length of fused wire, the first wire bond and the second wire bond are electrically connected in conjunction, and the second length is greater than the first length.

11. The circuit of claim 7, wherein: The first length of fused wire is a middle portion of a wire having two ends, the first length of fused wire being between the two ends, each end including one of the two terminal ends, the fused portion having a smaller diameter than the two end portions, the two terminal ends being attached to a component substrate of the EM connection point assembly.

12. The circuit of claim 11, wherein the EM connection point assembly further comprises: An EM connection point at the first terminal is formed at a ball bond connecting the first terminal of the wire to a metal pad at a wire bonding site on the component substrate.

13. A semiconductor structure for an electromigration timer, the semiconductor structure comprising: Semiconductor substrate; as well as an electromigration (EM) timer embedded in the semiconductor structure, the EM timer comprising a first contact and a second contact, the first contact having an adjustable characteristic for defining an electrical connection duration that terminates when an electromigration-induced void forms an open circuit condition at the EM interface; in: the first contact being in electrical communication with the second contact at the EM interface where the first electrical contact overlaps the second electrical contact; and The adjustable properties of the first contact include the surface area of ​​the EM interface and a thin current carrying member that limits current flow through the EM interface to a specified amount.

14. The semiconductor structure of claim 13, wherein the tunable characteristics at the electromigration interface include a contact width, an overlap length, and a contact thickness of each of the first and second contacts, and a contact width and thickness of the thin current carrying member of the first contact.

15. The semiconductor structure of claim 13, further comprising: A dielectric material isolates a portion of the first contact from a portion of the second contact to define an overlap length at the electromigration interface.

16. The semiconductor structure of claim 13, wherein the first contact and the second contact are comprised of metals that form an electromigration pair of dissimilar metals.

17. The semiconductor structure of claim 16, wherein the first contact is copper (Cu) and the second contact is aluminum (Al).

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