TRANSIENT ELECTRONIC DEVICE WITH ION-EXCHANGED GLASS TREATED INTERPOSER
A transient electronic device utilizes a glass-based interposer that is treated using ion-exchange processing to increase its fragility, and includes a trigger device operably mounted on a surface thereof. An integrated circuit (IC) die is then bonded to the interposer, and the interposer is mounted to a package structure where it serves, under normal operating conditions, to operably connect the IC die to the package I/O pins/balls. During a transient event (e.g., when unauthorized tampering is detected), a trigger signal is transmitted to the trigger device, causing the trigger device to generate an initial fracture force that is applied onto the glass-based interposer substrate. The interposer is configured such that the initial fracture force propagates through the glass-based interposer substrate with sufficient energy to both entirely powderize the interposer, and to transfer to the IC die, whereby the IC die also powderizes (i.e., visually disappears).
This application is a continuation of U.S. Ser. No. 15/689,566, filed Aug. 27, 2017, which is as divisional of U.S. Ser. No. 14/694,132, filed Apr. 23, 2015, now U.S. Pat. No. 9,780,044.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
This invention is based upon work supported by DARPA under Contract No. HR0011-14-C-0013 (3765). Therefore, the Government has certain rights to this invention.FIELD OF THE INVENTION
This invention relates to transient electronics, and in particular to interposers utilized in transient electronic assemblies.BACKGROUND OF THE INVENTION
Large area sensing is critical for a variety of military, ecological and commercial interests and has historically been served through the use of centralized long-range sensors. However, rapid improvements in miniaturization of electronic systems have significantly improved the capabilities of small sensor devices. These micro-sensors have the potential to create “large N” distributed networks with advantages in operational adaptability, non-traditional sensing modalities that are only possible with close proximity, increased sensitivity and knowledge extraction through networked intelligence.
While distributed network systems have remarkable promise, their realistic use is limited by risks associated with their accumulation in the environment, detection and defeat, and exploitation due to inability to maintain positive control (unlike centralized long-range sensors).
The phrase “transient electronics” refers to a relatively new family of electronic devices that disappear (disaggregate and disperse) within a set period of time, making them ideally suited for distributed network systems. Conventional transient electronic systems typically rely on the use of soluble substrates and electronic materials (such as silk). When placed into solvent (typically water), these conventional substrates and electronics slowly dissolve into solution. As such, a distributed network system made up of conventional transient electronic devices can be expected to “disappear” over a relatively short amount of time (e.g., after periodic rainfall).
Although the conventional transient electronic approaches achieve the goal of causing the electronics to “disappear” after use, the long dissolution period required to achieve complete disaggregation and dispersal make the conventional approaches unfit for discrete (e.g., military) applications that require rapid and complete disaggregation upon command. Moreover, the conventional approaches utilize materials that are not compatible with existing integrated circuit fabrication and assembly techniques, requiring the development of new IC fabrication processes at significant cost.
Interposers are well-known electrical interfaces in the context of semiconductor device packaging, and are typically disposed between an IC die (chip) and a standardized semiconductor package structure, such as a ball-grid array (BGA) package or a pin-grid array (PGA) package. Interposers typically include a flat insulator substrate (e.g., either a rigid insulator such as FR4, or a flexible insulator such as polyimide) through which multiple metal conductors extend between corresponding contact structures (points) that are disposed in two different patterns on opposing substrate surfaces. That is, a first set of contact points disposed on one side of the interposer substrate are formed in a pattern that matches corresponding contact pads on the IC die to facilitate IC-to-interposer connection (e.g., by way of surface mounting techniques), and a second set of contact points on the opposing side of the interposer are arranged in a second (different) pattern that matches corresponding contact structures disposed on an inside surface of the host package to facilitate surface mounting of the interposer to the host package. The metal conductors pass through the interposer substrate to provide signal paths between corresponding contact structures of the first and second sets. With this arrangement, when the host package structure is subsequently connected, e.g., to the printed circuit board (PCB) of an electrical system, the interposer facilitates passing signals between the IC die(s) and the electrical system by way of the I/O pins/balls of the host package.
Interposers were originally typically utilized to reroute IC die connections to corresponding contact points on standard package structures, but more recently serve other purposes as well. For example, as advances in semiconductor fabrication facilitate smaller IC die having correspondingly finer pitched IC die contact pads, interposers are also utilized to spread the finely spaced IC die contact points to wider pitches that are more compatible with conventional package structures. In this case, the interposer includes first contact points arranged in a finely pitched (first) pattern on one surface, and second contact points arranged in a widely pitched (second) pattern on the opposing surface, with conductive metal vias and traces extending through the substrate and along the opposing surfaces to provide electrical signal paths between associated first and second contact points. In addition to spreading finely spaced IC die contact points to wider pitches, interposers are being used to secure two or more die into a single package structure.
What is needed is a transient electronic package assembly that is compatible with existing IC fabrication techniques, and achieves sufficiently complete, on-command disaggregation of IC die disposed thereon to provide both security and anti-tampering protection by way of preventing access to the intact integrated circuit implemented on the IC die.SUMMARY OF THE INVENTION
The present invention is directed to a transient electronic device in which at least one integrated circuit (IC) die is mounted in a package structure by way of an intervening glass-based interposer, where the interposer includes a glass substrate that is treated to contain a sufficient amount of ions such that it fractures (powderizes) in response to a transient event triggering signal, and in doing so to also fractures (powderizes) the IC die(s) bonded thereon. Similar to conventional arrangements, the novel interposer includes a first set of contact points (i.e., metal pads or other contact structures) disposed on a first substrate surface and arranged in a (first) pattern that matches corresponding contact pads of the IC die, a second set of contact points disposed on the opposing substrate surface and arranged in a (second) pattern that matches corresponding contact structures of a package structure, and conductors extending on and/or through the substrate that form electrical signal paths between associated first and second contact points. According to an aspect of the invention, the IC die is fixedly attached to the interposer, and the interposer includes a glass substrate that is rendered fragile by way of ion-exchange treatment such that an initial fracture force generated by a trigger device in response to a trigger signal propagates through the interposer and powderizes the IC die. Specifically, the ion-exchange treated glass substrate is treated using known ion-exchange processes such that the glass is rendered with enough stored energy to generate secondary fractures in response to the initial fracture force such that the secondary fractures propagate throughout the glass substrate, whereby the glass substrate completely disaggregates (“powderizes”) into micron-sized particulates (i.e., ≤100 μm across) using a mechanism similar to that captured in a Prince Rupert's Drop. By fixedly attaching the IC die to the glass substrate utilizing a suitable conventional bonding technique (e.g., anodic bonding or by way of sealing glass), the secondary fractures also propagate into the IC die with sufficient energy to powderize the IC die (i.e., substantially simultaneously with the powerderization of the interposer substrate). The present invention thus facilitates the production of transient electronic devices and systems in which functional circuitry formed on the IC die(s) effectively disappears (powderizes) in a significantly shorter amount of time than is possible using conventional (e.g., soluble substrate) approaches. Moreover, by configuring the trigger device to initiate powderization upon detecting unauthorized tapering (e.g., tampering with the package structure or a printed circuit board to which the transient device is mounted), the present invention provides both security and anti-tampering protection by preventing unauthorized access to the integrated circuit implemented on the IC die while it is intact. Further, because the interposer is compatible with low-cost existing IC fabrication techniques, the present invention facilitates the production of transient electronic systems including electronic devices with minimal (or potentially without any) modification to core IC fabrication process.
According to an embodiment of the present invention, the interposer's glass substrate comprises a thin glass wafer/sheet (e.g., having a thickness in the range of 100 μm and 300 μm) of an ion-exchange specific glass (e.g., all silicate glasses having adequate alkali compositions) that is etched (e.g., using laser, mechanical or chemical etching techniques) to include multiple through-glass via (TGV) openings. The TGV openings are then filled with a conductive material (e.g., a metal such as copper), where the conductive material preferably has a Coefficient of Thermal Expansion (CTE) that is matched to (i.e., +/−10% of) the CTE of the ion-exchange specific glass, whereby the conductive material forms metal via structures having opposing ends that are exposed on the opposing substrate surfaces. Contact points (e.g., metal pads) and optional metal trace structures are then respectively patterned on one or both of the opposing substrate surfaces, the contact points being arranged in the desired patterns mentioned above, and the optional metal traces being patterned to provide electrical connections between corresponding pairs of upper/lower (first/second) contact points and opposing ends of associated metal via structures, thereby forming the interposer conductor (conductive path) between the corresponding pairs of upper/lower (first/second) contact points.
According to a presently preferred embodiment, a transient event trigger device is fabricated or otherwise disposed on each interposer when the interposer contact structures and metal trace structures are formed on the glass substrate. The trigger device includes an actuating mechanism that controls the release of (i.e., generates and applies) the initial fracture force in response to a trigger signal (e.g., an externally delivered current pulse) that is supplied to the trigger device. In alternative embodiments, the actuating mechanism comprises one of a device configured to apply resistive heating to the glass substrate, and a device configured to apply a mechanical pressure to the glass substrate. By configuring the trigger device in this way, upon receiving a trigger signal, the actuating mechanism is able to generate and apply a sufficiently strong initial fracture force to the glass substrate such that the interposer suddenly and catastrophically powderizes with sufficient force to assure complete destruction (powderization) of the IC die(s) mounted thereon.
According to another aspect of the invention, the IC die are fabricated and fixedly attached to the glass substrate using fabrication and die bonding techniques that assure coincident powderization of the IC die with the interposer. In a presently preferred embodiment, the IC die includes an IC device that is fabricated using standard silicon-on-insulator (SOI) fabrication techniques (i.e., such that the functional circuitry is implemented as an SOI integrated circuit structure). In one embodiment, the IC die is attached to the glass substrate using anodic bonding, which provides good interface adhesion for allowing crack propagation from the glass substrate to assure destruction of the adhered chip. In an alternative embodiment, another bonding method, such as using sealing glass, may be utilized. By forming the functional circuitry as SOI integrated circuits and anodically bonding the IC die to the glass substrate, reliable powderization of the IC die into small particulates during transient events is achieved. In another embodiment, the IC die is “thinned” (e.g., subjected to chemical mechanical polishing) either before or after the bonding process to reduce a thickness of the IC die, which further assures powderization of the IC die during a transient event.
According to another embodiment of the present invention, a method for producing transient electronic devices includes at least partially forming the interposer structure described above and subjecting the glass substrate to an ion-exchange treatment such that the frangibility of the glass substrate is increased. An optional shallow ion-exchange process is performed after the via etch to increase the frangibility along the via sidewalls. The trigger device (described above), the interposer contact structures and metal trace structures are formed/disposed on the glass substrate either before or after the ion-exchange treatment. One or more IC die are then fixedly attached (e.g., by anodic bonding) to an upper (first) surface of the treated glass substrate such that IC contact points are electrically connected to corresponding (first) interposer contact structures, and then the interposer is mounted onto a package structure such that contact structures disposed in a second pattern on the package structure are electrically connected to corresponding (second) interposer contact structures disposed on the lower (second) surface of the glass substrate. As described above, the interposer's glass substrate is subjected to ion-exchange treatment such that its ion content is increased until the treated glass substrate is sufficiently fragile to generate secondary fractures in response to the initial fracture force supplied by the trigger device, and the IC die is bonded to the treated glass substrate such that the secondary fractures propagate into the IC die with sufficient energy to powderize the IC die. The final particle size after triggering is based upon factors such as the glass substrate thickness, the level of ion-exchange processing, the die bonding process and the initial fracture force. In one embodiment, the IC die is patterned to provide fracture points (features) that assist in controlling the final fractured particle size (i.e., the fracture features are formed such that, when the glass substrate is powderized, the IC chip fractures along the patterned fracture features).
According to alternative specific embodiments the transient electronic device manufacturing method involves either sheet level interposer patterning or die level interposer patterning. In each case, multiple interposer cores are integrally disposed on a single glass sheet (i.e., the glass substrate of each interposer core is formed by a corresponding portion of the glass sheet). In the sheet level patterning approach, interposer contact structures and trigger devices are formed on each interposer core, then the glass sheet is diced to separate the individual interposers, which are then subjected to ion-exchange treatment (e.g., individually or in a batch), and then IC dies are then bonded onto each of the interposers. According to the die level patterning approach, the glass sheet is diced to separate the individual interposers and ion-exchange treatment is performed before interposer contact structures and trigger devices are formed on each interposer core, then IC dies are bonded onto each of the interposers. The main differences between these two approaches are cost and performance. Patterning the interposer layer before dicing will improve throughput and reduce cost but ion-exchanging the glass with patterned metal layers will also create a non-uniform surface stress profile which may reduce the frangibility. On the other hand, ion-exchanging individual die before patterning will provide a more reliable frangible substrate but the added cost of patterning individual pieces may not be favorable. Other variations to these exemplary approaches are evident to those skilled in the art.
These and other features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings, where:
The present invention relates to an improvement in transient electronic devices. The following description is presented to enable one of ordinary skill in the art to make and use the invention as provided in the context of a particular application and its requirements. As used herein, directional terms such as “upper”, “upward”, “lower”, “downward”, are intended to provide relative positions for purposes of description, and are not intended to designate an absolute frame of reference. Various modifications to the preferred embodiment will be apparent to those with skill in the art, and the general principles defined herein may be applied to other embodiments. Therefore, the present invention is not intended to be limited to the particular embodiments shown and described, but is to be accorded the widest scope consistent with the principles and novel features herein disclosed.
Referring to the middle and upper portions of
Referring to the bubble located in the upper right portion of
As depicted in the upper left portion of
Referring again to the upper left portion of
As described in additional detail below, trigger device 130 functions to initiate powderization (fragmentation) of IC die 120 during a transient event by way of generating and applying an initial fracture force onto glass substrate 111 in response to an externally generated trigger signal TS. Specifically, trigger device 130 is configured to generate an initial fracture force in response to externally generated trigger signal TS, and is operably attached to upper surface 112 of glass substrate 111 such that the generated initial fracture force is applied onto glass substrate 111. As explained below, the initial facture force is generated with sufficient energy to cause powderization of interposer 110 and IC die 120.
According to an aspect of the invention, glass substrate 111 comprises an ion-exchange specific glass material (i.e., a glass that is receptive to ion exchange treatment), and interposer 110 is fabricated using processes that render glass substrate 111 sufficiently fragile such that, in response to the initial fracture force generated by trigger device 130, secondary fractures are generated and propagate through glass substrate 111 with sufficient energy to powderize glass substrate 111. Specifically, after an interposer core is generated in the manner described below, glass substrate 111 is subjected to treatment (tempering) using known ion-exchange processes such that the ionic content of glass substrate 111 (i.e., the amount of ions contained in glass substrate 111) is increased to a point that renders the glass sufficiently fragile such that, during a subsequent transient event, secondary fractures are generated in glass substrate 111 in response to the initial fracture force applied by trigger device 130. Further, as indicated by device 100(t1) at the lower portion of
According to another aspect of the invention, IC die 120 is fixedly attached to interposer 110 such that the secondary fractures generated in glass substrate 111 during a transient event are transmitted with sufficient force to also powderize IC die 120. By fixedly attaching IC die 110 to glass substrate 111 utilizing a suitable conventional bonding technique (e.g., anodic bonding or by way of sealing glass), the secondary fractures generated in glass substrate 111 also propagate into IC die 120 with sufficient energy to powderize IC die 120 (i.e., substantially simultaneously with the powerderization of interposer 110, as depicted at the bottom of
Referring to block 211 in
Referring to block 213 in
Referring to block 215 in
Metal via structure 117A are then formed in each TGV openings 114A using a suitable method. Referring to block 217 in
The interposer cores described above are then processed to provide completed interposers onto which IC dies are mounted. According to alternative exemplary embodiments, interposer cores are processed using either sheet level patterning or die level patterning. An exemplary sheet level patterning process is described below with reference to
Starting with the integral interposer cores shown in
Die level patterning, which is depicted in
As also depicted in
In addition to the localized heating approach described in the previous embodiment, other trigger devices may be utilized to generate the initial fracture required to generate powderization of the device. For example, suitable trigger devices may be produced that generate localized fracturing using by initiating a chemical reaction on the surface of the glass substrate, or by applying a localized mechanical pressure (e.g., using a piezoelectric element) on the glass substrate.
Although the present invention has been described with respect to certain specific embodiments, it will be clear to those skilled in the art that the inventive features of the present invention are applicable to other embodiments as well, all of which are intended to fall within the scope of the present invention.
15. A transient device comprising:
- an integrated circuit (IC) die including a semiconductor substrate having an electronic circuit formed thereon, and IC contact pads disposed in a first pattern on a surface of the semiconductor substrate, the IC contact pads being operably coupled to the electronic circuit;
- a package structure including a package substrate, a plurality of first package contact structures disposed in a second pattern on a first surface thereof, a plurality of second package contact structures disposed on a second surface thereof, and a plurality of package conductors extending through the package structure between the first and second surfaces such that each package conductor forms an electrical path between an associated first package contact structure and an associated second package contact structure;
- an interposer comprising a glass substrate including a plurality of first contact points disposed in the first pattern on a first surface thereof, a plurality of second contact points disposed on a second surface thereof, and a plurality of interposer conductors, each interposer conductor being configured to form an electrical path between an associated first contact point and an associated second contact point; and
- a trigger device attached to the interposer and configured to generate and apply an initial fracture force on the glass substrate in response to a trigger signal, wherein the interposer is secured to the package substrate such that each of the second contact points disposed on the second surface are electrically connected to corresponding first package contact structures, wherein the glass substrate is configured such that secondary fractures are generated in the glass substrate in response to the initial fracture force and propagate through the glass substrate, and wherein the IC die is fixedly attached to the glass substrate such that the secondary fractures propagate into the IC die with sufficient energy to fracture the IC die.
16. The device of claim 15, wherein the glass substrate comprises a thickness in the range of 100 μm and 300 μm.
17. The device of claim 16, wherein the glass substrate comprises a silicate glass.
18. The device of claim 16, wherein the glass substrate defines a plurality of through-glass vias extending between the first surface and the second surface thereof.
19. The device of claim 18, wherein each the interposer conductor comprises a metal via structure extending through an associated through-glass via.
20. The device of claim 19, wherein the metal via structure comprises a conductive material having a Coefficient of Thermal Expansion (CTE) that is matched to a CTE of the glass substrate.
21. The device of claim 18, wherein at least some of the interposer conductors further comprises a metal trace structure disposed on one of the first surface and the second surface and extending from an associated metal via structure to one of an associated first contact point and an associated second contact point.
22. The device of claim 15, wherein the trigger device comprises an actuating mechanism configured to control release of the initial fracture force in response to an externally supplied trigger signal.
23. The device of claim 22, wherein the actuating mechanism comprises one of a device configured to apply resistive heating to the glass substrate and a device configured to apply a mechanical pressure to the glass substrate.
24. The device of claim 15, wherein the IC die is anodically bonded to the glass substrate.
25. The device of claim 15, wherein the IC die comprises a silicon-on-insulator (SOI) integrated circuit device.
26. The device of claim 15, further comprising
- one or more sensors configured to detect a tampering event; and
- a controller communicatively coupled to the trigger device and configured to trigger the trigger device in response to detection of the tampering event.
27. The device of claim 26, wherein the controller is communicatively coupled to the IC.
28. The device of claim 26, further comprising a housing and wherein the sensors are configured to detect tampering with the housing.
29. A method, comprising:
- providing a trigger signal to a trigger device attached to an interposer of a transient device, the transient device including: the trigger device; an integrated circuit (IC) die including a semiconductor substrate having an electronic circuit formed thereon, and IC contact pads disposed in a first pattern on a surface of the semiconductor substrate, the IC contact pads being operably coupled to the electronic circuit; a package structure including a package substrate, a plurality of first package contact structures disposed in a second pattern on a first surface thereof, a plurality of second package contact structures disposed on a second surface thereof, and a plurality of package conductors extending through the package structure between the first and second surfaces such that each package conductor forms an electrical path between an associated first package contact structure and an associated second package contact structure; an interposer comprising a glass substrate including a plurality of first contact points disposed in the first pattern on a first surface thereof, a plurality of second contact points disposed on a second surface thereof, and a plurality of interposer conductors, each interposer conductor being configured to form an electrical path between an associated first contact point and an associated second contact point;
- in response to the trigger signal, the trigger device generating and applying an initial fracture force on the glass substrate;
- the initial fracture force generating secondary fractures in the glass substrate that propagate through the glass substrate and into the IC die; and
- the IC die fracturing in response to the secondary fractures.
30. The method of claim 29, further comprising:
- sensing a tampering event; and
- wherein providing the trigger signal comprises generating the trigger signal in response to sensing the tampering event.
31. The method of claim 29, wherein generating and applying the initial fracture force comprises applying resistive heating to the glass substrate.
32. The method of claim 29, wherein generating and applying the initial fracture force comprises applying mechanical pressure to the glass substrate.