Patent Description:
A circuit card is the current state of the art for building assemblies of electronic devices including a plurality of integrated circuits ("chips"). These assemblies can be separated into multiple types: organic multilayer laminated printed wire board ("PWB"), low temperature co-fired ceramic ("LTCC"), and high temperature co-fired ceramic ("HTCC"). Using each of these technologies, circuit card assemblies have been fabricated.

In a superconducting supercomputer, many of the operating processing integrated circuits ("chips") are cooled to about <NUM>, but certain of the memory chips instead have a much warmer operating temperature of about <NUM>. Providing cooling at <NUM> is a costly activity, so every effort is made in superconducting supercomputer design to reduce the thermal parasitic load. This includes placing the assembly in vacuum (no convection), use of coatings and multilayer insulation to reduce radiation, and limiting the conductive thermal load between the "hot side" and "cold side" of the entire assembly.

One known method of achieving the desired operating temperatures for a superconducting supercomputer while avoiding thermal parasitic load even involves completely isolating the different-temperature chips in separate containers (e.g., vacuum containers or Dewars). Processing tasks must then be conducted via a very large number of wires extending several feet between the "hot side" and "cold side" containers, which adds considerable expense to the device and also appreciably slows down processing speed due to the distance the signals must travel.

Commonly available circuit cards have a minimum substrate thickness of <NUM> (<NUM>") with a deposited metal layer of about <NUM> (. <NUM>") thickness providing the circuit traces interconnecting the chips carried by the circuit card. In order to properly connect all the chips at <NUM> and <NUM>, the substrate will likely need to be thicker than the "standard" <NUM> (<NUM>") thickness, but as thickness increases, the thermal conduction parasitic load increases. The next issue at cryogenic temperature is the thermal expansion mismatch. Because the metal and dielectric layers are on the same order of thickness, the stress induced by changing temperatures between the two sides of the circuit card may lead to circuit card damage or warping. Warping may cause two primary problems: separation from the heatsink and device damage (lead separation).

The article "<NPL> discloses a fabrication technique of superconducting quantum interference device (SQUID) magnetometers based on Nb/AlAlOx/Nb junctions directly on a glass epoxy polyimide resin substrate, which has copper terminals embedded in advance. The advantage of this method is that no additional substrate and wirebonds are needed for assembly. Compared to conventional SQUID magnetometers, which are assembled with a SQUID chip fabricated on a Si substrate and wirebonding technique, low risk of disconnection can be expected. A directly-coupled multi-loop SQUID magnetometer fabricated with this method has as good noise performance as a SQUID magnetometer with the same design fabricated on a Si wafer. The magnetometer sustained its performance through thermal cycle test <NUM> times so far.

<CIT> discloses a SQUID (superconducting Quantum Interference Device) comprising two superposed superconductive layers with an insulating layer therebetween. A plurality of holes through the insulating layer filled with superconductive material form weak-links between the superconductive layers. One or more control lines superposed with respect to the superconductive layers provide magnetic flux through the area between the weak-links to control the zero voltage supercurrent flowing through the weak-links from one of the superconductive layers to the other thereby providing the switching function for Josephson superconductive circuits.

<CIT> discloses a micro-bridge type Josephson junction on a substrate comprising a first superconducting layer, a second superconducting layer arranged transversely over the first layer with an insulating layer therebetween, and a weak link between the first and second layers which is located in the insulating layer. The insulating layer may be formed by oxidizing the first layer prior to adding the second layer. The weak link is formed by directing a beam of high energy ions at the assembled layers, near the intersection of the inclined sides of the first and second layers respectively. The ions penetrate the surface to form a band which includes a localized region in the insulating layer having a reduced oxide concentration. This region acts as the weak link.

<CIT> discloses a high temperature superconductor junction and a method of forming the junction. The junction comprises a first high-Tc, superconductive layer (first base electrode layer) on a substrate and a dielectric layer on the first high-Tc, superconductive layer. The dielectric layer and the first high-Tc superconductive layer define a ramp edge. A trilayer SNS structure is disposed on the ramp edge to form an SSNS junction. The SNS structure comprises a second high-Tc, superconductive layer (second base electrode layer) directly on the first high-Tc superconductive layer, a normal barrier layer on the second high-Tc superconductive layer, and a third high-Tc superconductive layer (counter electrode) on the barrier layer. The ramp edge is typically formed by photoresist masking and ion-milling. A plasma etch step can be performed in-situ to remove the photoresist layer following formation of the ramp edge. A normal-superconductive (NS) structure can be optimally formed directly on the ramp edge following the plasma etch step to form an SNS junction. The SNS and NS structures are preferably formed in-situ.

<CIT> discloses a HTSC Josephson device wherein the barrier layer is a cubic, conductive material.

<CIT> discloses a substrate with metallic contact, in which at least one surface of the substrate is completely or partially provided with metallic contact. The metallic contact is provided with a matrix material for mechanical stabilization. Also a method for producing such a substrate is disclosed.

<CIT> discloses a printed circuit board (PCB) comprising an internal wiring layer, an insulating layer on the internal wiring layer, a via hole extending through the insulating layer, and an external wiring layer on the insulating layer. The internal wiring layer comprises at least one metal wiring layer. The via hole exposes the internal wiring layer. The external wiring layer is electrically connected to the internal wiring layer. The external wiring layer includes a mounting area on which a semiconductor chip is disposed and a non-mounting area on which a semiconductor chip is not disposed. A thickness of the mounting area is less than a thickness of the non-mounting area.

In an embodiment, a circuit card assembly is disclosed. A substantially planar substrate has longitudinally spaced first and second substrate end edges, transversely spaced top and bottom substrate surfaces, and laterally spaced first and second substrate side edges. At least a selected one of the top and bottom substrate surfaces has laterally arranged, longitudinally extending first, second, and third substrate regions. The first substrate region is directly laterally adjacent the first substrate side edge. The third substrate region is directly laterally adjacent the second substrate side edge. The second substrate region is located laterally between the first and third substrate regions. At least one circuit trace is located on the selected substrate surface. The portion of the circuit trace located in the first substrate region is made of only a first material. The portion of the circuit trace located in the third substrate region is made of only a second material. The portion of the circuit trace located in the second substrate region is made of both the first and second materials, wherein, in the second substrate region, the portion of the circuit trace made from the first material is at least partially arranged in direct longitudinal contact in the same layer with at least the portion of the circuit trace made from the second material.

In an embodiment, a method of providing a circuit card assembly is disclosed. A substantially planar substrate having longitudinally spaced first and second substrate end edges, transversely spaced top and bottom substrate surfaces, and laterally spaced first and second substrate side edges is provided. On at least a selected one of the top and bottom substrate surfaces, laterally arranged, longitudinally extending first, second, and third substrate regions are defined. The first substrate region is directly laterally adjacent the first substrate side edge. The third substrate region is directly laterally adjacent the second substrate side edge. The second substrate region is located laterally between the first and third substrate regions. At least one circuit trace is provided to the selected substrate surface. At least a portion of the at least one circuit trace in the first substrate region of the selected substrate surface is made from only a first material. At least a portion of the at least one circuit trace in the third substrate region of the selected substrate surface is made from only a second material. At least a portion of the at least one circuit trace in the second substrate region of the selected substrate surface is made from both the first and second materials, wherein making at least a portion of the at least one circuit trace in the second substrate region of the selected substrate surface from both the first and second materials includes placing at least a portion of a circuit trace made from the first material into direct longitudinal contact in the same layer with at least a portion of a circuit trace made from the second material.

For a better understanding, reference may be made to the accompanying drawings, in which:.

This technology comprises, consists of, or consists essentially of the following features, in any combination.

<FIG> depicts a circuit card assembly <NUM> apparatus which can be used in a "hot side cold side" environment. As described herein, the "hot side" (generally indicated by element number <NUM> in <FIG> ) could be in the range of about <NUM>-<NUM>, and more particularly about <NUM>, and the "cold side" (generally indicated by element number <NUM> in <FIG> ) could be in the range of about <NUM>-<NUM>, and more particularly about <NUM>, but any desired temperature differences could be accommodated with the described circuit card assembly <NUM>. For example, one of ordinary skill in the art could provide desired temperatures to accommodate desired operation of particular integrated circuit chips <NUM>. Moreover, the circuit card assembly <NUM> could also be used as desired in an isothermal environment.

As shown in <FIG>, the circuit card assembly <NUM> includes a substantially planar substrate <NUM> having longitudinally spaced first and second substrate end edges <NUM> and <NUM>, respectively, transversely spaced (i.e., a non-zero thickness) top and bottom substrate surfaces <NUM> and <NUM>, respectively, and laterally spaced first and second substrate side edges <NUM> and <NUM>, respectively. (The longitudinal direction Lo is defined as the horizontal direction, in the orientation of <FIG>, with the lateral La and transverse T directions both being orthogonal to the longitudinal direction, as shown. ) As shown and described here, the substrate <NUM> is substantially a rectangular prism, but could have any desired footprint or form factor for a particular use environment.

In addition to, or instead of, commonly used substrate materials such as multilayer printed wire board ("PWB"), the substrate <NUM> may be substantially made of glass, such as borosilicate glass (which may offer desirable durability and thermal conductivity properties to the circuit card assembly <NUM>), silicon, sapphire, quartz, ceramic, polyimide, liquid crystalline polymer or other low loss organic substrate, or any other suitable materials.

At least a selected one of the top and bottom substrate surfaces <NUM> and <NUM> (shown and described herein as being the top substrate surface <NUM>, for ease of depiction) has laterally arranged, longitudinally extending first, second, and third substrate regions <NUM>, <NUM>, and <NUM>, respectively. The first substrate region <NUM> is directly laterally adjacent the first substrate side edge <NUM>. The third substrate region <NUM> is directly laterally adjacent the second substrate side edge <NUM>. The second substrate region <NUM> is located laterally between the first and third substrate regions <NUM> and <NUM>, as shown in <FIG>.

During use of the circuit card assembly <NUM>, the first substrate region <NUM> may be kept at a significantly lower operating temperature ("cold side") than an operating temperature of the third substrate region <NUM> ("hot side"). The operating temperature of the second substrate region <NUM> may be in between the hot and cold side operating temperatures. The desired hot and cold side operating temperatures may be achieved in any desirable manner, including via conduction or flow-through heat sinks, thermal siphon cooling cold plates, cooling fluid immersion baths, spray cooling, impingent jet cooling, or any other desired temperature regulating or thermal control mechanism.

Stated differently, a dual-temperature circuit card assembly <NUM> not according to the present invention only present for illustration purposes may include a substrate <NUM> having at least one substantially planar substrate surface <NUM> and <NUM> defining a lateral dimension La. A first substrate region <NUM> can be defined on a first lateral portion of the substrate surface <NUM> and <NUM>. The first substrate region <NUM> is maintained at a first temperature during operation of the circuit card assembly <NUM>. A third substrate region <NUM> is defined on a second lateral portion of the substrate surface <NUM> and <NUM>, laterally spaced from the first lateral side. The third substrate region <NUM> is maintained at a second temperature, significantly higher than the first temperature, during operation of the circuit card assembly <NUM>. A second substrate region <NUM> is defined on the substrate surface <NUM> and <NUM> laterally between the first and third substrate regions <NUM> and <NUM>.

With reference to <FIG>, at least one circuit trace <NUM> is located on the selected top and/or bottom substrate surface <NUM> and/or <NUM> (here, the top substrate surface <NUM> is shown). The circuit trace <NUM> is shown schematically in the Figures, for ease of depiction and description, as a general area upon the top substrate surface <NUM>-as a somewhat ladder-shaped region in <FIG> and as a substantially I-shaped region in <FIG>. However, one of ordinary skill in the art will be aware that the areas/regions shown as a "circuit trace" <NUM> in the Figures could actually be comprised of thousands of extremely small-resolution electrically conductive pathways laid out upon the selected substrate surface, with each pathway leading between different pairs of contacts of various ones of the plurality of chips <NUM> of the circuit card assembly <NUM>. For example, one individual chip <NUM> could be linked to and from other chips <NUM> via over ten thousand individual connections for just that individual chip <NUM>. Moreover, the areas of the top substrate surface <NUM> shown in the Figures as having, or not having, circuit traces <NUM> thereupon are not definitive. One of ordinary skill in the art could readily provide circuit traces <NUM> for a particular use environment of the circuit card assembly <NUM> without limitation by the dramatically simplified depiction herein. The circuit traces <NUM> could be provided by lithography, additive manufacturing, or in any other desired manner.

The portion of the circuit trace <NUM> located in the first substrate region <NUM> is made of only a first material. The portion of the circuit trace <NUM> located in the third substrate region <NUM> is made of only a second material. The portion of the circuit trace <NUM> located in the second substrate region <NUM> is made of both the first and second materials. In other words, at least one circuit trace <NUM> is located on the substrate surface <NUM>, and any portion of the at least one circuit trace <NUM> which is located in the first substrate region <NUM> is made only of a first material, any portion of the at least one circuit trace <NUM> which is located in the third substrate region <NUM> is made only of a second material, and any portion of the at least one circuit trace <NUM> which is located in the second substrate region <NUM> is at least partially made of both the second and third materials.

For example, the first material (in the "cold side" first substrate region <NUM>) may be partially or wholly niobium, and the second material (in the "hot side" third substrate region <NUM>) may be partially or wholly copper. These first and second materials are given as predetermined examples useful in achieving desired performance results for a particular configuration of the circuit card assembly <NUM>, but are not limiting. For example, gold could be used for the first and/or second material as desired, such as if the expense of gold were justified by the conductivity results. Copper and niobium are given as examples here because of the superconductivity properties of niobium at <NUM> and common processes available for copper at <NUM> for a particular example use environment of the circuit card assembly. That is, at about <NUM>, niobium is a superconductor, which may be desirable for a circuit card assembly <NUM> design. Above the niobium transition temperature of about <NUM>, however, niobium is a poor conductor, so the circuit trace <NUM> will transition to copper, in this example, or could transition to any other higher-temperature superconductor.

The circuit trace <NUM>, or portions thereof, may be at least partially formed on the selected top and/or bottom substrate surface(s) <NUM> and/or <NUM> via an additive manufacturing process, such as, but not limited to, selective laser sintering (SLS), fused deposition modeling (FDM), direct metal laser sintering (DMLS), stereolithography (SLA), cladding, electron beam melting, electron beam direct manufacturing, aerosol jetting, ink jetting, semi-solid freeform fabrication, digital light processing, <NUM> photon photopolymerization, laminated object manufacturing (LOM), <NUM> dimensional printing (3DP), and the like.

The additive manufacturing process for formation of the circuit trace <NUM>, when used, may help provide precise control of the thicknesses of the metal and dielectric layers. This process uses deposition rates on the order of. <NUM> inches/second (<NUM> Angstroms/second), which assists with achievement of predetermined thicknesses of metal traces and dielectric layers. With these parameters under tight process control, RF performance of the circuit card assembly <NUM> may achieve a desired level. Some example layer thicknesses for the circuit trace <NUM> are approximately <NUM> × <NUM>-<NUM> inches (<NUM> Angstroms). These extremely thin traces facilitated by additive manufacturing offer a very small cross section, and thus lower thermal parasitic losses than if the layers were made thicker.

The additive manufacturing process also does not require the use of etching and the associated costs of handling of the spent reagents, which may be hazardous and highly reactive. By only printing the material that is needed for the circuit trace <NUM>, material waste may be reduced. In addition, the additive manufacturing processes are compatible with much larger panel sizes than etching, including reel to reel processing, which may further reduce the manufacturing cost, even if the large sections are cut into smaller sizes.

In <FIG>, one individual circuit trace <NUM>'~representative of the myriad individual connective pathways that could be encompassed within the general "circuit trace" region <NUM>~is shown in dash-dot line extending in a conductive manner between two individual chips 106a and 106b. That is, at least one first operational chip 106a is located in the first substrate region <NUM> and conductively contacts at least a portion of at least one circuit trace <NUM>' in the first substrate region <NUM>. At least one second operational chip 106b, then, is located in the third substrate region <NUM> and conductively contacts at least a portion of the same at least one circuit trace <NUM>' in the third substrate region <NUM>, as shown in <FIG>. Accordingly, the first operational chip 106a is placed into indirect conductive contact with the second operational chip 106b via at least a portion of the at least one circuit trace <NUM>' located in the second substrate region <NUM>. The term "indirect" is used here with reference to this electrical connection to differentiate an "indirect" circuit trace assisted connection from a "direct" chip-to-chip contact.

With further reference to <FIG>, the portion of the individual circuit trace <NUM>' located in the first substrate region <NUM> (indicated generally at a) may be made only of the first material, the portion of the individual circuit trace <NUM>' located in the third substrate region <NUM> (indicated generally at γ) may be made only of the second material, and portion of the individual circuit trace <NUM>' located in the "transitional" second substrate region <NUM> (indicated generally at β) may be made of both the first and second materials, to assist with transitioning the electrical connection through the intermediate-temperature regions between the "hot side" and the "cold side".

<FIG> depict details of the relative positioning of the first and second materials <NUM> and <NUM>, respectively, in the "transitional" second substrate region <NUM>, in side (<FIG>) and top (<FIG>) views. As shown in these Figures, in the second substrate region <NUM>, the portion of the circuit trace <NUM> made from the first material <NUM> is in at least partial conductive contact with the portion of the circuit trace <NUM> made from the second material <NUM>. More specifically, in the arrangement of <FIG>, the portion of the circuit trace <NUM> made from the first material <NUM> is at least partially arranged in direct transverse contact (up and down, in the orientation of <FIG>) with at least the portion of the circuit trace <NUM> made from the second material <NUM> (not according to the present invention, only present for illustration purposes). That is, the second material <NUM> could lie atop the first material <NUM> (or vice versa) to attain the desired mutually conductive contact.

Turning to <FIG>, then, in the second substrate region <NUM>, the portion of the circuit trace <NUM> made from the first material <NUM> may be at least partially arranged in direct longitudinal contact (into and out of the paper, in the orientation of <FIG>, and up and down, in the orientation of <FIG>) with at least the portion of the circuit trace <NUM> made from the second material <NUM>. That is, the second material <NUM> could lie beside the first material <NUM> on the first substrate surface <NUM>. The first and second materials <NUM> and <NUM> need not be in direct physical contact in the longitudinal arrangement of <FIG>, as long as sufficient electrical contact is made between these portions of the circuit trace <NUM>.

While <FIG> schematically depict the first, second, and third substrate regions <NUM>, <NUM>, and <NUM> in a left-to-right fashion, it is contemplated that the order of these three regions could be reversed, with the labels for the first and second materials <NUM> and <NUM> being switched accordingly. That is, the circuit card assembly <NUM> is agnostic and apathetic as to which of the first and second materials <NUM> and <NUM> is located atop (in <FIG>) or to a particular longitudinal side (in <FIG>) of the other, and one of ordinary skill in the art can readily provide circuit trace(s) <NUM> having desired first/second material <NUM>/<NUM> construction as desired for a particular use environment. It is also contemplated that various combinations of the transversely and longitudinally arranged first and second materials <NUM> and <NUM> could be used in a single circuit card assembly <NUM>, or that the first and second materials <NUM> and <NUM> could be place in any desired conducting arrangement with one another, whether or not specifically shown and described herein.

For any arrangement of the first and second materials <NUM> and <NUM> making up a single circuit trace <NUM> in the second substrate region <NUM>, there is no requirement that the materials be placed symmetrically or evenly in any dimension-one of ordinary skill in the art may readily provide any desired layout of the circuit trace(s) <NUM> in the "transitional" second substrate region <NUM> as desired. It is merely contemplated that the portion of the circuit trace <NUM> located in the second substrate region <NUM> will be made of both the first and second materials <NUM> and <NUM>-that is, that both the first and second materials <NUM> and <NUM> may be found (possibly at varying positions upon the substrate surface and in varying proportions) in that portion of the circuit trace <NUM> which spans the second substrate region <NUM>. However, it is also contemplated that- even in the second substrate region <NUM>~a portion of the circuit trace <NUM> located near the transition to the first substrate region <NUM> may be mostly or wholly made from the first material <NUM> and a portion of the circuit trace <NUM> located near the transition to the third substrate region <NUM> may be mostly or wholly made from the second material <NUM>.

Finally, the substrate <NUM> itself could either be substantially even/solid and featureless (as shown in <FIG>) or could include a plurality of slots <NUM>, as shown in <FIG>. The substrate <NUM> can be a significant to the thermal parasitic load of the circuit card assembly <NUM>. One way to reduce thermal transfer through the substrate <NUM> and thus reduce the overall thermal parasitic load is to make the substrate <NUM> relatively thin, in the transverse direction-a glass material can be used to make a substrate <NUM> which is only <NUM>,<NUM> (. <NUM>") thick. Inclusion of slots <NUM>, such as those shown in <FIG>, or some other through-aperture(s) or blind cavity(ies) in the substrate <NUM> can also further reduce the amount of material in a longitudinally-cut cross-section, which can also help control the thermal parasitic loads. Since, for most use environments of the circuit card assembly <NUM>, there will be no chips <NUM> in the second substrate region <NUM>, that may be a desirable area to include slot(s) <NUM>, though one of ordinary skill in the art can provide and position any desired reduced-material areas (like the slots <NUM>) suitably to achieve desired thermal transfer effects.

In addition to facilitating a very thin cross-section, a glass or other suitable material for the substrate <NUM> may also help provide a compatible coefficient of thermal expansion (CTE) between the hot and cold sides <NUM> and <NUM> of the circuit card assembly <NUM>. By coordinating the CTEs of the various structures of the circuit card assembly <NUM>, the thermal stresses between the chips <NUM> and the substrate <NUM> may be reduced, which can help avoid warping, lead detachment, or other undesirable thermal expansion/contraction related effects.

Claim 1:
A circuit card assembly (<NUM>), comprising:
a substantially planar substrate (<NUM>) having longitudinally spaced first and second substrate end edges (<NUM>, <NUM>), transversely spaced top and bottom substrate surfaces (<NUM>, <NUM>), and
laterally spaced first and second substrate side edges (<NUM>, <NUM>), at least a selected one of the top and bottom substrate surfaces (<NUM>, <NUM>) having laterally arranged, longitudinally extending first, second, and third substrate regions (<NUM>, <NUM>, <NUM>), the first substrate region (<NUM>) being directly laterally adjacent the first substrate side edge (<NUM>), the third substrate region (<NUM>) being directly laterally adjacent the second substrate side edge (<NUM>), and the second substrate region (<NUM>) being located laterally between the first and third substrate regions (<NUM>, <NUM>); and
at least one circuit trace (<NUM>) located on the selected substrate surface (<NUM>, <NUM>), with a portion of the circuit trace (<NUM>) located in the first substrate region (<NUM>) being made of only a first material (<NUM>), a portion of the circuit trace (<NUM>) located in the third substrate region (<NUM>) being made of only a second material (<NUM>), and a portion of the circuit trace (<NUM>) located in the second substrate region (<NUM>) being made of both the first and second materials (<NUM>, <NUM>), wherein, in the second substrate region (<NUM>), the portion of the circuit trace (<NUM>) made from the first material (<NUM>) is at least partially arranged in direct longitudinal contact in the same layer with at least the portion of the circuit trace (<NUM>) made from the second material (<NUM>).