EP4631316A1

EP4631316A1 - Reinforced transitions on electrically conducting structures

Info

Publication number: EP4631316A1
Application number: EP23805587.5A
Authority: EP
Inventors: Roland Steim; Marc Robert Hauer; John Cotte; Young Hoon Kwark
Original assignee: Dyconex AG; International Business Machines Corp
Current assignee: Dyconex AG; International Business Machines Corp
Priority date: 2022-12-06
Filing date: 2023-11-13
Publication date: 2025-10-15
Also published as: WO2024120757A1

Abstract

The present invention relates to a device (1) for conducting an electrical current, comprising an electrically insulating substrate (3) comprising a first side (3a), a first electrical conductor (4) arranged on the substrate (3) and comprising a first portion (40) protruding from the first side (3a) of the substrate (3), and a first metallic layer (2) arranged on the first side (3a) of the substrate (3), wherein said first metallic layer (2) comprises a transition region (20) overlapping at least a region of said first portion (40) of the at least one conductor (4). According to the present invention, a second metallic layer (6) is arranged on said transition region (20) of the first metallic layer (2) to reinforce said transition region (20).

Description

Reinforced Transitions on Electrically Conducting Structures

The present invention relates to a device for conducting electrical current as well as to a method for producing such a device.

Such devices can be formed as printed circuit boards and often comprise a transition between copper conductors (particularly contact pads) and sputtered metals.

Particularly, electrically conducting structures are known in the prior art as shown in Fig. 1, that comprise a thin sputtered layer 2 on a transition region A from a polyimide foil 3 to a relatively thick copper conductor 4. The sputtered layer 2 (e.g. niobium, Ni/Cu, titanium, NiCr) typically has a layer thickness in the range from 0.05 pm to 1 pm, while the thick copper layer/conductor 4 tends to have a layer thickness in the range from 5 pm to 36 pm.

However, said transition region A is unfortunately susceptible to mechanical stresses such as bending. The thin film 2 can break in the area A of this bending zone. Moreover, due to the strong difference in thickness by a factor of 10 to 100, the thin metal film 2 sees a strong change in properties (strength, CTE, resistance, or the like) in the area A of the transition, which is unfavorable for a reliable contact and easily leads to a predetermined breaking point.

Based on the above, the problem to be solved by the present invention is to provide a device for conducting an electrical current and a method for producing such a device that assure a higher mechanical stability of said junction and a more reliable electrical contact. This problem is solved by a device having the features of claim 1 as well as by a method having the features of claim 13. Preferred embodiments of these aspects of the present invention are stated in the corresponding dependent claims and are described below.

According to claim 1, a device for conducting an electrical current is disclosed, the device comprising: an electrically insulating substrate comprising a first side, a first electric conductor arranged on the substrate and comprising a first portion protruding from the first side of the substrate, and a first metallic layer arranged on the first side of the substrate, wherein said metallic layer comprises a transition region overlapping at least a region of said first portion of the at least one conductor.

According to the invention, a second metallic layer is arranged on said transition region of the first metallic layer to reinforce said transition region.

Particularly, the invention thus provides a technical solution for the transition of a thin layer (sputtered, thermally evaporated, etc.) from a substrate to a thicker conductor (e.g., out of copper) as typically used in classical PCB technology. The reinforcement of the first metallic layer (e.g., sputtered layer) in the transition region by preferably local plating, leads to better mechanical and electrical stability of the critical transition region. The invention may be applied to electronic applications or components, which usually require higher mechanical stability at junctions between different conductors as well as a reliable electrical contact between electronic components. Non-limiting examples for such components include temperature sensor, heating elements or super conductors or resistors, e.g., a dump resistor.

Accordingly in one embodiment the device according to the invention is designed as a superconductor device, a heating element, or temperature sensor, wherein particularly the first metallic layer is designed or configured as a superconductor.

According to another embodiment of the present invention, the device is designed as a resistor, particularly a dump resistor, wherein the first metallic layer forms a resistive conductor, and the first conductor forms a conductive track or a contact pad for electrically contacting the resistive conductor. Particularly, the first metallic layer as stated above may have various forms, e.g., a straight line, a spiral, a zig-zag line, a meander, or a plane.

According to a preferred embodiment of the device according to the present invention, the first metallic layer is a sputtered metallic layer. Preferably, the first metallic layer comprises a thickness (i.e., normal to the substrate) in the range from 0.05 pm to 1 pm.

Furthermore, according to a preferred embodiment of the device, the first metallic layer comprises or is formed out of one of niobium, titanium, gold, or combination thereof, e.g., gold and niobium.

Further, according to yet another preferred embodiment, the second metallic layer is a (galvanically) plated metallic layer. Preferably, the second metallic layer comprises a thickness (i.e., normal to the substrate) in the range from 3 pm to 36 pm. Preferably, the second metallic layer comprises a metal that can be (galvanically) plated without a significant effort.

Consequently, according to preferred embodiment of the device according to the present invention, the second metallic layer comprises or is formed out of one of copper, gold, nickel, platinum, silver, or a combination thereof.

Furthermore, preferably, in an embodiment, an intermediary metallic layer is arranged between the first and the second metallic layer. Preferably, the intermediary metallic layer comprises a thickness in the range from 50 nm to 200 nm. According to a preferred embodiment, said intermediary metallic layer is a sputtered metallic layer.

Further, in a preferred embodiment of the device, the intermediary metallic layer comprises or is formed out of one of the following metals: copper, gold, copper, titanium, nickel, platinum, palladium, or silver, particularly a combination of gold and copper. Preferably, the intermediary metallic layer is configured as diffusion barrier and/or for minimizing contact resistances. Furthermore, according to a preferred embodiment, the substrate (which can be shaped as a foil in particular) comprises or is formed out of one of: a polyimide, a liquid crystal polymer a fiber-reinforced polymers, e.g. an epoxy resin or polyimide, BT(bismaleimide triazine)- epoxy, or an Ajionomoto Bild-up Film (ABF).

Within the meaning of the present invention, the term "liquid crystal polymer" is used in the meaning known to and commonly used by a person skilled in the art. A "liquid crystal polymer" refers in particular to an aromatic polymer, which has highly ordered or crystalline regions in the molten state or in solution. Non-limiting examples include aromatic polyamides such as aramid (Kevlar) and aromatic polyesters of hydroxybenzoic acid, such as a polycondensate of 4-hydroxybenzoic acid and 6-hydroxynaphthalene-2-carboxylic acid (Vectran).

According to yet another preferred embodiment of the device, the first conductor on a second side of the substrate, the second side facing away from the first side of the substrate, wherein the second conductor is electrically connected to the first conductor by a connecting portion extending through an opening in the substrate. Such connection portion is also referred to as via.

Preferably, the first conductor and/or the second conductor comprises or is formed out of copper. Preferably, the first portion of the first conductor and/or the second conductor comprises a thickness in the range from 5 pm to 36 pm.

Furthermore, the first conducting conductor and/or the second conductor may be at least partly designed in form of a contact pad, e.g., for making electrical connection to the device. Alternatively, or in addition, according to a preferred embodiment, the first conductor and/or the second conductor may be at least partly designed in form of a conductive track that may be used to electrically connect two electronic components to one another.

According to yet another preferred embodiment of the device according to the present invention, the first metallic layer and/or the second metallic layer is/are covered by an insulating layer. Alternatively, or in addition, in an embodiment, the second side of the substrate is covered by an insulating layer, wherein here the second conductor (particularly designed in form of a contact pad) is at least partially exposed (i.e., is not covered by the insulating layer). Preferably, in an embodiment, the respective insulating layer comprises or is formed out of one of: a liquid crystal polymer, a polyimide, a solder mask, an acrylic acidbased adhesive, or polyphenylene ether.

According to a further aspect of the present invention, a method for producing a device for conducting an electrical current is disclosed, wherein particularly said device is a device according to the present invention as described herein, the method comprising the steps of: providing an electrically insulating substrate comprising a first side, wherein a first electrical conductor is arranged on the substrate and comprises a first portion protruding from the first side of the substrate, sputtering a first metallic layer onto the first side of the substrate, so that said first metallic layer comprises a transition region overlapping at least a region of said first portion of the at least one conductor, and providing a second metallic layer on said transition region of the first metallic layer to reinforce said transition region.

According to a preferred embodiment of the method according to the present invention, providing the second metallic layer comprises sputtering an intermediary metallic layer onto the first metallic layer and plating the second metallic layer onto the intermediary layer.

Furthermore, according to preferred embodiment of the method, a portion of said intermediary layer adjacent the second metallic layer (e.g., the portion of the intermediary layer not being covered by the second metallic layer(s)) is removed by means of etching.

In the following, preferred embodiments of the present invention as well as further features and advantages of the present invention are described with reference to the Figures, wherein

Fig. 1 shows a conducting structure according to the prior art having a thin sputtered metallic layer overlapping a copper conductor leading to an unfavorable predetermined breaking point at the transition of the sputtered layer from the substrate to the copper conductor, and

Fig. 2 shows a schematical cross-sectional view of an embodiment of the device for conducting an electrical current according to the present invention.

Fig. 2 shows an embodiment of a device 1 according to the present invention. According thereto, the device 1 comprises an electrically insulating substrate 3 (e.g., formed out of polyimide) that comprises a first side 3a and a first electrical conductor 4 (designed in form of a contact pad and/or a conductive track) arranged on the substrate 3 and comprising a first portion 40 protruding from the first side 3a of the substrate 3. The device 1 further comprises a first metallic layer 2 arranged on the first side 3a of the substrate 3, wherein said first metallic layer 2 comprises a transition region 20 overlapping at least a region, particularly an edge, of said first portion 40 of the at least one conductor 4.

As indicated in Fig. 1 showing a conducting structure known in the art, such a situation often leads to the problem that the transition region A of the sputtered layer 2 from the substrate 3 to the thicker conductor 4 forms a pre-determined breaking point leading to cracks in the structure, particularly under bending loads.

According to the invention, as shown in Fig. 2, a second metallic layer 6 is therefore arranged on said transition region 20 of the first metallic layer 2, which transition region 20 extends from the substrate 3 over the conductor 4. This reinforces the transition region 20 and prevents damages of the first metallic (e.g., sputtered) layer 2.

Particularly, the first metallic layer 2 may be a conductive pattern or track of Nb (niobium) that may be applied to the substrate 3 and the conductor 4 by way of sputtering. In addition, a thin intermediary layer 5 (e.g., a copper layer that preferably has a thickness in the range from 50 nm to 500 nm) may be sputtered directly onto the Nb conductors 2. After applying a new resist structure, the second metallic layer 6 (e.g., Cu) is selectively (galvanically) plated onto the intermediate layer 5 in the vicinity of the transition region 20 and may comprise a thickness in the range from 3 pm to 36 pm) and thus reinforces the transition region 20 of the first metallic (e.g., niobium) layer 2. Mechanical stresses thus no longer occur directly at the transition region 20, and the sensitive niobium-to-copper contact is protected in particular. The sputtered copper (intermediary layer 5) on the first metallic layer 2 (e.g., niobium) may be removed by differential etching of the excess intermediary layer 5 by an amount of about at least 1 pm. In this process, the clad copper 6 is only insignificantly thinned.

Furthermore, as indicated in Fig. 2, the device according to the invention particularly comprises a second conductor 8 having a first portion 80 and being arranged on a second side 3b of the substrate 3, the second side 3b facing away from the first side 3a of the substrate 3, wherein the first conductor 4 and the second conductor are electrically connected by a connecting portion 9 (via) extending through an opening 30 in the substrate 3. In addition, the device may comprise additional insulating and conductor layers. For example, an additional insulating layer may be arranged on the first metallic layer 2 and/or the second metallic layer 6. Alternatively, or additionally, an additional layer may be arranged on the second conductor 8, wherein particularly a further conductor may be arranged on the additional layer. The further conductor may be connected to the second conductor 8 be a connecting portion, e.g., a through-going via.

Particularly, the device 1 may comprise several first conductors 4 and/or second conductors 8. Particularly, as exemplary shown in Fig. 2, two first conductors 4 may be connected in an electrically conducting fashion by the first metallic layer 2 (e.g., niobium). Preferably, the respective conductor 4 may be formed as a contact pad 4 or conductive track 4. The respective contact pad 4 or conductive track 4 may allow electrically contacting the device 1 from the outside. Particularly, in case of the device is designed as a superconductor device, the two contact pads 4 or conductive tracks 4 may be used to contact the first metallic layer 2, wherein the first metallic layer 2, particularly formed form niobium, forms a superconductor.

Furthermore, the first metallic layer 3 (e.g., niobium) and/or the second metallic layer(s) 6 may be covered by an insulating layer 70. Likewise, the second side 3b of the substrate 3 may be covered by an insulating layer 71 as well, with the first portion(s) 81 of the second conductor(s) 8 being at least partially exposed, so that the respective conductor 8 (e.g. contact pad) may be electrically contacted (e.g. by soldering a conductor to it). The respective insulating layer 70, 71 can be formed out of a liquid crystal polymer (LCP), a polyimide or another dielectric material, e.g., a polyimide or an adhesive.

Buildups of thick copper (etched classical PCB structures) 4 in combination with thin metal films 2 of other metals such as Nb are interesting structures for numerous applications. Here, the transition region 20 from the thin film 2 to the thick film 4 is always critical and a weak point. The invention offers a safe solution here. Particularly, in the context of the device 1 according to the present invention, via technology and the contact pads 4 or conductive tracks 4 for contacting may be designed in the classical thick film copper technology. The reinforcement of the transition region 20 offers a good possibility to protect the transition.

Furthermore, the method according to the present invention helps in case the interface between the thick (from the PCB structures) copper 4 and the sputtered layer 2 is disturbed (which can lead to increased resistances). Since the sputtered copper 5 is preferably immediately deposited in the vacuum chamber onto the sputtered Nb (or other metal) 2, there are no problems with oxidation. The copper growth of the clad copper 6 on the sputtered copper 5, as well as on the PCB copper 4 is very unproblematic. Another advantage of the present method is that the sputtered conductor 2 can continue to grow normally, planar, in the area of the transition where the plated copper 6 ends and does not have to bridge another step.

Claims

1. A device (1) for conducting an electrical current, comprising an electrically insulating substrate (3) comprising a first side (3a), a first electric conductor (4) arranged on the substrate (3) and comprising a first portion (40) protruding from the first side (3a) of the substrate (3), and a first metallic layer (2) arranged on the first side (3a) of the substrate (3), wherein said first metallic layer (2) comprises a transition region (20) overlapping at least a region of said first portion (40) of the first electric conductor (4), characterized in that a second metallic layer (6) is arranged on said transition region (20) of the first metallic layer (2) to reinforce said transition region (20).

2. The device according to claim 1, wherein the first metallic layer (2) is a sputtered metallic layer.

3. The device according to claim 1 or 2, wherein the first metallic layer (2) comprises or is formed out of one of: niobium, titanium, gold, or combination thereof.

4. The device according to one of the preceding claims, wherein the second metallic layer (6) is a plated metallic layer.

5. The device according to one of the preceding claims, wherein the second metallic layer comprises or is formed out of: copper, gold, nickel, platinum, silver, or a combination thereof.

6. The device according to one of the preceding claims, wherein an intermediary metallic layer (5) is arranged between the first and the second metallic layer (2, 6), wherein particularly the intermediary metallic layer (5) is a sputtered metallic layer.

7. The device according to claim 6, wherein the intermediary metallic layer (5) comprises one of the following metals: copper, gold, titanium, nickel, platinum, palladium, or silver.

8. The device according to one of the preceding claims, wherein the substrate (3) comprises or is formed out of one of: a polyimide, liquid crystal polymer, a fiber- reinforced epoxy resin, e.g. FR4, BT-Epoxy, or an ABF

9. The device according to one of the preceding claims, further comprising a second electric conductor (8) arranged on a second side (3b) of the substrate (3), the second side (3b) facing away from the first side (3a) of the substrate (3), wherein the second conductor (8) is electrically connected to the fist conductor (4) by a connecting portion (9) extending through an opening (30) in the substrate (3).

10. The device according to one of the preceding claims, wherein the first metallic layer (3) and/or the second metallic layer (6) is covered by an insulating layer (70), and/or wherein the second side (3b) of the substrate (3) is covered by an insulating layer (71) with the second conductor (42) being at least partially exposed.

11. The device according to claim 11, wherein the respective insulating layer (70, 71) comprises or is formed out of one of: a liquid crystal polymer, a polyimide, a solder mask, an acrylic acid-based adhesive, or polyphenylene ether.

12. The device according to one of the preceding claims, wherein said device is designed as a superconductor device, a resistor, a heating element, or temperature sensor.

13. A method for producing a device (1) for conducting an electrical current, the method comprising the steps of: providing an electrically insulating substrate (3) comprising a first side (3a), wherein a first electrical conductor (4) is arranged on the substrate (3) and comprises a first portion (40) protruding from the first side (3a) of the substrate (3), sputtering a first metallic layer (2) onto the first side (3a) of the substrate (3), so that said first metallic layer (2) comprises a transition region (20) overlapping at least a region of said first portion (40) of the at least one conductor (4), and providing a second metallic layer (6) on said transition region (20) of the first metallic layer (2) to reinforce said transition region (20). The method according to claim 13, wherein providing the second metallic layer (6) comprises sputtering an intermediary metallic layer (5) onto the first metallic layer (2) and plating the second metallic layer (6) onto the intermediary metallic layer (5). The method according to claim 14, wherein a portion of the intermediary metallic layer (5) not being covered by the second metallic layer (6) is removed by means of etching.