# US 9,753,217 B2 · Stress relief for electro-optical printed circuit board

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- Number: US 9,753,217 B2
- Document ID: US9753217B2
- Status: Granted
- Kind: B2
- Application number: 14/926,608
- Filed: 2015-10-29
- Published: 2017-05-04
- Granted: 2017-09-05
- Earliest claimed: 2015-10-29
- Assignees: Xyratex Technology Limited
- Applicants: Xyratex Technology Limited
- Inventors: Richard C. A. Pitwon
- Web page: https://patentgrep.com/patent/US9753217B2

## CPC

- G02B 6/122: Basic optical elements, e.g. light-guiding paths
- G02B 6/12004: {Combinations of two or more optical elements}
- G02B 6/1221: {made from organic materials}
- G02B 6/13: Integrated optical circuits characterised by the manufacturing method
- G02B 6/138: by using polymerisation
- H05K 1/0274: {Optical details, e.g. printed circuits comprising integral optical means (H05K1/0269 takes precedence; coupling light guides with opto-electronic components G02B6/42)}
- H05K 1/0271: {Arrangements for reducing stress or warp in rigid printed circuit boards, e.g. caused by loads, vibrations or differences in thermal expansion}
- H05K 2201/0187: with regions of different dielectrics in the same layer, e.g. in a printed capacitor for locally changing the dielectric properties
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- H05K: PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS

## Abstract

Electro-optical circuit boards may include one or more recesses to provide stress relief between multiple layers of the electro-optical circuit boards during variations in applied temperature. The one or more recesses may be included in the substrate and/or the optical layer of the electro-optical circuit boards. The one or more recesses may also contain a compliant material disposed therein to improve the flexibility of the substrate and/or the optical layer. For example, the compliant material may disperse thermal expansion stress within the electro-optical circuit board.

## Claims

### Claim 1

An electro-optical circuit board comprising:
a first substrate and a second substrate extending along a longitudinal direction;
an optical layer positioned between the first substrate and the second substrate and defining a first optical layer surface and a second optical layer surface opposing the first optical layer surface, the optical layer comprising:
a cladding layer extending from the first optical layer surface to the second optical layer surface,
one or more polymeric waveguide cores at least partially disposed within the cladding layer and extending along the longitudinal direction, and
one or more optical layer recesses extending into the cladding layer from first optical layer surface or the second optical layer surface; and
a compliant material disposed within the one or more optical layer recesses.

### Claim 2 (depends on 1)

The electro-optical circuit board of claim 1, wherein the compliant material has a Young's modulus of less than 1 GPa.

### Claim 3 (depends on 1)

The electro-optical circuit board of claim 1, wherein the optical layer defines a first optical layer side and a second optical layer side extending along the longitudinal direction, wherein the one or more polymeric waveguide cores are between the first optical layer side and the second optical layer side, wherein the one or more optical layer recesses are positioned between the first optical layer side and the one or more polymeric waveguide cores or between the second optical layer side and the one or more polymeric waveguide cores.

### Claim 4 (depends on 3)

The electro-optical circuit board of claim 3, wherein the one or more optical layer recesses comprises a first optical layer recess and a second optical layer recess, wherein the first optical layer recess is positioned between the first optical layer side and the one or more polymeric waveguide cores and the second optical layer recess is positioned between the second optical layer side and the one or more polymeric waveguide cores, wherein the one or more polymeric waveguide cores separate the first optical layer recess from the second optical layer recess.

### Claim 5 (depends on 1)

The electro-optical circuit board of claim 1, wherein the one or more polymeric waveguide cores define a center waveguide point that is equidistant from the first optical layer surface and the second optical layer surface, wherein at least one of the one or more optical layer recesses extends to at least the center waveguide point.

### Claim 6 (depends on 1)

The electro-optical circuit board of claim 1, wherein the one or more polymeric waveguide cores comprises a single mode waveguide.

### Claim 7 (depends on 1)

The electro-optical circuit board of claim 1, wherein the one or more polymeric waveguide cores comprises a multimode waveguide.

### Claim 8 (depends on 1)

The electro-optical circuit board of claim 1, wherein the one or more polymeric waveguide cores comprise at least five polymeric waveguide cores, wherein the at least five polymeric waveguide cores are parallel and coextending for at least a distance along the longitudinal direction.

### Claim 9 (depends on 1)

The electro-optical circuit board of claim 1, wherein the one or more optical layer recesses are coextensive with the one or more polymeric waveguide cores for at least a distance along the longitudinal direction.

### Claim 10 (depends on 1)

The electro-optical circuit board of claim 1, wherein the one or more optical layer recesses form undulating shapes along the longitudinal direction.

### Claim 11 (depends on 1)

The electro-optical circuit board of claim 1, wherein the one or more optical layer recesses comprise one or more discontinuous or discrete recesses positioned along the longitudinal direction.

### Claim 12 (depends on 1)

The electro-optical circuit board of claim 1, wherein at least one optical layer recess of the one or more optical layer recesses extends through optical layer from the first optical layer surface to the second optical layer surface.

### Claim 13 (depends on 1)

The electro-optical circuit board of claim 1, wherein each of the first substrate and the second substrate defines one or more substrate recesses extending into both the first substrate and the second substrate, wherein the compliant material is disposed in each of the one or more substrate recesses.

### Claim 14 (depends on 13)

The electro-optical circuit board of claim 13, wherein the one or more substrate recesses of the first substrate align with the one or more optical layer recesses, wherein the compliant material is disposed in both of the one or more substrate recesses and the one or more optical layer recesses.

### Claim 15 (depends on 13)

The electro-optical circuit board of claim 13, wherein the optical layer defines a first optical layer side and a second optical layer side, wherein the one or more polymeric waveguide cores extend a waveguide group width between the first optical layer side and the second optical layer side, wherein the one or more substrate recesses extend along the first substrate for at least a portion of the waveguide group width.

### Claim 16 (depends on 1)

The electro-optical circuit board of claim 1, wherein a compliant surface of the compliant material disposed within at least one of the one or more optical layer recesses is in a plane with the first optical layer surface or the second optical layer surface.

### Claim 17 (depends on 1)

The electro-optical circuit board of claim 1, further comprising a flexible substrate positioned between the second substrate and the optical layer.

### Claim 18

A system comprising:
an electro-optical circuit board comprising:
a substrate defining a first substrate surface and a second substrate surface opposing the first substrate surface,
a cladding layer embedded within the substrate between the first substrate surface and the second substrate surface, the cladding layer defining a first cladding layer surface and a second cladding layer surface opposing the first cladding layer surface,
one or more polymeric waveguide cores embedded within the cladding layer, and
an expansion joint comprising a compliant material having a Young's modulus of less than 1 GPa and located in the cladding layer and extending into the first cladding layer surface or the second cladding layer surface, and a coefficient of thermal expansion of the substrate is at least 10 ×10−6/° C. different than a coefficient of thermal expansion of the cladding layer; and
a storage device coupled to the electro-optical circuit board.

### Claim 19 (depends on 18)

The system of claim 18, further comprising a computing device coupled to the electro-optical circuit board.

### Claim 20

A method of reducing thermal expansion stress comprising:
providing an electro-optical circuit board, the electro-optical circuit board comprising:
a first substrate and a second substrate extending along a longitudinal direction,
an optical layer positioned between the first substrate and the second substrate and defining a first optical layer surface and a second optical layer surface opposing the first optical layer surface, the optical layer comprising:
a cladding layer extending from the first optical layer surface to the second optical layer surface,
one or more polymeric waveguide cores at least partially disposed within the cladding layer and extending along the longitudinal direction, and
one or more optical layer recesses extending into the cladding layer from the first optical layer surface or the second optical layer surface, and
a compliant material having a Young's modulus of less than 1 GPa and disposed within the one or more optical layer recesses;
heating the electro-optical circuit board to create thermal expansion stress within the optical layer; and
dispersing the thermal expansion stress within the compliant material.