Patent WO-2019241737-A1 (WO)
Title: Coaxial wire
Inventor: GRAY HALEY CAPRICE
IPC: H01L23/49
Filed: 2019-06-14
Abstract: A micro-coaxial wire (306a-c, 706a-c, 1106a-c) has a conductive core (316a-c, 716a-c, 1116a-c), an insulator (318a-c, 718a-c, 1118a-c) disposed on the conductive core (316a-c, 716a-c, 1116a-c) and a conductive shield layer (320a-c, 720a-c, 1120a-c) disposed on the insulator (318a-c, 718a-c, 1118a-c). The micro-coaxial wire may be a micro-coaxial wire (306a-b, 706a-b, 1106a-b) for power distribution or a micro-coaxial wire (306c, 706c, 1106c) for signal distribution. Micro-coaxial wires (306a-c, 706a-c, 1106a-c) may connect to a power connection point (324, 724, 1124) or to contact pads (214b-c) of a bare die (302), to solder balls (614b-c) of a packaged component (702) or to conductive material-filled vias (1107b-c) of a through-via- perforated (TVP) board (1004). Each connection between an exposed portion (334a-c, 336a, 734a-c, 736a, 1134a-c, 1136a) of a conductive inner core (316a-c, 716a-c, 1116a-c) and a connection point (214b-c, 324, 614b-c, 724, 1113d, 1113f, 1124) is fully encased in an insulator (332, 338, 340, 732, 738, 1132, 1138, 1140). A mass of conductive material (342, 742, 1142) establishes an electrical connection between a ground connection point (325, 725) on a substrate (104) or an electrically conductive plate (1113b) of an insulating substrate (1005) of the TVP board (1004) and the conductive shield layers (320a-c, 720a-c, 1120a-c) of the micro-coaxial wires (306a-c, 706a-c, 1106a-c). A micro-coaxial wire with a 50 Ω impedance has an overall diameter in a range of 0.2 μm - 550 μm, a conductive core with a cross- sectional diameter in a range of 0.05 μm - 130 μm, an insulator disposed on the conductive core with thickness in a range of 0.09 μm - 180 μm and a conductive shield layer disposed on the insulator with thickness in a range of 0.009 μm - 17 μm. A micro-coaxial wire with a 5 Ω impedance has an overall diameter in a range of 0.01μm - 550 μm, a conductive core with a cross-sectional diameter in a range of 0.05 μm - 304 μm, an insulator disposed on the conductive core with thickness in a range of 0.005 μm - 24 μm and a conductive shield layer disposed on the insulator with thickness in a range of 0.02 μm - 99 μm. The micro-coaxial wire may be fabricated by: receiving a length of insulated wire, depositing an adhesion layer (a seed layer) on the electrically insulating layer over the length of the insulated wire, depositing a masking bead, depositing an electrically conductive shield layer, removing the masking bead if present, removing the adhesion layer and the electrically insulating layer from underneath the masking bead and bisecting the electrically conductive core in the segment not covered by the insulating layer, the adhesion layer and the electrically conductive shield layer (e.g., using a wire cutter or a blade). Alternatively, the micro-coaxial wire may be fabricated using a specialised fixture by: receiving a length of insulated wire, depositing an adhesion layer on the electrically insulating layer using masking members of the fixture, removing t he masking members and replacing them with a second set of masking members, depositing an electrically conductive shield layer, removing the second set of masking members, removing the exposed portions of the electrically insulating layer and bisecting the electrically conductive core. Still alternatively, the micro-coaxial wires may be fabricated using a MEMS technique by depositing a masking layer (e.g., a polysilicon layer) on a substrate (e.g., a fused silica wafer), etching (e.g., by a hydrofluoric acid) to remove material from the substrate, in particular to form a semicircular first cavity is formed in the substrate, removing the masking layer, depositing a seed layer in the first cavity, depositing a first part of a conductive shield layer (e.g., a copper layer) on the seed layer such that the first part of the conductive shield layer lines the first cavity, thereby forming a second cavity by the first part of the conductive shield layer, depositing a first part of an electrically insulating layer (e.g., by spraying photo- definable polyimide material) in the second cavity such that the first part of the electrically insulating layer lines the second cavity, thereby forming a third cavity, depositing a seed layer in the third cavity and an electrically conductive core (e.g., a copper or gold flashed copper core) on the seed layer in the third cavity, depositing a second part of the electrically insulating layer on the electrically conductive core such that the first part of the electrically insulating layer and the second part of the electrically insulating layer encase the electrically conductive core, depositing a seed layer deposited on the second part of the electrically insulating layer and a second part of the conductive shield layer on the seed layer such that the first part of the electrically conductive shield layer and the second part of the electrically conductive shield layer encase the electrically insulating layer and performing a glass etching procedure (e.g. a hydrofluoric acid etching procedure) to release the micro-coaxial wire from the first cavity. At least some steps of the micro-coaxial fabrication methods can be performed in a reel-to-reel system, for example, with wires configured to travel from a first reel, through various coating/electroplating stages and onto a second reel. The reel-to-reel fabrication may receive a core wire of the micro-coaxial wire with a dielectric layer deposited thereon or receive a core wire of the micro-coaxial wire and deposit a dielectric layer thereon, in both cases followed by depositing a seed layer and a shield layer and winding the micro-coaxial wire onto a spool.