Design and test of a prototype of a flex cable for high speed transmission Jan Buytaert (CERN), Daniel Esperante, Pablo Vázquez, Jevgenij Visniakov (USC)

nDesign of the cable What we have done VELO Upgrade

nMeasure the S-parameters of decoupled lines with a VNA HP8719D (13.5 GHz) in Santiago nHelp with manpower to measure in other labs What we can do VELO Upgrade

nTo prove that is feasible to build a high speed flex cable in CERN labs n as no companies were found to produce longer than 55 cm (> 65 cm needed) nCharacterize the transmission lines (31 in total) nTest transmission through a fine pitch connector n Molex Cable design goals VELO Upgrade

nArea 1: effect of a miniature fine pitch connector n This area is cut-off in two pieces nArea 2: parameters of decoupled strip-lines nArea 3: parameters of edge coupled differential striplines nArea 4: effect of vias on gnd traces nArea 5: length dependance: 0, 56, 75, 100 cm Cable divided in areas for different studies VELO Upgrade Area 2 (6 lines) Area 1 (6 lines) Area 5 (4 lines) Area 4 (5 lines) SMA connectors on both ends Area 1 (6 lines) 570 mm (pyralux width – handling margin) 270 mm Area 3 (10 lines)

nEdge coupled differential striplines separated with gnd traces nMade out of 2 foils of pyralux AP- PLUS AP7229R n Dielectric Constant = 3.4 n Dissipation Factor (Loss tangent) = nZ is calculated with Rogers MWI-2010 tool which does not include Gnd traces overstimation (~ 5-10% ?) Cable profile VELO Upgrade Wd1Wd2DDg1Dg2 500 um S+S-Gnd 18 um GG TOP SIGNAL BOTTOM

nTwo groups of 3 lines, one group per side of the connector n (L1, L2, L3) = (L4, L5, L6) nL1, L2: S+ and S- match the pitch of the connector (L1 = L10 in Area3) n crosstalk and impedance n insertion loss of connector nL3: S+ and S- twice the pitch of the connector (L3 = L3 in Area 3) Area 1: miniature fine pitch (400 um) connector VELO Upgrade Coupled stripline L1L2L3L4L5L6 Wd Wd D Dg Dg G Zdiff 94,6 102,7 94,6 102,7 Total W

n(L1,L2), (L3,L4) and (L5,L6) are 3 pairs for differential transmission n Impedance, crosstalk, bit error rate (BER) n decoupled (area 2) versus coupled (area 3) transmission lines n(L3,L4) and (L5,L6): parameter Wd Area 2: decoupled striplines VELO Upgrade Decoupled stripline L1L2L3L4L5L6 Wd Wd D Dg Dg G 500 Z 48,2 45,6 Total W

n L1-L3: distance signal to signal D n L3-L5: distance signal to gnd Dg n L3, L6: width of signal Wd (D=500) Area 3: coupled differential striplines VELO Upgrade Coupled stripline L1L2=L8L3L4L5L6L7L8=L2L9L10 Wd Wd D Dg Dg G500 Zdiff10496,7102, ,596,791,694,6 Total W n L7-L9: width of signal Wd (D=250) n L10: D=400 um

nL1-L5 = L1-L5 of Area 3 (whitout vias on gnd traces) nNo vias gnd traces width G = 300 um Area 4: striplines without vias on gnd traces VELO Upgrade Coupled stripline L1L2=L8L3L4L5 Wd1280 Wd2280 D Dg Dg G Zdiff10496,7102,7 Total W

TOP ground layer VELO Upgrade

SIGNAL layer VELO Upgrade Lines are routed turning left – right to equalize all trace lengths Grid to avoid delamination

DRILL layer VELO Upgrade

BOTTOM ground layer VELO Upgrade Openings on top/bottom layers to allow quality evaluation: gluing, etching… of traces (and cutting-off)

nSurface mount SMA and find pitch connectors mounted directly on signal layer to avoid vias on signal traces n4 vias close to SMA connector and 1 via every 10 mm on gnd traces to improve ground connection Detail: end of transmission lines VELO Upgrade

Detail: fine pitch molex connector VELO Upgrade