SAS-3: Microwave laminates for connector test cards Ray Pavlak 24 March 2011
Background Microwave laminates (aka high frequency laminates) have been around for a long time Many applications in military, aerospace, and industry (both unclad and clad with a variety of metal choices) Microwave PCBs: amplifiers, mixers, PLLs, etc. Radomes (electrically transparent antenna covers) for radar & aircraft Test equipment and fixtures Due to “exotic” applications, material properties and dimensions are typically very tightly controlled Ideal for high performance PCB applications High repeatability Low loss Controlled impedance 24 MAR 2011
Advantages Wide range of properties available (dielectic constants and loss tangents) Low loss Tight tolerances Material properties (e.g. dielectric constant as tight as ±0.02) Dimensions Able to control impedance purely based on dimensions (if dimensions/stackup/trace widths chosen carefully) Low thermal expansion coefficient (good temp stability) Some are compatible with standard FR-4 processing Suppliers familiar with RF electrical performance needs Much characterization data available 24 MAR 2011
Disadvantages High cost PCB processing Limited number of vendors Not preferred for high volume production Acceptable for low volume test fixtures PCB processing Many are PTFE (Polytetrafluoroethylene or Teflon®) based and require special processing chemistry Not compatible with FR-4 processing Some are hydrocarbon ceramic based Compatible with FR-4 processing Not the highest performance, but far better than FR-4 Limited number of vendors 24 MAR 2011
Some Vendors Rogers Corporation Taconic Advanced Dielectric Division Corporate http://www.rogerscorp.com High frequency laminates http://www.rogerscorp.com/acm/producttypes/2/High-Frequency-Laminates.aspx Selector Guide http://www.rogerscorp.com/documents/776/acm/High-Frequency-Laminates---Product-Selector-Guide-and-Standard-Thicknesses-and-Tolerances.aspx Taconic Advanced Dielectric Division http://www.taconic-add.com Overview of PCB materials and properties, including a list of many additional high frequency laminate vendors http://www.speedingedge.com/PDF-Files/Materials_RickH2.pdf 24 MAR 2011
Example Rogers RO4350B FR-4 processing comaptible (hydrocarbon ceramic) Dielectric constant @ 10 GHz 3.66 ± 0.05 Dissipation Factor @ 10 GHz 0.0037 @ 2.5 GHz 0.0031 Available dielectric thicknesses and tolerances 0.0040" (0.101mm) ± 0.0007" 0.0066" (0.168mm) ± 0.0007" 0.010" (0.254mm) ± 0.001" 0.0133" (0.338mm) ± 0.0015" 0.0166" (0.422mm) ± 0.0015" 0.020" (0.508mm) ± 0.0015" 0.030" (0.762mm) ± 0.002" 0.060" (1.524mm) ± 0.004“ Available cladding: Copper in 0.5, 1, 2 oz. thicknesses More info: http://www.rogerscorp.com/acm/products/16/RO4000-Series-High-Frequency-Circuit-Materials-Woven-glass-reinforced-ceramic-filled-thermoset.aspx 24 MAR 2011
Performance Test Data 3 Different test board designs for different applications All have same functional configuration Southwest Microwave end-launch SMA 1.25 – 1.75 inch trace length (approximately) 100 Ω Differential pair (isolated 50 Ω traces - no coupling) SAS or FC backplane connector (No footprint optimization) All have same construction 0.062” thick 4-layer PCB Outer laminates are 10 mil thick Rogers RO4350B (½ oz ED copper) Inner dielectric is FR-4 prepreg as needed No solder mask to interfere with Z0 control Instead, traces plated with 30µ” gold over 100µ” nickel No impedance control specified to PCB vendor (dimensions only) Manufactured at different times by different vendors 24 MAR 2011
Measured TDR Performance Several samples of each board measured Calibrated TDR Measurements Agilent 86100C mainframe / 54754A TDR plug-in 30 ps 10-90% rise time (some ringing due to pushing bandwidth) Differential TDR calibrated at end of cables that mate with test board Z0 stays nominally within ±2 ohms (±2% Z0 tolerance) across all samples 24 MAR 2011
PCB Design 1 24 MAR 2011
PCB Design 2 24 MAR 2011
PCB Design 3 24 MAR 2011