1. SAS-3: Microwave laminates for connector test cards
Ray Pavlak
24 March 2011

2. 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

3. 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

4. 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

5. Some Vendors Rogers Corporation Taconic Advanced Dielectric Division
Corporate
High frequency laminates
Selector Guide
Taconic Advanced Dielectric Division
Overview of PCB materials and properties, including a list of many additional high frequency laminate vendors
24 MAR 2011

6. Example
Rogers RO4350B
FR-4 processing comaptible (hydrocarbon ceramic)
Dielectric 10 GHz ± 0.05
Dissipation 10 GHz @ 2.5 GHz
Available dielectric thicknesses and tolerances " (0.101mm) ± " " (0.168mm) ± " " (0.254mm) ± 0.001" " (0.338mm) ± " " (0.422mm) ± " " (0.508mm) ± " " (0.762mm) ± 0.002" " (1.524mm) ± 0.004“
Available cladding: Copper in 0.5, 1, 2 oz. thicknesses
More info:
24 MAR 2011

7. 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

8. 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
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9. PCB Design 1
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10. PCB Design 2
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11. PCB Design 3
24 MAR 2011