ATLAS Insertion Loss Correlation Study vs traceable VNA
Application Note AP8186 

Objective

The requirement of the ATLAS insertion loss correlation study was to assess the correlation between the following single ended and differential test methods:

  • Vector Network Analyser – 4 Port Differential and 2 Port Single Ended
  • SPP (Short Pulse Propagation) test method as specified in IPC TM-650 Test Methods Manual using Polar Instruments ATLAS Insertion Loss Test System (v14.04)
  • SET2DIL (Single Ended TDR to Differential Insertion Loss) / SET2SEIL (Single Ended TDR to Single Ended Insertion Loss) as specified in IPC TM-650 Test Methods Manual using Polar Instruments ATLAS Insertion Loss Test System (v14.04)
  • Polar Instruments Si9000e Insertion loss GHz PCB transmission line field solver – from design data and sectioning data measured with Scanning Electron Microscope (SEM)

(An additional objective was, in the case of the SPP method, to assess the correlation between the use of hardware Impulse Forming Networks (IFN) and a software emulated equivalent.)

Method

Three PCB boards (test coupons) were manufactured using industry standard Gerber data generated with the Polar CGen Coupon Generator (V14.02.)

Each coupon contained the following test traces:

  • Single ended SPP / VNA stripline test lines 30mm and 100mm accessed with Molex connectors
  • Differential SPP / VNA stripline test lines 40mm and 110mm accessed with Molex connectors
  • Single ended SET2SEIL stripline structure accessed with GGB style probe
  • Differential SET2DIL stripline structure accessed with GGB style probe
  • Single ended stripline Impedance structure accessed with Polar Probe footprint
  • Differential stripline Impedance structure accessed with Polar Probe footprint

Test coupon

The test coupon is shown below. The coupon is divided into three sections, SPP, SET2DIL and impedance

Test coupons

Testing

The VNA portion of the work was conducted by the UK's National Physical Laboratory (UK equivalent of NIST) using fully traceable VNA equipment.

SPP, SET2DIL, SET2SEIL and impedance testing was performed with Polar ATLAS Insertion Loss Test System software (V14.04) using a Tektronix DSA8300 with 80E04 sampling modules and Polar ATLAS 800 ESD Protection Module. SPP tests were performed both with PicoSecond Pulse Labs 5208 Impulse Forming Networks (IFN) and with Polar software modelled IFNs.

Modelling information was provided by Polar Instruments Si9000e Insertion loss GHz PCB transmission line field solver modelling software (V13.02)

Cross sectioning

Cross sectioning was performed by Spur Electron Limited, Havant, Hampshire, UK.

Scanning electron microscope inspection cross section images of a test coupon are shown below.

1st cross section

SEM coupon cross section (trace height)

2nd cross section

SEM cross section – detailed view (trace width)

Dimensions obtained from the cross sections were used in subsequent modelling in the Si9000e.

Graphical results

Raw data were transferred for comparison and presentation to Microsoft Excel. Spreadsheets were generated for both single ended and differential data and resulting graphs plotted.

The charts show measured data for VNA, SET2DIL and SPP, both with hardware IFNs (SPP in the charts) and with software modelled IFNs (charted as SPP No IFN.) Measured results for a typical coupon correlation test are shown below.

Raw data and regression are shown normalised to loss/10mm v frequency in GHz. Phase results are shown as rad/10mm v frequency in GHz.

VNA results are shown to 30 GHz, SPP and SET2DIL are shown to 20GHz (the sampling bandwidth limit of the DSA8300/80E04 TDR system employed.)

Raw Data

Raw data (loss/10mm v Frequency in GHz)

Regression

Regression data (loss/10mm v Frequency in GHz)

Phase

Phase (rad/10mm v frequency in GHz)

Conclusion

The charts of combined data show good correlation up to the measured bandwidth of 20GHz between VNA, SPP and SET2DIL.

The data sets using the software emulated and hardware impulse forming networks show extremely good correlation with the data sets in most cases overlying each other directly.