accounting for copper surface roughness for close correlation between simulation and measurement in...
TRANSCRIPT
Accounting for Copper Surface Roughness for Close Correlation between Simulation
and Measurement in a 10Gbps
Package Channel
Jacov Brener, PHY EM Design Engineer Intel Corporation, Datacenter and Connected Systems Group, Communication & Storage Silicon Engineering
• Motivation
• Measurement setup and results
• Initial correlation results
• Surface roughness Hall-Huray model
• Surface roughness measurement
• Final correlation results
• Summary
• Q&A
Agenda
2 J. Brener, “Accounting for Copper Surface Roughness for Close Correlation between Simulation and Measurement in a 10Gbps Package Channel”, November 26th 2013
Motivation
• TP1 is on the DUT balls [1]
• The only high speed channel exits in the test is package channel
• Need to account for package impact on waveform jitter, rise time, amplitude etc…
3 J. Brener, “Accounting for Copper Surface Roughness for Close Correlation between Simulation and Measurement in a 10Gbps Package Channel”, November 26th 2013
TP1
Silicon
Package
Board
PTH
BGA
C4 bumps Trace
Motivation cont.
• A typical 10mm package has BW of at least 20GHz
• Package effects mostly on waveform on the balls so we’ll focus on ILdiff magnitude
100GHz 3D full wave typical package channel model
4 J. Brener, “Accounting for Copper Surface Roughness for Close Correlation between Simulation and Measurement in a 10Gbps Package Channel”, November 26th 2013
Measurement Setup and Results
• 4 port 20GHz equipment • SOLT calibration • Dual side probing station
5 J. Brener, “Accounting for Copper Surface Roughness for Close Correlation between Simulation and Measurement in a 10Gbps Package Channel”, November 26th 2013
VNA
Package
Probes
Measurement Setup and Results cont.
• Low measurement noise • Low package to package variation • Good measurement repeatability
6 J. Brener, “Accounting for Copper Surface Roughness for Close Correlation between Simulation and Measurement in a 10Gbps Package Channel”, November 26th 2013
Initial Correlation Results
• Small correlation error in DC due to inaccuracy of the field solver • Nearly linear increase in the correlation error – looks like a loss mechanism • ~12.5% error @20GHz
7 J. Brener, “Accounting for Copper Surface Roughness for Close Correlation between Simulation and Measurement in a 10Gbps Package Channel”, November 26th 2013
Initial Correlation Results cont.
• Cross section of package traces were made to debug the correlation error
• Copper surface roughness was discovered to be on the order of skin depth in GHz range
• Both on the traces an the planes found to be equally rough
• Same phenomena occurs on boards and was discussed extensively in DesignCon [2]
8 J. Brener, “Accounting for Copper Surface Roughness for Close Correlation between Simulation and Measurement in a 10Gbps Package Channel”, November 26th 2013
Surface Roughness Hall-Huray Model
• Traditional Hammerstad model describes surface roughness as a repeating series of peaks and valleys [3]
• Models the surface as a 1 dimensional effective cross section [3]
9
RMSh0
2
21 arctan 1.
2
4Hammerstad
smoothr
rough
skin
smooth
RMSr
skin
f
hf
J. Brener, “Accounting for Copper Surface Roughness for Close Correlation between Simulation and Measurement in a 10Gbps Package Channel”, November 26th 2013
2
2
2
0
4
31
2
2
2
1Hall Huary
smoothr
rough
skin
smooth
r
rr
skin skin
f
a Ns
A
sf
a a
Surface Roughness Hall-Huray Model cont.
• Hall-Hurray model models a 2 dimensional surface [4]
• Describes the surface as an effective matrix of half-spheres [4]
10
a
J. Brener, “Accounting for Copper Surface Roughness for Close Correlation between Simulation and Measurement in a 10Gbps Package Channel”, November 26th 2013
N half-spheres per area A
Surface Roughness Measurement
• Copper surface was exposed from the dielectrics [5]
• SEM (Scanning Electro Microscopy) pictures were taken to visualize the phenomena [5]
• AFM (Atomic Force Microscopy) 3D profile map was taken for analysis [5] 11
J. Brener, “Accounting for Copper Surface Roughness for Close Correlation between Simulation and Measurement in a 10Gbps Package Channel”, November 26th 2013
Surface Roughness Measurement cont.
Results obtained from AFM [5]:
• RMS: RMS height
• SAD: Surface Area Difference
12
N
ZRMS
i
2)(
( _ _ )1
( _ )
i
j
real surface areaSAD
scan area
J. Brener, “Accounting for Copper Surface Roughness for Close Correlation between Simulation and Measurement in a 10Gbps Package Channel”, November 26th 2013
Final Correlation Results
Rough trace loss estimation [6]
13
1
20log
smoothrough
r
rough
l
f
Rwt
R j L G j C
j
Attenuation dB e
J. Brener, “Accounting for Copper Surface Roughness for Close Correlation between Simulation and Measurement in a 10Gbps Package Channel”, November 26th 2013
• Hall-Huray model usage decreases the error by a factor of 10 up to 13GHz • Hall-Huray model usage decreases the error at 20GHz to less than 5% • Hammerstad model is still away from reality
14 J. Brener, “Accounting for Copper Surface Roughness for Close Correlation between Simulation and Measurement in a 10Gbps Package Channel”, November 26th 2013
Final Correlation Results cont.
Summary
1. Package can and will become important
2. Surface roughness adds significant loss at GHz range and beyond for any PCB trace
3. Surface roughness can be accurately measured by AFM
4. Hall-Huray model proven to be effective
5. Accounting for surface roughness decrease correlation error by x2.5
15 J. Brener, “Accounting for Copper Surface Roughness for Close Correlation between Simulation and Measurement in a 10Gbps Package Channel”, November 26th 2013
Acknowledgments & References
• Acknowledgments: – Manukovsky Alex, Intel Corp.
– Valentina Korchnoy, Intel Corp.
• References
1. IEEE 802.3-2012, Clause 72
2. E. Bogatin, D. DeGroot, P.G. Huray, Y.Shlepnev, “Which one is better? Comparing options to describe frequency dependent losses”, DesignCon 2013
3. E. Hammerstad , O. Jensen, “Accurate models for microstrip computer aided design”, IEEE MTT-S Int. Microw. Symp. Dig., May 1980, pp.407–409.
4. S. Hall, S. Pytel, P. Huray, D. Hua, A. Moonshiram, G. Brist, and E. Sijercic, “Multigigahertz Causal Transmission Line Modeling Methodology Using a 3-D Hemispherical Surface Roughness Approach”, IEEE trans. Microwave Theory and Tech., vol.55, no.12, Dec.2007, pp.2614-2624
5. V. Korchnoy, J. Brener, “A Practical Method for Trace Exposure and Roughness Measurements and Implementation in High Speed Package Design”, ISTFA 2012, November 2012
6. W.R. Eisenstadt, Y. Eo“S-Parameter-Based IC Interconnect Transmission Line Characterization”, IEEE trans. Components Hybrids and Manufacturing Tech., vol. 15, no. 4, August 1992, pp483-490
16 J. Brener, “Accounting for Copper Surface Roughness for Close Correlation between Simulation and Measurement in a 10Gbps Package Channel”, November 26th 2013
Thank you!
Q&A