1. Silicon Valley Test Conference 2013
Configuration Dependent Test Socket Performance Gert Hohenwarter GateWave Northern, Inc.
Silicon Valley Test Conference 2013
South East Asia Test Symposium

2. Silicon Valley Test Conference 2013
Objective
Examine effect of different ground configurations on socket performance
Use HFSS 3D field simulator model output for socket configurations
Use real world PCB model in Mentor HyperLynx for overall performance assessment
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3. Silicon Valley Test Conference 2013
Simplified socket
Generate model output for ‘as tested’ configuration: 3x4 array
Silicon Valley Test Conference 2013
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4. Silicon Valley Test Conference 2013
Grounding
Ground-Signal-Ground
GG-S-S-GG
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5. Silicon Valley Test Conference 2013
Rationale
Insertion loss S21 (f)
Test configuration (grounded unused pins) = red
All 50 Ohms
(except one Ground) = green
All open
(except one ground) = blue
Silicon Valley Test Conference 2013 5
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6. Silicon Valley Test Conference 2013
To be avoided
Unused pins become resonators
Lowest frequency occurs for case of open on one end, short on the other
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7. Silicon Valley Test Conference 2013
Grounding
Performance changes with location and number of grounds
Insertion loss
S21(f)
sig out
# grounds
sig in
Return loss
S11(f)
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8. S-parameters handy for diagnosis, but….
… eye diagram is often used at frequency of interest when socket is combined with rest of circuit:
6 GB/sec
Bit-error rate (BER)
Silicon Valley Test Conference 2013 8
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9. Silicon Valley Test Conference 2013
Socket vs. PCB
Performance of socket is intertwined with performance of PCB.
Example: High speed circuit, 12 GB/s, cases 1 (blue),4 (green) and 8 (red)
Design File: GNDConfig.ffs
HyperLynx LineSim v9.0
U1_B01.19
generic
TDR
Net001
TL1 J2
Via1b_HFSSDesign1.s2p
Po...
TL2 J1
7_S2POut_1.s2p
Port1
Port2
TL5
R10_B00
DR41D_B0...
Net004
Silicon Valley Test Conference 2013 9
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10. Silicon Valley Test Conference 2013
Load board
Real world load board parameters are set up in Mentor HyperLynx simulator in order to generate a representative signal path model
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11. Complete signal path with PCB
Socket:
Socket is modeled as a connector between device-under-test (DUT) and load board
Socket is modeled as a connector between device-under-test (DUT) and load board
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12. Complete signal circuit with PCB
Device-under-test (DUT) is represented with its actual properties
Load board
Socket
Socket block can be either model output from 3D simulator or actual measurement results
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13. Real grounding, coupling, DUT@50 Ohms
Insertion loss S21 (f)
FEXT,NEXT (f)
Device-under-test (DUT) is assumed to have 50 Ohm termination
Silicon Valley Test Conference 2013 13
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14. Real grounding, coupling, real DUT with L,C,R
Insertion loss S21 (f) and FEXT,NEXT (f)
Device-under-test (DUT) is represented with its actual properties
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15. Ground position dependence
Cases: Ground near a signal pair, ground far from pair ground between pair – 2 different types of socket
Z = 35 Ohms Z = 49 Ohms
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16. Silicon Valley Test Conference 2013
Far ground
3 GB/s signal through one connection and NEXT plus FEXT
-> Eye worse for near 50 Ohm socket but crosstalk lower
NEXT/FEXT
Z = 35 Ohms Z = 49 Ohms
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17. Silicon Valley Test Conference 2013
Near ground
3 GB/s signal through one connection and NEXT plus FEXT
-> Eye worse for near 50 Ohm socket but crosstalk lower
NEXT/FEXT
Z = 35 Ohms Z = 49 Ohms
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18. Ground between signals
3 GB/s signal through one connection and NEXT plus FEXT
-> Eye worse for near 50 Ohm socket / crosstalk very comparable
NEXT/FEXT
Z = 35 Ohms Z = 49 Ohms
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19. 50 Ohm socket comparison ground between signal pins
Two (near 50 Ohm) sockets with comparable (good) – 1dB points
-> Ground between pins results in very comparable performance
NEXT/FEXT
Z = 49 Ohms Z = 49 Ohms
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20. 50 Ohm socket comparison ground adjacent to signal pins
Two (near 50 Ohm) sockets with comparable (good) – 1dB points
-> Ground adjacent to pins no longer sufficient to avoid Xtalk
NEXT/FEXT
Z = 49 Ohms Z = 49 Ohms
Silicon Valley Test Conference 2013 20
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21. Silicon Valley Test Conference 2013
Conclusion
Socket design, analysis and measurement for SI is straightforward
but
Socket optimization for a given application can be case specific
Overall system analysis is mandatory as frequencies increase
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