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- 1. The Electromechanical Design of a Spring Pin Based WLCSP Contact Engine and it’s Effect on Signal Fidelity.<br />Mike Fredd<br />Cascade Microtech<br />June 12 to 15, 2011<br />San Diego, CA<br />
- 2. IntroductionGoal<br />To better understand the electrical implications of the mechanical features in WLCSP spring pin based contact engines.<br />June 12 to 15, 2011<br />IEEE SW Test Workshop<br />2<br />
- 3. Agenda<br />What is a Spring Pin Based WLCSP Contact Engine?<br />Spring Pin Circuit Performance Requirements.<br />Electrical Performance - Datasheets.<br />Contact Circuit Equivalent Models.<br />Analytical Analysis.<br />Techniques For Model Fitting.<br />Pin Placement in Contact Engine.<br />3<br />April, 2010<br />
- 4. IntroductionWhat is a Spring Pin Based WLCSP Contact Engine?<br />4<br />April, 2010<br />For the purposes of this presentation a WLCSP contact engine is a spring pin type of contact in a dielectric housing for wafer level probing using pitches ranging from 300 m to 500 m.<br />
- 5. Spring Pin Circuit Performance Needs<br />Power Delivery. <br />Low Inductance to avoid ground bounce and power rail collapse.<br />Signal Integrity. <br />Digital <br />High Speed Edges <br />RF<br />Controlled Impedance<br />5<br />April, 2010<br />
- 6. Data Sheet Comparisons<br />A survey of datasheets shows an inconsistant reporting of electromechanical parameters.<br />At a minimum these mechanical factors need to be known for electrical characterization.<br />Length, Pitch, Radius, Conductivity and Dielectric Constant.<br />From these parameters all of the following can be modeled.<br />Loop, Partial and Mutual Inductance.<br />Shunt capacitance or Mutual capacitance.<br />S-Parameters, Phase Delay, Band Width, Rise Time and Isolation.<br />6<br />April, 2010<br />
- 7. Data sheet values<br />The methods used to extract, calculate or measure the lumped element electrical parameters are important in understanding how to use them in practice or when comparing pins.<br />Lumped element equivalent model parameters are only valid when the physical Length << /10.<br />When the Length is not << /10 microwave models should be used.<br />7<br />April, 2010<br />
- 8. Inductance<br />8<br />April, 2010<br />The lowest self inductance does not mean highest bandwidth. <br />High bandwidth is obtained by controlled impedance.<br />
- 9. Inductance<br />Loop inductance is the only inductance parameter that can be measured directly.<br />Self and mutual Inductance are only mathematical concepts that cannot be measured directly.<br />The inductance of a single pin can be calculated and uniquely assigned to a pin.<br />9<br />April, 2010<br />
- 10. Capacitance and Resistance<br />Capacitance can be modeled from measurements or simulation.<br />This can be bounded by calculation as well.<br />Resistance<br />Is the smallest factor to model and the easiest to calculate.<br />10<br />April, 2010<br />
- 11. Spring Pin Partial Inductance<br />Partial Inductance may be uniquely calculated in piecewise segments using the magnetic vector potential.<br />11<br />April, 2010<br />A2<br />A1<br />M12<br />
- 12. 12<br />April, 2010<br />Spring Pin Partial Inductance and Partial Mutual Inductance Between Two Straight Parallel Segments<br />A2<br />A1<br />M12<br />
- 13. Mutual Inductance and the Integration Path for Two Pins Carrying a Shared Current.<br />13<br />April, 2010<br />I2<br />I1<br />The sign of the mutal inductance coefficients comes from the dot product of <br />
- 14. Model Topologies<br />A survey of the electrical models shows an attempt to attribute inductance to length, capacitance to separation and resistivity to material effects.<br />There are many lumped element models used to extract the lumped parameters of spring pins.<br />14<br />April, 2010<br />
- 15. Models<br />15<br />April, 2010<br />
- 16. Techniques For Model Fitting<br />The model is best fit to the measured s-parameters. <br />S11 and S21 are used to fit the impedance profile.<br />The model can be used up to the condition of L<</10.<br />16<br />April, 2010<br />
- 17. Length << /10<br />17<br />April, 2010<br />
- 18. Model Output<br />June 12 to 15, 2011<br />IEEE SW Test Workshop<br />18<br />HFSS<br />DATA<br />
- 19. Pin Placement<br />At frequency the inductance of pins in parallel are not the reciprocal sum of the recipricals due to the mutal inductances.<br />Due to the proximity effect current is not shared equally between all pins.<br />19<br />April, 2010<br />
- 20. Inductances from a Square Array<br />20<br />April, 2010<br />
- 21. Summary<br />21<br />April, 2010<br /><ul><li> For optimal power and ground performance. partial Inductance should be used as the main metric to compare contact engines
- 22. Mechanically compare the length to radius ratio.
- 23. Beware of stated inductance values in datasheets.
- 24. When high bandwidth is desired a matched impedance is required.
- 25. The dielectric constant of the housing becomes important.
- 26. Z is a function of L and C.</li></li></ul><li>Summary<br />22<br />April, 2010<br /><ul><li> Inductance should be extracted from an analytical, simulation and measurement.
- 27. Lumped element extractions are accurate when L << /10
- 28. The industry should develop a more standarized way to specify and determine WLCSP spring pin lumped element circuit parametrs.</li></li></ul><li>23<br />April, 2010<br />References: Clayton R. Paul, Inductance Loop and Partial<br />Thank You and Have a Nice Day<br />

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