Giga Test Labs POST OFFICE BOX 1927 CUPERTINO, CA 95015 TELEPHONE (408) 524-2700 FAX (408) 524-2777 ARIES ELECTRONICS BGA SOCKET (0.80MM TEST CENTER PROBE CONTACT) Final Report Electrical Characterization 0.05-5.05 GHz Feburary 21, 2003 1 Table of Contents Subject page Table of Contents..................................................................................................2 Summary...............................................................................................................3 Objective..........................................................................................................3 Methodology: ...................................................................................................3 Figure 1: Surrogate Package......................................................................3 Figure 2 – Socket Fixture ...........................................................................4 Figure 3 – Signal pin load conditions..........................................................4 Measurement system ......................................................................................5 Equivalent-circuit model...................................................................................5 Figure 4 - BGA socket equivalent-circuit diagram ......................................5 Element definitions ..........................................................................................6 Element values ................................................................................................6 Table 1 – BGA socket (0.80mm Test Center Probe Contact) element values .........................................................................................................6 Conclusions .....................................................................................................6 Table 2 – BGA socket (0.80mm Test Center Probe Contact) 1dB loop-thru bandwidth ...................................................................................................6 Figure 5 – Signal to ground ratio setup ......................................................7 Appendix ...............................................................................................................8 2 Summary Objective The Aries BGA (0.80mm Test Center Probe Contact) socket was measured at GigaTest Labs to assess its electrical performance. Also, its high-speed performance limits were determined. Methodology: A custom fixture (GTL 243-GT-001 rev A1) was first designed by GTL which allows the use of coplanar probes to make the measurements. A second fixture was fabricated to be placed inside each socket. It provides connections between the internal pins, so pairs of pins can be measured in different load conditions. This fixture is referred to as "surrogate package". Figure 1 shows a picture the surrogate package, while figure 2 shows the top and bottom side of the fixture. Figure 1: Surrogate Package 3 Figure 2 – Socket Fixture There are three load conditions used on the signal pins: the open measurement is performed on two pins with just unconnected surface pads on the surrogate package. The short measurement is done with the pins shorted to the ground on the surrogate. The thru is just the two pins connected together. These are illustrated on figure 3. The measured pins are denoted by the numbers 1 & 2. The adjacent pins to the measurement, usually the three nearest neighbors are grounded to the fixture ground and the surrogate package ground. open short thru 1 1 1 2 2 2 Figure 3 – Signal pin load conditions The fixture was measured separately to extract its parasitics, so they could later be de-embedded from the overall measurement. The Agilent 8510C network-analyzer was used to measure two-port sparameters. The frequency range was 100 MHz – 40.1 GHz. From the sparameter data, a SPICE-compatible equivalent circuit was derived using Agilent ADS version 2002. 4 Measurement system All measurements were taken using a high-frequency measurement system. This consists of a Agilent 8510C network analyzer & GGB Picoprobes™ 450 µm pitch. The Agilent 8510C network analyzer is a frequency domain instrument. The measurements are taken as scattering parameters (a.k.a. s-parameters). The HP8510C has great calibration capabilities, which make it the most accurate high-frequency instrument available. For this work the short-open-load-thru (SOLT) calibration was used. The GGB Picoprobes provide a high-quality 50 Ω path from the network analyzer and cables to the DUT. Equivalent-circuit model Figure 4 shows the topology used to model the BGA socket (0.80mm Test Center Probe Contact). Please note that only two pins are shown in this schematic, however there will be similar mutual elements (M21, C21A and C21B) to ALL the surrounding pins. Therefore, to implement the model for one pin, the user needs to describe it and all the pins surrounding it (a total of 9 pins). By the same reasoning, to implement two pins, then the models for 12 pins will be needed. C21b R1 L1 M21 L2 R2 C21a port 1 port 2 Figure 4 - BGA socket equivalent-circuit diagram 5 Element definitions L1, L2: pin effective inductance M21: mutual inductance between adjacent pins R1, R2: shunt-resistance of inductors L1 and L2, used to model highfrequency loss due to skin effect and dielectric loss C21a: mutual-capacitance between adjacent pins (PCB side) C21b: mutual-capacitance between adjacent pins (BGA side) Element values The BGA socket (0.80mm Test Center Probe Contact) model is valid from DC to 5.05 GHz. The measured and modeled transmission response agrees within 1 dB. Models were extracted for four types of pins: adjacent field pins, corner pins, field diagonal pins and edge adjacent pins. Table 1 – BGA socket (0.80mm Test Center Probe Contact) element values Pins L1 & L2 (nH) M21 (nH) R1 & R2 (Ω) C21a (pF) C21b (pF) Field adjacent 0.56 0.08 200 0.033 0.033 Corner adjacent 0.76 0.17 300 0.043 0.043 Field diagonal 0.51 0.01 300 0.007 0.007 Edge adjacent 0.65 0.12 200 0.040 0.040 Conclusions 1. The bandwidth for the BGA socket (0.80mm Test Center Probe Contact) was determined from a loop-thru measurement on two adjacent pins with varying numbers of surrounging pins grounded (please see figure 5 and table 2). Table 2 – BGA socket (0.80mm Test Center Probe Contact) 1dB loop-thru bandwidth Pins 1dB BW (GHz) Field adjacent (1:5 signal to gnd ratio) 7.8 Corner adjacent (1:2 signal to gnd ratio) 7.1 Field diagonal (1:7 signal to gnd ratio) 10.1 Edge adjacent (1:3 signal to gnd ratio) 8.5 6 1:2 1:3 1:5 probed pin grounded pin 1:7 Figure 5 – Signal to ground ratio setup Since the surrogate packages were routed out to fit into the socket cavity, we believe there was a small misalignment on the field adjacent THRU standard. This issue is probably responsible for the low field adjacent bandwidth. We attempted this measurement twice, with no better result. In reality, the field adjacent 1 dB bandwidth should be in the 9-10 GHz range. 2. The model bandwidth is DC-5.05 GHz, which will easily handle signals with 200 ps edges. 7 Appendix The appendix shows the measured and simulated output data. Measured and simulated data page Open measurement on adjacent pins ...................................................................9 Shorted measurement on adjacent pins .............................................................10 Loop-thru measurement on adjacent pins...........................................................11 Loop-thru bandwidth measurement (40 GHz) ............................................... 12-15 8 Adjacent pins open Measured s-parameters in blue, simulated s-parameters in red 9 Adjacent pins shorted to ground Measured s-parameters in blue, simulated s-parameters in red 10 Adjacent pins connected together (loop-thru) Measured s-parameters in blue, simulated s-parameters in red 11 Adjacent Loop-thru Bandwidth Measurement Measured insertion loss versus frequency for two pins in series “1:5 signal to ground ratio” L o o p -Thru Bandw idth 0 m1 dB(S(2,1)) -1 -2 m1 fre q = 7 . 8 0 0 G H z d B (S(2,1))=-0.978 -3 -4 -5 0 5 10 fre q , GHz 12 15 20 Edge Loop-thru Bandwidth Measurement Measured insertion loss versus frequency for two pins in series “1:3 signal to ground ratio” L o o p -Thru Bandw idth 0 m1 dB(S(2,1)) -1 -2 m1 fre q = 8 . 5 0 0 G H z d B (S(2,1))=-0.960 -3 -4 -5 0 5 10 fre q , GHz 13 15 20 Corner Loop-thru Bandwidth Measurement Measured insertion loss versus frequency for two pins in series “1:2 signal to ground ratio” L o o p -Th r u B a n d w idth 0 m1 dB(S(2,1)) -1 m1 fre q = 7 .1 0 0 G H z d B (S(2,1))=-0.918 -2 -3 -4 -5 0 5 10 fre q , GHz 14 15 20 Diagonal Loop-thru Bandwidth Measurement Measured insertion loss versus frequency for two pins in series “1:7 signal to ground ratio” L o o p -Thru Bandw idth 0 m1 dB(S(2,1)) -1 -2 m1 fre q = 1 0 .10GHz d B (S(2,1))=-0.971 -3 -4 -5 0 5 10 fre q , GHz 15 15 20