Probe Pattern Design for Low-Cost and High-Speed Loopback Test. Norman Chunghwa Precision Test Tech

Transcription

1 Probe Pattern Design for Low-Cost and High-Speed Loopback Test Norman Chunghwa Precision Test Tech

2 Overview VPC Test Structure The Importance of Impedance Continuity Impedance Control on Probe Pattern The Best Transmission Structure Examples of How to Find the Most Appropriate Solution Conclusion 2

3 VPC Test Structure For VPC test ATE Bridge Beam PH Wafer Pogo Pin PCB Space Transformer(Substrate) Probe Card For fine-pitch fan out routing Why using Substrate? Substrate PH Wafer C4 Pitch 50um 3

4 VPC Test Structure What are CHPT s solutions for high speed signal on card? DFT CHPT in IC design flexibility. Phase Excellent Impedance Control, Loopback + Bias-T and low cost The speed of signal is getting faster with the evolution of the technology. Excellent Impedance Control, Excellent Impedance Control Loopback + Bias-T and low cost 4

5 VPC Test Structure ST Loopback +Bias-T Design AC DC DC DC -10dB Good S-Parameter AC DC 20GHz FB right on high speed trace to avoid stub. 100Ω+5% 100Ω-5% Good Impedance Control CHPT is specialized at PCB/PC design for good SI. USB3.1 (10Gbps) 5

6 The Importance of Impedance Continuity Blue Key Factor 6

7 The Importance of Impedance Continuity Good eyes opening Only ST 10Gbps (USB 3.1 Gen2 ) 7

8 The Importance of Impedance Continuity 1mm 7mm Probes cause worse eye opening. V length When length is 7mm 1mm : It occupies 0.116λ λ=6 (> λ o /20) (5GHz =42 Signal) o (5GHz Signal) λ =60mm ST for + Probe 5GHz speed signal (in air) 10Gbps (USB 3.1 Gen2 ) 8

9 The Importance of Impedance Continuity 166Ω USB3.1 (10Gbps) To adjust pattern 124Ω USB3.1 (10Gbps) Eye Opening could be improved by optimizing pattern(signal and GND) for better impedance continuity. 9

10 The Importance of Impedance Continuity ø Pitch Current Loop Length Wire Pitch Loop Inductance Z o Wire Length Loop Inductance Z o ø Loop Inductance Z o Key factors of impedance control on open-wire T-Line : 1. Pitch (Signal to GND) 2. Length 3. Diameter (Z o = ) 10

11 Impedance Control on Probe Pattern The key factors of impedance control for pattern : Probes Change Probe Pattern W/O Change Probe Pattern Signal (Differential Pair) GND Increase Impedance Decrease Impedance Decrease Reflection GND Probe Quantities Probe Pitch Probe Length Probe Cross-Section x a y b No GND 6 GND 11

12 Impedance Control on Probe Pattern GND Probe Quantities(fixed pitch, length and cross-section) Speed : USB 3.1 Gen2, 10Gbps GND Probe x 0 GND Probe x 2 GND Probe x 6 7Ω 21Ω Delay Time ST Delay Time ST Delay Time ST 12

13 Impedance Control on Probe Pattern Probe Pitch(fixed quantities, length and cross-section) Speed : USB 3.1 Gen2, 10Gbps x y x = 130um, y =141um x y x = 108um, y =121um x y x = 93um, y =101um 24Ω 26Ω Delay Time ST Delay Time ST Delay Time ST 13

14 Impedance Control on Probe Pattern Probe Length(fixed quantities, pitch and cross-section) Speed : USB 3.1 Gen2, 10Gbps ST Probe Die Signal Path MEMS ST(Zo) Probe (Z 1 ) Die RX(Z L =Z o ) Length = 7000um Length = 6000um Length = 4000um Z in Z Z in in Z L + jz1 0 = Z1 Z + jz 0 Z Z = Z1 Z if 0 = in lim 0 1 = Z L L Z Z1 Z L jz1 tan β jz tan β L 1 L + + jz1 tan β jz tan β L When Z 1 () length is shorter, Z in would be close to Z L. When Z L =Z o, there is no reflection on this structure. Z in 14

15 Impedance Control on Probe Pattern Probe Cross-Section(fixed quantities, pitch and length) Speed : USB 3.1 Gen2, 10Gbps a b Type A(30um x 35um) Type B(41um x 42um) Type C(43um x 55um) a b a b 32Ω 16Ω Delay Time ST Delay Time ST Delay Time ST 15

16 Impedance Control on Probe Pattern Key Factors of Impedance Control 1GND Probe Quantities 2Probe Pitch 3Probe Length 4Probe Cross-Section Variables of Probe Pattern Eye Opening Performance No GND Probe 2 GND Probe 6 GND Probe X = 130um, y =141um X = 108um, y =121um X = 93um, y =101um Length = 7000um Length = 6000um Length = 4000um Type A(30um x 35um) Type B(41um x 42um) Type C(43um x 55um) Eye opening performance: Bad Medium Good 16

17 The Best Transmission Structure According to the previous experiment results, we could reach to the best pattern for good eye opening and impedance continuity. DUT + Probe(before optimization) + ST DUT + Probe(after optimization) + ST 74Ω Delay Time ST Delay Time ST Probe pattern can be optimized to improve impedance discontinuity. Speed : USB 3.1 Gen2, 10Gbps 17

18 Design For Testing(DFT) CP Testing End In Product IC Design Phase ST ST 7mm 0.1mm Probe Die DFT should If not, the take only impedance way is to continuity choose of the pattern appropriate into consideration. type. 18

19 Example1 with DFT Consideration For a chosen/fixed with 43um x 55um cross-section, five combinations of pitch and GND quantities can achieve better SI. After Optimization Before Optimization DFT Key Factors can of design Impedance both Control GND Probe Quantities Probe and Pitch Probe Pitch to get better SI. GND Probe Quantities 2GND X = 130um, y =141um Eye Opening Speed : USB 3.1 Gen2, 10Gbps Key Factors of Impedance Control GND Probe Quantities Probe Pitch 6GND X = 93um, y =101um 6 GND X = 89um, y =111um Eye Opening GND Probe Quantities Probe Pitch 4GND X = 98um, y =81um x y 4GND X = 82um, y =101um No GND 6 GND 2GND X = 89um, y =81um 19

20 Before Optimization Key Factors of Impedance Control GND Probe Quantities 2GND Example2 w/o DFT Consideration For chosen/fixed pitch and GND Probe Quantities of 141um S to S and 130um S to G design, five combinations of cross-section and GND quantities can achieve better SI. If not, choose type for better Probe SI. Cross-Section 43um X 55um Eye Opening Speed : USB 3.1 Gen2, 10Gbps After Optimization Key Factors of Impedance Control GND Probe Quantities 6 GND 6GND Probe Cross-Section (Cobra Probe) φ= 101.6um(4mil) Length=5175um φ= 76.2um(3mil) Length=4851um Eye Opening GND Probe Quantities Probe Cross-Section a b 4GND 4GND φ= 101.6um(4mil) Length=5175um φ= 76.2um(3mil) Length=4851um No GND 6 GND 2GND φ= 101.6um(4mil) Length=5175um 20

21 Conclusion The best transmission structure should consider impedance continuity between and space transformer. Probe pattern is also a key factor for high speed SI performance, therefore, it is necessary to be aware how to optimize pattern for impedance continuity. Four key factors of pattern should be optimized as below: GND Probe Quantities Probe Pitch Probe Length Probe Cross-Section x a y L b No GND 6 GND 21