Effect of Signal-Ground Pin Assignments on Signal Transmission Characteristics of Barrel-Less Pogo Pin

Transcription

1 Effect of Signal-Ground Pin Assignments on Signal Transmission 1 1, First Author Kongju National University, mjkim@kongju.ac.kr Abstract Signal transmission characteristics of the barrel-less pogo pins are analyzed using 3-dimensional electromagnetic field simulation. To obtain better signal transmission, the insertion loss and the reflection loss of the pogo pins are calculated with various signal-ground pin assignments. The effects of the signal transmission characteristics of the pogo pins on the increase in the number of the ground pin are investigated. Their characteristic impedances (Z 0 ) are also calculated to analyze the frequency response of the pins. Keywords: Signal transmission characteristic, barrel-less pogo pin, characteristic impedance, signal-ground pin assignment 1. Introduction Pogo pin is a device used in automated test equipment (ATE) system to establish an electrical connection between the semiconductor package and the printed circuit board [1]. The pogo pin usually has a form of an empty cylinder containing a spring and two plungers as shown in Figure 1. Also, they are usually arranged in a dense -dimension array, connecting together a number of electrical contacts in the test socket [-4]. In the applications of high speed operation, the pogo pins should be designed to allow not only high reliability across the repetitive cycles but also high fidelity transmission of the electrical signals. The signal transmission properties of the pogo pins are critical for the test systems to operate at multi-gigabit data rate [5-8]. The pins must make a good and reliable electrical contact with its body. Therefore, it is necessary to impede a substantial current along with the spring of the pin because its large inductance can degrade the signal transmission. To reduce the electrical contact of the pogo pin, a barrel-less pogo pin is proposed and its signal transmission characteristics is investigated in this work.. Signal Transmission Analysis Figure 1. Cross sectional view of pogo pin in the test socket In general, a pogo pin has a cylindrical barrel to support the top and bottom plungers mechanically. But there is a limitation to apply in the electrically function test of a fine-pitch ball grid array (FBGA) package with less than about 0.3 mm of pitch because the barrel has larger diameter. Therefore, a barrel-less pogo pin is proposed and used for FBGA package. 3-dimmensional model of a barrel-less pogo pin used in this work is shown in Figure. The pogo pin is designed for 0.3 mm pitch device and consists of three components. Its materials of International Journal of Digital Content Technology and its Applications(JDCTA) Volume 7, Number 11, July 013 doi : /jdcta.vol7.issue

2 body, spring, and plunger are beryllium copper, stainless steel, and phosphor bronze, respectively. The pin s length is 4.0 mm and the diameter of the body is 0.4 mm. Figure. Barrel-less pogo pin with plunger, spring, and body It is known that the impedance matching with 50 is critical in determining its signal transmission characteristics []. Therefore, the fidelity transmission of the electrical signals is substantially affected by the signal-ground pin assignments. In this work, the barrel-less pogo pins are arranged with one signal-carrying pin surrounded by various ground pins. The signal transmission properties of the barrel-less pogo pins are analyzed using 3-dimmensional electromagnetic field simulation (ANSYS HFSS). In the calculations of the pin s signal integrity, several pin assignments for signal and ground are considered as shown in Figure 3. All pins are constantly separated in a length of 0.3 mm. The dotted circle presents the empty site that the pin is not arranged. The pogo pin s simulations are carried out with eight assignment conditions from one grounded pin to eight grounded pins. Figure 4 shows 3- dimensinal model with one signal-carrying pin and eight grounded pins (a) (b) (c) (d) (e) (f) (g) (h) Figure 3. Pin assignments for signal and ground from (a) one signal-carrying pin and one grounded pin to (h) one signal-carrying pin and eight grounded pins The signal transmission characteristics are instigated using the analysis of the insertion loss and the reflection loss in this work. Figure 5 shows the calculation results of the insertion loss with the various pin assignments. As the number of the ground pin assigned in Figure 3 increases, the insertion loss of the pins has improved gradually and then presents almost the same curves over more than four grounded pins. These results demonstrate that the five, six, seven, and eight grounded pins have a little effect on the insertion loss. 75

3 Figure 4. 3-dimensinal model with one signal-carrying pin and eight grounded pins Figure 6 shows the calculation results of the reflection loss with the various pin assignments. The reflection loss of the pins is also enhanced continuously as an increase of the grounded pin. But, there is a little improvement as more than four grounded pins. In conclusion, the similar trends are presented in the insertion loss and reflection loss. These results verify that one signal pin surrounded by four grounded pins is an optimum pin assignment for its signal transmission. Figure 5. Insertion loss of barrel-less pogo pins with various ground pin assignments Figure 6. Reflection loss of barrel-less pogo pins with various ground pin assignments 76

4 The frequency response characteristics of the pin assignments are investigated with an increase of the grounded pin. The frequencies of -1 db loss in the insertion loss and -0 db loss in the reflection loss are shown in Figure 7. In the insertion loss of Figure 7, the frequency of -1 db loss is increased as the number of the ground pin. However, its values are maintained almost constant over more than three grounded pins. The frequency of -0 db loss is a reasonable criterion for evaluating the performance property in the reflection loss and is shown in Figure 7. In three grounded pins or less, there is a continuously increment of the frequency of -0 db loss in the reflection loss. But, in more than four grounded pins, the frequency values keep a constant value. These results demonstrates that the pin assignment with one signal pin and four adjacent ground pins shows substantially optimum signal transmission property. Figure 7. Frequency response characteristics of barrel-less pogo pins Figure 8. Characteristic impedance of barrel-less pogo pins One of the important factors in determining the frequency performance of the pogo pin is an impedance matching. It is well known that the impedance mismatch may cause a reflection noise and then degrade the signal fidelity. Therefore, the characteristic impedance (Z 0 ) of the pins is investigated and presented in Figure 8 to analyze the frequency response characteristics f the pin. The characteristic impedance (Z 0 ) of the pin is calculated from the following equation: 77

5 Z 0 (1 S ) Z R (1 S 11 11) S S 1 1 where Z R is the reference impedance of 50. Table 1 shows the frequency response and the characteristic impedance of the barrel-less pogo pins over the number of the ground pin. As the number of the ground pin increases, Z 0 is gradually reduced and remains constant over more four grounded pins. The impedance mismatch is gradually decreased in more than four grounded pins as shown in Figure 8. Therefore, the reflection loss and the insertion loss of the pin are also enhanced continually. Table 1. Frequency response and characteristic impedance of barrel-less pogo pins Number of ground pin Frequency of -1 db loss in insertion loss (GHz) Frequency of -0 db loss in reflection loss (GHz) Z 0 ( ) Conclusion The signal transmission properties of the barrel-less pogo pins with various ground pin assignment are analyzed. In this work, it is verified that the pin assignment of the four grounded pins surrounded by one signal pin provides an optimum signal transmission. 4. Acknowledgements The research was supported by the International Science and Business Belt Program through the Ministry of Science, ICT and Future Planning (former Education, Science and Technology) (01K001564). Also, this work was supported by the research grant of the Kongju National University in References [1] H. Barnes, J. Moreira, H. Ossoinig, M. Wollitzer, T. Schmid, M. Tsai, Development of a pogo pin assembly and via design for multi-gigabit interfaces on automated test equipment, In Proceedings of Asia-Pacific Microwave Conference, pp , 006. [] R.-B. Sun, R.-B. Wu, S.-W. Hsiao, D. De Zutter, Compromise Impedance Match Design for Pogo Pins With Different Single-Ended and Differential Signal-Ground Patterns, IEEE Transactions on Advanced Packaging, vol. 33, no. 4, pp , 010. [3] B. B. Szendrenyi, H. Barnes, J. Moreira, M. Wollitzer, T. Schmid, M. Tsai, Addressing the Broadband Crosstalk Challenges of Pogo Pin Type Interfaces for High-Density High-Speed Digital Applications, In Proceedings of IEEE International Microwave Symposium, pp. 09-1, 007. [4] J. A. Gasbarro and M. A. Horowitz, Integrated pin electronics for VLSI functional testers, IEEE J. Solid-State Circuits, vol. 4, no., pp , [5] R.-Bo Sun, C.-Y. Wen, R.-B. Wu, A New Isolation Structure of Pogo Pins for Crosstalk Reduction in a Test Socket, IEEE Transactions on Components, Packaging and Manufacturing Technology, vol. 1, no. 4, pp , 011. [6] N. Amin, L. Z. Yi, A Practical Investigation on the Root Causes of the Mechanical Damages of Pogo Pin Type Test Sockets to IC packages in Final Test, In Proceedings of IEEE International Conference on Semiconductor Electronics, pp ,

6 [7] D. H. Han, V. Prokofiev, W. Leigh, L. Polka, T. Ruttan, High frequency modeling and characterization of pin and land grid array sockets, In Proceedings of IEEE Electronic Components and Technology Conference, pp , 003. [8] B. Tunaboylu, Electrical characterization of test sockets with novel contactors, IEEE Transactions on Device and Materials Reliability, accepted,