Issue link: https://iconnect007.uberflip.com/i/1248324
70 PCB007 MAGAZINE I MAY 2020 nects performed similarly through 10 Ghz. At higher frequencies in the range of 10–30 GHz, the Samtec Z-Ray connector showed the high- est levels of insertion loss compared with the other interconnects. In this range, the elasto- mer showed higher insertion rate values when compared with the PTH via which performed similarly to the sintered via and the reflowed ball kit. In fact, the sintered via and PTH via again performed similarly through all frequen- cies up to 30 Ghz. At the highest test frequen- cy range (greater than 30 GHz), the PTH via showed the lowest levels of return loss while the reflowed ball kit experienced the highest levels. As previously noted, interconnects were not optimized to a 50-ohm impedance environ- ment, which leaves room for optimization of the structure as a whole. Since the focus of this testing was on the comparison of the intercon- nect structures and not the vias themselves, we were not concerned with meeting the 50- ohm model as much as differences between each sample. The sintered via had similar impedance to the PTH via, but the sintered via did show the highest impedance value at the interconnect when compared to the other methods. The reflowed ball kit and ISC also showed similar results to the PTH via. The Samtec Z-Ray con- nector showed a double peak in impedance, which would have adverse effects at higher frequencies. This double peak is a direct result of the composition of the connector (pin + FR- 4 + pin); this is shown in Figure 19. The re- flowed ball kit and ISC elastomer results were left off of this chart for clarity as results were similar to the PTH via. Rise time degradation was evaluated for each of the interconnect types. The evalua- tion showed that all structures showed similar and acceptable values in the 20–80% range. The sintered via had the lowest delay (AVG = 335.7 ps), while the ISC Elastomer had the highest delay (AVG = 385.1 ps). For reference, the PTH via was AVG = 339.4 ps. The Samtec Z-Ray connector showed some variation due to the impedance mismatch in the connector. Figure 20 shows the rise time degradation for the PTH via and the Samtec Z-Ray connector. Finally, another key element to picking the proper solution is flatness across the contact pad array. Flatness was evaluated using a laser Figure 20: PTH via and Samtec Z-Ray connector rise time degradation. Figure 19: PTH via, sintered via, and Samtec Z-Ray connector impedance.