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MAY 2020 I PCB007 MAGAZINE 71 fer to our customers, it did show that the inter- connect method chosen needs to be selected care- fully based upon the ap- plication. A combination of flatness and electri- cal performance require- ments must be considered when selecting an option. With that being said, in our study, it was ob- served that the sintered via compared most favor- ably to the PTH via over most frequency ranges when comparing inser- tion and return loss. It had the lowest delay and similar impedance to the PTH via, which would indicate acceptance for high-frequency applica- tions. It also showed flat- ness results that were sec- ond only to the PTH via test sample, making it a good alternative where flatness is a critical requirement. In the two connectors that were evaluated based upon insertion and return loss, the Sam- tec Z-Ray connector would be a viable option for low-frequency applications (less than 10 GHz). However, due to an impedance mismatch in the connector related to its construction, its use would be prohibited at higher frequen- cies. Conversely, the Plastronics HPin connec- tor would be an option at higher frequencies but not at lower frequencies where it performed worse than the Samtec Z-Ray connector. Neither of these connectors had favorable planarity re- sults and, therefore, could not be recommended where flatness was a critical requirement. Lastly, the ISC elastomer and reflowed ball kit solutions showed worse return and inser- tion loss compared to the alternative meth- ods, which would indicate that without further testing, these interconnect methods should be avoided in high-speed applications. In addi- tion, the planarity results showed more varia- measurement technique on a RAM/QVI CMM unit. Figure 21 shows the measurement results. The data showed that the reflowed ball kit had the worst flatness rating, and the PTH via was, as expected, the "flattest" sample. The sintered via and elastomer showed similar flatness re- sults. Both connector samples that were evalu- ated showed more flatness variation. It is important to note that we attempted to minimize deflection for the temporary inter- connects (Samtec Z-Ray and Plastronics con- nectors and ISC elastomer) by building a shim slightly lower in thickness than the thickness of the FR-4 in the connectors or elastomer. This was done to minimize any deflection that may occur when press-fitting these samples. Even with these precautions, the data showed a larg- er variation that is present with these types of interconnects. Conclusion While this exercise provided a lot of use- ful electrical characterization data for each of the different interconnect types that we of- Figure 21: All test samples, flatness.

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