Solder reflow plays an important role in the success and performance of high-bandwidth RF connectors. Sometimes, when a high-bandwidth RF connector is soldered together with an optimized PCB launch, the results can be unpredictable. It is important to investigate the root causes of solder reflow variation and analyze what techniques can deliver consistent performance across frequencies.
In a new white paper from Samtec, “Impacts of Solder Reflow on High Bandwidth RF Connectors,” authors Michael Griesi (RF Design & Simulation Engineering Manager) and Chris Shelly (retired Senior RF/SI Modeling Engineer) analyze the impact of their design choices for a specific push-on connector, its PCB, and the process. Using simulations and measurements, the team steps through its detailed development process to achieve the optimal design and better control solder flow.
The design team began with an initial two-piece contact, traditional design shown in the figure. Note the “tombstoning” effect that was found on some of the sample connectors, where they were tilting on the PCB. Snap on connectors such as this need to stay firmly on the board, with the center contacting the board. The initial connector design was targeting 40 GHz bandwidth when soldered onto a PCB; however, simulations showed performance of less than 25 GHz.
As a first step, the design team experimented with the thickness of the gold plating and the insulator’s coefficient of expansion. Other topics investigated include solder wicking and pooling, PCB pad design, and tuning the solder reflow process. In the end, the final design had thinner gold plating, higher temperature insulators, and a single-piece swept contact. To further address performance concerns, the team added a chamfer to the bottom of the connector, a solder control tail on the PCB pad, adjusted the thermal profile, and other process adjustments. All of these changes, the analysis that led to them, and the results are covered in great detail in the white paper.
The performance challenges experienced with this connector design process are not unique to this type of connector. At high frequencies, every little detail matters. To achieve optimal performance, it is important to have robust simulation capabilities and multiple troubleshooting and analysis tools. The challenges of solder reflow and the impact it has on performance extends to all high-bandwidth RF connectors. At Samtec, work continues in simulation, manufacturing process, PCB and connector design to continue to optimize performance in the presence of solder reflow.