How does solder reflow affect RF connectors?

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By Janine Love, Samtec.

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 optimised PCB launch, the results can be unpredictable. It is important to investigate the root causes of solder reflow variation and analyse 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 modelling engineer) analyse the impact of the 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 solder flow control.

The design team began with an initial two-piece contact, traditional design shown in the image. The ‘tombstoning’ effect that was found on some of the sample connectors can be quite clearly seen, where the connectors were tilting on the PCB. Snap on connectors such as this need to stay firmly on the board, with the centre 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 design step, the 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. At the end of the design process, 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.

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 optimise performance in the field of solder reflow.

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How does solder reflow affect RF connectors?

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