Soldering Semi-Rigid Cable to PCBs

By Contributed Article | April 07, 2014

When soldering semi-rigid cables to PCBs, a number of design considerations must be taken into account to maximize performance.

This information was provided by Micro-Coax.

Semi-rigid cables can be soldered directly to PCBs and are an excellent solution for transmitting amplified signals across PCBs. The cables offer outstanding shielding and insertion loss characteristics, thus improving system performance and reducing power consumption. To successfully apply this technique, engineers should consider the following:

Solderability

Bare copper outer conductors will oxidize over time, potentially reducing solderability. Many end users specify a tin-plated coating for the copper jacket in order to improve soldering onto their circuit boards. Though not required and slightly more expensive, tin plating may improve reliability and reduce inspection requirements for solder joints.

Dielectric Expansion

Standard PTFE dielectrics will extrude under elevated temperatures such as typical circuit board reflow profiles. Any extrusion may cause damage to nearby components, failure of center conductor solder joint, or in rare cases, catastrophic failure of the copper outer conductor itself. Dielectric extrusion can be eliminated through the use of “LL” dielectrics made from low-density PTFE. The “LL” material is mechanically stable under temperature extremes, making it an ideal choice for reflow applications.

Lead Forming

Installation onto thru-hole or SMT circuit boards may be improved by forming center conductor leads at a right angle to or coplanar with the bottom of the copper outer jacket. Lead forming is best accomplished by automated “hands-free” techniques that ensure repeatability and minimal added assembly cost.

Assembly Forming

Densely packaged circuit boards often require a cable route with bends. Automated techniques for bending are recommended for the same reasons as lead forming above.

Marking

Marking may be applied to the cable outer jacket via ink jet technology to allow location-finding by pick-and-place vision systems. While feasible, this technique does carry an additional cost.

Packaging

Cables must arrive at the end user’s assembly line free from defects. Packaging is often the most critical and overlooked parameter for ensuring cable quality. Typical techniques include custom plastic trays with individual troughs for each cable assembly; Styrofoam trays etched to cable configuration; PVC tubes cut to extract part length; and cardboard boxes with foam rubber inserts.

For more than 50 years, Micro-Coax has specialized in delivering high-quality custom transmission line solutions and providing custom technical solutions for signal transmissions from point A to point B in the most challenging environmental conditions.