RF Welder
At its core, RF welding is the process of heating two pieces of material to the melting point and joining them before solidification. Polymer welding is all around us yet we rarely notice the subtle weld line or think about the process that makes it possible. RF welding occupies a growing niche due to the unique benefits of high duty cycle, good process control, and the ability to repeatably produce high quality welds.
The Challenge
A medical device manufacturer needed to update a product design that included RF-based sterile welding capability by adapting their technology to a more highly integrated package and to satisfy updated international regulatory requirements. Success of the project would be measured by a reduction in size by one-fourth while meeting or exceeding performance and regulatory criterion.
Packaging Challenges
Primary to any effort in reducing size of an RF circuit is the successful selection and implementation of components. In this case, the primary RF loading coil was constructed from air wound coil stock, which is physically large, expensive to integrate, and susceptible to mutual inductance effects. TCB Engineers brought 25 years of RF design experience to bear on the challenge through a combination of custom magnetic design and vertical integration strategies.
The Solution
Reducing the inductor size proved challenging because high flux densities precluded leveraging the size reduction advantages of ferrites. After considering relevant technical and business factors, the size reduction challenge was accomplished through the development of a compact magnetic design consisting of a custom flat-wire inductor and shield assembly less than one-tenth the size of its predecessor. The custom inductor exhibited superior magnetic performance, but necessitated development of a flat wire coil winder and a metrology system for acceptance testing.
Manufacturing Challenges
While the flat wire coil provided size and cost benefits, the task of producing them presented additional challenges. TCB Engineers worked closely with the customer’s contract manufacturer (CM) to address the unique manufacturing challenges associated with producing high quality flat wire RF coil assemblies.
Preventing damage to wire insulation during winding and controlling finished dimensions were accomplished through design of a custom winding anvil. A precision motion system and associated LabVIEW software provided the winding speed & torque control fundamental to repeatability. Combined, the winder and associated quality controls allowed the CM to produce finished goods with an inductance variation of less than 1% and minimal scrap, both of which contributed significantly to overall profitability.
Putting It All Together
While preliminary EMC screening revealed a well-behaved and robust RF source, a specific harmonic non-compliance was noted. After considering several solution paths and associated business factors, the addition of a simple passive filter was chosen. Evolution of the concept is shown, and it proved effective toward homologation of the product to new markets while minimizing design changes.
Conclusions
The project exceeded the primary goal of size reduction, facilitated vertical integration, improved quality, and opened new market opportunities. This demonstrates TCB Engineers' unique ability to provide complete solutions to our customer's toughest problems.