In 2023, a new customer came to us with a problem. They had a critical rigid-flex circuit in an important new product, but their current flex circuit vendor had issues delivering usable parts. They struggled to hold the impedance requirements within tolerance from part to part, and batch to batch.
The customer’s design and stackup had passed their impedance modeling, and since some of the parts they received did work, it didn’t seem to be just a design issue. The problem was deeper—an inconsistency in manufacturing execution. With a product launch looming, they needed answers fast and turned to us for expertise.
Our Take:
Our initial review of the customer’s design revealed some complicated features – challenging, but not impossible to manufacture. These were immediately flagged as potential sources of failure.
Next, we carefully examined the failed parts themselves. Our suspicions were confirmed: the inconsistencies originated in those difficult-to-manufacture features. Specifically, we noticed significant variations in the traces from one part to the next. This variation came from manufacturing techniques, not the design itself. In this case, an imprecise and inconsistent etching process caused the quality issues.
The customer’s impedance model was based on the ideal etched features. But the reality was the inconsistent etching process led to the inconsistent traces, ultimately affecting impedance and causing part failures. This inconsistency translated directly into inconsistent impedance, and ultimately, part failures. So, while the design was correct, and had passed DFM review, the design relied on consistent, reliable execution of the etching, which the customer wasn’t getting from their current vendor.
The customer asked if we could manufacture the part while maintaining acceptable yields without requiring a complete redesign. We were confident in our capabilities but knew our impedance calculations differed from their previous vendor’s. Unlike a generic model, our calculations are based on a proprietary data set developed from thousands of successful jobs, fine-tuned to our specific equipment and its real-world output.
To demonstrate the accuracy of our approach, we cross-sectioned a failed part from the previous vendor and compared its etching to our own. When the customer plugged our trace geometry into their impedance calculator, the numbers aligned perfectly. This confirmed the necessity of adjusting the trace and space dimensions based on our refined process. With this alignment, we moved forward with a small prototype run to fine-tune production.
Embracing the Challenge:
Understanding the complexity of the design, we suggested a small prototype run. This would allow us to fine-tune the manufacturing process and ensure we could hit their yield targets.
With our first batch, our yield was around 60%. Though this was much higher than the previous manufacturer, it still wasn’t where the customer needed it to be. We had our work cut out for us.
We tightened our manufacturing processes and increased yields to just over 78%. Progress, yes, but still short of the high 90s where the customer needed us to be. We needed a different approach.
The persistent issue? Etching. So, we took a step back and examined our imaging process—the foundation of etching. Imaging involves applying and selectively exposing a photo-sensitive film, which directly impacts the precision of etched traces.
To bring the yields up further, we worked directly with the customer, our materials suppliers, and our imaging equipment suppliers. Through collaboration, our production manager and process engineers came up with an innovative new way to reliably produce rigid-flex circuits with similar trace topography in outer layers. Though it required us to rethink our approach to imaging and etching, we were confident that we could achieve the results that we needed for our customer. We all decided to move forward with this new approach.
The Outcome:
The result? We achieved yields over 96%, and earned the production order from the customer. Our updated approach to imaging and etching was a resounding success.
We spent the next six months validating these changes internally before implementing these revised procedures for all our rigid-flex production. This breakthrough allowed us to eliminate three separate chemical processes while simultaneously delivering more precise and reliable etching results.
The Takeaway:
This case highlights how failure analysis can drive innovation, and how a challenge can become an opportunity to refine processes and implement groundbreaking techniques that improve outcomes for all our customers.
At Flex Interconnect Technologies these are the types of solution-focused projects that our team gets excited about. It was an opportunity for us to partner with the customer to understand their project requirements. With the talent of our engineers, and the cooperation of our entire production team, we were able to come up with meaningful solutions for both the customer, and our own manufacturing processes. We’re not just manufacturing circuits; we’re building solutions. And we’re excited to see what challenge comes next.