Issue link: https://iconnect007.uberflip.com/i/1108006
APRIL 2019 I FLEX007 MAGAZINE 25 certainly appreciate GraftWorx not wanting to make an implantable. Having built several implantable parts here, we know the head- aches that go along with that. Moody: When we were first presented with this, one of the initial conversations was, "This is going to be a rigid-flex design." Then, it became evident talking with Tony that doing a standard rigid-flex construction wasn't going to meet their needs; it was going to be too rigid. To meet the form factors required for the end product, we had to sit back and think about how to make a rigid-flex without any rigid materials and still keep the integrity. There is a very thick stackup on either end of the board connected by two layers of copper with the flex circuit in the middle. The rigid section has some requirements that we normally address with certain materials used specifically for rigid-flex. Removing the rigid-flex concept, we all had to take our heads out of that box and put them somewhere else to come up with a flexible rigid-flex design. The challenge for us internally concerned what materials to suggest. Typically, you want to keep acrylic adhesive out of a rigidized section of a board, but in this case, there weren't alter- natives available to us to meet the end product requirement. We had to go back to using stan- dard flexible materials with acrylic adhesives to hold the rigidized section together, and we knew those challenges were going to be pri- marily in the drilling and subsequent plating of the through-holes in that area. We had to do some redesigning and reconfiguring in how we were going to drill those sections. It comes down to a mechanical aspect of feeds and speeds in the drilling department and how to best keep the hole wall integrity for good plating. Again, the end product—medical device sensing—needs to work; it's not a com- mercial or consumer application. High reliabil- ity had to be part of the concept going into it. Those were the primary things that we had to sit back and think about when Tony came to us and said, "No, you can't do a rigid-flex, but those end areas need to be a little rigid because we have a bunch of components out there, bat- tery included." Other than just telling Tony, "We can do this kind of line and space; we can have this kind of pad size, annular ring, etc.," the general requirements of the circuit had to be incorporated into what ended up being a very specialized construction and mechanical build sequence for us internally. Matties: Tony, you started by saying that this relationship with Lenthor strengthened your results. Flannery: Absolutely. Our final product is a lot higher quality than if we tried to go a conven- tional route without the benefit of their innova- tion. There were times we'd have a phone call about navigating challenges, but they made it look easy all the way through. They did a fantastic job coming up with ways of preserv- ing the quality of their patterning and through- holes and vias, despite the fact we had this weird, wonky, multilayer design. We depended heavily on their level of quality control (Fig- ure 3). By doing 100% continuity testing and X-ray and visual inspection of post-assembled parts, the delivered board yields were near perfect. Lenthor is ISO 9001:2008 certified and IPC-6013 Class 3 qualified. Focusing on quality early in the development cycle meant we could focus on our product and not spend time chas- ing down gremlins from fabrication defects. Figure 3: Focusing on quality early during the development process saved time by allowing the company to focus on the product instead of chasing down defects.