Design007 Magazine


Issue link:

Contents of this Issue


Page 29 of 101

30 DESIGN007 MAGAZINE I APRIL 2020 to cost, availability, and production. At a com- pany I worked for, we had mechanical engi- neers come to us with a performance require- ment—a board had to flex or bend into an arc to be installed. They knew that flex materials were expensive. They were considering cost, but they were trying to come up with a me- chanical solution that involved normal FR-4 materials. They came to us with a requirement that a surface-mount board had to bend a cer- tain amount to be installed, and its radius typi- cally would exceed the amount that we like to with rigid-flex boards, which is by nothing, as it induces stress on the SMT components. We reluctantly took on the challenge. We sent the board out to our prototype supplier to be prototyped with very thin laminates. It came back to us in panel form. And this board was assembled with the LEDs, and then ex- cised from the panel and bent to install into the machinery. We were looking at this and thinking, "You're going to crack the LEDs." But they installed the boards and plugged it in, and guess what? The board worked. All the LEDs came on. We're scratching our heads, thinking, "Give it a few weeks. The stresses are going to trans- fer into the LEDs, and they're finally going to crack in this board, and it's going to fail." Weeks went by, and it seemed that everything worked well. How do they do that? We ap- peared to have mud on our face from a PCB design standpoint. We released the design, and the board was released for volume production in China. The boards came back, and they looked the same. But weeks later, we started getting phone calls from the final test and inspection department. There were failures, and the lights weren't lighting up. There was a mushroom cloud over our facility! What happened? I called our CAM guy at the board shop to find out what he did to provide the solution for us. And he said, "We used real- ly 'juicy' prepregs on this design to solve your problem." That made sense because I could take this board and wiggle it. This FR-4 board would flop around. It was so juicy, meaning low glass content with lots of resin on it. It was basically a custom material, custom- laminated board, using custom dielectrics that were not specified, and even if they had been, the offshore suppliers didn't have access to these materials. They built it out of normal FR-4 laminates, which are a lot more rigid, as we knew. The new, offshore-supplied boards had stress induced when they were bent into shape—a lot of stress. And it did pop a lot of the LEDs. This is what happens when the availability of the materials used during proto- types is ignored in production. Shaughnessy: One hand doesn't know what the other is doing sometimes. Dack: We use those types of metaphors quite often. We rob Peter to pay Paul when our left hand doesn't know what our right hand is do- ing. Exactly. Cost-aware design involves a lot more than proper layout techniques. It also means looking ahead and connecting with all of the engineering, manufacturing, and supply chain stakeholders to try to foresee and keep problems from happening at volume produc- tion. As your survey respondents said, most of the cost savings are realized in manufactur- ing. You're managing the design, and it's up to you to look out for these things before they can occur. Shaughnessy: Good stuff. Thanks for your time, Kelly. Dack: No problem. Thank you. DESIGN007 They were considering cost, but they were trying to come up with a mechanical solution that involved normal FR-4 materials.

Articles in this issue

Archives of this issue

view archives of Design007 Magazine - Design007-Apr2020