Design Is a Pivotal Piece of the Puzzle


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As a field applications engineer at TTM Technologies, which has fabrication and manufacturing locations around the world, Julie Ellis sees a wide variety of customer design requirements. In this interview with the I-Connect007 Editorial Team, Julie explains how PCB designers can influence the development of the PCB. She shares a variety of tips and tricks that designers can implement early in the design process to help optimize fabrication and assembly later on and keep small issues from becoming big problems downstream.

Andy Shaughnessy: Julie, with your job you have a pretty circumspect view of design and manufacturing. Can you start by giving us an idea about your job and some of the designs that you see crossing your desk?

Julie Ellis:  My main task is to support customers’ designs for manufacturability by understanding their requirements and providing stack-ups and design guidelines for rigid circuit boards that are within TTM fabrication capabilities and process tolerances. I also help customers understand how fabrication processes affect capabilities, so they accept design modifications that assist in manufacturing.

The work I see coming across my desk includes components for EV charging and power conversion, Lidar, radar, back-up and industrial scanning cameras, ultrasound, defibrillators, and glucose monitoring. They require stack-ups ranging from four-layer heavy copper boards to 32 layers with three lamination cycles and mechanical blind holes and advanced HDI, which I define as 0.4-mm pitch BGAs and smaller.

Oftentimes, I’m trying to help customers design products that can also easily be transferred over to Asia and run on mass volume production lines without any advanced requirements that add cost. I work to ensure that prototypes fabricated here in North America are already designed with pre-approved stack-ups to run without modification at the final production volume site or sites. TTM calls this Seamless Global Transfer, and it works best when implemented in the planning stages of a new design.

I also review designs for cost savings. For example, in Asia, materials are 40 to 50% of a fabricator’s cost, compared to less than 20% in the United States.  When we get into high-volume manufacturing, optimizing material utilization can save a customer several percent on the final assembly if we can keep a lowered cost on the PCB by planning the PCB dimensions to fit very well on a fabrication panel. If the circuit board is small, TTM often works with our customers to calculate the best multiple-up array with rails for assembly that can still fit optimally on the fabrication panel. The most common fab panel size is 18” x 24”, but we also mass-produce 21” x 24” panels at many sites.

Shaughnessy: Sometimes, I get the feeling that the designers don’t realize how much control they have over the final product. What are some of the common errors that you see coming in that you wish that you could just tell the designer, “If you just did this...?”

Ellis: If you just…came to me for your stack-up and design rules first, I wouldn’t have to tell you that nobody can fabricate this design in mass production. I request of my customers that they come to me at initial startup of a product before they even bother to route any circuitry, because designs get so complicated that it’s very challenging for them to go back and make changes if they’ve violated standard fabrication design guidelines. It’s really stressful to explain to an engineer why his design isn’t suitable for mass production, so I prefer to avoid that like the plague.

To read the rest of this interview, which appeared in the June 2019 issue of Design007 Magazine, click here.

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