Issue link: https://iconnect007.uberflip.com/i/1276973
72 DESIGN007 MAGAZINE I AUGUST 2020 Johnson: What's the best way for an EMS pro- vider to communicate a design to their cus- tomers? Dack: Through education. EMS providers must learn to engage with designers through social media outlets and trade publications. Both sides must engage. For example, the mission of the Printed Circuit Engineering Association (PCEA) is to bring the manufacturing suppli- ers together to discuss and build awareness from all of these perspectives. They are off to a great start in getting this accomplished. Myth #2: Copper Can Be Flooded Close to the Board Edge—Panelization Johnson: Speaking of going from prototype to production, another myth concerns board out- lines and panelization relative to EMS work. What do you see there? Dack: Another ongoing, problematic trend we see in manufacturing is a lack of cop- per imaging pullback from the board edge. We need to get designers to understand that when their design goes to volume, it must be conveyorized—processed on manufacturing assembly lines. To conveyorize a design, cer- tain amounts of clearance must be allowed in the design so that the secondary and ter- tiary operations of production have room to operate. One thing that's on our hit list in the DFM auditing world is to verify there's enough copper pullback. Copper pullback refers to the distance between the nominal designed board edge and the copper, and whether the copper is flooded, exists as a via or a land, or exists as a trace. Is there enough distance between that copper image and the glass epoxy FR-4, polyimide, or material edge to process? Ironically, electronics industry forums often recommend the opposite of what the EMS pro- vider needs. The conversations I've read on design forums have asked, "How close can we get this copper to the board edge?" or, "I designed a board and flooded it right to the edge, and it was successful," as if there's a need to get copper to the board edge. Some newer designers didn't have the depth of knowledge to know where their board was going to be manufactured. By pulling the copper out, or by not leaving enough space between the board edge and the copper, they hurt the depaneliza- tion methods for the board. There are also several breakout methods to be considered in panelization. Individual PCBs can be tab routed, which uses a routing tool to carve a slot around the board. This creates a void between the edge of the panel and the board by leaving tabs or small areas of attach- ment while retaining the circuit board design. Often, Often, perforations are added to these tabs to allow for breaking the tab and excising the board. If there's not enough space between copper and one of these tabs—especially if it has the perforations or mouse bites at the point of breaking—the tool can leave a frayed edge, which will extend into the copper and dam- age it; it may expose the copper surface leav- ing bare metal, which is not considered accept- able with IPC specifications. Insufficient copper clearance at the board edge reduces our ability to utilize mouse bites. Another depanelizing strategy is V-scoring the board edges using a circular saw tool with a "V" edge that cuts a straight line on the top surface and on the bottom surface, leaving a small web of material in between. As designers, we like to refer to a one-third equation for a V-score. V-score blades come in differing angles. There are narrow 30-degree angles and wide 45-degree angles used for different purposes. However, depending on the depth of the V-score and the width of the angle, designers can get into trouble not pulling back the copper enough because the V-score is going to cut away a certain amount of material on the top and bottom edges of the board, causing more problems. V-scoring and tab routing are the two main excising methods. There's also laser scoring, which is used a lot more in flex manufactur- ing. If there's not enough room between the copper and polyimide material, it will cause grave problems for laser excising because of the differences of the materials—copper ver- sus polyimide.