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SEPTEMBER 2020 I DESIGN007 MAGAZINE 109 laminating FR-4 stiffeners to the flex, the high- pressure lamination process can put undue stress on the plated through-hole barrel, sub- sequently making the circuit less reliable. ENIG Final Finish Another manufacturing note often seen is a customer's own specified ENIG thickness that does not align with IPC-6013 (or IPC-4552) requirements (Table 2). This superseding note can also cause a price increase. The reason to try to always use the IPC ENIG thicknesses is that the factory sets up their ENIG line to adhere to the IPC ENIG standard. If the customer specifies a different plating parameter that does not meet IPC-6013 speci- fications, the factory must allow all normal products to completely clear the plating line, then modify the plating line and separately process the non-standard product. The plat- ing line is then changed back to the normal parameters to continue plating the rest of the panels to the standard IPC ENIG parameters. Changing the normally accepted plating speci- fications unless specifically needed only cre- ates a higher-cost circuit board. Material Specifications It is advised not to place detailed material brands on the print unless the customer has specific reasons to do so. Please allow IPC specifications to determine the material selec- tion. For example, it is common for a customer to specify Dupont™ AP8515R (1/2-oz. copper x 1-mil polyimide x 1/2-oz. copper) on the manufacturing print. Simply specifying 1/2- oz. copper x 1-mil polyimide x 1/2-oz. copper on the print, and/or per IPC-4204/11 material is sufficient. This eliminates redundancy, as well as reduces the chances of an error while trying to decipher the manufacturing notes. By calling out materials by name brands, you may have increased the cost of your circuit by 10–20% with no real reason to do so! Print Templates Another suggestion is to create print tem- plates and use a fresh template when designing new circuits. If you should have questions on how to lay out a good print template, contact your flex provider and allow them to guide you. When working with customers, I recommend that they never copy and paste from previous projects, as this leads to copying notes that sim- ply do not pertain to the current project. Using print templates and filling them in on a per-proj- ect basis will help eliminate costly mistakes. If in doubt as to the acceptability of your manufacturing notes, ask your flex engineer to help redline your prints so they will be accept- able to any flex manufacturer. This will elimi- nate confusing deviations or redlines next time the circuit is built or quoted. Conclusion To summarize, utilize IPC-6013 for stan- dard specifications as this allows processes and yields to perform at their best. Keep notes standard and have print templates to work from, and you likely will see improved results related to attaining the products that you desire and an improved cost. In my next article, I will get into details related to certain requirement- driven occasions where one might choose to supersede the IPC-6013 specification, but trust most often in following IPC-6013, and you will be served well! FLEX007 Tony Plemel is a senior applications engineer with Flexible Circuit Technologies. Table 2: IPC-6013 ENIG requirements.

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