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48 PCB007 MAGAZINE I JULY 2019 Important Features The following list highlights the 14 most im- portant features for designing and producing a reliable PCB as seen by NCAB Group. Note that some of these features are not included in IPC standards, but NCAB finds these particu- lar constraints to be critical. IPC standards are guidelines for the industry, but they are not al- ways comprehensive in terms of producing the most robust board feasible. For high-reliability and/or high-technology circuit boards, guide- lines usually need to exceed IPC standards to increase performance and lifetime. 1. 25-micron nominal hole plating per IPC Class 3 2. No track welding or open circuit repair 3. Cleanliness requirements beyond those of IPC 4. Tight control on the age of specific finishes 5. Internationally known base material types used—no local or unknown brands allowed 6. Tolerance for copper-clad laminate is IPC-4101 Class B/L 7. Defined solder mask, ensuring accordance to IPC-SM-840 class T 8. Defined tolerances for profile, holes, and other mechanical features 9. Specific solder mask thickness (IPC does not require this) 10. Defined cosmetic and repair requirements (IPC does not require this) 11. Tighter requirements for the depth of via fill (IPC requires 60%, but we require at least 70%) 12. Peters SD2955 peelable as standard 13. Specific qualification-and-release process for every purchase order 14. No X-outs accepted At the same time, boards should be designed in a way that they can be manufactured reli- ably by as many factories as possible. The ex- tra investment in thought up front gives the product better lead times overall while main- taining quality. Applying the very latest technology required by the component manufacturers often on- ly increases the challenge level. For example, if you can avoid BGA escape routes that use six or seven different layers of blind or bur- ied vias and reduce it to a standard multilayer board, it's a good idea to do so. Reduced layer counts do away with all of the extra drilling and plating processes, significantly reducing costs while also improving the manufactur- ability of the product. By keeping manufactur- ing options as open as possible through smart design, this will allow easier switching from one production facility to another. Further, this reduces the design's overall supply chain risks. If one factory, for example, is underperforming or dealing with a technical issue, production could more easily move to another facility. The riskiest PCB design is one that is limited to a single factory's unique processes. Data and Documentation But there is more to reliability than just the manufacturing process or careful design prac- tice. Reliability is achieved through the mind- set that plans the entire process from design through delivery. Therefore, it is critical that complete and concise information, build notes, and instructions are provided to your PCB sup- plier and that the partner demonstrably puts quality first. Look for a partner with a seam- less approach that will take the project from prototype manufacturing to production manu- facturing without sacrificing quality or reliabil- ity. Design teams do their part in this reliabil- ity process by creating a complete and detailed manufacturing package.

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