A Guide to High-reliability PCBs from Design to Specification

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In our daily lives, we constantly interact with electronic products, and all of these products contain a printed circuit board (PCB). Because the PCB serves as the interconnect for all the various components required for the electronic system to function reliably, it is often referred to as the key component.

Thus, it comes as no surprise that PCB reliability is a critical factor right from the start of the PCB production process. If a PCB has a reliability issue, the end product itself is at risk. The important thing is getting it right the first time. Trying to improve reliability once the product is designed and in production can lead to massively high costs for the product owner. In some cases, such as medical equipment or motor vehicles, it could even become a matter of life or death.

Creating reliable PCBs is an outcome of considering all aspects that can affect reliability as early as possible in the design process. The further down the design process, the more expensive and risky it can be to fix. Because its design has been tailored to a specific function and application, you can’t compare a PCB to other components. As a custom component, the PCB’s role is critical. A good board design improves the reliability of the end product and lessens the risk of failure. Furthermore, as technology advances, design solutions become increasingly complex, which requires more comprehensive planning in terms of design and manufacturing. It follows, of course, that the more complex the function of the PCB, the more complex both construction and manufacturing becomes.

Important Features

The following list highlights the 14 most important 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 particular constraints to be critical. IPC standards are guidelines for the industry, but they are not always comprehensive in terms of producing the most robust board feasible. For high-reliability and/or high-technology circuit boards, guidelines 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 reliably by as many factories as possible. The extra investment in thought up front gives the product better lead times overall while maintaining quality.

Applying the very latest technology required by the component manufacturers often only increases the challenge level. For example, if you can avoid BGA escape routes that use six or seven different layers of blind or buried 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 manufacturability of the product. By keeping manufacturing 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 practice. Reliability is achieved through the mindset 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 supplier and that the partner demonstrably puts quality first. Look for a partner with a seamless approach that will take the project from prototype manufacturing to production manufacturing without sacrificing quality or reliability. Design teams do their part in this reliability process by creating a complete and detailed manufacturing package.

To read the full article, which appeared in the July 2019 issue if PCB007 Magazine, click here.



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