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PCB007-Apr2020

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132 PCB007 MAGAZINE I APRIL 2020 Why Do We Reject Good Products? Why does the electronics industry reject good products when it's not always needed? Every year, fully functional PCBs are scrapped due to cosmetic "failures" that are not approved. Is this right, or do we need to make an even more precise set of rules on how to handle this not only to avoid unnecessary claims but also to save the environment? Can a more conscious approach and education on what to be consid- ered as failures help make the industry to be greener? Form, Fit, and Function: Not Functioning? The defects I'm addressing in this column can be small scratches, solder mask discolor- ations, minor copper residues, inclusions, and other defects. All of these are minor and ac- cepted by IPC-A-600 and IPC-610 or not men- tioned. Why are such issues not in the stan- dard? If you look at IPC-A-600, it focuses on issues that affect form, fit and function. A rule that is repeated in almost every chapter is acceptabil- ity—unless it reduces the spacing, hole diam- eter, or line width below the limits specified in the procurement documentation. This means that the designer should give restrictions for minimum insulation distances allowed on the finished PCB. My experience is that very few designers pro- vide this information, which means we should follow default rules according to the IPC stan- dards. But that also brings us to all the open questions IPC calls AABUS, or "as agreed be- tween user and supplier." IPC requires these questions to be discussed between the user and the supplier, which is worth a separate column itself. In addition to these documented issues, we have a cosmetic "gray zone." Cosmetic Defects Related to Solder Mask Most of the cosmetic defects we observe to- day are related to solder mask. Such issues could be discoloration caused by thickness variations or small scratches that come from handling in the PCB factory or during transportation, unpacking at the customer site, inspection, or even the assembly process. It could be solder mask defects over dielectric areas—inclusions of small particles that meet IPC A-600 but are rejected by the in- spector. What Is the Risk of Using a Product With Cosmetic Defects? Defining risk is never easy. Some industries are clear on risk, such as medical, automotive, and defense. Still, we have a term in the medical standards that calls for judgment: ALARP, which stands for "as low as reasonably practicable." There's also ALARA, which means "as low as reasonably achievable"—a term often used in the regulation and management of safety-critical and safety-involved systems. Figure 1: Do fully functionable PCBs really need to be scrapped? (Source: Elmatica)

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