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Design007-Sept2019

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52 DESIGN007 MAGAZINE I SEPTEMBER 2019 get the job done: What size should this via be? Check the standard. What do you mean I used the wrong trace width? Check the standard. How should I document this process? Check the standard. Like the colors that were carried into battle, today's standards can still offer us the ability to identify authority, lead us in the right direction, and even offer protection. If we can just get over our annoyance, perhaps this fresh perspective will illuminate standards in a new light. Identification of Authority To the untrained eye, one circuit board may look pretty much like any other, but as we know, there are major differences between them. Not only are they different in purpose and design but also in how they are manu- factured for specific industries. If you are de- signing medical equipment, for instance, you will have to meet many different regulatory requirements from organizations, such as the Food and Drug Administration (FDA), World Health Organization (WHO), and Internation- al Electrotechnical Commission (IEC), among others. If called upon by any of these regula- tory organizations to provide specific infor- mation on how your equipment was manu- factured, you need to be ready to provide the required documentation. This documentation can include the quality control processes that were used during assembly as well as compo- nent and material traceability records. The reasons for this are pretty obvious; you don't want low-level workmanship used in the pacemaker that is going to be implant- ed in someone's chest to regulate their heart- beat. And if there is ever a question on parts or materials used in a piece of equipment, you need to be able to trace it back to its source as quickly as possible. As a medical equip- ment manufacturer, you will want to have your circuit boards built by an assembler that is registered with standards such as ISO 13485. Standards like these are what identify a PCBA manufacturer as being authorized to build circuit boards to the high level of qual - ity you need for the medical equipment you are creating. Direction All of us who have laid out PCBs for a liv- ing probably share many of the same career experiences, such as not having a clue what PCB layout was really all about when we first started. If you're like me, you probably started out throwing parts on the board and connect- ing them up until one of the older hands in the department would critique my work and point out my mistakes: • "This small part is getting shadowed by this large part, and it won't wave solder correctly." • "You have too much metal going into this pad compared to the other pad, and your resistor is going to tombstone during reflow." • "Your part placement is too tight, and the rework technicians are going to end up hating you. We don't want to clean up the mess in here after they beat you to a pulp!" (okay, I might have embellished that last one a bit). The point is that a lot goes into designing a PCB so that it can be successfully and efficient- ly manufactured. I learned much of it slowly through tribal knowledge, and fortunately, I had some really good teachers. But many de- signers don't have the advantage that I had of working with experienced designers for train- ing, and they end up making a boat-load of costly mistakes. Some of these can be correct- ed while others require a redesign, and sadly, some will result in the design being scrapped. If only there was some clear direction on how If we can just get over our annoyance, perhaps this fresh perspective will illuminate standards in a new light.

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