Issue link: https://iconnect007.uberflip.com/i/1529118
48 DESIGN007 MAGAZINE I NOVEMBER 2024 ment team stay within budget by providing cost estimates and ballpark figures related to materials, fabrication, and assembly. Prototyping: is has long been an impor- tant step in developing a new product and can oen be sped up by employing rules of thumb. e purpose of the prototype is to establish the viability of the product and expose any intrin- sic and/or unseen weaknesses in the design. It is a way to make and break things faster—a modern manufacturing mantra that won't lead to "analysis to paralysis." Time constraints: Product developers have come to appreciate time, which is the most valuable commodity in life, whether that applies to products or people. When develop- ment timelines are tight, rules of thumb and guidelines can help expedite the process and reduce the need for extensive research. An Overview and a Few Examples Over time, the industry has developed differ- ent rules of thumb. Some were quite useful in their day but lost relevance with the fast pace of technology. Capacity of current in traces: One rule of thumb with deep roots is related to the current- carrying capacity of traces, specifically that a conductor trace's width should be roughly 1 mil (25 µm) for every amp of current draw anticipated. is rule harkens back to when 1-ounce (1.3 mil) copper was the de facto stan- dard for foil. It is a relatively "safe" rule, but it should be modeled when putting design into practice. Similarly, there was a recommenda- tion for some years that the designer maintain at least 3 mils (75 µm) of clearance between traces for basic applications to prevent electri- cal shorts and issues with manufacturing tol- erances. is is, of course, a rule that is today seeing increased violations as HDI and UHDI with much finer circuit features become more common. Plated through-holes and microvias: Plated through-hole vias were the first instan- tiation of a circuit feature not designed to receive a component pin. is followed the realization that a plated hole was a superior and much less costly solution to sticking a wire into a non-plated hole and making con- nection from side to side by soldering the ends of the wires to copper pads. Realizing that all holes are "a waste of space," designers and manufacturers had to compromise relative to the aspect ratio. For example, a 6-mil hole in an 062" thick board has an aspect ratio of roughly 10:1 and the same 6-mil hole size in a 0.120 mil has a 20:1 aspect ratio. is was not easy in earlier times; however, using today's advanced plating chemistries, printed circuit boards with such features can be fabricated using build-up technologies and employing blind vias. ey are increas- ingly being specified as a result. While not impossible with thicker boards to plate higher aspect ratios, employing plated through-vias in designs is not always desirable because they are necessarily larger. However, it is quite possible to design build-up boards with blind vias hav- " ese are simplified guidelines based on the practical experiences of both individuals and the industry at large... "