Design007 Magazine

APRIL 2022 I DESIGN007 MAGAZINE 93 line widths should be greater than 0.006" and at least 0.030" high. • Space letters at least 0.008" apart so they don't bleed together. • No legend nomenclature should overlap a copper pad or plane area. • is is especially important for surface mount pads and fiducials. • White is the standard legend ink color. Use the fabrication print notes to specify special features to be screened onto the board, and non-standard colors. • All legend should be kept 0.003" (minimum) away from solder mask clearance. Nomenclature Letter size: • Screened: 0.006" line width minimum • Photoimageable: 0.004" minimum Table 3 lists recommended letter sizes. Note: Nomenclature placed over parallel or heavy copper traces may have poor legibility. Color: • White (epoxy) preferred • Yellow (epoxy) • Black and white (LPI Ink) is also available Considerations Nomenclature over solder (HASL) will have poor adherence. Nomenclature placed over bare copper before HASL and immersion sil- ver/tin will have an apparent copper "halo" aer the HASL or immersion silver/tin. e artwork will need to be modified if this is not acceptable to the customer. Understanding the cost drivers in PCB fab- rication and early engagement between the designer and the fabricator are crucial ele- ments that lead to cost-effective design suc- cess. Following your fabricator's DFM guide- lines is the first place to start. DESIGN007 Anaya Vardya is president and CEO of American Stan- dard Circuits; co-author of The Printed Circuit Designer's Guide to… Fundamentals of RF/Microwave PCBs and Flex and Rigid-Flex Fundamentals; and author of Thermal Management: A Fabri- cator's Perspective. Visit I-007eBooks.com to download these and other free, educational titles. He also co-authored Fundamentals of Printed Circuit Board Technologies and provides a discus- sion of flex and rigid flex PCBs at RealTime with… American Standard Circuits. To read past columns or contact Vardya, click here. Table 3: Recommended letter sizes.

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