FLEX CIRCUITS DESIGN GUIDE

More documents

Recommendations

Info

Standard Design Recommendations Holes General requirements for pads, access holes and annular rings Feature Single-layer Double-layer Multilayer Pad* 0.060" (1.5mm) + t 0.030" (0.76mm) + t Outer pad: 0.030" (0.76mm) + t Inner pad: 0.025" (0.63mm) + t Major 0.050" (1.3mm) + t 0.030" (0.76mm) + t 0.030" (0.76mm) + t access hole* Minor 0.015" (0.38mm) + t 0.015" (0.38mm) + t 0.015" (0.38mm) + t access hole‡ t = nominal through-hole diameter. Vias Minco can provide circuits with covers that have no access holes exposing the vias (called 'tented vias'). Minco can also provide blind and buried vias in multilayer and rigid-flex circuits. Blind vias connect the top or bottom conductor layer to adjoining layers, but the via does not extend through all layers. A buried via only connects internal layers and is not exposed in the finished circuit. Blind and buried vias increase circuit cost, but they free up space for additional conductors on the non-drilled layers. Tented Via Blind Via * Pad and major access hole design requirements are based on typical annular ring requirements of 0.015" (0.38mm) minimum for a single-layer, 0.005" (0.13mm) minimum for all external layers, and 0.002" (0.05mm) minimum for multilayer innerlayers. ‡ Customer must allow tangency (see the Glossary for a definition of tangency). For more information on access holes (major and minor) annular ring, pads, and thruholes, see the Glossary on pages 28 – 30. Access Hole Annular Ring Through-Hole Major Access Hole Buried Via Thruhole or Through-hole Plated through-holes (PTH) connect together the top, bottom, and any required internal conductor layers. PTHs are drilled oversize to accommodate the thickness of the copper plating that will cover the entire barrel of the hole as well as the surface of the outer pads. Exterior pads may be plated along with the entire foil surface or selectively plated just at the PTH site. Outer Pad Through Hole Inner Pad 16 Plated Wiring Hole Minor Access Hole Stiffener holes Stiffener holes should be a minimum of 0.015" (0.38mm) in diameter larger than the access hole. It is better if the access hole underneath the stiffener hole is a minor access hole in order to increase the stiffener web between holes and to prevent potential solder wicking between the stiffener and the circuit. The customer must allow tangency. Round stiffener holes are less expensive than slotted stiffener holes, and as mentioned before, thinner stiffener material (less than 0.031"/0.79mm) is less expensive to process.
Standard Design Recommendations Holes Wiring holes Minco can drill through-holes as small as 0.0039" (0.10mm). A 0.020" (0.50mm) through-hole size is typical. Standard finished hole tolerance is ±0.003" (0.08mm). For all circuits, the finished through-hole size should be 0.003" (0.08mm) to 0.010" (0.25mm) larger in diameter than the component lead. This depends on the number of leads per component, and the positional tolerance of the component leads. Surface mount access Minco can provide flex circuits with areas that are specifically designed for surface mount components. Because covers are drilled, not silk-screened, round access holes are easier to provide. Square access holes will add to cost because the pad access area would have to be punched out with a punch-and-die. Square pads with round access holes are a good compromise. Below are some ideas for configuring pads for surface mount. It is best to specify round (instead of slotted), throughholes. This will reduce drilling time and cost. Access Hole Access Hole Leads Pads Whenever possible, design pads larger than the access holes. If space is critial, use hold-down tabs. Hold-down tabs are especially important for single-layer circuits, because a single-layer circuit does not have the added strength of plated throughholes. A variety of hold-down tab designs are available. Photoimageable coverlay materials are also available, and can provide intricate, irregular shaped openings for dense surface mount patterns. Soldering tips • Since polyimide absorbs moisture, circuits must be baked (1 hour @ 120°C) before soldering. • Pads located in large conductor areas, such as ground planes, voltage planes, or heat sinks, should be provided with relief areas, as illustrated. This limits heat dissipation for easier soldering. Thermal relief • When hand soldering pins in dense clusters, try not to solder adjacent pins one after another. Move around to avoid local overheating. Pad fillets Pad fIllets improve etched yield and material strength. Fillets are appropriate when the pad diameter is greater than the connecting strand width. Acute angles at the interface between conductors and pads are to be avoided by using fillets to minimize the concentration of stress at the interface. Before fillets After fillets • Minco can solder connectors or components (SMT or Thruhole) as an added service. • Minco can supply circuits in panel form for easier component assembly. 17
Page 1 and 2: FC302(A) FLEX CIRCUITS DESIGN GUIDE
Page 3 and 4: How to Get Started 1. Understand Ho
Page 5 and 6: Design Options Rigid-flex Hybrid ha
Page 7 and 8: Design Guidelines Manufacturing a f
Page 9 and 10: Design Guidelines Circuit types Rig
Page 11 and 12: Minco’s General Capabilities Test
Page 13 and 14: Minco’s General Capabilities Cond
Page 15: Standard Design Recommendations How
Page 19 and 20: Standard Design Recommendations Mat
Page 21 and 22: Value Added Design Options Stiffene
Page 23 and 24: Value Added Design Options Custom a
Page 25 and 26: Request a Quote Artwork checklist M
Page 27 and 28: E2E — Engineer to Engineer Early
Page 29 and 30: Glossary Impedance The measurement
Page 31 and 32: Next Steps Minco welcomes the oppor

FLEX CIRCUITS DESIGN GUIDE

Create successful ePaper yourself

Delete template?

Save as template?