Standard Design Recommendations

Holes

G e n e r al r e quir e m e nt s for p a d s , a cc ess ho lesa Vi as nd a nnu la r rin gs
Minco can provide circuits with covers that have noaccess holes exposing the vias (called 'tented vias'). Minco can also provide blind and buried vias in multi- layer 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. F ea tur e Sin gle - la y e r Dou ble - la y e r Mu l ti la y e r 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 access hole * 0.050" (1.3mm) + t 0.030" (0.76mm) + t 0.030" (0.76mm) + t Minoraccess hole‡ 0.015" (0.38mm) + t 0.015" (0.38mm) + t 0.015" (0.38mm) + t T ented ViaB l ind Via Buried t = nominal through-hole diameter. * 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) mini- mum for multilayer innerlayers.‡ Customer must allow tangency (see the Glossary for a definition oftangency).For more information on access holes (major and minor) annular ring, pads,and thruholes, see the Glossary on pages 28 – 30. Via Thruho le or Throu g h-ho le
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. l arRing Access Ho l eAnnu T hrough-Ho l e T hrough Ho l eOuter PadInner Major Access Ho l e Pad P l ated WiringHo l e Minor Access Ho l e Stiff e n e r ho les
Stiffener holes should be a minimum of 0.015" (0.38mm) indiameter 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. 16