Pads, access holes, and annular ring general requirements
For more information on access holes (major and
minor) annular ring, pads, and through-holes, see the
Glossary on pages 24-27.
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.
Stiffener Holes
Stiffener holes should be a minimum of 0.015" in
diameter larger than the access holes. 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") is
less expensive to process.
Feature
Single-Layer
Double-Layer
Multilayer
Pad*
0.060" + t
0.030" + t
Outer pad: 0.030" + t
Inner pad: 0.025" + t
Major access hole*
0.050" + t
0.030" + t
0.030" + t
Minor access hole
0.015" + t
0.015" + t
0.015" + t
t = nominal through-hole diameter
*Pad and major access hole design requirements are based on typical annular ring requirements of 0.015" minimum
for a single-layer, 0.005" minimum for a double-layer or more, and 0.002" minimum for multilayer innerlayers.
If hold-down tabs are used, then 0.030" is allowable.
Customer must allow tangency (see the Glossary for a definition of tangency).
Access Hole
Access Hole
Annular
Ring
Through-Hole
Tented Via
Blind Via
Buried Via
Application Aid #24
Tel: (763) 571-3121 K Fax: (763) 571-0927 K www.minco.com
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Summary :
Pads, access holes, and annular ring general requirements For more information on access holes (major and minor) annular ring, pads, and through-holes, see the Glossary on pages 24-27. 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.
Tags :
holes,stiffener,hole,ias,0015quot,0030quot,blind,buried,minimum,annular,ring,pad,layers