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In the AMITEC
core-less substrate, there are two different types of electrical Z-connecting features:
- Cu pillars for it’s thick film section and
- metal filled micro-vias for
it’s thin film section.
Dimension wise, a micro via differs
significantly from a Copper pillar.
The micro-via is usually one
order of magnitude smaller in diameter and in thickness when
compared to the Cu pillar. However, process wise, the concepts behind building these
Z-conductive structures are very
similar: Both these features are via posts coated by
a dielectric material which is then
polished to expose their top surfaces. Another build-up metal layer is formed on top of each exposed
pillar, or (micro-via) surface,
allowing electrical contact as per the designed electrical net-list. Since
both structures involve a surface planarazing step, Cu pillars as well as
micro-vias can be placed directly one on top of the other and under the
flip chip contact pads thereby clearing expensive substrate real estate
for routing.
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