SEPTEMBER 2021 I DESIGN007 MAGAZINE 41
Always indicate where the thickness mea-
surement is to be taken, for example:
– Glass to glass at rail guides
– Over gold contacts
– Over solder mask
Pure Build vs. Hybrid Build
e term "pure build" refers to a multilayer
PCB material construction that is composed
of the same type of material throughout the
stackup, such as a construction entirely of
FR-4, or one entirely of PTFE or other high-
frequency material. A hybrid multilayer PCB
uses materials with significantly different
critical properties than those associated with
a traditional "pure" multilayer PCB. e rea-
sons for using a hybrid construction in RF
multilayer PCB designs are typically driven
by cost, reliability, and/or electrical perfor-
mance.
Balanced Stackup Structure
Regardless of the material used, maintaining
a balanced construction (lay-up, stackup, etc.)
in relation to the Z-axis median of the board
will assure minimum bow and twist. is bal-
ance includes the following: dielectric thick-
ness of layer, copper thickness of layers and its
distribution and location of circuit, and plane
layers. Whenever possible, planes should be
balanced around the Z-axis median line of
the lay-up, and ideally located internal to the
board.
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
Standard 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 Fabricator's Perspective.
Visit I-007eBooks.com to download these
and other free, educational titles. He also
co-authored Fundamentals of Printed Circuit
Board Technologies.
Figure 3: A balanced construction is important with any PCB design, but is even more critical
with a hybrid material set using mixed dielectrics.
