3M TM Flexible Circuits
TECHNICAL BRIEF:
TECHNOLOGY
Signal Integrity /
Electrical Performance
High speed (high frequency analog and fast rise time digital) signals require special
attention to circuit design. Transmission line properties of circuits need to be carefully
considered. 3M employs state-of-the-art materials and uses high speed electrical
modeling tools and test equipment to ensure the highest performing transmission line
circuits. Some applications where signal integrity issues arise are:
• High speed digital
• Telecom circuits
• High speed computing
• Analog video
• DSP
• RF signaling
ADVANTAGES
3M’s thin flexible circuits offer electrical circuit design flexibility:
• Controlled impedance transmission line signal traces
• The ability to propagate very high speed/high data rate signals with low loss and
reduced cross talk
• Connection/bond points designed to minimize signal path discontinuities
• Miniaturization of electrical circuits using high performance materials
IMPEDANCE CONTROL
Transmission line components, such as signal traces, and lumped components, such
as bonding pad points (general interconnect to PCB, wirebond and BGA) may be
optimized for signal integrity. The characteristic impedance of an interconnect needs
to be matched to the circuit’s driving source and to the load for high speed signals.
Impedance matching minimizes signal transmission losses and reflections. Low dielectric
constant materials offer reduced capacitive coupling and therefore have lower cross
talk and allow faster signals than other more common/typical dielectrics.
Physical layout of the materials is used to control impedance. Figure 1 shows items that
are taken into account when making impedance controlled circuit traces.
TYPICAL PROPERTIES
Dielectric and conductor properties combine with the conductor shapes and positions
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Fig. 1 - Properties affecting electrical/signal properties
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to form the resistive, capacitive, and inductive
properties of the resulting circuits. Low dielectric
constant, low loss dielectrics such as polyimide
and LCP (liquid crystal polymers) are employed in
3M’s thin, flexible circuits. Polyimide and LCP have
dielectric constant (DK) of 3.4 and 2.9 respectively
and dissipation factor (loss tangent) of 0.01 and 0.003
respectively, all at 1 GHz to over 20 GHz. Copper
features are made with pure (99.99%) copper. Typical
dielectric thicknesses are 25 µm and 50 µm, and trace
width and space dimensions may be 33 µm or less.
Copper thickness can be from 6 µm to 25 µm or more
as required.
BASIC TRACE CONFIGURATIONS
There are several options for signal traces
and reference traces/planes to meet customer
specifications for mechanical flexibility while
providing excellent signal integrity. Single-ended and
differential signals configurations are available with a
broad range of characteristic impedances that match
the requirements of applications with signaling rates
up to 10 Gigabit and higher.
Single metal layer flexible circuits, like those shown
in Figures 2, 3, and 4, offer the greatest mechanical
flexibility and provide a variety of signaling
configurations for high data rate applications.
2 - METAL LAYER
Covercoat
SIG -
SIG +
Dielectric Material (Polyimide or other)
REF (copper)
Fig. 5 - Two metal layer with differential signal and reference plane (differential
signaling)
Two metal layer circuits provide tighter signal
coupling for single-ended and differential pairs and
higher density circuits by using one layer as reference
and leaving the top signal layer available for signal
lines.
3M employs state-of-the-art modeling tools and test
equipment working in both frequency domain
(S-parameter models, VNA test equipment) and time
domain (Spice models, TDR test equipment) to ensure
the highest performing electrical/signal transmission
line circuits.
1 - METAL LAYER
Covercoat
RE F
SIG
Dielectric Material (Polyimide or other)
Fig. 2 - One metal layer with signal and reference traces (balanced signaling)
RE F
SIG +
SIG -
RE F
Dielectric Material (Polyimide or other)
Fig. 3 - One metal layer with differential signal and reference traces
(differential signaling) G-S-S-G configuration
RE F
SIG +
RE F
SIG -
RE F
Dielectric Material (Polyimide or other)
Fig. 4 - One metal layer with differential signal and reference traces (differential signaling)
G-S-G-S-G configuration
3M is a trademark of 3M Company.
Important Notice
Before using this product, you must evaluate it and determine if
it is suitable for your intended application. You assume all risks
and liability associated with such use.
Warranty; Limited Remedy; Limited Liability
This product will be free from defects in material and manufacture
as of the date of purchase. 3M MAKES NO OTHER WARRANTIES
INCLUDING, BUT NOT LIMITED TO, ANY IMPLIED WARRANTY
OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR
PURPOSE. If this product is defective, your exclusive remedy shall
be, at 3M’s option, to replace or repair the 3M product or refund the
purchase price of the 3M product. Except where prohibited by
law, 3M will not be liable for any loss or damage arising from
this 3M product, whether direct, indirect, special, incidental or
consequential regardless of the legal theory asserted.
3
Electronic Solutions Division
6801 River Place Blvd.
Austin, TX 78726-9000
800 676 8381
www.3M.com/microinterconnect
Printed in USA.
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Post-consumer fiber
© 3M 2003 80-6201-3001-5