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Corporate Headquarters:
1506 Gladding Court
Milpitas, CA 95035
408.945.8787
Fax 408.945.0347
www.lenthor.com
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Flex Facts
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1. Where Did Flex Circuits
Originate?
2. What Makes Up A Flexible Circuit?
3. How Does The Makeup Of A Flexible Circuit Compare
To A Rigid Board?
4. What Benefits Will I Get From Using Flexible
Circuits?
5. What's New With Flexible Circuits?
6. Can Flex Circuits Be Used In Every Application?
7. What Types of Flexible Circuits Are Available?
8. How Can I Design A Flexible Circuit To Improve
My Product's Design?
9. O.K., I'm Sold On Flexible Circuits. Now How
Do I Go About Getting Some?
10. Who Should I Contact for Flex Circuit Expertise?
1. Where Did Flex Circuits Originate?
The flexible circuit has just recently come of age as an interconnection
device, although it was originally developed over twenty years
ago.
Designers of applications from car stereos and cameras, to heart
pacemakers and disk drives, have all reaped the benefits of
flex circuits. More applications are being discovered every
day.
The flexible circuit was originally designed as a replacement
for bulky wire harnesses. Simple circuit designs helped to solve
space and weight problems that could not be resolved using traditional
wiring methods.
As technology advanced in leaps and bounds, new products required
more compact packaging, minutely defined electrical impedances,
and error-free product performance. Flexible circuitry gave
the package engineer ways to miniaturize circuits, increase
functional capacity, and improve reliability.
In addition to being flexible, flex circuits can be designed
to meet highly complex special con figurations, and hostile
operating environments are easily withstood by flex.
New products demand savings in space and weight with greater
reliability. Because of these demands, the twenty-year-old technology
of flexible circuits has come of age.
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2. What Makes Up A Flexible Circuit?
A basic flexible circuit is made of a flexible polymer film
laminated to a thin sheet of copper that is etched to produce
a circuit pattern.
Patterns can be created on both sides of the film. Interconnections
are achieved with plated through-holes, yielding an almost unlimited
adaptability between various component parts. A polymer overcoat
is often added to insulate and environmentally seal the circuit.
Flexible circuits can also combine several single- or double-sided
circuits with complex interconnections, shielding, and surface
mounted devices in a multi-layer design. These multi-layer designs
can also be combined with rigid circuit boards to create a rigid/flex
circuit capable of supporting devices as needed.
The most widely used polyimide film is KAPTON®, because
of its high heat resistance, dimensional stability, dielectric
strength, and flexural capability. The characteristics of this
raw material help the flex circuit maintain a high degree of
durability, and also help it survive hostile environments.
3. How Does The Makeup Of A Flexible Circuit Compare
To A Rigid Board?
One thing that flexible circuits and rigid printed circuit boards
have in common is that they both allow repeatable connections.
Conductor routings in a flexible circuit are determined just
like a rigid PC board by a single artwork, rather than by individual
wirings.
Flexible circuits also allow extra-fine lines, as low as 2 mils
on 4-mil centers, allowing high -density device population and
reduced circuit size and weight.
But flexible circuits have one important advantage over rigid
PC boards in that they give designers a third dimension with
which to work. Flexible circuits can bend and shape around two
or more planes during installation. They can solve space and
weight problems by replacing several bulky boards with a single
thin one. While in use, flexible circuits can also bend and
flex up to 500 million times without a failure. This is something
a rigid PC board simply cannot do.
4. What Benefits Will I Get From Using Flexible Circuits?
Flexible circuits provide four major benefits over rigid PC
boards.
Design Freedom
The most immediate benefit that flexible circuits give a package
designer is an almost unlimited degree of design freedom.
Flex circuits can fit in tight spaces. They can bend, fold,
twist, change in width many times and even flex from a rolled
configuration. This gives the package designer the freedom to
relocate other parts and subassemblies where they will optimize
circuit and equipment operation. The designer is no longer restricted
by the space demands of bulky, rigid PC boards.
Simplifying circuit geometry and placing surface mount devices
directly on the circuit can also improve the circuit design.
Intricate patterns that may be difficult to achieve with rigid
board connector pins can be designed into the flexible circuit
artwork. Greater circuit complexity is achieved in a much smaller
space.
Space and Weight Savings
Because flexible circuits can be bent, twisted and rolled to
suit the contour of the equipment, designers can enjoy a space
savings of up to 75%.
The larger surface-to-volume ratio of flexible circuits also
allows increased heat dissipation and lighter current capacity.
Denser device populations and lighter conductors can be designed
into a product, freeing space for additional product features.
Even used as a flat circuit, flex saves space. The typical hard
board is 62 mils thick, while a flex circuit is a mere to 4
to 11 mils.
The different raw materials used in flex also offer a weight
savings as high as 70% versus the rigid board.
High Reliability and Durability
Flexible circuits are made from precise replicas of artwork
for superior manufacturing repeatability. The etched circuits
replace the solder and hand wiring connections of the rigid
board, completely eliminating wiring errors.
The durability of the KAPTON polyimide survives vibration and
shock that would damage a rigid board. KAPTON also provides
increased thermal conductivity, providing an ideal thermal path
to a heat sink.
In designs that have moving parts, the flexible circuit can
move and flex up to 500 million times without a failure. The
exceptional thermal stability of KAPTON also allows the circuit
to with stand applications with extreme heat.
Cost Savings in Production
Production of designs using flexible circuits requires less
manual labor and reduces the probability of production errors.
The use of flexible circuits eliminates the high cost of routing,
wrapping, and soldering wires.
Complete interconnection systems are installed or replaced,
rather than individual hard PC boards. This greatly eliminates
wiring errors and reduces manufacturing costs. This automation
also reduces the chance of human error and increases reliability
in the design.
Low volume applications benefit the most when circuit designs
are very complex. Most high volume applications get lower production
costs regardless of the complexity of the circuit.
In addition, as simpler, more direct methods of integrating
circuits are discovered, the cost savings realized by flex increases.
The use of conductive ink, anisotropic adhesives, and additive
circuitry are ideal in designs using flex.
5. What's New With Flexible Circuits?
Advances in surface mount technology, mounting devices directly
on circuits, have led to exceptional space and cost savings.
KAPTON's excellent thermal stability provides a better base
for surface mounting than hard boards. Because the compliant
base film places less stress on soldered joints, thermal mismatch
is less likely to occur.
With conductive adhesives, surface mount chips can be mounted
on double-sided flex circuits. This eliminates the problem of
soldering one device on a hard board, then soldering again on
the other side, disturbing the previous connection.
Tape automated bonding (TAB) is another space-saving technology
for which flex is ideal. Because KAPTON film can be etched so
accurately, windows can be placed on the flex circuit to hold
devices. The devices can then he soldered into place with TAB.
Rigid/flex combinations are perhaps the fastest growing flexible
circuit designs. These hybrids combine the best features of
rigid boards with the design flexibility of flexible circuits.
These rigid/flex boards provide a higher component density and
better quality control. Designs can be rigid where support for
components is needed, and flex around corners and in areas requiring
extra space.
Another new flex circuit technology is called Bend/flex. Made
of a copper-clad glass-polyester epoxy laminate, Bend/flex is
a kind of flexible circuit that bends once to form to designs,
yet maintains its rigidity. Bend/flex can support electronic
components without stiffeners, and can allow auto-insertion
of components before bending into its final shape.
Available in thicknesses of 15, 20, and 30 mils, Bend/flex can
be drilled, blanked, plated, pierced, and wave soldered on one
or both sides. It can replace mother/daughter board combinations
or even rigid/flex combinations in some designs.
Advancements in the design of application-specific integrated
circuits (ASIC) have helped flex become commonplace in many
consumer electronics like cameras, computers and home entertainment.
6. Can Flex Circuits Be Used In Every Application?
The benefits of flexible circuits are realized in most every
application requiring high volume or high degree of accuracy.
In high volume applications, highly automated fabrication methods
reduce human handling of the circuits, reducing both cost and
probability of error. Applications like cameras, printers, disk
drives, and automotive panels all benefit from high volume flex
efficiency.
High accuracy circuits for aerospace and medical applications
benefit from the flex circuit's ability to handle ultra-fine
lines and tight tolerances in an age of miniaturization.
Flexible circuits have been incorporated into several industries
throughout the years including:
Automotive radios, cassette players, electronic control systems
and on-board computers
Personal and mainframe computers, disk drives, and
printers
Consumer electronics like calculators, stereos, cameras,
and compact disk players
Telecommunications equipment, telephone handsets,
and switching systems
Industrial controls, machine tool controls, and robotics
Jet engines, navigational and flight control systems
Heart pacemakers, hearing aids, and other medical
applications.
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7. What Types of Flexible Circuits
Are Available?
There are three basic types of flexible circuits, varying in
degrees of complexity. These three types of circuits can be
used in different combinations to solve most every interconnection
design problem.
The simplest circuits are single-sided flexible circuits. They
provide maximum flexibility for dynamic applications and can
withstand hundreds of millions of flex cycles These simple circuits
are also the most easily adaptable to SMT, TAB, and other developments
in circuit technology.
Double-sided circuits are somewhat limited in their capacity
to flex because of a thicker, more complex level of design.
The ability to interconnect between sides using through-hole
plating helps double-sided circuits carry complex designs, and
still maintain flexibility
Multilayer circuits are ideal for complex, highly populated
design requirements. Large numbers of conductors can be designed
into a small package. Flexibility may be somewhat limited, de
pending on the number of layers in the design. These multi-layer
circuits are ideal for rigid/flex designs, combining a multilayer
flex circuit with a hard board.
Multilayer circuits are the ideal problem-solving technology
when confronted with design challenges like unavoidable crossovers,
specific impedance requirements, elimination of crosstalk in
sensitive circuits, additional shielding or ground planes, and
high component density.
8. How Can I Design A Flexible Circuit To Improve My
Product's Design?
In designing a flexible circuit, it is essential to consult
a flexible circuit expert early on in the design process. Flexible
circuit manufacturers are not just production lines. They are
manufacturing consultants and experts in the field of flexible
circuitry.
Before beginning your flex design, examine your product requirements
thoroughly. Know all the electrical requirements, dimensional
restrictions and assembly limitations. Consult flex circuit
design guides throughout the design process to take full advantage
of design trade-offs and improvements.
Start designing your flex circuit early, preferably as you start
the design of your product. There are many variables in the
design of a flex circuit. Conductor spacing, component addressing,
designing for bend areas, and covercoat configuration and shielding
must all be determined before your first prototype is produced.
By contacting a flex specialist early in the design process,
you can get qualified design assistance, and be sure all design
factors have been taken into account. A flex specialist can
also check designs for manufacturability and even suggest design
improvements for cost savings and improved performance.
A prototype of the circuit should be built as soon as possible
to allow time for design improvements. A prototype also helps
your flex specialist further evaluate his ability to produce
the design for you. At Lenthor Engineering, we can rush these
prototypes to you in as fast as 24 hours.
9. O.K., I'm Sold On Flexible Circuits. Now How Do I
Go About Getting Some?
Remember that the flexible circuit manufacturer is essentially
a design and manufacturing ser vice organization. Although flexible
circuitry is different than hard board designs, it is not difficult
to design and manufacture if you have the proper assistance.
The best way to become acquainted with a flexible circuit manufacturer
is to take a tour of their facilities. Evaluate their experience
and production capabilities, and bring them in early in the
design process to take full advantage of their flex expertise.
A flex circuit expert can find the best cost and performance
value with a total systems approach.
At the conceptual stage, he can determine if your design is
particularly suited for flex circuits. At a later stage, he
can evaluate and reevaluate designs as they progress, assisting
with connector selection, fabrication techniques, assembly procedures
and prototype testing.
If your design and prototype is completed early in your design
process, it also allows your vendor adequate time to develop
schedule and quotations for artwork, tooling, and production.
This helps the flex circuit manufacturer serve you better with
quality, low-cost circuits, and on -time delivery.
10. Who Should I Contact for Flex Circuit Expertise?
Your local flexible circuit expert is Lenthor Engineering. Our
team of flexible circuit specialists can provide you the design
and production assistance described in the preceding pages.
Lenthor Engineering prides itself in producing quality flexible
circuits with consistent on-time delivery and one of the shortest
turnaround times in the flex circuit industry. For some designs,
we can even get you a prototype flex circuit in as little as
24 hours.
Whether you require a simple, single-sided flex circuit or a
high-density, complex design, Lenthor Engineering can solve
your design problems with high-quality products made just for
you.
If you want to learn even more about flexible circuits and what
they can do for your product designs, call Lenthor Engineering
now.
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