How to improve flexibility and bend radius
Single-layer circuits are the best choice for dynamic
(flex-in-use) applications. Generally, double-layer or
more circuits are best suited to static applications where
the circuit flexes only during installation. The minimum
allowable bend radius depends on a number of factors,
and is best defined in IPC-2223. Approximate circuit
thickness is slightly less than the sum of the insulator,
adhesive, and foil layers. Some ideas to increase
Circuits with two layers or more can be selectively
plated to improve dynamic flexibility.
It is best to keep the number of bends to a minimum.
Stagger conductors to avoid to the I-beam effect, and
route conductors perpendicular to a bend.
Do not place pads or through-holes in bend areas.
Factory forming is an option you may want to
consider. Most constructions can be factory formed,
depending on geometry. Because circuits are
flexible, formed circuits will relax in time. Form
tolerances apply only to the part in the constrained
position. Consult Minco for more information on
Do not place potting, discontinuities in the cover,
discontinuities in the plating, or other stress
concentrating features near any bend locations.
Unbonded layers in a relatively thick multilayer or
rigid-flex circuit are an option in order to improve
flexibility, but this may be more expensive.
Minco can provide an epoxy or RTV fillet to reinforce
the edges between the flexible and rigid areas of a
Polyimide has a high initial tear strength, but once a tear
starts, it propagates easily. All inside corners must be
radiused. The larger the inside radius, the greater the
tear strength. If tearing is a concern, polyimide-
insulated circuits can be designed with tear stops at the
inner corners, for corners of 120° or less. Minco can
incorporate internal or external polyimide or Teflon tear
stops. Polyimide or Teflon tear stops will add to circuit
Staggered conductors vs. I-beam effect
Factory formed circuit
Application Aid #24
Tel: (763) 571-3121 K Fax: (763) 571-0927 K www.minco.com