Standard Design Recommendations

Design differences and special considerations

D e fin e circuit p a r a m e t e r s b y a pp l ic a tion Sp e ci al con s id e r a tion s for ri g id-f le x
It may be helpful to use a paper template to represent the circuit.Experiment with bending and forming the template to optimize shape and fit. When designing the final shape, consider how the circuits will lay out on a processing panel (“nesting”). The greater the number of circuits per panel, the lower the cost.Another consideration concerns rigid-flex. While Minco is capa-ble of building a traditional rigid-flex board for you it may not be your best choice. Multilayer or stiffened flex boards may be able to meet your requirements for component and board mounting at reduced cost. • Rigid-flex is the ideal solution for applications with multiplerigid PCBs having SMT components on both sides and requir- ing interconnects between the rigid PCBs.•Before designing a rigid-flex circuit, make certain that it istruly what you need. If the circuit only has a few layers, stiffen- ers are a less expensive alternative to rigid-flex.•It is most cost effective to build a rigid-flex with an even num-ber of layers. All rigid portions of the circuit should have the same number and stack-up of layers.•Observe aspect ratio (hole depth/hole diameter) limits (seeCapabilities on page 10).•Minco builds circuits up to 16 layers, but costs increase signifi-cantly above 10 layers.•Expect a trim tolerance similar to that of a steel rule die fromhole-to-border and border-to-border. Hole placement within a cluster of holes and from cluster-to-cluster will have a ±0.005" (0.13mm) tolerance within a single rigid area.•Minimum inside corner radius of 0.031" (0.79mm) is standard,but smaller radii are available.•Unbonded layers can increase flexibility in multilayer flex cir-cuits, but this option is more expensive. Specify unbonded layers only in areas of the circuit that will bend.•Minco can provide an epoxy fillet on stiffener edges that willbend or flex.•For rigid-flex circuits, it is less expensive to have platedthrough-holes in the rigid portions only. •Minco can provide blind and buried vias in rigid-flex circuits. F le x circuit vs . h a rd b o a rd s
Designing a flex circuit is only one step away from designing ahardboard. The most important design difference to keep in mind is the three-dimensionality of a flex circuit. Creative bending and flexing can save space and layers. Other important differences:•Flex circuits both require and permit looser tolerances thanhardboards.•Because arms can flex, design them slightly longer thanrequired. D es i g n tip s to minimiz e circuit co s t
•Consider how circuits will be “nested”on a panel. •Keep circuits small; consider using a set of smaller circuitsinstead of one large circuit.•Follow recommended tolerances whenever possible. •Design unbonded areas only where they are absolutely necessary. •If circuits have only a few layers, using stiffeners can be far lessexpensive than a rigid-flex circuit. vs.BendBendDesiredCircuit 14