WE GO WHERE OTHERS WILL Flexible Circuit NOT And Heater .

FLEX CIRCUIT CLASSES / TYPESCircuit Classes:IPC 6013 Type 1Flex circuits fall into 3 classes (1-3 per IPC-6013) based on the level ofinspection and testing required, and also by the performance requirements of the finished product. Single conductive layer Insulating material one or both sides Access to conductors on one or both sides Class 1 circuits have the minimum inspection, testing and performance requirements. These circuits are the least expensive and aretypically used in applications such as disposable electronics (e.g.musical greeting cards) and RFID tags.Access HolePolyimide CoverAdhesive Class 2 circuits have moderate inspection, testing, and performancerequirements. Class 2 circuits are more expensive than class 1 andare typically found in applications such as cameras, medical diagnostic equipment, and cell phones.Polyimide SubstrateCopper Pad Class 3 circuits have the highest level of inspection, testing andperformance requirements. Class 3 circuits are the most expensiveof the 3 classes, and are typically found in applications that involvethe taking or maintaining of life. Applications would include implantable cardiac devices and military/aerospace electronics.IPC-6013 Type 2Circuit Types: Two conductive layers with flexible insulating film between themFlex circuit type is determined by the number of conductive layers,construction/materials, and the presence or absence of plated throughholes. The common flex circuit types (1-4) are illustrated at right. Afifth flex circuit type (type 5) is very uncommon and is not shown. Type5 circuits are two or more layers without plated through holes. Plated interconnect holes Insulating cover material on one or both sides Access to conductors one or both sidesAccess HolePolyimide CoverAdhesiveCopper PadPolyimide CoverCopper-PlatedThrough HolePolyimide Substrate4

FLEX CIRCUIT CLASSES / TYPESIPC 6013 Type 3Type 1-Single Layer FlexDual access is accomplished on a single sided flex bylaser skiving openings on the bottom side of the flex. Three or more conductive layers Flexible insulating material between layers Plated interconnect holes Insulating cover material one or both sides Access to conductors one or both sidesAccess HoleCoverCopper PadPolyimide SubstrateBond PlyPolyimide SubstrateAdhesiveCoverCopper-Plated Through HoleIPC 6013 Type 4Type 4-Rigid FlexRigid flex circuits combine rigid FR-4 areas for dense component population interconnected with flexible polyimide areas which can be bent to accommodate overallpackaging needs. Two or more conductive layers Insulating material may be rigid or flexible Plated interconnect holes through flexand rigid materials Access to conductors one or both sidesthrough cover material or SMOBCPolyimide CoverAdhesivePolyimide CoverAdhesivePolyimide SubstrateCopper PadRigid MaterialCopper-Plated Through Hole5

FLEX CIRCUIT MECHANICAL DESIGN STEPSReview electrical schematic/net list toestimate approximate layer count. Accountfor all signal and plane layers. Also, referto the Conductor Width Nomograph (page11) for any conductors with high currentrequirements. Multiply the number of layersby .0055" to get the approximate overallthickness of the circuit (if your circuit hascontrolled impedance requirements, thismultiplier may be larger).Review mechanical requirements/solidmodel to determine minimum bend radii.Determine and evaluate bend ratio.Determine flex termination method(s).Create a “paper doll” of the proposed flexcircuit outline. The first paper doll outlinecan be created with just a ruler and a pencil,but subsequent iterations should then betransferred to a CAD program so that youcan keep track of your modifications. Placethe paper doll in the assembly to checkform and fit. Don’t forget to account for thetermination hardware. Make modificationsas required to optimize fit.Keep the assembler in mind during thefit check. If the paper doll tears duringinstallation, it may signal possible assemblyproblems. A flex circuit that is difficult to installwill add time (cost) to the assembly, and canbe a reliability risk due to possible damageto the circuit during the installation.Objective: Provide low profile interconnect for3 small PCBsBEFOREAFTERStep 1: Layoutcircuit footprint onCAD and create apaper doll.Step 3: Createpolyester mock-up.Step 2: Checkpaper doll for fit.Step 4: Checkpolyester mock-upfor form and fit.Step 5: Contact flex vendor to makemechanical mock up. This mock upshould accurately reflect the actualmaterials of the final circuit.Final step: Flex circuitRe-create the paper doll using .010"polyester sheet material. You can usuallyuse a standard copy machine to print thecircuit outline. Cut the model out and checkfor form and fit and modify as necessary. Thepolyester is a bit stiffer than paper and willbetter represent the mechanical propertiesof the flex circuit.Obtain a mechanical sample from yourflex circuit vendor. This sample will beconstructed from the same materials asthe final flex, but will not have any etchedcircuitry (only solid copper). All componentholes and circuit outline features should berepresented. Connectors can be glued inplace with epoxy to give a true sense of thefinal fit. This will be the final opportunity totweak your design prior to ordering actualcircuits. If you have followed the steps above,6the mechanical sample should require few, ifany, modifications.

STANDARD MATERIALSFlexible Circuit Technologies can work witha wide variety of flex circuit materials togive you the electrical and mechanical performance you require. However, to get thelowest possible cost for your flexible circuit,it is advisable to design your circuit usingstandard materials whenever possible. Usinguncommon materials in your design can addsignificantly to both the cost and the leadtime of your circuit.Insulating Material:Stiffener Material: Polyimide Film .001", .002", .003" Glass Reinforced FR4 (epoxy) Polyester Film Polyimide Film (non-reinforced) .005" PENFinal Finishes: PET ENIG Solder Mask ENEPIG PICConductive Material: Copper Foil ¼ oz (9 um), 1/3 oz., ½ oz.,1 oz., 2 oz. Hard Nickel/GoldAdhesive: HASL Epoxy .001", .002" Immersion Tin Constantan Modified Acrylic .001", .002" Tin Plate Cupro-nickel Prepreg Organic (OSP) Inconel PSA Silver Filled Epoxy Adhesiveless Carbon AluminumTERMINATIONSVirtually any connector or component thatcan be mounted on a rigid PCB can also bemounted on a flex circuit. In addition, flexcircuitry offers many other options includingunsupported fingers and insulation displacement connectors. Contact your FCT Applications Engineer to discuss which terminationoption will work best for your application.Circular ConnectorSMT ConnectorInsulation Displacement ConnectorsZIF Connector TerminalRight Angle ConnectorCard Edge ConnectorsCrimp Pins7

COST DRIVERSEvery designer is looking for ways to decrease costs without sacrificing performance. IPC research has shown that PCB designers driveover 75% of the circuit cost based on the decisions they make. It isimperative that the flex designer understand what features add valueand what features add only cost. Designers should never sacrifice reliability to save costs, but at the same time, many flex circuits are overspecified resulting in additional costs that add no additional value.Here is a list of the features that drive the majority of your circuitcost: Circuit Type (i.e. type 3 vs type 4)—Rigid flex circuits aretypically more expensive than multilayer flex with stiffeners.Scrutinize your design to determine if your application requires arigid flex construction, or if a multilayer with stiffeners will work. Ifin doubt, call your flexible circuit manufacturer and ask. Layer Count—As the number of layers increase, so does thecost. More layers will require additional materials and processingtime. Processing high layer count flex or rigid flex can also be verytechnically challenging which may result in reduced yields. Drawings Overly or Too Tightly Dimensioned—It isimportant to remember that you are purchasing a flexible circuit,not a machined part. The materials used to manufacture flexiblecircuits both permit and require looser tolerances than rigid PCBs.Each dimension placed on a drawing will have to be verified, soask yourself, “is this dimension adding value, or just cost?”. Allnon-critical dimensions on your flex circuit drawing should bedesignated as reference. Circuit Class (i.e. class 3 vs class 2)—Class 3 circuits requireadditional testing, inspection, and construction requirements whichmake them more expensive. Review the requirements of yourapplication to determine the proper class for your flex circuit. Circuit Size and Shape—Most flexible circuits are constructedin panel form. The greater the panel area a circuit occupies, thegreater the cost. There are instances where even a small changein outline can result in a large cost decrease. The illustration belowshows how a slight modification to the flex shape allows for abetter nesting of the flexes on the panel, resulting in two morecircuits per panel. Dissimilar Layer Counts in PTH Areas—All areas that haveplated through holes should have the same layer count andconstruction. Multiple Final Finishes—While multiple final finishes cancertainly be accomplished, it usually requires a series of handmasking operations that will add cost. Small Features—Because of the inherent dimensional instabilityof flex circuit materials, small circuit features (i.e. via pads) cancause processing difficulties and reduced yields. There are instanceswhere it would be less expensive to add additional layers withlarger features, than to design with very small features. For thisreason, it is advisable to contact FCT early in the design stage forguidance. Blind and Buried Vias—These are significantly more expensivethan through holes.Laser cutting can eliminate the time andcost of tooling during prototyping. It canalso be an effective way to cut out uniqueshapes within a flex circuit.8

FLEX CIRCUIT DESIGN GUIDELINEScopper, it also attacks the edges of theconductors resulting in what is referred to as“under-cut”.OverviewScrutinize your design for stress concentration features. Stress concentration features are the predominant single cause formechanical failures in flexible circuits (i.e.cracked/broken conductors, torn insulatingmaterial, etc.). To avoid stress concentrationpoints, the construction of the circuit shouldnot change in, or immediately adjacent to,the bend area. In a bend area, there shouldbe no change of conductor width or thickness or direction, no termination of platingor coatings, no openings in covers or outerinsulating materials, and no holes of anykind in a bend zone. If you would like yourflex circuit design evaluated for stress concentration features free of charge by an FCTApplications Engineer, call 888-921-6167or 763-545-3333, or submit your design atwww.flexiblecircuit.comPoor Design-Fingers stop short of coverGood Design-Fingers extend under coverBend RatioBEND AREANOTPREFERREDACCEPTABLE PREFERREDConductors should always change directionswith soft curves rather than sharp corners.When curves are not an option, 2- 45 degreecorners are preferred over 1-90 degree corner.NOTPREFERREDACCEPTABLEPREFERRED When possible route small conductors onthe inside of a tight bend. Small conductors ( .007") will tolerate compressionbetter than stretching. Placing these conductors on the inside of a bend will reduceor eliminate tension forces. Do not stack conductors on top of eachother on multiple layers creating an “Ibeam” effect. Stacking conductors will essentially increase the overall circuit thickness thereby decreasing flexibility and thecircuit’s ability to bend reliably.GoodDetermine and evaluate the minimum bendratio of your design. This will be your singlebest indicator of whether your flex circuitmay experience problems in service. Bendratio is bend radius: circuit thickness.Preferred Bend Ratios Are:Single Layer10:1Double Layer20:1Multiple LayerConductor RoutingAdhesivePolyimideIdeal: Conductor width greaterthan 5x conductorAs copper foil thicknessincreases,thickness.so doesthe amount of undercut. This makes it verydifficult for the flex manufacturer to create very small conductors on very thick foil.There are also variations in the etching process (primarily etchant strength which varieswith the amount of copper in the solution).For this reason, the designer must factor in aprocessing allowance for strand width (andspacing). For optimum etch yields, conductor widths should be at least 5 times greaterthan the thickness.Copper FoilThicknessPlatedCopperNon-platedCopper¼ oz /- .001"(25 um) /- .001"(25 um)½ oz /- .001"(25 um) /- .001"(25um)1 oz /- .002"(50um) /- .001"(25um)2 oz /- .003"(75um) /- .002"(50 um)It is advisable to maximize conductor widthwherever possible. For example, if yourdesign requires .005" conductor width tosqueeze between pads in an isolated area,the conductor should flare back out to .010”.012” once the conductor clears the tightarea. This will improve the manufacturingetch yields, which in turn means a loweroverall circuit cost to you.BadConductorsFlexible circuit conductors are manufacturedusing a photo-etch process which starts witha full sheet of copper. Conductors are formedby masking the desired conductive paths,and then chemically removing all unwantedcopper, leaving the desired circuit patterns.As the etchant dissolves the unmasked9Not PreferredPreferredPREFERREDPREFERREDWhen possible, conductors should be routedthrough bending or flexing areas with theconductors perpendicular to the bend. Thiswill minimize stress on the conductors duringflexing and maximize circuit life.Ideal: Conductorwidth greaterthan 5x conductorthickness.NOT NOTPREFERREDPREFERRED10:1ConductorWidthBEND AREA

CONDUCTOR WIDTH NOMOGRAPHThe conductor width nomograph on the opposite page will assist you in determining theconductor widths necessary to carry variouscurrent loads. The nomograph was reprintedfrom IPC-2152. Refer to IPC-2152 for a morein-depth analysis of various features andvariables that affect current carrying capacity of copper conductors.Using The NomographExample #1:If design requires 2 amps @10 c temp rise, conductor would be eithera) .018” wide on 2oz Cu, orb) .036” wide on a 1oz Cu, orc).072” wide on 1/2oz Cu1. Find the current matching your requirements on the left side of the upper chart.2. Move to the right until you intersect thecurve that corresponds with the maximumtemperature rise allowed. Keep in mindthat the temperature rise is from systemoperating temperature (not necessarilyroom temp).3. From the intersection point of the current/temp rise, move straight down to the lower graph to where you intersect the copperweight of the conductors.4. Move to the left to determine conductorwidth.Example #2: How much current can a .100”wide conductor on 1oz Cu carry with 20 (max temperature rise) @ 10 Amps.ConductorWidthAdhesivePolyimide10

CONDUCTOR WIDTH NOMOGRAPH11

FLEX CIRCUIT DESIGN GUIDELINESPAD FilletsTear ReliefSMT Access OpeningsLAMINATEDTEFLON TABAT CORNERIt is a good idea to insert fillets on pads ateach location where a conductor enters apad. Pad fillets will reduce or eliminate potential stress concentration points.RELIEF SLOTLARGE CORNERRADIUSSLIT WITHRELIEF HOLEBefore FilletsThe two most common cover materials arepolyimide film and flexible soldermask. Themethods for creating access openings in the2 materials are very different and carry verydifferent design requirements. Access openings in polyimide film are created by drilling,routing, or punching, which limits the sizeand shape of the openings to what can bedone with a round bit or a tool. For this reason, SMT access openings in polyimide filmare either round or oval. Also, gang accessof multiple SMT pads is a common designpractice on flex circuits.This illustration shows the most common andeffective methods of eliminating tears in a flexiblecircuit. Copper tear stops are not shown becausethey have been shown to have limited value inkeeping a tear from starting or propagating.ViasFCT can provide circuits with through hole,blind, or buried vias. Through holes canconnect all layers at a via point. Blind viasconnect outer layers to adjacent layers, butdo not extend through the circuit. Buriedvias connect internal layers but do notextend to the outer layers. Blind and buriedvias will increase the cost of the circuit, butcan increase usable PCB real estate on nondrilled layers.After Fillets12Flexible soldermask, like regular PCB soldermask, is photo-defined so any shape opening is possible. Soldermask openings shouldbe made slightly larger than the SMT padsto ensure that the mask does not get on thepads if there is any misregistration in theprinting process.

FLEX CIRCUIT DESIGN GUIDELINESControlled Impedance andSignal IntegrityThe speed at which electronic devices are operating is continually increasing. The result isthat the characteristic impedance of all partsof the electronic assembly, including any flexor rigid PCBs in the system, need to havematching impedance. Impedance mismatcheswill cause signal reflections and degradationat each mismatch point, which in turn resultsin erroneous signals and ultimately devicemalfunction. The characteristic impedanceof a flex can be determined prior to manufacturing using an impedance calculator. AnFCT engineer can assist you with these calculations, or you can buy or download an impedance calculator. A number of factors willaffect the characteristic impedance of a flexPCB. The main contributors are: The dielectric constant of the insulationmaterials used to construct the circuit. The width of the traces carrying the signal. The distance of the signal traces from thereference plane layer(s). The thickness of the traces carrying thesignals. The distance between signal traces in differential impedance applications.The most common impedance requirementsrange from 50-75 ohms (single ended) or100-110 ohms differential. Achieving theseimpedance values in flex circuitry requiresthe use of thicker dielectric materials thanare normally used, resulting in an overallthicker and stiffer circuit.Plane Layers and ShieldingStiffenersReference plane layers and external shielding play a key role in both impedance controland signal integrity. FCT can add plane layers using:It is wise to rigidize SMT, connector, and other termination areas on your flex circuit withmechanical stiffeners. FCT can add stiffenersof various thickness made from epoxy glasslaminate (FR4) or polyimide film. In SMT applications, stiffeners should be applied tothe side opposite the SMT components. Onthrough hole connectors and other throughhole applications, stiffeners should be applied to the same side as the connector orthrough hole co

IPC-2152 Standard for Determining Current -Carrying Capacity in Printed Board Design. IPC-2221 Generic Standard on Printed Board Design IPC-2223 Sectional Design Standard for Flexible Printed Boards IPC-6011 Generic Performance Standard for Printed Boards IPC-6013 Qualification