5 Frequent Flexible Printed Circuit Style Errors Flexible Printed Circuitry (FPC) provides a tremendous opportunity for the packaging engineer and electronic designer. These versatile electronic wiring systems might be shaped, bent, twisted and folded into endless dimensional configurations...limited only by an engineer's origami creativity. Within this regard they provide substantial design benefits more than a two dimensional and inflexible rigid printed circuit board (PCB). This added dimension could make flex circuits a designer engineer's dream Rigid flex PCB, but with the addition of flexibility come some "rules" that want to be followed (sounds like an oxymoron??) to create specific a robust style is achieved. Various manufacturing approaches and material sets are used for FPC's and an instant distinction may be the dimensional properties. Rigid printed circuits are typically a lot more dimensionally steady vs. the typical polyimide film utilised because the constructing block in 98% in the flex circuits produced. This elevated dimensional variability implies a flexible circuit requires various style rules than its rigid printed circuit board relative. However, a lot in the design and style software program out there utilizes rigid PCB design and style guidelines and this can make manufacturing and functional troubles for the flexible circuit. Obtaining a flexible circuit design and style prepared for fab is referred to some within the market as "flexizing" the design and style Prototype PCB. The list below information five of the a lot more frequent techniques "flexizing" tends to make a style additional robust, more producible, and prepared for fabrication. Solder mask or coverfilm openings:In the course of fabrication flexible circuitry can demonstrate dimensional adjust just after exposure to processes like pumice scrubbing, copper plating, and/or etching. Whilst some alter may be accounted for, flexible circuitry design and style guidelines typically demand bigger tolerances to accommodate subsequent registrations for coverfilm, stiffeners, or die cutting. Further consideration is required for the adhesive squeeze out that happens through lamination in the coverfilm dielectric. Complicating the prediction of compensating style characteristics may be the myriad of processes and sequences expected to make a custom flexible circuit. The bottom line may be the openings in the coverfilm normally will need to let additional area in a flex circuit style. Spacing among solder pads and adjacent traces:Right here is definitely the tradeoff, i.e. design and style compromise, that will be made depending on item #1. When the coverfilm or soldermask openings are made bigger, the edges on the adjacent conductor traces may be exposed if they have been routed too close to a solder pad. This could bring about shorts if solder bridges amongst connector pins or pads. Physical size of the circuit is one more element that can affect registration capability. Normally a lot more space is needed involving a solder pad and an adjacent conductive trace to accommodate the coverfilm or soldermask placement tolerance. Stress points in conductors:Since flex circuitry is utilized in both fold to install and dynamic flexing applications, trace configurations which can be acceptable within a rigid PCB may possibly make problems in a flexible circuit. Conductor traces with sharp corners and acute junctures in the base of solder pads become natural "stress points" when the location close to them is flexed. This could result in trace fracture or delamination. A fantastic flexible circuit layout will have a smooth radius for conductor turn points (in place of sharp corners) and a gentile radius in the trace for the pad fillet in place of a sharp angle. Selective attachment of stiffeners will avert bending in soldered regions and is really a typical design and style practice. Stacked traces:Traces on opposite sides on the dielectric need to not directly "stack" on each and every other. Traces in tension (on the outdoors on the bend radius) might crack when the circuit is bent if they straight align in parallel with a trace on the opposite side. The traces in tension are forced farther in the neutral axis from the folded area and can fracture, specially with repeated bending. A great design practice is usually to retain the copper in the neutral axis of a bend by designing this area as a single conductive layer. When this isn't doable, a proper design and style will "stagger" the traces between top rated and bottom copper layers to prevent best and bottom alignment. Soldered joints as well close to bend point:A solder joint is formed by an intermetalic bond from the solder alloy towards the copper trace. Even though the copper trace is usually flexible, regions which have been soldered come to be pretty rigid and inflexible. When the substrate is bent close to the edge on the solder joint, the solder pad is either going to crack or delaminate. Either situation will result in really serious functional challenges. The bottom line is the fact that designing a flex circuit with standard PCB computer software can result in some severe manufacturability and reliability issues. It can be finest to perform with your flexible circuit supplier or possibly a flexible circuit design professional to either "flexize" the style before beginning fabrication or develop the layout straight from a net list. This will likely assure that the design might be manufactured to meet your desires.
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