Flexible Printed Circuits (FPC) offers a significant opportunity for the packing developer and electronic designer. These flexible electronic wiring systems can be shaped, bent, twisted and folded right into limitless dimensional setups … restricted just by a developer’s origami creativity. In this regard they provide substantial design advantages over a 2 dimensional and also rigid PCB. This added dimension can make flex PCB a developer engineer’s dream, however with the addition of versatility come some “regulations” that should be complied with to make certain a robust design is achieved.
Various flex PCB manufacturing methods and also material sets are utilized for flex PCBs and also an immediate distinction is the dimensional homes. Inflexible printed circuits boards are usually many more dimensionally secure vs. the typical polyimide film made use of as the building block in 98% of the flex PCB made. This raised dimensional variability implies a flexible circuits requires various design guidelines than its stiff printed circuit board family member. However, a lot of the design software readily available usages rigid PCB design rules and this could create PCB manufacturing as well as functional problems for the flex PCB. Getting a flex PCB design ready for manufacturing is described some in the industry as “flexizing” the design.
The list below details top 5 of the much more typical methods “flexizing” makes a design many more robust, a lot more producible, and also all set for flex PCB manufacturing.
1. Firm joints as well near flex factor:
A solder joint is created by an intermetalic bond of the solder alloy to the copper trace. While the copper trace is normally flexible, areas that have actually been soldered become extremely inflexible and also stringent. When the substrate is bent near the side of the solder joint, the solder pad is either visiting break or peel. Either circumstance will certainly create significant practical issues.
The bottom line is that creating a flex PCB with typical PCB software program could cause some significant manufacturability and dependability problems. It is well to deal with your flex PCB manufacturers or a flex PCB design professional to either “flexize” the design prior to beginning fabrication or produce the layout straight from a net list. This will guarantee that the design can be manufactured to satisfy your needs.
2. Stress factors in conductors:
Because flex PCB is made use of in both fold to set up and also dynamic flexing applications, trace configurations that serve in an inflexible PCB may produce troubles in a flexible circuits. Conductor traces with sharp corners as well as severe points at the base of solder pads become all-natural “stress points” when the location near them is stretched. This can result in trace crack or delamination. A great flex PCB layout will have a smooth span for conductor turn factors (rather than sharp corners) as well as a gentile distance from the trace to the pad fillet as opposed to a sharp angle. Selective attachment of stiffeners will prevent bending in soldered regions and also is a typical design technique.
3. Spacing between solder pads and also surrounding traces:
Here is the tradeoff, i.e. design compromise, which will be made based on item # 1. When the coverfilm or soldermask openings are made larger, the sides of the nearby conductor traces could be exposed if they were transmitted also near to a solder pad. This can trigger shorts if solder bridges between connector pins or pads. Physical size of the flexible circuits is an additional factor that can affect registration capacity. In general more space is required between a solder pad and also a nearby conductive trace to fit the coverfilm or soldermask positioning resistance.
4. Stacked traces:
Traces on other sides of the dielectric need to not directly “stack” on each other. Traces in tension (outside of the bend radius) may crack when the flexible circuits is bent if they straight align in parallel with a trace on the contrary side. The traces in stress are forced further from the neutral axis of the folded region and also could fracture, especially with repeated bending. A good design technique is to maintain the copper in the neutral axis of a bend deliberately this region as a single conductive layer. When this is not possible, a proper design will certainly “surprise” the traces in between top and lower copper layers to avoid top and also bottom positioning.
5. Solder mask or coverfilm openings:
During the flex PCB manufacturing the flexible circuits can demonstrate dimensional modification after exposure to processes like pumice scrubbing up, copper plating, and/or etching. While some change can be accounted for, flex PCB design guidelines typically need larger resistances to accommodate succeeding registrations for coverfilm, supports, or pass away cutting. Added factor to consider is needed for the sticky squeeze out that takes place during lamination of the coverfilm dielectric. Making complex the prediction of making up design features is the myriad of procedures as well as sequences needed to create a custom flex PCB. The bottom line is the openings in the coverfilm normally need to enable even more space in a flex PCB design.