The orientation of the grain of the copper aluminum foil has a definite effect on the flexural life of a design. Grain instructions is of greatest importance with flex PCB layouts fabricated making use of Rolled and Annealed (RA) or typical Electro Deposited (ED) copper aluminum foil. With vendor-electroplated copper on sputtered movie, alignment is not as critical since there is no particular grain direction. The impacts of grain direction on flexural life can be substantial.
MAINTAIN FLEXURAL ARC SMALL
For optimal flex life, it is best to maintain the range of the flexural arc or complete angle of flexure of the circuit for dynamic designs as small as possible (that is, flex the circuit over the tiniest possible range). This is a vital strategy made use of in later design hard disk drive applications that enables them to accomplish the high flex life biking they currently show.
OFFER THE LARGEST BEND RADIUS POSSIBLE
Supplying the largest functional radius through bend locations is specifically important for dynamic flex, but it could likewise be important in flex PCB applications that are evidently fixed in nature. The graphic and also simple formula highlight the result of bend span size on the copper aluminum foil. As the calculation concludes, the elongation needs for the copper aluminum foil increase significantly as bend span decline.
STANDARDS FOR MINIMUM BEND RADII
Bending and bending are innate and sought-out attributes of flexible circuits. Getting the design right, nonetheless, needs focus on well established design methods and also typical, longstanding standards. Finite element evaluation (FEA) and also model-detail later on in this chapter.
For normal flexing of flexible circuits. For really high flex life dynamic flex circuit layouts, fabrication and testing of prototypes remains the preferred method of design verification.
CREASING AND FOLDING flex PCB
Wrinkling and also difficult folding of flex, while not a favored practice, can be effectively completed with some focus to particular information. When needed, the circuit ought to be bonded to prevent it from flexing back at the crease or fold line. Strain alleviation is additionally recommended. It is very important to keep the construction balanced for ideal flexural endurance life. The optimal copper for such stress flexing applications will be a lowstrength, high-elongation copper. Totally annealed soft copper is normally a great selection for applications calling for a tiny radius bend.
BENDING flex PCB TO HOLD SHAPE
When bending flex PCB items for fixed, form-to-fit applications, holding shape is a preferable condition. Nevertheless, often flex PCB has elastic memory, a condition that can be gotten over by complying with principles for forming flexible circuits to fit completely in their application, such as making best use of the metal area. Copper, or any other steel one may utilize for a conductor, will completely deform plastically when bent if its elastic limit is gone beyond.
Several polymers will certainly additionally permanently warp if their elastic limit is exceeded. Their limitation, nonetheless, is sometimes greater than that of metal (elastomers are usually omitted, though they could take a set gradually). Thus, when the composite structure that we currently call a flex PCB is curved, the metal foil has literally deformed, while the polymer is still most likely to be in its flexible variety.
OFFER METAL DOMINANCE IN BEND AREA
In order for the copper (or various other steel) to avoid the polymer from snapping back, it has to overwhelm the flexible memory of the polymer. Copper is stronger as well as higher in elastic modulus, however if the traces are little or the copper is a low percentage of the local area, the remnant flexible stress in the polymer might cause the flex PCB to fall back to its original level shape. This method approaches the practices utilized by flexible circuit manufacturers to preserve dimensional stability.
WIDEN CIRCUIT TRACES THROUGH THE BENDING ZONE
If circuit weight is a problem, the location of added copper can be localized. In such instances, the circuit attributes are widened in the area of the bend and then decreased in width once again as they get in as well as leave. Circuit traces should taper to the new width in both directions.
IDENTIFYING BEND AREA LENGTH
There is a simple technique to get a first-order approximation of the size of the bend area to which the traces are broadened. Identify the circumference of an imaginary circle having actually the desired bend span and multiply that result by the bend angle divided by 360 (i.e., the levels in a circle). This should guarantee that an enough amount of the bend location is loaded with the broader copper traces. Nevertheless, a little added size might be needed depending upon the building and construction.
USAGE THICKER COPPER IN BEND AREA
If broadening the traces alone does not help completely, after that a couple of analogous approaches could be taken into consideration: using a thicker metal aluminum foil or utilizing a thinner flexible base material.
The objective stays the same as they were in the first case, making certain that the steel can bewilder the polymer in order the hold the last shape. There are advantages and negative aspects to both paths. Making the copper thicker might make etching a little bit harder. It will certainly also take longer to engrave and make use of more chemistry. On the other hand, making the polymer thinner might make handling a little bit harder and the toughness of the final assembly will not be as excellent as the alternative method.
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