Flexible PCBs Be Folded Or Creased
Many of the same rules that apply to rigid PCBs also apply to flex and rigid-flex circuits. The most important factor to consider when designing a flex PCB is the amount of bending it will undergo during use. The circuit must be able to bend and twist without cracking or damaging the copper traces. This will typically require the use of a flexible material and an appropriately configured design.
A flexible pcbs can be either a single- or double-sided board, with either a single or two layers of copper on each side of the dielectric. Single-sided flex circuits are the most common, while double-sided boards are used to accommodate high density surface mount components and more complex designs. Both types of flex circuits are fabricated using a thin polymer or polyimide film as the base.
The conductor layer is typically made from electro-deposited (ED) or rolled and annealed (RA) copper foil. The RA method produces a smooth, flat copper foil with a column-array structure that is accessible to both roughening and etching processing. ED copper, on the other hand, has a fish scale texture and is inaccessible to both roughening and etching. To achieve the best balance between flexibility and conductivity, it is often necessary to use both RA and ED copper in a hybrid design.
Can Flexible PCBs Be Folded Or Creased?
In addition to the thickness of the substrate, a key consideration is how much stress will be placed on the copper when the flex circuit is bent and twisted. The flex circuit manufacturer will perform a stress analysis to determine how the board will react in different positions and will set a minimum bend radius based on these results.
The best way to minimize stress on the traces is by minimizing the number of folds and by using wide traces in bending areas. This will spread the load over a larger area and reduce the probability of damage during assembly. It is also a good idea to route traces perpendicular to the bending direction whenever possible and to avoid transition layers in bending zones.
Another way to reduce stress is by incorporating alignment features like notches or registration marks into the design, as this will help ensure accurate folding and alignment during assembly. Finally, if any folded sections are expected to be stressed during assembly, the design can be modified to include pad fillets or additional reinforcement in these areas.
Some flex circuits have mechanical stiffeners added to their outer layer to increase their resistance to bending and humidity. In some cases, shielding can also be added to the flex circuit to prevent electromagnetic interference and protect against environmental factors. Finally, it is always a good idea to create test prototypes of the flex circuit and physically fold and unfold them. This can help identify any unforeseen issues that may arise and allow the design to be modified before production begins.
