Tutorial For The Rigid Flexible PCB Design Elements Difference

Most of the design elements of rigid PCBs have been applied to the design of flexible PCBs.

However, other elements need attention.

1. Current carrying capacity of the wire

Because e flexible printed circuit boards have poor heat dissipation (compared to rigid printed circuit boards), sufficient wire width must be provided. When large current-carrying wires are placed face to face or close to each other, additional wire widths or spacing must be given to allow for heat concentration.

2. Shape

Wherever possible, rectangles should be preferred because they save on the substrate. Adequate free margins should be left near the edge, depending on the amount of space available in the substrate.

In shape, the inner corners should look round; The sharp interior angles may cause tearing of the plate.

Smaller wire widths and spacing should be minimized. If geometrical space permits, the tightly arranged thin wires should become wide. Conductors terminating at plated through holes or component mounting holes should run smoothly through the pads. As a general criterion, any variation from a straight line to an image Angle or different line widths must be as smooth as possible. The sharp Angle will naturally concentrate the stress and cause the conductor to fail.

3. The flexibility

As a general criterion, the bending radius should be designed as large as possible. Using a thinner laminate (e.g., 50μm copper foil instead of 125μm copper foil) and a wider wire better increases the likelihood that it will withstand more cyclic bending. For a large number of bending cycles, single-sided flexible printed circuit boards generally show better performance.

4. Solder pad

Around the pad, there is a change from a flexible material to a rigid material. This area is more prone to conductor breakage. Therefore, pads should be avoided in areas prone to bending. The general shape of the pad should be like a teardrop, and the film must cover the joint of the pad.

5. Rigid reinforcement

In the mass production of small electronic devices such as small calculators, flexible printed circuit boards with rigid laminated stiffeners bonded to them have become popular and are more cost-effective.

The flexible PCB is equipped with a rigid plate (e.g. Grade G-10) with suitable slots to facilitate later separation. After component assembly and wave soldering, the rigid plate is cut into different sections so that it can be easily folded into the desired shape.

These particular requirements indicate that there are only a few steps to design flexible plates, far fewer than to design rigid plates. However, its important design differences must be kept in mind:

1) The three-dimensional space of flexible printed circuits is important because bending and flexibility applications save space and reduce laminates.

2) Compared with rigid plates, flexible plates have lower tolerance requirements, allowing a wider tolerance range.

3) Because the wings can bend, they are designed to be slightly longer than required.

To minimize circuit costs, the following design techniques should be considered:

1) Always consider how the circuits are assembled on the panel.

2) the circuit should be small, should consider using a series of small circuits instead of a large circuit.

3) Follow the recommended usage tolerances at all times.

4) Design element bonding areas only where necessary.

5) If the circuit has only a few layers, it is much cheaper to use a stiffener than a rigid-flexible printed circuit.

6) Specify a 0.0001 in a binder for each oz of copper-clad material (including electroplated copper).

7) It is sometimes cheaper to make circuits with no shielding pads and no overlay.