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What should be paid attention to when designing a flexible circuit board?

Release time: 03/11/2018

The advantage of the flexo plate is that it can be assembled to where it needs to be bent. However, for the flexo plate, its performance is affected by the number of bends and the environment. In many cases, it cannot be used repeatedly, and the flexible board can be found. Designed are relatively simple lines. At present, the design of many circuits is based on the design of existing packaged devices. There is also a problem in soldering the devices on the flexographic plate. It is necessary to ensure the bendability of the board and ensure good soldering of the device. contradictory. For devices such as BGAs, it is not possible to design on a flexible board, and its high density determines that it can only be used on rigid printed boards. Therefore, when a rigid part is required when a flexible board is required, it is designed as a rigid-flex board.

Most of the design elements of rigid printed circuit boards have been applied to the design of flexible printed circuit boards. However, there are still some places that require special attention.

1. Current carrying capacity of the wire

Because flexible printed circuit boards have poor heat dissipation (compared to rigid printed circuit boards), sufficient wire width must be provided. When some wires carrying large currents are placed face to face or adjacent to each other, additional wire width or spacing must be given in consideration of the problem of heat concentration.

2. Shape

  The rectangle should be preferred wherever possible, as this would result in better substrate savings. There should be enough free margins near the edges, depending on the possible remaining space of the substrate. In shape, the inner corner should appear to be circular; the pointed inner corner may cause tearing of the panel. Smaller wire widths and spacing should be minimized as much as possible. If the geometric space allows, the thin wires that are closely packed should become wide wires. Wires that terminate at the plated through holes or component mounting holes should be smoothly searched into the pads. As a general standard, any change from straight line to image angle or different line width must be as smooth as possible. Sharp corners cause stress to naturally concentrate, causing wire failure.

the design of flexible printed circuit boards

3. Flexibility

  As a general standard, the bend radius should be designed to be as large as possible. The use of thinner laminates (for example: replacing 50 μm copper foil with 50 μm copper foil) and wider conductors can better increase the likelihood of more cyclic bending. For a large number of bending cycles, single-sided flexible printed circuit boards usually show better performance.

4. Pad

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

5. Rigid reinforcement board

  In the mass production of small electronic devices such as small calculators, flexible printed circuit boards incorporating a rigid laminated laminate have become popular and are also more cost effective. The flexible printed circuit board is mounted on a rigid board (such as gradeG-10) with suitable slots for future separation. After component assembly and wave soldering, the rigid plate is divided into different sections by cutting to facilitate folding into the desired shape.