In the design of printed circuit board should first determine the arrangement of components and installation methods. The elements of the layout of the elements, the elements as far as possible in a regular arrangement to get a uniform assembly density. High-power components should also be arranged around the thermal components, and other components to have enough distance. The heavier components should be placed close to the printed circuit board support point. Elements are arranged in the direction and density of air convection. Components should be arranged in a straight line in electrical order, and strive to compact to shorten the length of printed wire. If the circuit must be divided into blocks due to the board size limitation or due to the shielding requirements, each printed circuit board should be made as a separate functional circuit. To facilitate individual adjustment, testing and maintenance. In this case, the lead-out of each printed circuit board should be minimized.

1. Arrangement of components
Components in the printed circuit board arranged in three ways, that is, irregular arrangement, coordinate arrangement and grid arrangement (or coordinate grid arrangement).
① irregular arrangement Arrangement is the element in the printed circuit board plane can be arranged in any direction. Although this arrangement appears to be somewhat messy in appearance, it has certain advantages in meeting its electrical characteristics. The use of irregular arrangement is mainly to reduce the length of the printed wire, the wiring length of the components in order to achieve the purpose of reducing the wiring inductance and distribution parameters. So this arrangement is suitable for high frequency (30MHz or more) circuit. Another advantage is that the use of printed circuit board is high, and is conducive to reducing the high-frequency signal in the transmission of the loss.
② coordinate arrangement. In the coordinate arrangement, the axial direction of the component is parallel or perpendicular to the printed circuit board. When the printed circuit board is not rectangular, the axial direction of the element is parallel to or perpendicular to the sides of the printed circuit board or the side of the printed circuit board. The advantages of coordinate arrangement is neat appearance, easy to check and repair, commonly used in low frequency (30MHz below) the circuit.
③ square grid components and printed circuit board around the vertical or vertical, and the components of the threading hole are located in the intersection of the grid. A grid (grid) is an orthogonal grid of two parallel equidistant lines. For determining the connection position on the printed circuit. There is no uniform stipulation in the international grid. International Electrotechnical Commission (I.E.C) provides grid spacing of 2.54mm, China in the national standard (GB.1360-78) provides that the basic grid is 2.5mm. When you need to use a smaller grid spacing, you should set the auxiliary grid. The spacing of the auxiliary lattice is one quarter of the basic lattice spacing (0.625 mm) or one half (1.25 mm). When the grid spacing is required to be smaller than 0.625 mm, 0.1 mm or 0.1 x 10-n mm (n = 1, 2, 3, ...) can be used. When the grid is arranged, the span of the component is determined by its length, but it should be an integer multiple of the basic grid. In addition to the lead hole of the component, other holes in the plate (structural holes, process holes, positioning holes, etc.) should also be located at the intersection of the grid. The advantages of grid arrangement are: neat appearance of the components; easy to find the test point when the maintenance; printed circuit board processing hole is easy and accurate; easy to use mechanized assembly.

2. Component layout requirements
① components to be distributed evenly, the same density, the direction of arrangement and density should be conducive to air convection.
② components should be placed on the component surface, unless the adjustment or other reasons, generally do not lay on the welding surface components.
③ each component of the end, there should be a separate threading hole, generally do not allow the two components of the end of a pinhole hole sharing.
④ plate components should not be three-dimensional cross and overlapping installation, the components used coordinates and grid arrangement, should be arranged neatly, the same components of the end span to be as consistent as possible, except when the printed wire cross is difficult, but still Should be arranged according to a certain ratio of grid distance and pitch ratio.
⑤ the distance between the elements of the threading hole to choose the right, should not be between the components of the shell collided, or make the shell and the components of the end of the collision. Between the component shell or between the feet should be guaranteed to leave a certain safety gap, the safety gap can be based on the component operating voltage of 200 volts per millimeter.
⑥ double-sided printed circuit board components should be arranged as little as possible on the printed wire. Components of the shell, especially the components of the ground shell, should be careful to avoid collision with the printed wire caused by short circuit.
⑦ When the printed board is mounted upright, the components of the larger volume should be placed in the axial direction of the component and the horizon, so that the components in the transport and movement have better mechanical strength.
⑧ components of the installation height should be reasonable, the same height should be consistent. For the power of the larger resistance, do not use close to the floor installation.
⑨ larger volume of components, fixed on the printed circuit board, can not rely on its own end of the fixed, but should be fixed with a metal bracket. And installed near the printed circuit board support point, so that the warpage of the circuit board to a minimum.
⑩ high-power heating elements should not be arranged around the thermal components, poor heat resistance components should be installed in the air upstream (entrance). Dissipative power, good heat resistance components should be installed in the air flow downstream (exit).