Dimensions and identification of component terminals on circuit boards

In order to assemble the components on the printed board reasonably, firmly and reliably, the span and spacing of the components on the printed board should be designed according to the size of the component terminals.

Components whose lead-out ends allow bending are called soft lead-out components. Such as resistors, capacitors and low-power transistors. Although the pin distance requirements of such components are not strict, the size directly affects component arrangement, appearance, and assembly density. Therefore, in order to make the arrangement of components well-proportioned and beautiful, the size of the terminal is very important. Since there are many specifications and different appearances of soft lead-out components, the designer should determine the pin size of the soft lead-out components according to the data given in the relevant manuals.

The span of the element: the span of the element is determined according to the size of the element. In typesetting, identical elements should have the same span. For elements arranged in squares, the span should be an integer multiple of the smallest square. For components arranged according to coordinates, although the contact positions on the printed board can be arranged flexibly, the span of each component should be as consistent as possible to facilitate mechanized production and the appearance of the board.

For axial lead-out components, such as diodes, resistors, etc., when the lead-out end is bent, the distance S between the bending point and the root of the lead should be equal to or greater than 2 times the diameter of the lead, and the bending radius r should be equal to or greater than the diameter of the lead d. Generally, at least 1mm interval is reserved on each side.

When determining the span, 2mm can be added according to the length of the element body, and the upper limit of the integer multiple of the square can be taken. The span of the components shown in Figure b is between the upper limit of 2cm and the lower limit of 1.75cm, which is an integer multiple of the square (2.5mm), and the upper limit of 2cm should be taken as the span. In order to ensure the utilization rate of the printed board and the appearance of the board without affecting the assembly strength of the component, the maximum span should not be more than 2 times the length of the component body, as shown in Figure c. The span of the unidirectional lead-out element can be equal to or slightly larger than the lead-out line itself. As shown in Figure a, the span can be 1.5cm. If the span is too large, it will affect the appearance of the board and occupy too much of the board; if it is too small, it will affect the stability of the components. The maximum span should not exceed one quarter of the diameter (or length) of the body, as shown in Figure b. For elements arranged in squares, the span should be an integer multiple of the squares.

Dimensions and identification of component terminals on circuit boards

Spacing of components To facilitate assembly and improve assembly density, the spacing of components should be reasonably arranged. Generally, the minimum spacing is equal to the sum of the radius (or half the thickness) of adjacent components plus the safety gap b (b is 200V/mm). When determining the spacing of components, the following factors should also be considered: the power resistor should be placed in a place where it is easy to dissipate heat and away from the thermal element; larger devices should pay attention to their tolerance effects. Taking into account the above factors, the spacing of components should be larger, but at the same time, the appearance of the board should be considered. In general, larger components require slightly larger spacing.

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