Analysis of plate assembly in PCB plate design

In order to achieve maximum production and minimize costs, PCB plate design should take into account certain restrictions. Moreover, human factors should be taken into consideration before embarking on the design work. These factors are detailed below:

1, the wire spacing is less than 0.1mm will not be able to carry out the etching process, because if the etching liquid can not effectively spread in the narrow space, it will cause some metal can not be etched.

2 if the wire width is less than 0.1mm, fracture and damage will occur in the etching process.

3. The size of the pad should be at least 0.6mm larger than the size of the hole.

The following restrictions determine the design method of the panel:

1, for the production of the original film remake, camera size performance;

2, the original tabulation size;

3 minimum or maximum circuit board operation size;

4 drilling accuracy;

5, sophisticated linear etching equipment.

In the design, from the assembly point of view of the PCB board, consider the following parameters:

1 the diameter of the hole shall be determined according to the maximum material condition (MMC) and the minimum material condition (LMC). The diameter of the hole of a non supporting component should be selected such that the MMC of the pin is subtracted from the hole MMC, and the difference is between 0.15 -0. and 5mm. Also, for the ribbon pin, the nominal diagonal of the pin and the bore diameter of the unsupported bore shall not exceed 0.5mm, and shall be no less than 0.15mm.

2, reasonable placement of smaller components, so that it will not be covered by larger components.

3. The thickness of solder resist shall be no more than 0.05mm.

4, screen printing mark and any pad can not intersect.

5, the upper half of the circuit board should be the same as the lower half, so as to achieve symmetrical structure. Because the asymmetrical circuit board may bend.

From the point of view of the assembly of printed circuit boards, one important factor to consider is that particular attention should be paid to short-circuit problems that may be caused by the insertion of the components and their theoretical positions prior to welding. According to experience, the maximum allowable inclination of the component pins shall be maintained at 15 with the theoretical position. Within the angle. When the diameter difference between the hole and the pin is large, the inclination can reach up to 20 degrees. Vertically mounted components can achieve a slope of 25. Or 30 degrees, but this will lead to a reduction in package density. Figure 3-13 is a TO-18 type transistor at different pin gradient of the package diagram, TO-I8 type transistor installation position from the printed circuit board 2mm, if the aperture is Imm, the inclination can reach 20 degrees, of course, the pin itself without any inclination.

A plurality of circuit board assembly usually makes on-site maintenance as will be pulled out of the circuit board to be replaced as easy, of course, the prerequisite is independent of each circuit board can exercise its unique function, so that the replacement of the circuit board will not have a lot of demolition, ensure the welding / sealing off the least number of. Therefore, the design of a printed circuit board must take into account its maintainability.

The welding techniques and equipment needed for assembly also add many limitations to the design and layout of the circuit board. For example, in wave soldering, the maximum size of the groove, the distance to the edge, and the space to operate are important factors. At the same time, the designer has to be as conscious as possible about what the final product should look like and try its best to protect its most sensitive parts.