PCBA is transported through guide rail when SMT is processed, so it is necessary to set aside a pair of sides of cloth forbidden elements as transmission edges in PCBA design. In the electronic processing factory, the two long sides of PCB or the big board after assembly are usually taken as the transmission sides. Now let's introduce the technology side to you.
It is suggested that the limit of SMT is 3.0 mm. It is suggested that 5.0 mm should be used as the "no cloth area" of the conveying side.
If the cloth ban allowance is insufficient, the interference part will affect the solder paste or the components already placed after the PCBA is installed on the transmission guide rail. The interference part of the board edge can only be post welded or need to be made with another fixture, which will increase the production cost.
If the part is far enough away from the edge of the plate and will not be in the track range, there is no need to process another process edge. If the part is in the track range, the process edge must be added, and the process edge is used as the clamping edge area. According to the characteristics of the machine, the width of process edge usually needs 3-10 mm, and 5 mm is the most common.
Generally, the process side is added to the longer side, and the board enters the SMT machine vertically. In this way, the hardness of the board is relatively high, and it will not bounce due to the light pressure of the machine probe. However, the area of the process side of the lengthened edge is more, which in a disguise increases the average price of a single plate. If the hardness of the plate is enough, it can be added in the short direction, the process side area is small, the average cost of a single plate is reduced, and the board enters the SMT machine horizontally.
Mark points are usually used to align Mt. if there is no mark point in the plate, 2-4 mark points must be added diagonally at the process edge. The mark points are generally 1.0 mm in size and exposed copper and tin. In some cases, the process edge can be added or not added.
In the production of PCBA substrate, positioning is needed for forming and testing. Adding a special positioning hole in the process side, the shape is relatively standard, and positioning is more convenient. Therefore, 3-4 positioning holes with diameter of 2.0-4.0 mm will be added to the process side, and the diameter of 3mm is the most common.
