When SMT processing, it is generally necessary to consider the existence of certain errors during machine installation, and to facilitate maintenance and visual inspection. Adjacent binary device bodies should not be too close, and a certain safety distance should be left. So how close are the two components?

In addition to ensuring a safe distance between pads that is not easily short circuited, the maintainability requirements for vulnerable components should also be considered.The general assembly density requirements are as follows:

(1) 1.25mm between chip components, between SOTs, and between SOICs and chip components;

(2) 2mm between SOICs and between SOICs and QFPs:

(3) 2.5mm between PLCC and chip components, SOIC, QFP:

(4) 4mm between PLCC.

(5) When mixed assembly, the distance between the plug-in component and the chip component solder pad is 1.5mm.

(6) When designing PLCC sockets, attention should be paid to leaving aside the size of the PLCC socket body (as the pins of PLCC are located on the bottom inner side of the socket body).

Component layout rules

Under the conditions of design permission, the layout of meta components in SMT processing should strive to arrange similar components in the same direction, and modules with the same function should be arranged together as much as possible; Components with the same packaging are placed at equal distances for easy assembly, welding, and testing of components.

Safe distance between component bodies

QFP, PLCC. The common feature of these two devices is the four sided lead packaging, but the difference is that the lead shape is different. QFP is a gull wing lead, and PLCC is a J-shaped lead. Due to the four-sided lead packaging, the wave soldering process cannot be used.

QFP and PLCC devices are usually placed on the component surface of the PCB board. To perform secondary reflow soldering on the soldering surface, their weight must meet the requirement that the load-bearing capacity of the solder corner contact surface should be less than or equal to 30 grams per square inch.