PCBA Tech - About the coplanarity of SMT component pins

The use of SMT to mount components on the PCB surface has strict requirements on the coplanarity of component pins,because it directly affects the good contact between component pins and PCB pads, thereby affecting assembly and soldering performance.

When all the pin endpoints of the device are on the same plane,it has the closest contact with the PCB pad and better welding effect, but in fact,due to various factors such as manufacturing and transportation,all pin endpoints of the device are it is impossible to be on the same plane, and there will often be a certain coplanarity error.

1.Standard tolerance value of component pin interface

The standard tolerance value of pin coplanar of surface mount devices formulated by the Joint Electronic Devices Engineering Committee (JEDEC) is 0.1mm,which means that each pin of the device must be within the tolerance zone of 0.1mm.This tolerance zone consists of two planes, one is the PCB land plane,and the other is the plane where the device pins are located.

If the three lower points of all the pins of the device are on the same plane and parallel to the plane of the soldering area of the PCB, and the distance error between each pin and the plane does not exceed the tolerance range, the mounting and soldering can be carried out reliably, otherwise it may occur Welding failures such as false soldering and missing soldering of the pins.

The standard tolerance value of pin coplanar is 0.1mm, which is generally accepted by SMT assembly companies. At present, my country's electronic assembly industry is also following this standard. Practice has proved that when the pin coplanarity standard tolerance value is increased to 0.05mm, the assembly defect rate of the device can be reduced, but the device manufacturing cost and the coplanar inspection cost will both increase significantly.

2.The method of PCB component pin interface detection

There are many ways to detect the interface of component pins. The simplest method is to place the component on a plane and measure the value of the height of the pin that deviates from this plane in the most circular case. In the extension of this method, the components are placed on the optical plane, and the distance between the non-coplanar pins and the optical plane is measured with a microscope.

In fact, the high-precision placement systems currently in use generally have their own mechanical vision system, which can automatically detect the interface of component pins before placement, and can automatically detect components that do not meet the requirements of coplanarity. exclude.

The above is the relevant content about the interface of SMT component pins shared by the smt chip processing factory. If you need to know more about PCBA processing, SMT chip processing, COB bonding processing, post-plug-in welding processing, etc. For film processing related knowledge, welcome to visit the smt technical knowledge column of smt chip processing factory.