SMT solder joint shape and its morphological parameters
The shape of the solder joint generally refers to the geometric size that the molten solder can reach along the metal surface at the welding junction of the component solder foot and the PCB pad, as well as the contact angle with the metal surface and the solder fillet shape. In short, it is the appearance and structure shape of the solder joint after forming. It is closely related to many factors such as the geometry and geometry of the solder feet and pads, the properties of the solder, the soldering temperature, and the amount of solder. The solder joint shape parameter is the geometrical characterization of the solder joint shape.
The shape of the solder joint generally refers to the geometric size that the molten solder can reach along the metal surface at the welding junction of the component solder foot and the PCB pad, as well as the contact angle with the metal surface and the solder fillet shape. In short, it is the appearance and structure shape of the solder joint after forming. It is closely related to many factors such as the geometry and geometry of the solder feet and pads, the properties of the solder, the soldering temperature, and the amount of solder. The solder joint shape parameter is the geometrical characterization of the solder joint shape.
The three-dimensional shape of the solder joint on the front end of the wing-shaped pin surface mount device QFP and the PCB. The main parameters of the solder joint morphology include the contact angle% of the solder on the pad metal surface, the contact angle of the solder on the solder end metal surface, but the fillet height H, length L, and width B.
There are many types of SMT solder joints, and the corresponding solder joint shapes also have various forms. The generalized SMT solder joint form also includes the solder joint form of chip scale packaging. For example, the solder joint form of MCM can refer to the bare chip when the IC bare chip of MCM and the substrate are interconnected by flip-chip soldering (FC: Flip-Chip). The geometry of the micro-welding bumps and welding joints produced on the above. The shape of the solder joint between MCM and PCB refers to the geometry of the joint between the pins of the ball grid array on the surface of the MCM and the PCB.
The relationship between solder joint shape and solder joint quality
Theoretically, when the main parameters that affect the shape of the solder joint are determined, the corresponding reasonable solder joint shape will also be uniquely determined. If one or more of the main parameters has a certain allowable range, the corresponding qualified solder joint shape will also change within the corresponding allowable range. If the shape of a solder joint exceeds this range, the quality of the solder joint must not meet the requirements, and there must be unreasonable or faulty links in the assembly and welding process. According to the different defects of the solder joint shape, the corresponding solder joint quality problem type and failure source can also be analyzed. This is the corresponding relationship between the solder joint shape and the solder joint quality. Based on this corresponding relationship, scientific prediction, design, analysis, and control of the solder joint shape are effective methods and approaches to detect and control the quality of SMT solder joints.