The melting time of solder paste at both ends of the component is not synchronized or the surface tension is different. Poor solder paste printing, misalignment, and different sizes of component solder joints can all cause the melted end of the solder paste to be pulled up.
The design of solder pads is also a factor that affects the phenomenon of monument formation. The extension length of solder pads has a suitable range, and if it is too short or too long, it is easy to cause monument formation.
Brushing the solder paste too thick may cause the components to float up after melting, which may also lead to the phenomenon of standing a monument.
Improper temperature curve setting is also an important reason for the phenomenon of standing monument. Standing monument generally occurs at the moment when the solder joint begins to melt, and the slower the heating rate near the melting point, the more conducive it is to eliminating the phenomenon of standing monument.
The oxidation or contamination of one solder joint of a component, which cannot be wetted, or the contamination of the solder pad, silk screen printing, solder mask ink, adhesion of foreign objects, oxidation, and other situations may also lead to the phenomenon of standing a monument.
To address the issue of monument placement, the following measures can be taken:
Reasonably design the solder pad to ensure that its external extension size is reasonable, and avoid the wetting angle of the outer edge of the solder pad formed by the extension length being greater than 45 °.
Select solder paste with high activity to improve the printing parameters of the solder paste, especially the window size of the template.
Adjust the parameters of the SMT machine to ensure that the components are evenly immersed in the solder paste, preventing uneven wetting force on both sides due to time differences.
Adjust the temperature curve for each product to ensure full melting of solder paste, minimize thermal stress on PCB components, and minimize or eliminate various welding defects.