The phenomenon of tombstone often occurs during the reflow soldering process of chip components (such as chip capacitors and chip resistors), and the smaller the component volume, the more likely it is to occur. Especially in the production of SMD components with the package 1005 and 0603, it is difficult to eliminate the phenomenon of tombstone . In the reflow soldering process of surface mount technology, the SMT components will produce defects that cause detachment due to tilting. In the reflow soldering process of surface mount technology, the SMT components will produce defects that cause detachment due to tilting, which is known as the tombstone phenomenon (i.e. Manhattan phenomenon).
The reason for this is that the surface tension of the solder paste on the solder pads at both ends of the component is unbalanced when refluxing and melting. There are seven main reasons for specific analysis:
1. Uneven heating, uneven temperature distribution in the reflux furnace, and uneven temperature distribution on the board surface
2. The problem with components is that there are significant differences in the appearance and size of the welding end, the weldability of the welding end, and the weight of the components is too light
3. The material and thickness of the substrate, the thermal conductivity of the substrate material, and the thickness uniformity of the substrate are poor
4. The shape and weldability of solder pads vary greatly, as well as the thermal capacity and weldability of solder pads
5. Solder paste. The uniformity or activity of the flux in the solder paste is poor, and the thickness of the solder paste on two solder pads varies greatly. The solder paste is too thick, resulting in poor printing accuracy and serious misalignment
6. Preheating temperature too low
7. Poor installation accuracy and severe component deviation
The phenomenon of tombstone is caused by the uneven surface tension between the solder pads at both ends of the component during reflow melting, and the end with the higher tension pulls the component to rotate along its bottom.
