Tomb stone effect forms in the process of convection soldering,the surface tension of the solder paste is not balance in both of the chip’s ends.The components erect part or completely which we call it as Tomb effect or Draw-bridging effect.
It is often occur Tomb stone effect in the process of reflow soldering,the smaller the component is,the easier it occur,such as the components 1005 or 0603,it is very difficult to avoid Tomb stone effect.
The Tomb stone effect occur in two ends of component when the solder paste is melted because of the imbalance surface tension.There are many reasons why surface tension is imbalance,let us talking about it as the following:
1.When the preheating temperature is too low and preheating time is short,the probabilty will increase obviously which lead to imbalance surface tension between two ends of the component.So we should set the preheating process correctly,the preheating temperature is normally 150±10℃,preheating time is between 60 seconds and 90 seconds.
2.The size of solder plate.When we design the chip,we should keep the chip symmetry in order to get a good solder ponit.It is easy to slide if the chip is too wet.
3.The thickness of the solder paste.The thinner solder paste is,the smaller probability Tomb stone effect is.Because thinner solder paste has smaller surface tension.
4．The components are not mounted correctly.
5.The lighter components have high probability Tomb stone effect.