Solution to SMT grape ball phenomenon

Grape ball phenomenon , Generally, the solder paste is not fully fused and welded together , Instead, they gather into individual tin beads and stack them together , The formation of grape clusters .

SMT Causes of grape ball phenomenon

One 、 The solder paste is wet and oxidized

The main reason why the solder paste is oxidized by moisture is grape ball , Solder paste oxidation can be divided into many categories , For example, the personnel operate carelessly 、 Solder paste expired or stored improperly 、 Solder paste temperature recovery / Poor mixing , Cause moisture absorption of solder paste , Are possible causes of solder paste oxidation . Some steel plates ( network ) One of the possible reasons is that the solvent is not completely dried after cleaning .

Two 、 Solder paste flux volatilizes

The flux in the solder paste is an important factor affecting the melting of tin in the solder paste , The purpose of the flux is to remove the oxide on the metal surface , Lower the surface of the weld metal , In fact, another purpose is to coat the tin powder to protect it from contact with the air , If the flux volatilizes in advance , The effect of removing oxides on the metal surface cannot be achieved , Therefore, the solder paste shall be used up within a certain period of time after unpacking according to the regulations , Otherwise, the flux will volatilize and dry the solder paste . And if the preheating zone in the reflow is too long , It will make the flux volatilize excessively , The more chance there is of grape ball phenomenon .

3、 ... and 、 Insufficient reflow temperature

When the reflow temperature is not enough to provide the condition for complete melting of solder paste , The solder paste also has an organic grape ball phenomenon , The solder paste is printed on PCB If the amount of tin is less , The higher the chances of solder paste oxidation and flux volatilization , This is because the less solder paste is printed , The higher the contact ratio between the solder paste and the air , It is easier to cause grape ball phenomenon . So this is 0201 The components of will be 0603 The reason why the components of are more prone to grape ball phenomenon .

Solution improvement SMT The method of grapevine ball phenomenon ：

1. Use solder paste with better activity .

2. Increase the printing amount of solder paste .

3. Increase the opening width or thickness of steel plate to increase the printing volume of flux and solder paste , It can also improve the oxidation resistance of solder paste .

4. Shorten preheating time in reflow soldering curve , Increase the heating slope , Reduce flux volatilization .

5. Turn on nitrogen to reduce the oxidation rate of solder paste .

more SMT Industry technical knowledge , Query on the official website of Inter