SMT solder paste preservation method and correct usage

SMT solder paste preservation method:

First,solder paste preservation: Since the solder paste is a chemical product, it must be stored in a 5-8 degree refrigerator. The advantage is to reduce the activity of the chemical flux in the solder paste and prolong the service life of the solder paste. Placing solder paste at a high temperature will cause the solder paste to undergo a qualitative change,so it’s prohibited to let it in high temperature.

Second, solder paste return temperature: solder paste activity is greatly reduced during refrigeration, so put the solder paste at room temperature 2-4 hours before usage, restore its activity to achieve the best welding state.

Third, solder paste stirring:

a. Stirring is to uniformly mix the tin powder in the solder paste with the flux, but if the stirring time is too long, the shape and even the viscosity of the tin powder may be destroyed. The general stirring time is about 2 minutes.

b. If the solder paste surface produces a hard block before stirring, remove the surface hard block then can be used.

SMT solder paste usage method:

The basic principle of using solder paste: reducing contact with air, the less the better. When the solder paste is in contact with air for a long time, it will cause oxidation of the solder paste and imbalance of the flux composition. The consequences are: solder paste appears hard skin, hard block, refractory and a large number of solder balls.

How to use a bottle of solder paste multiple times:

1. Open cover time should as short as possible: open the cover. When taking out enough solder paste, cover the inner cover immediately. Do not take a little bit, open the cover frequently or always open the cover.

2. Cover the cover: After removing the solder paste, immediately cover the inner cover, press down firmly, and squeeze out all the air between the cover and the solder paste to make the inner cover and the solder paste in close contact. After making sure that the inner cover is pressed, screw on the outer cover.

3.The solder paste taken out should be printed as soon as possible: the solder paste taken out should be printed as soon as possible. The printing work should be continuous without stopping, and all the PCB boards to be processed should be printed in time, and placed on the workbench to wait for the surface-mounted components. Do not print sometimes and stop sometimes.

4. Disposal of excess solder paste that has been taken out: After all printing is completed, the remaining solder paste should be recycled to a special recycling bottle as soon as possible and stored separately from the air. Never put the remaining solder paste back into an unused solder paste bottle! Therefore, when using solder paste, it is necessary to accurately estimate the current used amount of solder paste, take out as much as required.

5.The problem of handling: If the surface of the solder paste has been crust, hardened, do not stir! Be sure to remove the hard skin and hard block. The remaining solder paste should be tested before it is officially used. If the trial effect is not good, you can only scrap it.