Control PCBA Soldering Problem at Source
-Preservation and Use of Solder Paste
Storage of solder paste
Solder paste should be stored in the refrigerator, its temperature should be controlled in 0℃ -10oC 0 range. Refrigerator temperature should be measured once per shift and recorded. SMD solder paste storage found beyond the control of temperature control, must be dealt with immediately.
1. Validity of solder paste: when sealed at 0℃~10℃, valid for 6 months. Storage at room temperature (25 ℃±3 ℃) is valid for one month.
2. The new solder paste is labeled, dated and filled in before it is placed in the refrigerator.
3. After the solder paste is unsealed, the placement time shall not exceed 24 hours. The solder paste must be sealed and stored in a cold storage in a clean, pollution-free bottle.
4. At the end of production or stop printing for some reason, the remaining solder paste on the steel mesh shall not be placed for more than 1 hour.
5. When printing stopped, the remaining solder paste should be used in a clean bottle, sealed and refrigerated separately. The remaining solder paste can only be used once in a row, and then the remaining solder paste should be scrapped.
Return temperature of solder paste
solder paste must be warmed back before use. The so-called return temperature is to put the solder paste at room temperature to make its temperature rise naturally to meet the requirements of use. There are two purposes of rewarming: take out from the refrigerator without rewarming directly, the outside hot air will condense into water droplets on the surface of the solder paste, and solder beads will be produced when the solder furnace is over welded; the solder paste has a high viscosity at low temperature and can not meet the printing requirements. It must be reheated before it can be used. solder paste removed from the freezer must be placed at room temperature (2~4 hours) to 25℃ before opening.
Stirring of solder paste
solder paste is a mixture of lead and solder in paste form. Before putting the solder paste into the printing machine, it is necessary to stir fully so that the flux and solder powder can be mixed evenly. The stirring time of the machine is about 3~5 minutes, depending on the mixing mode and speed.
Use of solder paste
1. The use of solder paste should follow the "first in first out" control, so it is numbered when the paste is fed.
2. It is advisable to add solder paste every 1 hour during use. Seal the solder paste bottle in time to avoid contact with air. The PCB after printing must be patch within one hour, after IR, or scrape, ultrasonic cleaning and reprint. After 8 hours, the solder paste in use on the steel plate and the opened solder paste should be put back into the solder paste bottle and stirred again. Generally about 5-6 minutes.
Finally, SPI solder paste inspection machine is the best tool to check solder quality.
Attention: If the solder paste accidentally touched hands and feet, should be immediately washed with soap, water, do not rub with the hand, a small amount of residue can be scrubbed with alcohol.