What is Solder Paste?
Solder paste is a mixture of metal solder powder formed by mixing with flux to connect printed circuit board pads with electronic components. The metals in the solder pastes are generally Tin, Lead, Silver, and Copper.
After solder paste printing of PCB, the Solder pastes temporarily holds the components in place and, after heating and melting, forms the mechanical bonds and electrical connections.
Solder Paste Types?
Solder Pastes for electronics are classified according to the particle size of the solder balls by IPC standard J-STD 005. The metal particle size in solder determines the print quality of solder paste.
Type 4 is usually best for solder pastes printing operations due to good printing quality.
Spherical-shaped solder particles always help reduce the surface oxidation recommended for good quality solder joint compared to odd sapped particles.
|IPC Type designation||Particle size (μm)|
Solder Paste storage conditions
Solder pastes must be stored in the original packaging in a cool place like a fridge at temperatures of +4ºС to +10ºС or as per manufacture guidelines.
The maximum storage life of solder paste is specified on the package. The solder paste with the expired storage life period specified on the original package label shall not be used and must be removed from production.
The term for storing the paste outside the fridge from the moment of its arrival from the warehouse until it is put into the fridge at the production division must not exceed 4 hours.
Put new pastes into the fridge, using the FIFO principle. If the paste is stored in packages or boxes, the usable shelf life of the paste is specified on the front wall of each package.
How to use Solder Paste
To prepare the paste for the paste printing process, the supervisor takes the amount of paste required for one shift from the fridge and puts it into the buffer of pre-prepared paste.
On all jars, it is required to mark down the date and time of taking them (taking the paste) out of the fridge. The paste must have been stored at room temperature for at least 4 hours when you use it.
When opening the container with the paste, put the identification marking on the lid or the side of the jar or a tube and specify the date and time when opened. Before applying it to the stencil, mix the paste in the jar using a blade carefully.
Never put back opened container with paste into the fridge !!!
The paste removed from the stencil for washing the stencil while transferring the line to a different product or during a stoppage of production should be put back into the jar (which must be closed tightly). This paste can be used within 72 hours, mixed with some fresh paste.
How to Handle and disposing of waste solder paste for SMD
The paste shall be removed from the stencil with the help of a scraper (a blade) into a separate container of “solder paste residues” if the line has been stopped or if it cannot be used on other lines.
The term for using the paste from when a jar or a tube has been opened is 72 hours.
The paste that has been on the stencil for more than 8 hours without adding fresh paste should be disposed of as waste. Empty jars and tubes should be thrown away into a particular container ( Dangerous waste).
Safety Guidelines when dealing with Solder Paste
When using soldering paste for electronics, follow safety guidelines in accordance with safety data sheets received along with Purchasing Solder Paste.
Safety data sheets must always be available on printing machines. So solder pastes how to use soldering paste is important from a safety point of view.
Purchasing Solder Paste
Solder Paste for electronics is usually used in bulk in the commercial PCB assembly process. Still, it is available to buy soldering paste in smaller quantities for minor prototype assembly or personal works.
There are a lot of online web portals where you can buy solder paste online in packaging like cartage boxes, solder paste syringes, or tubes. You can Oder as per your project requirements.
To purchase the best solder, please check buying Guide of
Soldering paste is very sensitive to temperature and humidity, so solder paste is used, and storing is very important for product life.
Solder Paste Printing quality control
The quality of the print, i.e., of the application of soldering paste for smd on the surface for soldering, is evaluated by the operator on the 1st board visually. A camera is used and installed at the supervisor’s desk if necessary.
In the operation process, the SPI machine monitors the quality of applying the paste. A typical process flow of SMT Line as per below
The control over the time of the soldering paste being on the stencil is done with the help of the watch. If the standstill lasts for over 1 hour, it is forbidden to use the paste in the production process, and it should be removed into waste if the process of paste printing is done with the help of the blades.
If the production stoppage is expected to last for over 1 hour, a stencil should be washed, and the paste should be removed into a tightly closed jar.
The acceptable relative air humidity in the production room in the area where the process of paste printing is taking place is recommended for best results: 45% + 5%, 45% -15%, and air temperature: +23°C ± 2°С.