What is Solder Paste ?
Solder paste is a mixture of metal solder powder formed by mixing with flux that used 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 as well the electrical connections.
| IPC Type designation | Particle size (μm) |
|---|---|
| Type 1 | 150-75 |
| Type 2 | 75–45 |
| Type 3 | 45–25 |
| Type 4 | 38–20 |
| Type 5 | 25–10 |
| Type 6 | 15–5 |
| Type 7 | 11–2 |
| Type 8 | 8–2 |
Solder Paste Types
Solder Pastes for electronics is classified according the particle size of the solder balls by IPC standard J-STD 005.The metal particle size in solder determine the print quality of solder paste.
Type 4 normally considered best for solder pastes printing operations due to good printing quality.
Spherical shaped solder particle always help to reduced the surface oxidation recomonded for good quality solder joint in comparison of odd sapped particles.
To purchase best solder please check buying Guide of Best Solder for Electronics Repairing
Solder Paste storage conditions
Solder pastes must be stored in the original packaging in a cool place like fridge at the 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 label of the original package, shall not be used and must be removed from production.
The term for storing the paste outside of the fridge from the moment of its arrival from the warehouse until putting it 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.
Solder Paste how to use in PCB Assembly
To prepare the paste for the process of paste printing, 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. By the time you use it, the paste must have been stored at room temperature for at least 4 hours.
At the moment of opening the container with the paste, put the identification marking on the lid or on 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 with carefully..
How to handle and disposing 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 “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 the moment 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 into waste. Empty jars and tubes should be thrown away into a special 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 paste how to use soldering paste is important for safety point of view.
Purchasing Solder Paste
Solder Paste for electronics normally used bulk in commercial PCB assembly process but it is available to buy soldering paste in smaller quantities for small prototype assembly or personal works.
There are a lot of online web portals where you can buy solder paste online in packaging like cartage box, solder paste syringe or tubes.you can Oder as per your project requirements.
Soldering paste is very sensitive with temperature and humidity so solder paste how to use and store 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. If necessary, a camera is used, which is installed at the supervisor’s desk.
In the process of operation, the SPI machine is used for monitoring 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 jar that is tightly closed.
The acceptable relative air humidity in the production room in the area where the process of paste printing is taking place recomonded for best results: 45% + 5%, 45% -15% and air temperature: +23°C ± 2°С.
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