Application of Solder Paste in SMT

Application of solder paste in SMT – Learn what solder paste is and how to use it to solder SMD electronic components onto PCB.
Here, we will learn about solder paste and its application in SMT. What is solder paste and how to use it?
1. What is solder paste?
2. Lead free solder paste
3. Silk screen printing machine
4. Solder paste mold
5. Availability of solder paste
6. How to obtain the best solder joint
What is solder paste?
The solder paste is just a suspension of fine solder particles in the flux. In the electronic industry, SMT uses solder paste to solder SMD electronic components to printed circuit boards.
The composition of the particles can be adjusted to produce a paste with the desired melting range. Other metals can be added to change the composition of the paste for special applications. The size and shape of particles, metal content and type of flux can be changed to produce slurry with different viscosity.
lead-free solder paste
With the implementation of RoHS (Restriction of Hazardous Substances) in the electronic industry in the EU and many other countries, most electronic companies are turning to lead-free. Lead free solder wire and solder paste are manufactured with different compositions and proportions. But the most popular and widely used ingredient and proportion is SAC (tin silver copper), which is 96.5% tin+3.0% silver and 0.5% copper.
The melting point of lead-free solder is higher than that of traditional 63/37 or 60/40 tin lead solder. Moreover, the luster of solder joints is not as good as that of tin lead solder
Screen printing machine
When selecting a screen printer for solder paste, some of the main functions to consider include the maximum size of the SMT PCB that can be processed, accurate screen alignment and repeatability control of printing, and the circuit board pressing mechanism.
Significant progress has been made in paste dispensers, sieving and templating pastes on substrates. Each method of dispensing solder paste has its advantages and disadvantages, but the most widely used method is used in rework and mass production.
Solder paste mold
There are three main methods for making templates:
1. Chemical etching
2. Laser cutting
3. Electroforming
Chemical etching is the oldest, most widely used and cheapest option. Laser cutting and electroforming, especially the latter, are attractive in applications where precision is critical. In addition to the type of formwork, the type of scraper is also important. Metal scrapers are widely used because they require less maintenance than rubber scrapers.
Solder Paste Availability
Solder paste has two forms: lead (with lead) and lead-free (without lead). It can be wash free or water-soluble. It is not necessary to clean the circuit board after soldering when using the wash free solder paste. Water soluble solder paste is easily soluble in water and harmless.
How to get the best solder joint
In order to obtain good printing effect, correct welding materials, correct tools and correct process must be combined.

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