There are lead solder paste and lead-free solder paste
As the name suggests, lead solder paste is a component containing lead, which is very harmful to the environment and the human body, but the welding effect is good, the cost is cheap, and it is suitable for some electronic products with no requirements for environmental protection. Lead-free solder paste is a component that contains only trace amounts of lead, which is less harmful to the environment and the human body, and belongs to environmental protection products, which are suitable for electronic products with environmental protection requirements.
Two, high temperature solder paste, medium temperature solder paste, low temperature solder paste
1. High temperature solder paste: generally refers to lead-free solder paste, solder paste melting point is generally above 217℃, SMT patch processing shows good welding effect.
2. Medium temperature solder paste: generally refers to lead-free medium temperature solder paste, solder paste melting point is generally about 170℃, medium temperature solder paste is characterized by the use of imported special rosin, good adhesion, can effectively avoid collapse.
3. Low temperature solder paste: the melting point of the solder paste is generally about 138 ° C, and the low temperature solder paste is mainly added with bismuth. When the components of the patch cannot accept the temperature of 200 ° C and above, and there is the demand for SMT reflow soldering process, low temperature solder paste can be used for welding process.
Second, the particle size of tin powder
According to the size of the particle diameter of tin powder, tin powder can be divided into 1, 2, 3, 4, 5, 6, six grades, of which the most commonly used is 3, 4, 5 tin powder. The finer the product, the requirements for tin powder will be smaller, but the smaller the tin powder, the corresponding will increase the oxidation area of tin powder.
The commonly used solder paste in the patch process has the following types:
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1. Lead-free solder paste for welding: mainly composed of Sn, Ag, Cu and other metal elements, does not contain lead, meets environmental requirements, and is suitable for the production of electronic products.
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2. Lead tin alloy solder paste for welding: the main composition is Sn, Pb and other metal elements, suitable for some electronic products with low environmental protection requirements.
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3. High temperature lead-free solder paste: the main components are Sn, Ag, Cu and other metal elements, with high melting point and high temperature resistance, suitable for some electronic products that need to withstand high temperature environment.
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4. Low temperature lead-free solder paste: the main composition is Sn, Ag, Cu and other metal elements, with a low melting point, suitable for some temperature-sensitive electronic products.
According to the melting point is divided into high temperature, moderate and low temperature three.
Commonly used high temperature tin silver copper 305,0307. Medium temperature tin bismuth silver, low temperature is commonly used tin bismuth, in SMT processing according to the different characteristics of the product to choose.
The commonly used solder paste in the chip circuit includes lead-free solder paste, semi-lead-free solder paste and leaded solder paste.
Among them, lead-free solder paste is the most popular option under the current environmental requirements, and it does not contain lead ingredients, so there is no problem of lead pollution.
However, lead-free solder paste requires high temperature heating, and the strength and toughness after welding are poor.
Semi-lead-free solder paste Add a small amount of lead on the basis of lead-free solder paste to improve the strength and toughness after welding, while avoiding the problem of lead contamination.
Leaded solder paste is excellent in welding strength and toughness, but there are environmental problems.
Therefore, the selection of solder paste needs to be considered according to the specific needs and environmental requirements.