The Role of Solder Paste in SMT Line

The Role of Solder Paste in SMT Line

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What is Solder Paste?

Solder paste is an indispensable and important material for the progress of electronic technology. It is used to solder electronic parts on circuit boards. Because the invention of solder paste promotes the miniaturization of electronic assembly technology, PCBA circuit boards continue to become smaller, and the ever-smaller IC components make the mobile phones we use more and more miniaturized. From the previous big phone to the current smart phone, the appearance is more and more beautiful, smaller size, more rich function.

The Composition of SMT Solder Paste

Solder paste, as the name suggests, is a paste-like object, which is very similar in shape to the toothpaste we use every day. The main component of solder paste is a combination of solder powder and flux.

If the ratio of solder paste is calculated by weight, the ratio of tin powder to flux is about 90%: 10%; because the tin powder is relatively heavy; if the ratio is calculated by volume, the ratio of tin powder to flux is about 50%: 50 %;

The Types of Solder Paste

1. According to environmental protection requirements, it is divided into leaded tin paste and lead-free solder paste (environmentally friendly solder paste):

Environmentally friendly solder paste contains only a small amount of lead. Lead is a substance that is harmful to human beings. In the electronic products exported to Europe and the United States, the content of lead is strictly required. Therefore, lead-free technology is used in SMT chip processing.

In the lead-free SMT chip processing process, it is more difficult to apply tin compared to the lead-based process, especially in the case of BGA, QPN, etc., then solder paste with a high proportion of silver will be used. The common ones in the market are silver with 3 points and silver with 0.3 points. Among solder pastes, silver-containing solder pastes are currently the most expensive.

2. According to the melting point, it is divided into three types: high temperature, medium temperature and low temperature:

Commonly used high temperatures are tin silver copper 305,0307. There are tin-bismuth-silver at medium temperature, and tin-bismuth is commonly used at low temperature, which is selected according to the different product characteristics in SMT chip processing.

3. According to the fineness of tin powder, it is divided into No. 3 powder, No. 4 powder, No. 5 powder solder paste:


Selection: In the SMT chip processing of generally larger components (1206 0805 LED lights), No. 3 powder solder paste is used because its price is relatively cheap.

In digital products, when encountering dense-footed ICs, No. 4 powder solder paste is used in SMT chip processing.

When encountering very precise welding components such as BGA, and demanding products such as mobile phones and tablet computers, No. 5 powder solder paste will be used in SMT chip processing.

Storage and use environment of solder paste in SMT Line

1. After receiving the solder paste, please put it in the refrigerator immediately and keep it refrigerated at 3-7℃. Note that solder paste cannot be frozen.

2. Preparation before solder paste printing: The solder paste is taken out of the refrigerator, and the following 2 steps must be performed before putting it into the printing process:

Do not open the package, leave it at room temperature for at least 4-6 hours, so that the temperature of the solder paste will naturally return to room temperature.

After the temperature of the solder paste reaches room temperature, it should be stirred to ensure that the components in the solder paste are evenly distributed before being put into printing. It is recommended to use professional stirring equipment, and stir in the same direction for 3 minutes.