What are the functions of using various metal elements in solder paste?

New types of welding materials have emerged along withSMTOne kind that emerged as The Times required.Solder pasteIt is a complex system composed of solder powder, flux and other additives. Solder paste has a certain degree of viscosity at room temperature and can initially bond electronic components to the designated positions. At the soldering temperature, as the solvent and some additives evaporate, the components to be soldered are soldered together with the printed circuit pads to form a permanent connection. The following solder paste manufacturer will explain:

1Antimony

Antimony is added to increase strength without affecting wettability. Prevent tin worms. Zinc, cadmium or galvanized metals should be avoided as they can cause the solder joints to become brittle.

2Bismuth

Bismuth can significantly lower the melting point and improve wettability. When there is sufficient lead and tin, bismuth will form a melting point of only95℃theSn16Pb32Bi52Crystals, these crystals diffuse along the grain boundaries and may cause faults in the solder joints at lower temperatures.

Therefore, when welding with bismuth-containing solder, high-power components pre-plated with lead alloy are desulfurized under load. This kind of solder joint is also prone to cracking. Have more than47％BiThe alloy expands when cooled, which can be used to counteract the thermal expansion mismatch stress. Prevent the growth of tin whiskers. However, the price is relatively high and the availability is limited.

3Copper

Copper can lower the melting point, enhance the thermal cycling fatigue resistance, and improve the wettability of the molten solder. It also reduces the dissolution rate of copper from the plate and slows down the formation of metal compounds in some of the leads in the liquid solder. It can promote the growth of tin whiskers. It is possible to use (about)1％The solution of copper in tin is used for inhibitionBGAThe dissolution of metallization beneath the film protrusions of the chip, for example, asSn94Ag3Cu3.

4Nickel

Nickel can be added to the solder alloy to form a supersaturated solution to inhibit the dissolution of metallization under the film protrusion.

5Indium

Indium can lower the melting point and extend ductility. In the presence of lead, it forms in114℃Ternary compounds that undergo phase transformation below. Very high cost (several times the silver color), low availability. It is prone to oxidation, which leads to problems in maintenance and remanufacturing, especially when flux cannot be used to remove the oxide. inGaAsDuring the period of chip attachment. Indium alloys are mainly used in low-temperature applications and for dissolving gold, which is much less than that in tin. Indium can also be used to weld many non-metals (such as glass, mica, aluminium oxide, magnesium oxide, titanium dioxide, zirconia, porcelain, brick, concrete and marble). Indium-based solders are prone to corrosion, especially when chloride ions are present.

6Lead

Lead is cheap and has appropriate properties. More wettable than tin. However, it is toxic and has been phased out in some countries. It can prevent the growth of tin whiskers and inhibit tin pests. Reduce the solubility of copper and other metals in tin.

7Silver

Silver provides mechanical strength, but its ductility is worse than that of lead. In the absence of lead, it can enhance the resistance of thermal cycling to fatigue. Use itHASL-SnPbCoated leadsSnAgThe melting point of the solder is179℃Adding silver to tin can significantly reduce the solubility of the silver coating in the tin phase. In eutectic tin-Silver3.5％AgIn alloys, it tends to formAg3SnIf the small plate is formed near the high stress point, it can be used as the starting position of the crack;The silver content needs to be maintained at3％The following is to suppress these problems.

8tin

Tin is usually the basic component in solder paste. It has good strength and wettability. However, it is inherently prone to the growth of tin whiskers,It dissolves silver, gold and other metals easily. For example, copper is a particular problem for tin alloys with high melting points and reflux temperatures.

9Zinc

Zinc can lower the melting point and is inexpensive. However, it is highly prone to corrosion and oxidation in the air. Therefore, zinc-containing alloys are not suitable for certain solders. For instance, the shelf life of zinc-containing solder paste is shorter than that of zinc-free ones. It can form brittleness in contact with copperCu-ZnIntermetallic compound layer.

10Germanium

Germanium in lead-free tin-based solders can inhibit the formation of oxides;Lower than0.002％It will increase the formation of oxides. The optimal concentration for inhibiting oxidation is0.005％.

Shenzhen JJY Industrial Technology Co., Ltd. is a company15As a manufacturer specializing in the research and development and customization of solder paste, lead-free solder paste and leaded solder paste for many years, if you want to learn more about soldering knowledge, please continue to follow JJY Solder Paste Factory and leave a message online to interact with us.