Water-soluble flux for lead-free solder

Abstract

The invention discloses a water-soluble flux for a lead-free solder. The water-soluble flux comprises the following components in percentage by weight: 2 to 5 percent of organic acid activating agent, 0.5 to 1 percent of surfactant, 0.2 to 1 percent of film forming agent, 10 to 15 percent of cosolvent, 0.1 to 0.5 percent of antifoaming agent, 0.05 to 0.35 percent of stabilizing agent, 0.1 to 0.5 percent of corrosion inhibitor and the balance of deionized water. The water-soluble flux special for the lead-free solder can be effectively matched with the lead-free solder and is particularly suitable for a lead-free solder which is used for a low-cost high-performance microelectronic package and consists of the following components in percentage by weight: 0.5 to 1 percent of Ag, 0.3 to 0.7 percent of Cu, 1 to 3 percent of Bi, 0.0002 to 0.0005 percent of P, 0.01 to 1 percent of Ce, 0.01 to 0.15 percent of Ni and the balance of Sn. The flux has high wetting capacity on the lead-free solder, can enhance the solderability of the lead-free solder, can meet the requirement of soldering temperatures of the lead-free solder, has a low corrosion effect on lead-free solder alloy and a small number of residues after soldering, and can be cleanly washed by water; and a dried circuit board has higher insulation resistance.

Description

technical field [0001] The invention relates to a flux used for flux in the microelectronics industry, in particular to a water-soluble flux for lead-free solder. Background technique [0002] Due to the requirements of global environmental protection regulations and the development of the electronic industry, lead-free electronic products are an inevitable trend. At present, the lead-free solders that are more researched and initially commercialized in the world are Sn-Ag and Sn-Ag-Cu eutectic alloys. However, in the process of research and use, it was found that compared with traditional Sn-Pb solder, lead-free solder has poor wettability, is easy to oxidize, and has a high melting point. The increase of the melting point means that the soldering temperature must be increased. On the one hand, it will cause damage to the components on the board surface. On the other hand, it will inevitably increase the volatilization of the active agent in the flux, which is likely to ca...

AI Technical Summary

Problems solved by technology

The previous water-soluble fluxes have strong activity and are also highly corrosive. After soldering, the printed board is sticky, which is not conducive to on-line inspection.

Moreover, the past research mainly focused on the development of flux products used in lead-containing solders, which cannot meet the needs of the current development of lead-free solders. Further research on water-soluble fluxes for lead-free solders is needed.

[0004] Sn-Ag-Cu alloys are a type of lead-free solder that has been studied internationally and has good application prospects. However, it was found during research and use that compared with traditional Sn-Pb solder, Sn-Ag- Cu-based lead-free solder has poor wettability, is easy to oxidize, and has a high melting point

Therefore, the flux suitable for Sn-Pb solder is not suitable for Sn-Ag-Cu lead-free solder. One is that this kind of flux can not help the wetting ability of Sn-Ag-Cu lead-free solder; -Ag-Cu based lead-free solder has a high soldering temperature. The increase of the melting point means that the soldering temperature must be increased. On the one hand, the increase in the soldering temperature makes the solder joints easier to oxidize, and at the same time increases the volatilization of the active agent in the flux. It does not have a good activation and protection effect, so that the solder joints are more likely to be oxidized