The Roles and Selection of Adhesive and Solvent in Solder Flux
Adhesives and solvents in the solder flux are important components of solder paste products. What are the main functions of adhesives and solvents? How to choose them?
The role of the adhesives in solder paste:
In the soldering process of microelectronics and semiconductor devices, we first apply the solder paste to the surface of the soldering metals through a certain process (printing, dispensing, scribing, jetting, etc.), and then place the electronic devices on the solder paste. The solder paste is heated and cured through a certain program. In this process, the role of the adhesive in the solder flux is mainly to bond the mounted SMC/SMD and make the printed solder paste have good conformality, which requires maintaining the edges and corners and integrity of the lines. The choice of adhesive depends on the placement speed of the placement machine. The mounted SMC/SMD moves with the high-speed movement of the placement machine table along the X-Y direction. The adhesive composition of the solder paste must be according to the operating speed of the placement machine to ensure the solder shape retention on the PCB after printing. As a result, the SMC/SMD will not be displaced or dropped during the placement process. However, too much adhesive will reduce the solder paste fluidity.
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The role of solvent:
Solvent plays the role of adjusting the viscosity of a solder paste. Solvents in solder pastes are multi-component, mostly composed of mixtures of polar and non-polar solvents with different boiling points. Solvent volatilizes quickly at a high temperature of 150~200℃, which allows the dissolution of various fluxes and extend the solder paste storage life. Popular solvents with high boiling points include ethylene glycol, diethylene glycol, etc.
The use of adhesives in solder fluxes requires careful design and validation.
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