Solder flux requirements for SMT patch processing

In the welding process of SMT patch processing, the materials that can purify the welding metal and welding surface and help welding are called flux, or flux for short. Flux is an indispensable process material in the process of soft brazing. Liquid flux is used in wave soldering and manual welding process. Flux and solder are used separately. In reflow soldering process, flux is an important part of solder paste.

SMT patch processing welding quality is bad, in addition to the solder alloy, components, PCB quality, welding process, but also with the performance of the flux, flux selection has a very important relationship. Next, we will introduce the requirements of SMT patch processing for flux.

Solder flux requirements for SMT patch processing

1. The appearance of flux should be uniform, transparent, without precipitation or stratification, and without foreign matter. Flux should not emit toxic, harmful or strong pungent odor gases and dense smoke, in order to help protect the environment. Its color should not change during the effective storage period.

2. Viscosity and density than molten solder is small, easy to be replaced. The flux density can be diluted with a solvent and should be 0.80-0.95g/cm3 at 23 degrees. Clean free flux should be within the range of (100±1.5) % of its nominal density.

3. The surface tension is smaller than the solder, the wetting expansion speed is faster than the molten solder, the expansion rate is > 85%.

4. The melting point is lower than the solder, before the solder melts, the flux can give full play to the role of welding aid.

5. The content of non-volatile matter should not be more than 15%, welding does not produce welding bead splash, does not produce poison gas and strong irritating odor.

6. The surface of the residue after welding should be non-viscous, non-touching, and the chalk on the surface should be easily removed.

7. No cleaning type flux requires solid content <2.0%, no halide, less residue after welding, no moisture absorption, no corrosion, good insulation performance, insulation resistance > 1*10 square ohm.

8. Water cleaning, semi-water cleaning and solvent cleaning type flux requires easy cleaning after welding.

9. Stable storage at room temperature.

Shenzhen kingford Co., Ltd. specializes in providing integrated PCBA electronic manufacturing services, including upstream electronic components procurement to PCB production and processing, SMT patches, DIP plug-ins, PCBA testing, finished product assembly and other one-stop services.

We provide PCBA processing services, starting from PCB circuit board production, our own PCB manufacturers (obtained the very strict TS16949 certification of the automotive industry), pay attention to the quality of the circuit board and PCBA quality control system.

With decades of experience in purchasing electronic components, we maintain long-term cooperation with large brands to ensure the original packaging and procurement channels of components. In the process of component packaging, the selection of Qianzhu and Letai solder paste, to ensure the reliability of welding, with automatic printing press, Panasonic high-speed SMT machine, up and down eight temperature zone reflow welding, AOI automatic optical detector, can effectively ensure the reliability and quality of electronic packaging process.

In addition, perfect IPC, IPQC, OQA and other management processes, clear job responsibilities, strict implementation of IPC electronic assembly acceptance standards. For PCBA testing, we have professional engineers to perform 100% batch testing using a variety of test stands, including access, noise, amplitude, signal, temperature, humidity, drop or to perform customer detailed test plans. All efforts are aimed at becoming a refined PCBA processing factory.