PCBA Tech - How to choose solder paste in pcba processing

How to choose solder paste in PCBA processing
Different PCBA products should choose different solder pastes. The composition, purity and oxygen content of the solder paste alloy powder, particle shape and size, and the composition and properties of the flux are the key factors that determine the characteristics of the solder paste and the quality of the solder joint. The following are the considerations for solder paste selection:

(1) According to the value and use of PCB circuit board products, high-reliability products require high-quality solder paste.
(2) The activity of solder paste is determined according to the storage time of PCB and components and the degree of surface oxidation.
1. RMA level is generally used.
2. R-level can be selected for high-reliability products, aerospace and military products.
3. PCB and components are stored for a long time, and the surface is severely oxidized. RA grade should be adopted and cleaned after welding.

(3) Select the solder paste alloy composition according to the specific conditions of the PCB board product assembly process, printed board, and components.
1. Generally, 63Sn/37Pb is used for leaded tin printed boards.

2. 62Sn/36 Pb /2Ag is used for printed boards containing palladium-gold or palladium-silver thick film ends and components with poor pin solderability.
3. In general, do not choose silver-containing solder paste for immersion gold boards.
4. Sn-Ag-Cu alloy solder is generally selected for lead-free process.
(4) Choose whether to use no-clean solder paste according to the product (surface PCB assembly board) requirements for cleanliness.
1. For the no-clean process, use solder paste that does not contain halogen or other weakly corrosive compounds.

2. High-reliability products, aerospace and military products, high-precision, weak-signal instruments and meters, and medical equipment involving life safety must be cleaned with water or solvent-cleaned solder paste, and the patch must be cleaned after welding.

(5) BGA. CSP, QFN generally need to use high-quality no-clean solder paste.

(6) When soldering heat-sensitive components, a low melting point solder paste containing Bi should be used.
(7) Select the alloy powder particle size according to the assembly density of smt chip processing (with or without narrow spacing).
SMD pin spacing is also one of the important factors for selecting alloy powder particle size. The most commonly used is No. 3 powder (25~45um) when the pitch is narrower, alloy powder particles with a particle diameter below 40μm are generally selected. Our factory is located in China. For decades, Shenzhen has been known as the world's electronics R&D and manufacturing center. Our factory and website are approved by the Chinese government, so you can skip the middlemen and buy products on our website with confidence. Because we are a direct factory, this is the reason why 100% of our old customers continue to purchase oniPCB.
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