Issue link: https://iconnect007.uberflip.com/i/1526114
SEPTEMBER 2024 I SMT007 MAGAZINE 19 does not print through the smallest stencil apertures, then Type 5 solder paste might be used for that product. Dispensing and jetting applications require smaller solder powder sizes (Types 5–7) to be consistently deposited in the small volumes required. e size is typically dictated by the provider of the solder paste coupled with the requirements of the equipment. Can you discuss the importance of flux types in solder pastes and how they influence the soldering process? Fluxes are the key technology of solder pastes and must work in conjunction with the solder powder, PCB, and components to create a solder joint. Solder powder could not easily create solder joints without flux, and we solder paste suppliers have our own "secret recipes." Fluxes are classified in J-STD-004 with the following system: • Material: Rosin (RO), resin (RE), organic (OR), inorganic (IN) • Activity: Low (L), moderate (M), high (H) • Halide content: 0 or 1 (≥ 0.05% by weight in the flux residue) is classification system gives some basic information about the chemistry of the flux and how it may perform in the soldering process. e flux has several expectations placed on it. Some key expectations include: • It must be stable/non-reactive with the sol- der powder that it is mixed with and provide long shelf life, stencil life, open time, etc. • It must provide rheological properties that make the solder paste suitable for printing, dispensing, jetting, etc. • It must remove oxides from the metallic surfaces of the solder powder, PCB pad, and component leads, and protect those surfaces from further oxidation during reflow in air. • It must aid in wetting and flow of the solder to form the solder joint. • No-clean flux residues must be "safe" to leave on the PCBA and not cause corro- sion, dendritic growth, or other electro- chemical failures during the life of the PCBA. Water-soluble flux residues must be easy to wash off with water, even under low standoff components. With so many electronic applications today being placed into harsh environments, to impart to IoT (Internet of Things), is there a dif- ference in the solder paste selection when elec- tronics are deployed into harsh environments? e solder pastes used for harsh environments typically contain "high reliability" alloys which can survive the environment. Table 1: Solder powder types and sizes