What Powder Size is No. 305 Solder Paste?

A

305 is an SAC305 alloy, referring to the tin-silver-copper composition, and has no direct relationship to which powder number the powder is. SAC305 paste can be made as 3#, 4#, 5#, or other powder sizes—the number refers to powder particle size: 3# suits ordinary components, 4# suits fine-pitch ICs and QFN, and 5# suits tiny parts like 0201 and BGA. When choosing, confirm both that the alloy is SAC305 and that the powder size matches the component lead pitch; do not look only at the 305 model and overlook the powder size.

As a common SMT material, 305 Solder Paste requires clear powder particle size specifications in practical applications, as this directly affects its fluidity, release performance, and solder joint formation during the printing process, and is also closely related to the volatilization rate of the Flux during Reflow Soldering.

In production line operations, if bridging or voiding occurs after 305 solder paste printing, the first step is to check whether the powder particle size of the solder paste meets the current process requirements. Coarse powder is prone to causing printing skips, while overly fine powder may increase the risk of sticking, which is particularly noticeable on high-density PCBs.

According to industry experience, 305 solder paste typically corresponds to a powder particle size of around 45 microns, but the specific value still needs to be adjusted based on actual production conditions. For example, when using an automatic printing machine, if excessive squeegee pressure or uneven printing thickness is observed, it may be caused by an overly large powder particle size, in which case trying a solder paste with a smaller particle size is recommended.

The powder particle size of 305 solder paste also affects its storage stability. Oversized particles are prone to settling during transportation or storage, leading to uneven distribution of the solder paste and thus affecting soldering consistency. Therefore, it is necessary to confirm whether the product parameters provided by the supplier are accurate during procurement.

During the process verification stage, it is recommended to observe the morphology of the solder paste after printing under a microscope, and simultaneously evaluate the soldering quality using test boards. If rough solder joint surfaces or cold soldering are found, it may be necessary to recalibrate the powder particle size of the solder paste to ensure it matches the aperture size of the printing stencil.

For procurement personnel, understanding the powder particle size standards of 305 solder paste helps avoid rework caused by mismatched specifications during selection, and also provides data support for subsequent process debugging. Mastering such technical details is crucial for improving overall production efficiency.

The powder particle size of 305 solder paste is not only a basic parameter but also a key factor affecting soldering quality. Correctly identifying and applying this parameter can significantly reduce uncertainties in production.