How to choose the right solder paste

Success is a matter of mastering the details, no matter how small. Something as seemingly insignificant as choosing the right solder paste can make or break an electronic assembly process. To make matters worse, there are a variety of solder paste options to choose from and while they may seem the same based on their classification, not all soldering products are created equal. Specialty solder pastes can be

more expensive but often offer additional benefits and should be considered depending on your needs.

Choosing the right solder paste can lead to more questions.

Variations in wetting properties, pore control, flux residue, alloy strength, alloy flexibility and other performance parameters can play a role. For example:

Leaded and lead-free Solder paste

The main practical difference between leaded and lead-free solder paste is the melting temperature. Lead-free solder paste has a higher melting point and is therefore a bit more difficult to work with.

When deciding which to use, the most important factor when deciding between leaded and lead-free solder paste is the target market. As mentioned in our last RoHS blog, ignoring. RoHS directives can be potentially costly.

If you are developing a product that will be sold to consumers and/or an international market, it is in your best interest to comply with RoHS and avoid lead-based solder pastes. Although they tend to be more expensive, it's an investment that can save you more in the long run.

Water soluble vs. not clean

The decision is often It depends on the cosmetics. Water soluble fluxes contain high molecular weight compounds such as B. Polymers that are not as effective in preventing reoxidation as rosin/resins.

Water soluble pastes give boards a cleaner look after the board has gone through the reflow stage, burn off the flux residue and wash off easily in a board washer. If you choose No-Clean, the flux has the same function as the water wash paste, but the residue remains on the plate. No-clean chemicals are generally rosin/resin-based materials. Rosin/resins are excellent rust barriers and protect "clean" surfaces during reoxidation reflux.  In addition to detracting from the aesthetics, experts have mixed opinions about the consequences of the remaining residue. 

Some claim that leftover flux residue becomes inert, but others claim that it can adversely affect the product later in the life cycle.

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