- Rosin: rosin is a natural product which is harvested from mainly pine trees. Rosin has a natural activity level (due to slightly acid character), a natural stickiness and a natural thickening effect. On top of this rosin can also prevent oxidation during reflow and has an influence on the paste viscosity. It will also contribute to a more insulating residue.
- Resin: resin is in fact synthetically made rosin. The main reason to manufacture synthetic rosin is to guarantee a more consistent and stable quality. Features as acidity, color and viscosity can vary in rosin due to atmospheric conditions. In order to keep the ideal features of rosin the rosin manufacturers have to modify the rosin chemically prior to delivery. Resin does show constant chemical and physical features but does not have the natural activity, tackiness and thickening effect of rosin.
- Stabilizators: these chemicals are in the paste to keep the paste stable during transport, storage and printing. They regulate the ability of the paste to keep a stable viscosity. Consistancy in viscosity is important during the printing process. If the paste looses its initial viscosity it can either slump or become dry with negative influence on printing
- Activators: the activators are inside the flux system to help the flux to
- 1. clean the surface of the board and component
- 2. reduce the surface tension
- 3. promote wetting of the solder paste. In Pb-free pastes the activators are very important towards having sufficient wetting
- Solvents: these high boiling alcohols are in the flux system to solubalize some of the other ingredients. They also help to clean the surface.
- Surfactants: these chemicals will clean the to be soldered surface and reduce the surface tension which helps the wettability of the solder paste
- Heat stabilizors: these ingredients will influence the stability of the paste during reflow. Heat stabilizors have a direct influence on the behavious of the paste during reflow. This will allow the paste to be used for instance with long and hot reflow profiles. They also act as oxidation protection.
- Rheological agents: these are also called thickeners. Rheological agents will give the paste its final viscosity and ability to keep the viscosity stable during storage and printing. They also contribute to the tackiness of the paste which is important for component placement
