PCBA will appear white around the pads after soldering, which will generally occur after PCBA wave soldering, PCB cleaning machine, storage and maintenance.
These white substances are mainly residues caused by.
1. wave crest surface floating with thin skin of tin oxide.
2. preheating temperature or curve parameters are not appropriate.
3. flux flow is too high, preheating temperature is low, eating tin time is too short.
4. flux composition, check the test and certification certificate.
1. Rosin in the solder.
Most of the cleaning is not clean, after storage, after the failure of the solder joints produced white material, are inherent in the flux itself rosin.
2. Rosin denatured material.
This is the board in the process of welding, rosin and solder generated by the reaction of the substance, and the solubility of this material is generally very poor, not easy to be cleaned, lingering on the board, the formation of white residue.
3. Organic metal salts.
The principle of removing the welding surface oxide is organic acid and metal oxide reaction to generate metal salts soluble in liquid rosin, after cooling and rosin to form a solid solution, removed with rosin in the cleaning.
4. Metal inorganic salts.
These may be metal oxides in the solder and flux or solder paste in the halogen-containing active agent, PCB solder tray in the halogen ion, the residual halogen ion in the component surface coating, FR4 material containing halogen material released at high temperatures when the reaction generated by the halogen ion, the general solubility in organic solvents is very small. If the cleaner is selected appropriately, flux residues may be removed; once the cleaner is selected and residues do not match, it may be difficult to remove these metal salts, thus leaving white spots on the board.
PCBA soldering after the pad is white, mainly flux residue, cleaning is not clean caused by the need to clean after welding.
