Analysis of the effect of residue on PCBA reliability
In the process practice and the failure analysis of PCBA, the author Residues on PCBA have been found to have a significant impact on the reliability level of PCBA, but are not valued by people, especially process engineers or related quality control personnel, although this is currently changing. High Temperature PCB supplier china.
However, since the reliability of PCBA is often caused by the user after a period of use, and the technical means of each manufacturer are limited, and the failure phenomenon cannot be related to the existence of the residue, it is impossible to understand and evaluate the residue to PCBA. The impact of reliability.
In the residue, the inorganic residue will reduce the insulation resistance and increase the leakage current between the solder joints or the wires. Under humid air conditions, the metal surface will corrode, and organic residues (such as rosin, grease, etc.) will form insulation. Membrane, which will prevent electrical contact between the contact surfaces of connectors, switches, relays, etc., which will increase with changes in environmental conditions and time, causing poor contact or even open circuit failure. Rogers PCB factory china.
Therefore, for the reliability and quality of PCBA, the presence of residues must be strictly controlled and these contaminants must be thoroughly removed if necessary.
Type and source of residue
The residue on the PCBA is mainly derived from the assembly process, especially the soldering process. Such as the use of flux residues, flux and solder reaction by-products, adhesives, lubricants and other residues. Other sources have relatively low potential hazards, such as contaminants and perspiration caused by the production and transportation of components and PCBs. Teflon PCB factory china.
These residues can generally be classified into three broad categories.
One type is non-polar residue, mainly including rosin, resin, glue, lubricating oil, and the like. These residues can only be removed by washing with a non-polar solvent.
The second type is polar residues, also known as ionic residues, which mainly include active substances in the flux, such as halogen ions, salts produced by various reactions. These residues need to be well removed, and polarities must be used. Solvents such as water, methanol, etc.
There is also a type of residue which is a weakly polar residue, mainly including organic acids and bases from the flux. For the removal of these substances, a complex solvent must be used.