In the product after SMT, the performance test is no problem, but to the customer after two or three months or more, that one of the key chip resistor 0603 package resistance becomes smaller and smaller from 24K to about 21K, I put all the lines around this resistance are disconnected, found resistance or 21K, then I the resistance from the board removed, the resistance is not bad, or 24K, use high-powered magnifying glass, the intermediate SMD package with flux residue and more, is not because of the flux and the residues have internal resistance, request the master answer!
The reasons are as follows:1, first of all, separate PCBA to analyze, will be completely tested with flux plates, do not weld the case;2, if in the absence of welding, or these circumstances, that is, the presence of flux resistance is smaller. That can be done by replacing the soldering flux or preheating the third segments of the wave soldering to 150-180 degrees to see if it can be heated to bake the halogen from the soldering flux itself;3, another case is the tin wire itself, because the tin line itself also exists to help welding flux, some manufacturers have put a halogen, it will inevitably produce leakage, itself is a halogen active agent, excessive use of conductive. The international allowed only 5 parts per thousand.4, because you are SMT patch, solder paste is also a key factor to check, to see if it will not conductive, such as you can test the resistance before the wave soldering, it is recommended to use well-known solder paste manufacturers. Such as thousand live, AF and so on. If the solder paste itself has leakage phenomenon, it must first improve from the source.Through the above points, you should be able to find the problem, I hope you will soon resolve the incident.
Look at your soldering flux type and content. Should the alcohol base be better?
Yes, the soldering flux will be conductive, and the resistance will certainly be smaller
