1. Measure the Absorbed Moisture of PCBA

　　Electronic components and PCB materials in some cases will absorb moisture during rework. A good way to monitor the board's humidity level is to measure the weight of the board before and after drying. We can use a precision electronic balance to weigh small circuit boards or samples. Then, pre-baking the circuit board at 100°C for two hours and let it cool. Next, we can weight the circuit board. After that, we should pay attention to the difference in the two weights. You can use the difference to optimize the pre-baking temperature and time. In applications where full drying is required, the weight of the cleaned pcba manufacturing components is lighter than that of uncleaned pcba.

　　You need enough time to get all the moisture that is adsorbed in the layers of the circuit away from pcba. Depending on the thickness of the board, this may take more than four hours. Since you want moisture (and possibly other solvents) to leave the circuit board, BQC thinks that the best way is to put the circuit board on the shelf, all the printed circuit boards should be placed vertically, leaving the circuit boards some room. If you pick them up, place them one on top of the other, or place them horizontally on the bottom of the oven, etc., then it is more difficult for moisture to leave the circuit board.

　　Once you start the drying process, you must put the circuit board in a sealed moisture-proof bag or dry box so that the circuit board can keep dry. Then, you must make sure that the moisture-proof bag is sealed. If you do not seal the moisture-proof bag in a vacuum environment, you do not expect the relative humidity in the moisture-proof bag to remain below 10% regardless of how much desiccant is put in the moisture-proof bag.

　　2. Whether the PCBA Needs to Be Baked After Cleaning?

　　After cleaning the reworked pcba, the board may need to be dried. Most of the assemblies are cleaned using water cleaning technology. In addition to water, there may or may not be other cleaning materials. After cleaning, they are allowed to dry instead of drying them. Only a few printed circuit board assemblies will use water during their cleaning and then they need to be extended the baking time in the oven. For a typical FR-4 type assembly, if drying is desired, baking at 105°C for 2-4 hours or baking at 65°C for 8-24 hours is sufficient.

　　In your cleaning agent, you will find that the drying requirement is also a function type of the drying system. If your cleaning agent blows water away from the assembly by using an air knife, it can increases the potential for a drying process, especially when you need to clean multilayer circuit boards. Air knife drying systems are usually part of an in-line cleaning system. If your cleaning agent uses a convection/radiative forced heating type technique to dry the assembly, then no drying is required.

　　We can offer pcba assembly service that can meet your demands.

　　If you have any projects, please contact with me chinaems@bqcdz.com