The humidity test is designed to determine the effects of humidity on the product and assure that the product will meet published specifications while being subjected to high humidity conditions. This is an accelerated test to uncover failure modes in components, assemblies and process, which may appear in the field during normal service, while keeping test time at a minimum. Performance tests are made at various intervals of the test duration and each test must pass for the design to meet the requirements of this section.
Hygroscopic materials (e.g., printed circuit boards, molded plastics, sealed components, etc.) will absorb moisture proportional to the applied vapor pressure and time of application. Excessive moisture penetration may cause swelling of material or contamination actions, destroying functional ability as well as causing leakage paths between sensitive circuits, result when moisture reacts with trapped chemicals from construction processes causing corrosion or severe etching of metal surfaces. In some cases dendritic growth can cause short circuits or high voltage flashover between closely spaced traces or pin spacing. The following humidity test is designed to accelerate the occurrence of these failure mechanisms if they exist.
So, how EMS fabricate a PCB Assembly? It is almost automatic production line now through SMT or wave soldering process to solder the electronic components on the board to instead of hand soldering by iron. Of course, you still can hand solder all electronic components on the board as manual by yourself but you must take high risk for the poor solderability quality and can’t do it mass production. Besides, the 0201 small chip are hard to be hand soldered on board and some of the package that design the soldering pads under the package body can’t be hand soldered. For example BGA, QFN, LGA package.
