Following several customer inquiries on this topic, we decided to dedicate time to address it and describe it in a “simple” way, hoping to be helpful and clear up any doubts.
When rework needs to be performed on a PCB, the issue of removing moisture from the printed circuit board and/or components is often a source of debate. In cases where wave rework, manual soldering, or conventional rework systems are planned, the printed circuit board, as well as the components mounted on it, must be free of moisture. If present, it can lead to problems (e.g., delamination, popcorning, etc.) during the rework phase.
PCBs as mentioned are highly sensitive to moisture (they are hygroscopic) and depending on their construction characteristics (type of laminates, number of layers, quantity of holes, thickness, etc.), if not protected, they can absorb enough moisture to compromise their integrity when subjected to thermal shocks such as soldering process temperatures, particularly reflow.
The most common defects that could result are delamination between the internal layers of the PCB, which are not always easy to identify. The same phenomenon occurs for a whole series of electronic components, especially “active” ones, such as integrated circuits, microprocessors, LEDs, CPLDs, etc.
The standards concerning the handling, treatment, and storage of components sensitive to this phenomenon are two: IPC-J-STD-033 for components and the more recent IPC-1601 for PCBs.
On average, all electronic component manufacturers clearly indicate the instructions for proper baking. Special attention must be paid to components sensitive to high temperatures, such as batteries, capacitors, plastic connectors, and glued components, which must be well protected. During rework, and based on proximity to the area being reworked, components more sensitive to reflow temperatures must be protected.
With the “advent of lead-free processes (RoHS compliant), the problem of” moisture absorption has become more acute.
Dry-Pack packaging with humidity indicators and PCB drying (Bake) procedures before processing are becoming a common and essential practice to avoid the aforementioned defects, especially for PCBs that may “remain on the shelf” for long periods, well beyond the time guaranteed by PCB manufacturers themselves.
Therefore: the practice of baking a PCBA (assembled PCB) and the component to be replaced is definitely an “activity ‘highly recommended’. This prevents defects caused by moisture trapped in boards subject to rework. Through this methodology,” moisture has the opportunity to escape slowly, without creating any internal mechanical stress.
