For rigid-flex printed circuit boards (PCBs), the space joining rigid material to flex material (Transition Zone) sometimes contains imperfections that, although acceptable, could impact effectiveness of the final part. Transition zone imperfections can include any of the following:
When a blow hole defect occurs during the assembly process as a result of the PCB card, the primary culprit tends to be entrapped moisture or air. With moisture, any non-plated and non-masked areas on a bare circuit board that expose internal laminate can be suspect to absorbing moisture. Absorption can occur either during the board fabrication process or from improper storage. Examples of highly suspect areas include non-plated drilled holes and routed features.
It is not recommended to bake boards with an organic solderability preserve (OSP) surface finish. Although baking a printed circuit board with an organic solderability preserve finish can have negative consequences, the process itself can have positive performance in specific applications. OSP is a very thin protective layer of material placed over exposed copper, typically using a conveyorized process to protect the copper from tarnish.
Within the printed circuit board industry the term "tenting" originally indicated that the mask would fully enclose the via at one end by forming a skin or tent over the opening. While dry film solder mask is more expensive, it is capable of forming a reliable tent, while liquid photoimageable solder mask (LPI) generally will not.
Generally pads are small round or square areas of copper which are normally used to make a connection to a component pin. If these pads are not sitting correctly or are lifted, it can cause the connection between the printed circuit board (PCB) and the component to fail.
Printed circuit boards (PCBs) with immersion finishes such as electroless nickel immersion gold (ENIG), immersion tin, silver, and OSP are appealing because they are lead-free. However, if handled improperly, these materials are susceptible to oxidation and corrosion from exposure to moisture and humidity. This oxidation causes dewetting after soldering, which can lead to poor joints at assembly and ultimately lead to failure of the board.