PCB boards also have a shelf life. After unpacking, they should be processed in time and cannot be stored for a long time. Assembled those beyond the shelf life of the PCB factory will cause harm to the PCB board;
Three Major Hazards of using expired PCB boards in PCBA
1. PCBA uses expired PCBs may cause oxidation of the pads on the PCB surface
Oxidation of the pads will result in poor solder, which may eventually lead to functional failure or risk of dropped parts. Different surface treatments of the circuit board will have different anti-oxidation effects. In principle, ENIG requires it to be used up within 12 months, while OSP requires it to be used up within six months. It is recommended to follow the shelf life of the PCB board factory to ensure quality.
The OSP board can generally be sent back to the board factory to wash off the OSP film and then re-apply a new layer of OSP. However, when the OSP is removed by pickling, it may damage its copper foil circuit, so it is best to contact the board factory to confirm whether the OSP film can be reprocessed.
The ENIG board cannot be reprocessed, and it is generally recommended to perform “pressure baking”, and then test whether there is any problem with the solderability.
2. PCBA uses expired PCB may absorb moisture and cause board explosion
Problems such as popcorn effect, cracking or delamination may be caused when the circuit board absorbs moisture and is reflowed. Although this problem can be solved by baking, not every board is suitable for baking, and baking may cause other quality problems.
Generally speaking, it is not recommended to bake OSP boards, because high temperature baking will damage the OSP film, but I have also seen some people take OSP to bake, but the baking time should be shortened as much as possible, and the temperature should not be too high, and it will be more difficult after baking. The reflow oven must be completed in the shortest time, which is a lot of challenges. Otherwise, the solder pads will be oxidized, which will affect the soldering.
3. The gluing ability of expired PCBs in PCBA may degrade and deteriorate
After the circuit board is produced, the bonding ability between its layers (layer to layer) will gradually degrade or even deteriorate with time, that is to say, as time increases, the bonding force between the layers of the circuit board will gradually decrease.
When such a circuit board passes through the high temperature of the reflow furnace, because the circuit boards composed of different materials will have different thermal expansion coefficients, under the action of thermal expansion and cold contraction, it may cause circuit board de-lamination & surface bubbles, which will seriously affect the reliability and long-term reliability of the circuit board, because the delamination of the circuit board may break the vias between the layers of the circuit board, resulting in poor electrical characteristics, the most troublesome is Intermittent bad problems can occur, more likely to cause CAFs (micro short circuits) without knowing it.
The harm of using expired PCBs is still quite large, so PCB Assembly should use PCB boards within the warranty period.