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All materials actually have a shelf life (Shelf-life), but some have a longer shelf life, and some have a shorter shelf life. What are the problems with using expired materials? Think about what will happen if you eat expired food? What are the problems with using an expired PCB (Printed Circuit Board)?
Before answering the question of "Expired PCB Use", we must first ask everyone, what is the role of PCB? What processing does it need to do in the PCBA factory?
The biggest role of PCB is to transmit electronic signals as the carrier of electronic parts, so if there are parts that cannot be soldered to PCB or contact points cannot effectively transmit electronic signals, it will affect the function of electronic products or cause intermittent functions. bad.
How are the electronic parts soldered to the PCB?
The current PCB soldering process almost always uses a high temperature of about 240-250 degree Celsius to melt the solder (solder paste or tin wire) and connect the solder feet of the electronic parts to the PCB. So the question arises. Can the expired PCB withstand at least two 250 The high temperature above degree Celsius will not cause problems. The reason why it is said to withstand the high temperature twice is because now the general PCBA process is a double-sided soldering board.
Based on the above understanding, we can now take a look at "What might happen to the use of expired PCB?" 』, the following problems may not necessarily occur, but they all have risks, so if you want to use expired PCBs, you must ensure that the following problems will not occur:
1. Expired PCB may cause oxidation of the solder pad on the PCB surface
Oxidation of the solder pads will cause poor soldering, which may eventually lead to functional failure or risk of dropouts. Different surface treatments of circuit boards 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 ( shelf life) to ensure quality.
OSP boards can generally be sent back to the board factory to wash off the OSP film and re-apply a new layer of OSP. However, when the OSP is removed by pickling, there is a chance to damage the copper foil circuit, so it is best to contact the board factory to confirm whether the OSP film can be reprocessed.
ENIG boards cannot be reprocessed. Generally, it is recommended to perform "press-baking" and then test whether there is any problem with the solderability.
2. Expired PCB may absorb moisture and cause the board to burst
The circuit board may cause popcorn effect, explosion or delamination when the circuit board undergoes reflow after moisture absorption. Although this problem can be solved by baking, not every kind of board is suitable for baking, and baking may cause other quality problems.
Generally speaking, OSP board is not recommended to bake, because high-temperature baking will damage the OSP film, but some people have also seen people take the OSP to bake, but the baking time should be as short as possible, and the temperature should not be too high. It is necessary to complete the reflow furnace in the shortest time, which is a lot of challenges, otherwise the solder pad will be oxidized, which will affect the soldering.
3. The bonding ability of expired PCB may be degraded and deteriorated
After the circuit board is produced, the bonding ability between the layer to layer will gradually degrade or even deteriorate over time. That is to say, as time increases, the bonding force between the layers of the circuit board will be reduced. Gradually decline.
When such a circuit board goes through the high temperature of the reflow furnace, because the circuit board composed of different materials will have different thermal expansion coefficients, under the action of thermal expansion and contraction, it may cause de-lamination and surface bubbles. This 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 may occur, and it is more likely to cause CAF (micro short circuit) without knowing it.
The above is an introduction to the risks of using expired PCBs
