What are the risks of using expired PCBs?

All materials actually have their shelf life, only some have a longer shelf life, while some have a shorter shelf life. So what are the problems with using expired ingredients? Think about what happens when you eat expired food. What would be the problem with using expired PCBs?

Before answering the question 'use of expired PCBs' we must first ask you, what is the purpose of a PCB? What processing does it require in a PCBA factory

The biggest role of PCB is as a carrier for electronic components to transmit electronic signals, so if there are parts that can not be soldered to PCB or contact points can not effectively transmit electronic signals, it will affect the function of electronic products, or cause intermittent malfunction.

How are the electronic parts soldered to the PCB?

The PCB soldering process now almost all use about 240 to 250 ℃ high temperature solder (solder paste or wire) melted after connecting the electronic parts solder pins and PCB, so the question arises, expired PCB can withstand at least twice the high temperature of more than 250 ℃ without problems, the reason for saying that withstand twice the high temperature because the general PCBA process is now a double-sided solder board.

Based on the above understanding, we can now look at the "use of obsolete PCB in the end what may happen? The following problems may not always happen, but they are all risks, so if you still want to use expired PCBs, you must ensure that the following problems do not occur.

1. the expired PCB may cause oxidation of the PCB surface solder pads

Oxidation of the solder pads will result in poor soldering, which may eventually lead to functional failure or risk of dropped parts. The effect of different surface treatments on the PCB will be different for oxidation, in principle ENIG requires to be used up within 12 months, while OSP requires to be used up within six months, it is recommended to follow the shelf life of the PCB board manufacturer (shelf life) to ensure quality.

OSP boards can generally be sent back to the board factory to wash off the OSP film and reapply a new layer of OSP, but there is a chance that the copper foil circuitry will be damaged when the OSP is removed by acid washing, so it is best to check with the board factory to see if the OSP film can be reprocessed.

ENIG boards cannot be reprocessed and it is generally recommended to "press bake" and then test the solderability for any problems. 2.

2. Expired PCBs may absorb moisture and cause bursting of the board

When a PCB is re-soldered after it has absorbed moisture, it may cause popcorn effect, popping or delamination. Although this problem can be solved by baking, not every board is suitable for baking and baking may cause other quality problems.

Generally speaking OSP boards are not recommended to be baked because the high temperature will damage the OSP film, but we have seen people take OSP to be baked, but the baking time should be as short as possible, the temperature should not be too high, and after baking it must be returned to the soldering oven in the shortest possible time, which is quite a challenge, otherwise the soldering pad will oxidise and affect the soldering.

3. The bonding ability of expired PCBs may degrade and deteriorate

The bonding ability between the layers of a circuit board (layer to layer) will degrade or even deteriorate over time, which means that the bond between the layers of the board will gradually decrease over time.

This is because the circuit board will have a different coefficient of thermal expansion because of the different materials used in the board. ), resulting in poor electrical characteristics, the most problematic is the possibility of intermittent problems, and may cause CAF (micro-short circuit) and do not know.

The above is the introduction of the use of expired PCB what risks.

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