This paper mainly introduces three hazards of using expired PCB.
1. Expired PCB may cause oxidation of welding pad on PCB surface
The oxidation of the pad will cause solder defects, whICh may eventually lead to functional failure or loss of parts. Different surface treatment of the circuit board for the effect of oxidation will not be the same, in principle ENIG requirements to be used up within 12 months, and OSP is required to be used up within six months, it is recommended that in accordance with the PCB board factory shelflife (shelflife) to ensure quality.
Generally, the OSP board can be sent back to the board factory to wash off the OSP film and then put on a new layer of OSP. However, the copper foil line may be damaged when the OSP is removed by pickling. Therefore, it is best to consult the board factory to confirm whether the OSP film can be reprocessed.
ENIG plate can not be re-processed, the general recommendation is to "press roast", and then test whether there is a problem.
2. Expired PCB may absorb moisture and cause board explosion
When the board is backsoldered after absorbing moisture, it may cause problems such as popcorn effect, exploding board or delamination. This problem can be solved by baking, but not every 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 also have seen some people will take OSP to bake, but the baking time should be as short as possible, the temperature can not be too high, after baking more must be completed in the shortest time back welding furnace, many challenges, otherwise the welding pad will appear oxidation, affect welding.
3. The bonding ability of expired PCB may degrade and deteriorate
After the circuit board is produced, the bonding ability between layers will gradually degrade or even deteriorate over time. That is to say, as time goes on, the bonding force between layers of the circuit board will gradually decline.
Such a circuit board after the high temperature of the backwelding furnace, because the circuit board composed of different materials will have different coefficient of thermal expansion, under the action of thermal expansion and contraction, it is possible to cause the circuit board delamination (de-lamination), surface bubbles, which will seriously affect the reliability and long-term reliability of the circuit board, Because the circuit board layer may break the circuit board layer between the conduction hole (via), resulting in poor electrical characteristics, the most troublesome is the possibility of intermittent poor problems, more likely to cause CAF (micro short circuit) without awareness.
The harm of using expired PCB is quite big, so designers in the future or to use the expiration of the PCB board ah.
How can PCB circuit boards distinguish good from bad from appearance
With the rapid development of mobile phone, electronics, communication industry, automatic driving, to a large extent, the PCB circuit board industry continues to grow and grow rapidly, people for the quality of PCB components, layers, weight, precision, materials, color, reliability and other requirements are increasingly high.
Also due to the fierce price competition in the MARKet, the cost of PCB board materials is also on the rise. In order to improve the core competitiveness of the industry, more and more manufacturers choose to try to monopolize the market at low prices. However, these ultra-low prices are often obtained through reducing the cost of materials and manufacturing costs, which leads to the quality of the pcb circuit board itself can not reach, so PCB circuit board devices are usually prone to cracks (cracks), easy scratches, (or bruises), its precision, performance and other comprehensive factors are not up to standard, Seriously affect the later PCB circuit board reliability, should prove that the sentence is not cheap good goods may not be true, but good goods must not be cheap is an ironproof fact, in the face of a variety of PCB circuit boards on the market, distinguish PCB circuit boards good or bad can start from two aspects; The first method is to judge from the appearance, on the other hand is to judge from the quality specification of PCB board itself.
The first factors to identify a PCB board:
First: Distinguish from the appearance of the circuit board is good or bad
In general, PCB circuit board can be judged by several aspects of the appearance of the analysis;
1. Light and color.
External PCB circuit boards are covered with ink, circuit boards can play the role of insulation, if the color of the board is not bright, less ink, insulation board itself is not good.
2, PCB circuit board size and thickness of the standard rules.
The thickness of the circuit board to the standard circuit board is different sizes, customers can measure and check according to their own product thickness and specifications.
3. Appearance of PCB circuit board weld.
Due to more parts of the circuit board, if the welding is not good, parts easy to fall off the circuit board, seriously affect the welding quality of the circuit board, good appearance, careful identification, the interface is very important.