The shelf life of flexible PCB is the time before assembly and use when they can be stored without a decrease in quality or performance. If you buy printed circuit boards, be sure to ask the flex PCB manufacturer about their shelf life. This lets you clearly understand this issue and also makes your future user experience more valuable. You should know that not all flex circuits have the same shelf life. The shelf life of flex PCBs depends on various factors, like the materials used, type of surface treatment, and storage conditions. and environmental factors. Let's look at it in detail next.
What factors affect the shelf life of flexible PCB?
You must know which factors affect the shelf life of flexible PCB so that you can clearly understand which factors are completely bad for your circuit boards.
1. Surface treatment
Short-term storage (up to 6 months)
OSP coating: OSP is one of the most sensitive surface treatments for shelf life. When stored correctly, it usually lasts about half a year. If the OSP layer is exposed to air, humidity, and high temps, it breaks down and makes the copper underneath.
Medium-term storage (6 to 12 months)
Immersion silver, and immersion tin: These coatings can last up to 12 months if stored properly. It is sensitive to environmental conditions and therefore requires controlled storage conditions to prevent oxidation.
Long-term storage (1 to 2 years)
ENIG coating: ENIG is a more durable finish with a shelf life of typically 1 to 2 years. The gold layer provides excellent protection against oxidation, which makes it ideal for flex PCBs that require long-term storage.
One major risk faced in the flex PCB production process is the complexity of soldering and forming strong solder joints that connect the flexible PCB components to the board. If oxidation occurs, this soldering can be affected, which is not good for the health of the board. The solder joints also become weak due to this oxidation. Therefore, to prevent this from happening, manufacturers consider using flex PCB components that have the same flexible PCB shelf life as the board.
2. Storage conditions:
Temperature: Flex PCBs should be stored in a cool and dry spot. High temps can speed up the degradation of the surface treatments, especially OSP, and might also affect the adhesives and other materials in the PCB.
Humidity: Humidity is crucial because moisture can cause the copper layer to oxidize and lead to other corrosion issues Flexible printed circuits should be kept in an environment with a relative humidity of 30-50% to prevent moisture damage.
Prevent contamination: Flex PCBs should be stored in anti-static, moisture-proof bags and kept in a clean area to avoid contamination from dust, oil, or chemicals that could affect the surface finish or material properties.
3. Material stability:
Polyimide substrates: The polyimide substrates used in flex PCBs are generally stable and have a long shelf life if stored properly. However, exposure to UV rays, heat, or chemicals can degrade the material over time.
Adhesives and bonding layers: The adhesives and bonding layers used in multi-layer flex PCBs are also stable under proper storage conditions, but may degrade if exposed to heat, moisture, or chemicals.
4. Packaging:
Different packaging types also greatly affect the shelf life of flexible PCB. Flex Plus can provide different packaging solutions for guests to choose from according to customer requirements. Among them, vacuum packaging is the most common packaging method.
Vacuum sealing: Some manufacturers vacuum seal flexible PCBs to protect them from moisture and contamination, thereby extending their shelf life.
Desiccant: Putting desiccant in the package helps absorb moisture and extend the shelf life.
5. Choice of flex PCB manufacturer
You will be able to evaluate their performance based on flex PCB production, material procurement, and flex PCB component assembly. Excellent flex PCB manufacturers have recorded flex PCB shelf life.
Speaking of this, we at Flex Plus strictly control the shelf life and clearly record and eliminate expired shipments to ensure reliable product quality.
Dangers of using expired flex PCBs
1. Causes oxidation
Oxidation issues will eventually damage the entire flex PCB structure. It also won't let you fully solder the flex PCB and will still leave gaps in the process. Therefore, the components cannot fully adhere to the board and there is a high chance that they will fall off as well. It is important to note that flex PCB surface finishes have different flex PCB shelf lives. Therefore, it is best to use the appropriate flex PCB surface treatment to firmly connect the parts to the board, then this problem can be easily solved.
2. Absorption of moisture
After flex PCB absorbs moisture from the air, it may cause thermal processing defects such as blistering, warping, cracking, electrical problems such as reduced insulation performance, and high-frequency signal degradation, while accelerating corrosion and material aging, affecting the long-term reliability of the product. To avoid these risks, measures such as moisture-proof packaging, appropriate storage environment, pre-bake treatment, and rapid processing should be taken to effectively reduce the negative impact of moisture on the performance of flexible PCBs.
An important tip here is that if you use OSP, make sure to complete the reflow process as soon as possible, otherwise, things will become complicated if you delay reflow.
Conclusion:
With the above information, I believe you should have a detailed understanding of the shelf life of flex PCB. In addition, regular inspections of flexible circuit boards in storage are required to check for signs of oxidation, loss of gloss, or other degradation. Regular inspections of surface treatment can help detect potential problems before they affect assembly. If flex PCB boards have been stored for a long time, electrical and mechanical testing before use can ensure that they are still suitable for the purpose.
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