Artist Alanis Morrisette has a song, entitled Ironic, which gives several examples of situations where someone finds themself not having what they need at the time that they need it. Certainly, all of us can identify with her in this. Sometimes, being left longing can be simply an annoyance, but at other times it can be quite significant. I suppose this is an excellent argument for being a hoarder or keeping what you may need in the future on hand now.
PCB storage warehouse
Whether you are a developer or OEM of circuit boards or electronics devices, not having the PCBs that you need when you need them can be a very significant problem. And similar to planning for component shortages, one of the best ways to avoid this contingency is PCB storage or volume buying significant numbers of boards to be able to meet demand or need. When warehousing boards; however, there are PCB storage guidelines that you should know and apply to ensure your boards remain viable throughout their shelf life. Before defining these, let’s make sure we understand why and when PCB protection is important during and after the development phase of the product lifecycle.
Why and When is PCB Protection Important?
Although circuit boards can be designed and built to perform extraordinary functions they are electronic devices. And all electronic devices are to some degree vulnerable. For boards deployed in aerospace, industrial, automotive or other harsh environments, pressure or temperature may be the greatest threats requiring that substantial protective measures be undertaken. However, PCB failure modes are not limited to these critical system utilizations. In fact, all PCBs must be protected prior to installation from threats, beginning with the development stage, as shown below.
When PCB Protection is Needed
Fabrication - PCB development begins with the fabrication of your boards. During this process, it is necessary to ensure there is no contamination on the materials used and no moisture gets trapped between layers.
Post Fabrication - Solder mask, which is applied to your board during fabrication, serves as protection against oxidation and handling which may introduce contamination prior to assembly.
Assembly - The soldering of components to your board can leave contaminates; such as flux residue; therefore, copper traces are protected by surface finishing that is applied during fabrication, and are cleaned afterward.
Shipping - Whether being shipped to you from your contract manufacturer (CM) or from you to a customer or client, your PCBs may be subject to unstable, high temperatures - that may result in moisture or low temperatures - that may cause cracking and lead to breakage. Having your boards protected, either by conformal coating or some other type of encapsulation, is one way to guard against these threats.
Storage - Next to operation, your boards will likely spend the most time in storage. Part of this may be between fabrication and assembly, if your CM is not a turnkey manufacturing services provider, but the majority will be post-assembly. Therefore, it is necessary to follow good PCB storage guidelines to ensure that your boards are ready when it comes time to put them in operation.
What You Should Know About PCB Storage
Storing bare (PCBs) or assembled (PCBAs) unprotected is flirting with disaster. And failing to recognize the fact that your boards can and will degrade faster over time if left unprotected can be an expensive lesson to learn when remanufacturing costs, unfilled deliveries and potential canceled deliveries start to eat away at your ROI. Fortunately, there are remedies that if applied can significantly reduce the possibility that you will lose any boards due to mishandling or bad storage practices.
The first step to take is to ensure that your CM follows good board handling and storage suggestions; such as those put forth in IPC-1601 Printed Board Handling and Storage Guidelines. These guidelines provide fabricators and assemblers with methods and information for protecting PCBs from the following:
- Solderability degradation
- Physical damage
- Moisture uptake
- Electrostatic discharge (ESD)
Used in conjunction with IPC/JEDEC J-STD-033D Handling, Packaging, Shipping and Use of Moisture, Reflow and Process Sensitive Devices, IPC-1601 provides standards for packaging and storage to minimize the possibility that your boards will incur contamination during manufacturing. Additionally, the shipping and storage guidelines included can be utilized along with an understanding of the impacts on the shelf life of assembled PCBs to compile a set of important PCB storage guidelines, as shown below.
Important PCB Storage Guidelines
- Apply appropriate surface finish during fabrication
Bare boards may require temporary storage after fabrication, but before assembly. To protect against oxidation and contamination during this period a suitable surface finish should be applied.
- Use non-moisture sensitive components, if possible
SMD components that are not moisture-sensitive have a virtually unlimited storage lifetime in environments with temperature ≤ 30°C (86°F) and 85% relative humidity (RH) prior to assembly. If packaged properly, these components should easily exceed the nominal post-assembly shelf life of 2-10 years. Moisture sensitive components, on the other hand, have recommended shelf lives that range from a day to one-year pre-assembly. For boards with these components, environmental control and storage containers will greatly determine the length of viability.
- Store boards in moisture barrier bags (MBBs) with desiccant
All boards should be stored in moisture barrier bags to prevent moisture from entering the bag and desiccant to absorb any moisture inside. However, do not use bags that have been stored for over a year.
- Vacuum seal MBBs
MBBs should be dry and vacuum sealed. This will give protection from ESD.
- Control the environment
Care should be taken to make sure there are no extreme temperature swings during storage or shipping as temperature differentiation will create moisture transfer or condensation. The best option is a controlled temperature environment below ≤ 30°C (86°F) and 85% RH.
- Ship or use the oldest boards first
It is also a good idea to always ship out or use the older boards first to minimize the possibility of boards being forgotten and exceeding the recommended shelf life.
|Tempo's Custom PCB Manufacturing Service
Built boards are not always immediately installed or deployed. Therefore, it is important to consider PCB storage guidelines to ensure they are ready when the time for operation comes. At Tempo Automation, ensuring that your boards are free from contamination is built into our process and we clean every board that leaves our smart factory.
And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in other CAD formats and Excel.