Regardless of the PCBA design, it always seems there is a sense of urgency attached to the board development process. That is, bringing the design to the production phase as soon as possible is always the goal. However, this must be done with a view towards avoidance of common PCB quality issues that may result in extended time for bring up, redesigns, and additional manufacturing costs. And although successfully reaching and executing board production is a primary objective, it is not the final one.
From the end user’s perspective, the most important factors for circuit boards are meeting functionality requirements and doing so reliably over the operational lifetime. Therefore, it is important to consider the state of the PCBA beyond production. This is better understood by realizing that in many cases, boards do not proceed directly to deployment from production. Instead, it is likely there will be some period of storage that may be years before the board is actually powered up for use. If not planned for, this interim may result in component degradation that can short-circuit your board’s ability to satisfy customer requirements.
Let’s take a look at what PCB storage guidelines should be followed throughout and beyond the board development process to prevent component failures, after first taking a look at common threats to component shelf life and reliability.
Common Threats to Component Shelf Life
Threats to your board’s component shelf life and ability to reliably perform once deployed are present throughoutthe board development process. This begins with component selection, where the following should be avoided.
Component Selection Threats
- Inferior components
Substandard parts exist for virtually all electronic components and it is incumbent on the designer to ensure that selections meet the operational and functional requirements for the design.
A major problem in electronics is the prevalence of counterfeit components. Thus, knowing and sourcing from reputable vendors is essential.
An often-overlooked threat is where your selected component is on the component lifecycle curve. If your
component is near or in the obsolescence phase, then opting to include it in your design will likely necessitate substitution or perhaps even redesign at some point during the board’s lifetime.
The threats listed above all pertain to the component supply chain management and are best avoided by knowing your sources and ensuring that component data and information is available and traceable. Assuring availability, functionality, and quality are the first criteria to stave off potential failures to the longevity of the shelf life for your board’s components. However, there are other PCB storage threats, as discussed below, that must also be addressed.
The Different Stages of PCB Storage
When referring to PCB storage guidelines, it is most common to focus on the time boards spend in distribution locations; such as warehouses and/or electronics retailers. It is true, that boards probably spend more time at this stage, yet it is not the only time that boards may be in storage, as shown below.
PCB Storage Stages
Depending upon which PCB manufacturer you choose, there may be a period between your board’s fabrication and assembly. In fact, it is likely these will be performed at separate facilities and by different manufacturers. During this period, boards are physically handled and can be exposed to the air resulting in contamination.
- Post-assembly (Shipping)
The final activities of assembly, which includes depanelization, are primarily intended to prepare the PCBAs for shipment. During transport, boards can be subjected to various temperatures that can impact component shelf life.
Most boards that are not immediately installed in a larger system will spend time in extended storage. PCBAs that are warehoused can suffer degradation due to oxidation, moisture buildup, or other contamination.
As shown above, boards may spend significant amounts of time in storage throughout and following the manufacturing processes. And, if PCB storage guidelines; such as those discussed in the following section, are not followed, the board and its components may fail prematurely.
How Following PCB Storage Guidelines Extend Component Shelf Life
Designing and developing PCBAs can be a complex process that requires a substantial expenditure of time and costs. To fully achieve the benefits and ROI for this process, protective actions should be taken during and after development to maximize the shelf life of PCBs and their components. And following the guidelines below will help you establish a plan to ensure components will last throughout their operational lifetimes.
PCB Storage Guidelines for Maximizing Component Shelf Life
✓ Utilize a secure supply chain
✓ Ensure that your CM follows PCB storage standards
✓ Use solder masking
✓ Apply an appropriate surface finish
✓ Make sure PCB assembly cleanliness specifications are applied
✓ Apply conformal coating when necessary
✓ Ship and store PCBAs in moisture barrier bags (MBBs) with desiccant
In conjunction with the guidelines above, the following standards and regulations should be consulted to establish your PCB storage guidelines.