Regardless of the purpose of a circuit board design, there always seems to be a sense of urgency involved in its development process. Bringing the design to the production phase as quickly as possible is always the goal. However, accomplishing this goal must be done with consideration towards avoiding PCB quality issues that can force redesigns and add additional manufacturing costs. Successfully taking a circuit board from design to production is a primary objective, but it is not the final one.
Once a circuit board is in the hands of its end user, the main concern will be that the PCBA meets its functionality requirements reliably over its operational lifetime. Therefore, it is imperative to consider how the PCBA will be stored beyond production to ensure it meets these requirements. In many cases, circuit boards are not directly deployed after production and instead are stored for a while before they are powered up for use. If good PCBA storage practices are not planned for upfront, the board may experience degradation and short-circuit its ability to satisfy customer requirements and expectations.
This article will examine what PCB storage guidelines should be followed throughout and beyond the board development process to prevent PCBA failures. But first, let’s look at some common threats to PCB component shelf life and reliability.
|Top Threats to PCBA Reliability Due to Storage Problems|
|Oxidation||Once the exterior metal surfaces of a PCB are exposed to air, oxidation can occur if not adequately protected and stored.|
|Contamination||Moisture, dust, and other contaminants can introduce problems such as mold or mildew to the board.|
|Grease||Improper handling of a PCB can introduce contaminants that will eventually corrode the board.|
|Electrostatic Discharge||Electronic components can be sensitive, and static can easily damage them.|
|Shock and Vibration||Solder joints, delicate components, and even board edge features can fracture by rough handling.|
|Thermal Stress||Extreme cold and heat, or the movement between these extremes, can degrade the integrity of the circuit board.|
Common Threats to Component Shelf Life
The PCBA development process is rife with threats to the shelf life of your circuit board, its assembled components, and its ability to perform reliably once deployed. These threats begin with component selection, where the following should be avoided.
Component Selection Threats
- Inferior components
Substandard parts exist for virtually all electronic components. 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. To combat this problem, PCB designers and manufacturers must source their parts from reputable vendors.
An often-overlooked threat is when PCB components approach the end of their lifecycle. If you select a part that is obsolete or close to it, you will likely have to go through a redesign at some point in the board’s lifetime to continue production.
The threats listed above are all part of what must be considered for good component supply chain management. To mitigate supply chain problems like this, knowing your sources and ensuring that component data and information are available and traceable is crucial. 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, as discussed below, there are other PCB storage threats that designers and manufacturers must address.
The Different Stages of PCB Storage
When considering PCB storage guidelines, focusing on the time circuit boards spend in distribution locations, such as warehouses and electronics retailers, is common. It is true that PCBAs probably spend more time at this stage than any other, but 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 of time between your board’s fabrication and assembly. In fact, the fabrication and assembly of the board will likely be performed at separate facilities and by different vendors. During this period, circuit boards are physically handled and can be exposed to the air, resulting in contamination.
- Post-assembly (Shipping)
The final activities of assembly, which include depanelization, are primarily intended to prepare the PCBAs for shipment. Circuit boards can be subjected to various temperatures during transport, impacting component shelf life.
Most boards not immediately installed after manufacturing 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. If PCB storage guidelines like those discussed in the following section are not followed, the board and its components may fail prematurely.
How Following PCB Storage Guidelines Extend PCBA Shelf Life
Designing and developing PCBAs is a complex process that requires substantial time and money. To fully achieve the benefits and ROI of this process, protective actions should be taken during and after circuit board development to maximize the shelf life of PCBs and their components. 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, designers and manufacturers should also consult the following standards and regulations to establish your PCB storage guidelines.