If you have ever lain on the beach on a cloudless, windless day, it is hard to imagine that the weather could ever cause any harm to anyone. Well, we surely know that severe weather conditions can wreak havoc. In addition to these rather severe demonstrations of the effects of weather are the more common occurrences that are sometimes overlooked until they are unavoidable; for example, the threats from overexposure to sunlight, inclement temperatures, rain, and snowstorms.
Electrostatic discharge (ESD) bags
The environment can pose threats for humans as well as PCBAs, albeit in different ways. In fact, some threats to your board’s performance and reliability can manifest themselves after manufacturing and before they are installed or deployed. These are in addition to threats that are either inherent or can occur during the PCB assembly process. Let’s take a deeper look at these threats and examine how they can impact the shelf life of assembled PCBs, which in turn degrades the expected performance and reliability of your boards.
Pre-Storage Threats to PCBAs
PCB assembly is the final stage of board build and is performed by your CM; yet, manufacturing optimization depends to a great extent upon your design process. The same is true for avoiding common PCB failure modes that can occur once your board is installed or in operation. Therefore, you and your CM should work together to alleviate or eliminate the possibility of failure. This includes considering threats during the interval after your board’s assembly and before it is deployed, which can be divided into pre-storage and storage.
Typically, neither pre-storage nor storage threats receive the level of attention that is warranted. However, pre-storage threats are the ones most often overlooked. Surely, you have had boards delivered that were simply stacked unprotected in a box, not knowing their transportation or handling conditions. Even if you take protective measures after receiving them, that does not guarantee that threats such as moisture or ionic contamination, which can be especially troublesome on precision medical device PCBAs, are not already present on your boards. In addition to negatively affecting or reducing your board’s reliability, these pre-storage threats can also impact the shelf life of your assembled PCBs.
Threats to the Shelf Life of Assembled PCBs
If you are in the development cycle or prototype iteration cycle, your boards will likely go directly to be tested. However, if your boards are in production, there is a good chance they will spend some time on the shelf after receipt from your CM, awaiting shipment and installation. The shelf life of assembled PCBs is how long your boards can remain viable during this storage period and it depends upon a number of factors, as listed below.
What Impacts the Shelf Life of Assembled PCBs?
- Design choices
The quality of components selected for your design greatly affects the assembled board’s shelf life. Therefore, you must consider component lifecycle (product and operational) when choosing components.
- Fabrication and pre-assembly
- Surface finish
Surface finishing is a PCB plating option performed at the end of bare board fabrication that protects your boards while being stored until they are assembled.
- Assembly processes
Depending upon the solder used and the specific soldering method, the shelf life for your boards can be as long as 10 years.
- Conformal coating
One of the best ways to protect your boards is to have industry-standard conformal coating applied by your CM. Failing to do so may expose your boards to contamination during storage.
The handling of circuit boards can introduce contamination. For example, sweat, dirt, or chemicals from cleaning can be left on the board.
- Shipping conditions
If your boards are not shipped in a temperature-controlled vehicle, moisture may form on the boards, seeping into its internal layers. This internal moisture may not be visibly detected and ultimately result in you shipping out defective boards.
- Storage environment
How you store your boards has the most direct effect on the shelf life of your assembled PCBs. If your boards become contaminated during this time, for example from moisture, oxidation may form within the nominal two to ten years of anticipated shelf life and necessitate baking or even discarding them altogether.
|Tempo's Custom PCB Manufacturing Service
There are many factors that may threaten your boards during storage. And shelf life degradation can be a significant problem if good PCB storage guidelines are not adopted. At Tempo Automation, our quality control capabilities include a wide range of surface finishes to protect your boards between fabrication and assembly. We also individually clean every board post-assembly and apply conformal coating to ensure your boards are maximally protected.
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.