Shelf-Life of Components and Common Threats

The two major threats to the shelf-life of components are:

--Component Selection Threats

--PCB Assembly Storage Threats

Component Selection Threats

Threats to the shelf-life of components on the board and their ability to perform reliably once the OEM has deployed the board, depends to a large extent on the development process of the board. Therefore, designers should be careful when selecting components and avoid the following:

1.Counterfeit Components:

Counterfeit components are a major threat to the electronics industry. Unscrupulous suppliers supply components they have purchased under shady deals, restamped components, and rejects from manufacturers, as genuine components.

2.Inferior Components:

Along with the supply of good and reliable components, a parallel grey market exists for substandard and inferior components, Designers must be careful 

and ensure that they source their components only from reputable suppliers to meet the functional and operational requirements for their design.

3.Obsolete Components:

Designers often overlook the threat of obsolescence, and select components that are at or near the end of their life-cycle curve. Overlooking the obsolescence of a component may involve looking for a substitute or in extreme cases, having to redesign the board at some point during its lifetime.
The above threats are all related to the way the OEMs handle their supply chain management. It is possible to avoid the threats by sourcing components only from known reliable suppliers and ensuring availability and traceability of component data.

PCB Assembly Storage Treats

Assembled PCBs undergo storage at three stages before their deployment. The stages are:

--Pre-Assembly at the Contract Manufacturer

--Post-Assembly during shipping

--Pre-Deployment at the OEM

Pre-Assembly:

Contract manufacturers maintain boards under various stages of work-in-progress before the assembly process completes. During this pre-assembly stage, partly finished boards travel between different stations where operators add on their part of the activity.

During this period, it is likely that operators handle the boards physically, which can cause contamination from body oils, atmospheric dirt, dust, and much 

more. A greater danger in this period is damage from Electro Static Discharge or ESD. Accumulation of static electricity due to various reasons can discharge through the components on the board, damaging them partially or fatally.

To avoid damage during the pre-assembly stages，we maintain clean rooms for assembly, our operators wear protective clothing, and we have anti-static 

measures in place.

Post-Assembly:

During shipping it is important to protect the boards from the vagaries of nature, such as temperature fluctuations, ingress of dust and moisture, and physical damage from shock and vibration.

Pre-Deployment:

The OEM may have many reasons for not deploying the assembled boards immediately after receiving them. These may include delay in receiving cabinets, firm orders, or others. As a result, the assembled boards may spend a considerable amount of time in storage before the OEM finally deploys them.Unless the OEM stores implements and follows PCB assembly storage guidelines, the board, and components on it may fail, and may not function properly on deployment.

PCB Storage Guidelines

In our company,we maintain and implement the following guidelines for ensuring the reliability of our assembled PCBs:

--Source components only from secure suppliers

--Follow standard anti-static procedures for PCB and component handling

--Use solder masking and appropriate surface finish

--Apply cleanliness specifications for assembly stages

--Apply conformal coating (with customer’s consent)

--Store and ship assembled PCBs in moisture barrier bags along with desiccant inside

--We comply with the following standards for PCB handling and storage:

*IPC/JEDEC J-STD-033C-1

*IPC/JEDEC J-STD-020E

*IPC 1601A