The storage of moisture sensitive electronic components and materials is problematic, and manufacturers with long term storage requirements face additional obstacles.

Requirements for long term storage are increasing. Why?

Component obsolescence 

Due to rapid changes in packaging design and material, companies find themselves forced to purchase additional quantities of components in order to guard against the impact of component obsolescence on their final product designs. This in turn creates an issue of long term inventory storage.

Short product lifecycles

Product lifecycles have become very short with new models being released sooner than ever before. However, many manufacturers in industries including automobiles, aviation and avionics, military and railway must guarantee the availability of replacement parts including PCBs for ten or even twenty years. This demands the advance purchase and extended storage of components and materials. Further complicating the problem is that most components cannot be stored for more than a few years without very special handling procedures.

Risks

Oxidation

After long-term storage, components and circuit boards are often no longer solderable, due to oxidation caused by the oxygen of the air (oxidant) and the humidity (electrolyte). However, if the humidity, which forms an invisible water film of few atomic layers on the surfaces, is lowered below 5% RH, this corrosion process is stopped. At the same time, other negative effects due to moisture absorption are also avoided.

Intermetallics

Intermetallic compounds form when two unlike metals diffuse into one another creating species materials which are combinations of the two materials. Intermetallic growth is the result of the diffusion of one material into another via crystal vacancies made available by defects, contamination, impurities, grain boundaries and mechanical stress. There are a number of locations within the electronic package where these dissimilar metals are joined. These include die level interconnects and wire bonds, plating finishes on lead frames, solder joints, flip chip interconnects, etc. Growth of intermetallics during the storage period can occur and reduce the strength.

Intermetallic growth rate is strongly temperature-dependent and doubles for each 10 ° C temperature increase.
This aging process can be slowed by appropriate cooling. However, the risk of whisker formation of tin alloys increases with decreasing temperature. Studies and practice have shown that a storage temperature of 12 ° C is optimal.

Dry Cabinets that also Cool

The XSDC-1402-52 cabinet from Totech will help you avoid the above risks…

• The compact design of the XSDC-1402-52 with the U-5000 dry unit delivers fast recovery <5% relative humidity.
• Height-adjustable and extendable shelves allow individual design of the interior.
• A powerful cooling unit can lower the internal temperature of the cabinet to 10 ° C. High insulation values are ensured by a glazed double-wall & a foam inner body.
• Settings and alarms are entered and managed via the display or online.
• Software allows you to monitor the storage conditions and the limit values can be assigned to each component.
• Standardized interface for integration into an existing ERP system to help you achieve your Industry 4.0 objectives.

Find out more about the XSDC long term storage Dry Cabinets.

Read our article on combating oxidation & inter-metallics in moisture sensitive components which appeared in the January 2017 issue of SMT Magazine.