IEC PAS 62435-2005 pdf – Electronic components – Long-duration storage of electronic components – Guidance for implementation.
2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 60068-2-1 7:1 994, Basic environmental test procedures – Part 2: Tests – Test Q: Sealing IEC 60068-2-20:1 979, Environmental testing – Part 2: Tests – Test T: Soldering IEC 6041 0:1 973, Sampling plans and procedures for inspection by attributes IEC 61 340-5-1 :1 998, Electrostatics – Part 5-1: Protection of electronic devices from electrostatic phenomena – General requirements IEC 61 340-5-2:1 999, Electrostatics – Part 5-2: Protection of electronic devices from electrostatic phenomena – User guide IEC 61 945, Integrated circuits – Manufacturing line approval – Methodology for technology and failure analysis IEC 62380: Reliability data handbook – Universal model for reliability prediction of electronics components, PCBs and equipment EN 1 90 000:1 995, Generic specification – Integrated monolithic circuits 3 Storage decision criteria Any creation of an electronic component inventory should be carried out • on the one hand, after having compared with the following additional solutions: ? modification to the printed board by adding a “backpack” macro-component;
3.1 Advantages 3.1 .1 Technical simplicity – Rapidity When the various steps of the storage process are finalized and validated, the creation of a stock is a simpler, faster and technically less hazardous solution than developing or modifying electronic boards. Storage can also be a temporary solution enabling equipment maintenance during modification or development of electronic boards. 3.1 .2 Solution durability Any equipment changes based on the use of new electronic components will be faced, eventually, with the obsolescence of these new components. Storage can resolve obsolescence problems until the end of the operating life of the equipment. 3.1 .3 Preventive storage Preventive storage (i.e., before the component becomes obsolete) presents several additional advantages compared with remedial storage (i.e., when the component has already become obsolete), for example, when − the component price has not become prohibitive as in the case of specific obsolete components which have become very rare; − the quality level is ensured if the component can be purchased direct from the manufacturer or approved distributor. When a component has been obsolete for a long time, it can only be found at specialists in purchasing, storage and resale of obsolete components (“brokers”). In this case, no component reliability guarantee will apply. 3.2 Hazards – Drawbacks 3.2.1 Generic aging hazard Stock dimensioning is based on the assumption of a constant component failure rate. The problem of generic aging of the components (“bath-tub curve”) cannot be easily taken into account and quantified. However, the existing electronic components seem to have extremely long lives provided that they are manufactured with all quality guarantees and that they are used in accordance with their specifications.
3.2.3 Incorrect control of reliability during storage Storage conditions shall be precisely defined and controlled, in order to guarantee the reliability of the components stored (see Clause 5). In addition, it is important to check the quality of the components to be stored (see Clause 4). This may lead to the setting-up of fairly heavy and costly infrastructure and procedures. Checking component quality may be an efficient means of reducing the risk of improper reliability control during storage. This can be done either by performing periodic sampling in order to carry out tests on the components (see Clause 6) or by checking that the components taken from the stock and used on the electronic boards operate correctly (provided that the consumption of the components in stock is sufficiently regular). 3.2.4 Freezing equipment functionalities Storing components to ensure equipment maintenance over a long time implies that the equipment functionalities be frozen. A long-duration storage solution is therefore not very compatible with the desire to upgrade equipment and functionalities. 3.3 Storage cost In order to assess the cost of a storage solution, various items should be taken into account, such as: – component purchasing; – validation/test of purchased component batches; – conditioning and de-conditioning; – stock management; – maintenance of installations dedicated to storage by means of manufacturing tests and/or repair; – staff ensuring storage, maintenance operations, etc.; – financial cost of tied-up stocks.