The Long-Term Storage Can o’ Worms A Guide to ensuring your equipment can still be built and maintained in years to come. Will you be able to build your product next year? Have you protected your component supply? Is your inventory safe? Are you really archiving your doc uments and data? Can you retrieve your archives? If you can honestly answer ‘yes’ to ALL the above questions, then you’ve already read this booklet ! 1 Contents Page Why do we store product? ............................ 2 Hedging against obsolescence? ..................... 3 The Archival Store ......................................... 5 Data storage ................................................... 5 Electronic Data storage .................................. 6 The Media ...................................................... 7 The Computer ............................................... 8 The Software & Data Format ......................... 9 Data storage, initial conclusions ................... 10 Choosing the media … .................................. 10 Considerations............................................... 12 Long-term storage and corrosion .................. 13 Our atmosphere............................................. 15 Methods of protection ................................... 16 Considerations for long-term Storage of Die & Wafer product 18 Initial assumptions for die & wafer storage .. 20 Known product sensitivities, or “How to damage die product ...” 20 Preparation for storage .................................. 23 Information needed before setting up a storage plan… 24 Speculation on future problems .................... 25 Initial conclusions on die & wafer storage .... 26 Die Banking ................................................... 27 Acknowledgements ....................................... 29 Annex 1. Glossary. ......................................... 30 Annex 2. ......................................................... 31 Why do we store product? production, are employed under the wrong circumstances. Where inventory is held, for how long, and at whose cost, is a major financial and Whilst this is an obvious question, it is one that can logistical factor for all manufacturers to address. often produce different answers. To the manufacturing engineer, it is to keep his In order to minimise the financial impact of having production line running, to the accountant it is large duplicate stores, one approach (often often a just another point of lost revenue, to the real favoured in accounting circles) is to have a single design engineer it is a source for quick “try-it-and- centralised store. While this may be more see” components, and to the store person it is their satisfactory from the financial angle, if any stores raison-d’être. are too remote from the point of usage, extra effort and time is wasted in transporting the call-off We sometimes store items as a buffer stock against items. our periodic or sporadic usage, smoothing out the requirement to re-purchase an item, or we may be In a fast-flowing assembly line, such as a car forced to store items because, when procuring manufacturing plant, the stores are split between a items, we are faced with a minimum order quantity centralised store, used as a intermediate-term (MOQ). Just try purchasing a single paper clip, buffer for incoming stock, and the in-line stores, sheet of paper or metal washer. which are in immediate proximity to the assembly bay or point of usage. This system works well, Inventory may be stored at any time during its provided there is sufficient flow from central to usage cycle, from raw BOM (bill of materials) and local store in pace with the stock consumption. BOF (bought out finished) through to the final end product, awaiting delivery or customer acceptance. Primarily, a store-person’s function is to satisfactorily hold, protect and monitor the Part-finished items may be stored for long periods, inventory such that items can be released in a and the final delivered product may well be a kit of timely and orderly fashion, either as single items or unassembled or partially assembled parts for the as kits of parts. There are many anecdotes, some customer to integrate or complete. apocryphal, involving stores personnel, generally relating to their reluctance to release product under Throughout the supply chain, “users” rely upon any circumstances … thus taking their “suppliers” to hold inventory to some degree or responsibilities to comical extremes. Quotes such as another. However, although purchasing/ “you can’t have it, it’s the last one”, “I can’t open the manufacturing methodology systems, such as JIT bag just to give you one” and “do you know what it (Just-In-Time), Kanban, Bottle-Neck management looks like?” are common. Centralising office etc., have been used, someone, somewhere, holds a material stores, such as for paper consumables, has stock of finished or partially-finished product to also led to some extremes, such as a one-mile maintain the production flow. These methodology round-trip to obtain a notebook or a ballpoint pen - systems can easily be upset when the inventory or hardly the most efficient use of someone’s time. distribution chain has a minor hiccup - often Believe what you will, it has happened! because these systems, which work well in mass- 2 Micross Components Ltd The item/inventory stores, therefore, can be seen ambient climate may also affect the effective shelf as both as a buffer /reservoir against consumable life of specific items. usage, and as an insurance policy against item obsolescence. In a perfect world where items could be stored indefinitely and when purchasing COTS Stores can be differentiated by their contents and (Commercial Off The Shelf) items as inventory, purpose. Two significantly different types of store there would be the options as to whether: exist, the consumable item store and the archival • manufacture immediately, store. • manufacture later, or • manufacture on demand. In general, the requirements of each type of store differ, but both take up valuable floor real-estate A simple example could be the supply of 100 that can be seen by accountants as a wasted asset. finished units over 10 years, on a regular supply The consumables store can be further analysed into basis using COTS components. Here, the options a fast-moving consumables store, or a long-term may be: storage point. 1. to build all 100 units immediately, whilst all the components are available, The fast-moving consumables store may often be 2. to build on demand, purchasing components computerised, with rapid mechanical storage and “just in time”, retrieval systems. Inventory is often then placed in 3. to purchase all component items up-front, and preferential locations - shelf lifetimes and stock then build on demand, or turn-around may then automatically considered. 4. to purchase all the “sensitive” components immediately, and use a mixture of options 2 Hedging against obsolescence? and 3. The long-term storage of some items can be impractical or may present an unacceptable hazard. Option 1 presumes that all 100 finished units can be Consideration as to their consumption versus stored without degradation, but it has the storage facilities and attendant costs is, therefore, advantage that the assembly and test jigs can be re- needed. Certain items are regarded as allocated once the total build is complete. environmentally unfriendly, toxic or flammable, and, dependant upon local legislation, may Option 2 is naturally fraught with obsolescence possibly require external monitoring, regulation issues, remembering that the “C” in COTS means and/or licensing. commercial. Other items may be unsuitable for long-term Options 3 and 4 also require storage without storage due to an inherent time dependant degradation, but only of the element components, degradation mechanism, often requiring careful or and even then only those components deemed to specialised packing to prevent deterioration. In be at risk of obsolescence. certain instances, storage orientation and/or 3 Micross Components Ltd Options 1, 3 and 4 require the creation of an engineering and purchasing. The choice of storing “obsolescence store”, or a type of bonded on- or off-site, multiple warehouses, or using an warehouse where the units can be stored and the external agent, and exactly what is to be stored components ring-fenced specifically for this order should be the concern of all departments. or project. Time for retrieval, physical location, control of inventory, storage methodology and damage/risk An obsolescence store may be created intentionally, analysis should be considered during the decision as an insurance policy against critical items phase. becoming unavailable, either in the short, medium or long term. The “store” may also be created Part of this obsolescence store may be the archival accidentally, by over-stocking, by the item being no store, where all the relevant documentation and longer required, or even unofficially in the know-how are stored along with the component, proverbial “engineer’s bottom drawer”. albeit in a separate location. This “know-how” may include the engineering notes and day-books, Individuals in a company may be more aware than assembly and build data, design and procurement others of the critical aspects of a component and/or details, CAD & CAM files, test program files and impending supply problems, and may decide to specifications. An “application sensitivity” chart is take their own independent remedial action when recommended, indicating what other faced with lethargy or intransigence from those plant/machinery/process/materiel/sub-contract who should know better. Whilst this latter service is needed to complete the build, verification approach may be applauded when it works, and use of the stored component. The effectiveness of the stored component is only as good as the surrounding systems, so if the manufacturing process is altered, the effect of that change on the stored components should be considered. With electronic components, the assembly processes might well have migrated to a Pb-free solder, so the component lead finishes and assembly temperatures of existing stored items become relevant, but if the component or sub- assembly tester is scrapped … ? it can be equally harmful in both preventing a more formalised approach to obsolescence, and the The actual physical obsolescence store may, means of storage with relevant traceability indeed, be part of the existing in-line stores with paperwork is often inadequate. the components within the obsolescence stores being regarded as pre-allocated, and kept in Long-term storage of components should be a quarantine against specific project or projects company-wide decision, with commitment from all demand. A degree of cross-project component relevant departments, including finance, standardisation can also limit the overall 4 Micross Components Ltd requirement in terms of that particular selected consumable items. The value, intrinsic to this store, component becoming designed-in across many is held not in the physical items present, but in the projects, the only caution being to prevent one associated data content, and, unlike the avaricious project consuming the stored consumable store, the value is very hard to component to the detriment of other projects. quantify. Certainly, the data held is a company asset without which the company might cease to In addition, standardisation of components can function. It is, however, often difficult to justify have positive implications when purchasing significant expenditure upon something, which in against fixed MOQs (Minimum Order Quantities), reality, is priceless. and can give leverage to the procurement departments when negotiating one-time buys. The The physical security of the archive store will not use of programmable logic, such as PALs, be mentioned further here, but should be a main PLDs and FPGAs should be considered; using the consideration when planning its location and same physical device with differing programmed access. functionality for many projects and applications. The use of a high-level synthesis design language, Data storage such as Verilog or VHDL, can greatly simplify the From the early 1960s onwards, media for storing upgrade path to newer or current parts. When data other than paper (and of course, tablets of using complex FPGAs, the programming station, stone), has historically inclined towards magnetic whether in-circuit or stand-alone, should be media. More recently, however, optical methods of considered as a candidate for archiving, along with data storage have been gaining ground. the requisite design and programming software. In the past, data has been stored as readable print The Archival Store or script on paper, and although there have been other methods of data storage, such as punched tape, card-decks, wooden blocks or metal-tang cylinders, the preferred choice has remained the printed word, as begun by Guttenberg and Caxton. Now, however, some printed data is effectively undecipherable without computer assistance (such as bar codes) but, in general, the data on paper is in the local language, which may be made computer- friendly by optical scanners and optical character recognition (OCR) software. Audio data has been stored on all manner of media, from the Edison wax disk and cylinders, through shellac 78s and vinyl 45s and 33s. Now, however, the compact The archival store is generally used to store data on cassette and CD hold sway, indeed, fewer Hi-Fi whatever medium is presented. The contents are generally regarded as insurance as opposed to 5 Micross Components Ltd systems now come with a cassette player, but treasure house of information when faced with almost none come with a record deck! component parts replacement or obsolescence Microfiche film has been used extensively to issues. Paper de-acidification technology is in compact the storage of paper documents, but has regular use in relation to the preservation of many been slowly giving way to more electronic means of our important historical documents. Much of storage. There are modern threats to even restorative work of paper and books is a continual traditional printed books, such as e-books, where ‘work-in-progress’ function at most large library the data is held on a semi-volatile electronic centres, especially on books printed during the last memory medium (disk or flash memory), and century, where the high-chlorine content of read/displayed by a suitable miniature computer. bleached paper creates an in-built destruction Whilst these e-books may be initially treated as mechanism. gimmickry, there is a growing trend away from traditional paper text; even public lending libraries Electronic Data storage now lend CDs, DVDs and tapes. Careful selection of the electronic medium is required, as there are many hazards in relying on Paper storage has always presented problems. this media that are not instantly apparent. It must Concerns of bulk, weight and flammability, be remembered that data to be archived must be coupled with the vulnerability to damage from retrievable, otherwise the purpose of archiving is water, chemical degradation and, of course, fire, negated. have not endeared its continued use as the medium of choice. At times it would appear that there is Full use of the Internet could well remove the need something to be said for “tablets of stone”. Old for single point data storage in the future, the data manufacturing drawings held on vellum may still being stored and retrieved simultaneously on be usable, whilst the old dye-line reproduction numerous different host computers and, as each methods have long since been obsolete. But despite computer is individually upgraded or replaced, the known issues, some forms of paper will continue to data is retained on other host computers. The main have a valuable place and be used for a long time objection to relying upon the Internet for data yet. storage is its currently perceived vulnerability, having both potential security issues and the Why does the legal profession like parchment? Because it danger that data may be uncontrollably replicated has an incredibly long life dependent on the ink used. and corrupted with great rapidity. Early Fax and printers, using thermal or “spark” Third party “data storage”/”data warehouse” printing technology certainly had issues with companies exist, and these are often used as a permanency and legibility. Even today many types suitable secondary location backup and repository of printer ink have known lifetimes. for critical or sensitive data. However, in today’s fast moving technology, old All electronic media requires the use of a computer data-books that were once considered redundant of some sort or another to retrieve the data and and ready for discarding, can now be seen as a 6 Micross Components Ltd convert it into a human-sensible format. So we are Optical media, such as the ubiquitous compact disk relying on four main precepts to recover this data: (CD) and the increasingly popular DVD disk, can also present problems. CD-Rs that are written by • The endurance and lifetime of the media itself. the average work PC have a distinct shelf life, and, • The presence of the specific media-reading dependant upon the storage ambience can lose hardware. data in 18 months or less, the quality of the initial • The associated computer. CD-R or CD-RW media is paramount. • The interpreting and display/application software. The Media When considering magnetic media such as tapes and disks, it is well known that the long-term storage of magnetic media has its own attendant issues. Problems of oxide-shedding and magnetic “punch-through” on magnetic tape quickly render a tape unusable, often in as little as 5 years if the tape has not been carefully stored. Platter disks are CD-R damage generally less susceptible, but “punch-through”, Photo: Alun Jones – Austin Semiconductors can still occur, and head-dust, caused by deterioration of the ferric-oxide bonding agent, can Shedding of the reflective aluminised coating and lead to irreparable damage to both the platter and delamination can also occur, and the sensitivity to read heads as soon as the platter is mounted. UV light and certain cleaning chemicals is well documented. There are other electronic storage mechanisms, such as holographic storage, ferro- optical disks, or bubble memory modules, which seem to have come and gone without having a major impact on the mass data storage market. The above picture shows damage to a CD-R disk that has been poorly stored. The reflective metallisation has peeled away onto the packing. The Media Reader. This is often the most critical item, as even if the data remains intact upon the storage media, the function of the media reader cannot be guaranteed. Floppy disks, in their many guises, can be Data formats change, sometimes rapidly, due in susceptible to mechanical and magnetic damage. part to the need for increased storage density and retrieval speed. 7 Micross Components Ltd What was once the media of choice in the 1970s and early 1980s, the open-reel ½ in. magnetic tape, has now become a museum piece. Suitable working data readers are few and far between, although some specialist companies maintain these readers for the sole purpose of data recovery. The ½ in. magnetic tape gave way to the QIC (Quarter Inch Cartridge) tape which many older Unix systems still use and maintain. In the PC world, the plethora of data standards has meant that the days of the QIC tape are numbered. Various cartridge-type tapes, from “audio-cassette” to DAT have been around, but it is highly likely How many of these types of storage media can you identify. And how many could you read? that the appropriate data reader is non-functional Photo: Alun Jones - Austin Semiconductors and obsolete. Unusual data readers, such as the Bernoulli disk, or the Sinclair Microdrive, became In the author’s opinion, Unix platforms have quickly marginalized, just as the old in-car 8-track tended to be more stable in their hardware and was superseded by the cassette player, which is computer data formats, using TAR or BAR now marginalized by the Compact Disk (which is generally as the archive data format onto QIC or being ousted by the DVD). Floppy disks have fared DAT tapes, but many newer QIC readers will not somewhat better, but few companies will have 8 in. accept the older 30MB and 60MB tapes, preferring or 5¼ in. floppy drives available and operational. the newer 150MB or 525MB tapes. On rare Even the 3½ in. floppy drive is being phased out on occasions, DAT tapes, with differing compression modern PCs. algorithms, may also present a problem. Integral with the reader is the native format of the The Computer data and operational commands, such that many Whilst this again appears obvious, some of the drives will not function without the appropriate early data readers, such as ½ in. magnetic tape software functions. Specialised driver software is, readers used dedicated computer hardware built therefore, required to operate the reader. into the main-frame of the computer, after all, MACs and PCs didn’t exist before around 1985 Very old teletype readers, such as the ASR-33, used (remember the BBC, Atari, Amstrad, Commodore punched tape, which could, at a pinch, be PET, Amiga, Sinclair Spectrum, ZX80/81 … if you deciphered into plain ASCII by human eye (I do, you’re getting on a bit !). know, because I used to have to do it!), but reading magnetic tape, even by using fine magnetic Other Unix or CPM boxes, often based upon the powder, is not really that viable. S100 buss system, had dedicated boards for magnetic tape and 8 in. floppy disk readers. Early PCs first had ISA then EISA based boards to 8 Micross Components Ltd control specific hardware … today it would be formats; we will always require a ”Rosetta Stone” difficult to find a modern PC that supported to “crack” the data-data translation. EISA based cards. The pace of computer development, especially PC development, gives Another issue arises due to the different versions of rise to potential problems with data archival in reader software; if converting a document from both the immediate and long-term time frames. Word ’95 or WordPerfect 3.0 to be acceptable to Word 2000 is tough - just picture the issues when Once again the Unix hardware platforms, such as converting from other operating systems, such as HP or SUN, have remained significantly more CPM/86, RDOS, VMS, Linux, MacOS, DRDOS, stable than their PC brethren. TOS, CROMIX or DOPSY. The Software & Data Format Happily, much of this older data is either in plain This can often be the hidden pit-fall, as even if a ASCII text format or direct binary, so conversion is new computer & hardware can be “cobbled” often straightforward, albeit tedious. Not all plain together to extract the data from the archive media, ASCII data need be Carriage-Return / Line-Feed there is no guarantee that the data will make any (<CR/LF>) bound; when computer memory was sense without some additional conversion expensive, link-list or tokenised ASCII data was software. Older data archival systems, especially also a common data format. those that were predominantly hardware bound, used data formats that are now quite alien to the When performing data conversion, it is often easy modern PC. Data character formats, such as EBDIC to pick out conversion errors if the data was and TRASCII, require significant re-translation originally human-sensible. But if the data was before it becomes human- or machine-sensible originally in pure binary, intended as computer- again. only, then conversion errors are often hard to detect and track down. Other data formats may be proprietary, such as the commonly used Portable Document Format (PDF) from Adobe, Word format from Microsoft or GDSII (Graphics Display System) of Calma (now part of Cadence). Whilst these formats may be well used and documented, they are none-the-less subject to “upgrades” and “revisions” beyond our immediate control. Many companies have attempted to standardise As an aside, it is worth noting that the Phoenician their documents and formats, selecting AutoDesk’s writing system known as “Linear A” is an archaic DXF format for all mechanical drawings, for textual format that has apparently been lost example, but are now reliant upon backwards forever, this could also apply to many “current” compatibility from the software supplier, or require 9 Micross Components Ltd