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May, 2017 Continued from page 71


transactional control systems of manufacturing, the more accurate and timely the data, and as a result, its usefulness.


Hierarchical Data Structure The nature of electronics assem-


bly is hierarchical. A finished prod- uct, represented by an assembly cell, is typically made up of raw materials and subassemblies. Each of the sub- assemblies is, in turn, a finished product of another assembly process, which itself is made up of raw mate- rials and may include other sub- assemblies. The assembly cell contains data


about the work order, process sequence, BOM, and the process traceability data, which is a record of the events and transactions that have taken place during the assem- bly process. It also includes the mate- rials traceability data, which has information about specific raw mate- rials and each subassembly. A raw material is differentiated


from a subassembly as any compo- nent that does not have a traceabili- ty record. Because this approach is modular, the traceability details of subassemblies can be combined easi- ly at a later date, either when the subassembly is used, or even later, as long as the unique ID of the sub- assembly is recorded. The data can later be imported


or simply referred to when stored in a connected system. The IPC-1782 standard defines


levels of both material and process traceability. Data gathered for mate- rial traceability may include unique material IDs, supplier and date code. The method of linking material traceability data through the use of unique IDs and the cellular structure of information keeps data from being repeated within the structure. Any specific material ID is needed only once and can be referred to by many reference designator positions across different assemblies. In the case of process traceabili-


ty, there are common elements of traceability data that apply to all processes and also additional requirements that depend on the specific process type. Common ele- ments include the list of materials consumed for an SMT process, as well as details of machine errors dur- ing operation. Data specific to a par- ticular process may include pass/fail test results, and process measure- ment data. The traceability structure also


includes data that is not product-spe- cific, such as maintenance cycles. This is kept separate from the assembly tree as it is time-based and can occur during production or between product cycles.


Implementing IPC-1782 The IPC-1782 standard is


designed to be as simple as possible to understand and to execute. However, the standard could not be simply a linear list of requirements. Understanding the data’s hierarchi- cal nature and content are necessary to get started. The specification of the standard will also eventually be supported by examples of how it can be applied and used, as well as exact- ly what each data field represents. To implement IPC-1782, use the risk assessment methodology


See at NEPCON China, Booth 1H17 and at SMT Hybrid Packaging, Booth 4A-240 Illustration of a hierarchical data structure approach.


www.us-tech.com


and IPC classifications to determine the target level of traceability. Level 1 traceability is the minimum that


should be expected for any manufac- turer of good standing. Level 4 is appropriate only for the highest


Page 73 New Levels of Traceability for Electronics Manufacturing


demands in the industry, especially where process data is concerned. For EMS companies, various levels of traceability may be required for dif- ferent lines of products. The next step is to compare the


calculated requirement with what is currently in place, represented by existing quality or management con- trol systems, or as negotiated with customers. Most of the data required for traceability is likely to already exist in a given operation, making it then a matter of establishing a com- munication method for the data to be brought together in the form that IPC-1782 calls for. Most automated machines in


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