Flexible circuits quality assurance

BASIC CONCEPTS IN FLEXIBLE CIRCUIT QUALITY ASSURANCE ... 

The basic concept of quality assurance for flexible circuits is the same as that for rigid boards, in the sense that any critical defect must be eliminated before shipping. This includes failures due to opens and shorts dimensional degradation of pad arrays, serious defects on conductors, substrates, coverlay, and so on. These defects need to be inspected for each circuit, whether it is flexible or rigid. Technically, however, there are several differences in quality assmance for flexible circuits because of their additional functions, such as dynamic flexing capability. 

The basic quality assurance concept for high-density flexible circuits is the same as for other circuit types. However, a difference for high-density flexible circuits is the acceptable defect size, which is one order smaller than that for traditional flexible circuits, necessitating higher inspection capabilities. Furthermore, new high-density flexible circuits contain additional structiues such as flying leads and microbump arrays that require additional inspection capabilities for reliable termination. Exact 3-D accuracy and uniform surface conditions are required. Dimensional allowances are smaller than 0.3 percent, and sometimes 2-ftm accuracy is required. 

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