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A comparison of automatic optical inspection systems for use with lead-free surface mount assemblies.

Wickham, M; Hunt, C (2002) A comparison of automatic optical inspection systems for use with lead-free surface mount assemblies. NPL Report. MATC(A)119

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With the move towards lead-free soldering technologies and the effect on joint integrity, there is a heightened interest in the performance of commercial automatic optical inspection (AOI) systems. A particular worry concerned any unforeseen problems in using existing AOI systems to inspect lead-free solder joints. In this NPL-industry collaborative study, a comparison has been undertaken of the ability of six commercial systems to detect known defects in solder joints on specially prepared assemblies. In order to allow each manufacturer to optimise his system for the assembly type used in the evaluation, a single set fifteen defect-free assemblies and fifteen assemblies incorporating defects was made available. Each system was then used in the inspection of ten further test assemblies with lead-free soldered joints containing defects whose numbers and locations were known. The defect types included missing components, misaligned components, components of correct size but wrong value, poor quality solder joints; components with wrong polarity, solder bridges and poor component planarity.
The results clearly demonstrate that all the systems can be used in the inspection of lead-free assemblies, and that AOI of lead-free surface mount assemblies presents no greater challenge than AOI of traditional SnPb soldered assemblies. Indeed, computer programs developed for SnPb assemblies can be adapted for use in lead-free assemblies, albeit with some changes in the accept-reject criteria.
In comparing the various system types (line scanner; vertical or angled camera systems) few major differences were found between their overall capabilities, all performing better at detecting some defects than others. Camera systems did generally out-perform the scanner system for location of misalignments of finer pitch components (the exception being QFPs), whilst angled camera systems did normally perform better with some J-lead defects such as bridges and joints with insufficient solder. In the majority of the defect categories, at least one system achieved a high rating, the exceptions being with R0603 wrong components and SSOP joints with insufficient solder.
Compared with the results of a previous AOI study on boards soldered using SnPb, the systems in this study achieved a greater success rate at locating misalignments and joints with insufficient solder in fine pitch QFPs, and wrong orientation in SOICs and J-leaded devices. The rates of false detection were similar in the two studies.

Item Type: Report/Guide (NPL Report)
NPL Report No.: MATC(A)119
Subjects: Advanced Materials
Advanced Materials > Electronics Interconnection
Last Modified: 02 Feb 2018 13:17
URI: http://eprintspublications.npl.co.uk/id/eprint/2478

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