Electronics Assembly Knowledge, Vision & Wisdom
2D and CT Scan X-ray for Joint Inspection
2D and CT Scan X-ray for Joint Inspection
Paper discusses the conventional 2D X-ray inspection and CT scan techniques and shows various illustrations of defects which are normally difficult to detect.
Analysis Lab

Authored By:
Nandu Ranadive
IBM Corporation
Poughkeepsie, NY, USA
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Summary
Connector technology used in the high density printed circuit boards demands high speeds and low signal to noise ratios. In order to improve the connector density, more and more connectors are going surface mount, with very high I/O count. I/O counts in excess of 5000 connections on a single connector site, are not uncommon. In order to provide connections to all the I/O's, the connectors often tend to be dense and have a very high profile. A reliable inspection of these connections is essential to reduce the defect levels and assess the long term reliability of solder joints.

A unique combination of conventional 2D X-ray inspection and CT scan (3D reconstruction) is used to inspect such joints. This unique combination has made possible, a reliable inspection of solder joints for defect like shifted connectors leads, low solder volume, solder climb, solder thieving etc. A quick identification of these defects was used to drive process corrective actions and reduce the test down times.

This paper discusses the combination techniques and shows various illustrations of defects which are normally difficult to detect. One great advantage of such a system is the ability to use it as a combination tool, or two stand-alone tools that can be used for various other types of inspections when needed. For instance, a 2D inspection tool was also used to inspect solder joints on standard SMT connectors, pin-thru-hole connections etc, and for analyzing internal component defects. The CT scan could be used for understanding other types of defects, such as, shorts internal to the components, internal structures of circuit boards etc.
Conclusions
Over two years, we have determined that the success rate of this 2D-3D combination was better than 95%. Stated differently, more than 95% of the boards deemed good by 2D and CT scan combination pass all EOL testing. Reducing defect levels at test is very critical, since the board have a lot of value add by the time they get to test.

In most instance, a lot of additional hardware is added before the boards get to test. Tester time is of prime importance. It is usually very time consuming to isolate and verify defects caught at by the tester. Also, a lot of hardware isassembly is sometimes necessary before the board can be sent to rework.

Early detection of defects has a couple of big advantages. Since x-ray inspection immediately follows SMT attach steps, x-ray feedback is almost real time, which is much more effective in correcting process glitches.

It is also more cost effective to capture defects early in the assembly cycles to eliminate lost value add. A library of defects could be made available to the operators on line, which serves as a comparison template. It is also useful as a training guide. This inspection combination has proven to be a valuable addition for enhanced product quality.
Initially Published in the SMTA Proceedings
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