Test Optimization to Improve Rework



Test Optimization to Improve Rework
Paper reviews how to use test machines to diagnose defects and how to reduce defects from a SMT line.
Analysis Lab

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Authored By:


Juan Coronado, Jorge Valle, Omar Garcia, Luis Manuel Zamora, Fernando Rodas, Mario Aguilar, Federico Santos, Carlos Alberto Robles, Zhen (Jane) Feng Ph.D., Dason Cheung, Murad Kurwa
FLEXTRONICS International Inc.

Summary


Currently with increasing PCBA density and complexity, it has become challenging to produce higher yields. Sometime we have to face a large number of rework boards in manufacturing. We use Automated X-ray Inspection (AXI) and 2DX for finding the defective location and type for printed circuit boards, however most AXI machines were designed to test boards directly from the SMT line (not for rework board). We are faced with two questions: 1) How can we effectively use test machines to diagnose the defects? And 2) How can we reduce defects for the current SMT line with Real test data and results?

This paper will discuss the following:

1. The X-ray machine is a Non-Destructive method for detecting defects on PCBA boards. How can we effectively use different X-ray machines (AXI and 2DX)?
2. How can we reduce test time? Set right Algorithm and Threshold for programming; manual test mode only for critical parts; several programs are just for critical components.
3. Real time data feedback to line. Prevention is much more important than detection.

We have done the following:
1. Evaluated AXI, 2DX, AOI, and other test machines' capability in order to understand their advantages and disadvantages, and to use them efficiently.
2. Kept the machines at the optimized conditions. Maintained AXI programs with high detection coverage and low false call ratio.
3. Performed sampling test for production boards at AXI.
4. For some critical parts, used individual program to test them at AXI or examine at 2DX.
5. Studied and analyzed the AOI, AXI, 2DX data, provided REAL time feedback to SMT line.
6. Used SPC data, focused main existing defects daily, found root cause, and solved issue as soon as possible with process, test and SMT programming engineers.

Conclusions


1. SPI, AOI, AXI and 2DX are Non-Destructive test machines that we need to use on RFI products due the poor testability, lack of test points and the heavy use of metals shields that complicate repair.

2. Use SPI and AOI as much as possible to inspect products on lines due to their short test time and early possible to detect defects.

3. Use AXI 100% for NPI and new package size in the new technologies.

4. Use 2DX image and data to set up accurate AXI Threshold for some critical packages. Use 2DX to examine components for which AXI testing cannot be used or the AXI data is unreliable.

5. The optimization testing method is still under observation with variable SMT products. Use a combination of test and inspection processes to inspect complicated boards with the most adequate and efficient manner.

6. We are still looking for an efficient and effective AXI machine which has an AXI advantage but also has a 2DX advantage which has a clear image for solder joints.

Initially Published in the SMTA Proceedings

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