SMTA International Conference Proceedings


NEW THOUGHTS ON TEST STRATEGIES

Author: Stig Oresjo
Company: Agilent Technologies
Date Published: 9/22/2002   Conference: SMTA International


Abstract: Today’s test engineers have significantly more challenges than just a few years ago. The board complexity is increasing with more components, more joints, higher densities, new package technologies such as area array packages, and 0402 and 0201 chip components. The higher component and joint counts create more defect opportunities which lead to lower yields for a given defect level.

At the same time, test and inspection alternatives are greater today with new technologies such as Solder Past Inspection (SPI), Automatic X-ray Inspection (AXI), and Automatic Optical Inspection (AOI). These new inspection technologies are well established and provide real alternatives. The Boundary-Scan test technology has also emerged as a popular electrical technique to complement In-Circuit Test (ICT) and Functional Test (FT). These new tools give more choices but also pose a new dilemma. Which is the right test / inspection strategy? Which is the right combination of these tools?

This paper will introduce an updated Complexity Index so a standard definition of board complexity can be applied to different boards. We will address the occasionally heard comment, "Test and inspection add no value." We will show that they indeed add significant value and that different board complexities have a very big impact on the economics of test / inspection. General defect level is very important when selecting the optimum test / inspection strategy and will be briefly discussed.

Two other important factors when selecting test strategies are different test systems’ test effectiveness, and where in the manufacturing process defects are introduced. We will discuss these two topics and share data from some studies performed. At the end the paper we will address some thoughts on what can be learned from this discussion, such as how should test / inspection be used in a process control fashion versus a defect containment fashion? And, how to apply the classical test strategy of divide and conquer in a new way with the availability of effective automatic inspection systems.

Key words: test / inspection strategy, AOI, AXI, ICT, functional test, defect containment, process control, test effectiveness.



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