1. Various technologies—from X-ray and optical inspection to functional electrical testing—have emerged to shorten time to market and reduce test costs while maintaining thorough fault coverage. Each technology has its own advantages:
2. Optical inspection can verify the part number and orientation of components.
3. X-ray inspection can assess the quality of solder joints.
4. Online testing can measure individual components.
5. Boundary scan testing can evaluate both components and interconnections.
6. Functional testing can identify failures that might elude other stages and ensure that the circuit board operates correctly.
7. However, applying all these methods indiscriminately to a PCB can be a costly mistake. Expensive capital equipment may overlap in their efforts. X-ray systems and boundary scan testers might both be looking for the same solder ball issues. This not only wastes resources but can also unnecessarily prolong test times.
8. A useful rule of thumb is to deploy equipment as early as possible in the manufacturing process to detect each type of failure. For example, avoid waiting until the online test stage to verify diode polarity; an optical inspection system can check this before the PCB undergoes solder reflow. This approach saves the cost of reworking defective boards and avoids additional optical and X-ray inspections later. Moreover, rework does not require skilled technicians to correct soldering errors.
9. Unfortunately, on a complex circuit board with thousands of nodes and components, it can be challenging to see individual issues clearly. The testability of a diode, for instance, may be influenced by other components, and each component may require its own logical approach for testability analysis. To address this, you can use testability analysis tools, which are invaluable for managing the complexity of modern products. Studies have shown that such tools can save up to $1 million and shorten time-to-market by three weeks.
Let me know if you need any more adjustments!
Of course, these tools need to describe the PCB test design that you can understand. This usually comes from the input file of the PCB design automation program, ranging from Allegro to Zuken-CFF. Test companies have adopted these different formats, but at the cost of translation work, you as a PCB tester customer will ultimately bear the responsibility. Efforts are being made to provide a standard format for file conversion.
One such standard is reflected in the XML schema used in version 2.0 of the format. According to the statement issued by the organization, the goal is “a single document that can fully describe printed circuit boards, printed circuit board components, assembly arrays, multiple components on sub-panels, circuit board manufacturing panels, quality-evaluation coupons and assembly/ Test equipment.” The GenCAM standard (initiated by GenRad and now part of Teradyne) will facilitate two-way data transmission between “design shops, bare board manufacturers, assembly plants, and test fixture companies” to keep information synchronized and ensure the quality of the final product.
Proprietary tool evaluation test
Despite the benefits of standards, standards-based products often lag behind proprietary tools in terms of performance and functionality. Tools based on standards such as GenCAM have not yet implemented the functions of proprietary test evaluation tools, including Agilent Technologies’ AwareTest and Teradyne’s D2B (Design to Build) software series, both of which are designed to distribute various test and inspection functions. In its current implementation of AwareTest xi, Agilent’s AwareTest aims to distribute the test work between the Agilent 5DX X-ray inspection system and the Agilent 3070 online test system (Reference 3). Under the guidance of AwareTest xi, 5DX will look for soldering defects on the circuit board; then, it will transmit 5DX program information to 3070 and perform necessary online tests to provide comprehensive but non-redundant test coverage. Two other Agilent programs supplement AwareTest xi: OmniNET software analyzes the CAD data before the circuit board layout to suggest the removal of test probes, and the Agilent 3070 Access Consultant performs similar functions after the layout. OmniNET forms the basis of the dialogue between design and test engineers, helping them to collaborate in the development of functional, testable PCBs.
AwareTest xi presupposes that it has been decided to combine X-ray inspection with online testing. How to know if this is the best solution for your PCB testing chores? Agilent proposed a simple calculation: Complexity index = [(C + J)/100] * D * M * S, where C = number of components, J = number of solder joints, S = 1 for double-sided PCB, 0.5 for single-sided PCB, High mixture M = 1, low mixture composition 0.5, D = 0.01 times the number of joints per square inch. For a high complexity index (above 125), Agilent recommends that you combine X-ray inspection with online inspection; for a medium index (between 50 and 125), combine X-ray or optical inspection with online testing; for a low index (less than 50), only use optical inspection or online testing.
Teradyne’s assembly testing department expanded its D2B software to support its Optima automatic optical inspection (AOI) platform, supplementing the D2B suite’s support for automatic X-ray inspection and online testing. The D2B software includes Windows-based tools and an open architecture that allows you to operate the integrated test and inspection platform with minimal data. The D2B software module includes the following components:
– GR Force/A3 allows you to obtain data from more than 30 CAD design formats and generate programs for various testing and inspection equipment. Before the cost of change becomes too high, it supports design test analysis early in the design cycle.
– GR Force/Strategist analyzes each PCB design, simulates the production line configuration, and determines the best strategy for programming test and inspection equipment.
– GR Force DesignView allows you to import board schematic information in label HPGL format. Whenever you select a component or signal, its graphical viewer can update the schematic and physical information at the same time, making it easy to browse complex design data.
