PCB Tech - How to use tools to manage PCB design and testing

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:

Optical inspection can verify the part number and orientation of the part.

X-ray inspection can determine the adequacy of solder joints.

Online testing can measure components individually.

Boundary scan testing can evaluate components and interconnections.

Functional testing can test failures that may have escaped other stages, and at the same time ensure that the circuit board operates normally.

However, throwing all these methods indiscriminately on a PCB circuit board would be a costly mistake. Expensive capital equipment will repeat each other's efforts. X-ray systems and boundary scan testers are looking for the same solder ball problem. Not only will you abuse your device, but you will also unnecessarily extend the test time.

There is a rule of thumb to guide you in the most effective use of inspection and electrical test systems: deploy equipment as early as possible in the manufacturing process to capture each type of failure. For example, don't wait until the online test stage to determine whether the diode is inserted with the correct polarity; the optical inspection system can check for you before the PCB goes through solder reflow. You can save the cost of soldering bad boards and make them go through the subsequent optical and X-ray inspection stages; in addition, rework does not require skilled technicians to remove the wrongly soldered parts.

Unfortunately, on a complex circuit board with thousands of nodes and components, you may not be able to see the trees in the forest. The reasonable method of testing the direction of the diode may be affected by many other components, and each component will compete with its own common sense solution for testability analysis. If you need help, you can use the testability analysis package, which can help you in the large-scale deployment common sense required for today's complex products. A study found that such tools can save $1 million and can be shortened by three weeks after listing.

Describe PCB

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 test 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

in

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 high complexity index (above 125), Agilent recommends that you combine X-ray inspection with online inspection; for medium index (between 50 and 125), combine X-ray or optical inspection with online testing; for low refraction Rate (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.