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The value of the in-circuit tester: directly and indirectly, ICT reduces scrap and process time.

THE INTENTION OF any printed circuit board manufacturing line is to offer competitive products that can meet customers' expectations. However, poor quality materials, board design problems and PCB process-related failures may impair product quality. Effective testing is crucial to ensure a product's competitive advantage.

The in-circuit tester is a good quality assurance tool for testing and detecting component failures and process defects. It uses electrical probes to test all the components of fully populated PCBs. It isolates and examines one component at a time, even when the devices are interconnected with traces. Component testing may be performed with a bed-of-nails test fixture and special test equipment.

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Unfortunately, with the advances and innovations in in-circuit testers over the years, some fundamental aspects have been forgotten. Perhaps it is time for a quick refresher.

In-circuit testers are workhorses of the electronics industry. They have done a great job of testing both analog and digital components fast and economically to detect common manufacturing process and components defects (TABLE 1). In most cases, they are much easier to program thanks to the built-in automatic test program generators. This is extremely helpful, as PCB feature sizes have shrunk while component complexity has increased. Engineers need not be concerned about the complexity of the board circuitry or component functionality when preparing the test program, as built-in circuit analyzer software helps to perform much of the work. This saves the time on program generation, while maintaining test coverage and effectiveness.
TABLE 1. Most Common PCB Defects

DEFECT POSSIBLE CAUSES POSSIBLE DEFECT TYPE
 SOURCES

Solder between pins Too much solder Wave/reflow Electrical/
 soldering structural

 Misregistered
 pins

 Bent pins

Solder opens Lack of solder Solder Electrical/
 applications structural

 Tombstoning Wave/reflow
 soldering

 Misplaced part

Wlissing component Lack of glue Solder Electrical/
 placement structural

 Shock

 Lack of solder

Wrong component or wrong Human error Placement Electrical
orientation setup

 Handling error Inventory
 handling

 Wrong
 specification

 Wrong marking

Bad component Dead on arrival Solder Electrical
 placement

 Handling damage

 Electrostatic
 damage


In-circuit testers have built-in power supplies for powering the boards, and many of them can be upgraded to do inline programming and sophisticated functionality testing. They also offer better test transportability and repeatability, making it effortless for end-users to transport test programs across systems. This flexibility helps improve time to market and reduce testing costs to a great extent.

In-circuit testers can identify most problems, whether they are open, shorts or bad components, making it much easier to diagnose the root cause of the defect. Furthermore, you can gather and analyze the measurement data to provide feedback for improving the manufacturing processes so that similar problems do not occur again in the future. This is the biggest payback of the in-circuit tester: It reduces rework and scrap costs by preventing or detecting problems as early as possible.

Let's look at an example. Suppose there is a recurring component failure issue. The failure ticket shows that it is failing on the higher end of the component tolerance of all the failed boards. After investigating, it is found that a wrong component was placed on the boards due to human error. The problem can be corrected immediately, and the rework cost for the failed boards is minimal.
TABLE 2. Summary of Time to Profitability

BOARD VOLUME TIME LINE OBJECTIVE

Low Time to market The aim is to test the first
 board in the shortest
 possible time

Significant Time to volume The aim is to market the
 goods in the shortest
 possible time

High Time to profitability The aim is to increase profit
 margin in the shortest
 possible time



In a case like this, it is important for the test technicians to really understand the manufacturing processes and the available test technologies so that they stay focused on the defects that are most important. The earlier in the production cycle you test, the more time and money will be saved, yields increased, manufacturing process problems reduced, and products delivered faster. This all adds up to faster and greater profitability. As stated, you can minimize the scrap and material costs. Another advantage is the cost-saving benefits of fewer failures occurring at the functional test systems, thus saving on capital equipment costs and allowing highly skilled technicians to take on more complex work.

Because test programs can be developed quickly, testing can start as soon as boards are available. This speeds time to market. Manufacturing process improvements are quicker to increase the output yield. By producing more volume and high-quality products with fewer resources, in-circuit testing is a very economical way to increase the bottom line.

ICT helps monitor the quality of the manufacturing process itself. It helps eliminate defects that can occur in boards and provides constant feedback so crucial to making continuous improvements that keep the production line moving.

With in-circuit testing, the integrity of the PCBs that go in the finished products can be verified before they leave the production floor. The cost of detecting defects later can be devastating not only in monetary terms, but in the impact on reputation and image.

WEE-SHENG YONG is a technical marketing engineer at Agilent Technologies (agilent.com); wee-sheng_yong@agilent.com.
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Title Annotation:TEST AND INSPECTION
Author:Yong, Wee-Sheng
Publication:Printed Circuit Design & Fab
Date:Apr 1, 2011
Words:858
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