EL Circuit Board Failure Analysis System

Description:

Many printed circuit board assembly defects cannot be identified easily using conventional methods such as ICT, FT, AOI, and AXI. Such defects include the following:

• Power-to-ground, low resistance and cable shorts
• Stressed components
• Faulty heat sink attachment
• Programming errors
• Defective BGAs, VCOs, and decoupling capacitors

Technicians and engineers spend many hours debugging boards with such defects. Often, these boards end up in the scrap pile. The EL infrared inspections system provides an alternative method of fault detection that can isolate these defects, thus filling the gaps between conventional test equipment. EL is an effective and economical tool that can reduce debugging costs and minimize scrap. When is used as the first screen of defective boards, EL can quickly provide useful troubleshooting information, dramatically reducing the time to repair.

Features:

EL can also be used to inspect boards for basic functionality. Although EL cannot provide the same detailed level of functional verification as a functional test, it can provide verification of basic board operation. Advantages of EL over traditional functional testers include low cost and fast setup. No custom hardware is required and tests can usually be setup in less than an hour. EL is ideal when the high cost of a dedicated functional tester cannot be justified.

Applications

• Quickly locate shorts, stressed components, and other defects
• Verify board functionality
• Analyze the thermal behavior of individual components
• Evaluate thermal management components

Software Features

• Model Board Comparison TM
• Sophisticated detection algorithms to detect short circuits
• Transparent picture overlay to locate defects

Camera Features

• 0.05°C sensitivity
• 320 x 240 uncooled infrared detector
• 100 micron spatial resolution (minimum)
• 30 frames/second thermal image capture and display

Enclosure Features

• 27" x 27" x 45" aluminum framed enclosure
• Blocks stray infrared emittance by the ambient environment
• B locks air currents generated by heating and air conditioning ducts
• M otorized infrared camera slide and controller precisely position the EL camera for Model Board Comparison and short circuit tests
• P latform with adjustable PCB mounts enable repeatable positioning of board sizes up to 22" x 20"

How It Works

Infrared Thermography

Infrared thermal imaging cameras are able to detect the infrared energy that is emitted by an object and create two-dimensional viewable images of that energy. The resulting infrared images represent the temperature distribution over the surface of the object. OptoTherm infrared cameras are sensitive to a specific band of the infrared spectrum between 7 and 14µm in wavelength. The majority of infrared energy emitted by objects less than approximately 200 ° C is within this wavelength band.

Circuit Board Infrared Analysis

The operation of circuit boards involves the flow of electrical current, which produces heat when passing through a circuit having resistance. Since thermal behavior is closely related to current flow, the temperature distribution on an operating package, component, or assembly can be a good, repeatable indication of its operational status. Therefore, infrared images of a circuit board can be analyzed to determine a board's operational status.

Infrared analysis test coverage is a function of the degree of electrical stimulation and power dissipation in the board and in its components. Circuits and components that are not electrically stimulated produce no resistive heat and therefore, cannot be evaluated by infrared analysis. In many cases, simply powering a board exercises the majority of component and circuits. In more complex boards, a diagnostic or functional test may be required to stimulate all areas of a board.

Most electronic packages, components, and assemblies lend themselves to failure analysis by infrared inspection as long as the following conditions are met.

• There is a clear line of site between the camera and board
• Current flows through the components and circuits that are to be tested
• The external surfaces of components are not composed of bare metal*

*Bare metals (unpainted, unanodized, etc.) have very low emissivity. Emissivity is the efficiency with which a surface emits infrared energy. Therefore, bare metals generally do not emit enough infrared energy to allow accurate measurement using infrared analysis. There are, however, surface treatments that can increase surface emissivity adequately to allow effective infrared analysis. For example, thin Kapton tape is often adhered to BGAs with stainless steel tops to determine the location of an internal short.

Example

		Low resistance and power-to-ground shorts are often the only areas that heat up on a board during a short detection test. The low resistance short picture below was located by applying 500 milliamps of current for 5 seconds.
		The precise location of the short was determined by overlaying a transparent visual picture of the board on the thermal image.

Short Detection Settings

Test Averaging enables you to detect shorts with a resistance under 1 ohm. Because low resistance shorts do not dissipate much power and heat, a series of tests are averaged together to increase test sensitivity.

The Auto Stop feature opens the I/O module relay, cutting off power to the board, as soon as the temperature on the short increases above a user-defined threshold. This safety feature can prevent damaging the board, while still locating the short.

Model Board Comparison

Model Board Comparison TM (MBC) is a software tool used to identify defects on PCBAs. Many printed circuit board defects such as shorts, defective ball grid arrays, and stressed components cannot easily be identified easily using conventional methods such as ICT, FT, AOI, and AXI. Many hours are spent debugging boards with such defects and often these boards end up in the scrap pile. MBC provides an alternative method of fault detection that can isolate these defects, thus filling the gaps between conventional debugging techniques.

MBC Defect Search

As boards are successfully troubleshooted using MBC, a description of each particular defect can be associated with the MBC test result images to create a defect database. Then, after each board has been tested, the resulting images are automatically compared to the images in the database in order to find the closest defect match. As more and more defective boards are added to the database, troubleshooting time can be reduced even further.

Example

Step 1 - Create Model

Create a golden board model by testing known good boards. The images below show the temperature changes that occurred on the board during the test.

Step 2 - Analyze

Test a defective board so that its thermal profile can be compared to the model. Areas on the board that are different from the model are highlighted and may indicate defects.

Step 3 - Locate Defect

Locate the defect by overlaying a transparent visual picture of the board.

Model Board Comparison Settings

Models are created by adding tests of known good boards to a group. Acceptance Criteria determines how the board is compared to the model. Board tests can be automatically saved to hard disk after each test.

Set the test length and the rate at which images are evaluated during a Model Board Comparison test.

Set the time that each relay will be activated during the test. Only one relay is needed when powering a board. Multiple relays can be used to perform more sophisticated tests such as powering different board planes or applying different loads at different times.

The results of an MBC test consist of a sequence of images that represent differences in thermal behavior between the test board and model throughout the test period. At the beginning of the test, there should be no thermal differences as both the test board and model were unpowered at this time. As the test progresses, areas of higher temperature may appear, identifying components that are higher in temperature than the model. Similarly, areas of lower temperature may appear that identify components that are lower in temperature than the model.

In many cases, defects such as short circuits are immediately identifiable after conducting an MBC test. Short under BGAs can often be narrowed down to an area less than 1 x 1 mm. Other failure modes, such as open or faulty components, may produce secondary thermal effects resulting in a number of suspect components. In these cases, the defect site is often identified as the location where anomalous thermal behavior is first observed. Secondary thermal affects on other components may then appear in later test result images.

If a defect is not immediately identified as the first thermal anomaly, an engineer or technician should then carefully examines the sequence of test results images in order to track down the true defect site. This person should have a good knowledge of board functionality and may need access to the board's electrical schematics . By examining the magnitude of thermal discrepancies and the order in which they occur during the test, the technicians should be able to narrow down their search to a small region of the board containing only a few suspect components. .

As an example, upon initial examination of the test result images, an area of lower temperature is displayed, possibly indicating that a component is not functioning properly. After inspecting the suspect component under X-ray, no internal defect can be found. Upon further analysis of the board's schematics, it is discovered that the functionality of the suspect component is controlled by the I/O output from a neighboring component. Although the test result images gave no indications of thermal anomalies on this component, after swapping out the component and retesting the board, it was found to be the root cause.

Applications

Scrap Recovery

EL is frequently used for the reclamation of PCBA bone piles. Because the value of bone piles can be in the millions of dollars, their recovery brings immediate and substantial financial benefits. EL typically enables OEMs and contract manufacturers to salvage over 50% of their bone piles. In such cases, the payback period can be as short as two to three months.

Rework

A great deal of time is spent debugging boards that have been kicked off the manufacturing line. Technicians use results from ICT, FCT, and other equipment to identify defects, often with little or no success. The composition of defects at this point in the manufacturing process is much different than at the end of the manufacturing line. At this stage, the majority of defects are often caused by power-to-ground shorts and bad components. EL has typically demonstrated a detection rate of over 75% when testing boards with such defects. When used as the first screen of defective boards, EL can quickly provide useful troubleshooting information, dramatically reducing time to repair.

RMA Repair

Circuit boards that have been returned from the field can present particular problems when troubleshooting. Many times technicians have little or no idea where to begin in the failure analysis process. EL can provide very helpful information, allowing technicians to narrow down their search to a small region of the board containing only a few suspect components.

In-line screening

EL provides an additional level of screening on the manufacturing line to identify defects that conventional test methods cannot detect. Stressed components can pass ICT and FCT only to fail early in the field and thus present reliability hazards. Many times, these components run hotter than normal and can be identified by EL before they leave the manufacturing plant. By using EL at the end of the manufacturing line, many of these defects can be identified long before they reach the scrap pile.

Functional Inspection

EL can be used to inspect boards for basic functionality. Although EL cannot provide the same detailed level of functional verification as a functional test, it can provide verification of basic board operation. Advantages of EL over traditional functional testers include low cost and fast setup. No custom hardware is required and tests can usually be setup in less than an hour. EL is ideal when the high cost of a dedicated functional tester cannot be justified.

Design Optimization

Because of increasing component placement density, as well as an increase in component power density, thermal imaging has become an important tool in the design process. EL aids board layout designers by helping them obtain and analyze thermal profiles of prototype boards and components. Thermal management problems can be resolved in the design phase before production begins, minimizing the high costs associated with troubleshooting and repair. Additionally, by developing an historical database of board and component thermal profiles, designers can incorporate the thermal behavior of boards and components much earlier in the design process.

Thermal Image Analysis Software

Thermalyze TM provides an extensive set of analysis tools to help you analyze data in many different and insightful ways. Use regions to measure temperature statistics within specific areas of an image. Record and play back thermal imaging movies. Subtract thermal images to measure temperature differences. Import and merge visual pictures with thermal images. Create real-time strip charts and 3-D profiles and more.

System Components

EL is supplied as a fully tested and operational system and includes the following components:

• InfraSight EL 320 thermal imaging camera with 50 ° x 37.5 °
• Thermalyze thermal image analysis software
• Enclosure with motorized camera slide, controller, platform, and PCB mounting blocks
• Dell tower PC with 19" LCD multimedia monitor
• I/O module (8 relay outputs, 8 digital inputs)
• Camera Link Video board (PCI)
• Camera Link video cable
• USB camera communication cable
• Infrared Camera power supply (12 Vdc)
• EL User Manual
• Thermalyze User Manual

InfraSight EL 320 Infrared Camera	EL enclosure	I/O module

Accessories

Thermalyze Offline Software

Thermalyze Offline is used to perform post-analysis of data on remote computers and to allow colleagues to view and analyze data on their own computers. Thermalyze offline software provides the same image analysis and file saving capabilities as the full version of Thermalyze. The offline version however, does not have the ability to capture real-time thermal images from an InfraSight camera and therefore cannot perform real-time analyses.

Circuit Board Test Probe Arm

The Circuit Board Test Probe Arm enables probing of surface mount devices (SMD) and is often used to power devices and circuits on a PCBA when detecting short circuits.

• Heavy base
• Flexible shaft
• Spring loaded tip
• Rotatable head
• Fine vertical adjustment knob
• PCB Test Probe Arm
• Connection post

Specifications

• Overall Length: 8.33” (211.5mm)
• Overall Height: 2.92” (74.2mm)
• Base Length: 2.53” (64.3mm)

Ordering

Malaysian customers please contact us for quotes. There are many options available. Besides, you may also surf for more information on EL Official Website.