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Article
Publication date: 1 April 1995

W.J. Ready, S.R. Stock, G.B. Freeman, L.L. and L.J. Turbini

Under certain environmental conditions, printed wiring boards (PWBs) respond to applied voltages by developing sub‐surface deposits of copper salts extending from anode to cathode…

Abstract

Under certain environmental conditions, printed wiring boards (PWBs) respond to applied voltages by developing sub‐surface deposits of copper salts extending from anode to cathode along separated fibre/epoxy interfaces. These deposits are termed conductive anodic filaments (CAFs) and, in this work, the dimensions and growth patterns of a CAF have been determined by serial sectioning. The CAF growth pathway is characterised and the spatial distribution of the copper salts is quantified with scanning electron microscopy (SEM) using backscattered electrons. The chemical composition of the CAF is determined using energy dispersive X‐ray analysis (EDS). Prior research using high‐resolution non‐destructive X‐ray microtomography is correlated with the serial sectioning data. The failure phenomenon known as CAF may pose serious long‐term reliability concerns in electronics applications exposed to adverse and hostile environments.

Details

Circuit World, vol. 21 no. 4
Type: Research Article
ISSN: 0305-6120

Article
Publication date: 1 September 2006

Laura J. Turbini

Conductive anodic filament (CAF) is a failure mode in printed wiring boards (PWBS), which occurs under high humility and high voltage gradient conditions. This paper aims to…

Abstract

Purpose

Conductive anodic filament (CAF) is a failure mode in printed wiring boards (PWBS), which occurs under high humility and high voltage gradient conditions. This paper aims to review the history of CAF from its identification in the 1970s to the statistical analysis of its failure mode and the factors that enhance its formation.

Design/methodology/approach

Charts the chronology and details the developments of CAF over the last 30 years.

Findings

CAF is a conductive copper‐containing salt created electrochemically that grows from the anode toward the cathode sub‐surface along the epoxy/glass interface. It can also grow from the anode on one layer to a cathode on another. CAF was first discovered in 1976 and was identified as a catastrophic failure mode. It is enhanced by high humidity during storage or use, by high voltage gradient between anode and cathode, by certain soldering flux ingredients, by hole drilling, multiple thermal cycles during processing, and by higher processing temperatures associated with lead‐free solders. CAF is a copper hydroxy chloride salt and is a semiconducting material.

Originality/value

Our analytical tools today are far superior to those of these early researchers. Early data were obtained from chart recorders and manual plotting. Today we have computers for automated data collection and analysis and the sensitivity of the scanning electron microscope has improved significantly. The researchers of the 1970s and early 1980s characterized the basic factors associated with CAF and in many ways we are just repeating what they have done.

Details

Circuit World, vol. 32 no. 3
Type: Research Article
ISSN: 0305-6120

Keywords

Article
Publication date: 1 June 2002

Clarissa Navarro

Increasing board densities, decreasing spacing between holes and features and the growing requirement for printed circuit boards to perform in high temperature/high humidity…

Abstract

Increasing board densities, decreasing spacing between holes and features and the growing requirement for printed circuit boards to perform in high temperature/high humidity environments have led to renewed concerns about possible reliability problems caused by the growth of Conductive Anodic Filaments (CAF). To date, there has been a lack of information on standardized test procedures and failure analysis methods for various types of prepregs and laminates.This paper introduces a standard test vehicle design and discusses suitable testing, failure analysis and board manufacturing methods. It also includes the requirements for CAF resistance and there is a discussion of material benchmarking tests with some preliminary results from this testing. These methods should be applicable to boards used in all market segments, including high density interconnect, and automotive applications.

Details

Circuit World, vol. 28 no. 2
Type: Research Article
ISSN: 0305-6120

Keywords

Article
Publication date: 2 February 2015

Ling Chunxian Zou and Chris Hunt

This paper aims to describe the development of an approach that uses a flexible substrate to investigate the mechanism of conductive anodic filament (CAF) growth and effect of…

Abstract

Purpose

This paper aims to describe the development of an approach that uses a flexible substrate to investigate the mechanism of conductive anodic filament (CAF) growth and effect of different material and manufacturing variables.

Design/methodology/approach

A new approach using a simulated test vehicle (STV) has been developed to study the CAF phenomena. The STV can be easily built under controlled conditions in the laboratory using different glass fibres and resin powder to investigate the effect of different variables separately on CAF. The advantage of the STV is that CAF can be formed in relatively short period in a controlled way, and CAF growth can be easily identified using a back-lighting under a microscope due to the thin flex material used as the test sample.

Findings

STV has been used to investigate a number of effects on CAF formation: different glass fibres, reflow process, acid contamination in drilled holes, desmear process and glass bundle size. The results demonstrate that for finished fibres acid contamination (plating solution) at the electrode was necessary for CAF formation. However, for unfinished glass fibres (loom state and heat cleaned) CAF can be formed without acid contamination. The reflow process significantly increases CAF formation. Running an aggressive desmear process and using large glass fibre bundle also increased CAF formation.

Originality/value

This new approach will be of benefit for printed circuit board (PCB) supplier to evaluate CAF performance on different resin systems and glass fibres to provide high CAF resistance quality PCBs. The test period (168 hours) would be much shorter than the traditional CAF testing (1,000 hours).

Details

Soldering & Surface Mount Technology, vol. 27 no. 1
Type: Research Article
ISSN: 0954-0911

Keywords

Abstract

Details

Soldering & Surface Mount Technology, vol. 17 no. 3
Type: Research Article
ISSN: 0954-0911

Article
Publication date: 1 September 2006

Keith L. Rogers and Michael G. Pecht

To show how the use of conductor spacings below 4 mil in printed wiring boards (PWBs) can introduce an unanticipated failure mechanism, leading to current leakage and short…

Abstract

Purpose

To show how the use of conductor spacings below 4 mil in printed wiring boards (PWBs) can introduce an unanticipated failure mechanism, leading to current leakage and short circuit failure.

Design/methodology/approach

The tests in this study were conducted in accordance with IPC‐TM‐650 2.6.25, using boards designed with conductor spacings between plated through holes (PTHs) ranging from 6 to 3 mil and from 8 to 3 mil between PTHs and ground planes. The board types and conductor spacings were selected to include current and future printed circuit board fabrication technology.

Findings

For PWBs that may be used in harsh environments where the relative humidity and temperature may approach those of the test environments, even for relatively short periods of time, spacings of 4 mil or less in the materials tested may not be appropriate. However, it is unlikely that the 85°C and 85 percent RH conditions are the minimum conditions to induce this failure mechanism. More tests at lower temperatures and relative humidity combinations should be conducted to evaluate conditions at which this type of failure begins.

Originality/value

The value of the paper lies in that the tests show that the IPC industry standard for conductive filament formation (CFF) testing of PTH‐PTH conductor spacings of 4 mil or less, at 85°C/85 percent RH can introduce a CFF variant failure mechanism, and therefore, may need to be modified to ensure that the test conditions accelerate the CFF mechanism and not other low resistance paths.

Details

Circuit World, vol. 32 no. 3
Type: Research Article
ISSN: 0305-6120

Keywords

Article
Publication date: 1 January 1994

J. Guinet, X. Lambert and D. Bono

The corrosive power of solder pastes is studied by implementing a new method compatible with the common rules of use. The entire methodology is fully described. The results show…

Abstract

The corrosive power of solder pastes is studied by implementing a new method compatible with the common rules of use. The entire methodology is fully described. The results show evidence of corrosion with some solder pastes that have been identified by microscopic and EDX analysis. The corrosion mechanism is ‘mouse bite’ and conductive anodic filaments. A ranking of the different solder pastes tested is given and pass criteria for this new method of evaluation are proposed.

Details

Soldering & Surface Mount Technology, vol. 6 no. 1
Type: Research Article
ISSN: 0954-0911

Article
Publication date: 1 February 1991

L.J. Turbini, G.B. Freeman, M.H. Smith, J.D. Finney, R.D. Boswell and J.F. Lane

A new corrosion test for assessing flux residues is applied to marginally cleaned water soluble fluxed test boards and low solids/no clean fluxed test boards. This test method…

Abstract

A new corrosion test for assessing flux residues is applied to marginally cleaned water soluble fluxed test boards and low solids/no clean fluxed test boards. This test method developed by Bono has been modified to accelerate the corrosion process. The corrosion mechanism observed in this study is conductive anodic filament (CAF), a corrosion mechanism proposed in 1979 by Lando et al. It is postulated that this degradation mechanism is due to the high bias voltage (190 V) coupled with the high humidity (85%) and high temperature (85°C) conditions used in this test. Important parameters in the test method are discussed and recommended refinements are given.

Details

Soldering & Surface Mount Technology, vol. 3 no. 2
Type: Research Article
ISSN: 0954-0911

Article
Publication date: 1 March 1992

L.J. Turbini, J. Schodorf, J. Jachim, L. Lach, R. Mellitz and F. Sledd

Today's emphasis on alternative flux technology as an approach to eliminate the use of chlorofluorocarbons (CFCs) requires an understanding of the corrosion potential of the new…

Abstract

Today's emphasis on alternative flux technology as an approach to eliminate the use of chlorofluorocarbons (CFCs) requires an understanding of the corrosion potential of the new fluxes. In 1989, Dr David Bono proposed that monitoring the effect of different soldering fluxes on the rate of corrosion of a copper wire printed on a circuit board would provide quantitative information on the corrosion potential of a flux. Further analysis of this testby Turbini et al. revealed that the degradation mechanism associated with Bono's test is the growth of conductive anodic filaments along the glass fibres of the epoxy‐glass boards. The original test method has been revised, and the test coupon redesigned with the goal of developing a standard, quantitative test method to characterise soldering fluxes. This paper will describe the equipment, test coupon and electrical circuitry associated with this proposed test method. Procedures chosen to reduce error sources associated with electrical noise will be reported and explained.

Details

Soldering & Surface Mount Technology, vol. 4 no. 3
Type: Research Article
ISSN: 0954-0911

Article
Publication date: 1 April 1996

B. Rudra, M.J. Li, M. Pecht and D. Jennings

Laminated substrates are used widely in the manufacture of multichipmodules (MCM‐L) by the electronic packaging industry. Of late, the thrust hasbeen towards higher density…

256

Abstract

Laminated substrates are used widely in the manufacture of multichip modules (MCM‐L) by the electronic packaging industry. Of late, the thrust has been towards higher density circuitry to achieve improved performance and reduced size. This has led to the use of finer lines and spacings, smaller drilled holes and buried vias in organic laminates leading to reliability issues such as electrochemical migration. One of the forms of electrochemical migration is known as conductive filament formation. Conductive filament formation is an electrochemical process. In accelerated environments of temperature and humidity, organic laminates can develop a loss of insulation resistance between conductors, eventually resulting in loss of electrical function of the circuit. The paper aims at discussing electrochemical migration in general, and conductive filament formation in particular, and its impact on the reliability of MCM‐L.

Details

Circuit World, vol. 22 no. 1
Type: Research Article
ISSN: 0305-6120

Keywords

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