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Surface insulation, electrochemical migration and various other insulation resistances are terms which are often glibly used, sometimes even incorrectly. This paper categorises different types of insulation resistance and catalogues about twenty practical applications of insulation resistance measurement, each with its ideal general conditions of measurement (test voltage, bias voltage, bias polarity, test voltage period, test frequency, test duration, temperature, humidity, test pattern type, test pattern dimensions, voltage gradients, tolerances, etc.) This description is independent of any of the nearly forty known, often contradictory, standards, most of which no longer correspond to the practical printed circuit or assembly of today. Also discussed are the different technologies of insulation resistance measurement, starting with the original non‐electronic ‘Megger®’ types through to modern laboratory electrometers and, finally, instrumentation specific to the practical measurement of printed circuit insulation resistances, including static and dynamic types. The importance of automatic statistical analyses is emphasised, especially with production testing as well as qualification procedures. This paper is aimed not only at those wishing to learn what modern insulation resistance testing is all about, but also at experienced persons wanting to marshall their thoughts about the fundamental meanings of insulation testing for different applications and specifications.
The purpose of this study is to show that the humidity levels for surface insulation resistance (SIR)-related failures are dependent on the type of activators used in…
The purpose of this study is to show that the humidity levels for surface insulation resistance (SIR)-related failures are dependent on the type of activators used in no-clean flux systems and to demonstrate the possibility of simulating the effects of humidity and contamination on printed circuit board components and sensitive parts if typical SIR data connected to a particular climatic condition are available. This is shown on representative components and typical circuits.
A range of SIR values obtained on SIR patterns with 1,476 squares was used as input data for the circuit analysis. The SIR data were compared to the surface resistance values observable on a real device printed circuit board assembly. SIR issues at the component and circuit levels were analysed on the basis of parasitic circuit effects owing to the formation of a water layer as an electrical conduction medium.
This paper provides a summary of the effects of contamination with various weak organic acids representing the active components in no-clean solder flux residue, and demonstrates the effect of humidity and contamination on the possible malfunctions and errors in electronic circuits. The effect of contamination and humidity is expressed as drift from the nominal resistance values of the resistors, self-discharge of the capacitors and the errors in the circuits due to parasitic leakage currents (reduction of SIR).
The methodology of the analysis of the circuits using a range of empirical leakage resistance values combined with the knowledge of the humidity and contamination profile of the electronics can be used for the robust design of a device, which is also important for electronic products relying on low current consumption for long battery lifetime.
Examples provide a basic link between the combined effect of humidity and contamination and the performance of electronic circuits. The methodology shown provides the possibility of addressing the climatic reliability of an electronic device at the early stage of device design by using typical SIR data representing the possible climate exposure.
The use of surface insulation resistance testing has been restricted to QC laboratory applications. The extension of this technique to modern electronics and, in…
The use of surface insulation resistance testing has been restricted to QC laboratory applications. The extension of this technique to modern electronics and, in particular, to contamination control of SMAs has forced the development of new methods of SIR measurement. These have revealed that existing standards are rapidly becoming obsolete because the premises on which they are founded are no longer valid. Even more alarming, it is revealed that we are rapidly reaching, not only the limit of our knowledge in the field, but also the technical limits of existing standard materials used in industry today. This paper is a warning against too much complacency, as the risk of running into real problems, at all process stages, will become very pertinent within a few years. The technical content of this paper is based on about three years' study of the subject resulting in the measurement of SIR at about 10 V, as opposed to the traditional values of 100 and 500 V, which have been proved to be of little value with conductor spacings such as are usual on SMAs.
Bellcore has two generic physical design criteria for telecommunications product cleanliness. Residual insoluble contamination levels are monitored by surface insulation…
Bellcore has two generic physical design criteria for telecommunications product cleanliness. Residual insoluble contamination levels are monitored by surface insulation testing, and soluble ionic species by solvent extract conductivity testing. The previously undefined relationship between the two has been elucidated and is reported in this paper. Contamination of insulation resistance test pattern surfaces with LiBr at the criterion limit of 1 μg NaCl equivalent per cm2 results in surface insulation resistance levels in the 109 to 1010 ohm range, which is the criterion level. A discussion correlates the Bellcore cleanliness criteria with satisfactory performance of today's leakage sensitive ICs. Contamination levels at or above 5 μg NaCl equivalent per cm2 result in significant circuit corrosion and migration at 85°C/85% relative humidity stress, clearly indicating unsatisfactory field performance for a product with such contamination levels.
Owing to the incessant demand for reductions in the size of portable electronics, new dense packaging technologies are required. Reflow soldering is still mainly used for…
Owing to the incessant demand for reductions in the size of portable electronics, new dense packaging technologies are required. Reflow soldering is still mainly used for component joining on the substrate. In tiny joints such as those in flip chip (FC) assemblies the flux effect is vitally important and needs to pass a narrower performance window than in ordinary surface mount technology (SMT). The determination of the suitability of a flux, as reported in this paper, is twofold; first, the flux must perform well in its intended purpose and second, the flux must not leave harmful residues causing leakage or electromigration. The first test used was the wetting balance test for all fluxes. Fluxes accepted on the basis of the wetting tests were then subjected to the surface insulation resistance test (SIR).
Modern electronics is characterised by the increasing level of integration in printedcircuit board (PCB) technology and the reduced insulation spacing between…
Modern electronics is characterised by the increasing level of integration in printed circuit board (PCB) technology and the reduced insulation spacing between adjacent conductors. Surface insulation resistance (SIR) measurement has often been used alone to determine the cleanliness of PCB assembly; however, when proper SIR measurement is used in conjunction with surface leakage current (SLC) measurement, the result can reveal the dynamic nature of surface electrochemical migration (SECM) processes at the microscopic level, and the effect of such processes on product quality and reliability. This paper presents a newly developed measurement methodology, which measures SLC per square unit area at a sampling rate that is orders of magnitude higher than that of conventional SIR measurement methods. It is aimed to capture the transient surge of SLC which is detrimental to the functionality of product.
For many years the analysis of contaminant residues on PWB surfaces has been of major importance to the industry. While the identification of residues left on metallic…
For many years the analysis of contaminant residues on PWB surfaces has been of major importance to the industry. While the identification of residues left on metallic surfaces has proven to be relatively straightforward, the analysis of organic contamination of similar composition to that of the underlying board surface has not been as successful. Through the use of modern XPS instrumentation, the non‐ionic component of water soluble flux has been identified and differentiated from the chemically similar FR‐4 and soldermask substrates. This paper presents the XPS results for a series of experiments aimed at determining the location and relative concentration of water soluble flux residues on standard surface insulation resistance (SIR) comb patterns. The data show that the water soluble flux residue is not present as a uniform coating on the board surface but appears in localised sites in high concentrations while being absent in other locations. Through more aggressive cleaning procedures the sites of high residue concentration can be significantly reduced.
For reliable telecommunication systems, Bellcore recommends that Surface Insulation Resistance (SIR) be monitored at key points in printed wiring board and circuit pack…
For reliable telecommunication systems, Bellcore recommends that Surface Insulation Resistance (SIR) be monitored at key points in printed wiring board and circuit pack manufacturing. The Bellcore SIR criteria are based on the old ‘Bell System’ test pattern having 0·025 inch conductor line widths, and 0·050 inch conductor spacings. Since divestiture, many equipment suppliers have suggested using different test patterns, or even conductors on actual product for SIR testing. Also, with the trend to high density packaging and smaller conductor spacings, the Bellcore pattern now represents old technology. This work confirms and advances prior work suggesting pattern translation based on the SIR per square concept. Essentially exact SIR per square correlation has been found over an order of magnitude of pattern conductor space widths. Critical experimental techniques to modify the FR‐4 epoxy surface appropriately and an important theoretical hypothesis involving shadowing (proven experimentally) are developed in this work.
This paper aims to find a way to improve the surface insulation, corrosion resistance and mechanical properties of Fe-Cr-Al electrothermal alloy, exploring the best…
This paper aims to find a way to improve the surface insulation, corrosion resistance and mechanical properties of Fe-Cr-Al electrothermal alloy, exploring the best oxidation condition and analyzing the oxidation mechanism.
Electrochemical workstation was used for anodic oxidation, and the effect of current density, ethylene glycol concentration and oxidation time on properties of the film were investigated by resistivity test, scanning electron microscope, electrochemical tests (potentiodynamic polarization and electrochemical impedance spectroscopy) and mechanical tests, and the oxidation process was analyzed by X-ray photoelectron spectroscopy (XPS).
According to the potential-time curves of anodic oxidation and the analysis of XPS, the whole oxidation process can be divided into four stages. When the current density is 0.8 A/dm2, the ethylene glycol concentration is 10%, and the oxidation time is 60 min, the film has the best corrosion protection, mechanical properties and surface morphology. The resistivity of the samples is about 13 orders magnitude than that of the matrix.
In this paper, a protective electrically insulating film was prepared by anodic oxidation in an alkaline electrolyte solution. The oxidation conditions were optimized and the oxidation mechanism was analyzed.
Electrical testing of PCBs is important to ensure the maintenance of adequate insulation between tracks and from side to side of the boards; the properties of the base…
Electrical testing of PCBs is important to ensure the maintenance of adequate insulation between tracks and from side to side of the boards; the properties of the base materials should not be degraded below an acceptable level before boards are loaded with components. The paper describes testing methods relating to resistance, voltage clearance, capacitance, inductance, insulation resistance, volume resistivity, dielectric measurements, Q factor, and DC resistance of tracks and holes.