Insulation Resistance Test Research Articles

Characterising Soldering Fluxes

For a number of years electronic manufacturers of printed circuit assemblies have used rosin‐based soldering fluxes. Post‐solder cleaning was accomplished with chlorinated or chlorofluorocarbon (CFC) solvents. With the elimination of these solvent options due to their destructive effect on the stratospheric ozone layer, manufacturers are considering alternative cleaners for rosin flux or new flux choices which can be cleaned with water or left uncleaned. Many of the flux formulations are relatively new and their long‐term effect on the performance of products manufactured with them is unknown. Although ionic contamination testers can alert one to the ionic levels remaining on an assembly, there is no direct relationship between the total ionic level and the corrosivity of the soldering flux. Surface insulation resistance testing is used in the industry, but the results are misunderstood by many. This is due to the fact that SIR data represent a complex dependency on a number of factors including (1) the test conditions (temperature, humidity, bias), (2) the area of interactions (often referred to as the number of squares), (3) the separation between lines on the interdigitated comb pattern, (4) the presence or absence of bias voltage during the test and (5) the nature of the substrate. All of these factors have been the driving force to develop a quantitative screening test for soldering flux residues. This test, originally reported by Dr David Bono, is being modified and developed at Georgia Tech to provide a quantitative evaluation of flux residue corrosivity. This work, in collaboration with the work being performed by the French UTE, will result in a new international standard. This paper reports the latest data on this important test development.

Electromigration vs SIR

The IPC‐SF‐818 surface insulation resistance (SIR) test data taken with the use of a variety of halide‐free, no‐clean fluxes are analysed against Bellcore TR‐NWT‐000078 electromigration (EM) test data. Neither test results show correlation with bulk flux resistivity, flux water extract resistivity, flux residue moisture pick‐up, and flux corrosivity without bias. However, in the case of rosin fluxes, the insulation resistance behaviour in both SIR and EM tests is a function of the pH value of fluxes. This phenomenon is more significant in the SIR test. In the case of low‐residue, no‐clean fluxes, only the SIR test displays such a pH dependent relationship. Data suggest that the 50 volts bias voltage used in the SIR test may be responsible for this, and can be explained with a high‐bias‐voltage‐induced electrolysis mechanism which is further promoted by a high pH environment. This failure mechanism is absent in the EM test which utilises 10 volts bias voltage, and probably will not occur under the normal 5 volts application conditions. Overall, the SIR test seems to be more stringent while the EM test appears to be more realistic.

Characterizing Soldering Fluxes

AbstractFor a number of years electronic manufacturers of printed circuit assemblies have used rosin-based soldering fluxes. Post-solder cleaning was accomplished with chlorinated or chlorofluorocarbon (CFC) solvents. With the elimination of these solvent options due to their destructive effect on the stratospheric ozone layer, manufacturers are looking to alternative cleaners for rosin flux or to new flux choices which can be cleaned with water, or left uncleaned.Many of the flux formulations are new and their long-term effect on the performance of product manufactured with them is unknown. Although ionic contamination testers can alert one to the ionic levels remaining on an assembly, the corrosivity of the residues is not directly related to the total ionic level, but only to certain ionic species. Surface insulation resistance testing is used by many in the industry, but the results are complex and often misunderstood.All of these factors have been the driving force to develop a quantitative screening test for soldering flux residues. This test, originally conceived by Dr. David Bono, has been modified and developed at Georgia Tech to provide a quantitative evaluation of flux residue corrosivity. This work, in collaboration with the work being performed by the French standards group, will result in a new international industry standard. This paper reports the latest data on this important test development.

The Chemical Design and Optimisation of a Non‐rosin, Water‐soluble Flux Solder Paste

This paper describes the approach used by the authors to select the flux materials for a simple water‐soluble solder paste flux formulation, what those materials were, and how they interacted to give the correct properties. Consistency of formulation and performance are discussed with emphasis on the need for adequate process parameter control as with any formulation. With this water‐soluble paste formulation various circuit card designs were successfully built possessing 25‐mil pitch, and larger, components. The cards were cleaned in aqueous cleaners and passed IBM standard insulation resistance testing.

Field testing instrumentation

The author reviews the progress of instrumentation for testing installed electrical power apparatus up to the present. He also discusses current work and the possibilities for future development. Particular attention is given to DC insulation resistance tests, DC field testing, AC insulating power factor testing, VLF testing, and partial-discharge testing in the field.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Interrelating surface insulation resistance test patterns : A. S. L. Chan and T. A. Shankoff. Circuit Wld15(4), 34 (1989)

Interrelating surface insulation resistance test patterns : A. S. L. Chan and T. A. Shankoff. Circuit Wld15(4), 34 (1989)

A Correlation between Surface Insulation Resistance and Solvent Extract Conductivity Cleanliness Tests

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.

The Surfactant Flux—A New Flux for the Ozone Age

The development of a new type of flux—the surfactant flux—is described. This flux is applied in a very thin layer and must be totally dry before soldering. It is not necessary to clean PWBs after soldering for functional or aesthetic reasons. Even the results of the surface insulation resistance (SIR) test suggest no need for cleaning. The flux allows a very high soldering speed, at least double that of normal fluxes. Thus the heat input into the materials involved is minimised, with the consequence of less damage. It is not the chemicals which make the flux highly active but the concept. This new concept makes it possible to design non or low corrosive fluxes in a wide range for purposes where highly corrosive fluxes must be used today.

Low Voltage Insulation Resistance Measurement of Printed Circuits and its Implications

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.

On the utility of insulation resistance tests to assess the life performance of printed wiring boards : E. T. Eisenmann. Circuit Wld12(2), 45 (1986)

The traditional way of engineering production systems requires static information flows within and in between automation software, from field control software to manufacturing operations management. The common understanding of data and its containing information is realized by implicit assumptions on data semantics. In contrast, the vision of future production systems as cyber-physical systems (CPS) focuses on intelligent production facilities, which are characterized by autonomous behavior and dynamic, cooperative interactions. As a consequence, data and information that are stored and exchanged within CPS cannot rely on the assumption that other software systems are aware of data semantics. A means to solve this issue is ontologies – an approach being intensely discussed and applied for enhancing data with semantics. However, reuse of ontologies within the automation domain is hampered as ontologies are developed for specific use cases without having reusability in mind. In this paper, these drawbacks of ontology development are discussed and an approach for maximizing reusability through modularizing ontologies for different fields of the automation domain is presented.

Contamination Control: Quo Vadis?

This paper essentially describes what is believed will become the norm in contamination control over the next decade, as applied to laminate and PC manufacture, components, assembly, soldering and protection. Particular attention is paid to the special requirements imposed by the increasing use of surface mount technology, especially when trying to extrapolate current techniques towards modern applications. Test methods are mentioned and these are also likely to undergo considerable development over the next few years but, above all, more precise, scientifically‐established standards are urgently needed for both ionic contamination and surface insulation resistance testing. Cleaning technology is, of course, an essential part of contamination control and future development of both solvent and aqueous methods will lie in a better understanding of the time‐energy relationship required to break contamination‐substrate bonds at a molecular level.

On the Utility of Insulation Resistance Tests to Assess the Life Performance of Printed Wiring Boards

Based on new data insulation resistance tests have little capacity to predict the life performance of double‐sided rigid printed wiring boards. This conclusion arises from an elaborate insulation resistance evaluation after 2300 hours of accelerated life testing. The study considers the effects of two sources of contamination and five material combinations on the initial insulation resistance at 23°C and 90% RH. Life test samples were exposed to four levels of humidity and three levels of temperature. Using 1 Megohm as failure criterion there are clear‐cut effects of humidity, temperature and material combination, but there is only a weak correlation between failures and the initial insulation resistance.

Insulation Resistance and High-Potential Testing: Advantages and Limitations

Downtime caused by electrical equipment breakdown or cable faults can often be substantially reduced by the use of highvoltage dc testing as a maintenance tool. The relative merits of ac versus dc testing, general principles of dc testing, types of tests, methods of performing the actual tests, and interpreting the results are explained. The value of insulation resistance measurements and their relationship to testing is discussed. Safety precautions are also given.

The detection of incipient breakdown of oil-immersed Bakelized paper contaminated by water

The insulation-resistance test is used as a non-destructive method of detecting the presence of water in insulating components in service. Water penetrates only the outer layers of oil-immersed Bakelized paper leading to the formation of a low-resistance surface skin. It is shown that, by taking account of the operating conditions, a critical surface conductivity can be estimated above which the insulation will fail in service.The correlation between conductivity under working conditions and insulation resistance is described. A method of estimating a rejection limit of insulation resistance for a component in service is suggested. The measurements needed are stated.

Diagnoses of A-C Generator Insulation Condition by Nondestructive Tests [includes discussion

Data are presented from comparison of nondestructive and destructive tests on several synchronous generator stators ranging from 800 to 33,000 kva. It is shown that the breakdown voltage of the weakest point in a winding can be forecast nondestructively by insulation resistance tests at increasing voltages. A new method of stating dielectric-absorption effect is suggested and its value as a criterion of mechanical strength of hidden insulation is indicated. The detection and location of internal voids in coils, by ionization tests of established types, are described and comment is made on the relation of such voids to interturn and interstrand faults. The simple test equipment used is briefly described. A routine test program based on the findings is outlined. Proposals are given for lines of further study. Tests to date have been concerned chiefly with the varnish-bondedmica type of insulation, but there are indications of wider applicability.

High-Voltage Measurements on Cables and Insulators

This paper presents some of the results of a series of high-voltage tests on cables and insulators, extending over a period of eight years, to determine the electrical characteristics of the insulation. Leakage current, insulation resistance, and watt input tests were made with direct and alternating current. Paper-insulated and rubber-insulated cables and a 27,000-volt porcelain insulator were tested. From these tests several conclusions were drawn, the principal ones being as follows: 1. Insulation resistance of paper and rubber-insulated power cables increases to a maximum with increasing applied d-c. voltage, the characteristic depending upon the temperature. 2. It is necessary to use shields as well as guards in making tests to determine the electrical characteristics of cable insulation under d-c. voltage stresses above the ionization point. 3. The watt input to the insulation of a paper cable under d-c. stress, at a given temperature, depends upon the character of the voltage wave; the greater the ripple, the greater the watt input. 4. It is necessary to use shields as well as guards in making tests on short cable samples to determine the a-c. electrical characteristics, such as dielectric loss of cable insulation under voltage stresses above the ionization point. 5. The ionization point is very variable depending upon the physical circuit, together with the atmospheric conditions, and represents, in reality, local air breakdown. 6. The better (i. e.

Tests of Paper-Insulated High-Tension Cable

The paper deals with those tests which are involved in specifications. The discussion is from the standpoint of the purpose and significance of the various standard tests which are made rather than that of the technique of the details of testing. A considerable number of data are given. The subjects treated are purpose and importance of tests of cable; insulation resistance test; high-voltage test; dielectric loss and power-factor test; ``ionization'' test; bending test; accelerated life test; preparation of samples for high-voltage tests and tests of components. The possible significance of wide variation in some of the properties of cable is discussed. The relation found between time and voltage based on a large number of tests of both three-conductor and single-conductor cable is discussed at considerable length. A test for stability of the impregnating compound is described as is also a proposed standard load for dielectric-loss testing. Some data are given showing the effect of repeated bending on lead and how that effect is influenced by the tensile stress in the lead. The paper concludes with a list of the ways by which, in the author's opinion, progress can be made in the improvement of the quality and the design of paper-insulated high-tension cable.