Vadimas Verdingovas

Influence of sodium chloride and weak organic acids (flux residues) on electrochemical migration of tin on surface mount chip components

Abstract The electrolytic properties of sodium chloride and no-clean solder flux residue, and their effects on electrochemical migration and dendrite growth on surface mount chip capacitors were investigated. The leakage current dependency on concentration of contaminants was measured by a solution conductivity method and compared with current measurements using DC voltage. The effect of electrolyte concentration and potential bias on the probability of electrochemical migration was investigated using a water droplet method on chip capacitors. The results from leakage current and conductivity measurement showed a difference which is caused by polarization effects, and demonstrated existing issues when indexing contamination levels on printed circuit board assemblies using a standardised solvent extract method. The experimental results showed that dendrite growth was dependent on the type and amount of contamination. The probability of migration becomes less dependent on the amount of contamination for sodium chloride at high concentrations. However, for organic acids from flux residues the migration probability shows an abrupt decrease with increasing concentration, which is attributed to a pH change in the condensed electrolyte phase.

Relative effect of solder flux chemistry on the humidity related failures in electronics

Purpose – This paper aims to investigate the effect of no-clean flux chemistry with various weak organic acids (WOAs) as activators on the corrosion reliability of electronics with emphasis on the hygroscopic nature of the residue. Design/methodology/approach – The hygroscopicity of flux residue was studied by quartz crystal microbalance, while corrosive effects were studied by leakage current and impedance measurements on standard test boards. The measurements were performed as a function of relative humidity (RH) in the range from 60 to ∼99 per cent at 25°C. The corrosiveness of solder flux systems was visualized by the ex situ analysis using a gel with tin ion indicator. Findings – The results showed that the solder flux residues are characterized by different threshold RH, above which a sudden increase in direct current leakage by 2–4 orders of magnitude and a significant reduction in surface resistance in the impedance measurements were observed. Practical implications – The findings are attributed t...

Allergic nickel dermatitis caused by playing the guitar: case report and assessment of nickel release from guitar strings.

Ulrik F. Friis1, Torkil Menné2, Morten S. Jellesen3, Per Møller3, Vadimas Verdingovas3, Thomas R. Jensen3, Jacob P. Thyssen2 and Jeanne D. Johansen1 1Department of Dermato-Allergology, National Allergy Research Centre, Copenhagen University Hospital Gentofte, 2900 Hellerup, Denmark, 2Department of Dermato-Allergology, Copenhagen University Hospital Gentofte, 2900 Hellerup, Denmark, and 3Department of Mechanical Engineering, Technical University of Denmark, Kemitorvet, 2800 Lyngby, Denmark

Decomposition of no-clean solder flux systems and their effects on the corrosion reliability of electronics

No-clean flux systems are used today for the soldering of electronic printed circuit board assemblies assuming that all the aggressive substances of the flux will vanish during the soldering process i.e. evaporate, decompose or being enclosed safely in the residues. However this is not true in most cases, as the flux residue left on a printed circuit board assembly is a key factor compromising the corrosion reliability under humid conditions. This investigation focuses on the chemical degradation of three kinds of solder flux systems based on adipic, succinic, and glutaric acid as a function of temperature, thus simulating the soldering process. Differential Scanning Calorimetry, Fourier Transform Infrared Spectroscopy, and Ion Chromatography were employed for decomposition and residue analysis. Aggressiveness of the residue was investigated using a pH indicator gel test and by acid value determination. Effect on corrosion reliability was investigated by exposing the test printed circuit board assemblies to humidity after pre-contaminating with pure acids and desired solder flux systems and measuring the charge transferred between electrodes under applied potential bias. Results showed that the fluxes do not decompose fully within the temperature regime of the soldering process, leaving behind significant level of weak organic acid residues. The residue depending on the type and amount can be can be very aggressive towards the corrosion on the printed circuit board assemblies. The glutaric acid based flux showed highest leakage current when exposed to humidity compared to the adipic and succinic based fluxes.

Colorimetric visualization of tin corrosion: A method for early stage corrosion detection on printed circuit boards

Abstract A majority of printed circuit board surfaces are covered with tin, therefore tin corrosion under humid conditions and movement of tin ions under the influence of an electric field plays an important role in the corrosion failure development. Tracking tin corrosion products spread on the printed circuit board assembly (PCBA) provides a basis for the mechanistic understanding of PCBA corrosion failures and leak current tracks which eventually can lead to electrochemical migration. This paper presents a method for identification of such failures at the early stage of corrosion by using a colorimetric tin ion indicator applied as a gel. The examples provided in this paper include visualization of corrosion caused by weak organic acids found in solder fluxes, corrosion profiling on the PCBAs after climatic device level testing, and failure analysis of field returns.

Simulation of electronic circuit sensitivity towards humidity using electrochemical data on water layer

Climatic conditions like temperature and humidity have direct influence on the operation of electronic circuits. The effects of temperature on the operation of electronic circuits have been widely investigated, while the effect of humidity and solder flux residues are not well understood including the effect on circuit and PCBA (printed circuit board assembly) layout design. This paper elucidates a methodology for analyzing the sensitivity of an electronic circuit based on parasitic circuit analysis using data on electrical property of the water layer formed under humid as well as contaminated conditions. Some commonly used circuits are analyzed as case studies and flux related contaminations of PCBA from process is used as an example to show how different flux chemistry and humidity together compromise the circuit functionality.

On the Effects of Atmospheric Particles Contamination and Humidity on Tin Corrosion

The effects of hygroscopic atmospheric particles are investigated in relation to the corrosion of tin. Surface insulation resistance test boards were directly contaminated both with ambient particles sampled in the field at Milan, Italy, and with pure saline particles generated in the laboratory. An innovative particle deposition device was used to uniformly coat circular spots on to the test board surfaces. Deliquescence and crystallization of the water-soluble compounds were detected by observing the impedance response to varying relative humidity (RH) conditions with a gradual and continuous ramps. The effects of the adsorption/desorption kinetics and of the temperature on the deliquescence and crystallization RH values were also investigated. Leakage current measurements at 5-V dc highlighted the ability of atmospheric particles to promote corrosion and electrochemical migration at RH levels far below condensing conditions (100% RH).

Analysis of surface insulation resistance related failures in electronics by circuit simulation

Purpose At first, to show that the humidity levels for SIR failures are dependent on the type of activators used in no-clean flux systems, and secondly, to demonstrate the possibility of simulating effects of humidity and contamination on the printed circuit board components and sensitive parts if typical SIR data connected to the particular climatic condition is available. This is shown on representative components and typical circuits. Design/methodology/approach A range of surface insulation resistance values obtained on SIR patterns with 1476 squares was used as an input data for circuit analysis. The SIR data were compared to the surface resistance values observable on the real device PCBA. Surface insulation resistance (SIR) issues at the component and circuit level were analysed based on the parasitic circuit effects owing to the formation of water layer as an electrical conduction medium. Findings This paper provides a summary of the effects of various weak organic acids (WOAs) contamination repre...

Electrochemical migration of lead-free solder alloys in Na 2 SO 4 environment

The effect of sulphate ion concentration on electrochemical migration of lead-free solder alloys was investigated with the use of water drop tests, by applying an in-situ optical and electrical inspection system. According to the Mean-Time-To-Failure (MTTF) values it was found that in the case of 0.1 and 1 mM Na<inf>2</inf>SO<inf>4</inf> solutions X alloy (composition in wt%: Sn=90,95%, Ag=3,8%, Cu=0,7%, Bi=3%, Sb=1,4%, Ni=0,15%) has higher migration susceptibility than SAC305 alloy (composition in wt%: Sn=96,5%, Ag=3%, Cu=0,5%). However on higher concentration levels, MTTF decreased and the failures usually happened in the same time on each solder alloy type. Failures were not happened in the case of X covered boards in case of 10 mM concentration.

Corrosion reliability of lead-free solder systems used in electronics

Corrosion reliability of five Sn-Ag-Cu (SAC) based lead-free solder alloys under humid and corrosive conditions has been investigated to understand the microstructure effects on corrosion performance. Electrochemical experiments such as potentiodynamic and potentiostatic tests were conducted in 3.5 wt% sodium chloride electrolyte at room temperature. Microstructure of the solder alloys and corrosion surface morphology was evaluated using light optical microscope (LOM) scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). During the potentiostatic tests, the cathodically active Bi phase in No. 5 alloy introduced pitting in the Sn phase nearby, whereas AgsSn phase prompted pitting on the adjacent to ß-Sn phase in No. 1–4 solder alloys (Table 1.).