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6. Synergetic effect of temperature and humidity on the leakage of KOH electrolyte and related reliability of zinc-air batteries

Author

Rao, Jyothsna Murli, Yadav, Abhijeet, Conseil-Gudla, Helene, Ambat, Rajan, Rao, Jyothsna Murli, Yadav, Abhijeet, Conseil-Gudla, Helene, and Ambat, Rajan

Abstract

The Zinc-air primary batteries (ZAB’s) are prone to electrolyte leakage upon exposure to high temperature and humidity conditions. Potassium hydroxide is a hygroscopic and corrosive compound and it can cause various electrochemical corrosion failures for the attached electronics inside a device. In this study, the effect of temperature and humid conditions on the leakage of Potassium hydroxide electrolyte from three different Zinc Air Battery variants were investigated. The batteries were exposed to hot and humid conditions, and a qualitative Gel test with pH indicator was used to visually observe the leakage from the individual set of battery variants. The residues of the released electrolyte was identified by FTIR and quantified using a titration method. SEM-EDS analysis was also performed to examine the surface of the batteries and sealants for eventual damage. The related effect of electrolyte leakage on the reliability of the batteries was performed by a voltage discharge test. The hygroscopicity properties of pure Potassium hydroxide were studied using a water sorption/desorption equipment and was correlated with electro impedance spectroscopy analysis using an interdigitated test board. The results from the study indicate that the increase in temperature caused an increased amount of electrolyte leakage under saturated humid conditions. Leakage of Potassium hydroxide electrolyte caused damage to the sealant gasket, clogged the oxygen ventilation holes of the batteries, and exhibits high hygroscopic properties when exposed to high temperature and humid conditions.

Published
2022

8. Reflow Residues on Printed Circuit Board Assemblies and Interaction with Humidity

Author

Conseil-Gudla, Helene, Li, Feng, Ambat, Rajan, Conseil-Gudla, Helene, Li, Feng, and Ambat, Rajan

Abstract

Ionic residues resulting from the soldering process is an important parameter in connection with humidity robustness of Printed Circuit Board Assemblies (PCBAs) due to their ability to enhance moisture absorption and surface conductivity. For reflow process, residues are trapped under the components, and the morphology of the residues can change with humidity exposure resulting in the release of ionic components. In this work, trapped residues below the components from reflow process of several commercial PCBAs were characterized before and after exposure to humidity conditions. PCBAs used for the analysis had undergone multiple reflow heating profiles by single and double reflow plus additional passes to understand heating effects. The morphology change of the trapped residues under components upon humidity exposure was observed using optical and scanning electron microscopy. The conductivity of the localized extracted solutions was measured and NaCl equivalency was determined. The solder paste materials were analysed for their water sorption property, while the effect of humidity on electrical property was assessed using electrochemical impedance spectroscopy using test PCBs. The results show that the change in morphology and level of activator release of residues were a function of the flux type, PCBA characteristics such as component standoff height and number of reflow cycles. Water layer formation upon humidity exposure and electrical properties on test PCBs are correlated with water sorption of the flux part.

Published
2021

14. Experimental Study of Moisture Ingress in First and Second Levels of Electronic Housings

Author

Conseil-Gudla, Helene, Hamm, Gerald, Mueller, Lutz, Hain, Mathias, Ambat, Rajan, Conseil-Gudla, Helene, Hamm, Gerald, Mueller, Lutz, Hain, Mathias, and Ambat, Rajan

Abstract

Moisture uptake of polymer materials used for electronic packaging and moisture ingress into automotive electronic sensor housings have been studied by exposure to constant and cyclic humidity and temperature conditions. The first-level housing is made of epoxy molding compound (EMC) and encapsulates the sensor silicon-chip. The second-level housing is made of polybutylene terephthalate and contains the EMC attached to a printed circuit board (PCB). The novel approach was to perform in situ measurements of the temperature and the relative humidity (RH) inside the EMC next to the silicon chip, and to measure the humidity transfer from outdoor to the second, and through the first-level housings up to the chip. The effect of the presence of PCB and the self-heating of components have been investigated. The results showed that the time constants for humidity to reach 63% of outdoor conditions are about 2 and 7 days at 60 degrees C for the second-and first-level housings, respectively. Exposure to cyclic conditions showed that the internal RH tends to reach a steady state, close to the mean value of the cyclic outdoor profile, while the presence of polymeric materials (as PCB) can act as a humidity buffer and absorb and desorb water when subjected to temperature fluctuations.

Published
2018

15. Parametric study of interior climate in electronic device enclosures and corrosion reliability

Author

Conseil-Gudla, Helene

Abstract

Dette ph.d.- arbejde, støttet af Det Frie Forskningsråd, Teknologi og Produktion via projektet ”Improved climate control inside electronic equipment (ICCI)” og af ”Innovationskonsortiet for pålidelig elektronik” (IN-SPE) har til formål at opnå en øget forståelse af klimatiske påvirkninger på elektroniks pålidelighed. Primært fokuseres der på veldefinerede undersøgelser af det interne klima i kabinetter til indkapsling af elektronik. Elektronik anvendes som styresystemer i mange anvendelser og kabinetter med elektronik kan være placeret inde såvel som udendørs. Et ukontrolleret klima inde i sådanne kabinetter kan forårsage fugt relaterede fejl, især på printkort. Dette ph.d.-projekt resumerer detaljerede undersøgelser af faktorer som udendørs klimatiske profiler, indkapslingsdesign, fugtstyringsløsninger samt materialerelaterede fejl og effekten af temperatur og fugt på klimatisk pålidelighed af elektronik. Artikel 1 fokuserer på printkort overflader og effekten af kloridforurening, elektrisk felt og fugtighed. Artiklerne 2 og 3 er relateret til forureningsprofilen på printkort og omhandler lodningsprocessen, dekomponering af flus systemer og deres indvirkning på elektronikkens pålidelighed. Artikel 4 vedrører vandabsorption i materialer såsom printkort laminater og loddemaske, mens artikel 5 fokuserer på fugt opbygning under konstante betingelser inde i elektronik kabinetter og undersøger effekten af parametre som hulstørrelse, hulform og materialers vandoptag. Artikel 6 beskriver en undersøgelse af fugtopbygning i en elektronik indkapsling udsat for cykliske forhold og undersøger "pumpeffekten" på grund af forsinkelse i temperaturændring forårsaget af termisk masse. Artikel 7 beskriver arbejde gennemført under eksternt forskningsophold hos Robert Bosch i Tyskland og vedrører dynamikken i fugtindtag med in-situ måling af temperatur og fugt i epoxy støbte materialer. Artikel 8 indeholder en klimaprofilering af forskellige geografiske placeringer med modellering af fugt opbygning. Artikel 9 vedrører anvendelse af tørremiddel som fugt kontrol i elektronik kabinetter. Samlet set viste undersøgelserne tydeligt betydningen af forurening (flusrester eller salte) på overfladen af printkort, hvilket vil reducere tærskelværdien hvor fejl (korrosion og elektrokemisk migration) kan forekomme på printkort. Loddemaskematerialet absorberer mere fugt end printkort laminat materialet og tilstedeværelsen af fugt i disse materialer kan ændre de dielektriske egenskaber. Fugtindholdet i indkapslet elektronik er afhængig af indkapslingsmaterialet og eventuelle utætheder eller revner i foringsvægge. Diffusionsparametre og vandopløselighed af selve indkapslingsmaterialet skal overvejes, især når det udsættes for cykliske betingelser. Elektronik produkter anvendes i forskellige geografiske områder, hvor klimaforholdene kan være meget forskellige, og fugtigheden inde i et fuldt hermetisk lukket polymer indkapsling kan nå et mætningsniveau i løbet af få uger på grund af temperaturændring. Tilstedeværelsen af termisk masse inde i enheden kan også fungere som et sted for lokal fugtopbygning på grund af høj termisk kapacitet. På grund af stor evne til at absorbere vand kan tørremiddel anvendes som fugtkontrol inde i elektroniske kabinetter, men en regenereringsproces er nødvendig for at undgå vandmætning af tørremidlet der kan forårsage øget fugt indhold inde i kabinettet. The current PhD work is supported in part by the Danish Council for Independent Research, Technology and Production Sciences through the ICCI (improved climate control inside electronic equipment) project and in part by the Innovation Fund Denmark through the IN-SPE (innovation consortium for sustained performance of electronics) project at DTU. The aim of this project is to obtain a deeper understanding and improvement of climatic reliability of electronic devices by performing parametric studies of interior climate in electronic enclosures. Electronic control systems are used in all sorts of modern technological devices be it outside or indoors. Uncontrolled local climate inside the enclosures for these systems causes several humidity related failures, especially on the printed circuit board assemblies (PCBAs) placed inside. This PhD project focusses on detailed parametric studies of the influencing factors, such as outdoor climatic profiles and enclosure design, but also of humidity control solutions and materials and corrosion humidity related failures. Paper 1 focusses on printed circuit board surface finish and effects of chloride contamination, electric field, and humidity on corrosion reliability. Papers 2 and 3 are related to the contamination profile on typical PCBAs caused by soldering processes, and on the decomposition of no-clean solder flux systems and their effects on the corrosion reliability of electronics. Paper 4 concerns water absorption in electronic materials such as PCBA laminates and solder masks, while Paper 5 focusses on the humidity build-up in typical electronic enclosures exposed to constant conditions, investigating the effect of parameters such as hole size, hole shape, casing material, and the resistor-capacitor (RC) approach for modelling was attempted. Paper 6 is a study of the humidity build-up in a typical electronic enclosure exposed to cycling conditions and studies the effect on corrosion reliability specifically investigating the “pumping effect” due to delay in temperature change in presence of heavy thermal mass. Paper 7 is about the study carried out during external research stay at Robert Bosch, Germany and concerns the dynamics of moisture ingress in first and second level electronic housings with in-situ measurement of T and RH in an epoxy mold compound. Paper 8 is a study of climate profiling of different geographical locations, with RC modelling of humidity build-up in electronic enclosures and their reliability prediction. Paper 9 concerns the use of desiccant as a humidity control in electronic enclosures. Overall, the investigations clearly showed the importance of the presence of contamination of flux residues and sodium chloride on the surface of the PCBAs, which will reduce the humidity thresholds at which failures (corrosion and electrochemical migration) appear on the PCBAs. The solder mask material absorbs more moisture than the laminates of the PCBAs, however the presence of moisture in laminate as well as solder mask material will increase the dielectric properties and can create voids and blisters during the reflow soldering process. The moisture ingress into the electronic enclosures will arise by any presence of leaks or cracks in the casing walls, while diffusion and solubility of the polymeric casing material have to be considered, especially when exposed to cyclic conditions. Electronic products are used in varying geographical locations, where climate conditions can be very different, and the moisture inside a fully hermetic polymeric enclosure can reach a saturation level in few weeks due to temperature change. The presence of thermal mass inside the device can also act as a site for local humidity build-up due to its high thermal capacity, and enhances the moisture uptake inside the electronic device. Due to their high ability to absorb water, desiccant can be used as humidity control inside electronic enclosures, but a regeneration process is needed in order to avoid desiccant water saturation and even humidity increase in inside the enclosures.

Published
2017

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