Laszlo Gal

Electrochemical migration of silver on conventional and biodegradable substrates in microelectronics

Water drop (WD) test and a contact angle measurement method were used to investigate the electrochemical migration (ECM) behavior on different microelectronic substrates with silver conductor lines in all cases. Environment friendly substrates were also investigated in this study as possible candidates of the conventional ones. ECM is kind of short failure phenomenon, which can lead to series defect in case of operating microcircuits, when moisture appears on/in a conductor-dielectric-conductor system. The results show that the novel biodegradable substrate patterns can have a significant higher ECM risk comparing to the conventional ones. The main causes can be the different wetting behavior and the different conductor line accuracy of the technological processes.

The effect of NaCl on water condensation and electrochemical migration

The effect of NaCl crystals on water condensation and on electrochemical migration processes (ECM) were investigated in case of different lead bearing and lead-free solder alloys on FR4 substrate during a special Thermal-humidity Bias (THB) test, called dew point test. The dew point test simulated the water condensation process and ECM, which processes were followed by in-situ optically and simultaneously electrically as well. The results showed that NaCl crystals can accelerate the condensation intensity, hence they played role as condensation cores. Furthermore, water droplets have formed locally “water bridges” between adjacent conductor lines. On the other hand, after the dissolution of NaCl crystals the ECM processes were accelerated. Finally precipitates and dendrites were formed resulted in shorts.

Investigating of electrochemical migration on low-ag lead-free solder alloys

Among the conditions of high humidity, elevated temperature, and voltage applied, metals and alloys in electronic components and assemblies can cause insulation failures by forming so called dendrites due to the electrochemical migration (ECM) failure phenomenon. This effect causes short-circuit failures of the electronic circuits, which might lead to catastrophic failure. The ECM behavior of lead-free micro-alloyed low Ag content solder alloys (SAC0307 and SAC0807) were compared with common used SAC305, SAC405 and with the traditionally lead-bearing solder alloys: Sn63Pb37 and Sn62Pb36Ag2 as references. In order to carry out the ECM investigations, water drop (WD) tests were made on standard comb patterns in 1 mMol NaCl and 1 mMol Na2SO4 solutions as well. The results have shown that the SAC0807 low Ag content micro-alloyed solder alloy could have a relative weak resistance against ECM.

Experimental 13.56 MHz RFID cards on biodegradable substrates

The paper presents experimental research on investigating the production and testing aspects of ISO/IEC 14443 contactless RFID tags fabricated on biodegradable cellulose acetate (CA) biopolymer-based Printed Circuit Boards (PCB). Our approach reduces the harmful plastic waste by substituting the standard materials of the cards with biodegradable substrate. Also, with common PCB fabrication methodology the prototyping and production becomes cost-effective for the novel material. The paper will detail the manufacturing steps and the different aspects of production for the prepared cards. The preliminary functional results show promising examples of a functional, standard 13.56 MHz RFID reference cards.

Corrosion investigations on lead-free micro-alloyed solder alloys used in electronics

The corrosion properties of different lead-free solder alloys (including novel low Ag content solder alloys) were investigated using the potentiodynamic polarization test method in 3.5 wt% NaCl solution. The results showed that most of the investigated lead-free micro-alloyed solders have better corrosion properties compared to the commonly used SAC305 lead-free solder alloy. The main causes of the different corrosion properties could be the different composition types and concentration of the alloying components.

Optimizing solder joints on biodegradable PCBs with vapour phase soldering

The paper focuses on biodegradable Printed Circuit Boards (PCB) from the aspect of PCB fabrication technology and soldering. Different biodegradable Cellulose Acetate (CA) PCBs were used during the tests (one sided and two sided), and the possible application of pre-preg was also taken into account to improve pad adhesion on the base material. The surfaces of the boards were evaluated in order to obtain information about copper adhesion. FR4 test boards were also investigated as a reference, both for soldering and surface analyses. The soldering profile setup was focused on minimizing high temperatures on the heat-sensitive biopolymer substrates. The soldering profiles were created with a custom vapour phase soldering (VPS) device. The customized solder profile setting is conducted with an adaptive temperature-tracker sample holder. The boards and the solder joints were investigated with non-destructive optical microscopy, X-ray microscopy (deformation and joint analysis), and destructive shear tests. The results are promising for future application of biodegradable PCBs.

Soldering tests with biodegradable printed circuit boards

The paper presents soldering tests on biodegradable printed circuit boards (PCB) focusing on different alternative base materials. The aim of the work was to investigate and optimize different low-temperature soldering profiles on cellulose-acetate (CA) and polylactide (PLA) biopolymer-based PCBs with the application of special lead-free solder alloy suited for the temperatures. The investigations were focused on the minimization of the heating effect on the heat-sensitive biopolymers, where on the other hand, sufficient thermal energy is required to melt the solder alloys. The soldering profiles were created with a custom vapour phase soldering (VPS) approach where the heat transfer is controlled with an adaptive height-setting, temperature tracking sample holder. The profiles were evaluated according to their heating factor values. The soldered joints were evaluated with X-Ray microscopy and Shear Tests. The deformation of the PCB tracks was also investigated. The preliminary results reveal the priority of CA for further experiments.

Low Cost Interconnection Technology for Fast Prototyping of Multichip Modules

Recognising the immediate need for improvement of the technological capabilities of low cost, high performance electronic circuit modules in countries of Central Europe, the leading research institutions and small/medium-size enterprises of Hungary, Romania and Slovenia with the support of relevant institutions of the United Kingdom and Belgium have applied for the assistance of the European Union to establish fast prototyping low cost multichip module (MCM) technology facilities. In this Project the Department of Electronics Technology, Technical University of Budapest (TUB) will improve its laminate based (MCM-L) technology and will establish mounting and bonding facility for the assembling of the modules. The Project will realise research and technology development targeted on industry, improving the research capabilities of the Hungarian industry in the filed. The manufacturing system will integrate new processing technologies with well-established ones in all development phases, including design, manufacturing, assembling and test; its application will result in faster prototyping and shorter production period. In addition, problem-oriented knowledge of MCM technology can be given to students, who are interested in modern realisation of circuit modules.

Electrochemical migration of copper in pure water used in printed circuit boards

Electrochemical migration (ECM) behaviour investigations were carried out on “oxide-free” and highly oxidized copper surfaces in pure water. It was shown in our previous paper that the oxidation number of copper ion mainly depends on the oxide layer thickness of the copper surface; in the case of “oxide-free” copper surface the Cu1+ ions dominated, while Cu2+ ions were mainly formed in the case of highly oxidized copper surface, which modify the standard electrode potential and also the solubility product constant of copper-hydroxides, thus can effect on the mean time to failure (MTTF) caused by ECM. In order to verify the effect of different copper ions (Cu1+ vs. Cu2+) on MTTF, water drop (WD) tests were carried out on both copper surfaces. The results showed that in the case of “oxide-free” copper the MTTF value was lower than in the case of highly oxidized copper.

Measurements of water contact angle on FR4 and polyimide substrates relating electrochemical migration

Contact angle measurements of water droplets were carried out on fiberglass epoxy resin and polyimide substrates related to water condensation effect as an antecedent process of electrochemical migration. It was shown in our previous paper that water condensation intensity depends mainly on the surface roughness (which determines capillary condensation) and on the heat diffusivity of the substrate material as well. However, not only water condensation intensity has a high impact on electrochemical migration but also the water wettability of the surface. The wettability of the different substrates was estimated by the contact angle calculation using the drop shape method. The results correspond to the surface roughness and heat diffusivity differences of the substrates, thus the time to failure values.