Effect of contaminants on electrochemical migration

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Supervisor:
Dr. Medgyes Bálint Károly
Department of Electronics Technology

In our rapidly changing world, the electronics industry is experiencing a large-scale advancement. Through the course of electronic production, conductive tracks’ density is getting higher on printed circuit boards, which are to be found in almost every apparatus and appliance surrounding us. Granted the decrease of conductor trace spacing, electrochemical migration (EMC) is one of the processes leading to malfunction for which the possibility of occurrence is exceedingly enhanced. To improve the possibilities of avoidance, it is essential to become aware about the operations of this physical-chemical mechanism. Throughout our daily interactions, appliances are exposed to various external impacts during which they come into contact with some moisture, thus providing opportunity for migration to take place.

In my thesis I studied the impact of certain contaminating substances/matters on EMC on gold (Au), copper (Cu) and tin (Sn) conducting layers. Measurements could be divided into 2 categories regarding the contaminating matters.

The first section deals with Sodium Chloride (NaCl) and its effects, examined on an Au conductor. Based on the MTTF (mean time to failure) data, in case of minor NaCl quantity (0,1 mMol) a short-circuit occurs. Further incensement of NaCl concentration slows down the progress, while at an amount of 10 mMol it stops. However, after an additional measure of polluting matter (500 mMol, saturated) malfunction recurred and accelerated. Most probably, it became as a consequence of the electrolyte’s salt content milling the Au layer beyond the copper, which had actually caused the dendrite.

In the next session, the contaminating agent was Sodium Sulfate (Na2SO4). Tests carried out on a Cu conductor have demonstrated, that in small concentration, dendrite development (0,1-1 mMol) is faster than with deionized water. In solutions containing more Na2SO4 than that (e.g.: 10 mMol) process slowed down, then at higher concentrations (500 mMol, saturated) the short-circuit provoking dendrite increase ceased. In the case of Sn samples results were slightly different. At a fairly low concentration (0,1 mMol Na2SO4 ) short-circuit occurred sooner, than in the instance of clear water. By further increasing of the concentration (1 mM) failure mechanism slowed down, then ceased (10 mMol). Though contrarily to the Cu measures in a 500 mMol solution dendrites reappeared, with an additional amount (saturated solution) MTTF increased, that is, failure process decreased.

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