Richard Berenyi

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.

Effect of patterned copper layer on selective polymer removal by 355 nm laser

Ab s t r a e t Optimization of lascr parameters is a challenge in case of microvia drilling. It is even more complicated to find the right parameters for large area scanning, where not only pulse energy and burst play important roles but also pulse repetition rate, scanning speed and overlap. In case of selective material removal the above process parameters define the amount of the ablated material (etch depth) and the processing time. This paper dcscribes results of experiments carried out to find correlation between the process parameters and the quantity of the ablated material. Flexible polyimide substrates of different thicknesses were processed by frequency trippled, Q-switched Nd:YAG laser. The samples were examined by surface profiler and their cross-sections by optical microscope. The experiments showed that the amount of the ablated polymer is influenced by the features of the patterned copper layer. Even though there is no direct interaction between the laser beam and the copper layer, the thermal conductivity of the circuit pattcm influences the temperature of the processed polymer. Because of this phenomenon there is a need to control the laser processing parameters according to the circuit pattern. The correlations we have found between the process parameten and thc etch depth make this controlled laser material removal possible.

Real-time monitoring of electrochemical migration during environmental tests

More and more reliability and quality problems of electrical assemblies have to be solved due to the trend of miniaturization and the even higher level of integration. In some cases these failures can lead to catastrophic failure. The phenomenon of electrochemical migration is one of the most dangerous failure mechanism which usually results in short resistive circuits. In this paper electrochemical migration (ECM) failure phenomena is be investigated which was real-time monitored by the measurements of electrical parameters of conductor patterns with immersion Ag and immersion Ag finish coated with Sn60Pb on Printed Wiring Boards (PWB.) Highly Accelerated Stress Test (HAST) and Thermal Humidity Bias (THB) tests were carried out and Mean Time To Failure (MTTF) comparison was investigated between immersion Ag and immersion Ag coated with Sn60Pb.Only preliminary investigations were presented in order to determine the steps of the full ECM process on different substrates, surface finishes, solder alloys under various climatic conditions. The key findings were that the MTTFs during HAST tests were significantly shorter than in case of THB tests.

Laser via generation into flexible substrates

The microelectronics industry is moving toward smaller feature sizes. The main driving forces are to improve performance and to lower cost. From the performance point of view the small distances between chips together with the short interconnection routes have of great importance in order to achieve faster operation. The application of polymeric materials for the insulating and protective layers of interconnect substrates is beneficial to the performance and to the cost of a circuit module as well. An advanced technology for the fabrication of very high density interconnects applies microvia flexible substrates. This technology has particular significance for the interposers of chip scale packages. Laser processing of polymeric materials applied for via generation, image transfer, contour cutting, etc. has proved to be an efficient tool for the fabrication of interconnect substrates. The paper describes some results of a research project that aims at the application of CO/sub 2/ and frequency multiplied Nd:YAG lasers for drilling via holes into copper clad flexible laminates of polyimide, epoxy and polyester base materials. The effect of the application of an interfacing (adhesive) layer is also the topic of the investigations. The physics of processing using a wavelength range from the far infrared radiation of the CO/sub 2/ laser till the UV wavelengths of frequency quadrupled Nd:YAG lasers are considered to be modeled, examined and evaluated.

Laser Manufacturing of Mechanical Structures in Flexible Substrates

In microelectronics industry the main driving forces are to improve performance and to lower cost. From the performance point of view the small distances between chips together with the short interconnection routes have of great importance in order to achieve faster operation. The application of polymeric materials for the insulating and protective layers of interconnect substrates is beneficial to the performance and to the cost of a circuit module as well [1-2]. An advanced technology for the fabrication of very high density interconnects applies multi-folded 3D (three-dimensional) microvia flexible substrates, where laser via and bending window generation technology has particular significance [3]. Bending window generation is a unique application of laser material processing. A bending window can be used in a flexible circuit to define the exact position of the bending edge as well as the radius and the angle of the deformation. It is produced by reducing the thickness of the flexible substrate in a well-defined, narrow window. The paper gives an overview on laser processing of flexible polymer materials to produce bending windows for multi-folded 3D substrates.

Electrochemical migration of Sn and Ag in NaCl environment

The impact of chloride ion concentration on electrochemical migration (ECM) of tin and silver was studied by using an in-situ optical and electrical inspection system. It was found, that in both cases, dendrites grow not only in an electrolyte solution at low chloride concentration but also in an electrolyte at medium and high or even saturated chloride concentrations as well. According to the results, the migration susceptibility has decreased at low and medium concentration levels in both cases. However, the ECM susceptibility of Ag has increased, while the migration susceptibility of Sn was decreased at the saturated concentrations.

UV laser based direct structuring

Conventional continuous wave and long pulse (nanosecond) laser ablation is used in many fields, such as direct PCB structuring process. In this regimes the dominant process involved is the heating of the target material through the liquid phase to the vapour phase, resulting in expansion and expulsion of the desired target material. Frequency-tripled UV Nd:YAG laser spot is used at focal point, however we can conveniently change the power, pulse repetition rate and beam scanning speed to get optimum surface energy density for selective material removing.

Vapour phase soldering on flexible printed circuit boards

The paper presents experimental results about Vapour Phase Soldering on flexible printed circuit boards, where the standard Surface Mounted Technology process was used for investigation. Test boards were prepared from FR4 type Printed Circuit Boards and single-sided flexible polyimide substrates. Lead-free SAC305 paste and different chip size surface mounted resistors were used for the test assembly. The soldering was performed with heat-level vapour phase method in a commercial oven. The tests were composed of different board setups: where the FR4 or the flexible boards were soldered without fixtures, and where the flexible boards were supported by fixtures. The results were evaluated with X-ray microscopy, cross-section optical inspection (IMC tests) and shear tests. The conclusion reveals similar quality factors in all cases, rendering vapour phase soldering a plausible alternative reflow method for soldering on flexible printed circuit boards

Utilization of laser technologies in the preparation of the physical structure of a miniature electrochemical cell used for biosensor researches

antibodies to their specific antigens. The third main part of biosensors exploits hybridization, the specific recognition process between complementer singlestranded DNA strands A new miniaturized electrochemical cell has been

Electrochemical migration investigations on Sn-Sb solder alloys using 3.5 wt% NaCl solution

ECM (electrochemical migration) is sort of short failure mechanism that can lead to series defect in case of loaded circuits, when moisture exist on/in a conductor-dielectric-conductor system. Water drop (WD) test and scanning electron microscopy — energy disperse spectroscopy (SEM-EDS) methods were used to investigate the ECM behavior on different Sn-Sb alloys and pure Sn was the reference. The results show that all of the samples have similar ECM risk comparing to the pure Sn. However, in case of Sn95-Sb5 solder alloy antimony was found in the dendrites next to Sn content, which was dominated during the ECM processes in all cases.