Péter Gordon

Investigation of intermetallic compounds (IMCs) in electrochemically stripped solder joints with SEM

Abstract In this work we compare the microstructures of intermetallic compounds (IMCs) in electrochemically stripped solder joints created by two different soldering methods (vapor phase soldering (VPS), and selective laser soldering with a CO2 laser). After the selective removal of the Sn phase with amperometry, the microstructure and structural composition of the IMC can be revealed in a detailed way, which is unlike any other previously published methods. The differences between the IMC microstructures of the technologically different solder joints were analyzed with optical microscopy and scanning electron microscopy (SEM). Energy dispersive spectroscopy (EDS) measurements were utilized to identify the different intermetallic phases (Ag3Sn, Cu6Sn5). Significant differences were observed in the IMC structures of solder joints prepared by different technologies.

Thermal Simulation of UV Laser Ablation of Polyimide

Our aim is to provide a simulation tool for manufacturing processes that takes the influence of temperature distribution thus the underlying copper pattern and pulse repetition frequency into account. To establish such simulation software a finite element model was set up which is able to describe the thermal processes and ablation induced by laser irradiation of polymers. The etch rate description usually applied for excimer lasers was slightly altered to be adequate for Gaussian lasers by writing pulse energy instead of fluence. This theoretical consideration was proved by experiments. The experiments also revealed the temperature dependence of etch rate and the influence of pulse repetition frequency on the amount of ablated material. The experimental and simulation results are in good agreement.

Microstructure Comparison of Soldered Joints Using Electrochemical Selective Etching

The microstructure of the commonly used SnAgCu (SAC) lead free solder alloy was investigated. SAC solder bumps were soldered by two different soldering techniques (Vapor Phase Soldering (VPS), Laser reflow). Since the soldering profile of the VPS method is considerably different from the temperature profile of the laser reflow soldering, the created microstructures are expected to be diverse. Selective electrochemical etching was applied on cross sectional samples in order to extract the tin from the cross sectioning plane. In this manner the spatial structure of Cu6Sn5 and the Ag3Sn intermetllic compounds (IMCs) was highlighted. The microstructures of the samples were analyzed with optical microscopy and Scanning Electron Microscope (SEM) on cross-section samples. The composing elements were identified by SEM-EDS.

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.

Distance learning - how to use this new didactic method in education of electronics engineering?

Distance learning (DL) is an instructional delivery system that connects learners with educational resources. In microelectronics and microsystems interconnection and packaging technology, the preparation of electronics engineers for the ever growing requirements is especially a challenge for todays education, and there is an essential need for the application of advanced curricula and teaching methods. In the present paper, the driving forces for the development of curricula and didactic methods are outlined, followed by the detailed discussion of the needs for and the applicability of distance learning. Then, an example is provided for the application of the Internet-based performance centered instructions (IPCI) model for providing Web-based DL experiments in the special field of surface mounting technology (SMT) for students of electrical engineering and graduate engineers interested in microelectronics packaging and interconnection technology. Finally conclusions are drawn and further efforts are outlined.

Simulation and indirect measurement of temperature change in polyimide induced by laser ablation at 355 nm

Thermal effect plays an important role during frequency tripled nanosecond Nd:YAG laser ablation of polyimide. This paper describes simulation results and experimental investigations of laser induced temperature change in polyimide. The experimental results show that the ablation rate is temperature dependent, which means the underlying copper layer and the pulse repetition frequency (PRF) influence the etch depth. Based on our model it is possible to control the processing parameters according to the pattern geometry for a better exploitation of laser micromachining

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.

SensEdu-an Internet course for teaching sensorics

Conventional teaching of sensors, based on lectures, static written materials, laboratories, etc., has become rather difficult at all levels of education, recently. The main objective of the described project is the development of a multimedia supported education material that teaches the application of microelectronics and packaging technologies in designing smart sensor devices for the next generation intelligent systems. The new approach of teaching sensorics tries to exploit all advantages of multimedia computer aided teaching not only for keeping the competitiveness but also in order to overcome the above specific difficulties of the particular area. The course material will be available for the technical community, for other university professors for teaching, and also will continuously be developed on the Internet and on CDs. The paper will highlight the structure of the course material and demonstrate the animated sensor examples.

The correlation between the mechanical and electrochemical properties of solder joints

The mechanical properties of a solder joint is partially determined by the microstructure of the solder. This microstructure is formed during the soldering process and it highly depends on the technological parameters. We have introduced a new selective electrochemical sample preparation method in which the tin phases can be removed from a cross-section of a solder joint, while the intermetallic phases stay intact. For the quantitative characterization of the revealed intermetallic microstructure we also introduced a novel method. We compare the electrochemical impedance spectrum of the polished surface of the cross-sectioned sample to the spectrum measured after the selective material removal. The peak shear force values of components soldered with different cooling rates are compared to a composed arbitrary unit which is proportional to the total surface of the intermetallic compounds in the solder bulk.

Investigation of the wetting properties of Cu 6 Sn 5 intermetallic compound

The intermetallic compound (IMC) layers formed during the soldering processes of electronic products are commonly agreed to have poor wetting properties but there are several studies which came to an opposite conclusion. The present study aims at basic, systematic experimental investigations to gain experience on the wetting properties of the intermetallic compounds. Intermetallic layers with different morphology were generated by multiple reflow cycles. The samples were analyzed by scanning electron microscopy and cross-sectioning. SAC305 solder balls were reflowed on the surface of Cu6Sn5 layer. The wetting property of the IMC layer was concluded from the spreading of the solder balls. It was found that the surface of intermetallic structure has indeed poor wetting properties, regardless of the morphology of the surface.