Ioan Plotog

PCBs with different core materials assembling in vapor phase soldering technology

The increasing demand for high integration with continuous decreasing dimensions, maintaining quality and low cost for electronic modules brought on the market new types of printed circuits boards (PCBs), having different material core as substrate. Taking into account only rigid PCBs, glass for applications requiring high levels of cleanliness (medical apparatus) or dedicated to work in high humidity environmental conditions. In the practice, the EMS companies become to have difficulties for assembling the PCBs with glass core determined by high differences of the thermophisical properties compare to classical FR4, being hardly to adjust the SMT lines parameters. In this paper it is analyzed the influence of the PCB substrate thermophysical properties over lead-free solder joints quality and reliability as results of two soldering technologies, classical infrared-convection (IRC) and vapor phase (VPS). The experiments emphasize the differences regarding soldering thermal profile determined by the glass core of the PCB substrate. The optimum soldering solution for this PCB type will be provided. The results are undeniably that PCB support material is very important for the statement of the thermal profile of the process.

4 P soldering model for solder joints quality assessment

The reliability of microelectronics components and assemblies it should be considered as expression of solder joints functionality. The functions are in close connection with the microstructure of the solder joints, which are the result of the soldering Process temperature gradient action over the trinomial solder alloy/Paste, electronic components terminals/Pin and PCBs Pads finishes. Consequently the solder joints quality can be correctly evaluated taking into consideration not only the severally intrinsic parameters of the trinomial elements, Pad-Paste-Pin, but also interrelate the complex reaction at the interface between them and interdependence with the soldering Process parameters. Therefore the solder joints can be considered result of a complex function of 4P elements defined before. In the paper, a 4P Soldering Model will be proposed in order to characterize the solder joints quality, emphasizing dynamics of Pad-Paste-Pin-Process elements synergistically interactions. The different pad finishes (NiAu, ImmAg, ImmSn, HASL, OSP) realized on PCBs having different core material, (FR4, Glass, Al, Cu, Al2O3), the components terminals/pins/balls having different finishes, the different solder paste type and the reflow soldering process (infrared-convection/vapour phase/LASER) with their typically parameters are the 4P Soldering Model variables. Practical experiments were designed in order to study 4P Soldering Model elements, Pad-Paste-Pin-Process, interactions.

VPS solution for lead-free soldering in EMS industries

The goal of an EMS company is to assure maximum assembling quality by minimum costs. This means minimizing losses on technological lines, minimizing defects and re-work time, optimizing assembling process in order to use minimum proceedings. The challenges are the lead-free technology with its increased temperature - could be up to 260degC when using infrared/convection techniques (IR/C) - and the appearance of circuits on glass or metal core (Copper, Aluminum) with its increased thermal mass. The paper is the result of seeking the optimum solution to assemble electronic components using lead-free technology on these kinds of printed circuits boards. Vapour Phase Soldering (VPS) is an old and forgotten technique especially due to the environment impact and to its low productivity. VPS was brought in front by lead-free technology by some major advantages: - the accurate control of the temperature at the maximum 230degC; - simultaneously, continuously and uniform heating of the surfaces, regardless the shape, color and thermal mass of printed circuit board (PCB), solder paste and components; - the remove of the oxygen or other gas molecules from soldering zone eliminating thus the need of using nitrogen.

Power LED efficiency in relation to operating temperature

In this paper there are presented investigations regarding power IR LED efficiency in relation to operating temperature in order to define the reference values and conditions for using such devices for realizing long range proximity sensors, especially for applications in the automotive domain. The previous experiments done regarding the power LED used for infrared sources emphasize the optical power dependency to temperature. The new experiments were designed for measuring optical power and temperatures of LED heat sink and case, respectively of star and square type circuit boards (thermally conductive insulated metal substrate - IMS), at different points in the same time, for different values of LED driving current and various ambient temperatures, in order to make a correlation between LED efficiency and temperature. The results obtained and presented in this paper will be used further as references for designing an anticollision warning system with applications into automotive domain. Keywords: Power

Lead-free electronic system integrated in a Vapour Phase Soldering equipment prototype

The purpose of this paper is to present the applied research work, performed in POLITEHNICA University of Bucharest, Center for Technological Electronics and Interconnection Techniques (UPB-CETTI) in the frame of one European project and two diploma projects, oriented to the development of a VPS (Vapour Phase Soldering) equipment using ecological, lead-free, electronics and tailored to small and medium size electronics companies (SME) needs. The VPS technology seems to be today the most appropriate for many EMS companies, especially for SMEs. The lead-free electronic system developed in UPB-CETTI is in the stage of integration in a VPS equipment prototype, which is under construction in these months. The system can be embedded also in plotters, cutter plotters or milling/drilling equipment for PCB manufacturing.

VPS technology and applications

The electronic equipments become day by day more important part of human society. As consequence the requests for performance are more divers and complex, not only from electronic packaging point of view, but also from environment challenges. The electronic equipments production is realized in majority using surface mounted technology on assembling line. The electronic components assembling process on PCBs becomes a key issue in electronic packaging reliability. The I/O density of the components is continuously increasing while the soldering area is dramatically reducing. In the same time the PCB substrate and the final finish of the PCB have more and more diversity. Under such circumstances the solder joints resulting from the soldering process represent an important outcome for the PCB assembling. Moreover, the Lead-Free soldering requests, imposed by the RoHS Directive, can cause difficulties in obtaining a high quality/reliable soldering process. The vapor phase soldering (VPS) technology could be an efficient alternative because of its high efficient and uniform heating characteristics. A good control of the soldering temperature, the oxygen free soldering atmosphere, and especially, the higher rate of heat transfer, represent the main advantage of the VPS technology. The paper presents some applications of VPS technology related to the PCBs characteristics.

Mechanical Characteristics of Electronic Printed Circuit Obtained by the Vapour Phase Soldering Process

The goal of the present paper is to describe some mechanical aspects regarding the adhesion of the copper layer deposit on the rigid support of printed circuit boards (PCB) used in electronic technology. In order to highlight the adhesion of the copper layer in correlation with different rigid support, there were performed some micro-scratch tests using a dedicated system. The mechanical strength is obtained by shear test. The paper novelty presents a mechanical experiment which will describe the tribological properties with influence on the reliability of electronic assemblies

Thermal investigations of solder joints used in power applications

A good way to characterize the quality of a solder joint is its thermal behavior at different currents and the current capabilities. The electrical current capabilities have been discussed in many other studies, but thermal investigations were not performed very often. The team developed a series of tests on boards with different configurations, and in all cases was proven that the solder joints heat up much less than the components or the tracks, and their temperature increases due to thermal conductivity from the surrounding elements.

Investigations on electroluminescent tapes and foils in relation to their applications in automotive

The electroluminescent (EL) tapes or foils having barrier films for an additional level of protection against the toughest environments conditions, offer a large area of applications. The EL lights, due to their characteristics, began to be used not only in the entertainment industry, but also for automotive and aerospace applications. In the paper, the investigations regarding EL foils technical performances in relation to their applications as light sources in automotive ambient light were presented. The experiments were designed based on the results of EL foils electrical properties previous investigations done in laboratory conditions, taking into account the range of automotive ambient temperatures for sinusoidal alternative supply voltage. The measurements for different temperatures were done by keeping the EL foils into electronic controlled oven that ensures the dark enclosure offering conditions to use a lux-meter in order to measure and maintain under control light emission intensity. The experiments results define the EL foils characteristics as load in automotive ambient temperatures condition, assuring so the data for optimal design of a dedicated inverter.

Solder joints properties as function of multiple reflow Vapor Phase Soldering process

The continuous trend towards high density and miniaturization of electronic devices involves the use of multiple reflow processes in assembling technologies for second level of interconnections in electronic packaging hierarchy. According to the “4P” Soldering Model concept (4PSMC), considering the Pad-Paste-Pin-Process elements as Key Process Input Variables (KPIV), the solder joints are the result of KPIV synergistically interactions and correlations with consequences over their microstructure. In the paper, taking into consideration the cooling rate influence over intermetallic compounds (IMC) formation and microstructure, there was described the investigations over electrical and mechanical properties of solder joints resulted from multiple reflow Vapor Phase Soldering (VPS) process, in terms of 4PSMC. Maintaining the pad, pin and paste of KPIV as references measurements of solder joints resistances and shear forces were perform as function of VPS processs number for two values of cooling rate, respectively IMC microstructures and stereofractography studies. The results of the studies performed and presented in the paper will be use for improving process control in order to assure the solder joints reliability, to minimize losses on VPS lines, to reduce defects number and rework time.