Gaudentiu Varzaru

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.

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.

Lead/lead free solder joints comparative electrical tests as function of microstructure and soldering thermal profile

The solder joints properties are determined by the specific morphology of their microstructure. In the paper are presented the comparative resistance measurements of the solder joints resulted by usage of lead/lead-free solder pastes from Vapor Phase Soldering Processes (VPS) having thermal profile with two different cooling rate, slow one (0.5 K/s) and rapid one (4 K/s). The results will be promote to develop the practical applications of this soldering technology and to contribute at realization of a data base useful for better selection of lead-free solder paste in the design and manufacturing area.

Investigation on the efficiency of thermal relief shapes on different Printed Circuit Boards

As known, thermal relief is a technique used to separate soldering pads or plated through-hole vias from large copper planes in order to reduce soldering dwell time by providing thermal resistance during the process, thus minimizing the heat transfer to the plane. However, during normal operation, the same thermal resistance limits the heat transfer for power component dissipation. The narrower the thermal pad, the greater temperature increasing during power dissipation. Hence, the dimensions of the thermal pads are critical. The work presents the results of a practical approach not for a hole via or a pad for an ordinarily component connected to a large copper area, but a medium power Surface Mounting Device, SMD, using the Printed Circuit Board, PCB, as heat sink. There are taken into consideration different thermal pads and there are investigated by temperature measurements with thermocouples and thermovision. The variables are the thermal pad dimensions, the area of the radiant surface, the base material of PCB, and the reflow soldering process. It is analyzed the effect of the thermal pad versus the temperature on the soldering pad and beyond the thermal pad and on the case of the device during reflow soldering process and during operation

Shear strength function of temperature for lead/lead-free alloys samples obtained with different cooling rate

Usually, the experiments concerning solder joints mechanical stress resistance are shear tests types that offer shear forces (SF) values for solder joints corresponding to surface mounted resistors (SMR) having different case types, but revealing the absence of reference values concerning Lead/Lead-Free solder alloys (L/LFSA) especially for samples having the same geometry as the SMR, being result of real soldering process. In the paper are presented the experiments designed in order to obtain reference values of shear forces (RVSF) for the solder alloys samples having the same transversal section as resistor 1206 case type, assembled in vapour phase soldering (VPS) processes characterized by different values of the cooling rate, for different body temperatures according to the homologous temperatures (HT) concept. The experiments results consisting in qualitative and quantitative analyses and references values of Lead/Lead-Free solder alloys SF, offering in the same time a data base useful in some solder alloys design and their qualification process (QP) into domains exempted by RoHS 2 EU Directive.

Thermophysical properties of some Low Temperature Lead-Free solder pastes dedicated to automotive applications

The maximum temperature of all parts of automotive electronics equipment is given by the location and can vary between 358 K and 478 K. RoHS EU Directive in the context of the manufacturing costs reduction, necessity led automotive industry to create new Low-Temperature Lead-Free (LTLF) solder pastes family. In the paper, the thermophysical properties of the alloys from ALPHA® CVP-520 (SnBiAg) and ALPHA® OM-535 (SBX02) test samples having as a source solder pastes were compared with similar from ALPHA® OM-6106 (Sn62) solder paste. The presented work extend the theoretical studies and experiments upon heat transfer in VPSP in order to optimize the technology for soldering process (SP) of automotive electronic modules and could be extended for home and modern agriculture appliances industry.

Surface insulation resistance testing of solder pastes with protective coating

This paper presents the results obtained after performing SIR testing in order to evaluate different solder materials. The scope of the test was to determine the effects of the reflow process used and of a protective coating on surface insulation resistance (SIR) in the presence of medium heat and high humidity for several solder pastes. There were used special designed test pattern boards according to IPC-B-24 and several solder pastes with no-clean fluxes: SAC305, OM338PT, OM5300, SN100C and SN100C-XF3. After 110 hours, the measurements showed the reduced values of the average surface insulation resistance. The optical inspection did not show any electrochemical formation (dendrites) between conductors.

Multicriterial approach correlation of the solder joints functional tests results

The assembling of the electronic components on PCBs becomes a key issue in electronic packaging reliability. 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. Considering the reliability of electronic modules as expression of solder joints functionality, could be emphasized the lack of tests over solder joints functionality on assembling line. Usually are realized optical inspections and, in precise situation, X-Ray analysis are done over assembled PCBs being followed by “in circuit” electrical functional tests. The defects type “hide” or “cold/dry joints” could be not found. In the paper are presented the results of the functional tests of solder joints realized in two soldering technology, infrared-convection and vapor phase. Regarding to thermal functionality, infrared analysis of temperature distribution on the surface of a populated PCBs using thermovision were done. A correlation among functionality, reliability and thermovision functional analysis will be realized based on the experiments results. In consequence, the authors emphasize thermovision as available in circuit indirect test method for “hide” defects of solder joints.

Printed circuit boards with different material core assembling quality analysis based on 4 P Soldering Model

The increasing demand for high integration with continuous decreasing dimensions, maintaining quality and lowering costs for electronic modules brought on the market new types of printed circuits boards (PCBs), having different material core. Taking into account only rigid PCBs, there are currently used metals (Al, Cu, brass), for applications requiring excellent thermal management (RF modules, power leds), or glass, for applications requiring high levels of cleanliness (medical apparatus), or specific polytetrafluoroethene (PTFE) materials for microwave applications (Arlon, Rogers). In the practice, the Electronics Manufacturing Services (EMS) companies become to have difficulties for assembling the PCBs with different core materials determined by high thermal capacity being hardly to adjust the Surface-mount technology (SMT) lines parameters. In this paper it is analyzed the influence of the PCB support over some of the parameters of 4P Soldering Model and the consequences on the quality of the soldering. There were used four types of boards with different types of pad finishes, same solder paste, same pin finishes and two different processes. The results are undeniably that PCB support material is very important for the statement of the thermal profile of the process.

1D and 2D solutions for traceability in an Electronic Manufacturing Services company

Recording every aspect of the manufacturing process, from materials to production processes, whether at the board level or the entire system build, thus providing full product and process traceability, helps manufacturers to limit the scope of product recalls and reduces associated recall costs, while providing for compliance to a variety of environmental and safety regulations across all segments of the industry. The requirements of the Quality Assurance Systems in Electronic Manufacturing Services (EMS) and not only, has a continue demand for more information to be recorded onto the accompanying data storage vehicles that consist mainly of different types of labels in order to accomplished the traceability demand. The compatibility of bar code and data matrix with the traceability demands of the EMS is an actual issue and the choice of one over the other an every day question for the manufacturers. The paper is looking into this subject attempting to make a classification of the usage of data matrix and bar code systems and attempting a comparison of the two methods in accordance with the production requirements.