Mihai Branzei

PCBs thermophysical properties in lead-free assembling process assessment

As elements of interconnection structures at level two in electronic packaging, the pads could be considered as a particular solution into a virtual space defined by the materials, geometry, surface finishes and substrate [1, 2]. The assembling processes emphasize the substrate contribution over thermal mass and heat transfer [3]. Each of the pad particular solution defined in the design stage will have unique values of thermophysical properties (THP) [2]. In the paper it will be presented the results of the THP measurements for different types of PCBs having particular solutions defined by the pad finishes, geometry and substrate materials using ANTER equipments (FlashLine 3000 thermal diffusivity system and Unitherm1161V dilatometer type). Finally, scientific and practical conclusions shall be drawn in order to improve the quality, reliability and increase the energetic efficiency of the reflow soldering process.

Aspects on thermophisycal properties of interconnection structures for power LEDs applications

The printed circuit boards (PCB) and the dedicated interconnection structures have an important role for the thermal regime of power LEDs modules (PLEDM). There are two situations from the point of view of the heat transfer sense: toward PLEDM during assembly process, and from PLEDM to environment during operation. Their thermophisycal properties influence both heat transfer processes and its mandatory to know the values of thermal conductivity and thermal diffusivity of the interconnection structures, in order to select the appropriate solution in different power LEDs applications. This paper presents the measurement results of three types of PCBs interconnection structures and makes a comparative analysis between them, in order to categorize them in terms of performance and create a data base for PLEDM design.

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.

Microstructure comparative analysis of the solder joints based on SAC/SN100 soldering alloy type depending on the cooling rate

Microstructural analysis in the section of solder joints show a multilayer structure composed of IMC layers caused by the interface phenomena specific to soldering processes and a typical volume, unaffected by these phenomena, but depending of soldering process thermal profile, especially by the cooling zone parameters. In the paper were theoretically studied and experimentally evidenced genesis of the multilayer structure depending on the type of alloy and the specific cooling rate of the soldering process. Experiments were designed in order to obtain similar volumes of solder joints unaffected by the interface phenomena, taking into consideration Vapour Phase Soldering (VPS) processes characterized by different cooling rates and 6 types of Lead-Free solder pastes. The results highlight the microstructural differences in the unaffected by dissolution and diffusion volume of solder joints, between and for each type of solder pastes depending on the cooling rate. Based on these practical results could be improved the thermal profile of the soldering processes in VPS technology in order to increase the solder joints reliability.

Comparative shear tests of two low melting point solder pastes relating to their thermal diffusivity

In a vehicle, for electronic components, the working temperature may vary between the limits 358K and 478K. The manufacturing costs reduction necessity combined with the RoHS2 EU Directive consequence lead to create new Low Melting Point Lead-Free (LMPLF) solder pastes family. In the paper, are presented the shear tests of the solder joints (SJ) and thermal diffusivity (ThD) measurements made on samples cast from LMPLF solder pastes (ALPHA®CVP-520, and ALPHA®WS-852) into Vapour Phase Soldering Process (VPSP) characterized by different cooling rates (0.5K/s and 4.0K/s). The paper deals with the continuation of studies on the influence of thermal transfer (mainly thermal diffusivity) in the VPS process on the mechanical properties (shear tests) of the solder joint, for the new LMPLF alloys recently implemented in the automotive industry [1]. In this regard, it is emphasized the influence of solder joint shear force (SF) properties, depending on their ThD as function of solder alloy, which “set” the rate of heat transfer (convective versus conductive) to the substrate (PCB).

Pressure Influence on the AlCrFeNiMn/Graphite High Entropy Composite Microhardness

During the last years, mechanical alloying technique for high entropy alloys (HEAs) has been more often approached due to the good homogenous chemical distribution and near net shape technology provided by the respectively process. A new composite material having the matrix as HEA reinforced with graphite particles was designed. The graphite particles addition in the high entropy matrix (AlCrFeNiMn) improves the particles weldability during mechanical alloying and assures a good creep behavior for the final product. The aim of this paper is to investigate the pressure influence on the microhardness as dependence of sintering parameters which can be reflected also on the microstructure. The high entropy composite was completely alloyed after 40 hours of milling. The obtained composite was pressed using different pressures values in order to investigate the pressure influence on the microhardness and microstructure. The samples were investigated using optical microscopy, scanning electron microscopy, X-rays diffraction and microhardness tests. The microhardness values for all the samples were between 300 – 700 HV.

Influence of high temperature exposure on the adhesion of a micro-composite refractory enamel to a Ni–18Cr–12W superalloy

Abstract A new micro-composite refractory enamel (MCRE) was designed to play a multifunctional protective role (thermal barrier coating, corrosive and erosive protection) for the hot working parts made of EI868 superalloy sheets i.e. burning chambers, fire tubes, volets, eclises, etc. The effect of the isothermal heating at elevates temperature (800 °C, 900 °C) were, for the first time, investigate for MCRE/EI868 couple. The adhesion strength has shown an enhancement of about 100% when the couple was heated at 800 °C or at 900 °C for 10 h compared with the unexposed one. SEM-EDS, OM, XRD, EDP-XRFS and SDAR-OES investigations support a chemical bonding mechanism between MCRE and EI868 substrate via a transient interface layer. Elemental EDS distributions show that the Cr selective oxidation is responsible for the formation of the transient layer. The XRD measurements can be correlated with the contribution of the spinellic transformation of the SiO2, Cr2O3, NiO to the adhesion enhancement. The most important result reported herein is the adhesion strength enhancement of the MCRE coatings to the EI868 supperalloy by isothermal treatment. Accordingly, the MCRE behaves as a self-healing coating. Noteworthy, the working lifetime of the MCRE-EI868 couple can be significantly enhanced if an optimum pre-treatment is applied before it comes into service.

Low Rigidity Ti-Nb-Ta-X (X=Cr, Zr, Ag, In) Alloys with Improved Properties

The paper is focused on microstructure characterisation of five bulk metastable β-type Ti-based alloys, with improved mechanical properties, composed of non-toxic (bio inert) elements like: Nb, Ta, Cr, Zr, Ag, and In. These types of alloys designed in this study, are expected to have also higher corrosion resistance in biological media and good performance such as lower Young’s modulus of elasticity, greater strength, good workability, also in as cast state. However, high strength as well as low Young’s modulus is required for the implants subjected to cyclic loading under complicated stress conditions. Thus, the major aim is decreasing the Young’s modulus and increasing the tenacity of these alloys.

Comparative shear tests of some low temperature lead-free solder pastes

The range of electronic components and as a consequence, all parts of automotive electronic equipment operating temperatures in a vehicle is given by the location of that equipment, so the maximum temperature can vary between 358K and 478K1. The solder joints could be defined as passive parts of the interconnection structure of automotive electronic equipment, at a different level, from boards of electronic modules to systems. The manufacturing costs reduction necessity and the RoHS EU Directive3, 7 consequences generate the trend to create new Low-Temperature Lead-Free (LTLF) solder pastes family9. In the paper, the mechanical strength of solder joints and samples having the same transversal section as resistor 1206 case type made using the same LTLF alloys into Vapour Phase Soldering (VPS) process characterized by different cooling rates (slow and rapid) and two types of test PCBs pads finish, were benchmarked at room temperature. The presented work extends 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. The shear forces (SF) values of the LTLF alloy samples having the same transversal section as resistor 1206 case type will be considered as references values of a database useful in the new solder alloy creation processes and their qualification for automotive electronics domain.