Comparative study on proper thermocouple attachment for vapour phase soldering profiling

In this paper the wetting properties of lead free solder alloys were investigated on different printed circuit boards (PCB) during Vapour Phase Soldering (VPS), which is an alternative reflow method with non-conventional heat-transfer mechanism. Our motivation was to investigate the phenomenon on PCBs with different thermal capacities, with different heating power and with different solder alloys. The aim of the research is to clear the relations between the thermal capacities of the) PCBs and the spreading of the solder on it, and to investigate the effect of the change of heating power on the solder spreading during VPS. In addition, the impact of the VPS on different solder alloys and the performance of the VPS machine in the wake of the contact angle quality was investigated. Findings show that the thickness of the PCB is not affecting significantly the spread and the wetting. The composition of the alloy, the paste, and the heating power points to observable differences in the final results.

The paper focuses on biodegradable Printed Circuit Boards (PCB) from the aspect of PCB fabrication technology and soldering. Different biodegradable Cellulose Acetate (CA) PCBs were used during the tests (one sided and two sided), and the possible application of pre-preg was also taken into account to improve pad adhesion on the base material. The surfaces of the boards were evaluated in order to obtain information about copper adhesion. FR4 test boards were also investigated as a reference, both for soldering and surface analyses. The soldering profile setup was focused on minimizing high temperatures on the heat-sensitive biopolymer substrates. The soldering profiles were created with a custom vapour phase soldering (VPS) device. The customized solder profile setting is conducted with an adaptive temperature-tracker sample holder. The boards and the solder joints were investigated with non-destructive optical microscopy, X-ray microscopy (deformation and joint analysis), and destructive shear tests. The results are promising for future application of biodegradable PCBs.

Shadow moire technique is already well-established as a technique for evaluating component warpage. Improvements to the metrology have increased its usefulness for evaluating various board-level manufacturing technologies. This experiment used the technique for two key board-level applications: i) Bare printed circuit board (PCB) warpage during the lead-free reflow: PCB warpage is becoming more significant due to the higher temperature required for lead-free reflow. This work used shadow moire dynamic reflow simulation to explore the effect of three variables - board thickness, glass transition temperature, and vendors - on board warpage. The test data showed clearly that board thickness is the most significant variable; ii) Assembled board warpage under mechanical preload from thermal solutions and under thermal cycling: One of the heatsink design approaches for desktop motherboards is to apply a preload to the CPU area of a motherboard in order to ensure thermal performance. This approach requires a more careful control of the preload. Board warpage is significant and is identified as a good metrology for preload estimation. Motherboards under three different preloads in the CPU area were measured. Both the global board warpage and the local board warpage around the CPU area were measured for preload correlations. The measured board warpage was correlated to the board preload successfully. In addition to these two issues, other examples are discussed briefly to demonstrate the capability of the board level shadow moire technique. The work proved that the metrology has become an indispensable thermal-mechanical analysis for manufacturing technology evolutions.

PurposeThe purpose of the paper is to focus on the research into components with specific thermal properties and their influences on the reflow soldering process.Design/methodology/approachAfter a brief introduction, the paper gives an overview of the necessity of thermal management on printed circuit boards (PCBs) and the possible effects on the manufacturing of electronic devices. In the next sections, different test boards are presented for investigations into different thermal effects during soldering. The last section deals with the influences of molded interconnected devices (MIDs) on the reflow soldering process.FindingsThe investigations show that components from the thermal management influence the reflow soldering process more or less. The highest impacts on the soldering process are from components with a thermal connection to the electrical component and its solder joint. All results from the investigations have in common that the thermal influence can only be compensated by increasing the temperature during soldering. However, this significantly increases the risk of overheating the electrical components or the PCB itself.Research limitations/implicationsThis paper shows only the influence of some of the effects caused by thermal management on the reflow soldering process. Furthermore, vapour phase soldering is not considered, but actual investigations are carried out on vapour phase soldering ovens as well.Originality/valueThermal management becomes more and more important with the increasing functionality of electrical components and electronic devices. This topic has been the subject of a large number of articles. However, this paper deals with influences that thermal management has on the soldering process during the manufacturing of the electronic device.

The paper presents soldering tests on biodegradable printed circuit boards (PCB) focusing on different alternative base materials. The aim of the work was to investigate and optimize different low-temperature soldering profiles on cellulose-acetate (CA) and polylactide (PLA) biopolymer-based PCBs with the application of special lead-free solder alloy suited for the temperatures. The investigations were focused on the minimization of the heating effect on the heat-sensitive biopolymers, where on the other hand, sufficient thermal energy is required to melt the solder alloys. The soldering profiles were created with a custom vapour phase soldering (VPS) approach where the heat transfer is controlled with an adaptive height-setting, temperature tracking sample holder. The profiles were evaluated according to their heating factor values. The soldered joints were evaluated with X-Ray microscopy and Shear Tests. The deformation of the PCB tracks was also investigated. The preliminary results reveal the priority of CA for further experiments.

Purpose In this paper, analytical modelling of heat distribution along the thickness of different printed circuit board (PCB) substrates is presented according to the 1 D heat transient conduction problem. This paper aims to reveal differences between the substrates and the geometry configurations and elaborate on further application of explicit modelling. Design/methodology/approach Different substrates were considered: classic FR4 and polyimide, ceramics (BeO, Al2O3) and novel biodegradables (polylactic-acid [PLA] and cellulose acetate [CA]). The board thicknesses were given in 0.25 mm steps. Results are calculated for heat transfer coefficients of convection and vapour phase (condensation) soldering. Even heat transfer is assumed on both PCB sides. Findings It was found that temperature distributions along PCB thicknesses are mostly negligible from solder joint formation aspects, and most of the materials can be used in explicit reflow profile modelling. However PLA shows significant temperature differences, pointing to possible modelling imprecisions. It was also shown, that while the difference between midplane and surface temperatures mainly depend on thermal diffusivity, the time to reach solder alloy melting point on the surface depends on volumetric heat capacity. Originality/value Results validate the applicability of explicit heat transfer modelling of PCBs during reflow for different heat transfer methods. The results can be incorporated into more complex simulations and profile predicting algorithms for industrial ovens controlled in the wake of Industry 4.0 directives for better temperature control and ultimately higher soldering quality.

The paper presents fundamental investigations into the field of vapour phase soldering, specially focusing on the effect of large surface mounted components (e.g. shadowing and possible consequent tombstoning). During the vapour phase reflow the heat transfer processes are based on condensation and the temperature distributions are affected by the geometry and thermal masses of the heated assemblies. The paper investigates the problem from the aspect of components with high thermal mass, which may affect the process of condensation, due to their increased thermal requirements. The experimental is based on FR4 type printed circuit boards, where large packages (SMD capacitors) are attached with SMD adhesives on the top surface of the board at specified locations. The thermocouples are fixed in bores inside the PCB at given locations to highlight any possibility of shadowing (caused by condensate flow blocking effect or vapour consumption) and inside the components where any significant transient effects serve information about the process itself. The measurements are logged with a custom data logger device, which was developed specifically for the investigations. The initial results show that shadowing might not be a problem even near large components, however the overall heating characteristics of the board and the components are affected by the relatively large thermal masses of the applied packages.

This paper presents the results of a development of a condensation soldering technology and machine, which is particularly suitable for lead-free soldering. Because vapor phase or condensation soldering is a high effective heating method with a sharp maximum peak and very small differences in temperature, it is possible to carry out reflow soldering for high melting lead-free solders with a good wetting quality and low thermal stress in substrate and components. For the industrial use it is very important to realize this condensation soldering as an inline process, without changing of transport direction and in an open system. For a fast solution of this task a very effective project team with partners from industry, applied research and science was made up. A laboratory version of this new machine was constructed and tested. So it was possible to realize first trials with actually printed circuit boards from production.

The eddy-current testing technique is an interesting method for detecting defects on bare printed circuit boards. This technique detects various defects without mechanical stress to PCB patterns. Usually various pickup coils are used in an ECT probe as a magnetic sensor. Pickup coil sensors, however, do not show enough S/N ratio to detect defects in high-density PCBs, whose conductors are less than 100μm. We propose a new ECT probe with a spin-valve giant magnetoresistive (SV-GMR) sensor for inspection of PCBs. SV-GMR sensors show high sensitivity to a small magnetic field in one direction. This sensor senses a magnetic field as varying its resistance unlike inductive sensors such as a pickup coil.In this paper, we investigated the sensing properties of a SV-GMR sensor with changing axes, frequencies, and magnetic field amplitudes, and discussed problems that could occur in replacing a pickup coil with SV-GMR.

Context. Thermal inertias of atmosphereless icy planetary bodies happen to be very low.Aims. We relate the thermal inertia to the regolith properties such as porosity, grain size, ice form and heat transfer processes to understand why it is low. We interpret the dichotomy in thermal inertia of the surface of Mimas in terms of changes in regolith properties. We predict how the thermal inertia of these bodies may vary with heliocentric distance depending on these properties.Methods. We combine available models of conductivity by contact or radiation to understand what heat transfer process is predominant.Results. The magnitude of the thermal inertia of a porous icy regolith is mainly governed by the crystalline or amorphous ice forms, and the quality of contacts between grains. Beyond the orbit of Jupiter, thermal inertias as low as a few tens J/m2 / K/s1/2 are difficult to reproduce with plausible porosity and grains sizes made of crystalline ice unless contacts are loose. This is, on the contrary, straightforward for regoliths of sub-cm-sized grains made of amorphous water ice. This study points out the importance of including the temperature dependence of thermophysical properties of water ice forms and the radiative conduction in thermal models of these bodies. The relatively high thermal inertia of the leading face of Mimas can be explained by a regolith of crystalline ice grains in tight contacts, which are eventually sintered by the bombardment of high energy electrons. The low thermal inertia of its trailing face is easily reproduced by a regolith of moderate porosity with sub-mm-sized grains of amorphous ice. The characteristic decrease of thermal inertia with heliocentric distance of icy atmosphereless surfaces and the very low thermal inertia of relevant trans-Neptunian objects are easily explained if amorphous ice is present at cm depths below a thin layer of crystalline ice.

This paper delves into various methodologies for enhancing the quality, design, and optimization of Printed Circuit Boards (PCBs). With the development of the technology, the importance of Printed Circuit Board(PCB) is recently mentioned by more and more people who is trying to make progress of human technology. The classification of PCB defects, a crucial step in ensuring product reliability, is discussed on several categories of defects in PCB, highlighting recent advancements such as fuzzy c-means segmentation, which significantly improves defect detection accuracy. When producing, the layout is quite significant. In a conference, a group of scientists used a thermal layout modelling and optimization routine to make the board having more space to put circuit on it. Methods to ensure PCB quality during production are examined, focusing on optical and electrical testing. The PCB design process is also explored, emphasizing the importance of those considerations before production. Finally, the paper reviews innovative approaches to PCB layout optimization, particularly in managing heat dissipation and dynamic behavior through advanced simulation techniques.

The investigation deals with soldering processes modeling in machines for surface mounting technologies (SMT) with new type of low inert heaters for the middle infrared spectral region. Its purpose is to be used for electronic control in soldering techniques for surface mounted devices (SMD). The approach to thermodynamic processes description is considered. The main parameters of heat transfer processes are analyzed. The proposed model describes heat transfer processes in soldering camera as a function of time and camera dimensions. The influence of the main parameters of heaters' operation and hot gas circulation in the camera on the temperature distribution upon the PCB (printed circuit boards) is investigated

A coupled thermal‐structural dynamic model of a beam under non‐Fourier thermal shock and its approximate solution are developed in the present study. Meanwhile, the analytical solution for thermally induced vibration (TIV) of a beam without thermal structural coupling effects is also derived. The thermal relaxation ratio (i.e., the ratio of thermal relaxation time to the thermal characteristic time of the structure) is introduced to represent non‐Fourier effect. The effects of inertia parameter, rotational inertia parameter and thermal relaxation ratio on TIV behaviors are studied. Results indicate that the beam with specific thermal relaxation ratio and inertia parameter will exhibit unique “resonance” phenomenon, where structural frequencies are close to the thermal bending moment variation. Furthermore, the influencing factors of thermal flutter (TF) are also explored, including thermal relaxation ratio, heat flux incident angle, uncouple absolute rotation angle, and boundary conditions. It is found that TF stability is not related to non‐Fourier effect. The larger difference between the heat flux incident angle and the quasi‐static rotation angle implies better TF stability. This work enhances the understanding of the non‐Fourier effect and its role in thermal‐structural dynamic behaviors, extending beyond Fourier‐based models.

Experimental study results of a droplet ignition and combustion were obtained for coal-water slurry containing petrochemicals (CWSP) prepared from coal processing waste, low-grade coal and waste petroleum products. A comparative analysis of process characteristics were carried out in different conditions of fuel droplet interaction with heated air flow: droplet soars in air flow in a vortex combustion chamber, droplet soars in ascending air flow in a cone-shaped combustion chamber, and droplet is placed in a thermocouple junction and motionless in air flow. The size (initial radii) of CWSP droplet was varied in the range of 0.5–1.5 mm. The ignition delay time of fuel was determined by the intensity of the visible glow in the vicinity of the droplet during CWSP combustion. It was established (under similar conditions) that ignition delay time of CWSP droplets in the combustion chamber is lower in 2–3.5 times than similar characteristic in conditions of motionless droplet placed in a thermocouple junction. The average value of ignition delay time of CWSP droplet is 3–12 s in conditions of oxidizer temperature is 600–850 K. Obtained experimental results were explained by the influence of heat and mass transfer processes in the droplet vicinity on ignition characteristics in different conditions of CWSP droplet interaction with heated air flow. Experimental results are of interest for the development of combustion technology of promising fuel for thermal power engineering.

The eddy‐current testing technique gives a new skill for inspection of bare printed circuit board (PCB). The combination of the high‐sensitive micro eddy‐current testing (ECT) probe and the image processing technique enables us to inspect defect (disconnection, and chipping crack) on the trace of bare PCB. This paper deals with the structure of the probe and characteristics to apply the ECT approach to the inspection of high‐density PCB. We proposed the ECT probes of the meander coil (transmitter) and Spin‐Valve Giant Magnetoresistance sensor(receiver). The high frequency excitation up to 5 MHz enables us to detect the disconnection on the trace of less than 100 μm width and 35 μm thickness.