Attila Géczy

Low temperature soldering on biopolymer (PLA) Printed Wiring Board substrate

The applicability of decomposable biopolymer (polylactide - PLA) as Printed Wiring Board (PWB) substrate was investigated. A novel approach for low temperature reflow soldering was applied. Different types of PLA boards were prepared and each type was qualitatively characterized. The realized circuit was designed for the use of Surface Mounted (SM) components. The low maximum process temperature of PLA boards was a key aspect to set soldering temperatures. 58Bi42Sn solder alloy was chosen to match the lower soldering temperature range required by the PLA board material. Steps of reflow soldering technology (stencil printing, component placement, reflow soldering) were applied using 0603 discrete components and were inspected during the circuit assembling process. Hot soldering iron, IR radiation, hot gas method and Vapour Phase Soldering (VPS) were applied for heat transfer during the experiments. VPS was found the best for heat transfer to melt the low temperature (138 °C) solder alloy. The results verified the flexibility and usability of the VPS in the field of special applications. The quality of boards was examined with cross-section optical inspection; the solder joints were evaluated with shear force tests. Typical failures were also analyzed.

Conductive layer deposition and peel tests on biodegradable printed circuit boards

Biodegradable plastics are novel materials which can be degraded by organic methods. The aim of the work was to investigate the usability of a cellulose-acetate (CA) and a polylactide (PLA) based material as a printed circuit board (PCB) with conductive layer peel tests. The common types of conductive layer coating processes were proposed: copper foil lamination, copper electroplating and thick film conductive layer deposition. The paper focuses solely of copper foil lamination. The laminates were examined by optical microscopy. The copper layer peel tests were mainly used to determine the bonding strength of the conductive layer, according to the instructions of IPC-TM-650 standard. Future investigations will involve application and test of the other conductive layer deposition processes, also the possible soldering methods, and thermal stability of the biodegradable PCBs.

Characterization of vapour phase soldering process zone with pressure measurements

Purpose – The purpose of this paper is to present a novel approach on the process zone characterization for direct feedback regarding the state of vapour, in order to assure a better monitoring, control and understanding of the process.Design/methodology/approach – Different pressure sensors were applied in an experimental vapour phase soldering (VPS) station, where the hardware setup was dedicated to the current experiments. Static and dynamic pressure values were analyzed and correlated with additional thermal measurements.Findings – The results reveal the dynamics of the vapour blanket generation. The correlated measurements show different stages of the process initialization, highlighting better accuracy than sole temperature measurements of saturated vapour identification. It is possible to trace the height of the available saturated vapour blanket with static pressure measurements.Practical implications – The VPS process may benefit from the more precise saturation detection, giving better control o...

Package–on–Package – Review on a Promising Packaging Technology

Package-on-Package (PoP) components are BGA packages stacked on each other. With this method not only board space is saved, but signal routes are also shortened. It was presented by a cooperation of Amkor and Nokia [1]. The vertical 3 dimensional stacking of BGA components broadens the possibilities of planar surface mounting technology. The PoP technology is constantly evolving; the latest solutions offer wide variety of bumping and stacking technologies. This paper is a review on this aspiring 3D packaging method. Preliminary soldering experiments with dummy packages are also presented.

Comparative study on proper thermocouple attachment for vapour phase soldering profiling

Purpose – The paper aims to present a comparative study of various thermocouple (TC) attaching methods for the proper measurement of soldering temperature profiling during vapour phase soldering (VPS). The heat transfer process during VPS is different from common methods, while the required heat for reflow is provided by the condensation. The condensate is a flowing layer on the board, where the dynamic behaviour also affects the local conditions on the surfaces. Temperature measurements based on TCs are also affected this way; it is important to investigate the process for deeper understanding. Design/methodology/approach – Bare printed circuit boards (PCBs) were prepared for standard K-Type TCs attachment with industry standard materials: kapton polyimide tape, aluminium tape, SMD adhesive and high-temperature solder (HTS). Heating experiments were performed in a batch-type VPS oven with Galden LS240 fluid and fixed oven parameters. Findings – According to the specific attachment requirements, HTS and A...

Soldering profile optimization for vapour phase reflow technology

Vapour Phase Soldering (VPS) is an alternative method for widespread reflow soldering technologies (e.g. infrared or convection type). VPS has emerged in the last few years after the introduction of Galden fluid. The vapour of Galden is used as the heat transfer medium. The main advantages of VPS are the lower peak temperature, nitrogen/oxygen-free inert atmosphere, the improvement in solder wetting and the reduction of the profiling time [1]. One disadvantage of VPS is the non-controllable, linear soldering profile achieved by common VPS soldering method [2]. With controlled dipping of solder goods into the vapour space, non-linear soldering profiles can be obtained. This method is called Soft-VPS (S-VPS) and was developed and patented by IBL. With this method, custom temperature gradients and profiles can be realized, reducing voids, tombstoning and avoiding high thermal stress on the boards [3]. This paper presents thermal profiling of an experimental VPS station from the aspect of this method, with a successful optimization of the process. The optimized profiles for low melting point (138 °C) lead-free Sn-Bi solder paste were inspected. Soldering results of 0603 chip size resistors were then evaluated with resistance measurements and x-ray inspection.

Investigating and compensating printed circuit board shrinkage induced failures during reflow soldering

Purpose – This paper aims to reveal the causes and find an efficient method to compensate the shrinkage to reduce failure costs. Reflow-induced printed circuit board (PCB) shrinkage is inspected in automotive electronics production environment. The shrinkage of two-sided, large PCBs results in printing offset errors and consequently soldering failures on smaller components during the reflow soldering of the second PCB side. Design/methodology/approach – During the research, the investigations had to adapt to actual production in an electronics manufacturing plant. A measurement method was developed to approximate the overall shrinkage of the given product. With the shrinkage data, it is possible to perform an efficient compensation on the given stencil design in computer-aided manufacturing environment. Findings – It was found that even with the investigated lower-quality PCB materials, the compensation on the stencil significantly reduces the quantity of failures, offering an efficient method to improve ...

Analysis of vapor phase soldering in comparison with conventional soldering technologies

Vapor phase soldering (VPS) has been investigated to improve the knowledge about the vapor generation, progression and condensation processes. Measuring methods for the investigations have been developed and applied. In an experimental VPS system the following parameters have been studied during the heating up and cooling down processes: the temperature distribution in the chamber by measurements using Pt thermistors of ladder arrangement; the temperature distribution in and the heating efficiency of the vapor blanket as function of height by varying the vertical position of the sample with temperature sensors on it; the height of the vapor blanket by a special fiber optic probe; the height of the vapor blanket by applying a floating polymer pillow as vapor level indicator; and the status of the vapor/mist/rain phases by optical inspection of light scattering. The experimental investigations show that high proportion of the vapor condensates in the space on the level of the cooling tube in the upper part of the chamber, therefore the vapor is rather in mist phase full with falling droplets of the condensed fluid, which has a determining effect on the heating efficiency of the medium.

Investigating the thixotropic behaviour of Type 4 solder paste during stencil printing

Purpose A measurement method has been developed to reveal the viscosity change of solder pastes during stencil printing. This paper aimed to investigate thixotropic behaviour, the viscosity change of a lead-free solder paste (Type 4). Design/methodology/approach The viscosity change of the solder paste during stencil printing cycles was characterised in such a way that the time-gap between the printing cycles was modelled with a rest period between every rheological measurement. This period was set as 15, 30 and 60 s during the research. The Cross model was fitted to the measurement results, and the η0 parameter was used to characterise the viscosity change. The number of printing cycles necessary for reaching a stationary state in viscosity was determined for various rest periods. Findings It was found that the decrease in zero-shear viscosity is significant (25 per cent) in the first cycles, and it starts to become stationary at the sixth-seventh cycles. This means a printing process can provide the appropriate deposits only after the 7th cycle with the investigated Type 4 solder paste. Originality/value Time-dependent rheological behaviour of solder pastes was studied in the literature, but only the viscosity change over continuous time at constant shear rates was examined. The time-gap between stencil printing cycles was not considered, and thixotropic behaviour of solder pastes was also neglected. Therefore, the authors developed a measurement set which is able to model the effect of time-gap between printing cycles on the viscosity change of solder pastes.

Experimental 13.56 MHz RFID cards on biodegradable substrates

The paper presents experimental research on investigating the production and testing aspects of ISO/IEC 14443 contactless RFID tags fabricated on biodegradable cellulose acetate (CA) biopolymer-based Printed Circuit Boards (PCB). Our approach reduces the harmful plastic waste by substituting the standard materials of the cards with biodegradable substrate. Also, with common PCB fabrication methodology the prototyping and production becomes cost-effective for the novel material. The paper will detail the manufacturing steps and the different aspects of production for the prepared cards. The preliminary functional results show promising examples of a functional, standard 13.56 MHz RFID reference cards.