Dirk Seehase

Energetic analysis of solder paste deposits as reference for soldering with selective heat

Strictly speaking standard reflow soldering processes are inefficient in terms of energy consumption. A large amount of energy is needed to heat up comparatively small solder joints. As a result the whole electronic assembly is stressed with heat, of which only a fraction is going into soldering. A reduction of process temperatures would improve this disproportion. To compensate for the resulting lack of energy, an exothermic reaction, releasing additional heat inside the solder paste deposits, could be applied. The potential of such a process has already been proven in earlier works [1], [5]. For the adjustment of such a sensitive process a better understanding of the energetic requirements for solder paste deposits in dependence of their size and temperature is required. In this work such results are generated by a practical measuring approach. Here, a chip resistor is used as a model to melt up particular solder joints through joule heating. The thermal energy is calculated by measuring electrical power over time.

Heat protection coatings for high temperature electronics

Highly-integrated electronic devices and printed circuit boards need to be protected against overheating. In this disquisition a concept is introduced to improve the thermal management of coated assemblies by means of functional additives based on earlier works [4]. It has already been proven that paraffin wax, zeolite molecular sieve and silica gel have the potential as thermal energy storage systems due to phase transition effects and sorption [1], [5], [6]. Here the cooling effects of these materials were analyzed by using a heating element (constantan on ceramic substrate) and chip resistors with different package sizes (2512, 1206, 0805, 0603). The covering of these testing elements with the investigated additives lead to a significant delayed heating and therewith to a short-period heat protection at pulse load condition. Nevertheless a re-cooling of the system could regenerate the cooling effects of the additives for multiple utilization; paraffin wax due to refreezing and zeolite/silica gel due to rehydration. The Application for coating technology indicates a significant improvement of thermal properties.

Behaviors of Printed Circuit Boards Due to Microwave Supported Curing Process of Coating Materials

Abstract The Application of a microwave supported curing process for coatings in the field of electronic industry poses a challenge. Here the implementation of this technology is represented. Within the scope of the investigation special PCB Test Layouts were designed and the polymer curing process examined by the method of dielectric analysis. Furthermore the coupling of microwave radiation with conductive PCB structures was analyzed experimentally by means of special test boards. The formation of standing waves and regular heating distribution along the conductive wires on the PCB could be observed. The experimental results were compared with numerical simulation. In this context the numerical analysis of microwave PCB interaction led to important findings concerning wave propagation on wired PCB. The final valuation demonstrated a substantial similarity between numerical simulations and experimental results.

Selective cooling of sensitive PCB components by means of silica gel based cover coatings

The safe operation of electronic assemblies and their components requires smart thermal management. Here a concept based on sorption processes is introduced to avoid local overheating. It is shown, that water desorption effects of silica gel can significantly delay the heating of sensitive electronic components. Furthermore the influence of ambient conditions (temperature, humidity) on cooling performance was tested by means of a climatic exposure test cabinet. After complete dehydration, silica gel is able to regenerate the water storage under ambient conditions for re-utilisation. Finally a polymer binder (acrylic resin) was used in order to produce an open porous silica gel based cover coating. The covering of sensitive components of a test PCB demonstrated the exceeding cooling effects of the new designed coating.

Material study for full-faced heating layers, integrated in printed circuit boards

Different materials which are suitable for heating the complete area of an electronic assembly when embedded within a printed circuit board (PCB) are studied in this work. The focus being, two foil type materials with a conductive layer and two paste materials with carbon filler. The suitability to integrate these materials in the process technology for PCB manufacturing is described and used to construct test samples for heating and perform preliminary tests.

Placement of embedded temperature sensors in a printed circuit board for a manufacturing process

The term of smarter production processes includes the improvement of the automatic control mechanism. Therefore, it is useful to provide more sensor data about the product itself. These information are gathered by sensors (e.g. temperature sensor) which are installed in a permanent position. To increase the quality of the products sensor data, the sensors can be implemented in the product itself, especially in a product like a printed circuit board (PCB). This particular product is used in a lot of different modern consumer devices and the embedding of electronic components directly into the PCBs substrate material is available. The appropriate placement of the integrated sensor is a challenging issue and will be discussed in this paper. The position influences the sensor readings and must be considered for the automatic control mechanism of the production plant. Therefore, a method is described for calculating the required parameter of the sensor position based on the PCBs layout information. For this, the main parameter is the time coefficient of the temperature gradient.

Thermoelectric generator for stand-alone electronic device operation in temperature test cabinets

When testing printed circuit boards in-situ in a test cabinet with a wireless connection, it is very hard to store the necessary energy, especially in a high temperature environment. With a thermoelectric generator (TEG) as an independent energy source in a climate test cabinet, the battery or the external power cable connections for the device under test (DUT) can be omitted. In this paper, we investigate the usability of a TEG in terms of how much energy can be produced by different test utilizations. To have an orientation of the maximum energy a TEG can harvest in such a cabinet, it is inevitable to create some boundary values with the equations based on the Seebeck effect. First experiment results prove that it is possible to archive enough energy to power low-energy radio transceivers for the in-situ data acquisition with a low duty cycle.

Reactive paste for reflow soldering of large components

For the energetic support of reflow soldering an exothermic reacting paste has been developed. This paste is applied on electronic assemblies adjacent to solder paste deposits before reflow soldering. During the reflow process a chemical reaction inside the paste is releasing energy in the form of heat. This heat is assisting in melting up the solder paste depots, hence allowing the processing of large components at lower peak temperatures. Such created solder joints are analyzed here towards their reliability. Also two examples of employing the reacting paste to aid in the soldering process of large components are given.