This work is derived from our recent studies about the new approach for interconnecting the electronic components without the use of solder alloys. The concept is generally called Solderless Assembly for Electronics Technology (SAFE). We will present the results of thermal analysis and measurements of electronic modules that were realized in SAFE technology. In a SAFE module, the natural convection from the top of a component is blocked by the resin, as a result of molding process. The interconnection of components and simultaneously the conductive tracks are realized using the same printed conductive paste. Having interconnections with higher resistance, supplemental to the heat generation in electronic components, in our case resistors and LEDs, will be added to the supplemental dissipation caused by the current flow.
The SW150 and the new types SW180 of Electrically Conductive Adhesives (ECA) dedicated to printing circuits1, meeting RoHS EU Directive2, were used, according to REACH EU Regulation3, to bond optoelectronics components, LED type, on test printed circuit boards (TPCBs) having daisy chain interconnection structures. Mechanical properties of LEDs bonds function of temperatures by measuring shear forces applied on each of bonded LEDs maintaining TPCBs at different temperature from ambient to 398 K (125°C), were investigated. The shear forces measured values, the LEDs bonds micro sections and the microfractography after shear testes analyses and interpretations, facilitate the construction of a database that provides support for the development of temperature-sensitive optoelectronic device assembling solutions by bonding, using ECA. These solutions ensure avoidance of their functional temperature failures during classical assembly processes, comparing ECA curing and reflow temperatures.
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.
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