Újraömlesztéses forrasztás stencilnyomtatási folyamatának modellezése

Napjaink elektronikus áramköreinek szerelésénél az egyik legkritikusabb lépés a forraszpaszta stencilnyomtatása, melynek alapos vizsgálata, pl. numerikus modellezéssel elengedhetetlen. Jelen cikk a stencilnyomtatási folyamat numerikus modellezésének lépéseit részleteiben tárgyalja. A peremfeltételek kritikus részeit, a geometriai valamint az anyagparamétereket egyaránt részletesen ismertetem. Bemutatom, hogy milyen módszerrel lehetséges a stencilnyomtatás numerikus modelljének validálása, a modell érvényességének ellenőrzése. Megmutatom, hogy milyen mértékben csökken a stencilnyomtató-kés szöge a nyomtatás közbeni késerő hatására. Ismertetem, hogy milyen mérési módszerrel mutatható ki a forraszpaszták viszkozitásának csökkenése a stencilnyomtatási folyamat során. Ugyanezen mérési módszerrel kimutatható a különböző szemcseméretű forraszpaszták reológiai tulajdonságai közötti különbség is. A reológiai tulajdonságok modellezésével kapcsolatban taglalom az elterjedt, Cross és Carreau-Yasuda anyagmodelleket. Végezetül ismertetem a gépi tanulás lehetséges alkalmazását a stencilnyomtatási folyamat optimalizálására

The influence of the crystallographic structure of the intermetallic grains on tin whisker growth

In this paper, the relationship between the crystallographic structure of Cu-Sn intermetallic grains and Sn whisker growth was investigated. In order to prevent the influence of the elements in the alloy composition and the effect of the soldering process on the formation of the intermetallic layer, 99.99% pure Sn was vacuum evaporated onto Cu substrates. The Sn layer thickness was sub-micron region (~400nm in average) to reach considerable and rapid compressive stress on the tin layer originated by the intermetallic formation. The samples were stored at room temperature for 1 month. Different types of whiskers (nodule and filament) and the layer structure underneath were studied with a scanning ion microscopy and transmission electron microscopy. It was found that not only the thickness of the intermetallic layer and shape of the intermetallic grains affects the whisker growth but the crystallographic structure of the intermetallic grains as well. The susceptibility of the Sn layer to whisker development is higher in those regions where the intermetallic layer is composed of monocrystalline grains instead of those regions, where it is composed of polycrystalline grains. This effect can be explained by the higher compressive stress generated by the monocrystalline intermetallics compared to the polycrystalline ones

Effect of current load on corrosion induced tin whisker growth from SnAgCu solder alloys

The effect of current load was investigated on corrosion induced tin whisker growth from SnAgCu (SAC) solder alloys. Three alloys were studied: two low Ag content micro-alloyed SAC and the widely used SAC305. The solder joints were loaded with six different DC current levels between 0 and 1.5A and they were aged in corrosive environment (85 °C/85RH%) for 3000 h. The morphology of the whiskers and the micro-structural changes of the solder joints were examined by scanning electron microscope. It was shown that the current load can decrease the corrosion of the solder joints and consequentially it can decrease whiskering as well

Introduction to Surface-Mount Technology

In chapter 1, the surface-mount technology and reflow soldering technology are overviewed. A brief introduction is presented into the type of electronic components, including through-hole- and surface-mounted ones. Steps of reflow soldering technology are outlined, and details are given regarding the properties of solder material in this technology. The rheological behavior of solder pastes is detailed, and some recent advancements in addressing the thixotropic behavior of this material are summarized. The process of stencil printing is detailed next, which is the most crucial step in reflow soldering technology; since even 60–70% of the soldering failures can be traced back to this process. The topic includes the structures of stencils, discussion of the primary process parameters, and process optimization possibilities by numerical modeling. Process issues of component placement are presented. The critical parameter (process and machines capability), which is used extensively for characterizing the placement process is studied. In connection with the measurement of process capability, the method of Gage R&R (repeatability and reproducibility) is detailed, including the estimation of respective variances. Process of the reflow soldering itself is detailed, including the two main phenomena taking place when the solder is in the molten state, namely: wetting of the liquid solder due to surface tension, and intermetallic compound formation due to diffusion. Solder profile calculation and component movements during the soldering (e.g., self-alignment of passive components) are presented too. Lastly, the pin-in-paste technology (reflow solder of through-hole components) is detailed, including some recent advancements in the optimization of this technology by utilizing machine learning techniques

Extrusion-based Direct Write of Functional Materials From Electronics to Magnetics

New micro- and nanoscale fabrication methods are of vital importance to drive scientific and technological advances in electronics, materials science, physics and biology areas. Direct ink writing (DW) describes a group of mask-less and contactless additive manufacturing (AM), or 3D printing, processes that involve dispensing inks, typically particle suspensions, through a deposition nozzle to create 2D or 3D material patterns with desired architecture and composition on a computer-controlled movable stage. Much of the functional material printing and electronics area remains underdeveloped for this new technology. There is a need to understand and establish the advantages and shortcomings of extrusion-based DW over other AM technologies for various applications. Further, the integration of extrusion DW with other AM technologies, such as stereolithography (SLA), remains an active area of research. In this study, we performed a comprehensive study of the relationships between ink properties/machine parameters and the printed line dimensions, including parametric studies of the machine parameters, an in-nozzle flow dynamics simulation, and a preliminary 3D comprehensive flow dynamics simulation. We explored the boundary and possibilities of extrusion-based DW. We pushed the limit of DW printing resolution, solid content of nonspherical particles, and printed polymer-bonded magnets with the highest density and magnetic performance among all 3D printing magnet techniques. We optimized the design of DW ink from rheological, mechanical, and microscopic perspectives. We are one of the first experimentalists as of author’s knowledge to perform bimodal highly concentrated suspension rheology analysis using nonspherical particles. Great improvements in solid loading were achieved by using the best large-to-small particle size ratio and large particle volume ratio found. The data and analysis could provide a new standard and solid experimental support for functional material printing