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The surface mount technology (SMT) assembly process for 0.4 mm pitch chip scale package (CSP) components was studied in this work. For the screen printing process, the printing performance of different solder pastes, aperture shapes and sizes was investigated. Square apertures and a fine particle size in the solder paste provided a better paste release. Besides optimising the printing process capability and minimizing the printing defects such as bridging and missing paste, the total volume of solder consisting of the paste and the solder ball has to be considered in order to maximize the final process yield. For the pick & place process, the accuracy required for the placement equipment was determined by studying the self‐alignment of the lead‐free CSPs (with Sn/4.0Ag/0.5Cu balls) during the reflow process using lead‐free Sn/3.9Ag/0.6Cu paste. The components were intentionally misplaced up to ∼50percent off‐pad. After reflow, x‐ray inspection showed that the components had aligned to the pad. By considering the stack‐up of the printed circuit board pad location and size tolerances, the solder paste printing tolerances and the placement tolerances, the required alignment accuracy for the pick & place equipment was established to meet the total process capability requirement.

The mechanical properties of Sn/Ag/Cu solder joints in combination with different component lead coating materials (Ni/Pd/Au, Sn/15 per cent Pb, Sn/2 per cent Bi, and Sn) are studied in this work using a lead pull test and free fall drop test. The results of this study show that the Sn/2 per cent Bi coated components provide the best performance under the drop impact loading followed by the Sn/15 per cent Pb, Sn and Ni/Pd/Au coated components. Failure modes and the structure of the coating surfaces were examined from cross‐sectioned samples using a scanning electron microscope. Furthermore, the wetting of the leads by the solder and thickness of the IMC layers were studied.

The wetting performance and intermetallic formation of a Sn/Ag/Cu alloy on printed circuit board (PCB) surfaces and on component terminations were studied in this work. Two different PCB surface finishes, immersion gold over electroless nickel (Ni/Au) and an organic solderability preservative (OSP), were studied. Chip components with Sn/Pb coating and a gull‐wing type component with 100% Sn coating were used in these experiments. Different reflow profiles were tested, and the dependence of the wetting performance, intermetallic layer thickness and the microstructure of the solder joints on the reflow profile were investigated.It was found that reflow process conditions did not significantly influence the spreading or intermetallic formation on either of the surfaces. Neither the wetting onto the component nor the general microstructure of the solder joints varied significantly with the reflow profile. When a Sn/Pb ‐coated component was used, the content and size of Pb‐rich phases in the solder joint increased with a longer time above liquidus or a higher reflow peak temperature.