Analog Devices Inc. (ADI) has been a major supplier of accelerometer devices in hermetic packages used for crash detection and vehicle dynamic control in the automotive industry. A major market pull from the handheld customers makes it imperative to develop thin plastic packaging solution for MEMS accelerometer. This paper details the backgrinding process developed to successfully thin the wafer-level-capped MEMS accelerometer. Functionality is maintained after packaging the thinned device, a significant effect in performance is observed. Three packaging solutions are evaluated to produce a 4x4xlmm3 Leadframe Chip Scale Package (LFCSP). The performance of the thinned accelerometer device using the thin packaging options are compared. Assembly issues of the thin packages are also discussed.
A wafer backgrinding solution is demonstrated to successfully thin wafer-level-capped MEMS accelerometers down to 250um thickness. Capped MEMS wafers are prepared for manufacturing by using wafer protective tapes. Holes are punched on layers of tape, matching the thickness of the caps, that serve as gap fills in-between caps and through the wafer edge.The capped wafers are fully supported while processing using standard backgrinding machines. Manufacturing issues and corresponding fixes to attain satisfactory result are also discussed. The thinned capped accelerometer device is packaged in a 4x4mm Leadframe Chip Scale Package (LFCSP) to check its performance.
Pure tin is widely used as a replacement of Pb-Sn eutectic alloy as finish and solder material. This study aims to determine how the increasing concentration of organic plating additives affects the carbon content and donor density of electroplated Sn. Pure tin was electroplated on an Al sheet in a Hull cell using a commercial plating solution. Plating was performed in electrolyte baths with primary additive concentration from 100 mL/L to 600 mL/L, and with secondary additive concentration from 8 mL/L to 48 mL/L. Current densities of 15, 8 and 3 A/dm2 were considered. The increased concentration of organic plating additives caused an increase in carbon content of the deposit from 5 wt.% C to 8 wt.%C. Mott-Schottky measurements showed increasing electron donor density of up to four orders of magnitude as a function of current density and carbon content. A higher current density during deposition causes the tin oxide film to reach the donor density saturation value at lower concentrations of organic plating additives. This suggests that current plays a role in the decomposition of organic additives, which results in the incorporation of carbon in the deposit.
This paper studies the relationship between flame treatment and mark permanency. UV cured ink marked PIaaic Leaded Chip Carriers (PLCC) have been exarnined for the cause of mark permanency failures. Competence of the mark was evaluated using chemical, moisture and mechanical tests. Ink to substrate type of failure was noted on packages which failed the tests. Results showed that packages subjected to flame trdatment prior to ink marking performed a lot better than the untreated. ln adhisive tape pull, packages exhibited a tenfold increase in mark adhesion after treatnient.Flame treatment using a mixture of hydrogen and oxygen is elrcctive in improving ink adhnion on the plattic package surface. Detailed electron spectroscopy for chemical analysis (ESCA) and l i m e of Flight Secondary Ion Mass Spectroscopy ('IWF-SIMS) to deterniine difference in surface composition between flame treated and untreated package showed the treated surface to have more oxygen-functionali7~d carbon which can improve adhesion. Measureinent of the actual contact angles of ink on flilnte treated and untreated surfaces showed a significant improvement from 44" to 35". This improvement in wettability translates to the enhanced reliability of the ink mark on treated surface.
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