Material investigation for pressure sensor package P-DSOF-8-1

The target of this study was to develop a semiconductor SMD low cost package suitable for an absolute pressure sensor. Key demands were an in-line concept for production (reel to reel) and an 'open package' due to micromechanically moveable structures at the sensor surface. A NiPd plated Cu leadframe was chosen, on to which a thermoplastic case was to be injection moulded. Several high temperature thermoplastic materials were investigated. Finally, a polymer was chosen for its good processability, dimensional stability, low impurities in the polymer (e.g. monomeric ingredients) and therefore a chemically clean surface. For die attach, a number of epoxy, silicone, and thermoplastic adhesives were checked. The evaluation was made with respect to good adhesion to the thermoplastic package and to low stress characteristics, due to the stress sensitive chip. The investigation then turned to an appropriate encapsulant for the composition. Eight different encapsulants were investigated until one specific silicone gel was found to be the most applicable. Key requirements were a low loss factor (tan /spl delta/), good creep behaviour and self-degassing behaviour. A two component material with fast curing characteristics was selected.