| abstract |
In the construction of electronic devices with one or more flip chips and, in some cases, one or more leadless components, mounted on a substrate, the interconnections are made with conductive adhesive deposited using specialized masks. A magnetic metal mask fabricated of a membrane of magnetic material is placed temporarily onto the face of a semiconductor wafer or of a circuit or other substrate. When properly positioned with respect to the wafer or substrate, such as by relational guide holes, the mask is held in place by the magnetic forces produced by a controllable electromagnet. Contact pad openings in the magnetic metal mask are formed by suitable means such as laser cutting or photo-etching. The magnetic metal mask may include a flexible interface layer on the side facing the wafer or substrate to assure tight sealing thereto, so as to reduce smearing and bridging of the conductive adhesive paste and avoid bridging between contact pads that might otherwise occur during deposition of the paste. Magnetic metal masks may be utilized for depositing various types of adhesives including both solder pastes and conductive and non-conductive polymer adhesives, on semiconductor devices, other electronic components, substrates for electronic devices and printed wiring circuit boards. |