Injection of Molten Solder (IMS) Technology for Solder Bumping on Wafers, Ceramic/Organic/Flexible Substrates, and Si Via Filling from Fine Pitch to Large Pitch

Abstract

We developed a tool of molten solder injection which is able to form solder bumping on wafers, ceramic/organic substrates, flexible circuits, and Si via filling from fine pitch to large pitch. One tool has capabilities of solder bumping on wafers from 15 microns diameter to larger than 1000 microns diameter, bumping on organic substrates from flip chip pre-solder to BGA size, soldering on flexible circuits with < 25 microns width of circle and square shape, and via filling of Si wafer with various via diameters. Also, this tool enables the change of solder composition to be very easy and fast because simple switch of the solder injection head allows to change the solder composition like switching an ink cartridge in an inkjet printer. The solder injection tool head contains a reservoir of molten solder of desired composition and a slot through which the molten solder is injected with an optimized combination of pressure and temperature. The solder injection slot of the head is configured in the portion of compliant material and low friction material such that this combination provides good wiping characteristics as well as allowing the IMS head to better track surface topography of an organic substrate. This paper will review key attributes of the molten solder injection tool and discuss differences in the processes required for each different applications of solder bumping on Si wafers and ceramic/organic/flexible substrates as well as filling solder into Si vias. We will describe data of 200mm wafer bumping results with different bump diameters and shape, solder bumping results on organic and ceramic substrates, soldering on flexible circuits, and via filling results of Si. Also, solder alloy flexibility of this technology has been demonstrated from low melting temperature Pb-free solders to high melting temperature Pb-free solders.