Abstract: A mask (stencil) having cells (openings) is disposed on a surface of a heater stage, and is then then filled (printed) with solder paste. Then a substrate is assembled to the opposite side of the mask. Then the solder paste is reflowed. This may be done partially inverted. Then the mask is separated from the substrate, either before or after cooling. Solder balls are thus formed on the substrate, which may be a semiconductor wafer. A method for printing the mask with solder paste is described.

Abstract: A mask (110; see also 160, 210, 260, 310, 408, 500, 702, 802, 904) having a plurality of openings (cells) is disposed on, or nearly on, the surface of a substrate (102), the openings (112) of the mask being aligned over a corresponding plurality of pads (104) on the substrate. The openings in the mask are filled with solder material (114). A pressure plate (120) is disposed over the mask to capture the solder material in the cells. Heat is directed at the mask (through the pressure plate) to reflow the solder. This is done in an inverted or partially inverted orientation. The stackup (assembly) of substrate/mask/pressure plate may be un-inverted prior to cooling. Mask configurations, methods of mounting the masks, and solder material compositions are described. The methods are robust, and are well suited to fine pitch as well as coarse pitch ball bumping of substrates.