Method for solder bumping, and solder-bumping structures produced thereby
A method for solder bumping provides a substrate and forms a film on the substrate. The film has openings therethrough. A stencil is aligned on the film. The stencil has openings therethrough over the openings through the film. Solder paste is printed onto the substrate and into the openings through the stencil and the openings through the film. The solder paste is reflowed to form solder balls therefrom. The stencil and the film are then removed.
1. A method for solder bumping, comprising:
providing a substrate;
forming a film on the substrate, the film having openings therethrough;
aligning a stencil on the film, the stencil having openings therethrough over the openings through the film;
printing solder paste onto the substrate and into the openings through the stencil and the openings through the film;
reflowing the solder paste to form solder balls therefrom; and
removing the stencil and the film.
2. The method of claim 1 wherein forming a film on the substrate further comprises forming a photoresist layer.
3. The method of claim 1 further comprising reflowing the solder and then cleaning the substrate.
4. The method of claim 1 wherein the film has a thickness of about 75 μm, and the stencil has a thickness of about 150 μm.
5. The method of claim 1 wherein the openings through the film have an equivalent diameter of about 350 μm, and the openings through the stencil have an equivalent diameter of about 400 μm.
6. A method for solder bumping, comprising:
providing a flip chip having under bump metallurgy layers exposed thereon;
forming a laminated dry film on the flip chip having openings therethrough over respective under bump metallurgy layers, to provide access to the under bump metallurgy layers therebeneath;
electroforming a metal stencil and aligning the metal stencil on the laminated dry film, the metal stencil having openings therethrough substantially centered over the openings through the laminated dry film to provide access to the under bump metallurgy layers therebeneath;
screen printing solder paste onto the flip chip and the under bump metallurgy layers and filling the openings through the metal stencil and the openings through the laminated dry film;
reflowing the solder paste to form solder balls therefrom upon and in electrical contact with the under bump metallurgy layers; and
removing the metal stencil and the laminated dry film.
7. The method of claim 6 wherein forming a laminated dry film on the flip chip further comprises forming a photoresist layer.
8. The method of claim 6 further comprising reflowing the solder and then cleaning the flip chip.
9. The method of claim 6 wherein the laminated dry film has a thickness of about 75 μm, and the metal stencil has a thickness of about 150 μm.
10. The method of claim 6 wherein the openings through the laminated dry film have an equivalent diameter of about 350 μm, and the openings through the metal stencil have an equivalent diameter of about 400 μm.