Method for forming bumps on a substrate
First Claim
1. A method for forming bumps on a substrate comprising the steps of:
- providing a semiconductor substrate having a plurality of metal pads;
providing a first stencil having a plurality of openings corresponding in pattern to the plurality of metal pads;
providing a second stencil having a plurality of recesses, each recess having a corresponding opening of the plurality of openings in the first stencil;
bringing together the first stencil and the second stencil such that each recess aligns with its corresponding opening;
filling the plurality of recesses in the second stencil with the solder;
filling the plurality of openings in the first stencil with a solder;
reflowing the solder in the plurality of recesses and in the plurality of openings to form a plurality of solder preforms;
removing the second stencil from the first stencil;
positioning the first stencil over the semiconductor substrate such that the plurality of openings with the plurality of solder preforms formed therein is aligned to the plurality of metal pads; and
reflowing the solder preforms in the plurality of openings to form a solder bump on each of the plurality of metal pads.
3 Assignments
0 Petitions
Accused Products
Abstract
Solder bumps are formed on a substrate, such as a semiconductor die (28) or wafer, using a screen printing and reflow operation. Solder paste (18) is screened into openings (14) of a stencil (10). The paste is reflowed within the stencil to produce a solder preform (22). The stencil and solder preforms are then aligned over the substrate to be bumped so that the preform aligns with a metal pad (30) on the substrate. The solder preforms are again reflowed, and the solder within the openings of the stencil is drawn onto the metal pad. To facilitate the transfer of the solder from the stencil to the metal pad, a second stencil (12) can be used to form a protrusion (27) on the solder preform. The protrusion contacts the metal pad during the transfer reflow operation to facilitate removing the solder from the stencil.
81 Citations
20 Claims
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1. A method for forming bumps on a substrate comprising the steps of:
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providing a semiconductor substrate having a plurality of metal pads; providing a first stencil having a plurality of openings corresponding in pattern to the plurality of metal pads; providing a second stencil having a plurality of recesses, each recess having a corresponding opening of the plurality of openings in the first stencil; bringing together the first stencil and the second stencil such that each recess aligns with its corresponding opening; filling the plurality of recesses in the second stencil with the solder; filling the plurality of openings in the first stencil with a solder; reflowing the solder in the plurality of recesses and in the plurality of openings to form a plurality of solder preforms; removing the second stencil from the first stencil; positioning the first stencil over the semiconductor substrate such that the plurality of openings with the plurality of solder preforms formed therein is aligned to the plurality of metal pads; and reflowing the solder preforms in the plurality of openings to form a solder bump on each of the plurality of metal pads. - View Dependent Claims (2, 3, 4)
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5. A method for bumping a semiconductor wafer comprising the steps of:
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providing a semiconductor wafer having a plurality of bump pads formed on a surface thereof; providing a stencil made of a material that is non-wettable by a solder, the stencil having a plurality of openings, each opening having a uniform, controlled volume and including a recess; dispensing the solder into the plurality of openings of the stencil; firstly reflowing the solder in the stencil to form a plurality of solder preforms, each solder preform corresponding in size and shape to its respective opening including having a protrusion formed as a result of the recess; positioning the stencil adjacent the semiconductor wafer such that the plurality of solder preforms aligns with and contacts the plurality of bumps pads via the protrusion of each solder perform; and secondly reflowing the plurality of solder preforms while the stencil is still adjacent the semiconductor wafer to form a solder bump on each bump pad of the plurality of bumps pads. - View Dependent Claims (6, 7, 8, 9, 10, 11)
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12. A method for forming bumps on a substrate comprising the steps of:
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providing a substrate having a plurality of terminal pads; providing a first stencil having a plurality of openings extending therethrough and corresponding in location to the plurality of terminal pads; providing a second stencil having a plurality of recesses corresponding in location to the plurality of openings; aligning the first stencil with the second stencil such that the plurality of recesses aligns with the plurality of openings; dispensing solder into the plurality of openings and into the plurality of recesses; reflowing the solder in the first stencil and the second stencil to form a plurality of solder preforms; removing the second stencil, leaving the plurality of solder preforms within the first stencil; aligning the first stencil with the substrate such that the plurality of solder preforms correspond in location with the plurality of terminal pads; and reflowing the plurality of solder preforms to form a plurality of solder bumps on the plurality of terminal pads of the substrate. - View Dependent Claims (13, 14, 15, 16, 17)
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18. A method for forming bumps on a substrate comprising the steps of:
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providing a semiconductor substrate having a plurality of metal pads; providing a stencil having a plurality of openings corresponding in pattern to the plurality of metal pads; filling the plurality of openings in the stencil with a solder; providing a spacer between the stencil and the semiconductor substrate and positioning the stencil over the semiconductor substrate and spacer such that the plurality of openings with the solder therein is aligned to the plurality of metal pads; reflowing the solder in the plurality of openings to form a solder bump on each of the plurality of metal pads; and removing the spacer from the semiconductor substrate. - View Dependent Claims (19, 20)
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Specification