Maskless Process for Solder Bump Production
Methods of producing a solder bump are presented. Preferred methods lack a requirement for masking a target substrate. Contemplated methods include forming a well around one or more bond pads on a wafer where the walls of the well are formed by a covering layer material, possibly comprising photoresist or passivation material. The well can be filled with a contact material. Contact material can comprise a solder paste or an under bump metallization layer, which can be placed within the wells as a contact bed for solder balls. A priori prepared solder balls, in solid form or in molten form, can deposited on the contact material to produce the solder bump.
1 . A method of forming a solder bump on a substrate, the method comprising:
providing a substrate having a bond pad, and having a covering layer that covers the substrate and that also forms a well around the bond pad;
depositing a contact material within the well in a manner where the contact material is in electrical contact with the bond pad;
placing an a priori prepared solder ball on the contact material; and
bonding the solder ball to the contact material to form the solder bump, where the solder bump is in electrical contact with the bond pad.
2 . The method of claim 1 , further comprising depositing at least one metallization film of a precursor material between the bond pad and the contact material.
3 . The method of claim 2 , wherein the precursor material comprises at least one of Palladium and Platinum.
4 . The method of claim 2 , wherein the step of depositing the at least one metallization film includes spraying the precursor material into the well on an exposed surface of the bond pad.
5 . The method of claim 2 , wherein the step of depositing the at least one metallization film includes dipping the substrate having the well into a bath comprising the precursor material, where the precursor material contacts an exposed surface of the bond pad.
6 . The method of claim 2 , further comprising removing an excess of the at least one metallization film from an external surface around the well.
7 . The method of claim 1 , wherein the covering layer comprises a passivation material selected from a group consisting of: a polyimide, a glass, and a nitride.
8 . The method of claim 1 , wherein the covering layer comprises a photoresist material.
9 . The method of claim 1 , further comprising increasing a depth of the well by adding an additional covering layer.
10 . The method of claim 9 , wherein the additional covering layer comprises a photoresist material.
11 . The method of claim 1 , wherein the contact material comprises a solder paste.
12 . The method of claim 1 , wherein the contact material comprises an under bump metallization layer.
13 . The method of claim 1 , further comprising reflowing the contact material to form a non-bump solder tab.
14 . The method of claim 13 , wherein the step of reflowing occurs before the step of placing the solder ball.
15 . The method of claim 13 , wherein the step of reflowing occurs after the step of placing the solder ball and results in an integral bond between the solder ball and the contact material.
16 . The method of claim 13 , wherein the step of reflowing consumes a first portion of an under bump metallization layer deposited between the contact material and the bond pad, and leaves a second portion of the under bump metallization layer intact.
17 . The method of claim 1 , wherein the step of placing the solder ball includes using a template having cells arranged to mirror a well pattern on the substrate, where at least some of the cells hold a molten prepared solder ball.
18 . The method of claim 1 , wherein the step of placing the solder ball includes using a template having cells arranged to mirror a well pattern on the substrate, where at least some of the cells hold a prepared solder paste.
19 . The method of claim 1 , further comprising planarizing exposed surfaces on the substrate.
20 . A method of forming a solder bump on a substrate, the method comprising:
providing a substrate having a bond pad, and having a covering material that covers at least some of a surface of the substrate and that also forms a well around the bond pad;
depositing a contact material within the well in a manner where the contact material is in electrical contact with an exposed surface of the bond pad at the bottom of the well;
reflowing the contact material to form a solder tab within the well;
planarizing exposed surfaces on the substrate to create an approximately level surface on the solder tab at a top portion of the well;
placing an a priori prepared solder ball on the solder tab in the well; and
bonding the solder ball to the contact material to form the solder bump, where the solder bump is in electrical contact with the bond pad.
21 . The method of claim 20 , further comprising repeating the steps of depositing the contact material, reflowing the contact material, and planarizing expose surfaces at least once.
22 . The method of claim 21 , further comprising repeating the steps of depositing the contact material, reflowing the contact material, and planarizing exposed surfaces at least twice.
23 . The method of claim 20 , further comprising depositing an under bump metallization layer material before depositing the contact material.
24 . The method of claim 23 , wherein the step of planarizing exposed surfaces includes removing excess of the under bump metallization layer material from surfaces external to the well.
25 . The method of claim 20 , wherein the covering material comprises photoresist.
26 . The method of claim 20 , further comprising increasing a depth of the well by depositing an additional layer of a covering material around the well.