Method for attaching chips in a flip-chip arrangement
View Patent ↗Polyimide is used as a spacer that also bonds together the elements that it is spacing apart. This is achieved by constructing the spacer on at least one of the wafers as is conventionally done, except that prior to performing the final curing of the polyimide precursor to form the final polyimide, the elements are aligned in a bonder and placed in contact with a pressure of 40 grams per square millimeter at a temperature slightly higher than the soft-bake temperature, as specified by the manufacturer of the polyimide precursor, for few minutes to promote tackiness. This holds the elements together, and the combined structure is then baked to fully cure the polyimide precursor into polyimide and complete the bonding.
1. A method for use bonding a first chip and a second chip to form a flip-chip assembly, the method comprising the step of:
forming at least one polyimide precursor spacer on said first chip;
bringing said at least one polyimide precursor spacer on said first chip into contact at a prescribed pressure with a structure of said second chip without any substance intervening between said at least one polyimide precursor spacer and said structure of said second chip; and
heating at least the point of contact of said at least one polyimide precursor spacer to promote tackiness of said at least one polyimide precursor spacer, whereby said spacer sticks to said structure of said second chip because of said tackiness of said at least one polyimide precursor spacer.
2. The invention as defined in claim 1 wherein, in said heating step, said point of contact of said at least one polyimide precursor spacer is heated to at least a temperature slightly higher than the soft-bake temperature of polyimide.
3. The invention as defined in claim 1 further comprising the step of heating said polyimide precursor spacer to cure it into a polyimide spacer.
4. The invention as defined in claim 1 wherein said prescribed pressure is about 40 grams per square millimeter.
5. The invention as defined in claim 1 said forming step further comprises the step of soft-baking said polyimide precursor spacer, wherein said soft-baking is performed by gradually heating said polyimide precursor spacer to a prescribed soft-baking temperature.
6. The invention as defined in claim 1 wherein said polyimide precursor spacer is formed from Arch Chemical's Durimide® 7520 and further comprising the step of curing said polyimide precursor spacer at a temperature below 350° C.
7. The invention as defined in claim 1 wherein polyimide precursor material that is employed to form said polyimide precursor spacer has a curing temperature specified by a manufacturer of said polyimide precursor material from which said polyimide precursor spacer is formed, said method further comprising the step of curing said polyimide precursor spacer at a temperature substantially below said manufacturer specified curing temperature.
8. The invention as defined in claim 1 wherein a plurality of said polyimide spacers are formed, each having sufficient space between itself and any adjacent spacer to enable polyimide byproducts to escape from each of said polyimide precursor spacers when said polyimide precursor spacers are cured.
9. The invention as defined in claim 2 wherein said temperature slightly higher than the soft-bake temperature of polyimide is about 120° C.
10. A method for use bonding a first chip and a second chip to form a flip-chip assembly, the method comprising the step of:
forming at least one polyimide precursor spacer on said first chip;
bringing said at least one polyimide precursor spacer on said first chip into contact at a prescribed pressure with a structure of said second chip without any substance intervening between said at least one polyimide precursor spacer and said structure of said second chip; and
heating at least the point of contact of said at least one polyimide precursor spacer to promote tackiness of said at least one polyimide precursor spacer, whereby said spacer sticks to said structure of said second chip because of said tackiness of said at least one polyimide precursor spacer;
wherein said forming step further comprises the step of soft-baking said polyimide precursor spacer, wherein said soft-baking is performed by gradually heating said polyimide precursor spacer to a prescribed soft-baking temperature.