Integrated circuit package and method

1. A method comprising:

receiving an integrated circuit die, the integrated circuit die comprising:

a contact pad on a semiconductor substrate;

a passivation layer on the contact pad and the semiconductor substrate;

a die connector extending through the passivation layer, the die connector being physically and electrically coupled to the contact pad, the die connector comprising a first conductive material, the first conductive material being a Lewis acid having a first acid hardness/softness index; and

a reflowable connector on the die connector, the reflowable connector comprising a second conductive material, the second conductive material being a Lewis acid having a second acid hardness/softness index; and

etching the reflowable connector and the die connector with an etching solution comprising a protective agent for the first conductive material and an etching agent for the second conductive material, the protective agent being an azole, the azole being a Lewis base having a first ligand hardness/softness index,

wherein a product of the first acid hardness/softness index and the first ligand hardness/softness index is positive, and a product of the second acid hardness/softness index and the first ligand hardness/softness index is negative.

2. The method of claim 1 , wherein the azole is a five-membered heterocyclic compound containing a plurality of nitrogen atoms.

3. The method of claim 2 , wherein the five-membered heterocyclic compound is a pirazole compound comprising methylpyrazole.

4. The method of claim 2 , wherein the five-membered heterocyclic compound is an imidazole compound comprising methylimidazole.

5. The method of claim 2 , wherein the five-membered heterocyclic compound is a triazole compound comprising benzotriazole.

6. The method of claim 2 , wherein the five-membered heterocyclic compound is a tetrazole compound comprising phenyltetrazole or phenyl-mercaptotetrazole.

7. The method of claim 2 , wherein the five-membered heterocyclic compound is a pentazole compound comprising pentazole (HN 5 ).

8. The method of claim 1 , wherein the die connector comprises:

a first conductive layer comprising the first conductive material; and

a second conductive layer on the first conductive layer, the second conductive layer comprising a third conductive material, the third conductive material being a Lewis acid having a third acid hardness/softness index,

wherein a product of the third acid hardness/softness index and the first ligand hardness/softness index is negative,

wherein the etching the reflowable connector reduces a first width of the first conductive layer by an amount in a range of 0.05% to 30%, and

wherein the etching the reflowable connector does not reduce a second width of the second conductive layer.

9. The method of claim 1 further comprising:

before etching the reflowable connector and the die connector, testing the integrated circuit die.

10. The method of claim 1 further comprising:

after the etching the reflowable connector and the die connector, depositing a dielectric layer on the die connector and the passivation layer.

11. A method comprising:

forming a contact pad on a semiconductor substrate;

depositing a passivation layer on the contact pad and the semiconductor substrate;

patterning an opening in the passivation layer exposing the contact pad;

plating a die connector in the opening and on the contact pad, the die connector comprising a first conductive material;

reflowing a reflowable connector on the die connector; and

etching the reflowable connector and the die connector with an etching solution to remove the reflowable connector, the etching solution comprising an etching agent and a protective agent, the protective agent being a five-membered heterocyclic compound containing a plurality of active sites for bonding to the first conductive material.

12. The method of claim 11 , wherein etching the reflowable connector and the die connector comprises immersing the reflowable connector and the die connector in a bath of the etching solution.

13. The method of claim 11 , wherein etching the reflowable connector and the die connector comprises spraying the etching solution on the reflowable connector and the die connector.

14. The method of claim 13 , wherein the spraying the etching solution comprises spinning the semiconductor substrate at a speed in a range of 100 RPM to 3000 RPM while flowing the etching solution over the semiconductor substrate at a flow rate in a range of 0.2 L/min to 2 L/min.

15. The method of claim 11 , wherein etching the reflowable connector and the die connector comprises etching the reflowable connector and the die connector at a temperature in a range of 5° C. to 50° C. for a duration in a range of 0.1 minutes to 120 minutes.

16. The method of claim 11 , wherein the etching solution comprises the protective agent at a concentration in a range of 0.0001% to 2%, the etching agent at a concentration in a range of 0.1% to 20%, and a solvent in a range of 0.5% to 50%.

17. The method of claim 16 , wherein the etching agent is iron(III) or copper(II), and the solvent is nitric acid or sulfuric acid.

18. A device comprising:

a semiconductor substrate;

a contact pad on the semiconductor substrate;

a passivation layer on the contact pad and the semiconductor substrate;

a die connector extending through the passivation layer, the die connector being physically and electrically coupled to the contact pad, the die connector comprising a first conductive material, the first conductive material being a Lewis acid having a first acid hardness/softness index;

a dielectric layer on the die connector and the passivation layer; and

a protective layer disposed between the dielectric layer and the die connector, the protective layer surrounding the die connector, the protective layer comprising a coordination complex of the first conductive material and an azole, the azole being a Lewis base having a first ligand hardness/softness index,

wherein a product of the first acid hardness/softness index and the first ligand hardness/softness index is positive.

19. The device of claim 18 , wherein the die connector has an outer region that comprises a compound of the first conductive material and the coordination complex, and an inner region that is free of the coordination complex.

20. The device of claim 18 , wherein the protective layer has a thickness in a range of 1 Å to 100 Å.