Uniform electrochemical plating of metal onto arrays of pillars having different lateral densities and related technology

1. A semiconductor die assembly, comprising:

a first semiconductor die having a major surface with non-overlapping first and second regions;

a second semiconductor die spaced apart from the first semiconductor die;

an array of first pillars extending heightwise from the first region of the major surface of the first semiconductor die toward the second semiconductor die, wherein the first pillars are configured to carry electricity between the first and second semiconductor dies; and

an array of second pillars extending heightwise from the second region of the major surface of the first semiconductor die toward the second semiconductor die, wherein the second pillars are electrically insulated from one or both of the first and second semiconductor dies,

wherein—

a lateral density of the first pillars is different than a lateral density of the second pillars by at least 5%, and

an average width of the first pillars is different than an average width of the second pillars by at least 2%.

2. The semiconductor die assembly of claim 1 , wherein a minimum lateral spacing between the first pillars is different than a minimum lateral spacing between the second pillars by at least 5%.

3. A semiconductor die assembly, comprising:

a first semiconductor die having a major surface with non-overlapping first and second regions;

a second semiconductor die spaced apart from the first semiconductor die;

an array of first pillars extending heightwise from the first region of the major surface of the first semiconductor die toward the second semiconductor die; and

an array of second pillars extending heightwise from the second region of the major surface of the first semiconductor die toward the second semiconductor die,

wherein—

a lateral density of the first pillars is lower than a lateral density of the second pillars by at least 5%; and

an average width of the first pillars is greater than an average width of the second pillars by at least 2%.

4. A semiconductor die assembly, comprising:

a first semiconductor die having a major surface with non-overlapping first and second regions;

a second semiconductor die spaced apart from the first semiconductor die;

an array of first pillars extending heightwise from the first region of the major surface of the first semiconductor die toward the second semiconductor die; and

an array of second pillars extending heightwise from the second region of the major surface of the first semiconductor die toward the second semiconductor die,

wherein—

a lateral density of the first pillars is lower than a lateral density of the second pillars by at least 5%; and

an average width of the first pillars is less than an average width of the second pillars by at least 2%.

5. A semiconductor die assembly, comprising:

a first semiconductor die having a major surface with a first region and a second region discrete from the first region;

a second semiconductor die spaced apart from the first semiconductor die;

an array of first pillars extending heightwise from the first region of the major surface of the first semiconductor die toward the second semiconductor die; and

an array of second pillars extending heightwise from the second region of the major surface of the first semiconductor die toward the second semiconductor die,

dummy pillars interspersed among the first pillars,

wherein—

a lateral density of the first pillars is different than a lateral density of the second pillars by at least 5%, and

an average height of the dummy pillars is at least 10% less than an average height of the first pillars.

6. The semiconductor die assembly of claim 5 wherein an average width of the first pillars is different than an average width of the second pillars by at most 3%.

7. The semiconductor die assembly of claim 5 wherein a minimum lateral spacing between the first pillars is different than a minimum lateral spacing between the second pillars by at least 5%.

8. The semiconductor die assembly of claim 5 wherein:

the first pillars are configured to carry electricity between the first and second semiconductor dies; and

the second pillars are electrically insulated from one or both of the first and second semiconductor dies.

9. A method for making a semiconductor die assembly, the method comprising:

electrochemically plating metal by an electrochemical plating process onto an array of first pillars extending heightwise from a first region of a major surface of a semiconductor die; and

simultaneously electrochemically plating metal by the electrochemical plating process onto an array of second pillars extending heightwise from a non-overlapping second region of the major surface of the semiconductor die,

wherein—

a difference between a lateral density of the first pillars and a lateral density of the second pillars has a first effect on relative metal deposition rates of the electrochemical plating process at the first and second regions of the major surface of the semiconductor die,

a difference between an average width of the first pillars and an average width of the second pillars has a second effect on the relative metal deposition rates of the electrochemical plating process at the first and second regions of the major surface of the semiconductor die, and

the second effect at least partially offsets the first effect.

10. The method of claim 9 wherein:

the semiconductor die is a first semiconductor die; and

the method further comprises—

electrically coupling the first semiconductor die to a second semiconductor die via the first pillars, and

thermally coupling the first semiconductor die to the second semiconductor die via the second pillars.

11. The method of claim 9 wherein:

the first effect causes a difference between an average plated height of the first pillars after the electrochemical plating process and an average plated height of the second pillars after the electrochemical plating process; and

the second effect reduces the difference by at least 50%.

12. The method of claim 9 wherein:

the first effect causes a difference between a maximum plated height of any of the first and second pillars after the electrochemical plating process and a minimum plated height of any of the first and second pillars after the electrochemical plating process; and

the second effect reduces the difference by at least 5%.

13. The method of claim 9 , further comprising forming a respective patterns for the arrays of first and second pillars by photolithography.

14. A method for making a semiconductor die assembly, the method comprising:

electrochemically plating metal by an electrochemical plating process onto an array of first pillars extending heightwise from a first region of a major surface of a semiconductor die;

simultaneously electrochemically plating metal by the electrochemical plating process onto an array of second pillars extending heightwise from a non-overlapping second region of the major surface of the semiconductor die; and

simultaneously electrochemically plating metal by the electrochemical plating process onto recessed dummy pillars interspersed among the first pillars,

wherein—

a difference between a lateral density of the first pillars and a lateral density of the second pillars has a first effect on relative metal deposition rates of the electrochemical plating process at the first and second regions of the major surface of the semiconductor die,

the dummy pillars have a second effect on the relative metal deposition rates of the electrochemical plating process at the first and second regions of the major surface of the semiconductor die, and

the second effect at least partially offsets the first effect.

15. The method of claim 14 wherein:

the semiconductor die is a first semiconductor die;

the method further comprises—

electrically coupling the first semiconductor die to a second semiconductor die via the first pillars, and

thermally coupling the first semiconductor die to the second semiconductor die via the second pillars; and

the dummy pillars are spaced apart from the second semiconductor die when the first and second semiconductor dies are electrically and thermally coupled.

16. The method of claim 14 wherein:

the first effect causes a difference between an average plated height of the first pillars after the electrochemical plating process and an average plated height of the second pillars after the electrochemical plating process; and

the second effect reduces the difference by at least 50%.

17. The method of claim 14 wherein:

the first effect causes a difference between a maximum plated height of any of the first and second pillars after the electrochemical plating process and a minimum plated height of any of the first and second pillars after the electrochemical plating process; and

the second effect reduces the difference by at least 5%.

18. The method of claim 14 , further comprising forming respective patterns for the arrays of first and second pillars by photolithography.

19. A method for designing arrays of electrochemically plated pillars in a semiconductor die assembly, the method comprising:

selecting a target width for first pillars in an array of the first pillars to extend heightwise from a first region of a major surface of a first semiconductor die of the semiconductor die assembly toward a second semiconductor die of the semiconductor die assembly; and

selecting a target width for second pillars in an array of the second pillars to extend heightwise from a non-overlapping second region of the major surface of the first semiconductor die toward the second semiconductor die,

wherein—

the first and second pillars are to be formed by an electrochemical plating process,

a difference between a lateral density of the first pillars and a lateral density of the second pillars has an effect on relative metal deposition rates of the electrochemical plating process at the first and second regions of the major surface of the first semiconductor die, and

selecting at least one of the target width for first pillars and the target width for second pillars includes selecting at least one of the target width for first pillars and the target width for second pillars to at least partially offset the effect.

20. The method of claim 19 wherein selecting at least one of the target width for first pillars and the target width for second pillars includes selecting at least one of the target width for first pillars and the target width for second pillars such that the target width for first pillars is different than the target width for second pillars by at least 2%.

21. The method of claim 19 wherein:

the first pillars are to have a lateral density lower than a lateral density of the second pillars; and

selecting at least one of the target width for first pillars and the target width for second pillars includes selecting at least one of the target width for first pillars and the target width for second pillars such that the target width for first pillars is greater than the target width for second pillars.

22. The method of claim 19 wherein:

the first pillars are to have a lateral density lower than a lateral density of the second pillars; and

selecting at least one of the target width for first pillars and the target width for second pillars includes selecting at least one of the target width for first pillars and the target width for second pillars such that the target width for first pillars is less than the target width for second pillars.