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C4 and Low-K Stress Mitigation by C4 Pitch Reduction in the Die Corners

IP.com Disclosure Number: IPCOM000246033D
Publication Date: 2016-Apr-27
Document File: 6 page(s) / 134K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a structure to mitigate the overall stresses in the two-dimensional (2D) or two and a half/three dimensional (2.5D/3D) stacked die. The approach includes reducing the C4 strains at the corner of the die to reduce the driving force that stresses the Back End of Line (BEOL) layers within the thinned die.

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C4 and Low-K Stress Mitigation by C4 Pitch Reduction in the Die Corners

A method is needed to mitigate the overall stresses in the two-dimensional (2D) or two and a half/three dimensional
(2.5D/3D) stacked die.

The novel solution is a structure that has the corner C4s in the high Distance to Neutral Point (DNP) regions on the side of the die connected to the laminate (for 2D case or for 2.5D/3D case grindside for F2F configuration, and device side for F2B configuration) at the minimum allowable pitch (

=150um. The approach adds dummy C4s to fill the gap between the core at the relaxed pitch (>=150um) and the die corners at the minimum pitch (<=150um). In addition, the approach adds the dummy bumps at the minimum pitch. Reducing the C4 strains at the corner of the die mitigates the driving force that stresses the Back End of Line (BEOL) layers within the die. In addition, for the 2.5D/3D case, having the corners at the reduced pitch and the rest of the bumps in the die at relaxed pitch frees space for additional Through Silicon Vias (TSVs) to be incorporated within the die layout.

In the 2D case for mechanical modeling, the effect of the following on reducing the C4 strain in the corner region of the chip modeled: (104 simulations)


 Decreasing the C4 pitch


 Number of rows to change the pitch


 Chip edge length


 Presence of absence of C4s

Figure 1: Summary of Mechanical Modeling - 2D Case

1


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Figure 2: Solution Modeling Structure - 2D Case

With mechanical modeling, C4 strain significantly decreases when the C4 pitch in the corner region of the chip is decreased. The C4 strain further decreases when dummy C4s are added in the gaps. A reduction in C4 strain leads to proportional decrease in the Ultra-Low K (ULK) stresses in the BEOL. This is critical for 2D as well as 2.5D/3D BEOL mechanical integrity and reliability. The decrease in C4 strain increased when the change was implemented for a larger number of...