Dam-like Metal Pad for Semiconductor Die Attach
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Solution Overview
Problem
Semiconductor device technologies face challenges with cross-contamination and die pad corrosion due to solder paste material flooding during clip bonding, particularly in Cu-based logic die pads, where organic foreign materials and corrosive byproducts are a concern.
Innovation Solution
A semiconductor device design featuring a metal pad with a thinner interior region and a thicker peripheral region, forming a dam-like structure to retain die attach material and reduce mechanical stress, while allowing for the attachment of interconnect plates or semiconductor dies with minimal risk of flooding and corrosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a uniform thickness metal pad is used for die attach, then the die attach material can be evenly distributed, but solder paste flooding occurs and causes die pad corrosion
Solution Approach 1:
The metal pad is designed with non-uniform thickness, featuring a thicker peripheral region (e.g., 20-50 μm) and a thinner interior region (e.g., 5-20 μm). The thicker peripheral region acts as a dam structure that prevents solder paste from flooding outward, while the thinner interior region provides sufficient bonding area for die attach material without causing flooding. This local variation in thickness resolves the contradiction by providing different functional properties in different regions of the same pad.
Solution Approach 2:
The solution moves from considering only the two-dimensional planar dimensions of the metal pad to incorporating the third dimension (thickness). By varying the thickness in the vertical dimension, the patent creates a three-dimensional dam-like structure that effectively contains solder paste within the interior region, preventing flooding while maintaining reliable die attach functionality.
2Reliability
If a thicker metal pad is used to prevent solder paste flooding, then corrosion is reduced, but mechanical stress on the substrate increases during heating and cooling
Solution Approach 1:
The metal pad employs local quality variation with a thicker peripheral region and a thinner interior region. The thicker periphery provides the necessary dam structure for solder paste retention, while the thinner interior reduces the overall mass that would generate thermal stress during heating and cooling cycles. This localized thickness variation resolves the contradiction by providing thickness only where structurally necessary for flood prevention.
Solution Approach 2:
The metal pad is effectively segmented into two functional regions with different thicknesses: a peripheral dam region and an interior bonding region. This segmentation allows each region to be optimized independently - the periphery for flood prevention and the interior for stress reduction - thereby resolving the contradiction between solder paste retention and mechanical stress.
3Stress or pressure
If a thinner interior region is used in the metal pad, then mechanical stress is reduced, but the bonding area for die attach material is decreased
Solution Approach 1:
The metal pad uses local quality differentiation where the interior region has reduced thickness to minimize thermal stress, while the peripheral region maintains greater thickness for structural support and flood prevention. The interior region's thickness is optimized to provide adequate bonding area for die attach material while keeping the overall mass low enough to reduce thermal stress during temperature cycling.
Data Source
AI summary
A semiconductor device includes a semiconductor substrate, a power transistor formed in the semiconductor substrate, the power transistor including an active area in which one or more power transistor cells are formed, a first metal pad formed above the semiconductor substrate and covering substantially all of the active area of the power transistor, the first metal pad being electrically connected to a source or emitter region in the active area of the power transistor, the first metal pad including an interior region laterally surrounded by a peripheral region, the peripheral region being thicker than the interior region, and a first interconnect plate or a semiconductor die attached to the interior region of the first metal pad by a die attach material. Corresponding methods of manufacture are also described.