Semiconductor Package UBM Pad Geometry for Corrosion-Free Bump Attach
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Solution Overview
Problem
Under-bump metal (UBM) structures in semiconductor packages are prone to corrosion when not fully covered by solder balls, compromising the board-level reliability.
Innovation Solution
A semiconductor package design featuring UBM vias and pads with convexly protruding surfaces, where metal bumps completely cover the UBM pads, preventing exposure and subsequent corrosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UBM structure surface is not completely covered by solder ball, then the manufacturing process is simpler, but the exposed UBM surface corrodes and reliability decreases
Solution Approach 1:
The patent applies preliminary action by forming a convex protrusion on the UBM pad surface before the solder ball attach process. This pre-formed convex shape ensures that when the solder ball is attached, it naturally covers the entire UBM surface including the protrusion, preventing any exposure that would lead to corrosion. The convex shape is created through controlled metal deposition that extends beyond the original planar UBM pad boundaries.
Solution Approach 2:
The patent changes the surface geometry parameter of the UBM pad from a flat plane to a convex three-dimensional protrusion. This parameter change in surface topology ensures complete coverage by the solder ball, as the convex shape creates a natural containment that prevents solder ball displacement or incomplete coverage, thereby eliminating exposed UBM surfaces that would be susceptible to corrosion.
2Reliability
If the UBM pad surface is made convexly protruding, then complete coverage by metal bump is achieved, but the manufacturing complexity increases
Solution Approach 1:
The convex protrusion is formed as a preliminary structural feature on the UBM pad before the metal bump attach process. This pre-formed geometry serves as a built-in guide and containment structure that ensures complete coverage during subsequent processing steps, eliminating the need for complex alignment procedures or multiple deposition layers to achieve reliable coverage.
3Object-affected harmful factors
If the UBM pad has a convexly protruding surface, then corrosion is prevented, but the manufacturing precision requirements increase
Solution Approach 1:
The patent modifies the UBM pad surface parameter from a two-dimensional plane to a three-dimensional convex protrusion with controlled height and radial extent. This parameter change creates a self-contained geometry where the protrusion height is sufficient to ensure complete coverage by the metal bump while remaining within controllable manufacturing tolerances. The specific dimensional parameters are optimized to balance corrosion prevention with manufacturability.
Data Source
AI summary
A semiconductor package is provided. The semiconductor package includes a redistribution structure having a front surface and a rear surface opposite the front surface, the redistribution structure including an insulating layer and a redistribution conductor provided in the insulating layer; a semiconductor chip provided on the rear surface and including a connection pad electrically connected to the redistribution conductor; an encapsulant provided on at least a portion of the semiconductor chip; under-bump metal (UBM) vias extending from the redistribution conductor to the front surface of the redistribution structure within the insulating layer; UBM pads provided on the front surface of the redistribution structure to correspond to the UBM vias, respectively, and each UBM pad of the UBM pads having an exposed surface convexly protruding away from the front surface of the redistribution structure; and a metal bump provided on the UBM pads and contacting the exposed surface of each UBM pad of the UBM pads.