Metal Pillar Solder Diameter Control for Chip Yield
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Solution Overview
Problem
Conventional chips with metal pillar structures experience solder bridges at fine pitches, leading to short circuits due to the larger diameter of the solder protruding beyond the metal pillar, which reduces yield rates.
Innovation Solution
The chip design includes a metal pillar structure where the solder's maximum diameter is equal to or less than the metal pillar diameter, with the solder positioned within a phantom zone extending from the peripheral surface of the metal pillar, using a multi-layered under ball metal layer and materials like copper, aluminum, titanium, nickel, or vanadium, and optionally a barrier layer to prevent intermetallic layer formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the solder maximum diameter is greater than the metal pillar diameter (conventional design), then the solder provides adequate bonding area, but solder bridges occur at fine pitches causing short circuits
Solution Approach 1:
The patent changes the critical parameter of solder diameter to be equal to or less than the metal pillar diameter, rather than allowing it to protrude beyond. This parameter change eliminates the solder bridge issue at fine pitches while maintaining adequate bonding area through the controlled diameter relationship between solder and metal pillar
Solution Approach 2:
The patent employs a multi-layered under ball metal layer structure (UBM) comprising different metal materials to control solder behavior. The specific layer composition and thickness are optimized to constrain solder diameter during the bonding process, preventing excessive protrusion while ensuring proper wetting and bonding area
2Productivity
If the pitch between adjacent metal pillar structures is reduced (fine pitch), then chip functionality is improved, but solder bridges between adjacent pillars increase short circuit risk
Solution Approach 1:
The patent applies different metal materials in the multi-layered UBM structure at different locations and depths to achieve localized control of solder behavior. The barrier layer and bonding layer have different material properties optimized for their specific functions, enabling precise control of solder wetting and diameter at fine pitches
Solution Approach 2:
The under ball metal layer is constructed as a composite structure with multiple metal layers (e.g., Cu, Ni, Sn, Pb, or their alloys) with different properties. This composite structure provides both the bonding functionality needed for fine pitch and the control mechanisms to prevent solder bridge formation
3Reliability
If the solder diameter is reduced to prevent solder bridges, then short circuit risk is reduced, but bonding area may be insufficient
Solution Approach 1:
The patent compensates for reduced solder diameter by optimizing the vertical dimension through multi-layered UBM structure with specific thicknesses. The bonding strength is maintained through the combined effect of controlled solder diameter in the horizontal dimension and optimized layer thicknesses in the vertical dimension
Solution Approach 2:
The multi-layered UBM structure uses composite materials with different bonding characteristics. The barrier layer prevents intermetallic growth while the bonding layer provides wetting and adhesion, ensuring adequate bonding strength even with reduced solder diameter
Data Source
AI summary
The present invention relates to a chip having a metal pillar structure. The chip includes a chip body, at least one chip pad, a first passivation layer, an under ball metal layer and at least one metal pillar structure. The chip body has an active surface. The chip pad is disposed on the active surface. The first passivation layer is disposed on the active surface, and has at least one first opening so as to expose part of the chip pad. The under ball metal layer is disposed on the chip pad. The metal pillar structure is disposed on the under ball metal layer, and includes a metal pillar and a solder. The metal pillar is disposed on the under ball metal layer. The solder is disposed on the metal pillar, and the maximum diameter formed by the solder is shorter than or equal to the diameter of the metal pillar. Therefore, when the pitch between two adjacent metal pillar structures of the chip is a fine pitch, the defect of solder bridge can be avoided, so that the yield rate is improved.