Solder Mask Pad Alignment via Pre-Solderable Layer
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Solution Overview
Problem
Existing integrated circuit mount systems face challenges with misalignment of solder mask layers and under bump metallurgy, leading to poor connection reliability, increased intermetallic cracking, and reduced pad density, which hinders the miniaturization and performance enhancement of integrated circuits.
Innovation Solution
The integration of solder mask pads with a pre-solderable layer on a substrate, providing precise dimensional control and alignment, reduces the planar dimensions of metal layers and improves the morphology of solder mask pads, enabling accurate and reliable electrical and mechanical connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the solder mask layer is applied to confine solder on pads, then solder confinement is improved, but misalignment with pads or UBM occurs leading to poor connection reliability
Solution Approach 1:
The patent introduces a pre-solderable layer as an intermediary between the solder mask layer and the pad/UBM structure. This pre-solderable layer acts as a mediator that compensates for alignment offsets, allowing the solder mask to be applied with standard precision while still achieving reliable solder connections to the underlying pad or UBM through the tolerant pre-solderable layer.
Solution Approach 2:
The patent changes the physical and chemical parameters of the interface layer by applying a pre-solderable coating that modifies surface properties. This layer changes the wetting characteristics and solderability parameters, enabling solder to reliably bond even when there is misalignment between the solder mask opening and the underlying pad or UBM structure.
2Manufacturing precision
If large pads and UBM structures are created to account for offsets, then alignment tolerance is improved, but solder mask confinement ability is defeated and intermetallic cracking increases
Solution Approach 1:
The patent applies local quality by creating a pre-solderable layer only in specific locations where alignment compensation is needed, rather than enlarging the entire pad structure. This localized approach maintains the original pad and UBM dimensions for optimal electrical performance while adding solderability and alignment tolerance only where required at the interface with the solder mask.
Solution Approach 2:
The patent solves the alignment problem by adding a new dimensional layer (the pre-solderable layer) between the solder mask and the pad/UBM, rather than expanding the planar dimensions of the pad or UBM. This vertical dimensionality change allows alignment compensation without affecting the horizontal confinement of solder or the electrical performance of the connection.
3Productivity
If feature size is reduced to increase circuit density, then circuit density is improved, but solder mask alignment precision becomes more difficult to achieve
Solution Approach 1:
The pre-solderable layer serves as a mediator that decouples the alignment requirements from the feature size scaling. As circuit features become smaller and alignment precision becomes more difficult to achieve, the pre-solderable layer provides a tolerant interface that maintains reliable solder connections even when alignment precision deteriorates due to miniaturization effects.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enhances the alignment and structural integrity of solder mask pads, reduces metal layer dimensions, improves routability, and increases the reliability of integrated circuit connections by minimizing copper lead blocking of crack propagation, thereby addressing the limitations of existing technologies.
Implementation Method 1
bond pads are often formed to include the input/output pad and one or more additional metal layers that promote wetting and metallurgical bonding with solder bump alloys
Implementation Method 2
The solder mask layer, which does not bond to the solder, confines the solder on the pads
Data Source
AI summary
An integrated circuit mount system includes an integrated circuit, a solder mask for the integrated circuit, and a solder mask pad on the substrate with the solder mask.