T-Shaped Solder Bump Formation for Flip Chip Reliability
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Solution Overview
Problem
The challenge in semiconductor device fabrication is to increase solder bump height for improved interconnect reliability without increasing the size of the Under Bump Metal (UBM) or adding to the processing cost, particularly for small contact pads, as existing methods face limitations in achieving high-density chip designs due to the size constraints and thermal expansion mismatches in multi-layer plastic flip chip packaging.
Innovation Solution
A method involving the creation of a T-shaped layer of solder compound using a patterned photoresist mask over the UBM, allowing for controlled etching and reflow to form a taller solder bump without altering the UBM size, thereby enhancing bump height and reliability while maintaining cost-effectiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional solder bump formation methods are used, then the processing cost is controlled, but the bump height is insufficient for improved interconnect reliability
Solution Approach 1:
The patent introduces a vertical dimension to the UBM structure by forming an elevated pedestal or raised platform beneath the solder bump. This pedestal extends the UBM laterally and vertically beyond the contact pad boundary, creating a stepped or multi-level structure that increases bump height without increasing the contact pad footprint area.
Solution Approach 2:
The UBM structure is segmented into multiple functional zones: a base layer covering the contact pad, and an elevated pedestal portion that extends beyond the pad boundary. This segmentation allows different regions of the UBM to serve different purposes - the base provides electrical connection while the pedestal provides mechanical support and height increase.
2Length of moving object
If the UBM size is increased to support taller bumps, then bump height improves, but the contact pad size must increase which reduces device density
Solution Approach 1:
The solution transitions from a two-dimensional expansion (increasing pad area) to a three-dimensional expansion (increasing UBM height and lateral extent beyond pad). The pedestal structure provides the additional UBM area needed for taller bumps without requiring an increase in the contact pad footprint, thereby maintaining high device density.
3Adaptability or versatility
If multi-layer plastic flip chip packaging is used to accommodate high pin count, then I/O capability increases, but thermal expansion mismatch and package complexity increase
Solution Approach 1:
The patent applies local quality by providing enhanced mechanical support and stress distribution specifically at the bump location through the pedestal structure. This localized reinforcement addresses thermal expansion mismatch issues at the critical interconnect point without requiring global changes to the entire package structure, thereby reducing overall complexity.
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 approach enables increased bump height and controlled adjustment of solder bumps without additional processing steps, addressing reliability concerns and cost issues, and allows for higher device density without compromising thermal performance or increasing material usage.
Implementation Method 1
The layer of solder compound is heated to a temperature and for a time sufficient to melt the solder compound and form a solder ball
Data Source
AI summary
A new method is provided for the creation of a solder bump. Conventional methods are initially followed, creating a patterned layer of Under Bump Metal over the surface of a contact pad. A layer of photoresist is next deposited, this layer of photoresist is patterned and developed creating a resist mask having a T-shape opening aligned with the contact pad. This T-shaped opening is filled with a solder compound, creating a T-shaped layer of solder compound on the surface of the layer of UBM. The layer of photoresist is removed, exposing the created T-shaped layer of solder compound, further exposing the layer of UBM. The layer of UBM is etched using the T-shaped layer of solder compound as a mask. Reflow of the solder compound results in creating a solder ball.