Localized Laser Reflow for Solder Bump Uniformity
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Solution Overview
Problem
Existing solder bump forming methods, such as stencil printing and micro ball placement, face issues like solder lift-up, missing bumps, and bump height variations, especially in high-density interconnection structures with small pitch and solder resist opening sizes, leading to low yields and contamination.
Innovation Solution
A method involving a mask with openings registered to electrode pads, where solder paste or balls are applied and then reflowed using localized heating, such as a laser beam, to form consistent solder bumps without lift-up issues, allowing for uniformity across varying pad sizes and pitches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If stencil printing method is used to form solder bumps, then the process is simple and cost-effective, but solder lift-up occurs causing missing bumps, bump height variation, and contamination
Solution Approach 1:
The patent segments the heating process by applying heat locally to individual solder bumps rather than heating the entire substrate uniformly. This localized heating approach allows each bump to be reflowed independently, preventing solder lift-up while maintaining process simplicity.
Solution Approach 2:
The invention applies different thermal conditions to different locations on the substrate. By using localized heating sources (such as laser or hot air jets) targeted at specific solder bump locations, the process achieves precise control over each bump's reflow without affecting adjacent areas, thereby eliminating lift-up issues.
2Productivity
If pitch and SRO size are reduced for high density interconnection, then interconnection density increases, but solder lift-up becomes more prevalent causing missing bumps and yield loss
Solution Approach 1:
The patent employs dynamic heating control where the heating source can be rapidly positioned and adjusted to match the reduced pitch and SRO dimensions. This dynamic adaptation allows the process to maintain reliability even as feature sizes shrink and density increases.
Solution Approach 2:
The invention replaces the mechanical stencil printing and uniform heating system with a more precise localized heating mechanism. This substitution enables accurate thermal delivery to each small solder bump location, preventing lift-up in high-density configurations.
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 eliminates solder lift-up problems, ensuring consistent bump height and reducing missing bumps, enabling reliable solder bump formation even at small pitches and mixed SRO sizes, thus improving die attachment yields and processing efficiency.
Implementation Method 1
reflowed using localized heating, such as a laser beam, to form consistent solder bumps
Implementation Method 2
the solder portions are reflowed by applying localized heating to each of the solder portions
Data Source
AI summary
A method of providing electrically conductive bumps on electrode pads of a microelectronic substrate. The method includes: providing a microelectronic substrate including electrode pads exhibiting an electrode pad pattern; providing solder portions onto respective ones of the electrode pads according to the electrode pad pattern; reflowing the solder portions to form solder bumps therefrom, reflowing comprising applying localized heating to each of the solder portions to reflow the same.