Sorting Mask for Mixed-Size Solder Bumps on Microelectronic Substrates
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Solution Overview
Problem
Existing solder bump forming methods, such as stencil printing and micro ball placement, are not suited for high-density interconnection structures and result in significant bump height variations and reliability issues when dealing with electrode pads and solder resist openings of differing sizes.
Innovation Solution
A method involving a sorting mask with openings of mixed sizes is used to place solder balls of corresponding sizes onto electrode pads, ensuring that each bump achieves a predetermined height through reflow, thereby maintaining consistent bump heights across varying pad and opening sizes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If stencil printing method is used to deposit solder paste onto electrode pads, then solder bumps can be formed, but bump height variation and missing bumps occur leading to low die attachment yields
Solution Approach 1:
The patent applies local quality by using a sorting mask with non-uniform opening sizes that correspond to different electrode pad sizes. Each opening in the mask is specifically sized to deposit the appropriate amount of solder paste onto pads of different dimensions, ensuring consistent bump heights across the substrate despite variations in pad geometry.
2Ease of manufacture
If micro ball placement method is used with uniform size balls, then solder bumps can be formed, but significant bump height variations occur depending on pad and solder resist opening sizes
Solution Approach 1:
The patent resolves this contradiction by introducing a sorting mask with locally varied opening sizes. The mask creates local quality differences in the ball placement process, where each region of the mask has openings sized appropriately for the underlying electrode pad size, ensuring uniform bump heights despite using uniform-sized balls and varying pad geometries.
3Productivity
If prior art methods are used for high density interconnection structures, then production can proceed, but missing bumps and bump voiding occur negatively affecting yields
Solution Approach 1:
The patent introduces a sorting mask as an intermediary element between the solder ball supply and the electrode pads. This mask mediator controls and regulates the ball placement process, ensuring reliable bump formation on high-density interconnection structures by preventing missing bumps and voiding through precise opening size matching to pad geometry.
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 provides precise control over solder bump volume and height, reducing voids, missing bumps, and electromigration issues, resulting in a more reliable chip attachment process.
Implementation Method 1
The solder balls are then heated and melted to form bumps
Data Source
AI summary
A method of providing electrically conductive bumps on electrode pads of a microelectronic substrate, and bumped substrate formed according to the method. The method includes: providing a microelectronic substrate including electrode pads; providing a sorting mask defining first openings and second openings therethrough, the second openings being larger than the first openings; disposing the mask onto the substrate such that the first openings and second openings register with respective ones of the electrode pads; providing first solder portions onto corresponding ones of the electrode pads through the first openings, and second solder portions onto corresponding ones of the electrode pads through the second openings, the second solder portions being larger than the first solder portions; reflowing the solder portions to form, respectively first solder bumps and second solder bumps on respective ones of the electrode pads; and removing the mask after providing solder portions and before reflowing.