Laminated Release Layer Package Structure for Solder Bridging Prevention
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Solution Overview
Problem
In package-on-package (PoP) structures, solder bridging occurs due to uneven copper pillars, leading to positional deviations and poor bonding, which reduces electrical performance and product yield.
Innovation Solution
A method involving a carrier with bonding pads, a laminated build-up portion, and a release portion is used to form conductive posts around a cavity, allowing for controlled height and uniformity, preventing solder bridging and ensuring reliable bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper pillars are formed by electroplating, then electrical connection is achieved, but the size of copper pillars is difficult to control and they tend to have uneven heights
Solution Approach 1:
The copper pillar formation process is segmented into two distinct stages: first forming copper seeds with uniform height through electroplating, then forming the final copper pillars through a second electroplating process. This segmentation allows independent control of each stage, ensuring uniform height while achieving reliable electrical connection.
Solution Approach 2:
Copper seeds are formed in advance with controlled height and uniform distribution before the main copper pillar formation process. This preliminary action establishes a uniform foundation that enables precise control of the final pillar dimensions and prevents height variations.
2Device complexity
If copper pillars have uneven heights, then fabrication variability increases, but positional deviation occurs to the joints between conductive elements and copper pillars
Solution Approach 1:
The patent implements a feedback mechanism where the height of copper seeds is precisely controlled and measured, and this information is used to adjust the subsequent electroplating parameters. This feedback loop ensures that final copper pillars achieve uniform height, preventing positional deviations in joint formation.
Solution Approach 2:
The patent changes key parameters including electroplating time, current density, and copper seed height to achieve uniform copper pillar formation. By optimizing these parameters, the process achieves both low fabrication variability and high joint positional accuracy.
3Productivity
If packages are stacked with smaller sizes and fine pitches, then space is saved and electrical performance is improved, but solder bridging easily occurs between solder balls
Solution Approach 1:
Copper pillars serve as an intermediary structure between the first and second packages, providing a stand-off effect that physically separates solder balls and prevents bridging. This intermediary enables close packaging while maintaining solder joint integrity.
Solution Approach 2:
The patent replaces the traditional solder-only connection system with a hybrid system using copper pillars and conductive elements. This mechanical substitution provides structural support and spacing, eliminating the need for solder balls to bridge gaps, thus preventing solder bridging while enabling compact stacking.
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
The method achieves a stand-off effect that prevents solder bridging and ensures reliable bonding between conductive posts and elements, improving product yield by maintaining uniformity and positional accuracy.
Implementation Method 1
the first metal layer and the second metal layer can be in physical contact with one another
Implementation Method 2
forming a plurality of through holes penetrating the built-up portion and filling a conductive material in the through holes to form the conductive posts
Data Source
AI summary
A method for fabricating a package structure is provided, which includes the steps of: providing a carrier having a plurality of bonding pads; laminating a laminate on the carrier, wherein the laminate has a built-up portion and a release portion smaller in size than the built-up portion, the release portion covering the bonding pads and the built-up portion being laminated on the release portion and the carrier; forming a plurality of conductive posts in the built-up portion; and removing the release portion and the built-up portion on the release portion such that a cavity is formed in the laminate to expose the bonding pads, the conductive posts being positioned around a periphery of the cavity. Therefore, the present invention has simplified processes.