Injection Molded Solder Balls for 3D Packaging
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Solution Overview
Problem
The formation of solder balls for 3D and 2.5D packaging processes is challenging due to stress concentration and electromigration failures, with existing methods like screen printing, solder ball dropping, and electroplating facing issues such as void creation, high costs, and inefficiency in large-scale fabrication.
Innovation Solution
The use of injection molding to form solder balls on a wafer, where a thick or thin final redistribution layer is patterned with holes over contact pads, and solder is injected and reflowed to create a pedestal and ball portion, suitable for flip-chip bonding, using materials resistant to high pressure and temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If screen printing or solder ball dropping is used to form solder bumps, then solder balls can be formed on contact pads, but voids are created during reflow due to flux material gasification
Solution Approach 1:
The solder balls are pre-formed through injection molding before the reflow process. This preliminary formation of solder balls with controlled composition and structure eliminates the need for flux material during reflow, thereby preventing void creation while ensuring reliable bonding.
2Manufacturing precision
If electroplating is used to form solder on contact pads, then solder can be deposited, but the process is too time consuming for large-scale fabrication
Solution Approach 1:
The patent replaces the electrochemical deposition process (electroplating) with a mechanical injection molding process. The injection molding process forms solder balls through mechanical injection and curing, which is significantly faster and more suitable for large-scale fabrication while maintaining precise control over solder ball formation.
3Ease of operation
If pre-formed solder balls are used in solder ball dropping process, then solder balls can be positioned, but additional expense is incurred and distribution is often incomplete
Solution Approach 1:
The patent merges the solder ball formation process with the wafer fabrication process itself. By injecting and curing solder material directly on the wafer contact pads, the process combines positioning and formation into a single integrated step, eliminating the need for separate pre-forming and dropping operations, reducing complexity, and ensuring complete distribution.
4Length of moving object
If joining pitch and bump size are reduced for fine-pitch 3D and 2.5D packages, then bandwidth and transmission length are improved, but stress concentration and electromigration failures increase
Solution Approach 1:
The patent changes the physical and chemical parameters of the solder material through controlled injection molding. By adjusting composition, density, and microstructure during the curing process, the solder balls achieve optimized mechanical and electrical properties that reduce stress concentration and electromigration effects, thereby improving reliability at fine pitch dimensions.
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 method reduces stress concentration and electromigration failures, enhances distribution efficiency, and is more cost-effective for large-scale fabrication by forming uniform solder balls with improved bonding capabilities.
Implementation Method 1
an injection head is then provided in physical contact with the molds and solder is injected into each
Implementation Method 2
The molds are then etched back and the injected solder is reflowed to form solder balls
Implementation Method 3
the injected solder is reflowed to form solder balls suitable for flip-chip bonding
Implementation Method 4
the injected solder is reflowed to form solder balls
Data Source
AI summary
Wafers include a contact pad on a surface of a bulk redistribution layer. A final redistribution layer is formed on the surface and in contact with the contact pad. Solder is formed on the contact pad. The solder includes a pedestal portion formed to a same height as the final redistribution layer and a ball portion above the pedestal portion.