C4 Buffer Block Structures to Prevent Solder Bridging
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Solution Overview
Problem
The controlled collapse chip connection (C4) bonding process is prone to bridging between neighboring solder balls, leading to electrical shorts and warpage issues during the reflow process, which affects the reliability and integrity of semiconductor device packaging.
Innovation Solution
Incorporation of buffer block structures made of dielectric material between neighboring pairs of bumps to provide structural support during bonding, reducing warpage and preventing joint bridging, thereby improving the joint formation process window.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If C4 bonding process is performed with solder balls, then electrical connections are formed between substrates, but bridging between neighboring solder balls occurs causing electrical shorts
Solution Approach 1:
A buffer block structure made of dielectric material is introduced as an intermediary element positioned between neighboring solder balls. This buffer block prevents direct contact between adjacent solder balls during reflow, eliminating the bridging issue while maintaining electrical connectivity through the solder joints.
Solution Approach 2:
The space between neighboring solder balls is segmented by introducing a buffer block structure. This segmentation physically divides the region between adjacent solder joints, preventing the solder material from bridging across the gap during the reflow process.
2Reliability
If solder balls are reflowed to form C4 joints, then bonding between substrates is achieved, but warpage occurs during the reflow process
Solution Approach 1:
The buffer block structure acts as a counterweight or support element that compensates for the warpage forces generated during reflow. By positioning dielectric buffer blocks between solder joints, the structure provides mechanical support that counteracts the warping tendency of the substrate and solder assembly.
3Reliability
If buffer block structures are added between solder balls, then bridging and warpage are reduced, but device complexity increases
Solution Approach 1:
The buffer block structures are designed with optimized parameters including size, shape, and material composition to provide maximum support with minimal added complexity. By carefully controlling the dimensions and placement of buffer blocks, the solution enhances reliability while keeping the structural additions simple and manageable.
Data Source
AI summary
A semiconductor structure includes a fan-out package comprising at least one semiconductor die, a redistribution structure including fan-out bonding pads, and a first underfill material portion located between the at least one semiconductor die and the redistribution structure; a packaging substrate comprising chip-side bonding pads; an array of solder material portions bonded to the chip-side bonding pads and the fan-out bonding pads; a second underfill material portion laterally surrounding the array of solder material portions; and at least one buffer block structure located between a respective neighboring pair of solder material portions within the array of solder material portions and between the fan-out package and the packaging substrate, and laterally surrounded by the second underfill material portion.