Flip-Chip Package Assembly With Cavity-Formed Solder Pads
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Solution Overview
Problem
In flip-chip packaging, the decreasing size of semiconductor dies and increasing number of connections lead to tighter pitch distances, making it challenging to prevent solder bridging and misalignment, resulting in defects and scrap during assembly.
Innovation Solution
The method involves forming cavities in the package substrate corresponding to post connects on the semiconductor die, depositing flux in these cavities, placing solder balls on the flux, and performing a thermal reflow process to form solder pads. The semiconductor die is then mounted onto these solder pads, and another thermal reflow forms solder joints, ensuring reliable attachment without misalignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the pitch distance between conductive post connects is decreased to accommodate smaller semiconductor dies and increased connections, then the integration density and number of connections increase, but solder bridging and misalignment defects occur more frequently
Solution Approach 1:
The invention divides the soldering process into two separate stages: first forming solder pads on the package substrate, then mounting the semiconductor die with post connects. This segmentation allows each stage to be optimized independently, preventing solder bridging by establishing fixed pad positions before die attachment, thereby maintaining high integration density while improving solder joint reliability at tighter pitches
Solution Approach 2:
The invention performs preliminary action by pre-forming solder pads on the package substrate before mounting the semiconductor die. This preliminary placement of solder material at precise locations eliminates misalignment issues during die attachment, as the solder pads are already positioned correctly on the substrate, enabling reliable connections even at reduced pitch distances
2Ease of manufacture
If solder balls are placed on the ends of conductive post connects, then electrical connections are formed, but balls can be missing or misaligned causing defects and scrap
Solution Approach 1:
The invention inverts the traditional approach by placing solder on the package substrate rather than on the semiconductor die's post connects. This reversal eliminates the problem of missing or misaligned solder balls, as the solder pads are formed precisely on the substrate before die attachment, improving manufacturing precision while maintaining ease of manufacture
Solution Approach 2:
The invention introduces solder pads as an intermediary element between the package substrate and the semiconductor die's post connects. These pads serve as fixed reference points that mediate the connection process, ensuring precise alignment and eliminating misalignment defects, thereby improving manufacturing precision without complicating the assembly process
3Measurement precision
If manual or automated visual inspection is performed to detect defects, then defective dies are identified, but completed and functional semiconductor dies are scrapped due to false positives
Solution Approach 1:
The invention performs preliminary action by pre-forming solder pads with precise geometry and positioning before die attachment. This preliminary structuring creates consistent, well-defined solder joints that are easier to inspect accurately, reducing false positives in visual inspection and improving defect detection accuracy without sacrificing yield rate
Solution Approach 2:
The invention changes the physical parameters of the solder joint formation process by using pre-formed pads instead of solder balls on post connects. This parameter change creates more uniform and predictable solder joint characteristics, enabling more accurate visual inspection and reducing false defect identification, thereby improving both measurement precision and productivity
4Ease of operation
If solder balls are misaligned or non-uniform in a flip chip assembly, then dies can tilt during die mount, but this causes additional defects, scrap and increased costs
Solution Approach 1:
The invention performs preliminary action by pre-forming uniform solder pads on the package substrate before die mounting. This preliminary preparation ensures consistent solder distribution and precise positioning, eliminating die tilt during mounting and preventing additional defects, thereby maintaining ease of operation while improving assembly quality and reliability
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 ensures the formation of uniform and reliable solder joints, reducing or eliminating shorts between solder joints and improving the alignment and integration of semiconductor dies in flip-chip packages.
Implementation Method 1
performing a thermal reflow process and melting the solder balls to form solder pads
Implementation Method 2
forming solder joints by performing another thermal reflow to melt the solder in the solder pads
Data Source
AI summary
In a described example, a method includes: forming cavities in a die mount surface of a package substrate, the cavities extending into the die mount surface of the package substrate at locations corresponding to post connects on a semiconductor die to be flip-chip mounted to the package substrate; placing flux in the cavities; placing solder balls on the flux; and performing a thermal reflow process and melting the solder balls to form solder pads in the cavities on the package substrate.