Perforated Substrate Opening for Underfill Dispensing in Flip-Chip PoP
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Solution Overview
Problem
The bleeding of excess underfill material onto contact pads of the substrate in flipchip PoP assemblies leads to electrical connection defects and reduced manufacturing yield, particularly in semiconductor devices with high input/output density.
Innovation Solution
A method involving the formation of a perforated opening in the bottom substrate of a flipchip PoP assembly, allowing underfill material to be dispensed centrally and controlled to minimize bleeding, with dispensing ceasing as the material approaches the perimeter of the semiconductor die.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If underfill material is dispensed with excess volume or not evenly distributed, then the underfill material can bleed onto contact pads of substrate, but this causes electrical connection defects and reduces manufacturing yield
Solution Approach 1:
The substrate is designed with a central opening that creates a localized dispensing zone. This opening concentrates the underfill material flow path and defines a specific dispensing region, ensuring uniform distribution only where needed while preventing bleeding onto contact pads. The opening acts as a spatial constraint that enforces local quality control on the underfill material placement.
2Productivity
If contact pads are placed closer to the footprint of semiconductor die to achieve higher I/O density, then the I/O density improves, but the bleeding of excess underfill material over contact pads becomes more acute
Solution Approach 1:
The substrate surface is segmented into distinct functional zones by the central opening: a dispensing zone where underfill material is released, and a protected zone where contact pads are located. This segmentation physically separates the underfill dispensing path from the contact pad area, allowing contact pads to be positioned closer to the die footprint for higher I/O density while preventing underfill bleeding through the spatial partitioning created by the opening.
3Manufacturing precision
If underfill material is dispensed centrally through an opening in the substrate, then even and uniform distribution is achieved, but this requires additional manufacturing steps
Solution Approach 1:
The central opening is formed in the substrate before the underfill dispensing step. This preliminary action of creating the opening structure in advance establishes a predetermined dispensing path and flow control mechanism. By preparing this flow-guiding structure beforehand, the subsequent underfill dispensing process achieves uniform distribution automatically through the geometric constraints of the opening, without requiring complex real-time dispensing control or additional manufacturing steps during assembly.
Data Source
AI summary
A semiconductor device has a flipchip semiconductor die mounted to a first substrate using a plurality of first bumps. An opening or plurality of openings is formed in the first substrate in a location central to placement of the flipchip semiconductor die to the first substrate. A plurality of semiconductor die is mounted to a second substrate. The semiconductor die are electrically connected with bond wires. An encapsulant is over the plurality of semiconductor die and second substrate. The second substrate is mounted to the first substrate with a plurality of second bumps. An underfill material is dispensed through the opening in the first substrate between the flipchip semiconductor die and first substrate. The dispensing of the underfill material is discontinued as the underfill material approaches or reaches a perimeter of the flipchip semiconductor die to reduce bleeding of the underfill material. The underfill material is cured.