Vacuum Underfill Process for Void-Free IC Chip Bonding
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Solution Overview
Problem
The formation of underfill voids during the underfill process in solder joints between connectors and electrical devices leads to reliability issues, such as solder pumping, electrical shorts, stress concentrations, and delamination, which are exacerbated by trends like larger chips, finer pitches, and complex devices like DBHi.
Innovation Solution
A method and apparatus that apply a vacuum during the underfill process, from deposition to thermal curing, to reduce and eliminate voids in the underfill material between an integrated circuit chip and a supporting substrate, using mechanisms like slits or holes in the substrate to facilitate vacuum application and sealing with a solder actuator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If underfill material is dispensed around the perimeter of the IC chip, then structural coupling is achieved, but voids form between the chip and substrate
Solution Approach 1:
A vacuum is applied to the chamber before underfill material is dispensed, removing air and gases from the gap between the chip and substrate. This preliminary vacuum treatment prevents void formation during subsequent underfill dispensing and curing processes
Solution Approach 2:
The process is conducted in a vacuum chamber that creates an inert environment during underfill dispensing and curing. This vacuum environment prevents air entrapment and void formation while the underfill material flows and cures between the chip and substrate
2Reliability
If vacuum is applied during underfill process, then voids are reduced, but process complexity increases
Solution Approach 1:
The vacuum application, underfill dispensing, and curing processes are merged into a single integrated vacuum chamber system. This allows all operations to be performed simultaneously or sequentially within the same controlled environment, reducing the need for separate processing steps and equipment
Solution Approach 2:
The vacuum chamber serves multiple functions: it removes air before dispensing, maintains vacuum during underfill flow, and sustains vacuum during curing. This multi-functional approach consolidates several process requirements into a single piece of equipment, managing complexity
3Area of stationary object
If larger chips are used, then device performance improves, but void formation increases
Solution Approach 1:
Larger chips are processed within a vacuum chamber that maintains an inert environment throughout underfill dispensing and curing. This prevents air entrapment in the larger gap areas and extends the void-free underfill process to accommodate larger chip dimensions
4Productivity
If finer pitch and narrower gap are used, then device density improves, but void formation increases
Solution Approach 1:
A vacuum is applied before underfill dispensing to remove air from the narrower gaps between features. This preliminary action ensures that even in high-density devices with finer pitch, the gaps are evacuated of air that would otherwise form voids during underfill flow
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 vacuum-assisted underfill process achieves a uniform and potentially voidless underfill, enhancing the reliability of solder joints by reducing shear stress, preventing crack formation, and ensuring structural integrity, even in complex devices.
Implementation Method 1
A voidless underfill process is provided that employs a vacuum opening to remove air and gases from the underfill
Implementation Method 2
solder joints between connectors and electrical devices
Data Source
AI summary
An electronic device is formed by dispensing an underfill material around a perimeter of an integrated circuit (IC) chip bonded to a supporting substrate. A void in present in the underfill material that is present between the IC chip and the supporting substrate. An opening is present through at least one of the IC chip and the supporting substrate into communication with the void. A vacuum may be applied to the void through the opening that is present through the IC chip to reduce a size of the void to a first volume. The opening that is present through the IC chip is sealed with a sealing plate. The underfill material is cured after the sealing of the opening to reduce of the void to at least a second volume that is less than the first volume.