Die Stack Flux Removal Using Low-Angle Spray and Immersion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In 3D semiconductor manufacturing, the small openings in devices make it difficult for flux removal fluids to penetrate and effectively remove flux and residues, leading to trapped fluids and contamination, which reduces yield due to the surface tension of traditional flux removal solvents and the vertical orientation of devices.
Innovation Solution
An apparatus and method involving an immersion bath with low surface tension fluid, ultrasonic energy, and fluid recirculation to facilitate fluid entry, followed by a spin station using high-pressure and low-pressure flux removal fluid sprays at a low angle to direct the fluid through small openings, combined with RPM cycling and nitrogen drying to ensure complete removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If traditional flux removal solvents are used with downward spraying, then the process is simple to operate, but the fluid cannot penetrate small openings less than 20 microns due to surface tension
Solution Approach 1:
The patent changes the surface tension parameter of the flux removal fluid by selecting liquids with inherently low surface tension properties. This allows the fluid to penetrate small openings (less than 20 microns) that traditional high surface tension solvents cannot access, thereby achieving complete flux removal while maintaining operational simplicity
Solution Approach 2:
Instead of spraying fluid downward onto the top of devices (conventional approach), the patent inverts the approach by immersing the substrate in the low surface tension fluid, allowing the fluid to penetrate upward into small openings through capillary action and pressure differential, achieving effective flux removal from bonded interfaces
2Stress or pressure
If high pressure downward spray is used, then fluid can be forced through openings, but the spray is ineffective at removing flux from 3D stacked structures
Solution Approach 1:
The patent inverts the conventional spray approach by immersing the substrate in fluid rather than spraying downward. This allows pressure to be applied from all directions and enables fluid penetration into small openings through the immersed configuration, making the process effective for 3D stacked structures where downward spray fails
Solution Approach 2:
The patent employs hydraulic principles by immersing the substrate in flux removal fluid and using fluid pressure (including ultrasonic agitation) to force penetration into small openings. This hydraulic approach is more effective than pneumatic spray for reaching flux in bonded interfaces of 3D stacked devices
3Productivity
If devices are reduced in size with smaller bumps, then device density and performance improve, but access for flux removal fluid is reduced or eliminated
Solution Approach 1:
The patent changes the surface tension parameter of the removal fluid to match the scaled-down dimensions of modern devices. Low surface tension fluids can penetrate openings of 20 microns or less, maintaining flux removal capability as device features continue to shrink and bump sizes reduce
Solution Approach 2:
By inverting the removal approach from spray-to-contact to immersion-to-penetrate, the patent maintains flux removal accessibility even as device density increases and openings become smaller. The immersed configuration ensures fluid can reach all bonding interfaces regardless of device size or stacking height
4Loss of time
If flux removal fluid is trapped within device structure, then the process appears complete, but yield is reduced due to redeposition of flux and contamination
Solution Approach 1:
The patent implements continuous rinsing action with low surface tension fluid throughout the removal process. This continuous fluid action prevents trapped solvent from evaporating and redepositing flux, ensuring complete removal of contaminants and maintaining high yield while completing the process efficiently
Solution Approach 2:
By using low surface tension fluid with appropriate wetting properties, the patent ensures complete coverage and penetration without trapping air bubbles or leaving residual solvent. The fluid parameters are selected to prevent redeposition, eliminating yield loss from incomplete removal
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
Effectively removes flux and residues from 3D packaging by ensuring fluid penetration and thorough rinsing, reducing yield loss and contamination, even in areas with openings less than 20 microns, by using a combination of immersion and spin processing techniques.
Implementation Method 1
the surface tension of many flux removal fluids will not penetrate the small openings
Implementation Method 2
As shown in FIG. 1, the substrate will stay within an immersion bath 25 for a period of time where agitation, ultrasonic energy and\or fluid recirculation through the bath will assist in fluid flow through device openings
Implementation Method 3
High pressure (up to 3,000 psi) or high velocity spray nozzles are oriented in a low angle (0 to
Implementation Method 4
The nitrogen source needs to in oriented at the small openings between the die in order to maximize nitrogen flow between the die for drying
Implementation Method 5
Optionally the substrate can be processed through a hot plate with nitrogen purge, generally indicated at 59 in FIG. 1, to ensure complete fluid removal
Data Source
AI summary
A system for removing flux from openings formed in a substrate that has openings (e.g., sized 20 microns or less) formed therein includes a spay nozzle device that has a spray nozzle arm that is formed at an angle of about 45 degrees or less for discharging fluid towards the openings in the substrate for flux removal. The angle is between about 30 degrees and 45 degrees.