Vertical Solder Reflow Oven for Fluxless Wafer Processing
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Solution Overview
Problem
Traditional horizontal solder reflow ovens face issues with uneven heat distribution, contamination, and lower throughput, particularly in fluxless reflow processes for semiconductor wafer packaging, which also result in a large footprint and wafer-to-wafer variation.
Innovation Solution
A vertical oven design with a reflow chamber that uses a plurality of wafer-support plates, vacuum or near-vacuum environment, non-reactive gas introduction, and a reducing agent for controlled temperature ramping and laminar flow to achieve fluxless solder reflow, employing either high-temperature thermal transfer fluid or infrared heaters with zone control for uniform heating and cooling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If traditional horizontal solder reflow ovens are used, then the process can be performed, but uneven heat distribution and wafer-to-wafer variation occur
Solution Approach 1:
The patent inverts the traditional horizontal oven configuration to a vertical configuration. Wafers are stacked vertically on support plates within a single chamber, allowing uniform heat distribution from heating elements positioned at the bottom and sides. This vertical arrangement eliminates the heat distribution non-uniformity inherent in horizontal conveyors, achieving consistent temperature across all wafers in the batch.
Solution Approach 2:
The heating system is segmented into multiple independent heating zones with separate control. Each zone can be independently adjusted to optimize heat distribution to different regions of the vertical chamber, ensuring uniform temperature profiles across all wafer positions and eliminating hot or cold spots that cause variation.
2Reliability
If traditional horizontal solder reflow ovens are used, then the process can be performed, but contamination occurs
Solution Approach 1:
The vertical oven operates in a controlled inert atmosphere (nitrogen or vacuum) that prevents oxidation of solder bumps and metal surfaces before soldering. The sealed vertical chamber maintains this protective atmosphere throughout the reflow process, eliminating contamination from atmospheric exposure that occurs in traditional horizontal ovens with open conveyors.
Solution Approach 2:
The patent extracts and removes the conveyor mechanism and multiple open chambers from the traditional horizontal oven design. By using a single sealed vertical chamber with batch processing, the system eliminates the sources of contamination associated with mechanical conveyors and repeated chamber openings, achieving cleaner solder joints.
3Productivity
If traditional horizontal solder reflow ovens are used, then the process can be performed, but lower throughput is achieved
Solution Approach 1:
The patent merges multiple processing functions (heating, cooling, inert atmosphere maintenance) into a single vertical chamber. Multiple wafers are processed simultaneously in batch mode on stacked support plates, eliminating the sequential processing time of horizontal conveyors and achieving higher throughput without sacrificing temperature control.
Solution Approach 2:
The patent transitions from horizontal linear processing to vertical three-dimensional stacking. Multiple wafers are arranged vertically in the Z-dimension, allowing parallel processing of many wafers in a compact footprint. This dimensional change increases throughput by processing entire batches simultaneously rather than sequentially.
4Productivity
If traditional horizontal solder reflow ovens are used, then the process can be performed, but large footprint is required
Solution Approach 1:
The patent utilizes the vertical dimension by stacking wafers on multiple support plates within a single chamber. This vertical arrangement allows high-volume batch processing in a compact horizontal footprint, dramatically reducing the equipment area required compared to horizontal conveyors that need extensive linear space for sequential wafer transport.
Solution Approach 2:
Multiple wafers are nested vertically on stacked support plates within the single vertical chamber. This nesting arrangement maximizes the use of vertical space, allowing many wafers to be processed simultaneously in a compact configuration that minimizes the horizontal footprint of the equipment.
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 vertical oven configuration ensures void-free solder joints with reduced contamination, higher throughput, and improved temperature control, resulting in a more efficient and compact process for semiconductor wafer assembly and packaging.
Implementation Method 1
a first port to bring the reflow chamber to a vacuum or near-vacuum level
Implementation Method 2
a predetermined laminar flow of the reducing agent inside the reflow chamber assists the fluxless solder reflow process
Implementation Method 3
a temperature control mechanism for controlled ramping up of temperature for the solder reflow to occur uniformly across all the wafers
Implementation Method 4
specially designed infrared heaters with independent zone control capabilities
Implementation Method 5
for controlled ramping down of temperature uniformly across all the wafers in the batch of wafers after the solder reflow has occurred
Data Source
AI summary
The present disclosure is directed to a compact vertical oven for reflow of solder bumps for backend processes in semiconductor wafer assembly and packaging. This disclosure describes a vertical oven which uses a plurality of wafers (e.g., an example value is 50-100 wafers) in a batch with controlled injection of the reducing agent (e.g. formic acid), resulting in a process largely free of contamination. This disclosure describes controlled formic acid flow through a vertical system using laminar flow technology in a sub-atmospheric pressure environment, which is not currently available in the industry. The efficacy of the process depends on effective formic acid vapor delivery, integrated temperature control during heating and cooling, and careful design of the vapor flow path with exhaust. Zone-dependent reaction dynamics managed by vapor delivery process, two-steps temperature ramp control, and controlled cooling process and formic acid content ensures the effective reaction without any flux.