Laser Wafer Joining with Fluid Pressure to Prevent Sensor Heat Damage
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Solution Overview
Problem
Conventional joining techniques using eutectic reaction between metal layers on wafers risk damaging sensors with heat, require long heating and cooling times, and limit metal selection due to thermal expansion mismatch, restricting freedom in material choice.
Innovation Solution
A joining apparatus using laser light to locally heat the metal layers, with a pressurizing mechanism applying pressure through a gas or liquid medium to prevent wafer sticking and damage, allowing rapid joining and increased material selection flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the two wafers are heated entirely together with a sensor to generate eutectic reaction, then the joining temperature is achieved, but the sensor is damaged by heat
Solution Approach 1:
The patent applies laser light to heat only the metal layers at the joining interface, while the sensor and other regions remain at lower temperatures. This localized heating achieves the eutectic reaction temperature (e.g., 500°C) at the joining place without exposing the sensor to damaging heat, thereby resolving the contradiction between achieving joining temperature and preventing sensor damage.
2Temperature
If the two wafers are heated entirely together to generate eutectic reaction, then the joining temperature is achieved, but the heating time becomes long
Solution Approach 1:
By concentrating laser energy on the metal layers at the joining interface, the patent achieves rapid localized heating to the eutectic reaction temperature. This eliminates the need to heat the entire wafer and sensor assembly, dramatically reducing heating time from potentially minutes to seconds, thus resolving the contradiction between achieving joining temperature and minimizing heating time.
3Stability of the object's composition
If the two wafers are cooled gradually to relieve thermal stress, then thermal stress is reduced, but the cooling time becomes long
Solution Approach 1:
Since only the joining interface was heated locally rather than the entire assembly, the temperature gradient and thermal stress are significantly reduced. This allows for much faster cooling without risking wafer breakage due to thermal stress, thereby resolving the contradiction between relieving thermal stress and minimizing cooling time.
4Adaptability or versatility
If metals with different coefficients of linear expansion are selected, then the degree of freedom in material selection is increased, but distortion occurs during temperature change
Solution Approach 1:
The patent heats only the metal layers at the joining interface locally, while the bulk wafers and sensors remain at ambient or lower temperatures. This localized heating minimizes thermal expansion differences between materials with different coefficients of linear expansion, preventing distortion even when using dissimilar metals. Thus, the contradiction between material selection freedom and distortion prevention is resolved.
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
Prevents sensor damage, reduces joining time, and allows selection of metals with different thermal expansion coefficients, enhancing process efficiency and flexibility.
Implementation Method 1
heat is applied locally to a place of contact between two metal layers as a target using laser light
Implementation Method 2
generate eutectic reaction at a place of contact between the metal layers, thereby joining the two wafers to each other
Implementation Method 3
the two wafers are interposed under pressure to bring the two metal layers into contact with each other
Data Source
AI summary
A joining apparatus joins a first joining target and a second joining target to each other using laser light, and comprises a first stage, a pressurizing mechanism, a second stage, and a laser light source. The first stage is transmissive to the laser light and is located on the side of a back surface of the first joining target. The pressurizing mechanism applies a pressure to the back surface of the first joining target. The second stage includes a pressure-receiving surface for receiving the pressure from the pressurizing mechanism at a back surface of the second joining target. The laser light source applies the laser light through the first stage to a place of joining between the first joining target and the second joining target. The pressurizing mechanism includes a pressure transmission medium composed of gas or liquid and applies the pressure to the back surface of the first joining target with the transmission medium in contact with this back surface.