Capacitive Sensor Substrate Edge Exposure for Laser Dicing
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Solution Overview
Problem
Capacitive sensors face issues with vacuum suction and laser dicing due to the entire top surface of the silicon substrate being covered with a protective film, leading to focal point shifts, attenuation of laser beams, and inefficient chip separation and handling.
Innovation Solution
Exposing the outer peripheral edge of the substrate from the protective film allows for stable vacuum suction and improved laser dicing by forming an insulating sheet and providing electrode pads on the exposed surface, enabling balanced suction and efficient chip separation without obstructing the dicing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the whole top surface of the silicon substrate is covered with the protective film, then the movable electrode is protected, but the laser beam focal point shifts and intensity attenuates during laser dicing
Solution Approach 1:
The protective film coverage is segmented: the dome-shaped protective film covers only the area above the movable electrode, while the outer peripheral edge of the substrate remains exposed. This segmentation allows the laser beam to focus accurately on the dicing line without being obstructed by the protective film, while still providing protection where needed.
Solution Approach 2:
Different regions of the substrate have different protective film coverage: the central region has dome-shaped protective film coverage for electrode protection, while the peripheral region remains exposed for laser dicing. This local differentiation resolves the contradiction between protection and dicing precision.
2Reliability
If the whole top surface of the silicon substrate is covered with the protective film, then the electrode is protected, but the suction collet cannot effectively suck the chip
Solution Approach 1:
The protective film coverage is segmented to leave the outer peripheral edge exposed, creating a dedicated suction region. The suction collet can now effectively contact the exposed substrate surface at the peripheral edge, establishing proper vacuum suction while the dome-shaped protective film continues to protect the electrode area.
Solution Approach 2:
The exposed outer peripheral edge acts as an intermediary region that facilitates vacuum suction without compromising electrode protection. This intermediate zone allows the suction collet to establish contact with the substrate while the protective film maintains its protective function over the electrode.
3Reliability
If the protective film covers the whole top surface, then manufacturing protection is improved, but production throughput decreases due to slower laser scanning
Solution Approach 1:
By segmenting the protective film coverage to exclude the outer peripheral edge, the laser beam can travel at normal scanning speeds during dicing without focal point shifts or intensity attenuation. This maintains high production throughput while the dome-shaped protective film continues to provide necessary electrode protection.
Solution Approach 2:
The protective film is applied with local quality differentiation: full coverage over the electrode area for protection, but no coverage at the peripheral edge to enable high-speed laser dicing. This resolves the contradiction between protection reliability and production throughput.
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
This solution ensures stable vacuum suction and improved throughput in capacitive sensor production by allowing balanced suction and preventing chip dropping during conveyance, while enhancing dicing efficiency by avoiding protective film obstruction during laser dicing.
Implementation Method 1
the wafer is scanned with a laser beam along a dicing street (cutting band), and a silicon substrate is modified by the laser beam to form amorphous silicon, thereby dividing the wafer along the dicing street
Implementation Method 2
vacuum suction hole 28 is evacuated or brought into a negative pressure to suck acoustic sensor 11
Implementation Method 3
a capacitor is constructed with diaphragm 14 and fixed electrode film 21 in order to convert an acoustic vibration into an electric signal
Data Source
AI summary
Diaphragm 33 is provided on a top surface of silicon substrate 32, and plate unit 39 is fixed to the top surface of silicon substrate 32 so as to cover the movable electrode film with a gap. Plate unit 39 is made of an insulating material. Fixed electrode film 40 is formed on a bottom surface of plate unit 39, and diaphragm 33 and fixed electrode film 40 constitute a capacitor. In an area around plate unit 39, a whole outer peripheral edge of the top surface of silicon substrate 32 is exposed from plate unit 39. On the top surface of the substrate 32, insulating sheet 47 made of the insulating material is formed in a part of an area exposed from plate unit 39, and electrode pad 48 electrically connected to diaphragm 33 and electrode pad 49 electrically connected to fixed electrode film 40 are provided on a top surface of insulating sheet 47.