Glass sheets (TGV, Through Glass Via), as a highly innovative material in the field of modern electronics, are gradually emerging and playing a key role. TGV glass sheets achieve efficient electrical connections between chips and chips, chips and packages by making vertical interconnection channels (through holes) on glass substrates, providing strong support for the miniaturization and high performance of electronic devices.
Technical principle of TGV glass sheets
Through hole formation technology
1. Laser drilling: This is a commonly used method to form through holes on glass sheets. A high-energy-density laser beam is focused on the glass surface to instantly evaporate or gasify the glass material to form a hole. For example, femtosecond laser drilling technology can accurately control the position and size of the hole, and its pulse width is extremely short (at the femtosecond level, 1 femtosecond = 10⁻¹⁵ seconds), with minimal thermal impact on the surrounding glass material, and can achieve high-precision, small-size through-hole processing, with the aperture usually reaching a few microns to tens of microns.
2. Wet etching: Through holes are made based on the corrosion characteristics of glass materials in specific chemical solutions. First, a layer of photoresist is coated on the surface of the glass sheet, and the designed through-hole pattern is transferred to the photoresist through the photolithography process. Then the glass sheet is immersed in the etching solution. The part of the glass not protected by the photoresist will be gradually corroded to form a through hole. This method is suitable for making through holes of larger size and relatively less demanding precision. Its etching rate and etching selectivity can be controlled by adjusting the composition and process parameters of the chemical solution.
3. Dry etching: The glass is etched using plasma technology. In a vacuum environment, the reactive gas (such as CF₄, SF₆, etc.) is excited by an RF power supply to generate plasma. The active particles in the plasma react chemically with the atoms on the glass surface to generate volatile products and be extracted, thereby realizing the etching of the glass. Dry etching has high etching accuracy and anisotropy, and can produce through holes with high aspect ratio (the ratio of through-hole depth to aperture). It is widely used in the manufacture of high-end TGV glass sheets.
Metallization filling technology
1. Physical vapor deposition (PVD): In a vacuum environment, metal (such as copper, aluminum, etc.) atoms are deposited into the glass through-hole by evaporation, sputtering, etc. Taking sputtering as an example, a metal target is set in a vacuum chamber, and the surface of the target is bombarded with an ion beam, so that the metal atoms are sputtered from the target and deposited on the inner wall of the glass through-hole. PVD technology can form a uniform and dense metal film in the through-hole, but its deposition rate is relatively low, and there may be certain difficulties in deep hole filling.
2. Chemical plating: This is a method of depositing metal in glass through-holes using chemical reactions. First, the surface of the glass through-hole is pretreated to make it catalytically active, and then the glass sheet is immersed in a plating solution containing a metal salt and a reducing agent. On the catalytic surface, the metal ions are reduced by the reducing agent and deposited to form a metal coating. Chemical plating can achieve good deep hole filling and uniform coating thickness, but the composition of the plating solution and process conditions need to be strictly controlled to ensure the quality of the coating.
3. Electroplating: Based on chemical plating, the deposition of metal ions in the glass through-hole is further accelerated by applying an external current. The glass sheet pretreated by chemical plating is used as the cathode and the metal plate is used as the anode, and is placed in the electroplating solution. Under the action of the electric field, the metal ions dissolve from the anode and deposit on the cathode (the surface of the glass through-hole), thereby realizing the metallization filling of the through-hole. Electroplating has a high deposition rate and good filling effect, which can meet the needs of large-scale production.
Performance characteristics of TGV glass sheets
Electrical performance
1. Low resistance: The metallized through-holes in the TGV glass sheets have good conductivity and can effectively reduce the resistance loss during signal transmission. For example, when copper is used as the filling metal, its resistivity is low, which can enable the signal to be transmitted quickly in the interconnection channel, reduce signal delay, and increase the operating speed of electronic equipment. For high-speed digital signal transmission, the low-resistance TGV glass sheet can ensure the integrity of the signal and avoid signal distortion.
2. Low capacitance and inductance: The glass material itself has a low dielectric constant. Compared with traditional organic packaging materials, the capacitance and inductance generated by the TGV glass sheet during signal transmission are small. This enables the signal to maintain a good waveform during transmission, reduce signal crosstalk and reflection, and improve signal transmission quality. In high-frequency circuit applications, such as the RF module of a 5G communication base station, the low capacitance and inductance characteristics of TGV glass sheets can meet the strict requirements for high-speed, high-frequency signal transmission.
Mechanical properties
1. High mechanical strength: The glass sheet itself has a certain mechanical strength. After special treatment and processing, the TGV glass sheet maintains the original strength of the glass, and its overall mechanical properties are further improved due to the enhancement of the metallized through-hole. For example, in the packaging of electronic equipment, TGV glass sheets can withstand certain external forces, such as pressure and vibration during chip installation, to ensure the reliability and stability of electronic devices.
2. Good thermal stability: Glass materials have a high softening temperature and a low thermal expansion coefficient. TGV glass sheets can maintain stable physical and chemical properties under different temperature environments. During the operation of electronic equipment, a large amount of heat will be generated. TGV glass sheets can work normally in a high temperature environment, and will not cause problems such as through-hole deformation and metal plating shedding due to temperature changes, ensuring the long-term reliability of electronic equipment.
Chemical properties
1. Corrosion resistance: The metallized coating on the surface of TGV glass sheets has been specially treated and has good corrosion resistance. In harsh environments such as humidity, acid and alkali, the metallized through-holes are not easily corroded, thus ensuring the reliability of electrical connections. For example, in some outdoor electronic equipment or electronic control systems in chemical production environments, TGV glass sheets can resist the erosion of chemical substances in the environment and maintain the normal operation of the equipment.
2. Chemical stability: The chemical properties of the glass material itself are stable and do not react with most chemicals. TGV glass sheets can maintain the stability of their structure and performance in various chemical environments, and their electrical and mechanical properties will not be affected by chemical reactions, which provides a guarantee for the application of electronic equipment in complex chemical environments.
TGV glass sheet manufacturing process
Glass substrate selection
1. Material property requirements: The substrate glass for making TGV glass sheets needs to have a series of specific properties. First of all, the glass must have high purity and low impurity content to ensure good electrical insulation and chemical stability. Secondly, the thermal expansion coefficient of the glass should match that of the metallization filling material to avoid cracks or separation between the through hole and the glass substrate due to thermal stress during temperature changes. For example, for copper metallization filling, a glass material with a thermal expansion coefficient similar to that of copper is usually selected. In addition, the glass should also have good optical properties and mechanical processing properties to facilitate subsequent photolithography, etching and other process operations.
2. Commonly used glass materials: At present, the commonly used TGV glass substrate materials are borosilicate glass, quartz glass, etc. Borosilicate glass has good thermal stability, chemical stability and mechanical properties, and its cost is relatively low. It is widely used in the manufacture of mid- and low-end TGV glass sheets. Quartz glass has higher purity, lower thermal expansion coefficient and excellent optical properties. It is suitable for high-end TGV glass sheet manufacturing with extremely demanding performance requirements, such as semiconductor chip packaging and high-performance optical sensors.
Photolithography process
1. Photolithography principle and process: Photolithography is a key process for transferring the designed through-hole pattern to the surface of the glass substrate. First, a layer of photoresist is evenly coated on the surface of the glass substrate, and then a photolithography mask with a through-hole pattern is placed on top of the photoresist, and the photoresist is exposed to ultraviolet light to cause a photochemical reaction. The exposed photoresist dissolves in the developer, thereby forming a photoresist pattern consistent with the photolithography mask pattern on the surface of the glass substrate. The accuracy of the photolithography process directly affects the size and position accuracy of the through-holes in the TGV glass sheet, which is crucial for the production of high-precision and high-density through-holes.
2. Development of photolithography technology: With the continuous increase in the application demand for TGV glass sheets, photolithography technology is also continuing to develop. At present, deep ultraviolet lithography (DUV) technology is widely used in the manufacture of TGV glass sheets, which can achieve sub-micron lithography accuracy. As the next generation of photolithography technology, extreme ultraviolet lithography (EUV) technology has higher resolution and can achieve the production of smaller through-holes, and is expected to play an important role in the future high-end TGV glass sheet manufacturing.
Etching and metallization process integration
1. Etching and metallization sequence: In the process of TGV glass sheet production, the sequence and coordination of etching and metallization processes are crucial. Generally, the glass through hole is etched first to form the required hole structure, and then metallization filling is performed. During the etching process, the etching depth and aperture must be accurately controlled to ensure that they match the subsequent metallization process. After metallization filling, the metal surface needs to be flattened, such as chemical mechanical polishing (CMP), to ensure the flatness of the TGV glass sheet surface and the reliability of electrical connection.
2. Process optimization and quality control: In order to improve the production quality and production efficiency of TGV glass sheets, the etching and metallization processes need to be continuously optimized. By adjusting the process parameters such as etching gas flow, RF power, and temperature, the etching rate and etching selectivity are controlled; during the metallization process, the deposition parameters, plating solution composition, etc. are optimized to ensure the quality and filling effect of the metal coating. At the same time, advanced detection technologies such as scanning electron microscope (SEM) and atomic force microscope (AFM) are used to detect the microstructure and performance of TGV glass sheets, so as to timely discover and solve problems in the process and ensure product quality.
Application fields of TGV glass sheets
Semiconductor and chip packaging
1. Chip-scale packaging (CSP): In chip-scale packaging, TGV glass sheets serve as an interposer to achieve efficient electrical connection between the chip and the packaging substrate through its internal metallized through-holes. TGV glass sheets can significantly shorten the signal transmission path, reduce signal delay and power consumption, and improve chip performance. For example, in the processor chip packaging of smartphones, the use of TGV glass sheet technology can achieve a more compact packaging structure and improve the integration and operation speed of the chip.
2. System-level packaging (SiP): For system-level packaging, TGV glass sheets can integrate multiple chips with different functions (such as processor chips, memory chips, RF chips, etc.) into one package to achieve miniaturization and high performance of the system. The low resistance, low capacitance and inductance characteristics of TGV glass can effectively reduce signal interference between chips and improve the overall performance of the system. TGV glass has broad application prospects in the packaging of miniaturized, high-performance electronic devices such as wearable devices and IoT terminals.
5G communication and RF field
1. 5G base station RF module: In the RF module of 5G communication base stations, TGV glass is used to make the interconnection substrate of RF circuits. Its low resistance and low loss characteristics can meet the requirements of 5G communication for high-speed and high-frequency signal transmission, effectively improve signal transmission efficiency, and reduce signal attenuation and interference. TGV glass can also realize the miniaturization and integration of RF modules, reduce the volume and weight of base station equipment, and reduce costs.
2. RF front-end module: In the RF front-end module of mobile terminals such as mobile phones and tablets, TGV glass can be used as a connection medium between antennas and chips. Through the efficient interconnection of TGV glass sheets, the performance of RF front-end modules can be improved, and the communication capabilities of mobile terminals can be enhanced, such as improving signal reception sensitivity and increasing signal transmission power, providing users with a better communication experience.
Sensors and micro-electromechanical systems (MEMS)
1. Sensor packaging: In the packaging of various sensors (such as pressure sensors, accelerometers, gyroscopes, etc.), TGV glass sheets can realize electrical connection and signal transmission between sensor chips and external circuits. The good mechanical properties and chemical stability of TGV glass sheets can protect sensor chips from the influence of the external environment and improve the reliability and service life of sensors. For example, in the electronic stability control system (ESC) of automobiles, pressure sensors are packaged with TGV glass sheets, which can accurately sense tire pressure changes and ensure driving safety.
2. MEMS device integration: For micro-electromechanical system (MEMS) devices, TGV glass sheets can be used as an integration platform to integrate MEMS chips with other electronic components. The high-precision through-hole production technology of TGV glass sheets can realize the precise interconnection between MEMS devices and external circuits, and promote the wide application of MEMS technology in the fields of micro-nano manufacturing, biomedicine, aerospace, etc. For example, in microfluidic chips in the biomedical field, TGV glass sheets can be used to integrate MEMS devices and sensors such as micropumps and microvalves to achieve precise control and detection of biological samples.
