Application Fields and Practical Key Points of Conductive Silver Adhesive

I. Core Application Fields

(I) Encapsulation and Interconnection of Electronic Components

• Interconnection between Chips and Substrates: In the connection of IC chips, sensor chips (such as temperature sensors and pressure sensors) and PCB substrates, conductive silver adhesive can realize current transmission through the “Die Attach” process. For example, the image sensor (CMOS) in the mobile phone camera module has a small chip size (usually only a few millimeters) and poor high-temperature resistance (it is easy to fail when the temperature exceeds 150℃). The room-temperature curing conductive silver adhesive (such as epoxy resin-based silver adhesive) is used, which can not only ensure that the resistance value is lower than 0.01Ω (meeting the signal transmission requirements) but also avoid high-temperature damage to the chip.
• LED Encapsulation: In Mini LED, Micro LED displays and lighting fixtures, conductive silver adhesive is used for the connection between LED chips and brackets/substrates. Compared with the traditional gold wire bonding process, silver adhesive interconnection can reduce lead resistance and improve heat dissipation efficiency (the thermal conductivity of silver is about 429W/(m·K), which is much higher than that of gold wire (314W/(m·K))). Especially in high-density LED arrays (such as Mini LED backlight modules), it can reduce the light attenuation problem caused by uneven heating and extend the service life of devices.
• Flexible Electronic Interconnection: In flexible displays (such as foldable mobile phone OLED screens) and flexible sensors (such as heart rate sensors of wearable devices), conductive silver adhesive needs to have good flexibility (the elongation at break is usually required to be ≥5%) to adapt to the use scenarios where devices are bent and folded. For example, in the connection between flexible PCB (FPC) and rigid substrates, polyurethane-based conductive silver adhesive is used. After curing, it can withstand repeated bending (bending radius ≤5mm) without degradation of conductive performance.

(II) New Energy Field

• Photovoltaic Modules: In thin-film photovoltaic cells (such as CIGS and CdTe cells), conductive silver adhesive is used for the connection between electrodes and cell sheets, as well as the sealing and conduction of the edge of the module. Compared with traditional welding strips, silver adhesive can reduce the stress damage of cell sheets (thin-film cells are only a few microns thick and easy to break due to the pressure of welding strips), and at the same time improve the weather resistance of the module — under the cyclic temperature of -40℃~85℃, the resistance change rate of silver adhesive can be controlled within 5%, meeting the 25-year service life requirement of photovoltaic modules.
• Power Batteries: In the tab connection of lithium-ion batteries and the conductive bonding of battery modules, conductive silver adhesive can replace the traditional laser welding or ultrasonic welding. For example, in cylindrical battery modules, thermally conductive conductive silver adhesive (thermal conductivity ≥10W/(m·K)) is used to connect battery cells and busbars, which can not only realize current transmission but also quickly conduct the heat generated during battery operation, reducing the risk of thermal runaway. In addition, in solid-state batteries, silver adhesive can also be used for the interface bonding between electrolytes and electrodes to improve ion conduction efficiency.

(III) Medical and Aerospace Fields

• Medical Electronics: In implantable medical devices (such as cardiac pacemakers and neurostimulators), conductive silver adhesive is used for the interconnection of internal components, which needs to meet biocompatibility (complying with ISO 10993 standard, no cytotoxicity and sensitization) and long-term stability. For example, in the connection between the electrode lead and the chip of a cardiac pacemaker, medical-grade epoxy conductive silver adhesive is used. In the human body fluid environment (37℃, pH 7.4), it can maintain stable conductive performance for more than 10 years without releasing harmful substances. In addition, in in vitro diagnostic equipment (such as blood glucose meters and immunoassays), silver adhesive is used for the preparation of sensor electrodes, which can improve the detection sensitivity (such as blood glucose detection error ≤5%).
• Aerospace: In the electronic systems of satellites and spacecraft, conductive silver adhesive is used for the bonding and conduction of components in high-temperature, vacuum and radiation environments. For example, the microwave devices (such as filters and amplifiers) in satellite communication modules need to withstand extreme temperature cycles of -60℃~120℃ and space radiation (total dose ≥100krad). Silicone rubber-based conductive silver adhesive is used, whose resistance change rate can be controlled within 3% after radiation, and there is no volatile matter in the vacuum environment (to avoid polluting satellite optical devices), meeting the aerospace-grade reliability requirements.

II. Key Technical Requirements in Application

• Conductive Performance: The volume resistivity is the core indicator. It is usually required to be ≤1×10⁻⁴Ω·cm in the electronic field and ≤5×10⁻⁴Ω·cm in the new energy field. For high-frequency applications (such as 5G communication devices), the dielectric constant (usually required to be ≤5) and dielectric loss tangent (≤0.005) should also be paid attention to to avoid signal attenuation.
• Bonding Strength: In electronic encapsulation, the shear strength is usually required to be ≥15MPa (for metal-ceramic bonding); in flexible electronics, the peel strength is required to be ≥5N/mm (for metal-flexible substrate bonding) to resist the stress when the device is bent.
• Environmental Resistance: High and low temperature resistance (no obvious performance change after cycling at -55℃~150℃), damp-heat resistance (placed in an environment of 85℃/85% RH for 1000h, the resistance change rate ≤10%) and chemical corrosion resistance (such as resistance to engine oil and electrolyte immersion) are particularly critical in the automotive electronics and new energy fields.
• Curing Conditions: The curing method is selected according to the production efficiency requirements. Room-temperature curing (25℃/24h) or low-temperature curing (60℃/1h) is commonly used in the consumer electronics field, while high-temperature rapid curing (120℃/30min) can be used in the industrial field. It should be noted that the curing temperature should not exceed the temperature resistance upper limit of the bonded device.

III. Usage Precautions

• Substrate Pretreatment: The bonded surface needs to be cleaned (to remove oil stains and oxide layers). Metal substrates can be treated by alcohol wiping or pickling, and ceramic/glass substrates can be cleaned by plasma to improve the bonding strength and conductive stability of the silver adhesive. If there is an oxide layer on the surface, it may lead to an increase in contact resistance (even exceeding 1Ω).
• Control of Gluing Process: When using a dispenser for gluing, the glue amount should be controlled (the gluing thickness is usually 50~200μm) to avoid excessive glue leading to glue overflow (polluting component pins) or insufficient glue leading to poor conductivity. After gluing, curing should be completed within the specified time to prevent the silver adhesive from absorbing moisture (which affects the bonding strength).
• Storage and Shelf Life: Conductive silver adhesive should be sealed and stored in an environment of -4℃~8℃ (to avoid silver powder oxidation or adhesive aging). After opening, it should be used up within 24h. The shelf life of different types of silver adhesive is usually 6~12 months. After the expiration date, the conductive performance and bonding strength should be re- tested, and it can be used only after confirming that it is qualified.