Classification and Selection Methods of Electronic Adhesives

Electronic adhesives for microelectronic packaging can be divided into two main categories based on packaging types: semiconductor IC packaging adhesives and PCB board-level assembly adhesives. Semiconductor IC packaging adhesives include epoxy molding compounds（EMC），LED Encapsulant，Die Attach Adhesives，Flip Chip Underfills，Dam and Fill Encapsulant。

PCB board-level assembly adhesives include:SMT Adhesives，COB Encapsulant，FPC Reinforcement Adhesives，CSP/BGA Underfills，Image Sensor Assembly Adhesives，conformal coating，Thermally conductive adhesive。

Curing Methods

Electronic adhesives can be classified by curing method into thermal curing, UV curing, anaerobic curing, moisture curing, UV + thermal curing, UV + moisture curing, etc. By material system, they can be categorized into epoxy resins, acrylates, and others.

Adhesives for Electronics Manufacturing

Common adhesives used in electronics manufacturing include epoxy resins, UV (ultraviolet) adhesives, hot melt adhesives, solder paste, anaerobic adhesives, and two-component adhesives.

Epoxy resins typically cure at high temperatures and provide strong bonding after curing, making them widely used in functional device bonding, underfill processes, etc. UV adhesives cure under ultraviolet light, offering low pollution and fast curing, making them ideal for encapsulation dispensing and surface coating applications.

In chip packaging, particularly LED chip packaging, die attach adhesives require specific bonding strength, thermal conductivity, and thermal resistance. Hot melt adhesives, such as structural PUR adhesives, feature low-temperature moisture curing, fast curing, and non-toxicity. Due to their unique advantages, they are gradually replacing other adhesive types.

Factors to Consider When Selecting Adhesives

Key properties of adhesives include rheological characteristics (viscosity, thixotropy, anti-sagging, tailing, shelf life/storage conditions, and pot life) and mechanical properties (tackiness, mechanical strength, heat resistance, curing cycle, electrical stability, etc.).

(1) When selecting an adhesive, ensure it meets environmental requirements first, then evaluate its performance in three aspects: pre-cure properties, curing behavior, and post-cure performance.

(2) Since two-component adhesives require precise mixing ratios and timing, increasing process complexity, single-component systems should be prioritized.

(3) Colored adhesives (typically red, white, or yellow) that contrast with solder mask and PCB materials are preferred for easy detection of missing components, adhesive volume, contamination on pads/components, or insufficient dispensing, aiding process control.

(4) The adhesive must have sufficient tackiness and wetting strength to ensure components remain firmly bonded to the PCB before curing. These properties generally increase with viscosity, and high-tack materials prevent component movement during placement and handling.

(5) For printing processes, the adhesive should exhibit good anti-sagging properties to maintain proper contact between components and the PCB, especially for taller components like SOICs and chip carriers. Adhesives with high thixotropy (typically 60–500 Pa·s) ensure better printability and consistent stencil deposition.

Adhesives should be insensitive to prolonged exposure to ambient temperature and humidity. Some advanced adhesives offer a print life exceeding five days, and unused material can be stored in containers for reuse.

(6) Prefer adhesives that achieve adequate bond strength with shorter curing times and lower temperatures. Optimal adhesives typically cure in 30–40s at 120–130°C. Post-soldering strength should ensure component stability and heat resistance, withstanding wave soldering shear forces. Curing temperatures must remain below the PCB substrate’s and components’ damage thresholds, ideally under the substrate’s glass transition temperature (75–95°C). Excessive bond strength complicates rework, while insufficient strength fails to secure components.

(7) Full curing should ideally occur in a single step. Minimal shrinkage during curing reduces component stress, and absence of gas emission prevents flux/contaminant entrapment, preserving PCB reliability.

(8) For larger components, UV-thermal dual-cure systems ensure thorough curing. A typical process combines UV and IR radiation, with some adhesives achieving IR cure in under 3 minutes. Some formulations require hybrid curing due to poor low-temperature performance.

(9) Post-cure, the adhesive should not interfere with subsequent processes (e.g., cleaning, rework).

(10) Cured adhesives must exhibit excellent insulation, moisture resistance, and corrosion resistance, particularly in humid environments, to prevent electrical migration and short circuits.