How to Select the Right Solder Paste for COB Packaging?

Selecting the right solder paste for COB packaging requires comprehensive consideration of chip size, packaging process, reliability requirements, and cost. As a specialized manufacturer in microelectronic packaging materials, Fitech's products stand out as the preferred solution for COB packaging due to their technical advantages and customized services. The specific analysis is as follows:

I. Selection Based on Chip Size: Ultra-Fine Particle Size for High-Density Packaging

The core advantage of COB packaging lies in high-density integration, yet shrinking chip sizes impose stringent demands on solder paste particle size. Fitech offers ultra-fine solder powders ranging from T6 (5-15μm) to T9 (1-5μm) for different chip dimensions, ensuring printing precision and joint reliability:

Mini LED (50-200μm): Recommend T6 or No. 7 powder (2-11μm) to meet soldering demands for chips as small as approx. 75μm × 150μm (0306), preventing bridging or cold solder joints. For example, Fitech's FTP-0176 solder paste, utilizing T7 solder powder, supports printing through apertures as small as 70μm with extended printing lifespan. It is widely adopted in Mini LED backlight modules for consumer electronics like televisions and monitors.

Micro LED (<50μm): Requires T8 (2-8μm) or T9 (1-5μm) solder powders to form micron-level solder joints. Fitech's Fitech™ mLED 1370 solder paste, utilizing Type 8 powder (2-8μm) low-temperature alloy, is specifically designed for Micro LED direct-view displays. It has been successfully applied in AR/VR devices, achieving reliable soldering under high-density integration.

II. Selection by Packaging Process: Low-Temperature/Medium-Temperature Alloys Balance Thermal Management and Strength

COB packaging directly bonds chips to substrates, requiring alloy selection based on thermal tolerance to reduce thermal stress and ensure joint strength. Fitech offers diverse alloy solutions from low-temperature to medium-temperature:

Low-Temperature Alloys (Melting Point 138-143°C): Examples include Sn42Bi57.6Ag0.4 and Fitech™ FL170. These significantly reduce thermal stress, protecting exposed LED chips, gold wires, and heat-sensitive substrates (e.g., flexible boards). Ideal for high-density, heat-sensitive COB applications such as outdoor advertising displays and traffic signage. Fitech™ mLED 1370 solder paste utilizes low-temperature alloys to achieve high-reliability soldering at ultra-fine pitches (e.g., 0.9mm) while withstanding environmental stresses.

Medium-temperature alloys (melting point 170-194°C): Examples include Sn64Bi35Ag1 and Fitech™ FL200, which balance thermal stress reduction with solder joint strength. The incorporation of micro-nano-sized Ag and Cu-enhanced particles improves mechanical properties, making it suitable for applications requiring thermal resistance, such as Mini LED backlight modules in automotive displays. Fitech's FL200 alloy solder paste achieves both low-temperature soldering and high strength through optimized alloy ratios.

III. Selection Based on Reliability Requirements: High-Activity Flux and Ultra-Low Vacancy Rate

COB packaging applications often involve harsh environments (e.g., temperature variations, humidity, salt spray), demanding exceptional thermal fatigue life and corrosion resistance from solder joints. Fitech ensures long-term joint stability through high-activity flux and ultra-low porosity technology:

High-activity flux: Ensures wettability and reduces soldering defects (e.g., cold solder joints, bridging). Fitech's solder paste utilizes specially formulated high-performance flux, achieving uniform coverage even in high-density packages to enhance soldering yield.

Ultra-Low Voiding Rate: Voiding rate <5%, even <3%, minimizes stress concentration points to prevent solder joint cracking or failure. Fitech's FTP-3057 series solder paste achieves ultra-low void content through optimized alloy composition and processing. It has passed 1000 thermal cycle tests (-40°C to 125°C) with minimal solder joint resistance variation, ensuring long-term reliability for outdoor displays, automotive displays, and similar applications.

IV. Fitech's Technical Advantages and Customized Services

With 20 years of expertise in microelectronic packaging materials, Fitech provides comprehensive support for COB packaging through its technical strengths and tailored services:

Sphericity and Particle Size Distribution: Fitech's solder powders feature 100% true sphericity and narrow particle size distribution, minimizing printing performance fluctuations and enhancing solder joint consistency. For instance, its ultra-fine solder powders (T6 grade and above) achieve >95% sphericity, ensuring micron-level solder joint precision in Micro LED packaging.

Adjustable Viscosity and Thixotropy: Fu Yingda offers solder pastes with tunable viscosity for diverse printing processes (e.g., inkjet printing, dispensing), preventing printing collapse and ensuring reliable release. Its inkjet-compatible ultra-fine solder paste achieves dispensing speeds up to 18k uph, meeting high-efficiency production demands.

Customization Services: Fitech develops bespoke solder pastes with specialized alloys and particle sizes tailored to specific client requirements.