Improved SMD technology and processes solidify the foundation for the stability of display products with a pixel pitch of 1.5 or higher.

In the iterative development of the LED display industry, display products with a pixel pitch of 1.5mm or higher have long dominated mainstream scenarios such as commercial displays, outdoor advertising, and public venues due to their high cost-effectiveness and ease of large-scale delivery. As the core packaging technology for these products, SMD (Surface Mount Device) LEDs have developed into a mature industry chain over decades. However, under traditional processes, products are prone to stability issues such as lamp failure, dead lamps, color shift, and brightness decay under long-term high-load operation and complex environmental adaptation, becoming a key bottleneck restricting the upgrading of their application experience. In recent years, with continuous improvements in SMD technology and processes, optimization across the entire chain, from mounting accuracy and soldering reliability to protection capabilities and heat dissipation efficiency, has effectively addressed the above pain points. This has led to a qualitative improvement in the stability of display products with a pixel pitch of 1.5mm or higher, further consolidating their dominant position in the low-to-mid-range display market and injecting lasting momentum into the high-quality development of the industry.

I. Pain Point Focus: Stability Shortcomings of Traditional SMD Displays with Pitches Above P1.5

Display products with pitches above P1.5 (including P1.5, P1.8, P2.0, P2.5, etc.) are widely used in outdoor large screens, corporate showrooms, conference rooms, transportation hubs, and other scenarios. These scenarios often place high demands on the long-term stable operation and environmental adaptability of display products. However, traditional SMD processes, due to technological limitations, have several shortcomings in stability, mainly concentrated in four aspects:

First, insufficient soldering reliability, frequent LED failures and malfunctions. Traditional SMD uses tin-lead alloy solder paste, resulting in brittle solder joints. Uneven solder paste printing and misalignment are common during the mounting process, leading to weak soldering between the LEDs and the PCB substrate. Vibration during transportation and installation, or the effects of thermal expansion and contraction during long-term operation, can easily cause solder joints to crack and detach, resulting in "LED failures," "caterpillar effects," or even the failure of an entire row of LEDs. The annual failure rate can reach 5%-8%, seriously affecting display integrity.

Second, weak protection performance and limited compatibility. Traditional SMD LEDs have exposed LEDs and solder joints, resulting in a protection rating of only IP20-IP30, which is insufficient to effectively resist dust, moisture, and corrosive gases. In humid, dusty outdoor environments or complex scenarios such as industrial workshops, LED oxidation and short circuits are prone to occur, leading to display malfunctions and significantly shortening product lifespan.

Thirdly, insufficient heat dissipation efficiency leads to noticeable light decay and color shift. SMD LEDs are connected to the PCB substrate via brackets, resulting in a long heat dissipation path and high thermal resistance (typically 8-12K/W). Products with a P1.5 or larger pitch are often large-area splicing, which easily accumulates heat during long-term high-brightness operation, causing accelerated light decay and color drift. After 1-2 years of use, brightness decay can reach over 20%, and color accuracy deviation exceeds the acceptable range for the human eye, affecting display consistency.

Fourthly, poor process consistency and insufficient batch stability. Traditional SMD manufacturing suffers from low stencil printing precision, inaccurate reflow soldering curve control, and a lack of comprehensive end-to-end inspection mechanisms. This leads to significant differences in brightness and color accuracy among mass-produced products, and some products even exhibit defects such as LED misalignment and tombstoning, increasing the cost and difficulty of later maintenance.

These shortcomings not only affect the end-user experience but also hinder the penetration of SMD in mid-to-high-end commercial scenarios, forcing the industry to accelerate process improvement and solve stability problems through technological upgrades.

II. Core Direction of Process Improvement: End-to-End Optimization to Solve Stability Pain Points

Addressing the shortcomings of traditional SMD processes, the industry is focusing on four core areas: reliable soldering, upgraded protection, optimized heat dissipation, and improved precision. End-to-end process improvements are being implemented through material upgrades, equipment iterations, and process standardization to comprehensively enhance the stability of display products with a pixel pitch of P1.5 and above, achieving the goals of "firm adhesion, effective protection, rapid dissipation, and good consistency."

(I) Improved Soldering Process: Strengthening the Foundation and Reducing the Risk of Lamp Drop

Soldering is a core element for the stability of SMD display products. Process improvements focus on solder materials, printing precision, and reflow control to reduce solder joint defects at the source:

Regarding solder materials, traditional tin-lead alloy solder paste has been abandoned in favor of SAC305 lead-free solder paste (96.5% tin + 3% silver + 0.5% copper). Its melting point has been increased to 217℃, resulting in a 40% increase in solder joint strength compared to traditional materials. Fatigue resistance and oxidation resistance are significantly enhanced, effectively preventing solder joint cracking caused by thermal expansion and contraction. Simultaneously, the solder paste formula has been optimized to improve flux activity, ensuring sufficient wetting of solder joints and reducing defects such as cold solder joints and false solder joints, lowering the solder joint void rate from 8% to below 1%.

For printing precision, a combination of high-precision stencil and 3D SPI inspection is employed. The stencil aperture accuracy is controlled within ±0.01mm. Based on the pad dimensions of LEDs with a pitch of P1.5 or higher, the aperture ratio is optimized (length-to-width ratio ≥0.66, area ratio ≥0.5) to ensure uniform solder paste distribution on each pad. The 3D SPI inspection equipment monitors solder paste printing quality in real time, immediately triggering an alarm and requiring rework for pads with solder paste deviations exceeding 10%, preventing printing defects from flowing into the next process.

In the reflow soldering process, the traditional "speed-first" approach is abandoned, and the temperature profile is strictly controlled: the preheating stage (150℃) is maintained for 90 seconds to fully activate the flux; the peak temperature in the reflow stage is controlled at 245℃±2℃ and maintained for 15 seconds to ensure complete solder wetting of the solder joints; the cooling stage uses gradient cooling to inhibit solder whisker growth and reduce thermal stress damage to the LEDs and substrate. Simultaneously, nitrogen-protected reflow soldering technology is introduced, controlling the oxygen concentration below 500ppm to reduce pad oxidation and further improve soldering reliability. Furthermore, large-size LED chips are reinforced with both bottom filler and structural adhesive. The bottom filler penetrates between the solder joints, acting as a "buffer" to enhance vibration resistance; the structural adhesive forms "mechanical anchor points" between the LED chip and the PCB, achieving double fixation in conjunction with the solder joints, reducing the LED chip drop rate from 15% to below 0.5%.

(II) Improved Protection Process: Upgraded Protection Levels for Complex Scenarios

Addressing the weakness of SMD protection, the industry has significantly improved the dustproof, waterproof, and corrosion-resistant capabilities of products through upgrades to packaging processes and optimization of protective materials, making them suitable for complex scenarios such as outdoor and industrial environments:

On the one hand, the "full-sealing" packaging process is being promoted. After the SMD LED chips are mounted and soldered, high-transmittance, yellowing-resistant silicone is used to encapsulate the LED chips and solder joints as a whole, forming a complete protective layer. This upgrades the product protection level from IP20-IP30 to IP54 and above, with some outdoor-specific products reaching IP65, effectively blocking dust, moisture, and corrosive gases from entering and preventing LED chip oxidation and short circuits. Meanwhile, the potting process has been optimized using automated equipment to ensure uniform adhesive layer thickness (20-50μm). This maintains the luminous efficiency of the LED chips while providing all-around protection, increasing the potting yield to over 99% and eliminating issues such as missed potting and excess adhesive.

On the other hand, the LED chip encapsulation material has been upgraded to use high-temperature resistant, UV-resistant, and anti-yellowing epoxy resin, replacing traditional ordinary resin. This avoids adhesive layer aging and yellowing caused by prolonged outdoor exposure, extending product lifespan. Furthermore, a nano-anti-glare coating is applied to the LED chip surface, improving light uniformity and enhancing surface abrasion resistance, reducing damage from physical impacts and further improving product stability.

(III) Improved Heat Dissipation Process: Optimized Heat Dissipation Path to Suppress Light Decay and Color Deviation

Insufficient heat dissipation efficiency is the core reason for light decay and color deviation in SMD display products. For products with a pixel pitch of 1.5mm or higher, characterized by large-area splicing and high heat dissipation pressure, the industry has made process improvements in two aspects: substrate materials and structural design.

Regarding substrate materials, traditional ordinary PCB substrates are abandoned in favor of high thermal conductivity aluminum substrates or aluminum nitride ceramic substrates. The thermal conductivity is increased from 1-2 W/(m·K) of traditional substrates to over 200 W/(m·K), significantly shortening the heat dissipation path and reducing the system thermal resistance to below 4.8 K/W, improving heat dissipation efficiency by over 60%. Simultaneously, a 2oz/3oz thickened rolled copper PCB design is adopted to reduce line voltage drop, ensuring brightness consistency over long distances and further improving heat dissipation capacity, preventing accelerated light decay of LEDs due to localized heat accumulation.

In terms of structural design, the module's heat dissipation structure has been optimized by adding heat dissipation fins or holes to expand the heat dissipation area and accelerate heat dissipation. Simultaneously, flip-chip packaging technology is adopted to eliminate gold wire interference, reduce heat accumulation, and lower the LED operating temperature by 15-20℃. This effectively suppresses light decay and color shift, extending the product's lifespan from the traditional 3-5 years to 5-8 years. Long-term brightness decay is controlled within 10%, and the color accuracy ΔE value remains stable below 1.5, ensuring consistent color across the entire screen.

(IV) Improved Testing and Control Processes: Enhancing Consistency and Ensuring Batch Stability

Consistency in batch production is crucial for the stability of display products with a pixel pitch of 1.5mm or higher (mostly large-area splicing). The industry has improved this by introducing intelligent testing equipment and perfecting the entire process control system to achieve precise control of process parameters and early prevention of defects:

In the testing stage, an "AOI + X-ray dual inspection" system has been established. After mounting, AOI (Automated Optical Inspection) is used to check for defects such as misalignment, misalignment, and tombstoning in the LED chips. Then, X-rays are used to inspect the solder joints at the bottom of the LED chips for voids and cold solder joints, ensuring that the mounting quality of each solder joint and LED chip meets standards. This increases the inspection coverage to 100%, reducing the batch product defect rate from the traditional 3% to below 0.5%. Simultaneously, AOI testing parameters have been optimized. By calibrating the light source intensity and imaging angle, a dynamic threshold judgment model has been established, reducing the false judgment rate from 1.2% to below 0.35%, improving testing efficiency and accuracy.

In the control phase, the MES system monitors all production process parameters in real time, including nozzle pressure (50-80 mbar), placement speed (100 mm/s), and reflow soldering temperature range (±1℃) of the pick-and-place machine. If any parameter exceeds the range, the machine is immediately stopped for adjustment to ensure process consistency. Simultaneously, each batch of products undergoes sampling for "temperature cycling (-40℃ to 125℃, 1000 cycles)," "damp heat testing (85℃/85% RH, 1000 hours)," and "vibration testing." Only products that pass all reliability verifications are released to the factory, proactively identifying potential faults and ensuring the stability of batch products. Furthermore, a process parameter baseline database is established, and DOE experiments are used to verify the process window for different LED combinations, avoiding cascading quality risks caused by adjusting a single parameter.

III. Improvement Achievements: Enhanced Stability and Expanded Application Boundaries

The end-to-end improvements to SMD technology have resulted in a significant leap in the stability of display products with a pixel pitch of P1.5 and above. This not only addresses the core pain points of traditional products but also further expands their application boundaries, driving the transformation of products from simply "usable" to "easy-to-use and durable," injecting new vitality into the industry.

In terms of product performance, the improved SMD display products have increased their mean time between failures (MTBF) from the traditional 30,000 hours to over 100,000 hours, reducing the annual failure rate to below 0.01%, and decreasing the incidence of common failures such as lamp drop and dead lamps by over 90%. The protection level has been upgraded to IP54 and above, enabling stable adaptation to complex outdoor environments such as humidity, dust, and extreme temperatures, requiring less frequent maintenance and reducing the total lifecycle maintenance cost by 60%-70%. Simultaneously, improved heat dissipation efficiency effectively controls light decay and color shift issues, with brightness decay remaining below 15% even after 3 years of use, and significantly improved color consistency, meeting the display requirements of high-end commercial scenarios.

From an application perspective, improved stability has enabled SMD display products with a pitch of 1.5mm and above to successfully penetrate more demanding scenarios: in outdoor advertising, they can operate stably under prolonged exposure to wind, rain, and direct sunlight; in industrial control, they can withstand the effects of workshop dust and vibration, achieving 24/7 uninterrupted display; in transportation hubs and public venues, large-area SMD displays have no obvious seams or potential faults, ensuring the stability and integrity of information transmission. Furthermore, the improved SMD products maintain high cost-effectiveness while achieving stability comparable to mid-to-high-end COB products, further consolidating their dominant position in the 1.5mm and above pitch display market. Since 2025, shipments of SMD display products with a pitch of 1.5mm and above have increased by more than 18% year-on-year, with outdoor applications showing growth exceeding 30%.

From an industry impact perspective, the improved SMD process has driven collaborative upgrades across the industry chain. Upstream material companies, such as those producing substrates, solder paste, and encapsulating adhesives, are accelerating technological innovation; midstream packaging companies are optimizing production processes and upgrading intelligent equipment; and downstream application companies are obtaining more stable and cost-effective display products, forming a virtuous cycle of "materials-packaging-application." Meanwhile, process improvements have allowed SMD to maintain its foothold in the low-to-mid-range display market against emerging technologies like COB, thanks to its cost advantages and improved stability. This has created a differentiated competitive landscape where "COB dominates the high-end market, while SMD dominates the low-to-mid-range market," driving the diversified development of the LED display industry.

IV. Future Trends: Continuous Process Iteration and Enhanced Stability

As demand for display products with a pixel pitch of 1.5mm and above continues to expand in outdoor, industrial, and commercial applications, market requirements for product stability will further increase. SMD technology will continue to iterate towards greater precision, efficiency, and durability.

In the future, process improvements will focus on three core directions: First, intelligent upgrading, introducing technologies such as AI visual inspection and digital twins to achieve intelligent control and defect prediction throughout the entire production process, further improving the consistency and stability of mass production; second, material innovation, developing packaging and substrate materials with higher thermal conductivity and greater aging resistance, combined with self-healing phosphor technology, to extend product lifespan beyond 150,000 hours, further suppressing light decay and color shift, and adapting to more stringent environmental requirements; third, process integration, deeply integrating SMD with flip-chip, CSP, and other technologies to optimize the packaging structure, maintaining cost advantages while further improving heat dissipation efficiency and protection performance, driving the penetration of SMD display products with a pitch of P1.5 and above into mid-to-high-end scenarios, while exploring integration with GOB and other processes to achieve a dual improvement in protection performance and ease of maintenance.

Conclusion

Continuous improvement of SMD technology is an inevitable choice for the industry to meet market demands and solve product pain points, and it is also the core support for SMD to maintain its competitiveness in the wave of LED display technology iteration. Through end-to-end process optimization encompassing welding, protection, heat dissipation, and testing, the stability of SMD display products with a pitch of P1.5 and above has achieved a qualitative leap. This not only solves long-standing industry problems such as lamp failure, light decay, and insufficient protection, but also further expands application boundaries and consolidates its dominant position in the low-to-mid-range display market.

In the future, with continuous process iteration and technological innovation, SMD will continue to leverage its mature supply chain and high cost-effectiveness to achieve breakthroughs in stability and reliability, providing superior product solutions for the P1.5 and above display market and driving the LED display industry towards high-quality and diversified development.