SMT red glue wire drawing refers to the phenomenon where the glue cannot be completely disconnected during the dispensing process, forming a filamentous connection, which may lead to uneven glue volume, pad contamination, and poor soldering. The following is an in-depth analysis combining industry practice and the latest technology:
Table of Contents
Ⅰ.Analysis of the formation of the core of red glue wire drawing
1. Material characteristics and parameter matching
-Imbalance between viscosity and thixotropy: When the viscosity of red glue is low or the thixotropy is insufficient, the fluidity of the colloid is too strong, and it is difficult to quickly restore the structural strength after dispensing, which can easily lead to wire drawing. For example, red glue with a thixotropy index below 5 has a significantly increased risk of wire drawing during high-speed dispensing.
-Temperature sensitive characteristics: The viscosity of red glue fluctuates greatly at low temperatures (such as insufficient temperature recovery after refrigeration) or high temperatures (ambient temperature>30 ℃), which may cause the colloid to be too thin or too thick, increasing the probability of wire drawing.
2. Equipment and process parameter settings
-Glue dispensing speed and pressure: If the glue dispensing speed is too fast (>50mm/s) or the pressure is too high (>0.6MPa), it will cause the gel to produce a tail when the needle tip detaches. For example, it is recommended to control the dispensing speed of component 0402 within 20-30mm/s.
-Needle nozzle design and condition: If the inner diameter of the needle nozzle is too small (<0.3mm) or worn and deformed, it will cause uneven colloidal shear force, resulting in wire drawing; Excessive spacing between the needle tip and PCB (>0.5mm) can also exacerbate the wire drawing phenomenon.
3. Environmental and operational factors
-Temperature and humidity effects: When the environmental humidity is greater than 65% RH, red glue is prone to moisture absorption, leading to a decrease in viscosity; Temperatures above 28 ℃ will accelerate colloid softening, both of which increase the risk of wire drawing. It is recommended to control the humidity in the workshop at 45% -60% RH and equip it with dehumidification equipment in the Dongguan area.
-Insufficient defoaming and stirring: Bubbles mixed in during storage or transportation of red glue, or not stirred evenly before use, can lead to uneven local viscosity and cause random wire drawing.
Ⅱ.Systematic solution for red glue wire drawing
1. Selection and pretreatment of red adhesive materials
-Choose high thixotropy red adhesive: The recommended thixotropy index is between 5-8. For example, Tedak TADHE red adhesive improves its shear strength by 30% through nanoparticle doping technology, significantly reducing its tendency to draw.
-Strict storage and temperature recovery: Red gum should be refrigerated at 5-10 ℃ and allowed to cool for 4-8 hours before use, with the temperature recovery time recorded to avoid fluctuations in colloid properties caused by temperature differences.
-Defoaming and stirring: Use a vacuum defoamer to process the colloid, or manually stir for 3-5 minutes (in the same direction) to ensure uniform viscosity.
2. Equipment parameter optimization
-Debugging of dispensing parameters:
-Speed and pressure: dynamically adjusted according to colloid viscosity, for example, high viscosity red glue is dispensed at a low speed of 20-30mm/s, with pressure controlled at 0.2-0.4MPa.
-Needle nozzle selection: For 0402 components, it is recommended to use a needle nozzle with an inner diameter of 0.3-0.5mm. BGA packaging uses a 0.8mm needle nozzle and is matched with a matrix dispensing layout.
-Enable suction function: Set the suction distance to 0.1-0.3mm to prevent colloid dripping.
-Temperature control: Preheat the dispensing head to 30-35 ℃, and control the heating slope of the curing oven at 1-3 ℃/s to ensure uniform solidification of the gel.
3. Environmental and process management
-Temperature and humidity control: The workshop should maintain 25 ± 3 ℃ and 45% -60% RH, and use a temperature and humidity recorder for real-time monitoring. If necessary, a dehumidifier should be installed.
-Optimization of Steel Mesh Design:
-The ratio of opening width to steel mesh thickness is greater than 1.5, and the area ratio is greater than 0.66. For example, the steel mesh thickness of 0402 component is 0.15mm, and the opening size is 0.25mm × 0.25mm.
-Using laser cutting and electropolishing technology, the roughness of the hole wall Ra is ≤ 0.8 μ m, reducing colloidal residue.
-Cleaning and maintenance: Clean the needle nozzle and steel mesh every 4 hours, using ultrasonic equipment and neutral water-based cleaning agents (such as Heming Technology W1000) to thoroughly remove residual colloids.
4. Detection and feedback mechanism
-Red glue wire drawing online monitoring:
-AOI visual inspection: Identify the height, diameter, and drawing situation of adhesive points through image processing algorithms, and adjust parameters in real time.
-Viscosity monitoring: Sampling and testing rheological properties every 4 hours to ensure viscosity fluctuations are less than 10%.
-Failure analysis: Conduct SEM/EDS analysis on defective wire drawing products to identify abnormal colloidal composition or process parameters.
Ⅲ. Industry Cases and Best Practices
1. Automotive electronics scene: In the M7 and glass diode mounting, Tedak Red Adhesive successfully reduced the wire drawing rate from 5% to 0.3% by optimizing the dispensing pressure (0.3MPa) and needle tip spacing (0.3mm), combined with 150 ℃/60s curing conditions, meeting the reliability requirements in the automotive vibration environment.
2. High density packaging of communication equipment: For scenarios where BGA spacing is ≤ 1.5mm, a matrix dispensing layout (spacing 0.8mm) and red glue with CTE value matching (12-15ppm/℃) are used. Combined with infrared thermal imaging monitoring, the curing furnace temperature difference is less than 5 ℃, effectively controlling the colloid collapse degree within ± 5% and reducing the wire pulling rate to below 0.1%.
3. Low cost solution for consumer electronics: By using Fuji NE3000S printing type red glue (thixotropy index 6.5), combined with trapezoidal steel mesh openings (15 ° side wall inclination angle), the adhesive point volume CPK value is greater than 1.67, the drawing rate is less than 0.5%, and the cost is reduced by 15% in 0201 component mounting.
Ⅳ. Risk avoidance and cost control
-Environmental compliance: Prioritize the use of water-based cleaning agents that meet RoHS/REACH standards (such as Heming Technology W1000) to replace traditional organic solvents, reduce safety hazards, and save 30% of waste liquid treatment costs.
-Inventory management: Adopting the first in first out (FIFO) principle, the inventory of red glue is controlled within 90 days to avoid performance degradation caused by expiration.
-Repair strategy: Use 180 ℃/90s reversible curing red glue, and during repair, soften the glue by locally heating it with a hot air gun to avoid mechanical scraping and damage to the solder pads.
Summarize
SMT red glue wire drawing is the result of the coupling of multiple factors such as materials, equipment, and environment. Through a systematic approach of material optimization, parameter optimization, environmental control, and closed-loop detection, the wire drawing rate can be controlled below 0.5%, meeting the high-precision requirements in fields such as consumer electronics and automotive electronics. At the same time, combined with the high humidity characteristics in Dongguan area, it is necessary to strengthen temperature and humidity monitoring and dehumidification measures to ensure process stability. In the future, with the application of technologies such as 3D printing dispensing and AI visual inspection, the red glue process is transitioning from experience driven to data-driven, further improving reliability and efficiency.
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