In early October, Micron's investment in Taiwan exceeded 1.6 trillion New Taiwan Dollars. Its second HBM advanced packaging plant in Taichung is scheduled to start operation this month, with four bases in Tongluo, Taoyuan and Tainan expanding production simultaneously. HBM stacked packaging imposes stricter bubble control requirements for high-viscosity materials such as underfill and silver paste. The supporting demand for silver paste defoaming machines in memory advanced packaging has risen accordingly. For packaging material enterprises and OSAT factories, achieving stable defoaming in high-viscosity silver paste systems has become a key factor affecting packaging yield.

Solution Background

An enterprise specializing in chip mounting and underfill materials needed to carry out small-batch defoaming verification on high-viscosity silver paste samples to support the introduction of HBM production lines for a memory client. Silver paste undertakes conductive and mechanical connection functions in chip bonding and packaging interconnection. Microbubbles remaining in the adhesive will form voids after curing, directly affecting thermal and electrical conduction reliability as well as packaging service life. The client’s original vacuum defoaming equipment suffered slow bubble floating, long processing cycles and cross-contamination of samples when handling high-viscosity silver paste. They hoped to complete process verification with SIENOX vacuum defoaming mixers.

Processing Challenges

Silver paste systems usually have high viscosity and high proportion of powder fillers. Once bubbles are trapped inside the high-viscosity medium, simple vacuum pumping cannot effectively release them. Meanwhile, silver paste is sensitive to shearing; excessive stirring will damage the dispersion of silver powder and impair the conductive network. In addition, the material feeding volume for HBM packaging adhesive is small per batch with frequent batch switching, requiring the equipment to balance small-batch processing efficiency and batch-to-batch consistency. Temperature control is a critical process parameter for this application and can be customized to match the equipment. SIENOX can adapt to clients’ specific process temperature requirements.

Why Choose SIENOX Equipment

SIENOX adopts planetary revolution and rotation plus vacuum defoaming mode. The container rotates while revolving, and the slurry forms complex flow under planetary motion. Bubbles inside the high-viscosity system are continuously brought near the liquid surface and then extracted under vacuum. The whole process does not rely on direct shearing by stirring blades, avoiding damage to the dispersion state of silver powder and resin. In view of this small-batch verification requirement, the MIX60 planetary mixing defoamer is selected, with a processing volume of 300ml and maximum vacuum degree of -98KPa. Its rotation speed range covers commonly used intervals for high-viscosity silver paste. Single-batch processing can be finished within several minutes, suitable for laboratory and small-batch trial production scenarios of packaging material manufacturers.

Processing Procedure

The process team loads a fixed amount of silver paste sample into a disposable defoaming cup according to the client’s formula. The vacuum degree is preset to -98KPa, and the ratio of revolution and rotation speed is set based on common parameters for high-viscosity slurry. After startup, the equipment completes planetary mixing and defoaming synchronously inside the vacuum chamber. The escape state of bubbles on the liquid surface is observed during operation, and the speed ratio is fine-tuned according to sample viscosity to prevent new bubbles from being introduced by excessive rotation speed. The customized temperature control module is configured in accordance with the client’s process curve to ensure silver paste is defoamed within the set temperature range and reduce the impact of temperature fluctuation on viscosity and curing behavior.

Processing Results

The treated silver paste samples have no visible bubbles to naked eyes and show uniform dispersion. Subsequent die attach and curing verification by the client proves the void rate meets the requirements of HBM packaging process. The client later introduced the same model into small-batch production lines for defoaming verification and small-batch supply of new-formula silver paste. With the concentrated release of HBM advanced packaging capacity, the demand for defoaming of high-viscosity silver paste and underfill adhesive will keep growing. The application scenarios of silver paste defoaming machines and high-viscosity vacuum defoaming machines in memory packaging and chip mounting will be further expanded.