Selecting the ultrasonic cleaning frequency is a core process decision that directly determines the cleaning effect, efficiency, and safety. There is no "single best frequency"; the key is to strike a balance between **"cleaning power"** and **"precision"** based on the product characteristics and contaminant nature.

The following is a systematic guidance principle and decision framework for selecting ultrasonic frequency:

Core Principle: How Frequency Affects Cleaning

· Low Frequency (e.g., **20kHz - 40kHz**):

  · Cavitation bubbles are large; energy upon collapse is strong, impact force is violent.

  · Strong cleaning power, suitable for removing heavy, strongly adhered contaminants.

  · Cavitation effect is concentrated, but the number of cavitation bubbles is relatively small, and the ability to penetrate fine structures is weak.

  · May damage soft, precision, or highly polished surfaces (causing "cavitation erosion" micro-pitting).

· High Frequency (e.g., **40kHz - 80kHz** and above, such as **120kHz,** or even **1MHz megasonics**):

  · Cavitation bubbles are small, collapse energy is gentle.

  · Cavitation bubbles are dense and more uniformly distributed, capable of penetrating finer crevices.

  · Cleaning power is more delicate, excelling at removing sub-micron, nanoscale particles, and light grease.

  · Surface-friendly to workpieces; risk of damage is extremely low.

Frequency Selection Decision Framework

Step One: Evaluate Product (Object to be Cleaned) Characteristics

This is the most important factor.

1. Material Hardness and Surface Finish

   · Hard, Durable (e.g., steel, hard alloys, ceramics): Can withstand strong impact; prioritize **low frequency (25-40kHz)** for high cleaning power.

   · Soft, Easily Damaged, High Polish (e.g., aluminum, copper, polished metal, glass, silicon wafers, precious jewelry): Must avoid damage; prioritize **high frequency (40kHz and above)**. For chips and optical lenses, **80kHz** or megasonics may be required.

2. Geometric Structure and Contamination Location

   · Simple structure, contamination on the external surface: Low or medium frequency is sufficient.

   · Complex structure with deep holes, micro-holes, blind holes, threads, crevices: **High frequency (e.g., 40kHz, 68kHz)** is better for cleaning these hidden areas due to its stronger penetration and denser cavitation effect. For structures with ultra-high aspect ratios (e.g., MEMS devices), vacuum ultrasonics combined with high frequency may even be needed.

3. Product Value and Cleanliness Standard

   · High Value, Zero Tolerance for Damage (e.g., aerospace components, medical implants): Even if soil is heavy, the tendency should be to start testing from a **higher frequency (e.g., 40kHz)**, or adopt a combined process of **"low-frequency pre-wash + high-frequency precision clean."**

   · Cleanliness required to reach the nanoscale level (e.g., semiconductor silicon wafers, LCD substrates): Must use high frequency (**68kHz, 80kHz**) or **megasonics (>700kHz)**.

Step Two: Analyze Contaminant Nature

1. Heavy, Strongly Adhered (e.g., polishing paste, wax, quenching oil, carbon deposits, oxide scale): Requires strong physical impact; prioritize **low frequency (25-35kHz)**.

2. Light Grease, Dust, Fingerprints, Nanoscale Particles: The dense cavitation effect of high frequency is effective for removal and safer; prioritize **high frequency (40kHz and above)**.

3. Mixed Contaminants (heavy oil on the surface, micro-particles in crevices): Consider a multi-step process, or use equipment with a **"sweep frequency"** function (to avoid standing wave dead spots) to accommodate different needs.

Step Three: Refer to Industry Common Practice (Quick Anchoring)

· Heavy Industry, Automotive Parts (engine components, castings): **20kHz - 28kHz**

· General Precision Manufacturing, Hardware, Electronic Assembly (PCB, connectors, mechanical parts): **28kHz - 40kHz** (Most common range)

· High Precision Electronics, High-End Optics, Medical Devices (surgical instruments, precision gears, optical lenses): **40kHz - 68kHz**

· Semiconductors, Silicon Wafers, Microelectronics, Disk Heads: **68kHz and above**, up to megasonics (**0.8-1MHz**)

· Jewelry, Watchmaking, Cultural Artifact Restoration: **40kHz** (with gentle cleaning agents), higher frequency or specialized equipment needed for particularly fragile items.

Key Considerations and Advanced Strategies

1. Power Density is More Important than Frequency: Frequency determines the "style" of cleaning (aggressive or delicate), while **"power density" ($\text{Watts}/\text{Liter}$)** determines the "intensity" of cleaning. A $40\text{kHz}$ high-power system may have stronger cleaning power than a $28\text{kHz}$ low-power system. Both need to be considered synergistically.

2. Synergy of Temperature and Cleaning Agent: Increasing the cleaning liquid temperature and selecting the appropriate cleaning agent can reduce reliance on pure mechanical force (low frequency); sometimes, using high frequency can also achieve good results.

3. "Multi-frequency" and "Sweep Frequency" Technologies:

   · Dual/Triple Frequency Equipment: Allows switching between different frequencies to handle different products or cleaning stages.

   · Sweep Frequency Function: Causes the frequency to fluctuate slightly around the center value, effectively breaking up standing waves and eliminating cleaning dead spots, which is important for improving uniformity.

4. Process Testing is Essential: Small-scale testing with actual products and contaminants is the golden rule before making a final decision. Observe the cleaning effect and check for surface damage.

Concise Selection Flowchart

Start Selection

    │

    ▼

Evaluate Product: Is it precision, fragile, or does it have complex microstructures?

    ├─ No → Is the contaminant heavy and strongly adhered?

    │     ├─ Yes → Select Low Frequency (20-35kHz)

    │     └─ No → Select Medium Frequency (28-40kHz) General Range

    │

    └─ Yes → Is the cleanliness requirement nanoscale/sub-micron?

          ├─ Yes → Select High or Ultra-High Frequency (68kHz and above, consider Megasonics)

          └─ No → Select High Frequency (40-68kHz)

Summary Recommendations

· General Starting Point: If there are no special requirements, **$40\text{kHz}$** is a good balance point, combining cleaning power with a degree of precision.

· Conservative Principle: When in doubt, it is safer to choose a **higher frequency** and ensure effectiveness by extending cleaning time, and optimizing the cleaning agent and temperature, which is much safer than using low frequency and risking workpiece scrap.

· Combination Approach is Most Efficient: For demanding applications, the most effective solution is often a multi-tank serial process of **"low-frequency aggressive attack + high-frequency refinement."**

Ultimately, the selection of ultrasonic frequency is a process technology that combines scientific principles with experimental validation. Clearly defining the conflict point between the product and the contaminant is key to making the correct choice.