Analysis of Fault Causes and Repair Solutions for Dual 8-inch Megasonic Systems

(I) Fault Cause Analysis

The megasonic oscillator mainly consists of a vibrating plate and a piezoelectric ceramic sheet, as shown in Figures 1 and 2. Figure 1 is a physical image, and Figure 2 is a schematic diagram of the distribution of the debonded areas of the ceramic sheet. The adhesion between the vibrating plate and the piezoelectric ceramic sheet relies on adhesive. Only when the connection is tight can the high-frequency mechanical vibration generated by the piezoelectric ceramic during normal operation be transmitted through the vibrating plate to the liquid, thereby generating megasonic waves in the liquid for cleaning.

After on-site drive testing, visual observation revealed that ceramic plates 1, 2, 3, 4, 5, 6, 8, 9, 10, and 11 exhibited areas of non-vibration during operation. Upon removing the protective cover of the vibrating chamber, further inspection revealed that some of these ceramic plates had detached adhesive, corresponding to the areas that did not vibrate during operation. Prying open the detached piezoelectric ceramic plates, as shown in Figures 3 and 4, was relatively easy, as the ceramic plates were suspended and no longer connected to the vibrating plate. In fact, several wires could be inserted into the detached area of ceramic plate 5. In summary, the cause of this malfunction can be determined as follows: the adhesive between the vibrating plate and the ceramic plates in some areas of the vibrating chamber aged, causing the ceramic plates in these areas to detach from the vibrating plate. Therefore, during system operation, the high-frequency vibrations emitted by the piezoelectric ceramics in these areas could not be transmitted, resulting in the appearance of megahertz waves in the corresponding locations in the cleaning fluid.

(II) Repair Plan

Inspection has confirmed that 10 ceramic tiles (numbers 1-11) have partially delaminated areas. This will result in some areas of the cleaning tank lacking megasonic waves, thus affecting the cleaning effect. To solve this problem, the partially delaminated piezoelectric ceramic tiles must be replaced with brand new ones (out of 10 tiles delaminated, only 2 are normal). In addition, although 2 piezoelectric ceramic tiles do not show delamination, their adhesive may have aged. To avoid the possibility of them delaminating later, it is recommended that they be replaced along with the other 10 delaminated piezoelectric ceramic tiles.

The vibratory box section requires the removal of 12 piezoelectric ceramic pieces. After cleaning the vibratory plate, brand new piezoelectric ceramics are installed in the corresponding areas. To restore the system's performance to near-original levels after repair, the replacement piezoelectric ceramics are custom-made, with the same brand and specifications as the original. Furthermore, the operating frequency of the repaired vibratory box is close to the original (around 1MHz, differing by about 10kHz), not exactly the same, but this will not affect the cleaning effect. However, to adapt the generator to the repaired vibratory box, some internal circuitry (filter board, etc.) needs adjustment, along with its operating frequency and other parameters.

After the ceramic plate replacement and adaptation work is completed, a 24-hour continuous aging test needs to be carried out on the system to detect the sound pressure value in the tank, so as to observe the repair effect and stability.