1. Aging and frequency

The causes of aging are complex. It is generally believed that the aging of the crystal is mainly caused by the falling off of the attachments on the surface of the wafer, the stress caused by the grinding process on the wafer, the change in the stress between the bracket and the wafer and the electrode film and the wafer formed by the mounting and coating process, the gas adsorbed on the crystal surface, and due to Changes in the electrode film surface caused by air leakage, etc.

Therefore, it is not difficult to understand that the same shedding will have a greater impact on those wafers of lower quality, and the same stress change will have a much greater impact on thin films than thick ones. This is the higher the frequency, the greater the aging. reason.

2. Measures to reduce the aging rate

Since surface shedding is one of the causes of crystal aging, the less shedding, the better. That is to say, the smoothness of the wafer surface will directly affect the aging of the crystal. A certain aging rate must be ensured. The higher the frequency of the crystal, the final The sand used for grinding should be finer, which means that the surface finish should be better. If you have higher requirements for aging, you can use a finer sand number until the surface is polished.

To reduce aging, we must pay attention to the following aspects:

(1) Ensure the smoothness of the wafer, including the smoothness of its edges;

(2) Deep corrosion process should be used to ensure that the damaged layer is completely removed;

(3) To ensure the cleanliness of the wafer, the wafer must be carefully cleaned multiple times: the support, external light and resonance components must also be cleaned;

(4) Adopt ion base shot coating process;

(5) Appropriately reduce the thickness of the electrode film to ensure the coating tolerance and minimize the amount of fine adjustment:

(6) To ensure the vacuum of coating and fine-tuning, it is best to perform ion bombardment cleaning before coating. During the coating process, the temperature of the wafer and the speed of sputtering affect the quality of the electrode film;

(7) The influence of the quality of the reeds of the bracket on the aging should be considered. Before and after coating, after mounting the glue, and after fine-tuning, high temperature baking should be carried out to eliminate the influence of stress. Baking aging is best carried out in an oven that can be vacuumed and filled with nitrogen;

(8) The quality of the conductive adhesive and the volatile matter of the conductive adhesive will also affect the aging of the crystal. Make sure that the conductive adhesive is completely cured before sealing. At least one cleaning should be done after dispensing;

(9) To prevent oxidation of the electrode, the inside of the crystal shell should be filled with high-purity nitrogen. During the processing, the exposure time of the electrode in the air should be minimized to prevent re-contamination of the wafer;

(10) Before the fine-tuning starts, use a strong excitation method to electrically clean the crystal.

(11) To ensure the high tightness of the crystal and low air leakage rate;

(12) The customer's use status, especially the size of the excitation power, will also affect the aging of the crystal. If the excitation power is large, the aging will increase.

(13) The last and most important point is accelerated aging.

After the crystal is made into a finished product, it is baked at high temperature, power-on baked, multiple high and low temperature shocks, low temperature storage, and multi-pass reflow soldering technology is used to reduce the aging rate as soon as possible.