Understanding the Analysis and Improvement Methods of OCA Optical Glue Bubble Causes

After the completion of vacuum lamination using a vacuum laminator, bubbles are easily left on the lamination surface. Most of the bubbles can be removed through debubbling, but there is a small chance of small single-point bubbles remaining. These small bubbles can be categorized into two types:

1. Poor debubbling:

   Small bubbles left after one debubbling process are difficult to remove again because the bubbles shrink while the relative area of the OCA optical glue increases, creating a wall effect. In other words, the pressure cannot effectively transmit to the small-area bubbles, leading to incomplete debubbling. This problem can be solved by using single-point pressure debubbling.

2. Bubble rebound:

   Bubble rebound refers to bubbles that reappear immediately or after a certain period of time following the completion of debubbling.

The causes of bubble rebound can be summarized into two types:

a. Stiffness-induced rebound:

   After applying pressure during G+G lamination, pressure is exerted on the TP ink segment, and the stiffness of the TP material does not disappear. This results in stiffness-induced rebound bubbles at the edge of the ink. These bubbles can be eliminated through single-point pressure debubbling. However, the TP stiffness will always exist, resulting in the possibility of reoccurrence. To address this, the "slow debubbling pressure release" method can effectively reduce the imbalance between TP stiffness stress and OCA optical glue stress recovery. Additionally, adjusting the parameters of the debubbling machine, such as reducing debubbling pressure and temperature, can be beneficial for reducing bubble rebound.

b. Stress-induced rebound:

   This type of Delay Bubble is the most troublesome. The rebound bubbles are caused by impurities in the OCA glue and OCA glue with TP/LCM interlayers. However, not all particles will cause this type of rebound bubbles, and it is not related to the size of the particles. It is not possible to prevent and control this type of rebound bubbles based solely on quantitative measurements. The key point lies in the three-dimensional shape of the particles. Generally, three-dimensional particles are more likely to generate bubbles.

Observation focus and summary of experience regarding bubble faults:

- Determine whether the fault bubbles are not completely debubbled or rebound bubbles (Delay bubble). For bubbles that are not completely debubbled, experiments can be conducted by extending the debubbling time, increasing debubbling pressure, and raising debubbling temperature. The priority order is time, pressure, and temperature.

- Determine whether the fault bubbles are between TP and OCA glue or between OCA glue and LCM. Use a magnifying glass to focus and determine which layer the bubbles are in. When between LCM and OCA, the focus clarity is the same as the RGB dot matrix clarity of LCM. Bubbles between TP and OCA glue are mainly caused by margin differences in the ink, full bonding (G+G) compressive stress, and debubbling stress. Optimize the rebound bubbles by reducing the bonding pressure between TP and LCM, debubbling pressure, and debubbling temperature.

- Determine whether the fault bubbles are caused by air or impurities. Impurity-induced bubbles contain three-dimensional impurities. It is crucial to manage the cleanroom and prevent impurities from entering the workshop and adhering to the lamination components.

Root cause:

Previously, the main cause of bubble defects was stiffness-induced rebound bubbles (one type of Delay bubble). This was primarily due to excessive pressure during G+G lamination and improper defoaming parameter settings, leading to bubble rebound after defoaming.

Improvement suggestions:

1. Understand the principles of defoaming and bubble generation, and adjust equipment parameters scientifically based on product characteristics.

2. Assign a dedicated person in the lamination workshop for unified management and problem analysis, gradually improving the overall yield.