The Reason And Solution Of The Touch Screen Bubble Rebound In The Deaeration Process After OCA Bonding

In the process of touch screen production, we need to use OCA to bond the sensor glass and the cover lens together. However, there will genrate air bubbles during the bonding process. So we need to use a defoaming machine for defoaming. After the application of the pressing machine, the bonding surface simply leaves bubbles, most of which we can use deaeration to remove. But a few percent of the chances will leave a small single point of small Touch Screen Bubble. There are two types of such small touch screen bubble. :

1.Poor Deaeration

The small bubbles left after one degassing are difficult to remove again. As the bubble shrinks, the OCA optical glue under the relative area becomes larger, forming a wall effect. In other words, the pressure cannot be effectively transmitted to a small area of bubbles. As a result, the degassing cannot be completed, and a single-point pressure degassing can be used to solve this problem.

2.Touch Screen Bubble Bounce

Bubble rebound refers to bubbles that recur immediately after deaeration or after a certain period of time. We can sumarize the reasons for this as the following characteristics:

1) Stiffness Type Regenerates Bubbles

After G+G is applied and pressed, pressure will be generated on the TP ink segment. The stiffness of the TP material will not disappear, so stiff and re-bubbles will occur at the edge of the ink. It can eliminate the single-point pressure defoaming . But the TP stiffness persists forever. This has the possibility of resending again. Here we use the "defoaming and slow pressure relief" method to effectively reduce the imbalance of TP stiffness stress and OCA optical adhesive stress recovery. In addition, after adjusting the parameters of the deaerator. Generally, reducing the defoaming pressure and lowering the defoaming temperature is beneficial to reducing the drum rebound.

2) Degassing Slowly To Relieve Pressure

Slow degassing and pressure release. Usually, the action of our degassing machine is that the pressure and temperature happen together or in time. Then set the start defoaming program according to the time. Cool down and reduce pressure until the deaeration time is over. According to the set pressure and the exhaust plan of the deaerator, the pressure relief time varies from 30sec to 60Sec! This pressure relief procedure has a big blind spot. That is, TP will not change much due to pressure and temperature. However, OCA optical glue is very sensitive to temperature and pressure. So when quickly release the pressure.

The stiffness of TP will recover soon, but it is temporarily controlled by the viscosity of the glue! However, the stiffness recovery of OCA optical glue is very slow. In this way, when the defoaming Module is out of the defoaming machine. OCA optical glue still has a certain core temperature. If the internal stress is small, the TP stiffness stress very easy to open and then generate small bubbles. Most of the places here have bubbles. And there is indeed a small amount of air quality inside, which is a rare name. Change the pressure relief program to keep the temperature unchanged. Then the pressure relief rate is less than 0.03Kg/M2 per second until there is no pressure to stop.

3) Stress-type Regenerating Bubbles:

This type of Delay Bubble is the most troublesome type. This type of re-bubbles is caused by OCA glue and particles (impurities) sandwiched between OCA glue and TP/LCM. But not all particles will have this type of bubble again. It also has nothing to do with the size of Particle, and it cannot be selected for prevention and treatment based on pure measurement. The most important point is the three-dimensional shape of Particle. Usually three-dimensional Particles simply generate bubbles."

Main Points And Experience Summary Of Touch Screen Bubble Fault Investigation:

1. Acknowledge whether the faulty bubble has not been cleaned or is it a delayed bubble. No de-cleaning bubbles go through the extended de-aeration moment. Add defoaming pressure and increase defoaming temperature for experiment. The priority is time, pressure, temperature.
2. Determine that the defective bubble is between TP and OCA glue. It is still between the OCA glue and the LCM, through the magnifying glass, the clarity of focus is judged on which layer. When between LCM and OCA, the sharpness of focusing is the same as that of RGB dot matrix of LCM. The air bubble between TP and OCA is primarily the difference in ink level. Full fit (G+G) compression stress and defoaming stress. After reducing the bonding pressure of TP and LCM, the deaeration pressure, and the deaeration temperature to optimize the rebound bubble.
3. Determine whether air or impurities. cause the problematic bubbles. There are three-dimensional impurities in the bubbles caused by impurities. We need to manage impurity bubbles  in a clean room. In particular, it bright the impurities on the incoming goods to the workshop and bonded parts. The fundamental reason is that the previous defective bubble products are mainly stiff recurring bubbles (a kind of Delay bubble. The first is that the bonding pressure of the G+G laminating equipment is too large, and the defoaming parameters are set unreasonably. Laminating stress and defoaming stress As a result, bubbles rebound after defoaming.

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