Introduction Overview
With the development of thin and light display terminal products, the bonding strength between the mobile phone screen and the middle frame directly affects the structural reliability of the whole machine. In the rapid inspection of the production line, how to efficiently evaluate the peeling force of viscose with portable tools has become a concern. The small push-pull force gauge is suitable for the sampling of peeling force of the adhesive layer on the edge of the screen due to its flexible operation and intuitive data.
Equipment and principle
Small push-pull force gauges usually use strain gauge sensors, with a common range of 50 N to 500 N and an accuracy level of ±0.5% FS. Its working principle is that when the probe applies tension to separate the adhesive layer, the sensor elastomer will deform, and the change of resistance value will be converted into a voltage signal by the bridge, and the real-time force value will be displayed after processing. During inspection, it is necessary to use special fixtures to fix the angle of the screen and probe to ensure that the peeling direction is perpendicular to the cemented interface.
Standard basis
At present, there is no rapid inspection standard for the viscose peel force of mobile phone screens in China, but the general adhesive peel strength test method can be referred to. For example, a standard stipulates that the specimen width of the 180-degree peel test is 25 mm and the tensile rate is 100 mm/min. In the actual rapid inspection, the parameters can be adjusted according to the width and thickness of the product adhesive layer, but the peeling rate and fixture angle need to be kept constant to ensure data comparability.
Test steps
Step 1: Fix the mobile phone screen assembly horizontally on the special fixture to ensure that the edges of the adhesive layer are exposed; Step 2: Hook the push-pull force gauge probe to the starting end of the adhesive layer, and adjust the probe axis and the cemented surface at a 90-degree angle; Step 3: Pull the push and pull force gauge at a uniform speed to record the maximum force value at the moment of complete peeling of the adhesive layer; Step 4: No less than 5 samples are randomly selected for each batch of products, and the mean value and coefficient of variation are calculated.
Data interpretation
The peeling force value should be converted into the unit width force value (N/mm) combined with the width of the adhesive layer. Table 1 lists the test results for a batch to determine process stability. If the force value of the unit width is lower than the lower limit of the internal control of the enterprise, the amount of glue applied or the curing process should be checked.
| Sample number | Peak peel force (N) |
| 1 | 8.2 |
| 2 | 8.0 |
| 3 | 7.9 |
| 4 | 8.3 |
| 5 | 8.1 |
The average value of this batch is 8.10 N, and the force value per unit width is about 0.32 N/mm (the width of the adhesive layer is calculated as 25 mm), which meets the limit requirements of the enterprise.
Influencing factors
The peel force value is disturbed by multiple factors: the uneven thickness of the adhesive layer leads to local stress concentration; the change of adhesive modulus when the ambient temperature and humidity are abnormal; The push-pull force gauge pulls the speed off the set value. It is recommended to carry out inspections under constant temperature and humidity conditions, and regularly calibrate the push-pull force gauge with standard weights.
Quick inspection points
In order to improve the inspection efficiency, the following measures can be adopted: connect the push and pull force gauge with the industrial computer to automatically collect peak data and generate reports; For the prefabricated fixture positioning hole of the same type of screen, the clamping time is reduced; Set the upper and lower alarm thresholds and prompt you immediately if you exceed the range. However, it should be noted that rapid inspection cannot replace type testing, and the peeling mode (cohesive failure or interface failure) still needs to be visually confirmed.
FAQs
Problem 1: The probe slipped and the value is low. Countermeasures: Choose a push-pull force gauge with an anti-scratch hook head, or apply a small amount of resin to increase friction. Problem 2: Impact spikes occur after the rubber layer breaks. Countermeasures: Set sliding average filtering in the acquisition software to eliminate instantaneous noise. Problem 3: The angle of the clamp is affected by loosening. Countermeasures: Use a quick clip-on mechanism and mark the angle scale.
Application expansion
This method can also be used to test the peel force of other size display modules, such as tablets or car screens. For the special-shaped adhesive layer, the shape of the contact surface of the probe can be customized. In addition, by comparing the peel force fluctuations between old and new batches of adhesives, supplier management can be assisted.
Epilogue
The small push and pull force gauge has practical value in the rapid inspection of the viscose peel force of mobile phone screens, and can effectively support the quality control of the production line through standardized operation processes and joint interpretation of data. In the future, the combination of automated sampling and data analysis can further improve inspection efficiency and reliability.
References
1. Standard for Bonding Peel Strength Test Method (Industry General Method)
2. Calibration specification for portable force gauge (general requirements for measurement)
3. White Paper on Mobile Phone Screen Bonding Technology (Internal Information of Industry Associations)