In the assembly of touchscreens (typically combined with displays into “modules”) to device casings, one-piece adhesive backing and L-shaped adhesive backing are the two primary mounting methods. Below, I will detail their differences and respective advantages.
1. One-piece adhesive backing, also known as “square adhesive” or “frame adhesive,” is a single sheet of double-sided tape pre-cut into a hollow frame shape. Its shape perfectly matches the mid-frame/front shell of a phone or device. After peeling off the release liner, it can be aligned and adhered to the casing in one go.
Assembly Method:
Completely remove the release liner from the one-piece adhesive frame. Align and press the entire adhesive frame onto the bonding surface of the casing in one motion. Then, peel off the release liner from the other side of the screen assembly, align it with the casing, and press to complete the assembly.
Advantages:
Superior Sealing Integrity: As a complete, closed adhesive frame, it provides a highly uniform and continuous bonding surface. This effectively prevents dust and moisture ingress from the sides into the device, offering enhanced dustproof and waterproof performance.
Uniform Bonding Strength: Even stress distribution across the entire perimeter ensures more balanced force absorption during drop and torsion tests. This reduces the risk of adhesive failure caused by localized stress concentration.
High aesthetic consistency: Eliminates potential misalignment or gaps from joining multiple tape segments, resulting in a cleaner appearance.
Disadvantages:
Higher cost: Production and mold costs for one-piece adhesive films are typically higher than L-shaped variants.
Strict tolerance requirements: Both the bonding surface of the casing and the adhesive film dimensions demand extremely tight tolerances. Minor casing deformation or excessive tolerances can cause weak bonding or bubbles in certain areas.
Difficult to repair: If screen removal is required, the entire adhesive frame must be softened using heat or other methods before detachment, making the process more challenging. Additionally, the adhesive backing cannot be reused.
2. L-shaped adhesive backing consists of multiple independent, short adhesive strips typically shaped like an “L.” These strips are applied segmentally around the device casing.
Assembly Method: Operators or automated equipment peel and apply each L-shaped segment individually to designated positions on the chassis. After all segments are affixed, the release paper covering them is removed. The screen assembly is then aligned with the chassis and pressed together during assembly.
Advantages:
Lower Cost: The simple structure of L-shaped adhesive strips minimizes material waste, typically resulting in lower production and procurement costs compared to one-piece adhesive strips.
High Tolerance Adaptability: This is the L-shaped adhesive's greatest advantage. Its segmented application allows better adaptation to minor irregularities or dimensional tolerances in the casing or screen module. Even if one area has slight protrusions or depressions, the adhesive strips in other segments can still provide effective bonding, offering higher fault tolerance.
Relatively Easy Repair: When disassembling the screen, a pry tool can be inserted into the gap of one or more L-shaped adhesive segments for gradual separation, making it easier than breaking an entire continuous adhesive frame.
Design flexibility: The length, quantity, and placement of L-shaped adhesive segments can be adjusted to match the required bonding strength in different areas. For instance, longer segments can be applied to corners prone to stress.
Disadvantages:
Relatively poor sealing: Minor seams exist between adhesive segments, creating potential pathways for dust or water ingress. Overall sealing performance is inferior to a single-piece adhesive backing.
Risk of Strength Inconsistency: Improper placement or omission of adhesive segments may result in localized bonding weakness. During impact, stress may concentrate at segment junctions, increasing the risk of adhesive failure.
Appearance Consistency: Multiple adhesive segments may exhibit uneven alignment during application. Though concealed internally, this remains a quality control consideration.
3. How to Select the Right Adhesive for Assembly?
Choose One-Piece Adhesive: Opt for one-piece adhesive when your product demands extremely high waterproof/dustproof ratings (e.g., IP67/IP68), features high production automation, and relies on a supply chain capable of strict dimensional tolerances.
Opt for L-shaped adhesive: When cost is the primary consideration, product structural tolerances may be larger, or production cycle times are less critical, L-shaped adhesive offers a more economical and practical solution. Commonly found in mid-range devices or products with lower waterproofing requirements.
In actual projects, engineers will weigh these two options based on design requirements, cost budgets, and production capabilities.