The Importance and Process Control Methods for Flatness and Perpendicularity of Tempered Cover Glass

Aug 17, 2026

Coverglass is a very important part of capacitive touch panel. Flatness and perpendicularity are two critical dimensional characteristics of tempered glass covers. They directly affect assembly quality, appearance, and long-term reliability of the final product.

Flatness

Flatness refers to the overall evenness of the glass cover surface.

Why it is important:

Poor flatness creates gaps between the glass cover and underlying components (e.g., touch panel or display), leading to poor lamination, air bubbles, or touch function failure.

It may also cause localized stress concentration, making the glass more prone to cracking under impact.

Perpendicularity

Perpendicularity refers to how vertical the side edge is to the bottom surface (i.e., deviation from 90°).

Why it is important:

Poor perpendicularity affects the fit precision between the glass cover and the middle frame or housing, resulting in assembly difficulties or uneven gaps.

In waterproof or dustproof designs, poor perpendicularity can lead to seal failure.

Summary: Although flatness and perpendicularity are microscopic dimensional indicators, they directly impact assembly yield, product appearance, and service life.

Process Control Methods to Ensure Flatness and Perpendicularity

1. Flatness Control

Stage	Control Measures
Cutting	Use high-precision CNC cutting equipment; regularly calibrate tool verticality and platform levelness
Edge Grinding	Control grinding wheel pressure to avoid local overheating and glass deformation
Tempering	Strictly control heating temperature (typically 680–720°C) and cooling air pressure; ensure uniform temperature distribution inside the furnace
Cooling	Keep cooling air grids parallel with consistent air pressure to prevent warpage from uneven quenching
Polishing	Maintain uniform polishing wheel pressure and stable workpiece fixturing

Key production checks:

First-article inspection for flatness using feeler gauges or laser flatness testers

2. Perpendicularity Control

Stage	Control Measures
CNC Edging	Use high-precision fixtures to ensure secure and vertical glass positioning; regularly calibrate spindle verticality
Chamfering	Maintain consistent chamfer angle and depth to avoid tilted edges
Inspection	Use 90° squares or CMM (coordinate measuring machines) for random edge perpendicularity checks

3. Common Measuring Tools

Parameter	Recommended Tool	Typical Accuracy
Flatness	Feeler gauge, granite surface plate, laser flatness tester	±0.05 mm
Perpendicularity	90° square, CMM, optical projector	±0.05 mm / 100 mm